Operation And Efficiency Of A Microaerobic System Treating Piggery Wastewater With High Ammonium And Low C/N Ratio

Manure-free piggery wastewater was characterized by high ammonium and low chemical oxygen demand to total nitrogen?C/N?ratio.The conventional technologies treating manure-free piggery wastewater are complex in processing,high in engineering investment and management cost,and poor in nitrogen removal.Based on the coexistence of aerobic and anaerobic microbiological in microaerobic condition,the novel upflow microaerobic sludge reactor?UMSR?and upflow microaerobic biofilm reactor?UMBR?had been devleloped in previous research,achieving efficiency nitrogen removal dominated by short-cut nitrification and denitrification,and anaerobic ammonium oxidation?anammox?.The microaerobic treatment process has the advantages in land saving,low cost,easy operation and management,high efficiency of nitrogen removal,but the power consumption was still a bit high.In order to further improve the efficiency of microaerobic biological treatment system and reduce treatment cost,the efficiency of UMSR under low temperature and the effect of hydraulic retention time?HRT?on the performance of UMBR were investigated.Futhermore,the efficiency of UMBR and UMSR was analyzed and compared.The quality of manure-free piggery wastewater would change along with the season or the production cycle,and its COD/TN ratio ranges from 1.0 to 3.5.The previous study showed that the influent C/N ratio had a great effect on the performance of UMSR,and the lower C/N ratio was more feasible for the synchronous removal of carbon and nitrogen in the microaerobic system.Therefore,sequencing batch reactor?SBR?was used to pretreat the raw wastewater for maintaining the constant influent C/N ratio of microaerobic system.The results showed that SBR could effectively pretreat the manurefree piggery wastewater to meet the requirement of influent C/N ratio.For treating manure-free piggery wastewater with lower COD ranging from 300 to 600 mg/L and COD/TN ratio ranging from 1.5 to 2.0,the sludge removal load of SBR should be controlled at 1.4-1.6 kgCOD/?kgMLSS·d?.For treating manure-free piggery wastewater with higher COD ranging from 700 to 1000 mg/L and COD/TN ratio ranging from 2.5 to 3.5,the sludge removal load of SBR should be controlled at 2.0-2.3 kgCOD/?kgMLSS·d?.To reduce the treatment cost,the performance of UMSR under lower temperature was investigated.With HRT 8 h,reflux ratio 45:1 and temperature not lower than 17 ?,the effluent COD,NH₄⁺-N and TN concentration of UMSR could meet the standard required by the Ministry Environmental Protection of China.The decrease of temperature would affect the nitrogen removal,but it would not significantly change the mechanism for denitrification in UMSR.Anammox was the most important approach for NH₄⁺-N and TN removal.Periodically removing the surplus sludge was beneficial to strengthen the mass transfer efficiency of UMSR under low temperature condition,but the improper operation of sludge discharge would cause the sludge scumming,affecting the nitrogen removal efficiency of UMSR.Reducing reflux ratio and improving operating temperature contributed to the enrichment of nitrogen removal functional bacteria and avoided the sludge scumming and loss.The influence of HRT on the treatment efficiency of UMBR was investigated.The results showed that COD,NH₄⁺-N and TN removal could maintain above 83% and the concentration in effluent could meet the standard required by the Ministry Environmental Protection of China with reflux ratio 45:1,25? and HRT not lower than 8 h.It was found that the UMBR with filler could avoid the sludge loss and keep higher biomass by comparing the treatment efficiency between UMBR and UMSR.However,the denitrification efficiency in UMBR was not good.The operation control of UMBR need to be further optimized.