Study On The Key Equipments&Technologies In WWTPs With The Process Of Oxidation Ditch

“Look up to quantity and down on quality, up to plant and down on network, upto sewage treatment and down on sludge disposal” used to be a main thinking amongdecision makers in China. These have maken some problems in wastewater treatment.In order to solve these problems, upgrade the wastewater treatment plants with theprocess of Oxidation Ditches（OD） in water discharge quality, energy saving andsludge disposal. Our study is focused on surface aerator of OD, grit chamber andsludge treatment and disposal, so as to develop more efficient equipments and getoptimal operation.The aim of the study is to investigate the oxygen mass-transfer characteristics ofthe vertical shaft tubine surface arerator to upgrade its power efficiency. A new type ofhigh efficiency surface aerator was developed with methods of test and simulation. Anew model of oxygen transfer characteristics of the surface arerator was set up withaid of MATLAB and CFD simulator. The model was applied in equipment developing,optimal operating in prcise aeration.3patents were applied related to thesetechniques.The grit in wastewater is high in Chinese wastewater treatment plants （WWTPs）.The particle size distribution is deferent to that of foreign contry. In China, most ofgrit removal equipments were introduced from overseas or copied from that of foreigncontrys, so the girt removal efficiency is very low. The study on the girt chamber wasfocused on developing a new high grit removal efficiency chamber and operatingoptimized with methods of tests and simulation.Using Statistical probability distribution method, analyze sludge characteristics,reasons, treatment and disposal situations of the sludge from the oxidation ditcheswastewater treatment plants in southern China，comparative study of the treatmentand disposal situations and future development trends of the sludge in EuropeanUnion，forecast future development trends of the methods used for treatment and finaldisposal of sewage sludge in southern China, and give some proposals for the sludgemanagement.As the results, it has been found that：1) A new type of high efficiency surface aerator was developed with powerefficiency of2.73kgO₂/kWh，however, the benchmarking is2.1kgO₂/kWh. 2) A new model of oxygen transfer characteristics of the surface arerator was setup. The model can be applied in equipment developing, optimal operating in prciseaeration.With aid of this model, we found that: There is a maximum power efficiencypoint, a sub-maximum power efficiency point and a minimum power efficiency pointfor this type of surface aerator, the submergence is283.5mm and the rotational speedis29.73r/m at the maximum power efficiency point; This result shows that it shouldbe controlled at the maximum power efficiency point in operation, and should keepconstant depth of immersion at a range of rotational speed from27.27r/m to2.88r/mand input power from81.3kW to131.4kW for this aerator in some occasion so as toget high power efficiency in operation;The input power is101.5kW at the maximumpower efficiency point, and the maximum input power is131.4kW in high powerefficiency area.3) Used a new method—continue sampling settling method, with aid ofnumerical simulation, to evaluated the grit chamber system, so as to optimaldeveloping the equipment and operating the system.The results show: the grit removal rate of the rotational flow grit chamberdecreases with water flow increase, and exists a break point, exists a optimized bladerotating speed with maximum girt removal rate. Continue sampling settling method isstable and quick, can realy evaluate the efficiency of the grit chambar, help toopotimize the operation of the system. With the help of a kind of air flow meter, tometer the air flow of the branch pipes of the aeration grit chamber for controlling theair flow, so as to study the relationship between aeration intensity and grit removalrate, it has been found that it is helpful to optimal operating.4) Using Statistical probability distribution method, analyze sludgecharacteristics, reasons, treatment and disposal situations of the sludge from thewastewater treatment plants with process of oxidation ditches in southern China，forecast future development trends of the methods used for treatment and finaldisposal of sewage sludge in southern China, and give some proposals for the sludgemanagement.As the results, the characteristics of OD sludge has been found that：the watercontent of the sludge with maximum probability density is78.73%. Volatile matter ofthe sludge is low:43.21%. High heat value is low:9.169.16MJ/kg-DS. The content of heavy metals can meet the standards of “The disposal of sludge from municipalwastewater treatment plant-Sludge quality for afforestation in gardens or forests”（GBT23486-2009）. The sludge from OD plants is suit for agricultural use, and cannot be used for incineration, but can be used for fuel after deeply dewatered.