Physical–anaerobic–chemical process for treatment of dairy cattle manure

An overall treatment process for the removal of nitrogen, methane production and obtention of valuable fertilizers from dairy manure has been investigated in laboratory scale. Solid and liquid fractions were separated by flocculation and screening. The solid fraction contained 81.6%, 84.4%, 58.6% and 85.2% of TS, VS, TKN–N and PT originally present in manure. Batch anaerobic digestion of this solid fraction at 50 °C resulted in methane production of 29.0 L CH4/kg. The liquid fraction, free of suspended solids, was satisfactorily treated at 35 °C in an upflow anaerobic sludge blanket reactor operating stably at an organic loading rate of 40.8 g COD/(L·d) reaching a methane production of 10.3 L CH4/(L·d). Accumulation of volatile fatty acids did not occur. Ammonia nitrogen concentration in the anaerobic effluent fluctuated between 850–1170 mg NH 4 + –N/L and was reduced to values less than 100 mg NH 4 + –N/L by struvite precipitation.