Effect of anaerobic digestion on nitrogen removal in treatment process of piggery wastewater

Anaerobic digestion is commonly used to remove the organic matter from the piggery wastewater. Complete digestion can remove most of the organic matters, but this also lowers the mass ratio of COD to N (usually as 1-3). Based on the theory of two-step digestion, the mass ratio of COD to N is kept high (7-10) by stopping the digestion at the step of hydrolysis, which benefits the denitrification later. A sequence batch reactor was used to treat these two kinds of wastewater. And the nitrogen removal of partly digested wastewater was more efficacious than that of the complete digested wastewater because of its high influent the mass ratio of COD to N. The effect of influent the mass ratio of COD to N on nitrogen removal was studied, the results indicate that the effluent NH4⁺-N concentration decreases with the increase of the influent the mass ratio of COD to N while the ratio is less than 10.5. The nitrogen removal of the wastewater with the mass ratio of COD to N of more than 10.5 is also inefficient because of the high COD (chemical oxygen demand) loading rate.