NITROGEN REMOVAL FROM SECONDARY EFFLUENT APPLIED TO A SOIL-TURF FILTER

NITROGEN REMOVAL FROM SECONDARY EFFLUENT APPLIED TO A SOIL-TURF FILTER
NITROGEN REMOVAL FROM SECONDARY EFFLUENT
APPLIED TO A SOIL-TURF FILTER
Elizabeth Leigh Anderson
A Thesis Submitted to the Faculty of the
DEPARTMENT OF SOILS, WATER, AND ENGINEERING
In Partial Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
WITH A MAJOR IN SOIL AND WATER SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 7 8
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of re
quirements for an advanced degree at The University of Arizona and is
deposited in the University Library to be made available to borrowers
under rules of the Library.
Brief quotations from this thesis are allowable without special
permission, provided that accurate acknowledgment of source is made.
Requests for permission for extended quotation from or reproduction of
this manuscript in whole or in part may be granted by the head of the
major department or the Dean of the Graduate College when in his judg­
ment the proposed use of the material is in the interests of scholar­
ship. In all other instances, however, permission must be obtained
from the author.
SIGNED:
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
Assistant Research Scientist
ACKNOWLEDGMENTS
I wish to express my gratitude to Dr. Ian L. Pepper for his
willingness to work, counsel, guide and review during the course of
this experiment.
My thanks to Dr. Gordon V. Johnson for his original
idea and his help in getting under way.
The author also wishes to extend thanks to Dr. Wallace H.
Fuller, Dr. William R. Kneebone, Dr. Donald F. Post, Dr. Jack L.
Stroehlein, Dr. Thomas C. Tucker, and Dr. Arthur W. Warrick for advice
suggestions, and comments.
The staff of the Soils, Water, and Engineer
ing Department will be remembered for their help and encouragement.
This work could not have been completed without the help of
many others.
Thanks to Lyzi Cattany, Bob Drake, Monte Edlund, Evan
Karol, Don Leftwich, Charles McKown, Dave Morris, Dr. David B. Marx
Carl Michaud, Jim Mullins, Lewis Munk, and Michael Turner.
This work is dedicated to Dr. Kenneth K. Barnes and his wife
Betty.
iii
TABLE OF CONTENTS
Page
LIST OF T A B L E S ................................................
v
LIST OF I L L U S T R A T I O N S ........................................
vi
A B S T R A C T ......................................................
vii
INTRODUCTION ..................................................
1
LITERATURE R E V I E W ....................
4
Mechanisms of Nitrogen Removal . . . . . . ...............
Nitrogen in the Soil E nvironment .........................
Tertiary Treatment of Wastewater .........................
Land Disposal of Wastewater .......................
Effluent Use for Irrigation and C r o p s ...............
Renovation of Effluent by Low Rate Land Application .
High Rate Infiltration-Percolation ...................
Spray-runoff Land T r e a t m e n t ........................
MATERIALS AND METHODS
........................................
M a t e r i a l s ............
M e t h o d s .............................
Effluent Application ............. . . . . . . .
Sample Collection . . . . . . . . . . . . . . .
Chemical Analysis ..................... . . . .
Effluent Application Rates ........ . . . . . .
Interpretation of Data . ...................
.
.
.
.
.
.
.
.
.
.
.
.
.
RESULTS AND DISCUSSION ........................................
Water R e c h a r g e ...........................................
Utilization . . . . . . . . . . . . . ................. •
Nitrogen Removal ................. . . . . . . ........ •
Nitrogen Transformations in Leachate .................
The Soil's Role ....................... . . . . . . . . .
5
8
11
14
15
17
20
22
24
24
27
27
27
28
29
29
32
32
43
53
63
64
SUMMARY AND C O N C L U S I O N S .....................................
69
LIST OF REFERENCES
72
LIST OF TABLES
Table
1.
Page
Effluent application rates used 3 June 1977 to 28 April
1978 . . ................................................
30
Analysis of variance for percent water recharge 11 July
1977 to 28 April 1978 .................................
33
3#
Percent water recharge means . . . . . . . . . . . . . .
J>6
4.
Total recharge volumes, total evapotranspiration volumes,
and total grass yields for 30 April 1977 to 28 April
1978 ......................................................
2.
5.
Analysis of variance for N utilization, 11 July 1977 to
28 April 1978
6.
Nitrogen utilizationm e a n s ..........................
7.
Total yields and percent N (organic -N and NH^-N) in
bermudagrass clippings collected for 16 weeks, 11 July
to 29 October 1977 ........................................
38
48
48
8.
Total yields and percent N (organic -N and NH^-N) in
ryegrass clippings collected for 22 weeks, 28 November
1977 to 28 April 1978
9.
Analysis of variance for percent N removed, 11 July
1977 to 28 April 1978 .................................
57
10.
Percent N removed means and average ppm -N in leachate •
57
11.
Total N removed by clippings and by soil processes from
30 April 1977 to 28 April 1978 .........................
58
12.
Percent N removed by s o i l ............................
v
67
LIST OF ILLUSTRATIONS
Figure
Page
1.
Effluent N composition during the year long study . . . .
26
2.
Percentage water recharge for all effluent application
rates on s a n d ................. .................... ..
34
Percentage water recharge for all effluent application
rates on m i x .......................................... .
35
Maximum and minimum air temperatures and rainfall
measured at Rincon Vista Turfgrass Research Center during
the year long study . ........... .......... ..
40
3.
4.
5.
6.
7.
8.
9.
10.
11.
Percentage water recharge, showing all five effluent
applicationrates averaged for each s o i l .................
42
Percentage N utilization for all effluent application
rates on s a n d ............................................
45
Percentage N utilization for all effluent application
rates on mix ........ ..
........ . . . . . .
46
Percentage N utilization showing all five effluent
application rates averaged for each soil . . . . . . . .
52
Percentage N removed for all effluent application rates
on sand . . . . . . ................... . . . . . . . . .
54
Percentage N removed for all effluent application rates
on m i x ......................................
Percentage N removed showing all five rates of effluent
application averaged for each soil ................. ..
5
62
ABSTRACT
This study investigated the use of a soil-turf filter for
renovation of secondary effluent#
Lysimeter plots were filled with a
sand, and a sand mixed with organic matter and soil, then seeded to
annual ryegrass.
In spring, the ryegrass was removed by close mowing
and seeded to bermudagrass.
Plots were drip irrigated twice a week
with Tucson secondary effluent at rates of 10, 17, 22, 34 and 43
mm/day.
Analysis of leachate, effluent and grass clippings allowed a
total N balance to be computed.
groundwater recharge was
Percentage of leachate available for
58# at the lowest rate and 72# at the highest
rate when values were averaged over 42 weeks for both soils.
Percent­
age of applied nitrogen removed by the sand-turf filter was 40 to 79#
and 48 to
87# on the mix-turf filter, and decreased as application
rate increased.
Percentage of applied nitrogen utilized by turf was
12 to 26# on sand and 18 to
application increased.
38# on mix, and decreased as rate of
Results of the 42 week study showed that the
N concentration in municipal effluent could be reduced from 20 ppm -N
to 10 ppm -N.
The sand-turf filter could renovate 17 mm/day and the
mix-turf filter 34 mm/day, and still yield leachate averaging less
than 10 ppm NO^-N.
than bermudagrass.
Results also indicated ryegrass utilized more N
INTRODUCTION
Tucson, Arizona is a city of 450,000 people totally dependent
on groundwater for meeting their water needs.
Fifty percent of the
water pumped into the distribution systems appears as return flow to
sewage treatment plants (Cluff, DeCook, and Matlock 1972).
Groundwater
levels have decreased 2 to 5 feet per year as use exceeds natural re­
plenishment (Groundwater Resource Management data 1977i from Department
of Soils, Water, and Engineering, University of Arizona).
Over 35
million gallons of secondary effluent per day are released into the
Santa Cruz river without consideration to nutrients in the effluent,
groundwater pollution, or water conservation.
Public Law 92-500
restricts discharge of wastewater into streams, lakes, and surface
water (Bouwer 1976).
Such restrictions have stimulated research on
tertiary treatment methods which lower the concentration of pollutants
found in wastewater.
Sidle and Johnson (1972) found turfgrass removed 90# of the
N applied in effluent.
Their plots were irrigated with 2.84 inches of
effluent whenever available soil moisture reached 40#.
After N was
removed by the soil-turf filter, 4096 of the applied effluent passed
below the root zone and was available for groundwater recharge (Johnson
1973)•
This study indicated the potential of a soil-turf filter for
renovation of municipal sewage effluent.
Wilson and Lehman (1967) in­
vestigated the potential of a grass filter for removing settleable
1
2
materials and reducing organic pollution in sewage effluent.
Results
showed overland flow using bermudagrass for filtration provided only
partial treatment of the effluent.
The grass height and density were
important in order to ensure filtration.
Bermudagrass was able to
tolerate prolonged flooding with sewage effluent.
Further studies by
Lehman (1968) using bermudagrass and soil columns indicated that
effluent application required proper management for maximum removal of
N and heavy metals.
Johnson (1973) cited several reasons for investi­
gating the use of turfgrass as a disposal system for nutrients in
effluent.
Turfgrass requires a relatively high constant level of N
throughout the year and can be grown year round in the Southwest.
Golf
coursess greenbelts, playgrounds and parks could be watered with
effluent; saving groundwater and promoting city-wide recreation.
Be­
cause treatment plants are generally on the periphery of cities where
acres of turfgrass could be developed for recreation, transmission of
sewage effluent would not require extensive pipe lines.
This study was conducted in order to determine the maximum
rate of effluent that could be applied to a soil-turf filter and yield
recharge water meeting United States Public Health Service (USPHS)
standards.
The goal was to determine the feasibility of using rec­
reational areas for effluent disposal, conserving groundwater, and
contributing quality recharge water.
The pollutant considered in
this experiment was nigrogen with NO^ being the major ion of concern.
Nitrogen is involved in the eutrophication of streams; nitrate (N0~)
can cause methemoglobinemia in infants and is poisonous to animals;
nitrite (N0~) is poisonous to humans (McKee and Wolf 1965).
There
are no USPHS limits on ammonium (HH^) or nitrite in drinking water.
Some countries limit NH^ to 0.5 ppm and NO” limits vary from 0.1 to
2 ppm (McKee and Wolf 1963)•
The NO” limit is 45 ppm or 10 ppm N0”-N.
LITERATURE REVIEW
Land application of wastes is a practice that has existed for
hundreds of years.
Yet only in the past few decades has man sought to
evaluate the effects of such a disposal system on his environment.
Studies of wastewater disposal are currently concerned with renovation
of effluent enabling direct discharge into streams, rivers, lakes, or
oceans without degrading the quality of natural waters; or use of
wastewaters for agricultural and recreational purposes in order to de­
crease demand on freshwater reserves.
Evans (1970) regarded waste as a valuable resource in the wrong
place, form, amount or time.
He stressed the need to convert waste to
a reusable product and the importance of neutralizing or converting
toxic substances.
In
1965 there were 2,400 land waste disposal systems •
being used for liquid wastes.
Nine hundred of these systems were in
the food processing industry (Evans 1970).
The traditional method of
waste disposal into surface waters is no longer feasible as dilution
water is less available.
Stream self-purification does not work on
many pollutants (Stephan and Weinberger 1968).
are water pollution and water supply.
increases freshwater supply.
The two major problems
Renovation and reuse of water
Pratt, Thorne and Wiersma (1977) cited
five factors that affect utilization of wastes:
economics, public
policies, research and development, quality control, and public accept­
ance.
Crops, forest, cities and people can all benefit if waste is
properly disposed.
4
5
Tofflemine and Farnan (1975) reviewed several studies showing
that land disposal of wastewater was more economical for small treat­
ment plants and plants needing tertiary treatment.
They cited examples
of high rate infiltration beds being used in Arizona, Massachusetts,
and New York.
Young and Carlson (1975) concluded that land application
of wastewater was the lowest cost alternative for improving water
quality in the southern United States.
Land treatment has the advan­
tage of being less sensitive to price flux when compared to tertiary
treatments involving large quantities of chemicals and energy.
Mechanisms of Nitrogen Removal
Nitrogen removal by soil mechanisms has been summarized by
Lance (1972):
biological denitrification, volatilization of NH^,
adsorption of NH^, fixation of NH^ by clay and organic matter, N
assimilation by microorganisms and vegetation, chemo-dentrification,
and leaching.
Generally the primary form of N in effluent is NH^.
Cation exchange capacity (CEC), organic matter content, and the clay
fraction determine a soil's capacity for NH^ retention.
Calcium and
magnesium ions will compete with NH^ for cation exchange sites.
Ammonium is held by the lignin fraction of organic matter.
The amount
of NH^ retained by organic matter or clay increases with pH due to pH
dependent charge.
Montmorillonite and vermicilite are both capable of
fixing NH^ in their clay lattice.
Volatilization of NH^ can occur in
an alkaline aqueous medium:
NHj + H20 + OH” -» NH^t + 2H20
Volatilization increases with temperature and when rapid evaporation of
6
water occurs.
Nitrogen can be assimilated by plants and microorganisms
as either NH^
or N0~.
Denitrification is a process involving microorganisms which
contributes to nitrogen removal from wastewater, but nitrification is a
prerequisite.
Nitrosomonas sp. are obligate autotrophic bacteria re­
sponsible for the oxidation of ammonium to nitrite.
This reaction is
the first step in nitrification and requires oxygen:
2NHJ + 30 2
2ND” + 2H20 + 4H+
Numerous heterotrophic organisms can convert reduced N compounds to
nitrite, including bacteria, actinomycetes, and fungi.
Nitrite can
result from the oxidation of amines, amides, hydroxylamines and oximes.
The conversion of nitrite to nitrate is the second and final step in
nitrification and is performed mainly by Nitrobacter sp. which are
obligate autotrophic bacteria.
This reaction is represented as:
2N°2 + 02 -» 2N0"
A few other heterotrophs, mostly fungi, can produce nitrates.
The
availability of oxygen in the soil, temperature, soil moisture, and
soil pH will influence this microbial activity.
The pH range for
nitrification is 5«5 to 10, with an optimum around ?•
Temperature
range for nitrification is 5 to 4o°C with an optimum around 30 to 35°C.
Dentrification occurs in an anaerobic environment where species
of the genera Pseudomonas, Achromobacter and Bacillus are able to use
nitrate and nitrite as terminal electron acceptors in the absence of
oxygen.
Autotrophs capable of reducing nitrates are Thiobacillus
dentrificans and Thiobacillus thioparus.
trification is:
A possible pathway for den­
7
2 HNOj -> 2 HN02 -» H 2N202
h
-Ng or NgO
At pH 4.9 to 5*6 nitrous oxide is usually formed.
nitrogen gas is the main form of N released.
At pH 7*3 to 7.9
Waterlogging of soil or
a decrease of oxygen in the soil pores induce dentrification.
In­
creasing oxidizable carbonaceous material increases the loss of
nitrogen gas.
Dentrification can occur in a temperature range of 2
to 60°C with an optimum around 25°C.
Lance (1972) reviewed the process of chemo-dentrification and
noted that it was unlikely this process would contribute to any sig­
nificant loss of N in land disposal of secondary effluent.
Effluent
generally contains 20 to 25 ppm-N and chemo-dentrification reactions
usually occur when ammonia-producing fertilizers are banded or when
large quantities of nitrite salts are added to the soil.
There are
several proposed reactions by which chemo-dentrification could occur.
All of these reactions assume an accumulation of NOg in the soil.
In
alkaline soils where volatilization could occur, NH^ accumulation is
toxic to Nitrobacter and could lead to NOg accumulation.
One proposed
reaction for chemo-dentrification is:
NH5 + HN02 -*N2 + 2H20
Two other proposed reactions are:
3 HN0_ -»2N0 + HNO, + H o0
2
3
2
R-NH2 + HN02 -+ R-OR + H20 + N2
Both of these reactions occur at pH 5 or less and have not been shown
to be of importance in N loss from soils.
8
Leaching of N from the soil could occur, depending on the
cations present in the water applied and their concentration.
Ammonium
could be replaced on the cation exchange site by another cation and
then travel below the root zone with soil water.
Nitrate is an anion
and tends to travel with soil water, being easily leached below the
root zone.
Vegetation and microorganisms incorporate N in their tissue,
removing N from the soil solution.
Vegetation may also contribute to
gaseous loss of N by promotion of denitrification in the rhizosphere
(Woldendrop 1962).
Nitrogen in the Soil Environment
Oxygen is necessary for the process of nitrification, which
must occur before effluent N can be denitrified.
Klausner and Kardos
(1975) found oxygen diffusion rates were not significantly different
when effluent was applied at rates of 0, 2.$, and $.1 cm per week.
Oxygen concentration was not affected by crop cover.
Preul and
Schroepfer (1968) point out that the major part of nitrification occurs
in the upper two feet of soil.
Adsorption will be the dominant mode of
NH^ removal in saturated flow until the capacity of the soil is ex­
ceeded.
Unsaturated flow can increase nitrification of effluent N.
Lance and Whisler (1972) flooded soil columns with effluent to evaluate
the optimum flood/dry cycle for N removal.
In this process, NH^ is held
on the soil's cation exchange sites and nitrified during the dry period.
When the column is flooded, NO” is leached from the soil.
This creates
a peak of high nitrate water at the beginning of the flood period and
water with a very low N content after the NO” is leached.
Lance,
9
Whisler and Bouwer (1973) determined that a five day dry period allowed
enough oxygen to enter the soil to oxidize all the NH^ applied when
flooding the soil with effluent for six days.
The highest oxygen move­
ment in the soil was obtained on a one day flood/one day dry, effluent
application cycle.
The oxygen demand can be estimated by NH^ and
organic N content of the effluent applied.
The nitrate anion can move freely through soil.
Corey, Nielson
and Kirkham (1967) found denitrification was increased 2196 by decreas­
ing the velocity of fluid movement through the soil from 1.32 to 0.11
cm/hour.
At the slower velocity there was more time for microbial
action on NO^.
Woldendrop (1962) showed that living roots stimulated "
denitrification by increasing oxygen consumption in the rhizosphere.
Roots also excrete organic substrates that can be used by denitrifing
organisms as H+ donors.
Several experiments have been conducted using
different energy sources and measurements of redox potential to deI
termine optimum conditions for denitrification.
Lance and Whisler (1976) found that methanol added to wastewater at the rate of 150 ppm increased N removal 12$.
When dextrose
was added to wastewater at the same rate, N removal increased to 90^.
Use of dextrose in the wastewater decreased infiltration due to soil
clogging.
This also reduced oxygen uptake in the dry periods, causing
incomplete nitrification.
reclaimed water.
The dextrose treatment increased NH^ in the
More research is needed to find out if an organic
carbon source added at the beginning of the flood period would be
effective in decreasing the nitrate peak that occurs in high rate in­
filtration systems.
Mann et al. (1972) found denitrification by
10
Thiobacillus denitrificems was significantly increased by adding sulfur
to the soil which is the energy source for this organism.
Soil texture
affected denitrification rates due to the ability of certain clays and
silts to provide adsorption sites between bacteria and insoluble sub­
stances.
Whisler, Lance and Linebarger (1974) measured redox potentials
in soil columns periodically flooded with sewage effluent.
cation occurred in the range of Eh = 200 to 300 mV.
Denitrifi­
Redox probes were
used to indicate where denitrification was occurring in the soil column.
When soluble C was added to effluent, the redox potential dropped to
-200 mV, indicating the oxidation states of other elements besides N
were becoming unstable.
Meek, Grass and MacKenzie (1969) found that
when the Eh was 300 mV or below there was a large loss of N by denitri­
fication.
The soil moisture level was 32# at field capacity.
At 34 to
4l# soil moisture the Eh was between 500-600 mV and NO” loss was 3*5
mg/250 gsoil.
When soil moisture was increased to 48# (saturation),
Eh decreased to 300 mV and N0~ loss increased to 29.5 mg/250 g soil.
The addition of organic matter at 48# soil moisture did not change the
Eh, but increased the NO” loss to 49 mg/250 g soil.
Smith, Gilbert
and Miller (1976) measured redox potentials on a cropped potato pro­
cessing waste water disposal field, which had a fluctuating water
table.
In the winter months when the water table was low, redox poten­
tials increased (300 to 600 mV) and denitrification was slow.
As the
water table rose in the summer, redox potentials decreased to -400 mV
and denitrification was rapid.
The soil contained enough organic mat­
ter from the processing water to supply energy for denitrification.
11
Denitrification would also be slower in the winter due to lower tem­
peratures.
Enfield (1977) designed a system to optimize nitrification-
denitrification in a soil column by using redox potential probes at
different soil depths.
By controlling redox potentials at 6 cm for
nitrification and 30 cm for denitrification N removal was 43^.
Municipal sludge was added to the soil column at the rate of 1.3 g
C/gN denitrified.
The addition of sludge into the soil increased N
removal from the wastewater by 905&.
Hill (1972) tested six Connecticut soils and classified them
as good or poor renovators after a two year study.
Acid soils removed
P04 , K+ , Ca**1"| and Mg"*"*1", but little NO^, Cl , SO^ or Na+ were removed.
Soils with the lowest permeability removed the largest amounts of
nutrients.
DeJong (1978) found similar results when sewage effluent
was applied to a sandy loam.
Chloride and SO^ both appeared before
one pore volume had leached through, indicating incomplete mixing be­
tween the soil solution and effluent.
Sodium, Ca4"1", and Mg44 adsorp­
tion was affected by exchange reactions between these cations.
Tertiary Treatment of Wastewater
Tertiary treatment of water is necessary to meet water quality
standards for wastewater discharge.
Stenburg, Convery and Swanson
(1968) pointed out that wastewater treatment should be tailored to the
waste involved and the quality of effluent required.
Pilot tertiary
treatment plants are a necessity to study the most effective and eco­
nomical way of operating tertiary treatment systems.
The District of
Columbia Water Pollution Control Plant in Washington, D.C. is testing
12
and evaluating different systems.
Two of the most promising systems
are ammonia stripping and biological nitrification-denitrification.
Ammonia stripping involves increasing the water’s pH to 11 then cir­
culating the water with 400 cubic feet of air per gallon to allow
volatilization.
This process can remove 959» of NH^ at a cost of 816
per million gallons of effluent, but is not effective on nitrified
effluent.
The nitrification-denitrification process involves micro­
organisms previously discussed.
For nitrification the wastewater is
aerated with activated sludge, an organic C source (methanol) added
and the wastewater run through a carbon or sand filter where denitri­
fication can occur.
This process can remove
85% of N in wastewater.
Stenburg et al. (1968) estimated that tertiary treatment costs S260
to $300 per million gallons.
Renovated water could be sold for reuse
and thus defray part of the tertiary treatment costs.
The South Tahoe Public Utilities District has been testing
several tertiary treatment methods since 1961.
Preserving the quality
of Lake Tahoe and the surrounding recreational areas was a major con­
cern.
The treatments used in this pilot study were chemical coagula­
tion, mixed media filtration with polyelectrolyte filter, and a carbon
adsorption filter (Culp 1968).
One of the processes tested used alum
to precipitate N and P in the wastewater.
The alum treated water was
subsequently filtered through two mixed media beds and passed upwards
through an activated carbon column, then chlorinated.
The expense of
using alum in tertiary treatment led to the development of a process
using lime, which can be reclaimed and reused.
Lime precipitates P
and increases the water's pH to 11 for ammonia stripping.
Culp (1968)
13
stated that this process was more dependable than denitrification and
that there were no liquid or solid wastes for disposal*
P removal with lime was 98%.
in removing
Nitrogen and
An activated carbon filter was effective
80% of the organics in the water.
Water from this treat­
ment plant was clear, colorless, odorless, free of coliform bacteria
and virus, and generally indistinguishable from drinking water (Slechta
and Culp 1967).
In 1963, Culp estimated that tertiary treatment would
cost $30 to $90 per million gallons.
In 1968, the actual operating
cost of the 7.5 million gallons per day plant at Lake Tahoe was $150
per million gallons.
Eliassen and Tchobanoglous (1968) cited ammonia stripping, ion
exchange, electrodialysis and electrochemical treatment of effluent as
methods for removing N from wastewater.
They said that nutrient re­
moval cost was greatly affected by the disposal method used for pollut­
ants removed.
St. Amant and McCarty (1969) used a six-foot filter of
one inch diameter gravel to reduce NO” content in wastewater.
Waste-
water was passed up through this filter for a one hour detention time.
Reduction of 20 ppm N0”-N was 90% when 60 ppm methanol was added to the
wastewater.
Water must be chlorinated after this treatment to oxidize
any NO^ present in the reclaimed water due to incomplete conversion.
Filtration of the renovated water was necessary to remove biological
solids and aeration was necessary to prevent any excess methanol from
depleting oxygen in the discharge water.
would be $1.55 per million gallons.
Cost of this tertiary process
This figure does not include
aeration, filtration, and chlorination.
14
Francis and Callahan (1975) discussed three methods of treating
high NO” wastewater:
oodified-activated sludge units, packed bed
reactor, and anaerobic columns.
The optimum pH range for denitrifica­
tion depends on the electron donor.
nitric oxide are produced.
form.
Below pH 7, nitrous oxide and
Above pH 7, nitrogen gas is the predominate
The optimum temperature range for denitrification was from 15 to
60 C, depending on the organism involved.
Modified-activated sludge
units require a long residence time to prevent loss of microbial mass.
A packed bed reactor contains an inert material, which provides surface
area for microbial growth, through which effluent is passed.
Biomass
accumulation necessitates periodic back washing of the filter.
Anaerobic columns have a lower pore space than a packed bed reactor
and can handle water containing 1000 ppm N0”-N which is low in sus­
pended solids.
Cations in the wastewater will determine the design to
be used.
Land Disposal of Wastewater
Thomas and Harlin (1972) categorized land treatment into three
approaches:
runoff.
infiltration-percolation, cropland irrigation, and spray-
High rate infiltration techniques can handle up to 91 m of
water per year.
Soil physical, chemical, and biochemical reactions
purify the wastewater.
less than 3 m per year.
removal.
Crop irrigation requires more land area, using
The crop is primarily responsible for nutrient
Spray-runoff can be used on impermeable soils and requires
a vegetative cover to improve wastewater quality as the liquid moves
over the surface.
Industrial plants using this method have found
15
decreases in suspended solids, oxygen demanding substances, and nitro­
gen.
Problems limiting the use of land treatment are:
heavy metals,
disease, soil properties, salt accumulation, aesthetic objections, and
availability of land close to the treatment plant.
Materials applied to the soil can be volatilized, retained by
physical or chemical adsorption, leached, biologically degraded, or
appear in runoff.
renovation are:
Characteristics of the wastewater which affect
pH, pollutant form and concentration, complementary
or accompanying ion concentration, disposal variation, and temperature.
Soil characteristics which influence renovation include:
bulk density,
particle density, clay mineralogy, CEC, and resident exchangeable ions
(Hajek
1969).
Effluent Use for Irrigation and Crons
Eastman (196?) cited the importance of land application in arid
and semi-arid lands.
In 1962, California, Arizona, Colorado, Nevada,
New Mexico, Texas, and Washington had
89# of the sewage treatment
plants that utilized land application of sewage effluent.
served
96.
of the population in the 17 western states.
These plants
Most of these
plants use wastewater for irrigation of crops not directly consumed by
humans and this irrigation practice started before World War II.
Irri­
gation with effluent may prevent pollution of surface waters, yet con­
tribute to groundwater pollution.
Reuse of wastewater was studied by Los Angeles in 19^9 (Parkhurst
1965)•
By 1962, a water reclamation plant at Whittier Narrows
was returning 12,000 acre-feet per year to groundwater and more water
16
reclamation plants were planned.
from residential areas avoiding
trial wastes.
These plants reclaimed wastewater
the complications of handling indus­
Reclaimed wastewater can also be used to prevent salt
water intrusion into groundwater supplies (Parkhurst 1965; White 1975)•
Livermore, California, uses reclaimed water for golf course ponds, for
fire protection, and for irrigation of golf courses, airport grounds,
and a junior college campus (Parness 1968).
To avoid discharging
wastewater into surface waters, St. Petersburg, Florida was spray irri­
gating parks and golf courses with secondary effluent (White 1975)•
By irrigating 2,500 acres around the city with effluent, potable water
supplies were conserved.
In Tucson, the Randolph Park sewage treat­
ment plant was designed to meet 7596 of golf course and park water re­
quirements during summer months (Roll 1974).
fertilizer costs.
Use of effluent reduces
Johnson (1973) suggests that cities can be viewed
as "effluent rich," when effluent available exceeds what is used on
recreational areas, or "turfgrass poor."
He suggests that effluent
rich cities develop more parks for recreation, effluent disposal, and
groundwater recharge to remedy being "turfgrass poor."
In Bakersfield,
California, municipal effluent has been used for irrigating agricul­
tural crops since 1912 (Crites 1975)•
million gallons per day, is used on
All the effluent produced, 15
2,500 acres.
The crops grown had
equal or larger yields compared to surrounding farms, except cotton
(Gossypium hirsutumL.) which was 20# lower.
This decrease in yields
illustrates the need for research into optimizing crop yields using
effluent.
Day has worked with effluent irrigation of crops since 1957
(Day, Tucker and Vavich 1962a) and finds more information is still
17
needed on:
maximum loading rate of effluent, effect of effluent on
soil properties, effect on crop yield and quality, and crop varieties
adapted to wastewater (Day 1973)•
After 14 years of effluent appli­
cation on a silt loam soil, Day, Stroehlein and Tucker (1972) found
increased soluble salts, nitrate in the C horizon, P in the surface
soil and modulus of rupture.
Infiltration rate decreased.
Sorghum
(Sorghum vulgare Pers.), barley (Hordeum vulgare L.), oats (Avena
sativa L.), and wheat (Triticum aestivum L.) have all been grown with
effluent giving equal or better yields than control plots grown with
equal amounts of fertilizer (Day, Tucker and Vavich 1962a, 1962b; Day,
Dickson and Tucker 1963, Day and Kirkpatrick 1973i Day, Rahman et al.
1974; Day and Tucker 1977)•
The malt quality of barley and the milling
and baking properties of wheat were lowered by effluent irrigation
(Day,"Tucker and Vavich 1962a).
Wheat hay had a lower relative feeding
value, but higher yields when grown with effluent (Day, Rahman et al.
1974).
Renovation of Effluent by Low Rate
Land Application
Kardos and Sopper (1973), working in Pennsylvania found that
corn (Zea mays L.), irrigated with 2.5 cm of effluent per week and
canary grass (Phalaris arandinacea L . ) , irrigated with 5 cm of effluent
per week were not effective in keeping NO^-N concentrations in the sub­
soil below 10 ppm.
A grass-legume hay mix and corn rotation could
renovate 5 cm per week.
Sopper and Kardos (1973) pointed out that
vegetation is a renovating agent and yields were increased with
effluent spray irrigation.
Overman and Ku (1976) grew rye (Secale
18
cereale L. ) , pearl millet (Pennisetum typhoides /Burrn?, Staff and C.
E. Hubb.), and ryegrass (Lolitun multiflorum Lam.) with effluent in
Florida.
Pearl millet utilized
50^ for rye and ryegrass.
cent utilization decreased.
received
70%> of N applied, compared to 67& and
As the amount of N applied increased, per­
At the highest application rate, plots
10 cm of effluent per week.
for these crops.
The effluent was deficient in K
Hortenstine (1976) irrigated Coastal bermudagrass
(Cynodon dactylon L. Pers) and three tree species growing on a spodosol
with 5 cm of effluent per week.
Because of a high water table, NH^
in the effluent was not nitrified.
moved P.
The spodic layer effectively re­
Hortenstine (1976) also found the EC of the soil solution
was increased by effluent applications.
Parker et al. (1974) reported
on lysimeter studies conducted using swine lagoon effluent.
effluent load was 2.5 cm/week.
The
Total N removed was 99&» 20# of which
was recovered in grass clippings on the lysimeters.
They found that
regulation of the size of aerobic and anaerobic soil reaction zones
for oxidation of NH^ to N0“ , and passage of nutrients sufficient for
energy requirements of denitrifying microorganisms, appear to be the
critical criteria for N removal.
In 1967i Pennypacker, Sopper and Kardos applied effluent on a
loam soil in a mixed hardwood forest, a red pine plantation, and an
old abandoned field in Pennsylvania.
%
and
5.8 cm per week.
decreased 75 to
Test plots were irrigated at 2.5
They found NO^-N decreased
86#, and P decreased 99#*
68 to 82#, organic-N
Renovation of the effluent
was achieved by filtration and adsorption through the soil, and
19
biological activity in the root zone.
Hook and Kardos (1978) found
that a hardwood forest on a sandy loam was an ineffective renovator of
effluent applied at 5 cm per week.
White spruce forest on a clay loam
irrigated at the same rate kept the NO”-N concentration below 10 ppm.
Factors to be considered in using forests for reclamation are:
litter
decomposition, humus mineralization and microbial population size.
Youngner, Williams and Green (197*0 spray irrigated chaparral in San
Bernardino National Forest at rates of 0, 1.9, 4.4, and 8.9 cm per
week.
Increasing the irrigation rate increased chaparral growth by
releasing the plants from limiting environmental factors.
with effluent altered species distribution in the area.
Irrigation
After three
years of treatment no evidence of stream or groundwater degradation
could be found.
The combined removal capabilities of the soil and
grasses accounted for nearly all the nutrients applied in the effluent.
Chadwick et al. (1974) used polluted river water in England to
spray heathland at rates of 4.9 to 18.3 cm/day.
the NH^ was removed.
At both rates, 96% of
At the low rate, 26% of the NO” was removed, but
at the high rate, NO” increased 14%.
The polluted river water (4 ppm
NH^-N and 7 ppm NO^-N) increased yields on the heathland, but did not
appear to affect the balance of plant species.
This system of disposal
improved groundwater recharge while purifying river water.
A camp­
ground in Minnesota has used a peat and sand filter with stalked blue
grass to treat effluent (Osborne 1975)•
This filter removed 46% of
the N applied, 99% of P applied, and 99% of the coliform bacteria.
This tertiary treatment allowed use of effluent water to replenish the
lake without causing eutrophication.
Parizek (1973) cites several
20
factors that should be considered when selecting a site for irrigation
with effluent.
Application rate and precipitation must exceed evapo-
transpiration in order for salts to be leached.
Good subsurface
drainage is necessary and the hydraulic conductivity of the soil must
allow a long enough residence time for renovation.
Soil thickness, ion
exchange capacity, and topographic setting are also important.
On any
land application system monitoring subsoil solution is essential.
High Rate Infiltration-Percolation
Crops and forests have been shown to be effective renovators
when effluent was applied at rates of 2 to 5 cm per week.
Bouwer,
Lance and Riggs (1974) have shown that high rate infiltration methods
can renovate 91 meters of effluent per year using 3*7 acres of infil­
tration basins for each million gallons per day of effluent.
rate of application, N removal is 30#*
At this
Purification of the effluent is
dependent on nitrification of ammonium and denitrification of nitrate
as described previously in Lance and Whisler* s (1972) work.
The flood/
dry cycle of effluent application must be experimentally determined for
maximum purification.
The optimum cycle will depend on the CEC of the
soil, exchangeable NH^ percent, infiltration rate, and NH^ concentra­
tion in the effluent (Bouwer, Lance and Riggs 1974).
Lance and
Whisler (1972) pointed out that the length of the flooding period
should not be increased beyond the soil's capacity to adsorb NH^.
The
high NO^ concentration occurring at the beginning of each flood period
can be collected, mixed with new sewage and reapplied, increasing N
removal to 8C$ (Lance, Whisler and Rice 1976).
Mixing the high nitrate
21
water with sewage increased the organic C content for denitrification.
Vegetation on the surface of high rate infiltration basins increased
denitrification and aided in maintaining a high infiltration rate by
filtering out suspended solids.
Bouwer (1970) noted that aesthetically,
recharge water has the advantage of being collected as groundwater and
in the process loses its identity as sewer water.
To avoid degrading
groundwater quality, renovated wastewater can be pumped out of the
aquifer at some point away from the application area (Bouwer 1976) and
reused for irrigation, industry or city needs.
Most quality improve­
ment of the wastewater takes place as it percolates through the first
meter of soil (Bouwer 1970).
Amramy (1968) cited an example in Israel where high rate in­
filtration was used.
The optimum cycle was found to be 2 to 3 days
wet and 7 to 8 days dry.
Total N was decreased 64 to 84#.
The water
was of potable quality except for the NO™ peak which occurred when
;
5
wastewater was applied after the dry period.
these basins decreased from an average of
920 days.
Infiltration rates on
80 cm/day to 50 cm/day after
After 18 months of using these basins the hydraulic conduc­
tivity of the subsoil decreased; this may have been due to salts in
the effluent affecting the clay subsoil.
Reclaimed water was mixed
with fresh water (2:1 ratio) to reduce NO^ and Cl” content prior to
reuse.
By excluding industries from the region that might contribute
harmful wastes, this reclaimed water was available for reuse, rather
than being disposed of in the sea.
The high rate infiltration method of wastewater reclamation
can be complicated by accumulation of suspended solids on the soil
22
surface forming a thin layer of high impedance (Bouwer, Rice and
Escarcega 197*0 •
problem.
Periodic clearing of the basin surface relieved this
Thomas (1973) cited soil clogging as the main disadvantage
of high rate infiltration systems.
Clogging usually occurs under
anaerobic conditions on the soil surface and can be remedied by drying
the soil surface.
Rice (197*0 determined that for a given suspended
solids load, impedance of the clogged layer increased with an increas­
ing hydraulic gradient.
Amount of water infiltrated increased with an
increased hydraulic gradient.
Increasing suspended solids in the
wastewater increased hydraulic impedance.
Suspended solids moved
further into the coarse sand creating a thicker layer of clogged soil.
Three years of infiltration decreased hydraulic conductivity 50 to
60%.
Rice (197*0 proposes this decrease in conductivity may be the result
of trapped
gas, unable to move through the clogged soil layer.
Spray-runoff Land Treatment
Law, Thomas and Meyers (1970) evaluated cannery wastewater
treatment in which
7.62 cm per week was applied to land with red canary
(Pholaris acundinacea L.), tall fescue (Festuca arundinacea Schreb.)
and red top (Agrostis stolonifera L.)grasses growing.
Runoff accounted
for 6l3» of the water applied, 21% of the wastewater entered the soil
and 18% of the water was lost to evaporation.
the N applied was removed.
The sandy loam soil had a greater treatment
efficiency than the clay loam.
3*6 million gallons per day.
In this treatment 85% of
This spray system had the capacity of
Bendixen et al. (1968) compared spray,
flood, and ridge-furrow irrigation as methods of wastewater renovation.
23
On a long term basis, spray irrigation removed 30# of N applied, flood
irrigation removed 17% and ridge-furrow irrigation 14#.
The conclusion
from these tests was that the ridge-furrow system would have the
longest life and was best adapted for use in northern latitudes.
Adriano et al. (1975) reported on long term land disposal of
food processing wastes.
Nitrate and PO^ exceeded public health stan­
dards in the groundwater at sites used 10 and 20 years for waste dis­
posal.
Vegetation on sites did improve nutrient removal.
Lehman
(1968) concluded that overland flow using Bermuda grass for filtration
did not reduce the N content of effluent.
In experiments using inter­
mittent flooding of soil columns seeded to bermudagrass, Lehman con­
cluded that the cycle of one day flood with 10 cm water and three days
dry would be the most effective for water renovation.
This study attempted renovation by secondary effluent applied
at high rates to a soil-turf filter.
Turfgrass was the crop chosen
for this study because it can be grown year round and the grass uti­
lizes large amounts of N.
Maintenance of the turf would be less costly
if effluent was used as fertilizer and water.
The use of effluent to
water recreational areas would leave more groundwater available for
household use
MATERIALS AND METHODS
This study was conducted at The University of Arizona* Rincon
Vista Turfgrass Research Center in Tucson.
The experiment was con­
ducted in order to determine the maximum rate of effluent that could
be applied to a soil-turf filter and yield recharge water meeting USPHS
standards.
For this study, effluent, recharge water, and grass clip­
pings were all analyzed for N to obtain the N balance for the system.
Materials
Twenty lysimeters were used in this study.
Ten units were
filled with 99% sand, 1% silt, and 4# clay, referred to as sand.
sand soil had a CEO of 2.1 meq/100 g soil.
tained
as mix.
The
The other 10 units con­
89% sand, 9% silt, 4$ clay and 2% organic matter, referred to
The mix soil had a CEC of 4.8 meq/100 g soil.
The organic
matter added to the mix soil was Loamite, a sulfuric acid treated red­
wood bark.
Both soils had a pH of 8.3 and were texturally sands.
Units were arranged in a split plot design, with two.different soils,
five application rates, and two replicates of each rate.
The lysimeters used in the study were one meter square by 60 cm
deep.
These units were constructed with wooden walls and lined with
sheets of 6 mil polyethylene plastic.
The bottom of the lysimeter was
sloped towards the center where a polyethylene tube was sealed into
the plastic lining.
Tubes leading out of each lysimeter were placed on
a slope so water would flow to an underground service area.
24
25
Barrels were placed in the service area, below the bottom of
the lysimeters, to collect leachate from the plots.
A glass tube was
inserted into the barrel and calibrated to indicate the amount of
water contained in each barrel.
Plastic tubes at the bottom of each
barrel were inserted to allow sample collection and drainage of the
barrels between irrigations.
A stand was built beside the plots to elevate barrels.
barrel was assigned to each plot.
One
The barrels were calibrated to over­
flow when they had been filled with appropriate amounts of effluent.
Effluent was delivered by gravity flow from the barrel to the plot,
using 15 mm drip irrigation tubing, with emitters that could deliver
four gallons per hour at 15 pounds of pressure.
The secondary effluent used in this study was obtained twice
a week from the Randolph Park Sewage Treatment Plant.
Effluent from
this plant is stored in a lagoon and used to water the surrounding
golf course and park.
Lagoon storage of effluent and seasonal changes
caused the nitrogen composition of the effluent to vary, due to
microbial transformations (Fig. 1).
In the summer the effluent con­
tained 17 to 23 ppm NH^-N, 0.5 ppm N0”-N, and 2 to 5 ppm organic-N.
In winter, values were 3 to 6 ppm NH^-N, 4 to 16 ppm N0~-N, and 1 to
5 ppm organic-N.
Two types of grass were used in this study.
A cool season
annual ryegrass (Lolium multiforum Lam.) was used from 30 April to 3
Jun e .1977 and from 4 November 1977 to 28 April 1978.
During the inter­
vening summer months plots were seeded to warm season bermudagrass
—
» nh ; - n
•--- - N O j - N
--------* organic-N.
14 28
II
MAY
JUNE JULY
25 9
23
6 20
3
17
AUGUST SEPT.
I
15 29
OCT.
12 26 10 24
7
NOV.
JAN.
DEC.
21 4
FEB.
18 4
18 I
MARCH
15 29
APRIL
1977 |1978
Figure 1.
Effluent N composition during the year long study,
&
27
(Cynodon doctylon L. Pers).
To insure a good stand of grass, addi­
tional tap water was applied between effluent applications during
reseeding.
Methods
Effluent Application
Plots were irrigated twice a week.
A 300 gallon tank trailer
with a pump welded to the side was used to transfer effluent from
Randolph Park to Rincon Vista.
Effluent was pumped into each barrel
0.5 to 1 hour depending on irrigation levels.
and barrels drained in
High infiltration rates for both soils eliminated ponding of effluent
on the soil surface.
Immediately after irrigation of all plots, drip
irrigation lines were removed.
In the service area, a hand-operated
vacuum pump or aspirator was used to evacuate air from lysimeter tubes
and initiate the flow of gravitational water.
drain four hours before
Plots were allowed to
250 ml leachate samples were collected from
each barrel in the service area.
Final leachate volumes, indicating
the amount of water available for recharge were noted the next day.
Collection barrels in the service area were emptied between irrigation.
Sample Collection
Samples of leachate were collected after four hours.
were frozen at 4 C after collection from the service area.
Samples
For each
two week period four 250 ml samples were combined to form a composite
sample of 1 liter of leachate from each lysimeter.
These combined
samples were stored at room temperature for 1 to 2 weeks, until
28
analysis.
A study of samples stored at room temperature showed no N
transformations occurred if the bottles were kept free of algae.
Effluent samples were collected at each irrigation, frozen
immediately, and later combined to form a composite sample before
analysis.
Nitrogen transformations were found to occur if effluent
samples were left at room temperature; therefore these samples were
always refrigerated.
Grass clippings were collected once a week when plots were
mowed to a height of 1.5 inches.
weighed to obtain total yields.
Clippings were dried at
86 C, then
Samples from both mowings for a two
week period were combined and ground for subsequent chemical analysis.
Chemical Analysis
Leachate and effluent samples were analyzed for N content using
micro-Kjeldahl techniques (Bremner 1965).
A 25 ml aliquot of leachate
or effluent was used in steam distillation for NH^-N and NO~-N.
Mag­
nesium oxide was added to the sample first for distillation of NH^-N.
Then Devarda1s Alloy was added to the same sample for distillation of
NO~-N.
Distillate was collected in boric-acid indicator solution and
titrated with
0.005 normal potassium biiodate.
A 50 ml aliquot was used in micro-Kjeldahl digestion to de­
termine organic-N.
A potassium sulfate-catalyst mixture was added to
the sample with 3 ml of concentrated sulfuric acid.
Samples were
heated for two hours to evaporate water and digest organic-N.
samples were subsequently distilled after the addition of
sodium hydroxide.
viously stated.
These
15 ml of 50#
The same indicator and titrant were used as pre­
29
Grass clippings were analyzed for organic-N using 100 mg
samples.
Catalyst and acid were added as previously described.
Grass
samples were heated four hours to allow for complete breakdown of
organic-N.
Samples were distilled after sodium hydroxide was added,
then titrated with
0.02 normal potassium biiodate.
Effluent Application Rates
Irrigation rates were based on consumptive water use rates
determined by Krans and Johnson (197*0.
Maximum consumptive water use
of creeping bentgrass (Agrostis palustris Huds.) occurred in August and
was 5 mm/day.
This maximum consumptive use served as a basis for de­
termining rates of effluent application.
In a preliminary study 30
April to 3 June rates of 1 to 4 times consumptive use were used.
daily basis this was 5 to 22 mm per day.
On a
Leachate from this study
indicated 95& of the N applied was removed.
On 3 June, the annual rye­
grass was removed and warm season bermudagrass reseeded.
Also, at
this time rates were amended to include two higher rates of application.
These rates were approximately seven and eight times consumptive use or
34 and 43 mm/day respectively.
' 42 week study.
Table 1 shows the rates used for the
Plots were allowed to equilibrate with these higher
rates for five weeks.
Plots receiving 10, 17, and 22 mm/day were not
changed for the entire year.
Interpretation of Data
The nitrogen balance of this system was based on a N input in
the form of effluent.
pings or N in leachate.
Nitrogen output was in the form of grass clip­
Additional losses of N occurred via
30
Table 1.
Effluent application rates used 3 June 1977 to 28 April 1978.
Rate in Multiples
of Consumptive Use
Rate (imn/day)
Liters Applied
Twice a Week
2
10
36
3
17
58
4
22
76
7
34
120
8
43
152
31
adsorption, denitrification, and volatilization processes in the soil.
Reactions occurring in the soil were determined indirectly as the dif­
ference between effluent-N input and clipping-leachate-N output.
The
efficiency of the soil-turf filter in removing N was evaluated by N
removed.
of leachate (liters) x total ppm N
of effluent (liters) x total ppm N
% N removed
The ability of the grass to utilize the applied N was determined by
percent utilization.
% N utilization = l VU of «UPPi°8». <g) * organic-H
x
100
iVol. of effluent (liters) x total ppm N j
The ability of the soil turf filter to supply water for reuse or groundwater recharge was evaluated by percent water recharge.
* water recharge . (%
£
g
%
£ £
*100
These are the three main criteria that were used to evaluate the effec­
tiveness of the soil-turf filter.
All data were statistically analyzed
for significant differences at p =
0.05 level.
RESULTS AND DISCUSSION
This study was conducted from 50 April 1977 to
Initially the treatments used were:
an additional
28 April 1978.
5i 10, 17, and 22 mm/day; with
22 mm/day treatment in which a water table was maintained
in the lysimeter.
After five weeks, the data collected indicated a
consistent 933» N removal. On 3 June the 5 mm/day rate was changed to
!
34 mm/day and the water table treatment was changed to 43 mm/day with­
out a water table.
Statistical analysis of all five rates started
with the sample period beginning 11 July.
The five week interim allowed
the plots to equilibrate with the new effluent application rates.
Water Recharge
Percent water recharge indicates the quantity of water that
would be available for reuse with this tertiary treatment system.
Statistical analyses of the study from 11 July 1977 to 28 April 1978,
showed that recharge, as affected by rates and soils, was significantly
different at p =
0.05 level and the main effect of time was significant
at p = 0.01 (Table 2).
Figure 2 illustrates recharge values for all
five rates, averaging replicates, on the sand soil for the year long
study.
Figure 3 illustrates the same data for the mix soil.
recharge for each rate was averaged for both soils over
periods, only the
When
21 time
10 mm/day rate was significantly different from the
other four rates, as shown in Table 3»
32
Rates were not broken down by
33
Table 2.
Source of
Variation
Analysis of variance for percent water recharge 11 July 1977
to 28 April 1978.
Degree of
Freedom
Mean
Square
F
Value
4
5811.89
5.28*
Soil
1
6335.90
5.76*
Time
20
1302.98
31.94**
R x S
4
969.00
R x T
80
158.15
S x T
20
26.70
.65
R x S x T
80
51.39
1.26
•Significant at the 0.05 level of probability.
••Significant at the 0.01 level of probability.
OO
OO
•
Rate
3 .88**
"Effluent Appllcolton Rate (mm/day)
—— ■ |o
100
*
• 17
o • 22
o - 5 4
--------- 4 3
Percent Water Recharge
.
H
28
II
Figure 2*
29
. AUGUST
SEPTEMBER
OCTOBER
K>
24
12
NOVEMBER DECEMBER
JANUARY FEBRUARY
MARCH
Percentage water recharge for all effluent application rates on sand.
Effluent Application Rate (mm/day)
------ ■
o
10
.1 7
Recent Water Rechar
o ■ 22
a ■ 34
----- -- 43
14
29
26
JULY
AUGUST
SEPTEMBER
12
NOVEMBER
DECEMBER. JANUARY FEBRUARY
1977 I 1978
Figure 3»
Percentage water recharge for all effluent application rates on mix.
36
Table 3»
Percent water recharge means.
Rate (mm/day)
Average # Water Recharge
Overall
Sand
Mix
10
58a
67
49
17
79b
82
77
22
70b
76
64
. 34
77b
79
75
43
72b
72
71
LSD = 11.4
Any two means with a letter in common are not significantly different
(p = 0.05).
37
soil because the analysis of variance showed that the rate by soil
interaction was not significant.
lowest on the recharge graph.
charge at the
The 10 mm/day rate is generally the
Figure 2 does show an increase in re­
10 mm/day rate during October and January.
Rainfall was
high during these months and this probably contributed to the increased
percentage of recharge.
The 10 mm/day rate was only twice peak con­
sumptive use, so soil moisture had a greater effect at this rate than
at the higher rates.
Table 4 illustrates the effect of evapotranspiration on re­
charge values.
As the effluent application rate increased, grass
yields increased.
By comparing yields and evapotranspiration, it is
clear that at the higher rates plants were consuming more water per
gram of clippings than at the low rates.
consumption of water.
These data indicate a luxury
In areas where recharge is a primary concern,
effluent application could be regulated to avoid excessive water loss
due to vegetative transpiration.
Table 4 also shows that as applica­
tion rates increased, volume of recharge water increased, even though
the percent water recharge showed no significant difference.
Growth rates would also influence the amount of water available
for recharge.
Table 4 shows a similar value of evapotranspiration per
gram of dry clippings for effluent application rates of
mm/day.
10, 17, and 22
At these rates, clipping yields increased with increasing
effluent application; while evapotranspiration per gram dry matter
averaged 2.4 liters/gram.
At effluent application rates of 34 and 43
mm/day, the difference between yields was not significant, but evapo­
transpiration per gram of dry clippings increased to am average of
Table 4.
Total recharge volumes, total eyapotranspiration volumes, and total grass yields for
30 April 1977 to 28 April 1978.
Rate
(mm/day)
Vol. Effluent
Applied
(liters)
10
3,744
2,352
1,719
1,392
2,025
554
762
2.51
2.66
17
6,032
4,746
4,496
1,286
1,536
644
930
2.0
1.65
22
7,904
5,986
5,034
1,918
2,870
758
960
2.53
2.99
34
12,480
8,936
8,563
3,544
3,917
798
1,084
4.44
3.61
43
15,808
10,586
9,824
5,222
5,984
770
1,098
6.78
5.45
Recharge Vol.
(liters)
Sand
Mix
Evapotranspiration
(Applied-Recharge)
Sand
Mix
Total Yields (g)
(dry wt.)
Sand
Mix
ET liters/g
Yield
Sand
Mix
VI
oo
39
6 liters/gram.
These data indicate at the high effluent application
rates, the turf reached a plateau in growth response.
A seasonal trend in recharge can be seen in Figures 2 and 3«
Recharge volumes in the summer months were lower than those in the
winter months.
This trend was due to seasonal variations affecting
the soil-turf filter.
Figure 4 shows temperature and precipitation
data collected at Rincon Vista during the study.
In the summer,
moisture loss increased due to evaporation from the soil surface, and
transpirational water loss by bermudagrass.
Relative humidity would
play an important role in determining transpirational water loss.
Be­
cause the soil surface is protected by turf, surface evaporation would
have a small effect on soil moisture loss.
In winter, cooler tempera­
tures and increased precipitation decreased moisture loss from the
lysimeters, increasing the volume of water for recharge.
In June and November all growing turf was removed (scalped)
and reseeded to the appropriate warm or cool season grass.
During
these periods of reseeding, plots were watered several times a day to
aid seedling establishment between effluent applications.
The increase
in percentage of water recharge during these months could be due to
this excess tap water maintaining soil moisture.
Percentages would
also be higher during these periods due to less transpirational water
loss because a turf stand was not established.
The
10 nan/day rate on
the sand soil showed a greater fluctuation during reseeding than the
same rate on the mix.
The 10 mm/day rate on the sand also appeared to
be more influenced by precipitation.
Peaks for
10 mm/day on sand
occurred in October and January, corresponding to periods of rainfall.
Temperature (°C)
MAXIMUM TEMPERATURE
Rainfall (cm)
MINIMUM TEMPERATURE
14 28
MAY
II 25 9
JUNE
23
JULY
6 20 3
AUGUST
17 I
SEPT.
15 29 12 26 10 24 7
OCT.
NOV.
21 4
DEC. , JAN. FEB.
18 4
18 I
MARCH
15 29
APRIL
1977 1978
Figure
4.
Maximum and minimum air temperatures and rainfall measured at Rincon Vista
Turfgrass Research Center during the year long study.
41
The larger water holding capacity of the mix soil probably buffered
these changes, so less fluctuation was seen, even at
10 mm/day.
At the 10 mm/day rate recharge from the sand soil averaged 18#
more than recharge from the mix.
At 43 mm/day rate the average re­
charge from the sand was 1.5# more than from the mix.
As rate of
effluent application increased, there was less difference in percent
recharge values between rates and less difference in recharge between
soils (Table 3).
Figure 5 illustrates the recharge trend for both
soils, averaging all five rates for each soil.
lower water holding capacity, averaged
The sand soil, with a
8# higher recharge than the mix.
Differences between soils over time were consistent, with no signifi­
cant interaction (Table 2).
This consistent difference between re­
charge values for the two soils, shown in Figure 5, indicated a physi­
cal property, rather than evaporation or transpiration which would
vary with season.
The difference in water holding capacity between
these two sand soils would be due to the presence of 4# more silt and
2# organic matter in the mix soil, which increased the water holding
capacity of the mix.
The effect of evaporation and transpiration on recharge is
shown by the seasonal trend in Figure 5*
Lower evaporation and trans­
piration in the winter months contributed to larger recharge volumes.
Lower yields on the sand (Table 4) were associated with lower transpirational loss and consequently higher recharge rates (Fig. 5).
The
evapotranspiration per gram of dried clippings at the two highest
application rates indicated that the turf on the sand soil used water
less efficiently than the turf on the mix.
This increased loss could
■ mix
o
60
14 28
MAY
II 25
JUNE
9 23 6 20 5 IT I
JULY AUGUST SEPT.
15 29
OCT.
12 26 10 24 7 21
NOV.
DEC. JAN.
4
18 4 18
FEB. MARCH
I 15 29
APRIL
1977 1978
Figure 5»
Percentage water recharge, showing all five effluent application rates
averaged for each soil.
tu
43
be due to increased transpiration or evaporation on the sand-soil
plots.
Increased yields on the mix soil indicated more leaf surface
area to transpire and actual ground evaporation was probably minimal.
The mix soil had higher grass yields and higher transpiration losses
(Table 4) decreasing the total volume of recharge water available for
reuse.
Seasons, soil water holding capacity, and turf growth all
affect the amount of recharge water available from this soil-turf
system.
Utilization
Percentage N utilization indicates the amount of N utilized by
turf for growth.
There were significant (p = 0.01) rate, soil, and
time effects on N utilization and these interacted with each other
(Table 5).
Figure 6 illustrates utilization values for all five rates,
averaging replicates, on the sand soil for the year long study.
7 shows the same data for the mix soil.
Figure
Dashed lines over time periods
in June and November indicate periods of scalping and seedling estab­
lishment.
During these times no clippings were collected.
Clippings
collected during scalping were not included on the graph or in sta­
tistical .analysis (except Table 4, and Table 11, p. $8).
Scalping
removed most of the organic matter from the soil surface and created
utilization values ranging from 39 to 117% on the sand and 55 to 154%
on the mix.
Figures 6 and 7 demonstrate that the lower application
rates had a higher percent utilization values than the higher applica­
tion rates.
As application rates increased, amount of N applied
44
Table 5.
Source of
Variation
Analysis of variance for N utilization, 11 July 1977 to
28 April 1978.
F
Value
Degree of
Freedom
Mean
Square
Bate
4
3597.72
53.89**
Soil
1
6063.34
90.82**
Time
18
2753.08
159.50**
R x S
4
190.93
2.86*
R x T
72
152.49
8.83**
S x T
18
93.12
5.40**
R x S x T
72
46.33
2.68**
•Significant at the 0.10 level of probability.
••Significant at the 0.01 level of probability.
r
E flhw it AppKeotion Rote (mm/doy)
-- - 10
e
■ 54
14
26
MAY
Figure 6.
JULY
AUGUST
SEPTEMBER
NOVEMBER DECEMBER
JANUARY FEBRUARY
MARCH
1977 | 1978
Percentage N utilization for all effluent application rates on sand.
vn
'£
47
increased, but N utilization was limited by N uptake and plant growth.
At the 10 ram/day rate, utilization accounted for 3296 of N applied
when averaged over soils and time (Table 6).
of the N applied was utilized.
At 43 mm/day only 1596
Table 6 shows the means for utiliza­
tion at each rate are significantly different at p = 0.05.
Rates were
not ranked on each soil because the analysis of variance showed rate
by soil interaction was not highly significant (Table 5)»
A seasonal trend can be seen in Figures 6 and 7, and Table 5
shows significant rate by time interaction.
A good turf stand and
favorable climate for the grass species used was necessary to maximize
N utilization.
August through September appear to be most favorable
for bermudagrass growth.
Decreasing utilization in October marked a
change in weather as shown by Figure 4.
grass for the cooler months.
able for ryegrass growth.
Plots were reseeded to rye­
February through April were most favor­
From these graphs there is evidence that
ryegrass utilized more nitrogen during its growing season than bermuda­
grass, regardless of rate.
Table 7 shows yield and percent N data for bermudagrass and
Table 8 shows the same data for ryegrass.
These tables show that as
effluent application rate was increased, yields and percentage of N
in clippings both increased.
The mix soil had higher yields on rye­
grass at all rates, and on bermudagrass at the 34 and 43 mm/day rates.
Percentage of N in clippings was higher on the mix soil at the 43
mm/day rate for both grasses.
The higher yields on the mix soil were
possibly due to ttye higher CEO of the soil and a higher water holding
capacity.
Since the soils responded differently, for all three
48
Table 6.
Nitrogen utilization means.
% N Utilization
Rate (mm/day)
Overall
Sand
Mix
10
32a
26
38
17
27b
22
33
22
22c
20
25
34
l8d
15
21
43
15e
12
18
LSD = 2 . 8
Any two means with a letter in common are not significantly different
(p = 0 .05)•
Table ?•
Total yields and percent N (organic -N and NH4-N) in
bermudagrass clippings collected for 16 weeks, 11 July
to 29 October 1977-
Rate (mm/day)
Total Clippings (g)
Sand
Mix
%N
Sand
Mix
3.44a
10
159a
196ab
3-52ab
17
l 89ab
259b
3-72b
22
205ab
272bc
3.81b
3.85b
34
250b
352c
3.88b
3.84b
43
202ab
372c
3.86b
4.12c
.
3.87b
LSD for #N = .206
Any two means with a" letter in common are not significantly different
(p = 0.05).
49
Table 8,
Total yields and percent N (organic -N and NH^-N) in rye­
grass clippings collected for 22 weeks, 28 November 1977 to
28 April 1978.
Rate (mm/day)
Total Clippings (g)
Sand
Mix .
%N
Sand
Mix
10
211a
304b
3 .82a
4.0?ab
17
263ab
390c
4.19bc
4.44cd
22
322b
385c
4.29bcd
4.39cd
54
390c
522d
4.42cd
4.49d
43
396c
496d
4.50d
4.78e
LSD for 95 N = .260.
Any two means with a letter in common are not significantly different
(p = 0 .05 )•
50
parameters tested with statistics, this illustrates the influence of
CEO and organic matter on soil-plant relations.
These tables show that
ryegrass did utilize more nitrogen as shown by the increased percent N
in clippings from both soils.
It is unclear, from these tables, if a
growth plateau has been reached at effluent rates of 54 and 45 mm/day.
The decreased yields are not significantly different.
These figures
may be an indication that higher effluent application rates would have
a detrimental effect on turf growth.
The turf plots showed yellowing in the last month of bermudagrass growth (October 1977) and during the first months of ryegrass
growth (December 1977 through February 1978).
During these months,
the turf growing was generally a yellowish green.
chlorosis was due to Fe
deficiency.
caused micronutrient deficiencies.
It is possible this
The soil's pH of 8.5 could have
Chlorosis on the high effluent
application rate plots was more severe and present throughout the turf.
!
On the low rate plots, chlorosis was spotty.
A yellow strip effect
occurred in the first month of the experiment (May 1977)•
At this
time the effluent being applied was predominantly NH^" -N.
Using the
drip irrigation lines, N H ^
was held on the cation exchange sites
nearest the irrigation line.
gation lines due to lack of N.
Yellow areas developed in between irri­
By rotating the drip irrigation lines,
an even distribution of N was achieved and the yellow strips
eliminated.
Periods of decrease in utilization and subsequent recovery;
as seen in September, December, and January, could have been due to
removal of too much leaf area by mowing.
Plots were mowed to 1.5
51
inches height every week, regardless of how much growth had occurred.
In weeks of rapid growth, this amounted to a proportionately larger
decrease in leaf area.
Although the remaining leaf area was nearly
the same, whatever the amount of growth removed, the decrease in leaf
area while the root system remained the same size would slow turf
growth.
In this situation, photosynthate would probably be used to
maintain root respiration, decreasing photosynthate available for leaf
growth.
Nitrogen uptake would be decreased as the turf would have
less leaf area for photosynthesis, therefore less energy for growth and
assimilation of N.
This decreased utilization illustrates a disad­
vantage of mowing by time intervals, rather than by turf growth.
Figure 8 summarizes N utilization with all five application
rates averaged for each soil.
Comparing the utilization means for all
time and rates, ttirf on the mix soil utilized 8# more N on the average
than turf on the sand soil.
Seasonal trends, decrease in utilization,
and subsequent recovery can also be seen.
Figure 8 illustrates the
soils responded differently over the year long study and Table 5 shows
significant soil by time interaction.
The difference in soil response
is illustrated by the fluctuating distance between the two soil lines.
Turf on the mix soil recovered faster from periods of stress than did
turf on sand.
Higher N utilization during the period of ryegrass
growth is evident from this graph.
High N utilization on the mix soil
demonstrates the fact that grass yields and $ N in clippings from the
mix soil were higher.
Higher yields on mix could be explained by the
higher CEC of the soil and higher water holding capacity.
The higher
Percent N Utilization
— ■ sand
14 28
MAY
II 25 9 23 6 20 3 17 I 15 29 12 26 10 24 7
JUNE
JULY
AUGUST
SEPT.
OCT.
NOV.
DEC.
21 4
JAN.
18 4
18 I 15 29
FEB. MARCH
1977 1978
Figure 8.
Percentage N utilization showing all five effluent application rates
averaged for each soil.
APRIL
53
CEC would allow for more NH^
adsorption, making more K available for
plant growth.
The part of this study concerned with N utilization brought up
several questions that require further research.
The effect of
cation/anion concentrations in the effluent on plant uptake of nutri­
ents and toxicity of elements in the effluent accumulated by the soil
are important questions that must be answered in order to maximize
turf removal of nutrients from effluent.
Management practices; such as
mowing, reseeding, and method of effluent application, also need to be
studied.
The difference in N utilization between bermudagrass and rye­
grass indicates that further research into turfgrass cultivars might
lead to selection of turf grasses more effective in renovation.
Nitrogen Removal
Recent N removal reflects the quality of recharge water col­
lected.
The USPHS standard for nitrogen in potable water is 10 ppm
N O ^ - N (McKee and Wolf 1963) •
mine water quality.
This was the criterion used to deter­
The average N content of the effluent for this
study was 20 ppm -N so a minimum of $0# N removal was necessary to
meet USPHS standards.
The organic -N content of the leachate was less
than 1.0 ppm N at all rates.
The ammonium concentration in the leach­
ate was less than 0.5 ppm N for all rates.
The nitrate concentration
varied with time of year, as shown in Figures 9 and 10, ranging from
less than 1 ppm N0”-N to 20 ppm N0~-N.
checked for N0~, but none was found.
Leachate samples were spot
Statistical analyses for this
i
Effluent Application Rote (mm/doy)
-- - 10
a
o
■ IT
"22
o
■ 34
■ 43
18
AUBU8T
SEPTEMBER
OCTOBER
NOVEMBER
DECEMBER. JANUARY FEBRUARY
8#
MARCH
1977 I 1978
Figure 9»
Percentage N removed for all effluent application rates on sand*
%
!
Effluent Application Rote (mm/doy)
' 80
-- ■ 10
*
o
o
• 17
s 22
b
34 .
------■ 4 3
8#
AUGUST
SEPTEMBER
18
NOVEMBER
DECEMBER
JANUARY FEBRUARY
MARCH
1977 | 1978
Figure 10.
Percentage N removed for all effluent application rates on mix
56
parameter showed the main effects of rates, soils, and time were all
significantly different at the p = 0.01 as shown in Table 9»
Figure 9 illustrates purification efficiencies for all five
rates, averaging replicates, on the sand for the year long study.
Figure 10 illustrates the same data for the mix soil.
the mean percent N removal.
ferent from the other rates.
Table 10 shows
The 10 mm/day rate was significantly dif­
The 17 and 22 mm/day and, 34 and 43
mm/day were also significantly different from each other.
Rates were
not ranked on each soil because the analysis of variance showed that
the rate by soil interaction was not significant (Table 9).
Figures
9 and 10 illustrate this relationship of rates and percent N removal.
The lowest effluent application rate consistently had the highest
percent N removal.
At 10 mm/day percent N removed was 8lS£ compared
to 44# N removal at 43 mm/day, when averaged over both soils and time.
Percentage of N removed was larger at the lower application rates due
:
partly to the fact that less N was applied.
Table 11 clarifies this relationship of percentage N removed
and amounts of N actually removed.
Even though percentage N removal
decreased with increasing effluent application rates, the amount of N
being removed increased with increasing rates.
This table also indi­
cates the important role of soil processes in effluent renovation.
As indicated by percent N removal (Table 10), the mix soil was more
effective in removing N than the sand soil.
Figures 9 and 10 show
that percent N removal was lowest during times of scalping in June
and November.
With no turf growing on the plots, the soil filter was
responsible for N removal.
This illustrates the role of utilization
57
Table 9-
Analysis of variance for percent N removed, 11 July 1977
to 28 April 1978.
Degree of
Freedom
Mean
Square
Rate
4
17525.55
40.62**
Soil
1
14661.56
33-99**
Time
20
2249.28
55.25**
R x S
k
118.62
.27
R x T
80
178.32
4.38**
S x T
20
111.22
2.73**
R x S x T
80
71.30
1.75**
Source of
Variation
F
Value
••Significant at the 0.01 level of probability.
Table 10.
Percent N removed means and average ppm -N in leachate.*
Sand
Average %
Leachate
N Removed
ppm -N
Mix
Leachate
Average %
ppm -N
N Removed
Rate
(mm/day)
Average %
N Removed
10
8la
75
5
87
2.6
17
60b
53
9.4
66
6.8
22
56b
49
10.2
64
7.2
34
48c
42
11.6
53
9.4
43
44c
40
12.0
48
10.4
LSD = 7.2
Any two means with a letter in common are not significantly different
(p = O.05) •
•Assuming 20 ppm -N in effluent applied.
58
Table 11.
Rate
mm/day
Total N removed by clippings and by soil processes from
30 April 1977 to 28 April 1978.
Total N Applied
in Effluent (g)
Total N
Removed (g)
Sand
Mix
Total N in
Clip (g)
Sand
Mix
Total N Removed
by Soil (g)
Sand
Mix
10
75.5
57.8
64.9
18.1
25.7
59.7
59.2
17
118.5
69.7
83.1
23.7
55.4
46.0
47.7
22
155.0
85.5
105.0
28.5
56.0
55.0
69.0
54
245.0
125.5
144.5
51.5
42.0
94.2
102.5
45
510.5
146.5
175.5
30.2
45.6
116.3
129.9
59
in maintaining a high percentage N removed.
Table 10 also shows which
rates of effluent met USPHS standards for N0~-N in the recharge water.
On the sand soil, up to 1? mm/day could be applied.
On the mix soil,
up to 34 mm/day of effluent still yielded potable water, based on
nitrogen content only.
Tables 10 and 11 clearly show the mix soil was more effective
at removing N.
Although both soils were texturally sands, the mix
soil contained 496 more silt and 2)6 organic matter.
tributed to a higher CEO in the mix soil.
These factors con­
It is also possible the
hydraulic conductivity of the mix soil was less than the sand, allowing
more time for nutrient absorption by plants, and adsorption of nutri­
ents by roots and soil.
Table 11 shows that N in clippings and N
removed by soil processes were both higher on the mix soil.
The
higher yields on the mix (Table 4) indicate the importance of CEC to
,plant growth.
Increased N removal on the mix soil could also indicate
greater root adsorption or denitrification.
Rate by time interactions were significant and this could be
caused by many factors.
Figures 9 and 10 show initially high values
of percentage N removal at the beginning of the study.
This was
probably due to NH^ adsorption in the soil as plots had not been fer­
tilized for three months prior to the study.
During the summer months,
until October, the N in the effluent was mainly present as NH^-N (Fig.
1).
The form of N in the effluent would affect N removal processes.
The initially high values of percentage N removal in this study, indi­
cate the importance of cation exchange reactions in removing N from
the effluent.
When NH^-N was the predominate form of N being applied,
60
this cation could be held on CEO sites for plant uptake, or adsorbed by
plant roots.
Ammonium held on cation exchange sites would also be more
available for microbial immobilization.
High N removal from August to October corresponds with high N
utilization during bermudagrass growth.
used by plants.
The adsorbed NH^ was being
Warmer summer temperatures could have increased micro­
bial activity contributing to increased N removal and increased turf
growth rates.
By the end of October the main form of N in the effluent
was N0”-N which is not adsorbed on cation exchange sites, but tends to
move with the soil water.
Figures 9 and 10 both show decreased per­
centage N removed during the months when the effluent was high in
N0~-N.
Nitrogen removal on the sand was decreased more than removal
on the mix.
Nitrogen removal could also have decreased in winter due
to lower temperatures decreasing turf growth and microbial activity.
Organic matter in the mix soil may have contributed to a larger microi
bial population by supplying adsorption sites for nutrients and
microorganisms, as well as increasing moisture available to micro­
organisms and plants.
Figures 6 and 7 both show that N utilization
increased in the winter when ryegrass was growing.
increased percent N in clippings of ryegrass.
Table 8 indicates
These factors indicate
that root absorption of N0~-N may have been important, during winter
months, for removing N from the effluent.
Rainfall and lower temperatures also contributed to decreased
N removal in October and January.
Figures 9 and 10 show large de­
creases in percentage N removed during these months which corresponded
to high rainfall (Fig. 4) and high N0”-N in effluent (Fig. 1).
High
61
rainfall increased soil moisture, increasing the velocity of effluent
movement through the soil.
Because soil particles were already water
coated, effluent moved through soil pores with less interaction with
the soil and root surfaces.
NOj and microbial uptake.
This would decrease plant absorption of
Microbial denitrification could be decreased
in the winter due to lower temperatures slowing microbial action.
All
these factors could contribute to the significant rate by time inter­
action as well as soil by time interaction.
The decrease in N removal at the end of January illustrates a
time when N utilization was increasing but percentage N removed de­
creased.
This showed, despite N utilization by turf, high rainfall
decreased the efficiency of root and soil processes to remove N.
These same events would contribute to decreased purification during
reseeding, when tap water was applied daily.
Effluent flow may have
been faster, decreasing cation exchange reactions and plant roots in
the soil would be acting as adsorption sites only, with ho active
uptake, due to removal of the growing turf.
Nitrogen removal in­
creased as a new turf stand grew.
Figure 11 shows percentage N removed with the five rates on
each soil averaged.
Percentage N removed for all times and rates by
the mix soil was 129» greater than removal by the sand.
Greater per­
centage N removed was observed during periods without rainfall, and
when a good turf stand was established.
ship similar to Figure 8 for utilization.
This graph shows a relation­
Figure 11 shows that the
soils responded differently over the year long study and this inter­
action was significant (Table 9).
The difference in soil response is
Percent N Removed
14 28
MAY
II
25 9 23
JUNE
JULY
6
20 3
17 I
AUGUST SEPT.
15 29
12 26 10 24
OCT.
NOV.
7
21
DEC. . JAN.
4
FEB.
18 4
18 I
MARCH
15 29
APRIL
197711978
Figure 11.
Percentage N removed showing all five rates of effluent application
averaged for each soil.
CTt
IX)
63
illustrated by the fluctuating distance between the two soil lines.
Sand-soil N removal was more drastically reduced in unfavorable periods,
and did not recover efficiency as rapidly as the mix-soil.
This inter­
action between soils over time, found in utilization and N removal
indicates the important role of CEO, root surface area, and organic
matter in these processes.
Variations in moisture, temperature, and
effluent composition affected the chemical reaction of cation exchange
as well as biological uptake and use of nutrients from the effluent.
These soil characteristics, in turn, affect turf growth.
The mix soil
appeared to be better buffered against fluctuations in the environment
and turf recovered more rapidly from adverse conditions.
These re­
sults suggest soils containing more clay and organic matter would be
able to remove more N from effluent.
Good soil conditions for turf
growth contribute to higher N removal by turf and by soil processes.
Nitrogen Transformations in Leachate
Organic carbon was not directly measured in this experiment,
but a time study of N transformations in leachate samples was conducted
in September, when NH^-N in the effluent was high.
Leachate samples
were taken from the 43 mm/day rate at 0, 1, 2, 3i 4, 3, and l8 hours.
No change in NH^ or NO” content was found between 5 to 18 hours.
In
the first five hours of the time study, NH^ content decreased and N0”-N
increased by 5 ppm in the mix leachate and 1 ppm in sand leachate.
This change from NH^ to NO™ indicated that autotrophic bacteria were
present in the leachate and had sufficient carbon dioxide or carbonate
to affect an increase in N0”-N.
The fact that the N0™-N content
64
remained constant indicated either a lack of denitrifying organisms or
a lack of organic carbon for denitrification.
Since denitrifying
bacteria are usually present in the soil, it is probable that lack of
denitrification was due to the absence of an energy source. Nitrite
levels were spot checked in leachate samples and no NO" was found.
This indicated nitrification of the effluent was complete.
As mentioned earlier, leachate samples stored at room tempera­
ture did not show any changes in NH^, NO", or organic-N content.
If
leachate samples were stored in the light, algae growing in the bottles
decreased the nitrogen content of the leachate.
Effluent samples
stored at room temperature did show NH^ to NO" transformations.
The Soil's Role
The soil's role in this soil-turf filter system was determined
indirectly.
The role of the soil system in renovation was considered
to be the difference between percentage N removed and percentage N
utilization.
Nitrogen removal statistics showed the soils were dif­
ferent at the p = 0.01 level.
sand.
The mix-soil removed more N than the
This could be explained by the higher CEC and organic matter
in the mix soil.
Because the mix-soil could adsorb more NH^, there
was more N available to soil microorganisms and plants.
There are
several soil processes that could contribute to purification:
tion, denitrification, and volatilization.
adsorp­
The role of adsorption is
clear from purification values for the first month.
Initial adsorption
of NH^ yielded purification efficiencies over 9096 even though utili­
zation was only 109$.
The CEC of the mix soil is 5 meq/lOOg soil.
65
This is more than twice the CEO of the sand.
This higher CEC con­
tributed to higher purification and utilization on the mix.
CEC played
a more important role in purification when NH^ was the predominate ion
in the sewage effluent.
Higher grass yields on the mix soil (Table
4)
could have resulted from increased adsorption of the NH^, increasing N
available for growth.
The higher yields on the mix soil could indi­
cate more root surface area for adsorption and absorption of N con­
tributing to greater N removal.
Denitrification is a biological process occurring in the soil
which would improve purification.
It is evident from this study that
nitrification was occurring in the soil because effluent applied (May
through September, as shown in Fig. 1) was predominately NH^ and the
leachate collected contained only NO^.
trification limited purification.
Conditions necessary for deni­
The sand soils used have hi$i in­
filtration rates and permeability, decreasing the possibility of
creating micro-anaerobic zones for denitrification.
The organic carbon
content of the effluent was another factor limiting denitrification.
Although organic carbon was not directly measured in this experiment,
the stability of NO~-N concentration in leachate samples indicated
that no denitrification was occurring, and hence the lack of an organic
carbon source.
This indicated any organic carbon originally present
in the effluent was consumed or filtered as it passed through the soil.
These results suggest purification of effluent could be improved by
maintaining a water table, for an anaerobic zone, and adding addi­
tional energy sources for denitrifying anaerobes.
could contribute to denitrification in the soil.
The turf rhizosphere
Roots use oxygen in
66
the soil, creating an anaerobic zone and contribute substrates that
could be used by denitrifying organisms for energy.
Volatilization could <have contributed to purification of
effluent.
In the summer months, when the effluent contained mainly
NH^ and was applied to plots with a pH of 8.3, conditions are favor­
able for volatilization.
Surface ponding of applied effluent could
increase volatilization.
Ponding did not occur on these soils due to
their high infiltration rates, so volatilization was not maximized.
Nitrogen would also be removed by microbial immobilization as well as
plant uptake.
Fluctuation in purification and utilization over time
was a result of environmental influences on these processes.
Comparing
Figure 8 for utilization to Figure 11 for purification showed that
although N utilization was increased in the winter months during rye­
grass growth, purification efficiency in the winter was not as high as
purification in the summer.
This indicated the importance of the soil
i
filter in purification.
Summer temperatures increased biological
activity and volatilization of NH^.
During the cooler winter months
biological activity was decreased because the temperatures"decreased
below the
25 to 30 C optimum for"nitrification and denitrification;
this subsequently decreased N losses due to soil processes.
The
higher utilization of N by ryegrass did not fully compensate for
decreased biological activity in the soil.
The importance of NH^
volatilization was not quantified.
Table 12 shows purification and utilization averages for the
21 time periods.
The differences between these values indicate the
percent N applied that was lost due to soil processes.
Increasing
67
Table 12.
Percent N removed by soil.
Rate
(mm.day)
Purification
Sand (.%)
Utilization
Differ­
ence
Puri­
fication
Mix (%)
Utili­
Differ­
zation
ence
10
75
26
49
87
38
49
17
53
22
31
66
33
33
22
49
20
29
64
25
39
34
42
15
27
53
21
32
43
40
12
28
48
18
30
68
the amount of N applied, decreased the percentage of N being removed by
the soil, although absolute values increased.
Table 11 shows that even
though percentage N removed by the soil decreased, the total amount of
N removed by the soil increased with increased effluent application
rates.
Table 11 indicates that the plateau for nitrogen removed by
soil processes has not been reached, since total quantities of N re­
moved increased with each rate.
Tables 7 and 8 show N removal by turf
increased as effluent application rate increased.
The yield plateau
for the grasses appears to occur between the 3^ or 43 mm/day rates.
By optimizing conditions in the soil for nitrification and denitrifi­
cation, N removal by the soil could be increased.
SUMMARY AND CONCLUSIONS
This experiment investigated the potential of a soil-turf
filter as a tertiary treatment for N removal from secondary effluent
applied in excess of consumptive water use.
Both soils were texturally sands.
Two soils were used.
The sand soil had a CEC of 2
meq/lOOg soil, the mix soil contained 2# organic matter, 4# more silt
and had a CEC of 5 meq/lOOg soil.
Lysimeter plots were drip irrigated
twice a week with effluent at rates of 10, 17, 22, 34 and 43 mm/day.
Leachate and effluent were analyzed for NH^-N, N0~-N, and organic -N.
Grass clippings were collected once a week.
weighed, and analyzed for organic -N.
Clippings were oven dried,
From these analyses a nitrogen
balance for the year long study was obtained.
The ability of the soil-turf filter to remove N from effluent
was evaluated by percentage N removed.
This parameter indicated the
percent of N applied that was removed by the soil-turf filter.
Nitrogen utilization indicated the percent of N applied collected as
grass clippings.
Water recharge indicated the percent of water
applied that would be available for reuse or groundwater recharge.
Results were evaluated using these three parameters.
This study showed that as effluent application rates increased,
percentage N removed and N utilization decreased.
Table 11 shows that
even though percentage N removed decreased, total amounts of N in
clippings and removed by soil processes increased with effluent
69
70
application rates.
The plateau for maximum N removal by turfgrass
occurred around the 3*+ to 43 mm/day rate.
with rate.
Soil removal of N increased
On the mix soil 34 mm/day of effluent could be applied and
yield leachate containing less than 10 ppm NO^-N.
17 mm/day would meet USPHS standards.
On the sand soil
Because N removal varied with
season and turf conditions, leachate water from these rates may not
always be less them 10 ppm N0“-N.
N removal for the whole year.
effluent could be applied.
more favorable times.
These rates represent an average
In seasons of low N removal less
Conversely rates could be increased during
During the year of this study, the total amount
of N applied at the 34 mm/day rate amounted to 2182 lbs. N/acre.
The
amount of N utilized by turf at the same rate was 338 lbs. N/acre.
At
this rate, 74# of the water applied was available for reuse, amounting
to 9 million gallons per acre per year.
lon per
To purify the 35 million gal­
day of effluent that Tucson produces would require 968 acres.
Table 4 indicated that increased effluent application rates
could increase water consumption.
Table 11 indicates increasing water
consumption did not increase the amount of N removed by the turf.
The
sand soil averaged 75# water recharge, compared to 67# recharge from
the mix.
The mix soil averaged 27# N utilization compared to 19# on
the sand.
Nitrogen removal by the mix soil averaged 64# compared to
52# on the sand.
The results indicated the important role of cation exchange
capacity, organic matter, water holding capacity, soil microorganisms,
and vigorously growing turf in removing N from effluent applied to a
soil-turf filter.
Selecting soils with a greater CEC could maximize
71
the effectiveness of the soil filter.
Selecting turfgrass genotypes
for maximum nutrient uptake would improve water purification.
Turf­
grass, as a filter, offers the advantage of growing year round and
providing recreational uses.
Use of effluent for watering parks and
golf courses would increase water for domestic use and could contribute
to groundwater recharge.
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