Study On Performance Of Advanced Treatment Of Secondary Effluent From Municipal Wastewater Plant By Combined Velocity-changed Biofilter

This dissertation carries out a full-scale experiment treating effluent for reclamation and reuse from a municipal wastewater treatment plant by combined velocity-changed biofilter (CVBF), which design patent belong to faculty of urban construction and environmental engineering Chongqing university. The capacity of filtering bed can be sufficiently utilized because the CVBF filtering rate is variable. The filter was divided into inside part and outside part. The former used a new type enzyme-catalyzed granular media in bed, which patented by faculty of urban construction and environmental engineering Chongqing university, and the latter adopted composite media. Study was made on the performance of CVBF in aerobic condition through aerating the outside part of the filter. When it is aerated, the filter simultaneously have characteristices of both submerged biofilter and biological aerated filter(BAF). A new type wastewater advanced treatment process has been achieved through the experiment. The experiment was made on two stages. Firstly, the CVBF was carried on different hydraulic loading in anoxic condition. Secondly the filter was aerated and tested in cross situation with three air flow rate (air/water at 1:1,3:1 and 5:1) and three hydraulic loading (influent flow rate was 100m³/d, 150m³/d and 200m³/d respectively). The optimal running parameters of the CVBF were defined and recommended according to the tested data. The conclusion is showed as follow: (1) In anoxic condition, CODcr and turbidity removal percentage are decline with hydraulic loading rising, but that of NH₃-N is reverse. When influent flow rate was 100m³/d, 150m³/d and 200m³/d respectively, COD_cr removal average percentage were 30.41%, 22.12% and 15.33% respectively; those of NH₃-N were 24.58%, 35.50% and 46.29%; and that about TP and turbidity were 17.37%, 10.54%, 4.41% and 56.99%, 60.40%, 46.34% respectively. (2) In aerated condition COD_cr removal percentage descended along with air/water (a/w) rate ascending when hydraulic loading is invariable; and the same along with hydraulic loading rising when a/w rate is invariable. When a/w rate mount up from 1:1 to 5:1 at flow rate 100m³/d, COD_cr removal average percentage were 46.36%, 32.27% and 24.99%; those at flow rate 150m³/d and at flow rate 200m³/d were 37.43%, 29.17%, 26.40% and 29.86%, 20.90% respectively. (3) In aerated condition NH3-N removal average percentage descended along with air/water rate ascending when hydraulic loading is invariable. When influent flow rate mount up from100m3/d to 200m3/d at a/w rate 1:1, NH3-N removal average percentage were 54.00%, 44.21% and 51.27%; those at a/w rate 3:1 and at a/w rate 5:1 were 50.23%, 30.14%, 32.96% and 31.60%, 32.49% respectively. (4) The effluent turbidity of CVBF rised along with air/water rate ascending when hydraulic loading is invariable; at the same time turbidity removal percentage was decline. In the four conditions tested, turbidity removal average percentage were 73.39%, 74.14%, 70.53% and 63.13% respectively. (5) TP removal main result from microorganism assimilation and aggradation of particle containing phosphorus. In aerobic condition, TP average removal were 17.35%, 12.49% and 4.99% respectively at three different hydraulic loading when a/w rate was 1:1. Those at a/w rate 3:1 and 5:1 were 15.50%, 10.73%, 7.84% and 15.97%, 6.83% respectively. (6) In aerated condition, the optimal running parameters of the filter were flow rate 200m3/d and a/w 1:1. Under the condition above, biofilter effluent CODcr average was 12.63 mg/L; those of NH3-N and turbidity were 0.78 mg/L and 1.19 NTU respectively. CODcr average removal percentage was 29.86%, those of NH3-N and turbidity were 51.27%and 63.13% respectively .The quality of effluent can meet the Urban Miscellaneous Water standard (GB/T18920-2002).