Forty-three biogas slurries from household biogas plants using different substrates were collected from different parts of China. The contents of chemical oxygen demand (COD)

ammonium nitrogen (NH4+-N)

phosphate (PO43-) and heavy metals were determined. The concentrations of COD in cow dung and straw as raw materials were higher than other treatments

reaching 6800 mg·L-1 and 5800 mg·L-1 respectively. The concentrations of NH4+-N in pig manure and mix manure were higher than other treatments

reaching more than 1800 mg·L-1. The concentration of NH4+-N in cow dung was significantly lower than that in other materials

with the average being 450 mg·L-1. Therefore

COD/ NH4+ ratio of 15 in the slurry with cow dung as raw material was significantly higher than those in other three materials (less than 5). The average PO43- concentrations of all raw biogas were lower than 80 mg·L-1. Mercury pollution was serious and universal in different materials and different provinces. Environment risk evaluation showed that the pollution in biogas slurries from Yunnan

Henan and Hubei was medium and could not be ignored.