Feasibility Study: Phosphorus Recovery from Household Solid Organic Waste

Feasibility Study: Phosphorus Recovery from Household Solid Organic Waste
Feasibility Study: Phosphorus Recovery
from Household Solid Organic Waste
Xiaoxia
Lu
Master of Science Thesis
Stockholm /2014/
Xiaoxia Lu
Feasibility Study: Phosphorus Recovery from
Household Solid Organic Waste
Supervisor:
Monika Olsson
Examiner:
Monika Olsson
Master of Science Thesis
STOCKHOLM /2014/
PRESENTED AT
INDUSTRIAL ECOLOGY
ROYAL INSTITUTE OF TECHNOLOGY
TRITA-IM 2014:11
ISSN 1402-7615
Industrial Ecology,
Royal Institute of Technology
www.ima.kth.se
Abstract
Phosphorus is an essential source with significance use in agriculture. Phosphorus is lost
in the human intensified global cycle and it is important to remove phosphorus from
water body. However, important and potential sources for phosphorus product which is
suitable and effective for fertilizer use may be ignored due to over emphasize on the
pollution prevention. This work aims to identify the potential of phosphorus recovery
from solid organic waste in Sweden. Based on the result of Material Flow Analysis of
phosphorus, solid food waste is identified the main solid waste fractions containing
phosphorus substances of phosphorus in Sweden. From the case study and comparison
of three alternatives, the possibility of recovery of phosphorus from household solid
food waste is analyzed. A SWOT analyst is applied to provide a best solution for
phosphorus recovery from food waste. The key drivers, the system boundaries for the
phosphorus recovery and collection, storage, transport and use of the phosphorus are
also discussed.
Key words: Phosphorus recovery; Solid waste; Food waste
I
Acknowledgement
Firstly, I want to thank my supervisor, Monika Olsson, who gives me guides and
suggestions encourages me throughout the time of the thesis work and inspires me
when I meet problems.
Secondly, I wish to appreciate all the workers from Svenskt Fågelkött AB, who kindly
explain the waste situation in the company patiently and answer my questionnaire
during my study visit.
Thirdly, I really appreciate workers from Falkenbergs Biogas AB, who answer my phones
and accept my telephone interview nicely.
Last but not least, I faithfully want to thank my parents and husband, thank you for your
support.
II
Table of contents
Abstract ................................................................................................................................. I
Acknowledgement ............................................................................................................... II
Abbreviations ......................................................................................................................IV
1 Introduction .................................................................................................................. 1
1.1.
1.2.
1.3.
1.4.
1.5.
1.6.
2.
Methodology and Scope............................................................................................... 5
2.1.
2.2.
3.
Global situation ............................................................................................................. 8
A Linköping case ............................................................................................................ 9
Input and Output of phosphorus for agriculture land in Sweden ............................... 10
Case studies ................................................................................................................ 11
4.1.
5.
System boundary........................................................................................................... 7
The progress of the report ............................................................................................ 7
MFA of phosphorus in food production ....................................................................... 7
3.1.
3.2.
3.3.
4.
The significance of phosphorus..................................................................................... 1
The human intensified global cycling of phosphorous.................................................. 2
Sources of phosphorus for recovery and reuse............................................................. 3
The significance of seeking potential source for phosphorus recovery ........................ 4
Phosphorus recovery from solid waste ......................................................................... 5
Aims and Objectives ...................................................................................................... 5
Phosphorus from the sludge of the biogas company.................................................. 12
Scenarios for the phosphorus recovery from food waste .......................................... 12
5.1.
5.2.
5.3.
Study area and background information .................................................................... 13
Description of scenarios .............................................................................................. 13
Comparison of the three scenarios ............................................................................. 15
6. SWOT of phosphorus recovery from food waste under Scenario C ........................... 18
7. Discussions ................................................................................................................. 20
8. Conclusion .................................................................................................................. 22
9. Reference.................................................................................................................... 23
Appendix ............................................................................................................................ 26
III
Abbreviations
USGS: US Geological Survey
FAOSTAT: Food and Agriculture Organization of the United Stations
SEPA: Scottish Environment Protection Agency
IV
1 Introduction
1.1. The significance of phosphorus
Phosphorus is essential resource for all life, including bacteria, plants and animals.
Human beings and livestock get phosphorus from crops which in turns mainly come from
phosphate fertilizers applied to agricultural soils to ensure high yields in modern human
society. Phosphorus has no substitute in food production which depends on a large and
continuous supply. This makes long-term availability and accessibility to phosphorus tied
up with feeding 9 billion people by 2050 (Cordell et al., 2009). Today, the world’s main
source of phosphorus is phosphate rock, around 90% of which extracted globally is for
food production while the remaining 10% is for industrial applications, for example,
detergents (Prud’homme, M., 2010). However, It takes around 10-15 million years to
form phosphate rock, which makes it a non-renewable resource. Furthermore, only a
small fraction of rock has high-grade utilized phosphorus and among these rocks, much
contains prohibitive levels of contaminants (such as cadmium), of which mining is
constrained (Cordell, 2010). Report from USGS shows that current reserves at 16,000
million tones of phosphate rock (containing approximately 30% phosphoric acid) and 85%
of these reserves are controlled by China, Morocco, the US, South Africa and Jordan
control, make Sweden a phosphate importer vulnerable to geopolitical tensions in these
countries, and to volatile prices (as demonstrated during the recent 800% spike in the
price of phosphate rock in 2008). Import quantity of phosphorus and other nitrogen
compounds has reached the peak of 6904 tons in 2005 (FAOSTAT, 2011). Figure1 shows
the import quantity in nutrients of phosphate fertilizers in Sweden from 2002 to 2008
(FAOSTAT, 2011). From the figure, the demand of imported phosphate fertilizers in
Sweden has been increased to 77,923 (tones of nutrients), almost five times as it was in
2002. Regardless uneven geological distribution of phosphate rock, the rate of
production of economically available phosphate reserves will eventually reach a peak
around 2034 (Cordell et al., 2009), which is in a similar way to oil and other
non-renewable resources with the finite nature. Meanwhile, due to an increasing
demand for food from a growing world population, the demand for phosphorus of
fertilizers use is expected to increase globally and steadily with an annual growth rate of
2.7% (Heffer and Prud’homme, 2008). Concerning the significance of phosphorus
resource, there is a need to look into the human intensified global cycling loop of
phosphorus for sustainable governance of phosphorus resource.
1
Import Quantity in Nutrients of Phosphate Fertilizers
(tonnes of nutrients) in Sweden - 2002-2008
Amount
77923
44985
38410
26730
28780
28020
2005
2006
15000
2002
2003
2004
2007
2008
Figure1 Import quantity in nutrients of phosphate fertilizers (P2O5 total nutrients) in
Sweden (Source: FAOSTAT, 2011)
1.2. The human intensified global cycling of phosphorous
Figure 2 (Liu et al., 2008) shows a simplified schematic of the human intensified global
phosphorus flows. The natural cycle contains one inorganic cycle and two organic cycles.
The inorganic cycle starts with tectonic uplift and exposure of phosphorus-bearing rocks
to the forces of weathering, continued with physical erosion and chemical weathering of
rocks forming soils which is gradually leaching to the rivers and sea where sedimentation
and sink of insoluble calcium phosphate occur. When the uplift of sediments into the
weathering rigime begins, the cycle also along with it starts again (Follmi 1996). The two
organic cycles mainly serve as part of the food chain, moving phosphorus through living
organisms. The land-based phosphorus cycle transfers phosphorus from soil to plants, to
animals, and back to soil again while the water-based one circulates phosphorus among
the creatures living in water bodies including rivers, lakes, and seas.
In the societal cycle, Phosphate rock is initially converted to phosphoric acid and further
processed to produce fertilizers, food-grade and feed-grade additives, and detergents
and other marginal applications include metal surface treatment, corrosion inhibition,
flame retardants, water treatment, and ceramic production. Part of the phosphorus
mined for fertilizer production enters human body through food chain showed in figure 2
and finally enters into land and water bodies as waste (Cordell et al., 2009). Losses of
phosphorus include mining losses, losses due to soil erosion (phosphorus eventually
ending up in the oceans sediments), crop losses as well as food losses. Furthermore,
when phosphorus-rich materials end up in landfill or in sewage sludge, losses also
happened.
2
Atmosphere
Wind erosion
Sea spray
Deposition
Deposition
Recycling
Dumping
Manure
Animal
production
Crop
production
Fodder
Organic waste
Organic
waste
Product
Harvesting
Crop residues
Farm- Soil
land
Erosion
runoff
Fresh
waters
Transportation
Oceans
Organic waste
Product
Household
Processing
Food
Industrial
processing
Organic waste
Deposition
Sedimentation
Weathering
Fertilizers
Phosphates
Food
Human
consumption
Processing
Organic
waste
Phosphate
ores
Mining
Phosphate
rocks
Tectonic
uplift
Sediments
Waste
handling
Discharging,
dumping
Figure 2 The human-intensified global phosphorus cycles (Source: Liu et al., 2008)
1.3. Sources of phosphorus for recovery and reuse
Phosphorus can be recovered from both mixed wastewater streams, and separate
organic waste fractions, including: urine, faeces, greywater, animal manure excreted
ex-farm animal carcasses and slaughterhouse waste (bones, blood, hooves etc), food
waste, detergents (laundry, dishwashing), other industrial wastes, crop residues
generated ex-farm (e.g. by the food processing industries). In addition to these ‘used’
sources, phosphorus can also be captured from new sources, such as mineral phosphate,
algae, seaweed, aquatic sediments and even seawater (Cordell et al., 2011). The total
amount of available phosphorus (in thousands of tones of P per year) in each source will
vary from country to country depending on a number of factors. Table 1 shows
concentrations of phosphorus and recovery approaches from different sources. High
concentration of phosphorus in organic fractions is crucial, which is linked with total
phosphorus available for recovery from a source and the viability of phosphorus recovery,
storage and transport.
3
Table1 the concentrations of phosphorus and recovery approach from different sources
(Source: Cordell et al., 2011)
P (% P by
Phosphorus sources
Phosphorus recovery and reuse process
weight)
Human urine
0.02-0.07
Storage and direct use
Human Faces
0.52
Composted/dry faeces
Human excreta
0.35
Incinerating toilet (EPA, 1999)
Recovery from wastewater treatment
Activated sewage sludge
1.4
plant
Sludge(from bigas
0.48-0.77
Composted
digester)
Struvite
13-14
Cow dung
0.04
Directly application
Poultry manure
1.27
Directly application
Farm Yard Manure(FYM)
0.07-0.88
Directly application
Rural organic matter
0.09
Vermi compost
0.65
Crop residues
0.04-0.33
Ploughed into field; ashes from burning
Urban composted
0.44
material
Oil cake
0.39-1.27
Meatmeal
1.09
Composted
Bonemeal
8.73-10.91
Composted
1.4. The significance of seeking potential source for phosphorus recovery
Animal manure as well as human excreta and urine is widely used as a natural source of
phosphorus fertilizer in most regions of the world, especially in parts of Asia (Matsui, S.,
1997). In Sweden, animal manure occupied more than 50% of the total phosphorus
fertilizer in 2011 (European Commission, 2011). However, unlike those developing
countries, all human excreta and urine enters into sewage water through city down-flow
pipe. Driven by the concerning of eutrophication problems caused by phosphorus
entering waterways (Driver, 1998), recovering phosphorus in wastewater sludge and
related numerous phosphorus recovery technologies and processes (Rittmann and Carty,
2001) are the main research directions. On the other hand, application of sludge in
agriculture is still a considering source due to concerns of contamination especially the
risk of heavy metals (Driver, 1998). According to SEPA (2002), only 21% of the sewerage
sludge was reused in agriculture in 2000. Considering the main use of phosphorus is in
fertilizer production, the quality of the recovered phosphorus and its effectiveness as a
fertilizer would be the first concern. This means some important and potential sources
for phosphorus product which is suitable and effective for fertilizer use may be ignored
due to over emphasize on the pollution prevention. In other words, there is a need to
look into other points rather than to focus on the “end-of-pipe” in the cycling of
phosphorus system.
4
1.5. Phosphorus recovery from solid waste
As societal use of phosphorus is mainly for food production, substantial flows of
phosphorus occur both upstream and downstream of the field. Though distributions vary
significantly by country or region (Schröder et al., 2010), global-scale of phosphorus loss
trend in all processes of food production has been identified by scientists (Liu et al., 2008;
Cordell et al., 2009; Schröder et al., 2010). Based on Cordell’s analysis (2009),
approximately 3 Mt/a of P is consumed in the food eaten by the global population, which
is only one-fifth of those mined in phosphate rock specifically for food production. On
the other hand, in 2011, a total of 4,349,910 tonnes of household waste was generated
in Sweden. Only 14.9% of the household waste went to biological treatment while 51.4%
of it was treated by incineration (Avfall Sverige, 2012). The large quantity of waste not
only indicates the effort needs to put into the solid waste management system but also
shows the potential of phosphorus recovery quantitively.
Driven by huge loss of phosphorus in food production and solid waste management in
Sweden, identifying the potential source for phosphorus recovery from the solid waste
streams is critical and essential.
1.6. Aims and Objectives
This work aims to identify the potential of phosphorus recovery from solid waste in
Sweden. More specifically, objectives to realize this aim are:
 Identify the state of research of phosphorus recovery from solid waste
 Identify the main solid waste fractions containing phosphorus substances of
phosphorus in Sweden.
 Analyze the possibility of recovery of phosphorus from potential sources.
 Suggest a method for recovery of phosphorus from solid waste and analysis the
feasibility.
2. Methodology and Scope
The main research method of this study was literature review and study visit. The
literature source includes peer reviewed papers and reports from authoritative data
sources, published books, investigation report of the statistics authority and government.
Documents and records were taken from organizations working on the related subjects.
The first hand data was collected through the study visit to Svenskt Fågelkött AB.
Interviews carried out at Fågelkött AB plants along with a field visit enabled insight into
plant operations and waste planning. A face-to-face interview was carried out by the aid
of questionnaires. Email contact with the company was also used to discuss about some
details of the working process of the company.
The criteria used for preparing this thesis could be summarized as below. The main
rationale behind this study is looking for practical and implementable data both from
others work in the research field and relate companies. Therefore, the accuracy of some
5
data used in this study is reliant on the figures given in the literature. The need for more
factual and measured data can be fulfilled when actual working plan carried out based
on the study result. The details for all purposes in this study have been maintained only
to the practical use and purpose of this study. Further work need to be done in order to
use the study result as project appraisal.
Methodology used for material flow analysis
Material flow analysis (MFA) is an analytical method of quantifying flows and stocks of
materials or substances in a well-defined system. In this study, MFA is used to identify
the main solid waste fractions containing phosphorus substances of phosphorus in
Sweden. As phosphorus is a reactive element and tends to diffuse into the environment,
it is difficult to achieve accurate material-flow accounting. To simplify matters, this paper
evaluated the total phosphorus flow by considering seven systems. The inputs and
outputs for each sector were estimated and were taken into account the total mass
balance. The method will be described in more detail in chapter 3.
Methodology used for scenarios
In Sweden, biological treatment and incineration are most important treatments for
household organic waste including food waste. Biological treatment is implemented
through anaerobic digestion or composting. Anaerobic digestion produces biogas and
phosphorus-contained-digestate is an excellent nutrient for the soil. Composting
produces long-lasting phosphorus fertilizer which contained various kinds of nutrients
used as soil improver in gardens and parks. Incineration is an effective method for
producing energy including heat and electricity from waste. With proper technology,
phosphorus can be also possible recovered from the incineration ash.
In order to analysis the possibility of recovery of phosphorus from potential sources,
three different scenarios based on the different treatment methods including
incineration, composting and anaerobic treatment were created to identify the best
treatment plan for the phosphorus recovery. Also, the alternatives are established
under the framework for Swedish waste management. Related target proposed by
Swedish Environmental Objectives is:” By 2015, at least 40 percent of food waste from
households, caterers, retail premises and restaurants will be biologically treated to
provide fertilizer and energy”. (Avfall Sverige, 2011)
Recovery rate of phosphorus is directly linked with the quantity of phosphorus from
different treatment. While whether the final product from different treatment methods
can be used on agriculture land is determined by P-content in the final product and its
substitution to chemical fertilizer. Thus, the study takes into recovery rate of phosphorus,
P-content in the final product and substitution to the chemical fertilizer of final product
into consideration during evaluation. The method will be described in more detail in
chapter 5.
6
2.1. System boundary
For the review of phosphorus loss and different phosphorus sources, this report takes
the whole world’s situation into consideration in order to obtain an overall
understanding about phosphorus loss. When suggesting the new potential source in the
scenario cases, this report just considers the Swedish circumstance. So results just adapt
to Swedish situation. If apply the results into other country, further research should be
done.
2.2. The progress of the report
This paper provides a three-step work to study the feasibility of phosphorus recovery
from household solid food waste rather than focusing on a specific technology or process.
Firstly, MFA is used to identify the main solid waste fractions containing phosphorus
substances of phosphorus in Sweden. Secondly, the case study which introduced an
industrial model is implemented to check the possibility to use the potential source
identified by MFA for phosphorus recovery. Thirdly, three scenarios are made to identify
if the industrial model can be used for phosphorus recovery from household solid food
waste.
3. MFA of phosphorus in food production
The research system includes seven different processes that include the production of
food (soil, animal and crop production), the processing of food (household and industrial
processing) and human consumption and waste handling. There are many flow streams
included in this system, but only the main flows, for example, the flow of fodder, fertilizer,
manure and food products, are shown in the figure 3. The research aims and objectives
are reflected from the system and the system border includes the processes related to
the consumption and production of food. Extraction of fertilizer from phosphates and
the fate of phosphorus in both inland and coastal water bodies are beyond the system
border. In order to compare Swedish situation with global situation, the food products
consumed are assumed to be produced and processed in the region. Thus, food
imported from outer systems is not included. The surplus flow refers the remaining
phosphorus not exported as animal product to the consumer or reused as manure
fertilizer in agriculture and phosphorus in bone and slaughter waste or dead animals.
In this study, the phosphorus entering into the soil as the form of fertilizer is defined as
100% P. Because of phosphorus recycling of internal system and land released
phosphorus, total out flow might exceed 100%. “%P” is based on the quantity of the P.
7
Phosphates
Fertilizer
Manure
Harvesting
Farmland
Soil
Crop
residues
Crop
production
Fodder
Animal
production
Product
Product
Organic waste
Human
Organic
fertilizer consumption
Erosion
Food
Household
Processing
Food
Surplus
Industrial
processing
Excreta
Waste
handling
Organic
waste
Organic waste
Organic waste
Organic waste
Waste deposit
Inland/
coastal
waters
Figure 3 the system for the food production and consumption (developed from
Tina-Simone Schmid Neset et.al., 2000)
3.1. Global situation
Figure 4 summarizes key findings based on Cordell et al. (2009). It indicated that the two
largest flows of lost P are soil erosion and runoff (57% of mined P) and surplus (50%).
The P flow from erosion and runoff usually are identified as a ‘‘non-point source,’’ for
example, agricultural drainage ditches or surface storm-water flow, which are not easily
captured before they reach a natural stream or river. Much of the P in runoff is
associated with particulate matter that can settle out in wetlands, rivers, reservoirs, and
lakes. Therefore, quickly capturing P from water flows with large quantity and low P
concentration is a big challenge to today’s technology. While The P flows in manure is
quite the opposite which has a small flow rate and a high concentration. Similarly, to
collect small streams of animal waste is not practical either from the global aspect.
The P discharged into human sewage treatment system and finally lost in the water body
and sludge is 19% combined. In Figure 4, the flow of lost P from the processing of food is
about 9%. The distribution of the lost P in the household processing and industrial
processing has not been identified clearly.
8
Phosphates
Crop losses
28%
Fertilizer
100%
Farmland
Animals from non-fertilized rangeland
Manure
58%
Soil
Harvesting
85%
Crop
Residues
14%
Crop
production
Fodder
19%
Product
25%
Organic waste
Human
Organic
fertilizer consumption
Erosion
57%
Food
20%
Household
Processing
Food
Animal
production
Product
4%
Surplus
50%
Industrial
processing
Excreta
20%
Organic waste
Waste
handling
Waste deposit
10%
Organic
waste
Organic waste
Organic waste
Losses
9%
Inland/
coastal
waters
Figure 4 global P flow (Source: Cordell et al., 2009)
This global phosphorus flow picture gave a general picture of how and how much
phosphorus flew and lost in every section of food production, processing and
consumption. Since the number would be different according the food production and
consumption in every country, there is a need to narrow the space scales to identify
every streams in the research system. In order to answer how the phosphorus flows,
which are the main flows, and how changes in consumption, agricultural production and
waste handling influence the flow of this resource, more specific data was needed. In
this paper, the study result of the flow of phosphorus in food production and
consumption in Linköping (Tina-Simone Schmid Neset et.al., 2000) has been adopted.
3.2. A Linköping case
Figure 5 shows the flow of phosphorus for the food consumption and production of
Linköping (Tina-Simone Schmid Neset et.al., 2000), which is situated in southern middle
Sweden. Once a centre of old culture region, it has today risen to be the fifth largest city
in the country and is known for known for its university and its high-technology industry.
The number of inhabitants is 104,232 in 2010 (Linköping Kommun, 2011).
9
Phosphates
Manure
90%
Fertilizer
100%
Harvesting
Farmland
Soil
Crop
residues
Crop
production
Organic waste
3%
Organic
Fertilizer
6%
Erosion
5%
Human
consumption
Food
29%
Household
Processing
Fodder
150%
Product
14%
Food
33%
Animal
production
Product
35%
Organic
Waste
10%
Industrial
processing
Excreta
29%
Surplus
35%
Organic waste
0.3%
Waste
handling
Organic waste
3%
Organic waste
3%
Losses
1%
Waste deposit
22%
Inland/
coastal
waters
Figure 5 Linköping P flow (developed from Tina-Simone Schmid Neset et.al., 2000)
Compared to the global P flows through the food production and consumption system,
the lost P from the whole system is smaller, which is 42%. The surplus is still the largest
stream of lost P (35%) while lost of P due to erosion is considerable smaller, which is only
5%. Crop loss is insignificant compared to other flows and not showed in the figure. The
deposit P from human excreta is 22%. Loss of P from organic waste from both household
processing and industrial processing is clear and significant (3%, respectively). Organic
waste from industrial processing reused for agriculture and animal production is 3% and
10% respectivelywhile only 0.3% of food waste from household processing has been
reused for animal production. Compared to the global P flow, manure used for
agriculture in Linköping has increased to 90%, which shows a relatively high P recovery
ratio in this area. Generally, the biggest difference of P flow between global situation and
Linköping case occurs in the food production process. In order to identify the
phosphorus recovery situation in whole Sweden, specific data about input and output of
phosphorus for agriculture land of whole Sweden is needed.
3.3. Input and Output of phosphorus for agriculture land in Sweden
Figure 6 shows the input and output of phosphorus for agriculture in 2009 in Sweden
(statistiska centralbyrån, 2011). It can be concluded that the major input of phosphorus
stream is manure (25,080 tones) instead of chemical fertilizer (9,060 tones), which shows
10
the reuse ratio of the manure in the research system is already very high in the whole
Sweden in 2009. Loss of phosphorus due to erosion is considerable small, only 2% of the
total input. This makes manure and runoff in the agriculture field not ideal sources for
capturing the lost P in Sweden.
Seeds
810
Deposition
920
Fertilizer
9060
Crop
35740
Soil
Soil improvement
1380
Farmland
Crop residues
650
Erosion
920
Sludge
1540
Manure
25080
Figure 6 Input and output of phosphorus for agricultural land by source in 2009. Tones
(source: statistiska centralbyrån, 2011)
Look back into the system for the food production and consumption (figure 5):
phosphorus recovery from organic food waste from the industrial food processing has
already been used for agriculture. While the P loss from household food processing has
not been recovered yet, this part of P loss might be a potential source in Sweden. To
check the possibility of P recovery from this source, this study looked into the industrial
model with specific data about how and how much phosphorus can be recovered for
organic food waste.
4. Case studies
Svenskt Fågelkött AB is a small meat processing company and their major products are
hen and chicken, lamb and sheep that are cut into specified pieces and as whole piece.
As the organic waste from the company are mixture of mostly intestine and bones, the
phosphorus concentration in the mixture waste can be assumed as 5% according to the
findings in literature (Cordell et al., 2009; Bernstad, 2011). The company sold the animal
waste to the biogas company named Falkenbergs Biogas AB. Mixed with food waste from
the community, manure, energy crops and miscellaneous, biogas was produced from the
waste during anaerobic digestion. The sludge is by-product of anaerobic digestion and
11
used as biofertilizer to be applied into agriculture land again (Falkenbergs Biogas AB,
2011).
Animal product
11242
Food processing
company
Organic waste
7573
Energy company
Food
3669
Sludge
Agriculture land
Biogas
Figure 7 Waste flow in tonnes from the food processing company to the energy company.
(Svenskt Fågelkött AB, 2011)
4.1. Phosphorus from the sludge of the biogas company
Svenskt Fågelkött AB sold 7,573 tons animal waste to the biogas company in the year
2010 (Figure7). The phosphorus content of the sludge will vary with what is digested.
However, in practical, the company does not separate the sources, which means sources
such as manure, residues from the food, energy crops and other wastes are mixed
together. The raw material required for the production of biogas is based on 90,000
tonnes of manure, 10,000 tons of residues from the food, 10,000 tons of energy crops
and 10,000 tons of other per year. The digestate after digesting is around 40%-60% of
the raw material and the calculated average of the phosphorus in the digestate is 1 kg
per ton (Falkenbergs Biogas AB, 2011). It means the animal waste from Svenskt Fågelkött
AB contributed to around 3,029 kg-4,544 kg phosphorus actually recycled in the year
2010. From these figures, it can be concluded that there is great potential to recovery
phosphorus from organic food waste
Though the potential of organic food waste for P recovery has been approved in this case
study, the composition of household organic food waste is different from industrial food
waste. Whether this treatment method can be also applied to household organic food
waste for P recovery needs further study through comparison of different scenario
treatment methods in chapter 5.
5. Scenarios for the phosphorus recovery from food waste
In this chapter, in order to figure out whether the above industrial model for the
phosphorus recovery from the organic food waste applied to the household organic
waste, three treatment alternatives for household organic waste including centralized
anaerobic treatment (industrial model), decentralized composting and incineration are
compared.
12
5.1. Study area and background information
The comparison between different treatment methods for the foods waste is based on
the statistical result of Swedish waste management. The quantity of treated household
waste was 4,363,880 tons in 2010 in Sweden (Avfall Sverige, 2011). There was 587,170
tons of household waste biologically recycled through anaerobic digestion or composting,
accounting for 13.5% of the total quantity of treated household waste and 47.7% of total
biologic treatment waste. Digestate can be applied to the agriculture land is 582,750
tons. It is showed in a survey carried out by Avfall Sverige – Swedish Waste Management
(Avfall Sverige, 2011) that 163 municipalities collect source-separated food waste. About
20 of them only collect food waste from restaurants and large-scale kitchens, while the
remaining municipalities have systems for households as well. According to the survey,
an additional 70 municipalities are planning to introduce systems for source-separation
of food waste. According to Avfall Sverige – Swedish Waste Management’s calculations,
214,230 tons of food waste (an estimated 24% of total food waste) was biologically
treated in 2010. This means if all the cities in Sweden introduced the systems for
source-separation of food waste, 892,625 tons food waste in 2010 would be treated
through biological treatment. Accordingly, the digestate can be used for agriculture as
fertilizer would incease greatly. (Avfall Sverige, 2011)
Table 2 the Waste treated biologically in 2010 in Sweden (Avfall Sverige, 2011)
Item
Tons
Total waste treated through anaerobic digestion
661,620
Total waste treated through composting
566,210
Total food waste treated biologically
214,230
Total quantity of household waste treated biologically
587,170
Digestate
582,750
5.2. Description of scenarios
According to Avfall Sverige (2011), around 892,625 tons household food waste produced
in 2010, which is assumed the amount of organic waste source-separating considering
incineration, composting and anaerobic digestion are used in the whole Sweden in
different cities in the scenarios. The waste characterization method used in this study
was assumed same between vegetable and animal food waste and the division between
the two was assumed 24:76 (Petersen and Domela, 2003).
Table 3 shows the P-content in the waste in the Southern Sweden. Since the food
structure varies little in the whole Sweden (Petersen and Domela, 2003), the waste
fraction of the scenarios in this study were based on the results showed in Table 3. The P
capacity in the food waste would be around 1,200 tons.
13
Table 3 Waste composition and P-content of the waste (Source: Bernstad, 2011)
% of source-separated
DS(%)
P-content
Type of waste
waste
(% of DS)
Vegetable food waste
64.6
23.0
0.23
Animal food waste
20.4
42.9
0.996
Other organic waste
12.8
51.8
0.198
Plastic
0.8
85.9
0.02
Paper/cardboard
0.8
77.7
0.013
Combustables
0.3
90.5
0.015
Mixed metals
0.1
91.7
0.025
Inert
0.2
92.7
0.012
Scenario A: Food waste and other organic waste are not separated and are incinerated
together with residual waste in a waste incineration plant.
In this scenario, food waste is disposed together with residual household waste,
collected and transported to an incineration plant. The methods used to extract
phosphorus from ashes include electro-kinetic, thermo-chemical, bioleaching and
accumulation, and wet chemical methods (Kalmykova and Karlfeldt Fedje., 2013). The
achieved P recovery can vary from 1%-70%.
Since the final quantity of phosphorus recovered would be decided by the extraction
technology (Kalmykova and Karlfeldt Fedje, 2013), this study adopt theoretical value of
phosphorus can be recovery from this treatment based on the wet chemical method
from the research result (Kalmykova and Karlfeldt Fedje, 2013), which have higher
efficiency and shorter processing time required compared to other method. The final
product of this scenario is incineration fly ash with acidic leaching and precipitation. The
chemical form of P in this final product is Ca3 (PO4)2. In the study, the ash sample was
collected from a mass burn combustor for incineration of municipal and industrial solid
waste in Sweden. The P-content in the fly ash is 5.9 kg (ton-1 fly ash) and 70% of the P
content of the ash can be recovered. The detailed technology and cost is not into
consideration. According to the Swedish Waste Management Report carried out by Avfall
Sverige (2011), 239,050 tons fly ash generated by incinerating 5,100,370 tons of waste in
2010. Ignored the co-effect of incineration of different wastes, 892,625 tons food waste
contributes to 41,836 tons fly ash.
Scenario B: Food waste together with other organic waste is source-separated by
households and treated in decentralized compost reactors on the level of residential
area.
In this scenario, food waste is source-separated, collected and transported to the
compost site. Composts are assumed emptied twice a year. Soil produced is collected
and transported to a storage factory, and finally packed in 50 kg-bag. Phosphorus exists
in both organic (Po) and inorganic (Pi) forms. Data regarding phosphorus content is
14
based on a site-specific value (Grahamn, 2003). Weight reduction is 50% and the dry
substance after composting is around 57%. P-content in the compost is 3.2 kg ton-1 DS.
Scenario C: Food waste is source-separated in paper bags by households.
In this scenario, food waste is source-separeted, collected and transported to a biogas
company. The organic fraction is assumed to be treated under mesophilic conditions.
Phosphorus exists in both organic (Po) and inorganic (Pi) forms. The fraction is assumed
to be co-digested with other waste, such as manure, energy crops and residues from
production industry. Co-digestion of these organic wastes can result in higher or lower
phosphorus content in the digestate. However, except the lost due to rejected food,
there is no loss of P during the treatment. Theoretical recovered P in this scenario, which
is calculated according the P content in the food waste before treatment (see appendix)
is not affected by the co-digestion. Data regarding rejected food waste, P-content in the
digestate and P-content in the final product are collected from the actual biogas plant.
Based on the figures from Falkenbergs Biogas AB (2011), the reject is assumed to be
18wt% due to incorrectly waste sorting by residents. P-content in the digestate and DS
are 1kg (ton-1 digestate) and 25 kg (ton-1DS) respectively. Since there is no loss of
macronutrients in the treatment chain, 892625 tons food waste contributes to 981 tons
P.
Scenarios
A
Table 4 P-content in the residues after three treatments
P-content
Theoretical
P-content of
Item
Reference
of source
recovered P
final product
41,836
Kalmykova and
5.9 kg ton-1
tons
-1
172 tons
30 kg ton DS
Karlfeldt Fedje,
fly ash
fly ash
2013
B
254,398
DS
C
-
3.2 kg ton-1
DS
1 kg ton-1
digestate
814 tons
3.2 kg
ton-1DS
Graham,2003
981 tons
25 kg ton-1DS
Falkenbergs Biogas
AB,2011
5.3. Comparison of the three scenarios
Table 4 shows the available P-content in the residues after treatment under the three
scenarios. P recovered efficiency and application of final product are analyzed as below.
5.3.1 Scenario A: P recovered from incineration fly ash
Based on the 70% P recovery efficiency obtained in this scenario, theoretical recovered P
from incineration fly ash is 172 tons, which accounts only 14.3% of the total P in the food
waste and other organic waste. Apart from efficiency of extraction method, P lost in the
incineration process and buried in the bottom ash would also contribute to the low
recovery rate. P loss varies from 28%-47% during incineration process, which is affected
15
by different incineration temperature. (Zhang et.al, 2000)
In this scenario, the P accounts for 3w % (dry weight) of the final phosphorus product
from incineration fly ash with acidic leaching and precipitation (Kalmykova and Karlfeldt
Fedje, 2013), which content is around 5 times compared to the fly ash. When compared
to commercial NPK mineral fertilizer which contains about 2.7% P, the obtained P
product contains similar P. However, the high content of trace element in the final
product prevents its application to agricultural land. Trace elements including Cd, Cr, Cu
and Pb exceed the Swedish limits for metal load through sludge application. (Kalmykova
and Karlfeldt Fedje, 2013) In order to avoid any contamination of agricultural land with
trace metals, the final P product cannot be used as first P source and applied directly.
5.3.2 Scenario B: P recovered from compost
Scenario B is the treatment where phosphorus can be recovered most in the form of
compost which contains 814 tons P and the recovery rate is as high as 68%. Compost can
be used to replace peat and commercial NPK mineral fertilizer directly. Studies of the
availability of N, P and K in compost show that percent of uptake of P amongst plants
fertilized with compost compared to uptake in plants where mineral fertilizers were used
is 100% while substitution ratio of N vary from 30%-50% (Dalemo et al., 1998; Patyk and
Reinhardt, 1997). A simplified model for replacement of chemical fertilizers has been
carried out by Bernstad and Jansen (2011). In the model, 81% of N has been lost in the
treatment chain due to emissions of NH3 during the aerobic degradation process. The
loss of N decreases the possibility to substitute commercial NPK fertilizer on farmland.
The P accounts for only 0.3w% of the compost, which is far lower than P in the low-grade
phosphate ores (2.2-2.4wt% P). It is not preferable for the P product to be used as a
secondary source and substitute virgin phosphate ore in the conventional mineral
fertilizer production.
5.3.3 Scenario C: P recovered from digestate
Due to rejection of food waste and other organic waste (18wt% of incoming waste and
50% DS in rejected material) in the pre-treatment in Scenario C (Falkenbergs Biogas AB,
2011), the recovery rate is 82%. The digestate contains 2.5% P, which is in the same level
as commercial NPK mineral fertilizer. The digestate can be applied to substitute the NPK
fertilizer directly. Many studies have examined the availability of N, P and K in digestate
compared to use of commercial NPK mineral fertilizer. (Bernstad and Jansen, 2011;
Möller et al., 2009; Krogstad et al., 2004) According to Haraldsen et al. (2010), when
applied at equal amount, digestate gave the same yield of spring as NPK chemical
fertilizer. Meanwhile, in the case of P, the uptake of P from digestate was also same as
from NPK. (Möller et al., 2009; Krogstad et al., 2004)
5.3.4 Summary
Same criteria factors including P-content of final product, the recovery rate of P, and
substitution ratio of nutrients to chemical fertilizer in this study are needed to compare
the three scenarios. The number of “+” is used to show the level of favored of the
16
scenarios in this study. (Table 5)
Table 5 the comparison of Scenario A, B and C
Scenario
Scenario
Criteria
A
B
P-content of final product (in %)
+++
+
Recovery rate of P
+
++
Substitution possibility of nutrients to chemical
+
++
fertilizer
Scenario
C
+++
+++
+++
Due to the extraction method, the P-content would be a reference figure for further
study and research in Sweden. Scenario A enabled the phosphorus in the food waste
concentrated in the incineration sludge. It is the same as wastewater treatment sludge,
application of incineration sludge in agriculture is still a considering source due to
concerns of contamination especially the risk of heavy metals. However, unlike
numerous phosphorus recovery technologies and processes for wastewater sludge,
research for incineration sludge is still on the beginning. From the both perspectives of
phosphorus recovery technology and present waste management goals in Sweden (Avfall
Sverige, 2011), Scenario A is not an idea option for phosphorus recovery. Within the
development of technology and driven force of energy, Scenario A may be supported by
some incineration companies. However the details of such a scenario in the future time
are outside the ambit of this study and need in-depth study to visualize the actual
outcome of this approach.
Scenario B is the treatment where phosphorus can be recovered in the form of compost
and compost can be applied as garden soil. However, this scenario takes the period of
two years without any energy recovery. The stakeholders will need to take a back seat in
planning and will have to critically identify returns under this scenario. Since compared
to 2009, composting is declining due to the interests of branches and large twigs turning
to incineration instead of to composting (Avfall Sverige, 2011).
Scenarios C is most favored in this thesis as part of implementation strategy (Table 5).
Phosphorus can be recovered most in this scenario (981 ton) and P content in the
digestate and the availability of P to crops are on the same level as commercial NPK
mineral fertilizer. This scenario is also in line with the waste treatment situation and
development trend in Sweden (Avfall Sverige, 2011). The biogas companies are willing to
work with government to get more sources for biogas products under this scenario
(Falkenbergs Biogas AB, 2011). The Swedish government policy on targeting environment
objective” By 2015, at least 40 percent of food waste from households, caterers, retail
premises and restaurants will be biologically treated to provide fertilizer and energy”
finds a scenario can be implemented in some typical cities (Avfall Sverige, 2011). The
cost effectiveness could be ideally tabulated if more concrete actual parameters are
given which remain out of the scope of this study.
17
6. SWOT of phosphorus recovery from food waste under Scenario C
Based on the analysis in Chapter 5, solid food waste is identified a potential source for
phosphorus recovery and reuse and this source has already applied (though not aimed at
phosphorus recovery and reuse) in some area in Sweden. However, many barriers need
to be crossed to make phosphorus recovery and reuse as mainstream practice due to the
gaps between science and policy, policy, economic, society and technology. For example,
a quality based phosphorus recovery technology may be energy consuming; new
recovery technology may not be accepted by small company due to high cost. To address
such conflicts, a system thinking of the approach is needed to achieve the ambition goals
of phosphorus recovery in this study. This SWOT analysis under Scenario C is from the
government perspective and the objective of the SWOT is providing a best solution for
phosphorus recovery from food waste.
STRENGTHS:
• Source-separating of the food waste is
needed and acceptable in Sweden
•phosphorus recovery is definitely needed
at national level
• phosphorus recovery from food waste is
an obvious recovery solution with a
lifelong policy base
OPPORTUNITIES:
• Gives another dimension to facilities that
produce digestate
•Business opportunities for biogas
companies
• Research inputs can be an add on for a
futuristic setup
• Bioenergy setup for the commune
• Good fertilizer product for farmers
• Better image for inhabitant
WEAKNESS:
• Existing source-separating system is
driven by waste management instead of
recovery of phosphorus
• It relies on government support for setup
• Depending on inhabitant interests
THREATS:
• Long term to realize source-separating of
the food in whole Sweden
• Risk of waste rejection by the biogas
companies due to misclassification by
inhabitant.
• Risk of changing stakeholders’ interests
in phosphorus recovery
STRENGTHS:
From the survey carried out by Avfall Sverige (2011), source-separating of food waste has
been implemented by several cities and are welcomed by most of other cities. In 2010,
18
Total food waste treated biologically is 214,230 tons (Avfall Sverige, 2011), which
accounts only 24% of total food waste. Under Scenario C, all food waste will be treated
biologically and the quantity of digestate will increase a lot. From figure 6, we can see
that soil improvement which is made of digestate is important and used in agriculture,
which can partly decrease the use of chemical fertilizer. It also served as an energy
solution for Sweden which has a history of green energy practices. Food waste is
separated by family and collected by biogas companies can prevent the odor from the
mixture waste in the collect points, which has manifold environmental benefit. Food
waste treated by biological measures can decrease the sludge which generated from
incineration and minimize the waste treated by landfill.
WEAKNESSES:
Though many cities in Sweden have introduced source-separating system for food waste
and they are treated through biological treatment, from which biogas is produced and
the digestate is used on farmland to replace commercial fertilizers. Collecting and
reusing household organic waste actually is driven by the need of waste management or
Swedish Environmental Objectives (Avfall Sverige, 2011). Reuse the digestate in the
agriculture to recover phosphorus is a secondary driver. This means separating organic
waste is mainly for the biogas production, the digestate product which contains
phosphorus is “by-product” in Sweden at present. If the fertilizer value of phosphorus in
digestate used as the primary driver, the quality of the recovered phosphorus and its
effectiveness as replacement of commercial fertilizers will be turned to the key. The
existing model for collecting the waste and biogas production might go though series of
revolution because of change of the driver. Relevant research and technology should also
focus more on the phosphorus recovery other than biogas production. The government
may spend a lot of effort discussing and comparing cost and benefit. People will be tired
of discussions/ planning and ignore the big benefit of phosphorus recovery.
OPPORTUNITIES:
According Falkenbergs Biogas AB (2011), the major source for biogas produce is manure.
Increasing food waste source may give another dimension to those biogas companies
that produce digestate. Since composting treatment is declining due to the energy
recovery concern (Avfall Sverige, 2011), source-separating of food waste could transfer
some portion of waste to anaerobic treatment. If businesses with varied competencies
can identify themselves in this movement with a larger goal of bioenergy production and
phosphorus recovery, it can provide jobs and even evolve to a model setup. Research
into phosphorus recovery systems is advancing at a fast pace in Sweden. Though the
system boundary has been drawn clearly and under scenario C the theoretical
phosphorus can be recovered from the food waste has been given in Chapter 5 (981
tons), the potential phosphorus can be recovered is affected by the key driver and
corresponding biological treatment technology a lot. Using inputs from the latest
research the government could build an interesting model for a showcase of phosphorus
19
recovery for other countries. Importantly, compared with other recovered source (sludge,
waste water), the quality of the recovered phosphorus as a fertilizer is proved in some
studies (Möller et al., 2009; Krogstad et al., 2004). The farmer’s dependence on chemical
fertilizers is reduced. According Avfall Sverige (2011), certificated quality labels can be
used on the product by the facilities that produce digestate from food waste.The energy
input, emissions and phosphorus loss associated with artificial fertilizers producing
processes is avoided. The inhabitant’s effort and contribution will win their good
reputation.
THREATS:
Even with policy support, it still takes time for the inhabitant to adapt the new
household waste classification. Misclassification will result in much waste being rejected
for anaerobic treatment by biogas companies. The figure in this research is 18wt%,
which is the main reason for phosphorus loss under Scenario C. Driven by the fertilizer
value of phosphorus-contained digestate, phosphorus recovery under scenario C is still
most favored for combined fertilizer and energy provision. However, in this case, reuse of
digestate is not just individual company’s behavior, but a solution for phosphorus
recovery from potential source and a socio-technical system including collecting, storage,
treatment and reuse. The institutional arrangements, regulations and policies need to be
changed and appropriate policy instruments to facilitate this option are needed.
Therefore, under scenario C, the system boundary for phosphorus recovery solution is
clarified as country in this study. Further, government, householders, biogas companies,
fertilizer manufacturers and distributors, farmers, food producers, distributors and
retailers, dieticians and nutritionists, consumers are important stakeholders who can
affect or be affected by the system. In this study, the government, biogas companies and
the householders are identified the key stakeholders. The government will manage and
finance elements and overall coordination of the system and the householders and
biogas companies are major participants and performers of the system. The decision of
source-separating of the waste is subject to environmental policies. Political parties can
make or break incentives to inhabitant and related companies.
7. Discussions
The feasibility of recovery of P from solid food waste was investigated in this study. MFA
method is used to identify the main solid waste fractions containing substances of
phosphorus in Sweden. A Linköping case is analysed in this study. In this case, the food
products consumed are assumed to be produced and processed in the region while food
imported from outer systems is not included. This assumption is consistent with
assumption made by previous study (Tina-Simone Schmid Neset, 2000). The total loss of
P in food process is 6% based on this assumption. However, 8.75% of food in Sweden is
imported from other countries in 2010 according to a World Bank report published in
2012 (Trading Economics, 2013). This means the total loss of P in food process accounts
more than 6%. On the other hand, loss of phosphorus due to erosion is considerable
20
small, only 2% of the total input in whole Sweden (Figure 6).Consequently, recovery P
from solid food waste is more crucial in Sweden compared to other country which relied
much on agriculture.
In order to check the possibility of P recovery from solid food waste, this study looked
into the industrial model with specific data about how and how much phosphorus can be
recovered from this identified waste fraction. As the large-scale, centralized recovery
system is preferred in this study, the spatial distribution of the solid food waste
(phosphorus recovery source) and the distance between the source and the farmland
(end users) are important for the feasibility of the project as well as the cost and benefit.
The energy consumption and the effect to the environment during transportation are
determined by the distance. Generally, large city with high population density is the
source of food waste containing phosphorus, which comes from the farm products.
Theoretically, returning the phosphorus from the city to the farm land will create a close
loop named “cradle to cradle”. However, the quantity of collected food waste, the
production of the digestate used as fertilizer of the biogas companies, the demand of
fertilizer of the farmland need to be considered when planning the project. Hence, the
life cycle costs of the projects associated with the collection, storage, transport,
treatment and reuse are determined by those factors. The life cycle costs of the whole
recovery and reuse system need to be compared with the life cycle costs of mineral
phosphate fertilizer from mine to farm land.
In this study, Scenarios Analysis are used to figure out whether the industrial model for
the phosphorus recovery from the organic food waste applied to the household organic
waste, three treatment alternatives for household organic waste including centralized
anaerobic treatment (industrial model), decentralized composting and incineration are
compared. Although the results from this study show a clear rank between compared
treatment methods (Table 5), the results are very sensitive to assumptions and the rank
can be changed depending on these assumptions. In Scenario A, the co-effect of
incineration food waste with other municipal solid waste has been ignored in this study.
Thus, the capacity of calculated fly ash contributed by incineration of food waste is
controversial. In Scenario C, digestate is used on sandy soils to replace commercial
fertilizers. If digestate is used on loamy soil, the total loss of nitrogen is larger than that
in Scenario B (Bernstad and Jansen, 2011). Compared to the assumed plant up-taken loss
in Scenario C and majority loss due to emission during composting phase in scenario B.
this loss is due to large nitrate runoff from clay soils and would results in a large
contribution to nutrient enrichment. It is also assumed that the produced digestate
substitute all use chemical fertilizer. Previous study (Lantz et al., 2009) shows that
digestate and chemical fertilizer are often used on the same field, but spreading in
different seasons. The leakage from the applied fertilizers and up-taken of P would be
affected in reality.
The results would also be affected by factors as technology development, future policy,
etc. Table 4 shows the P-content in the final product in three scenarios. The extraction
21
method and P-content in the final product in this study is based on the experimental
result from previous study on P recovery from MSWI fly ash (Kalmykova and Fedje, 2013).
The method will be modified to yield more P than this study and P in the final product
may increase. The most important issue in this scenario is that the application of P to the
agriculture is prevented by its heavy metal content. In the future method development,
P recovery can be complemented with extraction of metals, which makes Scenario A be a
considerable option. It should also be pointed out that the composting system simulated
in this study is low tech while high tech systems are being looked into and some are on
the market. The material loss during composting in Scenario B may decrease. Similarly,
with improvement of anaerobic treatment system, the recovered P from digestate in
Scenario C can increase
SWOT is used to analysis the feasibility of recovering P from solid food waste under
scenario C in this study. The result of this analysis directed towards households whose
participation is important to source-separation system of food waste for P recovery. As
food rejection occurs during pre-treatment process of anaerobic treatment. The rejected
food is treated by incineration and in the LCA study of the household food waste of
similar treatment system, around 18% P is lost in this pre-treatment (Bernstad and
Jansen, 2011). Therefore, households’ active participation can greatly increase the
feasibility of the strategy for P recovery in this study.
The SWOT of phosphorus recovery from food waste provides a clear picture of
phosphorus recovery under Scenario C, appropriate recovery scale and system to
address the key goals need to be discussed under Scenario C. Small-scale biological
treatment system has been used by some cities in southern Sweden (Bernstad, 2011).
However, the key objectives are the reduction of the solid waste and protection of the
environment, generated digestates in the treatment is a by-product and applying the
digestates into agriculture to reduce the mineral fertilizer use including phosphorus is
not the key driver. Considering the present waste separating and collecting system in
Sweden, centralized phosphorus recovery and reuse system has the advantage of
economy of scale compared to the household or community-scale retrofits. However,
centralized system needs decreased costs, energy and resource costs of networks,
technology costs which need to be considered by stakeholders.
8. Conclusion
The feasibility of phosphorus recovery from organic solid waste (mainly food waste) is
studied in this paper. Three different scenarios are made to indentify the best way to
recover phosphorus and Scenario C in which food waste is source-separated in paper
bags by households is most favored in this study.
The result of this study will be affected by technology development, future policy,
householders’ participation, etc. It indicates that phosphorus recovery from the solid
waste needs different stakeholders to be involved and work together to achieve the goal.
22
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Appendix
Fly ash: 239050*892625/5100370=41836
Theoretical recovered P in A: 41836*5.9=172
Theoretical recovered P in B: 254398*3.2=814
Theoretical recovered P in C:
(1-18%)*892625*(0.23*23%*64.6%+0.996*42.9%*20.4%+0.198*51.8%*12.8%) =981
26
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