Study On Mid-positioned Biological Aerated Filter For Treating Micro-polluted Source Water

BAF+conventional treatment process has a good effect in treating micro-pollutedraw water, and it has been applied broadly in water treatment technology. Insubtropical area, abundant aquatic organisms come into the BAF with raw water whenthe process operated, these organisms can attach to filter heads which lead to cloggedwater distribution system gradually, at last, all the filter heads need to be offeredregular cleaning or replacement; In addition, plenty of suspended solids are broughtinto the filter and cover on the surface of haydite in flood period, this not only affectsefficiency of mass transfer, but also leads to much more filter head loss, which needmore water and gas to wash, furthermore, frequently wash cause nitrifying bacteriaoutflow, which reduce the ability of the bio-oxidation degradation. My experiment isto use coagulation and sedimentation process remove most of the suspendedimpurities and other substances of raw water before entering the BAF, it’s calledmid-positioned BAF process, with using floating haydite, which can reduce theturbidity interception. The experiment is to study the optimization of mid-positionedBAF process operating parameters, comparatively analyze the effects ofmid-positioned BAF process and BAF+conventional treatment process in flood periodin order to direct production.Test results indicate:Precipitate of effluent and floating haydite characteristic make it’s hard formid-positioned BAF to form film naturally, ammonia removal rate is about20%whensix weeks passed; Inoculation method is useful, The entire startup process takes17days when the average water temperature is16.7℃.Biological filter can destroy of micro-flocs that affect sand filtration process, avice coagulant dosing point is added for micro flocculation in this process, theposition of vice one is between mid-positioned BAF and sand filter. In the event of18.9NTU average turbidity in raw water, the main point coagulant dosage16mg/L,vice point2mg/L, the final effluent turbidity reaches0.47NTU. Turbidity removal rateis97.52%, compared to conventional coagulant dosing method, coagulant is used10%less more by this way. During the contrast test period, in mid-positioned BAF process, with0.4gas-water ratio, all the ammonia, nitrite nitrogen, CODMnand turbidity in finaleffluent can meet drinking water standards; in BAF+conventional treatment process,with0.5gas-water ratio, the ammonia>0.5mg/L, nitrite nitrogen>0.1mg/L in somehigh turbidity period.In mid-positioned BAF process, it’s backwash cycle can be maintained at about7days; In BAF+conventional treatment process, if raw water turbidity is more than90NTU, it’s backwash cycle is two days, when the raw water turbidity is less than90NTU, it’s backwash cycle is three days; when it works, mid-positioned BAFprocess saves60%~80%energy compared BAF+conventional treatment process inunit time.