Treatment Of Municipal Wasterwater By Combined Process Of UASB And MBBR

Synthetic wastewater and municipal wastewater was treated by combined process of UASB+MBBR.The removal efficiency of soluble COD in UASB,the treatment effect of municipal wastewater by combined process,the contribution of pollutant removal in anaerobic and aerobic stage,and the advantage of combined process in sludge reduction were discussed.The main conclusions were gained as follows:(1)At the temperature of 20℃,mesophilic anaerobic sludge with low activity was used as inoculated sludge of UASB reactor,and the influent was synthetically soluble organic wastewater.The COD removal efficiency was at 30%to 50%,while the reaction was mainly hydrolysis acidification.(2)Under ambient temperature,with UASB as the pretreatment unit,MBBR as the following processing unit,the average removal efficiency of TCOD and SS respectively reached to 77.8%and 92.5%under the condition of HRT in UASB and MBBR was 7.7 hours and 10.3 hours respectively.The average TCOD and SS concentration of effluent was 75.7mg/L and 17.3mg/L respectively,which reached to the second-level discharge standard of "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant" (GB18918-2002).The sludge in the sedimentation tank returned to UASB to be concentrated and stabilized.The observed yield of sludge was 0.32kgVSS/kgCOD in this system which made the excess sludge reduction reached to 20%～40%compared with the activated sludge process.(3)In the experiment of treating municipal wastewater,the removal efficiency of TCOD and SS respectively reached to 56.1%and 77.3%in UASB reactor,which accounted for 70%and 81.9%of the removal efficiency of TCOD and SS in the combined process.The maximum specific methanogenic activity was 0.10,0.03 and 0.07gCOD-CH₄/gVSS·d of the sludge in the reactor used acetate,propionate and butyrate as substrate respectively at the temperature of 30℃.(4)In the experiment of treating municipal wastewater,when the dissolved oxygen in MBBR was 3.5mg/L,the effluent concentration of NH₄⁺-N was below ling/L,the removal efficiency of NH₄⁺-N was 97.7%,and the removal efficiency of TN was 22.9%which accounted for 70.8%of the removal efficiency of TN in the combined process.The maximum specific nitrification velocity in MBBR was 14mgNH₄⁺-N/gVSS·h at the temperature of 20℃.When the dissolved oxygen in MBBR was 2.0mg/L,the removal efficiency of TN was 29.9%.The degree of simultaneous nitrification and denitrification improved a little when the dissolved oxygen decreased.However,the shortage of carbon source became to the restrict factor because of the influent TCOD/TN ratio was only 2 to 3.