Design Parameters Optimization Of Rapid Sand Filter Under The Condition Of Influent With Low-turbidity

《Standards for Drinking Water Quality》(GB5749-2006) which took effectcompletely on1st July2012means finished water turbidity being lower than1NTU.So the turbidity of water from the sedimentation tank in water purification plantneed to be controlled at a low range, and particles reduce too.The operation anddesign of the filter are different from previous experience in this low turbidity waterconditions. If we still design filter basing on past experience, it will go against theinitial cost and energy consumption during operation. In this context, to improve theeffectiveness of filter operation, this thesis focused on the optimum design of thefilter with reducing the investment of the filter construction.Investigation results concerning operational behavior of35domestic waterworks show that V-filter is generally used. In most of water plant, the turbidity ofwater from the sedimentation tank is below2NTU even1NTU, while filter effluentis usually below0.5NTU. Uniform quartz sand media is one of the main media inpresent filtration technology application. On the one hand，the potential to improvefiltration rate and extend the filtration cycle is higher than single sand filter. On theother hand, it have advantages of the initial investment and management overmulti-media filter.In this paper，the method of comparative experiments was used to investigateeffect of filtration rate on the filtration performance through filtration column fillinguniform quartz sand which effective diameter d10is0.97mm. Results show that thefiltration rate varied from8-12m/h affects the turbidity and particles of effluentslightly under the conditions of influent turbidity being about0.8NTU. But as thefiltration rate increases, influent particles quickly penetrate the filter surface. Forlow values of both the filtration velocity and media size, the proposed parametersuggests that filters can be designed for lesser depth than the current standard.However, for any constant media size, the proposed design standard suggests thatthe depth should increase more than linearly with increases in the filtration velocity, in contrast to the current standard. Considering technical and economic analysis, itis more reasonable to control the filtration rate at8-10m/h when L/d10=1100.By mathematical analysis method combined with the data of filter productiontest, mathematical equations were derived between the effluent turbidity and headloss. Then turbidity of filter influent and effluent from2004to2012has beeninvestigated to analyse maximum head loss of the filter, as well as the full-year finalpre-backwash headloss value. So in the low turbidity water conditions, themaximum head loss should be lower to reduce the depth, rather than the originalstandard2.0-2.5m.