Ansökan 2002 till FORMAS Forskningsrådet för Miljö, areella näringar och samhällsbyggnad

Erik Levlin, Mark och Vattenteknik, Kgl. Tekniska Högskolan

 

MINIMIZATION OF CHEMICAL DEMAND FOR COMBINED PHOSPHORUS REMOVAL AND RECOVERY AT MUNICIPAL WASTEWATER TREATMENT PLANTS

 

RESEARCH PROGRAMME

 

BACKGROUND

 

Phosphorus removal from municipal wastewater has a long tradition in Sweden to protect receiving waters from eutrophication with the first plant for phosphorus removal in Åker municipality in 1961. Chemical precipitation was the only economically feasible technology known at that time and future implementation of phosphorus removal in Sweden has mainly been based on chemical precipitation with iron salts as dominating precipitation agent. Only a few plants are operated with biological phosphorus removal in Sweden, although this process technology is widely used internationally.

 

Recently, Swedish policy requires phosphorus to be recycled and, because agricultural sewage sludge re-use is increasingly limited, this is putting pressure on cities to develop phosphorus recovery systems. In a number of cases, authorisation to construct sludge incinerators is being given condition that phosphorus must be recovered. A national goal has been proposed to the Swedish government that at least 75% of phosphorus from wastewater and other biological wastes should be recovered at latest by 2010 without risks for health and environment. The Swedish Environment Protection Agency (SEPA) has been given a commission from the government to better evaluate possibilities to implement this goal and propose modifications. The commission shall be reported before Oct. 15 , 2002, and recently a draft "state-of-the-art" report on phosphorus recovery has been worked out (Balmér et al., 2002). Phosphorus recovery by spreading sludge on agricultural land has been stopped to a high extent due to resistance from the farmers´ organisation (LRF) and food industries. Recent food scandals in Europe have led authorities in Switzerland to propose a ban on the use of biosolids in agricultural land applications by 2005. Disposal of organic material to landfill will be forbidden in 2005. Difficulties to use earlier routes of final sludge disposal have led to a great interest in fractionation of sludges followed by recovery of different products and transfer of toxic materials into a small stream.

 

It seems likely that Swedish municipalities will face two requirements concerning phosphorus, i.e. high removal efficiency of phosphorus from the wastewater followed by phosphorus recovery from the formed sludge. These two requirements may lead to high investment and operational costs. There is, thus, a need to develop a scientific basis for such solutions that can be applied at existing plants and with a low demand of chemicals.

 

PRESENT SOLUTIONS FOR PHOSPHORUS RECOVERY AS PRODUCT

 

Phosphorus recovery as a product follows in most practical applications the following steps (see Figure 1):

·                 Transfer of soluble or colloidal phosphorus compounds into a biological (including enhanced biological phosphorus removal) or chemical sludge (use of chemical precipitation agents)

·                 Dissolution of the sludge by use of anaerobic treatment (in enhanced biological phosphorus removal) or addition of acids and bases in combination of thermal methods (thermal hydrolysis, incineration or supercritical water oxidation)

·                 Separation of phosphate from the phosphate-rich leachate from the other components by use of methods as chemical precipitation, crystallisation and ion exchange.

 

 

 

 

 

 

 

 

 

 


Figure 1.   Main steps in phosphorus recovery as a product.

 

 

A few systems are at present available for recovery of phosphorus in full-scale or near full-scale application (se Table 1).

 

 

Table 1.    Systems for phosphorus recovery in or near full-scale application at central municipal wastewater treatment plants.

Transfer of phosphorus into a sludge phase

Dissolution of phos­phate from sludge

Separation of phosphate from concentrated liquid

Commercial/

full-scale application

Enhanced biological phosphorus removal

Anaerobic treatment of phosphorus rich biological sludge

Crystallisation of calcium phosphates

Two plants in the Netherlands

Crystallisation of magnesium ammonium phosphate

Five full-scale plants in Japan (Unitika Ltd and Kurita Water industries)

Chemical precipitation with iron salts

Thermal and acid hydrolysis of digested sludge

Oxidation and chemical precipitation to ferric phosphate

KREPRO process studied at Helsingborg and with possible full-scale application in Malmö

Heat drying, incine­ration followed by sulphuric acid addition to sludge

Ion exchange to recover phosphoric acid

BioCon process studied in Brønderslev, Denmark, in pilot plant and planned as full-scale in Falun

Supercritical water oxidation followed by washing and alkaline treatment of rest product

Chemical precipitation with lime to calcium phosphate

Feralco process evaluated as a suitable treatment for Stockholm Water Co

 

 

The chemical demand for removal and recovery of phosphate as a product is related to:

·                  Amount of chemicals necessary for transferring soluble and colloidal phosphorus into a solid phase (biological or chemical sludge)

·                  Amount of chemicals necessary for dissolving phosphate from the sludge or ash/residue after treatment of sludge by methods as incineration and supercritical water oxidation

·                  Amount of chemicals necessary for recovery of a product

 

 

 

Suppose - as an illustration example - precipitation of hydrogen phosphate by ferric iron, dissolution of the precipitate by acids and recovery of a phosphate product as ferric phosphate:

 

Fe3+ + HPO42-     ¾® FePO4 + H+

FePO4 + 2 H+     ¾® Fe3+ + H2PO4-  

Fe3+ + H2PO4-     ¾® FePO4 + 2 H+

 

In the first reaction 2 ekv Fe3+/ekv phosphate, the second reaction 2 ekv acids/ekv phosphate and in the third reaction 2 ekv Fe3+/ekv phosphate are needed or totally 6 ekv chemicals/ekv phosphate recovered. Obviously, chemical demand for phosphorus removal and recovery in municipal wastewater handling is much more complex involving precipitation of other components (as ferric hydroxide) in chemical precipitation, dissolution of many other components in acid treatment of sludge, ash and residue and chemicals needed to separate the phosphorus product from other components. In addition considerations must be taken into chemical precipitant recovery, recycling of sludge to the influent, release of organic materials, and use, disposal or recycling of streams not involving phosphorus recovery. Although the complexity is high on the problem phosphorus removal/recovery, it seems reasonable to assume that a suitable way to solve this problem in a beneficial way is to use technologies that are efficient in chemical demand and involve as general possibilities:

·                  Low addition of chemicals to achieve phosphorus removal according to environmental requirements

·                  Selective dissolution of sludge, ash or residue to release phosphate from the sludge

·                  Selective separation of phosphate from leachate including recycling technology in phosphorus recovery

 

Examples of different chemical-efficient methods are illustrated in Table 2.

 

 

Table 2.    Examples of efficient methods in phosphorus removal and recovery related to chemical demand

Wastewater treatment

Phosphate dissolution from sludge, ash or residue

Phosphorus recovery from concentrated liquid

Enhanced biological phosphorus removal combined with poli­shing with chemical precipitation

Release of phosphate in anae­robic sludge treatment and enhanced by heating

Precipitation and crystallisation to recover calcium phosphates or magnesium ammonium phosphate or ion exhange for production of for instance phosphoric acid

Chemical precipi­tation with iron salts

Selective release of phosphate by alkaline treatment of rest products (for instance from supercritical water oxidation) or by hydrogen sulphide addition

Precipitation as calcium phosphate (and recovery of aluminate or sodium hydroxide in alkaline treatment or hydrogen sulphide in acid treatment)

Combined biological and chemical phos­phorus removal

Two-step release of phosphate from biologically and chemi­cally bound phosphorus, respectively

Precipitation, crystallisation or ion exchange in two separate concentrated phosphate streams as calcium phosphate, magnesium phosphate or phosphoric acid

 

 

PROJECT OBJECTIVES AND METHODOLOGY

 

Main focus in the project will be given to the examples n Table 2 to find efficient methods in phosphorus removal and recovery related to chemical demand and with emphasis on recovery methods. Thus, emphasis will be given to:

·                  Possibilities to modify existing plants in Sweden to minimize chemical demand of precipitation and to develop a sludge suitable for further treatment including phosphorus recovery

·                  Methods to release phosphorus from sludge, ash and residues involving as little as possible of other sludge components

·                  Handling of phosphorus rich liquids to give a suitable phosphorus product based on chemical precipitation, crystallisation or ion exchange (including recycling technology)

·                  System analysis of the suggested methods based on sustainability (extending the focus on minimizing chemical demand)

 

Methodology can be based on many articles and reports describing different options for phosphorus removal and recovery and different introductory experiments on phosphorus recovery by use of acids and basis. Main earlier studies that are the basis for further studies are described in Table 3.

 

Table 3.    Information for further studies of combined phosphorus removal and recovery based on compiled information from the div. of Water Resources Engineering, KTH (now dept. of Land and Water Resources Engineering, KTH)

Main project area

References (see reference list)

Enhanced biological phosphorus removal/chemical precipitation

A

Sludge quality and trends for sludge handling

B

Dissolution of sludge, ashes and residues by acids and bases

C

Special technology for phosphorus recovery (mainly ion exchange)

D

System approach to combined phosphorus removal and recovery

E

General aspects and technology in sludge handling with product recovery

F

 

 

The information in Table 3 can be seen as a platform to perform:

·                  Modelling and experiments of dissolution of different sludge components at different pre-treatments, different types of sludges and different pH-values

·                  Modelling and experiments of separation technology of different phosphorus rich liquids containing also other components from sludge

·                  Evaluation of different combined methods of phosphorus removal and recovery based on low necessary demand of chemicals and investment cost and sustainability

 

The research will be performed nationally in co-operation with municipalities, SEPA, Swedish Water Companies etc and internationally with organisations as CEEP and in the ongoing project of Swedish- Polish co-operation. The project will also be in co-operation with the MISTRA programme "Urban Water".

 

 

REFERENCES (cf Table 3)

 

F   Balmér P., Book K., Hultman B., Jönsson H., Kärrman E., Levlin E. Palm O., Schönning C., Seger A., Stark K., Söderberg H., Tiderström H. and Åberg H. (2002) System för återanvändning av fosfor ur avlopp. Draft report to SEPA 2002-01-14.

A  Fujii D. (2000) Evaluation of biological nutrient removal at Käppala wastewater treatment plant. Licentiate thesis, TRITA-AMI-LIC 2048.

F   Hultman B. and Levlin E. (1997) Sustainable sludge handling. Proceedings of a Polish-Swedish seminar, KTH, Stockholm, May 30, 1997. Advanced Wastewater Treatment, Joint Polish-Swedish report report No 2, TRITA-AMI REPORT 3045, ISBN 91-7170-283-0

E   Hultman B., Levlin E., Löwén M., Mossakowska A. and Stark K. (2001) Utvinning av fosfor och andra produkter ur slam och aska. Delrapport, Stockholm Vatten AB, R. Nr 6, 2001.

E   Hultman B., Levlin E., Löwén M., Mossakowska A. and Stark K. (2001) Utvinning av fosfor och andra produkter ur slam och aska. Slutrapport, Stockholm Vatten AB, R. Nr 2, 2002.

E   Hultman B., Levlin E., Mossakowska A. and Stark K. (2001) Effects of wastewater treatment technology on phosphorus recovery from sludges and ashes. 2nd International Conference on Recovery of Phosphates from Sewage and Animal Wastes, Noordwijkerhout Netherlands 12-13 march 2001.

F   Hultman, B. Levlin, E., Löwén M. and Mossakowska, M. (1997) Uthållig slamhantering. Förstudie. Stockholm Vatten AB, R. Nr 23 sept-97, Stockholm Vatten.

F   Hultman, B. Levlin, E. and Stark K. (2000) Swedish debate on sludge handling. Proceedings of a Polish-Swedish seminar, Cracow, May 29, 2000. Sustainable Municipal Sludge And Solid Waste Handling, Joint Polish-Swedish report report No 7, TRITA-AMI REPORT 3073, ISBN 91-7170-584-8. pp. 1-16.

E   Hultman B. and Löwén M. (2001) Combined phosphorus removal and recovery. Proceedings of a Polish-Swedish seminar, Nowy Targ - Zakopane Oktober 24-26, 2001 Wastewater sludge and solid waste management, Joint Polish-Swedish report report No 9, ISBN 91-7283-190-1. pp. 11-18.

C  Levlin E. (1998) Sustainable sludge handling – Metal removal and phosphorus recovery. Proceedings of a Polish-Swedish seminar, Nowy Targ, October 1-2, 1998. Advanced Wastewater Treatment, Joint Polish-Swedish report report No 3, TRITA-AMI REPORT 3048, ISBN 91-7170-324-1. pp. 73-82.

D  Levlin E. (2001) Recovery of phosphate and separation of metals by ion exchange. Proceedings of a Polish-Swedish seminar, Nowy Targ - Zakopane October 24-26, 2001 Wastewater sludge and solid waste management, Joint Polish-Swedish report No 9, ISBN 91-7283-190-1. pp. 81-90.

B  Levlin E. and Kapilashrami S. (2000) Sludge quality in Sweden – Inquiry results for year 1995 to 1997. Proceedings of a Polish-Swedish seminar, Cracow, May 29, 2000. Sustainable Municipal Sludge And Solid Waste Handling, Joint Polish-Swedish report report No 7, TRITA-AMI REPORT 3073, ISBN 91-7170-584-8. pp. 17-26.

C  Levlin E., Löwén M., Schmidt E., Hultman B. and Mossakowska A. (1998) Fosforutvinning ur aska, Stockholm Vatten AB, R Nr 54 nov-98.

F   Levlin E., Löwén M., Stark K. and Hultman B. (2001). Effects of phosphorus recovery requirements on Swedish sludge management 2nd World Water Congress of IWA, Berlin October 15-18.

B  Levlin E., Tideström H., Kapilashrami S., Stark K. and Hultman B. (2001) Slamkvalitet och trender för slamhantering. VA-forsk 2001-05, ISBN: 91-89182-56-1.

A  Rybicki S. (1997) Phosphorus removal from wastewater: A Literature Review, Advanced Wastewater Treatment, Joint Polish-Swedish report report No 1. TRITA-AMI REPORT 3042, ISBN 91-7170-247-4.

C  Stark K. (2001) Phosphorus release from sewage sludge by use of acids and bases. Proceedings of a Polish-Swedish seminar, Nowy Targ - Zakopane Oktober 24-26, 2001 Wastewater sludge and solid waste management, Joint Polish-Swedish report No 9, ISBN 91-7283-190-1. pp. 19-30.

C  Stark K. (2002) Utvinning av fosfor vid superkritisk vattenoxidation av avloppsslam. Vatten Vol. 58 Nr 2 (in print)

C  Stark K. Phosphorus recovery from sewage sludge by thermal treatment and use of acids and bases. Paper accepted to “Kemira-conference” in Gothenburg 17-19 June 2002.

E   Stark K., Hultman B. and Levlin E. (2002) New system technology for combined phosphorus removal and recovery. Poster presented at IWA-Conferens, Melbourne, Australia April 7-12 2002.

E   Stark K., Hultman B., Levlin E., Löwén M. and Mossakowska A. (2002) Calculation of chemical needs in combined phosphorus removal and recovery at Henriksdal WWTP, Sweden. Poster presented at IWA-Conferens, Melbourne, Australia April 7-12 2002.

C  Stark K., Hultman B., Mossakowska A. and Levlin, E. (2001) Kemikaliebehov vid fosforutvinning ur avloppsslam. Vatten Vol 57, Nr 3, pp. 207-215.

F   Stypka T., Płaza E., Stypka J., Trela J. and Hultman B. (2001) Regional planning and recovery as tools for sustainable sludge management. 2nd World Water Congress of IWA, Berlin 15-18 oktober.