[Study on the quality of digested piggery wastewater in large-scale farms in Jiaxing]

Pollution characteristics of digested piggery wastewater (DPW), including not only the chemical oxygen demand (COD), nitrogen and phosphorus but also the veterinary antibiotics and heavy metals, were investigated in ten large-scale pig farms in Jiaxing City. Results showed that the water quality of DPW greatly varied with farms and seasons. DPW in the spring group showed the highest pollutant concentration, with seven of the ten pig farms demonstrating COD of over 2 000 mg x L(-1), total nitrogen and ammonia nitrogen of over 1 000 mg x L(-1) and total phosphorus of over 60 mg x L(-1). Pollutant concentrations of DPW were lower in the autumn and winter groups, while the lowest was observed in the summer group. Unbalanced nutrient was observed in DPW, the carbon nitrogen ratio showed the lowest value of 0.8-4.3 in the autumn group. Four classes (tetracyclines, quinolones, macrolides and sulfonamides) of ten antibiotics and six heavy metals (Cu, Zn, Pb, Cd, Ni and Cr) were detectable in DPW from all the ten farms. Cu and Zn were the top two dominant heavy metals, with an average concentration of 1.88 mg x L(-1) and 7.63 mg L(-1), respectively. Tetracyclines (including Tetracycline, Oxytetracycline and Chlortetracycline) were always the dominant antibiotics. The total concentration of the ten antibiotics was in the range of 10.1 microg x L(-1) to 1090 microg x L(-1), far exceeding the antibiotics limit of 10 ng x L(-1) in the water environment specified by EU. Efficient but low cost treatment technologies are in urgent need in order to deal with the pollution by DPW, a wastewater that is not only difficult to remove nitrogen and phosphorus, but also seriously polluted by heavy metals and antibiotics.