Experimental Study Of Water Earthworm Eco-filters For Dispersed Domestic Wastewater

In recent years,China’s economic development has shifted from the stage of high-speed growth to the stage of high-quality development,and the effect of restoration and treatment of the ecological environment has gradually emerged,but the problem of water environment pollution in China still exists,in which the volume of decentralized domestic sewage fluctuates greatly,the scope of change is unstable,and most of it is discharged directly into the environment without treatment,causing serious pollution of the local water environment,and the traditional sewage treatment technology can no longer meet today increasingly stringent water treatment requirements.Therefore,the development of efficient and ecological new sewage treatment technology to deal with decentralized domestic sewage is an urgent need for water pollution prevention and control in China.Based on the water quality and discharge characteristics of decentralized domestic wastewater,this thesis proposes the introduction of water earthworms and plants in the eco-filter based on the eco-filter wastewater treatment technology to build a plant-water earthworm eco-filter to treat decentralized domestic wastewater.In this paper,we firstly conducted experiments to study the water removal effects of six species of plants,namely,reed,dry umbrella grass,calamus,balsamroot,water onion and plantain,in different seasons,and selected plants with better water purification effects.The plant-earthworm eco-filter was also studied in terms of different hydraulic load,density of water earthworms,plant density and hydraulic retention time on the treatment effect of decentralized domestic wastewater,which provided a suitable range of parameters for the efficient and stable operation of the water earthworm eco-filter.The main findings are as follows:（1）The six plants have the best effect on COD_cr,ammonia nitrogen and nitrite nitrogen purification in domestic wastewater in summer;the effect on COD_cr,ammonia nitrogen and nitrite nitrogen purification in domestic wastewater in spring and autumn is not much different;the effect on COD_cr and ammonia nitrogen removal in domestic wastewater in winter decreases significantly,and the effect on nitrite nitrogen removal in winter decreases significantly for all plants except dry umbrella grass and calamus.The removal effect of nitrite nitrogen in winter was significantly lower than that of all the other plants,except for A.calamus and A.arborescens;the removal effect of total phosphorus in domestic wastewater was not significantly different among the six plants in the whole year experiment.The analysis by pollutant index method showed that the removal effect of dry umbrella grass on domestic wastewater was better in the year-round experiment,and the average removal rates of COD_cr,ammonia nitrogen,total phosphorus and nitrite nitrogen were 67.72%,-4.71%,99.22%and 87.81%respectively.（2）After adding water earthworms,the eco-filters’ability to resist low temperature was significantly enhanced,and the removal effect of pollutants in domestic wastewater was improved in all eco-filters,and the removal effect in winter was improved more.The average removal rates of COD_cr,ammonia nitrogen,total phosphorus and nitrite nitrogen in the whole year were 71.45%,-1.33%,99.34%and 89.98%,and the removal rates of COD_cr,ammonia nitrogen,total phosphorus and nitrite nitrogen in winter were increased by 16.88%,26.08%,0.73%and 6.77%,respectively.（3）The water earthworm-dry umbrella grass eco-filter was more effective in purifying decentralized domestic wastewater under the conditions of hydraulic load of 0.5-1.5 m³/m²-d,water earthworm density of 1.5 g/L-2.0 g/L,plant density of 60 plants/m²,and hydraulic retention time of 7 days.The water earthworm eco-filter has low investment,low operation cost,simple and convenient management and operation,and has strong availability and applicability,which can significantly improve the problems of traditional eco-filter such as poor removal of pollutants under low temperature in winter and easy clogging leading to unstable water purification effect,etc.This study provides technical support for the treatment of decentralized domestic wastewater.