Study On Treating Normal And Micro-pollutants In Secondary Effluent With Combined Process Of Biological Sand Filter

When the secondary effluent after advanced treatment reuse to landscape water, notonly can achieve the circulation of water environment, but also can solve the problem oflandscape waters. When analysing the removal effect of advanced treatment process, it isalso need to evaluate the safety of reusable water.The combined process of biological sand filter was used as advanced treatment tosecond effluent from WWTP. The combined process was “coagulationsedimentation-ozonation-biological sand filter-activate carbon adsorption”. In order todetermine the operation parames, the removal effect of the turbidity, COD_Mn, UV₂₅₄,chromaticity was be analyzed in different ozone concentration and different hydraulicload. It also contrasts purifying ability in ordinary sand filter and biological sand filter.After the process operating a period of days, this experiment tests the heavy metal （Hg,Cd, Pb, Ni, etc）, endocrine （PAEs）, organic chlorinated pesticide（γ-HCH）. After that, itcan know the removal rate of each unit of the process and the health risk value ofmicro-pollutants.The results of the experiment show that removal effect of biological sand filter wasbetter then original sand filter. When the dosage of ozone was3mg/L and the hydraulicload of biological sand filter was6m³/m²·h and the hydraulic load of GAC was5m³/m²·h, the removal efficiency was best. With the best operation parameters, theaverage removal rate of turbidity and color and UV₂₅₄and COD_Mnin second effluent bythe combined process was89.4%,80.33%,67.43%,56%. The average data of thecombined process of the above was0.57NTU,5.5units,0.05and5.68mg/L. The averageremoval rate of heavy metal Hg and Cd and Pb and Ni by the combined process was82.71%,87.76%,62.72%,49.36%, the average concentration of effluent was0.64μg/L,0.0091μg/L,0.0815mg/L,0.004mg/L. To DBP and DiOP and γ-HCH, the averageremoval rate was85.10%,68.81%,72.40%, the average concentration was0.089mg/L,0.091mg/L,0.00182mg/L. The effluent quality meets the request of aestheticenvironment use in “The reuse urban recycling water-Water quality standard for scenicenvironment use”（GB/T18921-2002）.Integrated risk information system （IRIS） of the USEPA data points out that heavymetal Cd is carcinogenicity, Hg and Pb and DBP and DiOP are non-carcinogenicityt.Through calculating the life risk by the health risk evaluation model, the risk value ofCd and Hg and Pb and DBP and DiOP was between1.25×10^-10/a～1.29×10^-10/a, 4.81×10^-12/a～5.63×10^-12/a,1.29×10^-10/a～1.44×10^-10/a,1.99×10^-12～2.15×10^-12/a,1.02×10^-11～1.11×10^-11/a. It is far less than the largest acceptable of thenon-carcinogenic chemical risk level1×10^-6/a that the USEPA and the WHOdetermined and the non-carcinogenic chemical risk level5.0×10^-5/a that ICRPrecommended. Conclude from this: the combined process “coagulationsedimentation-ozonation-biological sand filter-activate carbon adsorption” as advancedtreatment is feasible.