An upflow microaerobic sludge reactor (UMSR) has previously been constructed to treat manure-free piggery wastewater with high NH4+-N and low COD/TN ratio

and illustrated a well synchronous removal of COD

NH4+-N and TN at 23℃ with a hydraulic retention time (HRT) 8.0 h and an effluent reflux ratio 45:1. To decrease the cost of wastewater treatment

effect of lower temperature on the performance of the UMSR was investigated in the present study. With the same HRT and effluent reflux ratio

the temperature in the UMSR was decreased from 20℃ to 17℃ and then to 15℃ stage by stage. The results showed that the drop of temperature had no observable effect on COD removal in the UMSR

which remained above 60% throughout the operation. However

the lower temperature showed a remarkable effect on nitrogen removal. When the USBR got steady in performance at 20℃

the NH4+-N and TN removal reached 98.9% and 79.8%

respectively. Since the temperature dropped to 15℃

NH4+-N and TN removal in the USBR was decreased to 61.8% and 39.7%

respectively. At 17℃

the COD

NH4+-N and TN removal averaged 62.4%

80.7% and 71.2%. The effluent COD

NH4+-N and TN of 71

55.5 and 80.7 mg·L-1

respectively

well met the Discharge Standard of Pollutants for Livestock and Poultry Breeding (GB 18596—2001). It was found that complete nitrification-denitrification

shortcut nitrification-denitrification and anaerobic ammonium oxidation (ANAMMOX) coexisted in the UMSR. Among the denitrification processes

ANAMMOX was the most important approach for NH4+-N and TN removal

and had not been changed by the dropped temperature.