Study On Domestic Sewage Treatment In Cold Area By Using Constructed Wetlands

The surface water and ground water have been severely contaminated,which was caused by the domestic sewage that due to inadequate treatment capacity of infrastructures and the limit of the some areas sewage treatment capacity pouring into rivers in a large amount without treatment.China has a very limited per capita water capability,choosing a economic and efficient sewage treatment process is very important.The constructed wetland has been attached great concern owing to the merits of less operation and maintenance requirements,good purification effect and high ornamental value. Temperature is a parameter of constructed wetland purifying effect. So carrying out the research about removal effect in different configurations of constructed wetland in northern cold city is great important to promote and use wetlands in the northern region.This paper studys the efficiency of N,P and COD removal in horizontal subsurface flow constructed wetland which include different substrates and plants.Sewage purification effect under different pollution load of pollutants in constructed wetland was discussed.The impact of cold area temperature in different types of constructed wetlands on the removal efficiency of N and P was investigated.A preliminary analysis is the characteristics of soil enzyme activity and microbial community structure with the ambient temperature varying. The results are as follows:In terms of effects of N,P and COD purification in different constructed wetland plants:Cannas and purple loosestrifes> Purple loosestrifes> Cannas> Vacuity contrast.Based on effect of the substrate of the constructed wetlands on pollutants purification,it can be found that the gravel substrate of constructed wetland had the highest removal rate of NO3--N,TN, COD,the slag substate had the high removal rate and the Ferric-carbon micro-electrolysis filler had the low removal rate. The Ferric-carbon micro-electrolysis filler had the best removal capacity of TP whose removal rate is as high as 90%,the gravel had the good removal capacity and the slaghad the poor removal capacity.The impact of different pollution loads on pollutants purification discovered that:under the high pollution load of ammonia nitrogen(13.64 g/m2)conditions, the gravel was used as substrate and the removal rate of NH4+-N,TP,COD of vacuity contrast,cannas, purple loosestrife in constructed wetland were lower than low pollution load of ammonia nitrogen(8.19 g/m2),the cannas and purple loosestrife enhance the removal rate of NH4+-N,TP and decrease the COD removal rate.under the high pollution load of total phosphorus(3.74 g/m2)conditions, the Ferric-carbon micro-electrolysis filler was used as substrate and different plants of constructed wetland were higher than low pollution load of total phosphorus(1.99 g/m2),the NH4+-N and COD removal rate was reduced.under the high pollution load of COD(48.05 g/m2)conditions, the slag was used as substrate and the COD removal rate of vacuity contrast,purple loosestrife,cannas and purple loosestrife in constructed wetland were lower than low pollution load of COD(30.45 g/m2),the cannas enhance the removal rate,the effects on removing NH4+-N and TP were going down significantly.The impact of temperature in constructed wetlands on the removal efficiency of N and P showed that:the removal effect of NH4+-N, NO3--N,TN was September(23℃~29℃)>October(17℃~21.5℃)>November(5℃~13℃).The gravel and Ferric-carbon micro-electrolysis filler substrates to the TP removal effect was September(23℃~29℃)>October(17℃~21.5℃)>November(5℃~13℃),the slag substrate showed September(23℃~29℃)>November(5℃~13℃)>October(17℃~21.5℃).The soil urease activities decreased with the temperature decreasing,the sucrose enzyme activity was first decreasing and then increasing with in temperature range.The soil microbial PLFAs in the constructed wetland were mainly unsaturated fatty acids,straight saturated fatty acids and branch saturated fatty acids. Hydroxyl fatty acids,cyclopropane fatty acids and polyunsaturated fatty acids were less.The number of bacteria was dominant, fungi followed, and antinomycetes is the least in soil microbial community, the proportion were 42.7%~50.8%, 14.2%~17.1% and1.1%~1.9%.