Enhanced Phosphate Release from Anaerobically Digested Sludge Through Sulfate Reduction
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This study was conducted to demonstrate enhanced phosphate release in mesophilic anaerobic digestion of sewage sludge in relation to sulfate reduction. Sulfate was added as sulfuric acid to influent sewage sludge at the three levels, 0, 461 and 922 mg-S/L (0, 14.4 and 28.8 mmol/L, respectively). The sewage sludge used was one without artificial modification for 70 days, and then chemically pre-precipitated one artificially prepared by adding 4 g/L (17.9 mmol/L) of FePO4·4H2O for 77 days (influent total phosphorus of 302 and 855 mg/L, respectively). The anaerobic digesters were operated at 35 °C and 20 days hydraulic retention time. The phosphate concentration in digested sludge at the final stage reached 7.3, 89 and 112 mg/L for the sewage sludge without artificial modification, and 114, 258 and 461 mg/L for the chemically pre-precipitated sewage sludge, at the three levels of sulfate addition respectively. The phosphate concentration was almost proportional to the sulfate concentration added, indicating that the introduction of sulfate to anaerobic digestion can enhance phosphate release. The enhanced phosphate release was attributable to sulfate reduction to sulfide and subsequent release of phosphate from ferric or ferrous phosphate. In addition to the above mechanism involving sulfate reduction, phosphate release was estimated to occur from ferric phosphate along with iron reduction. A possible disadvantage of involving sulfate reduction is that part of the methane is lost due to the consumption of methane precursors.
KeywordsAnaerobic digestion Chemically precipitated sludge Phosphate release Sewage sludge Sulfate reduction
Part of this research was supported by the Open Research Center Project for Private Universities, Ministry of Education, Culture, Sports, Science and Technology, Japan. The author also appreciates Mr. Y. Tanaka of Hokukon Co., Ltd., Fukui, Japan, for his assistance.
- 2.Morse, G.K., Lester, J.N., Perry, R.: The economic and environmental impact of phosphorus removal from wastewater in the European community. Centre Europeen D’Etudes des Polyphosphates E. V. Selper Publications, London (1993)Google Scholar
- 3.Ministry of Land, Infrastructure, Transport and Tourism: Handbook of phosphorus recovery in sewerage systems (2010). (in Japanese)Google Scholar
- 7.Gao, M., Qiu, L., Xie, K., Zhang, S., Wang, J.: Phosphorus recovery from excess sludge: possibility and future. 4th International Conference on Sustainable Energy and Environmental Engineering, Shenzhen, China, pp. 20–21 (2015)Google Scholar
- 12.APHA/AWWA/WEF: Standard methods for the examination of water and wastewater, 20th edn. APHA/AWWA/WEF, Washington DC (1998)Google Scholar
- 15.Komatsu, K., Yasui, H., Li, Y.-Y., Noike, T.: Modeling of dissolution/precipitation of inorganic compounds in anaerobic digestion of municipal sludge. Environ. Eng. Res. 45, 341–348 (2008). (in Japanese)Google Scholar
- 17.Ripl, W., Stammert, B., Wisemann, U., Karimnia, M.: Ruckgewinnung von Phosphor und Fallungsmitten (Eisen) aus Nachfallschlamm. Von Wasser. 70, 179–185 (1988)Google Scholar