Research On The Purification And Direct Utilisation Of Roof Runoff

With the development of the urbanization,the contradiction between water supply and demand is becoming increasingly conspicuous,and the pressure on the water environment also increases.In recent years,the expansion of impermeable land surface interference with the natural water cycle,lead to great loss of rain,and weaken the city's flood-control and disaster-combat capacity.In order to alleviate water shortages and improve the urban water environment,It is meaningful to give more attention to rainwater utilization.This study conducts the contrast of runoff quality of three types of underlying surface—roof,green surface and road surface.The analysis indicated that the quality of different underlying surface runoff show great difference—the quality of green surface runoff is better than roof runoff,and the road runoff is most seriously polluted, but all follow a similar law,that the pollutant concentration decreased along with rainfall duration and became stable gradually in the process of rainfall runoff.It also showed that the CODCr value of roof runoff in late period is less than 50mg/L and the SS content less than 10mg/L, and the quality can meet the water quality standard for urban miscellaneous water consumption and scenic environment use after simple treatment. It is therefore well suitable to directly utilize. It is therefore well suitable to directly utilize.This paper also proposes the soil vegetation system,adopted to purify roof runoff,and do the research on the law of purification efficiency of soil filtration column.The study indicated that the treatment effect of soil is closely related to soil structure,infiltration depth and pollutant loads.1.2m deep bed of artificial soil, consisting of 68% of natural soil,17% of sand and 15% of cinder of burned coal, presents a strong purification capability, buffering capacity and resilience. When the filtering bed purifies the roof runoff in later period, the ratio of COD elimination can be stabilized at about 75% , achieving a better purification effect. To the the first flush of roof, the impact of high load also can be well buffered.What'more,The plant and earthworms are able to strengthen the purification capability and restoring capacity of artificial soil.Besides,this article puts forward evaluation index system of environmental benefits of roof runoff direct utilization,based on the technical, economic benefits, social benefits and ecological benefits.Through fuzzy evaluation method,AHP method and Delphi method, the evaluation model was established and the weight of of each indicator is obtained. The plan for direct utilization of roof runoff of a subdistrict in Harbin is assessed based on the evaluating system. The result of assessment shows that the program has general economic benefits,but remarkable social and ecological benefits,and it reached a good level as a whole.