Influence factors of phosphorus recovery from biogas fermentative liquid

Taking the biogas fermentative liquid treated by anaerobic digestion process from livestock wastewater as the research object, the effects of organic compounds, suspended solid (SS), carbonate, and initial phosphate loads on the phosphorus recovery were investigated in different pH conditions by using two treatment methods: Batch-Influent and Continuous-Influent, using sodium hydroxide solution to lifting pH values in the Batch-Influent, while using aeration stripping from the bottom to lifting pH values in the Continuous-Influent. The results showed that the pH must be controlled higher than 8.5 to reduce the influence of organic compounds in Continuous-Influent. When pH value were higher than 8.0 and the concentration of SS were higher than 400 mg/L, the recovery rate of phosphorus Vp(t) decreased with the rise of concentration of SS while when pH value was 8.5 or 9.0, Vp(t) decreased to some extent; On the other hand, when pH value was 9.5, Vp(t) kept invariant about 73%. When the concentration of carbonate reached 2 mmol/L and pH value was 9.0, Vp(t) decreased by 11% yet, Vp(t) decreased by 7.8% when the concentration of carbonate reached 2mmol/L and pH value was 9.5. There was a little influence when pH value was 8.5. Vp(t) of the fermentative liquid whose initial phosphate loads were 50 mg/L were highest at any pH conditions or after 8 hours aerated. Compared with Batch-Influent, the influence of the four factors on the phosphorus recovery was less than Continuous-Influent.