Sludge handling and dewatering results in an additional load on biological wastewater treatment. Especially for the process of biological phosphorus removal, high phosphorus release during anaerobic sludge treatment is expected. In this study the reduction of phosphorus and nitrogen load from sludge liquor in different pilot scale tests was performed. The processes examined here are P-precipitation with salts of aluminium and iron, as well as pH-controlled precipitation with lime. For nitrogen removal this process can be extended to air stripping at high pH-values. The combined MAP (magnesia-ammonia-phosphate)-precipitation of ammonia and phosphorus was subject of the study, too. At proper applications of the different processes P and N removal could be attained.

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