Equipment Development And Research In An Airlift-reflux Combined Reactor

Nowdays,although more decentralized wastewater treatment processes have been applied in many areas,there were also many shortcomings such as larger area,complex equipment and so on.This thesis aimed at shortcomings above-mentioned,an airlifting-reflux combined reactor was developed mainly for treating decentralized wastewater in order to obtain optimum operating conditions,design parameters, meet the discharge standard and application of practical engineering.In this thesis , the reactor devices with 95L total effective volume,11.2h HRT, 200L/d handling capacity was carried out to conduct preliminary study.Major objectives were pollutant removal efficiency,reflux ratio,the volume ratio of reaction zones,sludge reduction and so on.The main results were presented as follows:(1) when reflux ratio was1.2,COD-sludge load was 0.27kgCOD/(kgMLSS·d)sludge in the aerobic zone was not return to the anoxic zone,only effluent after precipitation was returned,the average temperature was 13.9℃.The average effluent COD,ammonia and nitrate concentrations were 52mg/,2.5mg/L and 17.2mg/L respectively , average removal rates were 86.4% , 89.8% and23.7% respectively.Effluent turbidity was gradually increased to 22.8NTU from 5.3 NTU.(2) When reflux ratio increased to about 3,the sludge in settling zone was smoothly returned to the anoxic zone.water temperature was stable.The average effluent COD,NH3-N and TN concentrations were rfrom 49mg/L,2.5mg/L and 19.0mg/L reduced to 42mg/L,1.1mg/L and 5.0mg/L respectively,the average removal rate were from 88.2%,90.3%,and 24.9% increased to 89.5%,96.3% and 83.7% respectively.When the temperature dropped to 4.5℃,NH3-N and TN removal efficiency decreased obviously,but COD removal efficiency were less affected.(3) When COD-sludge load was about 0.30 kgCOD/(kgMLSS·d),air to water ratio was 30:1,the aerobic sludge settling performance was good,SVI value was about 110.Effluent COD, NH3-N and TN concentrations were 33.3mg/L,1.8mg/L and 5.9mg/L respectively, the average removal rates were 92.5%, 95.5% and 83.7% respectively,and the Effluent concentration was met to GB18918-2002 grade A standards. The average effluent turbidity was 3.4NTU.When COD-sludge load increased to above 0.49 kgCOD/(kgMLSS·d),the phenomenon of sludge bulking occurred,SVI value was increased to 363 from 68.Sludge concentration in settling zone was very low and some sludge was washed out.The result showed that COD-sludge load of 0.30 kgCOD/(kgMLSS·d) was conducive to the stable performance of the system.