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Nutrient removal and value added product formation from wastes via struvite precipitation

Final Report Summary - STRUVITE (Nutrient removal and value added product formation from wastes via struvite precipitation)

There is a large amount of animal manure and wastewater treatment sludge produced in many countries without proper management practices. In addition to other major pollutants, nitrogen (N) and phosphorus (P) threaten the quality of natural receiving environments and this is why improved N and P removal will not only reduce the environmental problems associated with N and P discharges, but also will provide a technique to recover the nutrients within the anaerobic sludge, which can further be used in land applications. Therefore, nutrient recovery from sewage sludge and other organic solid wastes in the form struvite has become the focus of many research studies. This is mainly because of limited P rock reserves, which are mainly exploited for the production of fertilizers. There are many additional benefits of recovering nutrients during the anaerobic digestion of the organics by fixing N and P as well.
The major goal of the this project was the investigation of the applicability of struvite precipitation technique (SPT) separately or coupled with in an anaerobic digester for recovering nutrients from the anaerobic digestion process (ADP) residues. Optimising SPT will not only improve the performance of ADP which is the most commonly used process for disposing many agro-industrial wastes, in terms of reduced the nutrient (nitrogen and phosphorus) loads discharged to natural aquatic environments, but also lead production of a value-added product in the form of struvite fertilizer.
The main results can be summarized as follows:
- Antagonistic interactions were found when mixtures of poultry manure and sewage sludge were digested with high F/M and high initial COD concentrations.
- The influence of excess Mg in the removal of NH4-N and PO4-P was significant; however, it was obvious that PO4-P concentration controls NH4-N removal by struvite formation.
- Unlike to the magnesium source the effect of phosphorus source on the removals of NH4-N and PO4-P removals is not considerable.
- Feeding the anaerobic digester by sewage sludge containing Mg2+ can be an option for the removal and recovery of N and P.
- Addition of Mg2+ along with the feed every day with a concentration based on the expected daily release of N from the destruction of VS did not cause any negative effects on the performance of reactor and did not result in any changes in the number of methanosaeta and methanosarcina.
- The influence of excess Mg in the removal/recovery of NH4-N and PO4-P was significant; however, PO4-P concentration controls NH4-N removal by struvite formation.
- The use of the acidic phosphorus dissolution process was applicable to the solid phase of the AD effluent and can be used as a preliminary step of SP experiments to obtain a nutrient rich solution.
- External addition of Mg and P led to more than 90.0 % recoveries of both NH4-N and PO4-P from the phosphorus-enriched solution.
- The precipitation processes are predicted in a broad extent, yet the predictions depend entirely on the database.
Based on these results it can be stated that the struvite precipitation is a viable option for the recovery of the nutrients in the anaerobically digested poultry manure and wastewater treatment sludge if both liquid and solid phases of the effluent are utilized. By exploiting this innovative approach, the potential socio-economic impact would be meeting a substancial fertilizer demand of a country (one-fourth of Turkey's domestic demand) while managing these wastes in sustainable way. The results of this project could be relevant to all stakeholders related to both environmental as well as agricultural fields.
Contact Details: Dr. Göksel N. Demirer, Middle East Technical University, Department of Environmental Engineering, Inönü Bulvari, 06800 Ankara-TURKEY, Phone: +90-312-210 58 67 Fax: +90-312-210 26 46, E.mail: goksel@metu.edu.tr Web Page: http://www.enve.metu.edu.tr