Study On Modificationof The Oxidation Ditch In Small-town Wastewater Treatment Plants

Wastewater treatment plants play an important role in pollutant reduction. Someproblems would appear during designing and constructing process. An analyze on aCarrousel oxidation ditch in one wastewater treatment plant of a small town inChongqing(hereafter calledA-WWTP) was systematicallyconducted,which pointed outthe reason why the aeration system do not work well. According to the result, measureswere proposed to improve this situation. Meanwhile, apilot plant experiment underdifferent operating conditions was conducted, providing a reference for A-WWTP andother WWTPs’ upgrades. The main conclusions are:①An analysis on the shortages of A-WWTP was conducted, and the4shortages isabout the over capacity, lacking of oxygen, improper push flow equipment, and badcontrol of internal reflux. A pilot plant experiment was conductedaccording to thesituation of A-WWTP, which wasimproved in the following points:Combine anoxictankand anaerobic tank as anoxictank; Apply fine pore diffusers; Add push flow equipment;Use pump to control internal reflux in the oxidation tank.②According to the pilot plant experiment,optimum operation was confirmed. Theinfluent rate could better be10m3/d. Theaerationrate could better be2m3/h~3m3/h. Thereflux ratio could better be200%. Sludgerefluxratio could better be50%~80%. Underthis optimum operation, the effluent quality can meet the required standard, and theremoval rate of SS, COD, NH3-N, TP can be96.5%、93.1%、98.9%、47.7%、92.6%.③An analysis on the treatment effect of differentaerationcondition was conductedwhen influent rate is10m3/d, aerationrate is2.5m3/h~2.7m3/h, reflux ratio is200%, andsludgerefluxratio is50%~80%. The result showed that it can efficiently remove nitrogenwhen properly reducing aeration zone and properly reducing the pushing speed. Afterthat, a method was taken to valuate the treating efficiency of each condition through thecomparison of amount of removal pollutants, which pointed that the aeration patternthree can meet the required standard and also be high-efficient.④According to the pilot plant experiment, when depth of water is between4.0and6.0m, it is feasible to use fine pore diffusers as aeration system. Modification schemeand proposals of operation were proposed for A-WWTP.