Study Of The Rural Domestic Wastewater Treatment By A Naturally Ventilated Biotower System

Rural domestic sewage has become one of the main sources of non-point source pollution.The construction of "beautiful China" begins with the construction of "beautiful countryside",and the rural domestic sewage caused by disorderly discharge leads to water ecological pollution.Rural sewage treatment problem is imminent.Because rural sewage with small-quantity of water,emissions,daily variation coefficient and relative dispersion characteristics,should be developed with high efficiency,low energy consumption,low cost,easy management and operation of the rural sewage treatment technology.Based on the characteristics of sewage in rural areas and the economic level,in this paper,we treat the rural domestic sewage in Yunnan by the self-design of the tower biological filter with polypropylene plastic ball packing.We studied the characteristics of different water quality of forming biofilm,and discussed the characteristics of the removal of pollutants and the removal characteristics of pollutants in the different filter media layers.Experimental studies show:The natural film forming method was adopted in this experiment start-up.The normal concentration influent needed less biofilm maturation time than the low concentration influent,36 days and 48 days,respectively.The biofilm-activated of the normal concentration influent was slightly higher than the low concentration influent,but there was no significant difference.The VSS/SS ratio were 0.7 and 0.64,respectively.During the biofilm culturing,the average removal rate of pollutants of the normal concentration influent was higher than the low concentration influent.But the average effluent concentration was the opposite.During stable operation,under the conditions of hydraulic loading(14.15 m3/(m2·d))and hydraulic retention time(2.45 h),the treatment performance of the tower biological filter on different contaminants of rural domestic sewage was studied.The experimental results showed that the tower biological filter achieved the average removal efficiencies of CODcr,BODs,SS,TN and NH4+-N were 87.0%,93.0%,91.5%,63.7%and 68.6%,respectively;the average effluent concentration were 36.4 mg/L,12.6 mg/L,17.92 mg/L,13.3 mg/L and 8.2 mg/L respectively.The TP removal efficiencies in the wastewater could reach to 68.7%,the average TP concentration in effluent could reach 1.75 mg/L.In addition to TP concentrations of the discharge meet the "urban sewage treatment plant pollutant discharge standard"(GB 18918-2002)second grade discharges standard,other indicators could meet the first class of B discharges standard.Under the same operation condition,the removal efficiency of pollutants in the different filter media layers of the biofilter was different.The removal rate of CODcr,BODs and TP decrease with the number of the layer increased,while TN and NH4+-N Increase.The removal of CODcr,BODs and TP mainly occurred in the middle and upper part of the filter.In the first three layers,the removal rates of CODcr were above 30%,24%and 20%,respectively;the removal rates of BOD5 were above 33.0%,25.0%and 22.0%,respectively;the removal rates of TP were above 20.0%,18.0%and 15.0%,respectively.While TN and NH4+-N removal mainly at the bottom filter layer.The removal rates of TN and NH4+-N were above 20%and 19.5%,respectively.Thus,this self-developed tower biological filter system has excellent capacity to resist impact load.Under the fluctuation of pollution load,the removal rate of pollutants is still stable,especially for the removal of CODcr,BOD5 and SS.Tower biological filter is suitable for the treatment of rural domestic sewage.The technology has unique advantages,and shows great value for extended application for the decentralized rural sewage treatment in mountainous and hilly areas.