Overview and description of technologies for recovering phosphorus from municipal wastewater
Introduction
Given the important role of phosphorus (P) containing mineral fertilizers in the total global supply of P (∼80%; Prud’Homme, 2010), future demand will clearly be driven by developments in the agricultural sector. Agriculture's demand for P will primarily be affected by population growth and changes in diet in part due to rising living standards in emerging and developing countries (Metson et al., 2012, Heffer and Prud’Homme, 2011). Countries lacking P deposits are entirely dependent on imports and are vulnerable to market fluctuations in fertilizer prices to ensure agricultural production and food security. The availability of the resource P is dynamic and dependent on price and technology (Scholz and Wellmer, 2013). National P balances demonstrate that European countries with enhanced wastewater collection and treatment (biological carbon removal and P removal, see Section 2.2) possess a large but often exploited and inefficiently used potential source of P in waste streams, especially in municipal wastewater of ∼1 kg P cap−1 yr−1 (Cordell et al., 2011, Egle et al., 2014a, Gethke-Albinus, 2012, Binder et al., 2009). However, globally human extractions are a very small part of the global anthropogenic P flows. Considering P losses and efficiency, proper manure management is certainly at least as important as sewage management (Scholz et al., 2014). In some countries, the imported P with feedstuff even submerges P in sewage. Direct agricultural application of wastewater (still practiced in many parts of the world) and sewage sludge is the simplest method of P recycling, although the plant availability of sewage sludge P is debated (Kahiluoto et al., 2015, Krogstad et al., 2005). Due to potential environmental and health risks primarily from heavy metals (HM), persistent organic pollutants (POPs), and pathogens, acceptance of direct sludge applications is low or decreasing in many European countries (Ott and Rechberger, 2012). Consequently, alternative disposal methods focus on co-incineration (cement kilns, power plants or municipal solid waste incinerators) where P is the irretrievably lost.
Potential methods of P recovery from wastewater consist of direct the separate collection of urine, secondary treated effluent from wastewater treatment plants (WWTP), digester supernatant, sewage sludge (SS) and sewage sludge ash (SSA) (Montag, 2008). These flows differ widely in terms of volume, P concentration, the form of P (dissolved as orthophosphate or biologically/chemically bound), the characteristic of the source (liquid, liquid/solid, solid), pollutant content (HM, POPs, pathogens) and the theoretical recovery potential (Table 1). An ideal approach would feature a high P recovery rate, economic efficiency, and a useful product with low environmental risks. Currently, well-developed and large-scale approaches differ appreciably in terms of these criteria. This article focuses exclusively on approaches for recovering P from municipal wastewater streams. The P recovery approaches address WWTP with strict European standards in P removal for landlocked countries (EC, 1998) and thermal sludge treatment options, namely fluidized bed reactors, which are state of the art in Europe. The general procedures of P recovery approaches have been published frequently, but the important details are frequently lacking (Montag et al., 2011).
Some approaches have received more attention than others have in the past and as such, we have varying degrees of knowledge about them. P recovery by precipitation from sources of dissolved P (orthophosphate) has been investigated in detail (Muster et al., 2013, Rahman et al., 2014, Doyle and Parsons, 2002). Therefore, optimum process parameters, resource demands, effects on WWTPs and characteristics of the products are well known. To recover P from sewage sludge, various sludge treatment options such as anaerobic treatment, thermal hydrolysis, (wet-) oxidation or wet-chemical leaching are necessary as a first step to dissolve P. The behavior of P and process inhibiting ions (Fe, Al, heavy metals) has been well studied and extensively described (Section 3.4). This knowledge is fundamental for taking further steps in pollutants removal and final P recovery. The same applies to procedural challenges, practicability, waste flows, and possible effects on the functioning of WWTPs. For metallurgic approaches, there is a lack of reliable data regarding mass balances and the fate of heavy metals within the process, and only the results of a few trials are available (Ingitech, 2009). Surprisingly, the current literature on P recovery from ash primarily describes approaches with little realistic potential for prospective practical application (Petzet et al., 2012, Donatello et al., 2010, Franz, 2008, Levlin, 2001). In contrast, SSA is already used to create recycled products using industrial processes (e.g., ICL Fertilizers®: fertilizer industry; Thermphos®: production of P4; EcoPhos®: production of phosphoric acid or animal feed). Numerous approaches have been developed in universities and private companies currently operating at pilot scale or full-scale, but details are not yet widely published. In general, many approaches for recovering P from ash are similar to those for treating raw phosphate ore (Nielsson, 1989). This article provides an overview on known approaches looking in detail at those with potential for full-scale implementation or which are already implemented. These approaches are characterized in the context of P removal from wastewater and at other access points of recovery (Fig. 1). Thus, a first criterion is the characterization of the optional P flows, thereby outlining the challenges for recovery technologies. Based on this knowledge, our review serves as a database for further integrated, comprehensive and comparative technical, environmental and economic assessments. The following items were investigated:
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Fundamentals of process engineering (e.g., process steps).
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Possible technical challenges.
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Quantification of resource demands (e.g., chemicals, energy).
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Effects on WWTP and resulting waste products.
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Illustration of the fate of potentially harmful substances.
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Characteristics of the final product (e.g., chemical compound, plant availability, heavy metals (Table A4)).
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P recovery potential of a technology (1) related to the input flow (e.g., sewage sludge) and (2) recovery potential in relation to the WWTP influent.
In addition to the literature review, the database contains information from interviews of plant operators, researchers, commercial companies, and by visiting existing plants. For selected technologies detailed material flow models are provided, generated with the Software STAN (Cencic and Rechberger, 2008). These models are the basis for material flow analysis (MFA; Brunner and Rechberger, 2004). Utilizing MFA input- and output flows will be balanced for a technology. Furthermore, MFA is an appropriate methodology to track the path of P and pollutants for assessing P recovery and depollution potential.
The recovery technologies are summarized in Appendix and present their status of implementation, the technological approach, the final product and the efficiency with regard to the WWTP influent (Table A1, Table A2, Table A3, Table A4). A comparison of costs is not part of this work, as a fair comparison requires a standardized initial situation (reference system) and technologies in a similar development stage. An attempt for economic assessment however, should be an essential part of future work.
Section snippets
P in wastewater
P enters the wastewater stream primarily in the form of excreted human metabolic products (urine, feces), food residues, and industrial source emissions. Additional to these P sources, detergents are a source of P in European countries. Therefore, a typical daily P load in municipal influenced wastewater in Europe is 1.5–2 g cap−1 (Henze et al., 2002, Zessner and Lindtner, 2005, Richards et al., 2015). P is present in many suspended and dissolved, inorganic, and organic compounds (Baumann, 2003).
P removal from wastewater
Urine separation
For nutrient recovery from urine, so-called NoMix installations or urine separation toilets are installed to avoid dilution and fecal contamination (Vinnerås and Jönsson, 2002). Urine contains approximately 50% of the total P and 80% of the total N of household wastewater, whereas its mass flow is less than 1% (valid for European combined sewer systems: 1.5–2 L cap−1 d−1) (Larsen and Gujer, 1996). Urine recovery in NoMix toilets is usually in the range of 30–50% (Zessner and Lindtner, 2005). This
Discussion
This overview of P recovery technologies from municipal wastewater highlights that although P recovery is intensively discussed on the international level, there is no “magic-bullet” solution and appropriate technology choice should be based on local conditions that determine several aspects of wastewater quantity, composition, treatment, and reuse. For many technologies, their technical feasibility has already been demonstrated and replicable data for detailed material- and energy flow
Conclusions
P in wastewater represents a high recycling potential. With an efficient use of sewage sludge, theoretically up to 50% of annually applied mineral P fertilizer in agriculture could be substituted in Europe (Egle et al., 2014a, Schoumans et al., 2014). Taking into account other important P imports as feedstuff and food, human excrements play a minor role in the anthropogenic P cycle. Currently, a wide range of approaches exists to recover significant amounts of P from wastewater. From a
Acknowledgements
This study was performed as part of the project “Phosphorus Recycling from Wastewater,” which was funded by the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management. We would also like to acknowledge the financial support provided by the Austrian Science Funds (FWF) as part of the Vienna Doctoral Programme on Water Resource Systems (DK-plus W1219-N22). The reviewers and additionally Christian Kabbe (P-REX) helped significantly to improve and keep this paper
References (208)
- et al.
Thermochemical treatment of sewage sludge ashes for phosphorus recovery
Waste Manag.
(2009) - et al.
Phosphorus recovery from sewage sludge with a hybrid process of low pressure wet oxidation and nanofiltration
Water Res.
(2012) - et al.
Pretreatment methods to improve sludge anaerobic degradability: a review
J. Hazard. Mater.
(2010) - et al.
Bioleaching of phosphorus from rock phosphate containing pyrites by Acidithiobacillus ferrooxidans
Miner. Eng.
(2006) - et al.
Towards global phosphorus security: a systems framework for phosphorus recovery and reuse options
Chemosphere
(2011) - et al.
Wet air oxidation for the treatment of industrial wastes. Chemical aspects, reactor design and industrial applications in Europe
Waste Manag.
(2000) - et al.
Emission characteristics of dioxins, furans and polycyclic aromatic hydrocarbons during fluidized-bed combustion of sewage sludge
J. Environ. Sci.
(2009) - et al.
Recycling and recovery routes for incinerated sewage sludge ash (ISSA): a review
Waste Manag.
(2013) - et al.
Production of technical grade phosphoric acid from incinerator sewage sludge ash (ISSA) 2010
Waste Manag.
(2010) - et al.
Struvite formation, control and recovery
Water Res.
(2002)
The Austrian P budget as a basis for resource optimization
Resour. Conserv. Recycl.
Past, present and future of biohydrometallurgy
Hydrometallurgy
Low cost struvite production using source-separated urine in Nepal
Water Res.
Phosphate fertilizer from sewage sludge ash (SSA)
Waste Manag.
Phosphorus recovery from digested sewage sludge as MAP by the help of metal ion separation
Water Res.
A review of wet air oxidation and Thermal Hydrolysis technologies in sludge treatment
Bioresour. Technol.
Review: Bacterial phosphate metabolism and its application to phosphorus recovery and industrial bioprocesses
J. Biosci. Bioeng.
Struvite precipitation from urine with electrochemical magnesium dosage
Water Res.
Potential phosphorus recovery by struvite formation
Water Res.
Sewage-effluent phosphorus: a greater risk to river eutrophication than agricultural phosphorus?
Sci. Total Environ.
Source separated urine-nutrient and heavy metal content, water saving and faecal contamination
Water Sci. Technol.
Influence of chemically and biologically stabilized sewage sludge on plant-available phosphorous in soil
Ecol. Eng.
Concentrations and specific loads of polycyclic musks in sewage sludge originating from a monitoring network in Switzerland
Chemosphere
Separate management of anthropogenic nutrient solutions (human urine)
Water Sci. Technol.
Agglomeration of struvite crystals
Water Res.
Comparative goal oriented assessment of conventional and alternative sewage sludge treatment options
Waste Manag.
Upgrading of sewage treatment plant by sustainable and cost-effective separate treatment of industrial wastewater
Water Sci. Technol.
Pilot-scale Study of Phosphorus Recovery Through Struvite Crystallization
Pilot-scale study of phosphorus recovery through struvite crystallization – examining the feasibility of applying the process technology
J. Environ. Eng. Sci.
Removal of phosphate from sewage as amorphous calcium phosphate
Environ. Technol.
Large-scale practical application of nutrient recovery from digested sludge as struvite
Phosphatelimination aus Abwasser
Recovery of phosphorus form sewage sludge and sludge ashes – applications in Germany and Northern Europe
Phosphorus removal and recovery from waste water by tobermorite-seeded crystallisation of calcium phosphate
Water Sci. Technol.
Impact of calcite on phosphorus removal and recovery from wastewater using CSH-filled fixed bed filters
J. Res. Sci. Technol.
Rückgewinnung von Nährstoffen zur Herstellung von Düngemitteln. Informationsbrochüre
Phosphorflüsse in der Schweiz. Stand, Risiken und Handlungsoptionen. Abschlussbericht. Umwelt-Wissen Nr. 0928
Hybrid anion exchanger for trace phosphate removal from water and wastewater
Water Res.
Optimierte Phosphor-Rückgewinnung aus Klärschlämmen durch ein Hybridverfahren aus Niederdruck-Nassoxidation und Nanofiltration
Thermische Klärschlammhydrolyse mit Nährstoffrückgewinnung – Auswirkungen der thermischen Klärschlammhydrolyse und der prozessintegrierten Nährstoffrückgewinnung auf die Stoffstrom- und Energiebilanzen auf Kläranlagen AZ 24507-23. Final report
Chemical leaching of metals from wastewater sludge: comparative study by use of three oxidizing agents [H2O2, FeCl3 and Fe2(SO4)3]
Water Environ. Res.
Elektrothermische Erzeugung von Phosphor. Chemie Ingenieur Technik 42 (4)
Phosphorus removal and recovery technologies. 1997 Environmental and Water Resource Engineering Section Imperial College of Science, Technology and Medicine, London SWU 2BU
Value from waste – struvite recovery at the city of Edmonton's gold bar WWTP
Practical Handbook of Material Flow Analysis
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