Application of struvite precipitation coupled with biological treatment to slaughterhouse wastewaters

In this study, struvite precipitation coupled with an activated sludge process was applied to slaughterhouse wastewaters. Biological treatability characteristics of the wastewater were evaluated in a wide organic loading range of 0.06-0.42 g COD (g MLVSS)(-1)d(-1) to assess COD removal as well as the extent of nitrification. Results of biological treatment of raw wastewater indicated that COD removal varied between 88% and 99% and complete nitrification was achieved at 0.1 g COD (g MLVSS)(-1)d(-1) and lower organic loadings. Biological treatment of the struvite-precipitated sample, which required no nitrification, yielded 86% COD removal at the organic removal of 0.3 g COD (g MLVSS)(-1)d(-1). Struvite precipitation of both raw and biologically treated wastewater was at effective stoichiometric magnesium and phosphate doses to ammonia and between pH values of 9.0 and 9.5, providing ammonia concentrations of 20-30 mg N L(-1) in the effluent and being independent of initial concentrations. The application of struvite precipitation both prior to and after biological treatment resulted in similar effluent qualities and provided the additional benefit of having a high-rate activated sludge system instead of a low organic loading system with nitrification-denitrification. An additional benefit of struvite precipitation was the production of sludge which had recovery potential as a fertilizer. Among the tested treatment schemes, biological treatment following struvite precipitation seemed to be more advantageous in terms of process stability.