Research Of Pre-Treatment Integrated Equipment For Small Town Sewage

Small town sewage treatment is one of the goals of national pollution controlstrategy. The traditional construction mode of urban sewage treatment plant has lots ofdisadvantages in the treating of small town sewage, such as long treatment process, highinvestment, complex management and large construction area, due to the largefluctuations in water quantity and quality of small town sewage. Compared toconventional sewage treatment mode, sewage treatment integrated equipment canintegrate the functions of various process structures. It has simple technological processwithout the procedures like design and civil construction, etc. In addition, the integratedequipment also have other superiority as small construction area, low investment, easyto operation and management, and thus more suitable for small town sewage treatment.Materialized Pretreatment is an important step for sewage treatment, mainly for theremoval of the SS, Grit and insoluble CODcr and TP in the Sewage. Pretreatmentequipments such as vortex grit device, inclined plate settler device, folding flocculationdevice can be provided for users, while integration degree and function are too limited.Therefore, there is an urgent need to develop integrated multi-function equipment thatsuitable for sewage characteristics of small town.A small town sewage pre-treatment integrated equipment was developed. Thisequipment integrates the functions of vortex grit chamber, folded plate flocculation andtwo baffle inclined plate sedimentation. The mud （sand） and water can be separated inthe device, and the insoluble CODcr and TP can also be removed from the water. Thedevelopment and application of this equipment resolve the problem in small townsewage treatment due to its outstanding characters as high-performance, low investmentand modularization.The primary target of this thesis is to carry out the pilot tests for our newlydeveloped equipment, and investigated the influences such as inlet water quality, waterhydraulic loading, propeller speed, chemical flocculant dosing, remaining sludgeflocculant dosing on the treatment effect. This provides a strong theoretical basis for theinnovation, improvement and operation of the reactor in future.The main results of the study are as follows.①Dimensions of sewage pre-treatment integrated equipment, designed treatmentcapacity, hydraulic retention time of vortex grit zone, hydraulic retention time of folding flocculation zone, surface load of inclined plate sedimentation zone, and hydraulicretention time of inclined plate sedimentation zone are3×1×3.1m,50m3d-1,40s,31.8min,1.44m³·m^-2·h^-1and125min, respectively. The hopper height of inclined platesedimentation zone is0.6m, water distribution zone height is0.6m, inclined plate zoneheight is0.87m, water zone height is0.70m, ultra-high zone is0.3m.②Sewage pretreatment integrated equipment runs under designed treatment loadof50m3· d-1, hydraulic load of1.44m³·m^-2·h^-1, the average removal rates of SS, CODcr,TP, and grit are60.8%,34.7%,23.2%,50.4%, respectively.Vortex grit zone mainlyremoves the sand, and does not exhibit removal of organic matter. SS and CODcrremoval increase with influent SS and CODcrconcentrations increasing. Equipment hasstrong ability to resist water quality fluctuation.③Sewage pretreatment integrated equipment runs under hydraulic load of1.44m³·m^-2·h^-1,2m³·m^-2·h^-1,3m³·m^-2·h^-1,4m³·m^-2·h^-1.The increase of influent hydraulicload leads to the decrease of SS, CODcr and TP removal. Equipment has strong abilityto resist hydraulic load fluctuation.④Sewage pretreatment integrated equipment runs under influent hydraulic loadof2m³·m^-2·h^-1, the hydraulic retention time of1.5h. The effects of different dosage ofaluminum sulfate, PAC, PFS and excess sludge on SS, CODcr, TP removal were studied.Results indiate that the sewage which carbon source is limited, when sewagepretreatment has high requirement on phosphorus removal, flocculant dosing order ofpriority: PFS, Aluminum sulfate and PAC. Excess sludge flocculation should not beoptional because it almost no removal of TP. The sewage which carbon source is notlimited, when sewage pretreatment have no requirement on phosphorus removal, thecost of adding excess sludge is lowest, and improve removal rate of the SS, CODcr, andreduce the organic load of the subsequent biological treatment,then reduce the amountof aeration. The excess sludge return to sewage pretreatment integrated equipment canalso improve the moisture content of the excess sludge, reduce sludge treantmentamount and reduce the cost of sludge treatment.⑤For sewage pretreatment integrated equipment, Power consumption of per tonwater is only0.007yuan, covering an area of3m2. The production cost is less than30,000yuan. The design treatment capicity is50m3·d-1, but still maintains a goodoperating results in the138m3·d-1, by calculation of138m3·d-1, an investment of215.9yuan·m-3d-1.The optimal flocculant PFS dosage is70mg·L-1, the removal efficiencies of SS, CODcr, TP were69.6%,48.7%,49.1%respectively. At this point, treatment cost of perton is3.5fen.