Research On Rainwater Regulation And Purification Technics Of Bioretention Area

Too much emphasis on the construction of modern urban in basic construction,large area of city underlying surface is changing,green infrastructure construction is ignored.Promoting the construction of ecological civilization and focusing on green infrastructure,our cities,on the concept of low-impact development,aim to transform into the "sponge city".However,in China,especially in the northeast,LID technology components and their performance optimization,design parameters,regulatory strategies are in the research started late,less research results,to guide the practice of science is not strong stage.Therefore,to carry out in-depth research in this field,great theoretical and practical significance.Bioretention area,belonging to stormwater runoff control facilities,is characterized by delaying point sources pollution and purifying rainwater infiltration,which is of significantly to manage waterlogging case of low-lying areas.From the low impact development standpoint,this study focuses on optimizing the penetration,retention and purification for bioretention,analyzing the engineering control parameters,furthermore,exploring the purification filter layer,the soil infiltration,and the plant cultivation.The results showed:The filter layer:selecting the zeolite and volcanic rock for the media,which have advantages in good mechanical performance and stable chemical property.The research had tested the filter adsorption properties in three hours,the adsorption on TP by the volcanic rocks was 7.9%,the zeolite was 1.4%;the adsorption on NH3-N:the zeolite was 57.27%,the volcanic rocks was 42.57%;the adsorption on CODcr:the volcanic rocks was 32.4%,the zeolite was 10.9%.For different rainfall intensity,the filter layer had the characteristics of stable effect,responding to different hydraulic loading.As a result,the best consequences appeared in the experimental group:the system CODcr removal rate was 76.27%on average at1.1m/d,while at 0.7m/d,the average removal rate of TP was 46.71%,the removal rate of NH3-N was 91.53%on average.The processing effect of bioretention facilities is influenced by the length of dry period,the result showed that When operating-drying schedule was 1:6,the average removal rate of CODcr reached the peak of 76.03%,the average removal rate of NH3-N was 93.87%to the peak,while the TP got the better performance at the minimum of dry period.Ameliorate the soil infiltration capacity:ameliorating the soil infiltration capacity of bioretention area by applying organic soil amendments.The best effect is mixed with 30%crushed straw accompanying with the initial infiltration rate of 7.72mm/min,the steady infiltration rate of 2.08 mm/min.By laying straw between the soil layer and the filter layer to plant root channel.The straw layer was the artificial substrate for microbes,which can prevent the system from blocking and improve the infiltration of rainwater purification ability.The plant cultivation:the study have tested the purification capacity of different herbs,including Zoysia tenuifolia,Cynodondactylon(Linn.)Pers,Trifolium repens L,Festuca rubra L and Agrostis stolonifera.The single plant had outstanding performance:the removal rate of CODcr by Zoysia tenuifolia was 70.50%on average,the average removal rate of NH3-N by Trifolium repens L was 93.07%,the average removal rate of TP by Agrostis stolonifera was 89.73%.the volcanic rocks was 32.4%,the zeolite was 10.9%.For different rainfall intensity,the filter layer had the characteristics of stable effect,responding to different hydraulic loading.As a result,the best consequences appeared in the experimental group:the system CODcr removal rate was 76.27%on average at1.1m/d,while at 0.7m/d,the average removal rate of TP was 46.71%,the removal rate of NH3-N was 91.53%on average.The processing effect of bioretention facilities is influenced by the length of dry period,the result showed that When operating-drying schedule was 1:6,the average removal rate of CODcr reached the peak of 76.03%,the average removal rate of NH3-N was 93.87%to the peak,while the TP got the better performance at the minimum of dry period.Ameliorate the soil infiltration capacity:ameliorating the soil infiltration capacity of bioretention area by applying organic soil amendments.The best effect is mixed with 30%crushed straw accompanying with the initial infiltration rate of 7.72mm/min,the steady infiltration rate of 2.08 mm/min.By laying straw between the soil layer and the filter layer to plant root channel.The straw layer was the artificial substrate for microbes,which can prevent the system from blocking and improve the infiltration of rainwater purification ability.The plant cultivation:the study have tested the purification capacity of different herbs,including Zoysia tenuifolia,Cynodondactylon(Linn.)Pers,Trifolium repens L,Festuca rubra L and Agrostis stolonifera.The single plant had outstanding performance:the removal rate of CODcr by Zoysia tenuifolia was 70.50%on average,the average removal rate of NH3-N by Trifolium repens L was 93.07%,the average removal rate of TP by Agrostis stolonifera was 89.73%.The purification test of diversity plant showed that the combination of Trifolium repens L and Zoysia tenuifolia performed better in the purification capacity than the single plant.The results showed:the removal rate of CODcr by LZ was 70.17%on average,the average removal rate of TP was 89.73%and the average removal rate of NH3-N was 90.50%.In this study,the combined test was experimented in small scale reactor,which had taken 30 days to complete the start.In the monitoring period,the results indicated:the drained water quality met GB/T18921-2002 water quality requirements for aesthetic environment use.The figures showed:the average concentration of TP was 0.44mg/L,the average concentration of NH3-N was 1.91 mg/L and the average concentration of CODcr was23.19 mg/L.