Research Of Anaerobic Phosphorus Removal Technics Of Piggery Wastewater

Piggery wastewater contains a lot of nitrogen and phosphorus. Nitrogen in water can be reinforced from air, so the restriction of water body eutrophication is mainly phosphorus. Thus, it is more significant to remove phosphorus from piggery wastewater. Anaerobic phosphate removal based on the biological reduction of phosphate to phosphine can be used to develop a new biotechnology of phosphate removal. Batch and continuous experiments were carried out to observe phosphorus removal from piggery wastewater in the process of anaerobic digestion. The reason for phosphorus removal and the influence factors were researched. The main achievements were as follows:(1) The results of batch experiments indicated that after 6-9 days anaerobic digestion, the total phosphorus removal rate of mixed liquor and anaerobic supernatant were respectively 38.1 % and 91.4% .(2) Mixed liquor and that was out of biologic activity were used to anaerobic digestion experiments, the results indicated that a part of phosphate was removed by transforming into gaseous phosphate. In the same time, the contribution of phosphate removed by physical and chemic ways were also significant. The contribution proportion of biologic, physical and chemic effects were respectively 35.7% . 46.0% and 18.3%. Because of the metabolization of microb, the environment was changed and some resolvable phosphate in wastewater aggraded chemically. That is biology has the accessorial function of inducing chemic depositing.(3) NaOH solution was used to absorb phosphine in biogas. There was 0.0860 — 0.436 mg total phosphorus (TP) was detected in the absorption solution, and the TP in mixed liqor was reducted 96.7~ 136 mg. The TP in absorption solution was only 0.889~3.21‰ that of reducted TP in mixed liquor. Thus, there may be some other gaseous phosphate existing in biogas.(4) The effect of phosphorus removal from wastewater under initial pH 5-9 was investigated. The results proved that, after 6 days' anaerobic digestion, the phosphorus removal rate of anaerobic supernatant under initial pH 7-9 was much higher than that of initial pH 5.(5) The effct of different sludge charge to phosphorus removal was investigated. The results indicated that while the sludge charge was in the range of 15.4 — 92.5 mg TP/g MLSS ? d, the TP removal rate of anaerobic supernatant may achieve to 87%.(6) The effct of different COD/TP ratio to phosphorus removal was investigated. The results indicated that while the COD/TP ratio was in the range of 20 to 40. the phosphate removal rate was relatively high.(7) The continuous experiments ran for 42 days. The results proved that the phosphorus and organic matter removal rates and biogas yield showed consistency. The TP and COD removal rate of HRT 3, HRT 6 and HRT 9 were above 80%. And for HRT 1, the TP removal rate was only 60%, COD removal rate was around 50%. The removal rates were so low ascribed to the high COD charge, and to the anaerobic system under acidification phase.