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Pollution Characteristics and Ecological Risk Assessment-Based on the wastewater quality investigation data from March 2009 to November 2014,the wastewater qualities from typical intensive pig farms were assessed in the Pearl River Delta by single and comprehensive pollution index model.The results showed that the key pollutants of the piggery biogas slurry (anaerobic digested wastewater) were fecal coliform (FC),total phosphorus (TP),ammonia nitrogen (NH3-N) and suspended substance (SS),with their average mass concentrations of 8.10 × 106L-1,81.76 mg· L-1,476.24 mg·L-1 and 464.58 mg.L-1 respectively,the comprehensive pollution indices were 5.27.In the long run,the direct discharge or irrigation of the biogas slurry could degrade fresh water and impose great risk to the ecosystem,and it is necessary to decontaminate them further.Purification Treatment with Microorganism Preparation-Compound Microorganism Preparation (CMP),Fermentation Microorganism Preparation (FMP) and Photosynthetic Microorganism Preparation (PMP) were used to remove BOD5,CODcr,NH3-N,TP,FC,and Total Salt (TS) from biogas slurry,and the effects were compared.The results showed that the maximal removal rates of BOD5,TP,FC were up to 61.5%,83.0%,99.0%,and those of CODcr,NH3-N,TS were up to 54.9%,48.4%and 31.8%.In conclusion,the removal rate of PMP was more effectively than CMP and FMP.Purification Treatment with Combined Microorganism Preparation-Ten Combined Microorganism Preparations were used to remove BOD5、NH3-N、TP、FC from biogas slurry,and the effects were compared.The results showed that the maximal removal rates of BOD5、NH3-N、TP、FC were up to 99.3%,98.7%,64.0%,99.9%.In conclusion,the removal rate of CMP3,CMP4 and CMP5 were more effectively than other MP.Optimization of Process Combination on Purification Treatment-Twelve process combinations were used to remove BOD5、NH3-N、TP、FC from biogas slurry,and their performances were compared.The results showed that the maximal removal rates of BOD5、TP、FC were up to 90.0%,82.0%,99.9%.The experiment verified the removal rate of PC1,4,6 was more effective than other process combinations.The present study could be used as an insight guide for further design and operation of full-scale wastewater treatment systems.