Technical Reform Primary Research Of Enhancinng Vorttex-type Grit Chamber Desanding

Because of urban construction and special landform, sand content of municipalwastewater is higher in mountain city that bring operation problems to sewage treatmentplant, such as the equipment is heavily damaged, the mixture MLVSS/MLSS reducesunconventionally, sand sediment in biochemical pool. At the same time, due to the lowBOD5content in wastewater, primary setting tank has been canceled in order to meetthe demand for carbon source in the process of N and P removal in most sewagetreatment plants. More sand goes into the body unit of sewage treatment plants thatthose problems become more seriously. This paper analyzes operation problems basedon investigation of performance of vortex-type grit chamber in typical sewage treatmentplants in the three gorges reservoir area. On the basis of relevant theoretical research,technical transform measures of enhancing desanding are proposed and applicated in asewage treatment plant in Chongqing. This paper studies the change of removal sandamount, the intercept effect of CODcr, suspended solids removal performance and theinfluenc on body unit of sewage treatment plant and preliminarily discusses thedesanding principle after technical renovation. The main conclusions include:①The wastewater sand content of sewage treatment plant in the three gorgesreservoir area is generally higher, actual sand removal amount is only50%oftheoretical sand removal amount of most vortex-type grit chamber and especially theremoval efficiency of fine sand is not favorable. The sand tube nozzle of gas strippingsystem is blocked easily. The air source-roots bloweris is worn badly. MLVSS/MLSS ofactivated sludge in biochemical pool is between0.27-0.57, which is far lower thannomal and numerous sand sediments on the bottom of biochemical pool.②Technical renovation measures for vortex-type grit chamber include:dismantlingaxial flow propeller, cover plate setted on the top of sand bucket, axial flow screw drivesystem on the top of pool and related pipeline; adding precipitation inclined plate at thebottom of points selection and at the circula edge of center sand bucket, adding chokeplate beside outlet; Vortex driving force is formed by reclaimed water jet system whichreplaces the original mixer.adjusting platform slope of points selection to12.5±2.5°;setting blow-down system at the bottom; using residual gas from aeration blower as gassource for putting sand; increasing the distance between sand tube head and thebottomof grit chamber; adding bell at the mouth of sand tube head; changing type of gas distribution holes from multipoint to central centralization.③The removal sand amount of grit chamber increased largely after technicalrenovation, inflow SS volume mean diameter decreases after treated by grit chamer andthe removal efficiencies of coarse and fine particulate matter increases properly. TheCODcr intercept rate is low, only3%-30%CODcr in inflow is removed, which isbeneficial to nitrogen and phosphorus removal. The grit chamber has a certainresistance to flow load and concentration load after technical renovation. After60days,the MLVSS/MLSS of activated sludge in aerobic pool increases from0.30to0.47.