Phosphate Recovery
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CURRENT PROJECTS ON PHOSPHATE RECOVERY
1) Calcium phosphate precipitation chemistry:
a)
heterogeneous nucleation of calcium phosphates and the effects
of inhibitors
b)
precipitation
reactions involving calcite and calcium phosphates
2) The production of waste water sludges for phosphate recovery
5) Feasibility of reuse of recovered phosphate materials in Holland
6) Seeded precipitation of calcium phosphates in wastewaters
7) Investigation of the economic feasibility and environmental efficiency of recovered struvite
8) Metal speciation and nutrient retention by anaerobic digesters
9) Struvite precipitation from sewage liquors, Poland
10) Process optimisation for struvite crystallisation, Treviso, Italy
1) Calcium phosphate precipitation chemistry:
a) heterogeneous nucleation of calcium phosphates and the effects of inhibitors
PROJECT COMPLETED
Publications:
- Van der Houwen, J.A.M., Cressey, G., Cressey, B.A. and Valsami-Jones, E., 2003. The effect of organic ligands on the crystallinity of calcium phosphate. Journal of Crystal Growth, vol 249/3-4 pp 572 - 583.
- Valsami-Jones, E., 2002. Phosphorus in wastewaters: is there a potential for recovery as calcium phosphate? Chimica Oggi (Chemistry Today), 5, 52-55.
- Van der Houwen, J.A.M. and Valsami-Jones, E., 2002. Towards understanding interactions between apatite surfaces and carboxylate ligands at the atomic level. Phosphorus Research Bulletin, 13, 31-38.
- Van der Houwen, J.A.M.
and Valsami-Jones, E., 2001. The application of calcium phosphate
precipitation chemistry to phosphorus recovery: the influence
of organic ligands. Environmental Technology, 22, 1325-1335.
- Valsami-Jones, E., 2001. Mineralogical controls on phosphorus recovery from wastewaters. Min. Mag., 65(5), 611-620.
b)
precipitation
reactions involving calcite
and calcium phosphates
PROJECT COMPLETED
Publications:
Plant, L. & House,
W.A., 2002. Precipitation of calcite in the presence of inorganic
phosphate". Colloids and Surfaces - A - 203, pp. 143-153.
2) The production of waste water sludges for phosphate recovery
Supervisors: Dr. Elaine
Dick*, Prof. Stephen Allen*, Dr. John Quinn
*School of Chemical Engineering; School of Biology and Biochemistry,
QUESTOR Centre,
The Queen's University of Belfast, N. Ireland
URL: http://questor.qub.ac.uk
Phosphate removal from wastewater is currently achieved by biological and/or chemical treatment methods, producing sludge with an increased phosphate content. These sludges can not at present be used by the phosphate industry as a source of phosphate (P-recovery) if there is significant iron or aluminium content or because P-rich solids are difficult to separate. This project will investigate a novel combination of treatment methods with the aim of producing sludge suitable for P-recovery. The project will involve the operation of a laboratory scale wastewater treatment plant, as well as the detailed examination of microbial physiology and surface chemistry.
3) Feasibility review regarding application of the REM-NUT ion exchange process for phosphate recovery from municipal waste water
Supervisor: Prof Lorenzo Liberti
Institute of Environmental Engineering, Polytechnic University of Bari, 70125 Bari, Italy Tel +39-080-5460368 - Fax +39-080-5460282 - E-mail: liberti@poliba.it
Update and revise the REM-NUT ion exchange process concept to target:
- phosphorus removal, on secondary treatment sewage plant effluent, down to EU urban waste water treatment Directive 91/271 discharge requirements for sensitive areas (1 or 2 mgP/l)
- recovery of phosphate in a form suitable for recycling in industrial processes or as an agricultural fertiliser
- calculate (on a theoretical basis) approximate mass balances for P, N, chemical addition as affecting the sewage works functioning, sludge production, REM-NUT operation and P-recovery
- establish estimated economic analysis of this system concept, taking into account current and anticipated costs for investment, chemicals, sludge disposal, sewage works investment and operation
- provide a summary of past literature and data regarding the fertiliser value of struvite (agronomic value / availability of P at different soil pH/conditions; economic market value) and the possibilities for use of struvite in fertiliser manufacturing or preparation processes, update this information (is struvite still marketed as a fertiliser? market value of comparable N/P sources).
- assess how the revised REM-NUT concept would fit in with existing or possible future nitrogen removal in sewage works (the revised REM-NUT will only remove a small proportion of waste water N, so that the sewage works will need to invest in biological or other N removal systems).
4) Identification and analysis of different possible pathways for phosphorus recovery for recycling from sewage sludges and in sewage sludge management
Supervisors: Prof. Bengt Hultmann
Kungl Tekniska Hgskolan Royal Institute of Technology Water Resources Engineering S - 100 44 Stockholm Sweden Email: bgh@aom.kth.se Tel : 46 8 790 6567 Fax : 46 8 790 8689
Project aims are:
- to identify and describe likely pathways for phosphorus recovery from sewage sludges and ashes
- to identify and describe how phosphorus recovery fits into different systems for sludge management
- to identify and describe different secondary effects on sludge handling (changes in sludge amounts, dewatering properties etc.) during phosphorus recovery
- to describe typical compositions of different sludges and ashes with special emphasis on how phosphorus is bound (including analytical procedures)
- to describe interactions between phosphorus removal and recovery technologies and possibilities for two-stage phosphorus recovery
- to identify areas requiring further research
5) Feasibility of reuse of recovered phosphate materials in Holland
Study commissioned by STOWA (Dutch water industry joint research association) and Thermphos (phosphate producer) from HASKONING Ingenieurs en architectenbureau Barbarossastraat 35, Postbus 151 NL-6500 AD Nijmegen Holland Tel 31 24 3284 341 Fax 31 24 360 4737 Email:ws@haskoning.nl
Aims:
- Establish a quantitative and qualitative picture of which residual phosphate-containing materials are currently available and could be used for the production of phosphorus.
- Determine the quality requirements that aluminium and/or calcium phosphate must satisfy before they can be used as a basic material by Thermphos.
- Determine the quantities of aluminium and/or calcium phosphate produced.
- Determine the quantity of phosphate that could possibly also be supplied as aluminium and/or calcium phosphate.
- Inventarize the quality and quantity of the ash residues of sewage sludge incineration.
- Determine the extent to which processes could be modified to make more aluminium or calcium phosphate available, and identify operators who would be prepared to carry out such modifications.
- Determine the financial and technological merits for sewage treatment plants of the cycle of use and reutilization of aluminium and/or calcium phosphate.
- Determine, from the point of view of investment and applied technology, the extent to which the reutilization of residual phosphate-containing substances will be feasible for Thermphos in the future.
6) Seeded precipitation of calcium phosphates in wastewaters
Investigators: Dr Dietfried Donnert and co-workers
Karlsruhe Research Centre Forschungszentrum Karlsruhe Technik und Umwelt PO Box 3640 - 76021 Karlsruhe - Germany. Tel : 49 7247 823213 Fax : 49 7247 823478 Email: dietfried.donnert@itc-wgt.fzk.de
Laboratory experimentation of calcium phosphate precipitation from solutions in concentrations comparable to those found in sewage works. Investigation of the effects of different seed crystals and of calcium carbonate/ dissolved inorganic carbon on the calcium phosphate precipitation process.
Papers
Phosphorus removal and recovery by crystallisation
Phosphorus removal combined with active filtration (in german)
P-recovery via crystallisation from waste waters
7) Investigation of the economic feasibility and environmental efficiency of reusing (as fertiliser or as a raw material for industry) struvite recovered from wastewater treatment works
Study by: Mark GATERELL, Rebecca Gay
Imperial College London Centre Environmental Technology Civil Engineering Building SW7 2BU - London - U.K. Tel. 44 171 594 7459 Fax. 44 171 594 6016/6053 Email: m.gaterell@ic.ac.uk
To investigate the economic feasibility and environmental efficiency of reusing Struvite recovered from wastewater treatment works (WWTW) and other waste streams. This analysis includes an economic evaluation of the recovery process, the identification and investigation of potential re-use options, in particular applications in the fertiliser industry, and the economic and environmental implications of adopting any such options.
- Carry out an economic analysis of Struvite recovery at WWTW and assess likely overall implications of struvite recovery on main wwtp operating parameters in particular nitrogen removal, sludge production and disposal (sludge volumes, nutrient content and other significant characteristics of sludge affecting the possible options, cost and environmental impact of disposal).
- Identify and assess potential re-use routes available, in the fertiliser industry or possibly in other sectors of the phosphate industries or the ciment industry, for the struvite recovered.
- Undertake an economic and environmental appraisal of options for the reuse of struvite identified above. This appraisal will be centred on recovery from WWTP but will take into account the possibility of recovering struvite from other sources: industrial waste streams, agricultural wastes.
8) METAL SPECIATION AND NUTRIENT RETENTION BY ANAEROBIC DIGESTERS
EPSRC Grant GR/K96946
INVESTIGATORS: Ms C.M.Carliell, Professor A.D. Wheatley, Dr. M. Ince, Department of Civil and Building Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU
Summary
Phosphate removal and recovery has and will become important to avoid eutrophication of sensitive waters. The phosphate removed from effluents is concentrated in the sludge. The most common form of sludge treatment in the UK is anaerobic digestion. There was a concern that the solid bound phosphate would be released when subjected to the low redox environment of anaerobic digestion.
Analytical methods were adapted for use in the complex anaerobic environment as a first stage to understanding phosphate mobility. The research reported here developed and modified the standard analytical techniques (Stover and Uhlmann methods) to make them applicable to anaerobic digestion. Changes to the standard analytical techniques are one of the outputs of this research.
Laboratory reactors were used to provide a well controlled environment to study the effect of using chemical flocculents for the precipitation of phosphate compared to biological methods. Calcium and magnesium were also artificially added to simulate their role in scale and struvite formation. The results have shown that increases in soluble phosphorus inhibits digester performance. The chemical equilibrium is normally dominated by the carbonate and sulphide species but this is easily altered by additions of phosphate. Phosphate precipitated with controlled quantities of iron in the laboratory remobilised during anaerobic reduction. Phosphate precipitated with aluminum did not resolubilise.
Field work was carried out on examples of chemical and biological phosphorus removal. The full scale iron dosed sludge did not show any elevated soluble phosphate, in fact the soluble phosphate results were below the detection limit. This was an interesting contrast to the laboratory results where less but controlled amounts of iron were added. Speciation studies showed the phosphate existed as predominantly iron phosphate.
The inference is that iron should be present in a slight excess to avoid re solubilisation on reduction in the digester. There is little chance of scale formation or inhibition because iron competes strongly for the phosphate. In the absence of sufficient ferrous ion then solubilisation or precipitation as struvite and scale is possible. Biological phosphorus removal does carry a greater risk of remobilisation. The formation of struvites in digester ancilaries after biological phosphorus removal has also been reported by others (Rabonowitz and Barnard 1995). In practice our research has shown this will be easy to control by further delicate adjustments to the interlinked inorganic balances. It could be altered by additions of other transition metals for nutrients as well as more iron. Further research on the role of ammonia and alkalinity together with more work on the calcium, magnesium and potassium balances has been suggested to help understand struvite formation.
9) Struvite precipitation from sewage liquors, Poland
INVESTIGATORS: Dr Jan Suschka, Technical University of Lodz, Filial Bielsko Biala Email:jsuschka@pb.bielsko.pl
Summary
Testing of different pilot struvite precipitation reactors in sewage
works. Study of parameters affecting the shape of struvite crystals
formed.
10) Process optimisation for struvite crystallisation, Treviso, Italy
INVESTIGATORS: Professor Paolo Battistoni and collaborators, University of Verona, Italy Email: idrotre@mta01.unian.it
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