Research On Purification Effect Of Subsurface Wastewater Infiltration System For Rural Sewage Treatment

With the rapid economic development of our economy and rising living standards inrural areas, environmental pollution caused by the rural sewage is becoming more andmore serious. Relative to the mature urban sewage treatment technology and process, ruralsewage treatment not only lack of funds and technical support, but also living dispersedmake sewage collection difficult, which is not suitable for the construction facilities forcentral treatment sewage. Therefore, we should seek appropriate technology and processfor rural sewage treatment that suitable for rural situation in china.Subsurface Wastewater Infiltration System (SWIS) has the features of less investmentin infrastructure, very cost of operation, good water outlet quality, recycling and et al.Moreover, SWIS has good environmental and economic benefits. However, the traditionalSWIS has problems, such as low hydraulic loading, large covers, easy to plug, whichlargely limited its application. For the above, this study from the viewpoint of practicalapplication, and synthesizing the latest domestic and international research results,optimized and improved the traditional SWIS. Through the laboratory soil columnsimulation test, this article analyzed removal effect of pollutants in domestic sewage ofimproved SWIS; monitored the number and distribution of microorganisms in the matrix,and studied the correlation between number of microorganisms and wastewaterpurification effects. The major results and conclusions are as follows:（1）Added fly ash and decomposed cow dung cooperate with soil in sewagetreatment, one can improve the system of hydraulic load and reduce the area, on the otherhand, fly ash has strong adsorption ability, thus can improve the removal efficiency ofpollutions.（2）The concentration range of COD, total phosphorus (TP), total nitrogen (TN) andammoniacal nitrogen (NH3-N) in rural sewage which into the SWIS is larger, but the twosystems were not blocked, and the water outlet stability and good quality during operation,which suggests that the system has high capacity for shock load.（3）Research on SWIS for sewage removal efficiency showed that, the pollutions insewage have a better removal effect, each index effluent concentration are reached the“urban sewage treatment plant pollution discharge standard”(GB18918-2002) in the levelof A standard. Moreover, concentration of TP reached the level of III of the “surface water environment quality standard”(GB3838-2002). Therefore, the treated water can berecycled, such as in agricultural irrigation, road cleaning, community greening and et al.（4）In contrast experiment of soil column, mainly analyzed the removal effect ofsewage in layered filling and mixed filling two structures. The results showed that: Theaverage removal rates of COD, TP, TN, NH3-N for system1(S1) were85.8%,98.1%,78.4%and93.7%, respectively, and for system2(S2) were87.1%,96.0%,73.4%and96.0%, respectively. Among the removal effects of these two systems, significantdifference in the TP, TN and NH3-N removal but little effect on COD were observed.（5）The test of space distribution of microorganisms in SWIS showed that, all kindsof microorganisms distribute widely in the infiltration matrix, however, the amount andspace distribution is different, and the number of microorganism are also different indifferent months. Among them, the maximum number is bacteria, indicating that thebacteria play a major roal in purifying wastewater. In space distribution, bacteria, fungi,ammonifying bacteria and nitrite bacteria in S2were reduced in amount from the surfacelayer to the bottom layer gradually, but denitrifying bacteria showed the oppositedistribution which caused by the different of ORP in substrate. However, due to the matrixare unevenly distributed, the space distribution of microorganisms in S1is not obvious,subject to furcher research.（6）The correlation between number of microorganisms and wastewater purificationeffects indicated: the number of bacteriaand COD removal rate was significantly correlated;the number of nitrite bacteria was significant correlation with NH3-N removal rate; thenumber of bacteria and denitrifying bacteria were significant correlation with TN removalrate, which indicating that the action of microorganism probably is the main way for theirremoval. The number of microorganism was not interrelated markedly to removal of TP,showing that microorganism in the process of TP removal is very limited.