Phosphorus Removal From Swine Wastewater Through Anaerobic Digestion

A sequencing batch semi-continuous anaerobic digestion experiment was carried out to study effect of anaerobic digestion on phosphorus removal from swine wastewater.Results show that the phosphorus removal rate of an anaerobic digester with hydraulic retention time (HRT) being 1,3,6 and 9 d was 65.0%,81.1%,82.7%,and 83.0%,respectively,and its COD removal rate was 54.5%,82.3%,87.0% and 85.9%,respectively.The phosphorus removing capacity of the digester increased with the increasing of its biogas yield,which suggests that phosphorus removal is closely related to methane production in the digester.Extractions of the sludge before and after anaerobic digestion revealed that precipitation of phosphate formed through chemical reaction during the process of anaerobic digestion played a critical role in removal of phosphorus.Orthophosphate,iron-bound P,reductant soluble P,calcium-bound P and mangesium-bound P,inorganic or organic polymer phosphorus increased by 0.0278-0.1015,0.0135-0.0810,0.2165-0.4305,23.4-54.8 and 7.2-21.5 mg·g^-1,respectively.Generally speaking,the longer the HRT,the greater the increment of phosphorus bound with various metals in the sludge.Taking into comprehensive consideration of HRT,efficiency of phosphorus and organic compounds removal,and biogas production rate,it is advisable to retain swine wastewater in the digester for 3 days.