Study On Technique For Upgrading Reconstruction Of Xiang Lake Wastewater Treatment Plant In Changsha City

In the process of building a resource-saving and environment-friendly society,energy conservation and emission reduction are attracting more and more attention.The Discharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002) comes into effect from Jul.1.2003in china. The limits on nitrogenand phosphorus in the effluent requirements are significantly increased. Lots ofwastewarer treatment plants are facing upgrading reconstruction. The situation andupgrading reconstruction of Xiang Lake wastewater treatment plant in Changsha cityare studied in this paper.Through the analysis on the situation of the Xiang lake wastewater treatmentplant in Changsha city, the conclusions can be induced: low effuluent water qualitystandards, small biochemical pool capacity, effluent without disinfection, notconsidering deodorant noise reduction measures, the low influent C/N and so forth.The following conclusions are drawed from the Analysis of small scale andmedium-sized trials of biological contact oxidation ditch: First, adding anoxic zonecan improve the nitrification effect to1mg/L, but the denitrification effect is notimproved obviously, mainly due to the carbon source. dosing external carbon sourcecan enhance the TN removal efficiency. Secondly, adding combined package carrierand suspended carrier has a slight nitrification effect but unobvious denitrificationeffect. Thirdly, adding combined carrier in the actual oxidation ditch can not makefull use of the DO density of the oxidation ditch, causing oxidation ditch flow speeddecreased and influencing the update of the filler surface biofilm instead. And theadsorption of the foam scum in the water will reduce the specific surface area of thefixing packing material. Thus it’s more appropriate to transform the original processinto bio-contact oxidation ditch process by adding suspended carrier. But suspendedfiller plug, settlement, strength and other issues need to be addressed.A suitable operation mode is proposed from the small pilot test of the biologicalcontact: anoxic hydraulic retention time is0.75h; the MLSS is2500~3500mg/L;suspended carrier dosing ratio is30%; internal reflux ratio is200%; a small amountof carbon source is casred according to the water. Besides, it is advised that the firstsurface aerating machine of the oxidation ditch can be replaced by submersible waterimpellers to enhance aeration supplemented by chemical phosphorus removal, and the effluent water quality can basically meet the level IV criteria specified inEnvironmental quality sandard for surface water (GB3838-2002) of TN≤12mg/L.In the MBR process, effluent quality is better. the use of chemical phosphorusremoval and adding carbon source as auxiliary means, the water of TN≤12mg/L,TP≤0.3mg/L, reducing the environmental risks of effluent reuse. But the MBRprocess higher cost and energy consumption, membrane fouling and other problemsmake it difficult to operate and manage. However, bio-contact oxidation ditch+clothfilter technology has better capacity to impact load, stable and reliable technology,flexibility, relatively low overall investment and a simple transformation, so it ismore reasonable to choose the bio-contact oxidation ditch+cloth filter technology.