Study On The Influencing Factors Of Determining The Water Depth Of Aeration Tank

In the engineering design of sewage treatment plant (or wastewater treatment station),Engineers usually select a aeration tank depth based on their experience. Influence relatedfactors are less considered in such considerations,so there will be some deviation in theengineering. In fact, there are many influencing factors about the aeration tank depth. Themainly4aspects in the following: effect of aeration tank’s covers area(F); effect of aerationtank’s structure cost; effect of the oxygen transfer, dynamic efficiency(Ep) and oxygenutilization rate(EA), effect of aeration equipment to the aeration tank depth.Calculating the single-seat aeration tank volume（V1） according to the method ofBOD-sludge load rate,and the water depth of aeration tank is H. We can see that the aerationtank water depth(H) and covers area(F) is in inverse proportion relationship. Aeration tankarea is a basic influence factor to depth(H)，When the sewage factory land area is large theaeration tank water depth will be shallower.And when the land area is small, the aeration tankwill be deeper..The aeration tank cost consist many aspects,in this paper, only discuss the total cost（C）including covers premium(CD) and structure of the tank body’s reinforced concrete price(Ct)of the aeration tank. For a sewage treatment plant,the single seat aeration tank’s volume(V1)and reinforced concrete price(T) are known, Aeration tank plane pool width(B) can be setaccording to needs, After analysis the conditions:V1=8000m3，T=1000yuan/m3，B=30m,Urban sewage factory land price D=80～500yuan/㎡, Calculating the total cost(C) has theminimum value and the corresponding optimum depth(H) under different land price. Thehigher the land price, the total cost of the corresponding higher,and the water depth ofaeration tank is deeper.When D≤350yuan/㎡, the optimum water’s depth is less than7.5m,sothe depth of aeration tank in these areas can be built lighter. When D≥350yuan/㎡, the landprice is more expensive, So the water depth become deeper, even more than7.5m. The transfer of oxygen in sewage, although the overall oxygen transfer coefficient(KLa)value is decreasing with the increasing water’s depth. But the saturated dissolved oxygen(CS)value is also increasing, and increaing even more, therefore the (CS-C) value is alsoincreased,so the oxygen transfer rate of R0increases with well depth increasing increaseslinearly. Increasing the aeration tank’s depth, the oxygen transfer rate will increases, and willbeneficial to utilization of oxygen,so we can design the aeration tank’s depth in the range of8.5m.The aeration tank’s Oxygen supply equipment,when the water depth is increasing, theoxygenation capacity of mechanical aeration will devices shrink.And the dynamic efficiencywill be low with the increasing water depth. The aeration tank with mechanical aeration,Designing depth should not be too large, and appropriate within5.0m. The powerefficiency(Ep), oxygen utilization rate(EA) of the blast aeration system will increases withdepth.But the pressure range of existing blower is limited. Most of the blower could work inthe water’s depth changing between0.5~20.0m.When aerate in deep water, the matchingpower of blower will increase greatly, and the running cost will be high in long term, so theaeration tank’s water depth with blast is far less than20m.It Should be under8.0m.This topic through compare and analysis the existing aeration tank’s depth and the dataaccording to the model analysis of suitable water depth obtained,then achieve the optimaldesign running water of aeration tank,and to provide reference for the engineering design ofsewage treatment plant (or wastewater treatment station). Nowdays the land resource isshortage,it can save land resources and reduce the construction cost objective.