The efficiency of biological aerobic treatment of piggery wastewater to control nitrogen, phosphorus, pathogen and gas emissions

Due to the water pollution and in order to reduce the nitrogen load applied on soils, biological nitrogen removal treatment of piggery wastewaters was developed in Brittany ( France), with 250-300 units running. Four types of treatment processes were built including a biological reactor allowing to remove about 60-70% of the nitrogen content as gas by nitrification/denitrification. The addition of different mechanical separators ( screw-press, centrifuge decanter.) led to concentration of phosphorus in an exportable solid phase, allowing a reduction up to 80% of the phosphorus applied locally on soils. Moreover, a reduction of the gaseous emissions was observed using this management process as compared to conventional management ( storage + land spreading) including ammonia ( up to 68%) and greenhouse gases ( 55%). Finally, the level of enteric and pathogenic bacteria was also decreased with the treatment process as compared to conventional management systems. However, in spite of these results, the significant cost of the treatment must be underlined and alternative systems including anaerobic digestion will have to be studied.