Purification Effect Of Different Facilities Of Rainfall Filtration System On Water Quality

Water scarcity and water-soil erosion has been one of the main conflicts restricting economic and social development in Loess Plateau.Because of rare precipitation,severe loss of soil and nutrients during rainy season,and poor quality of groundwater in Loess Plateau,it lacks clean irrigation water for the development of high-efficiency agriculture in local area.Meanwhile,in some rural areas,drinking water security is threatened by local conditions and rainwater is still the main source of domestic water use.Water cellars with different materials have different effects on water quality,even on people's health.Focused on issues including water-soil erosion,irrigation and drinking water scarcity,this research studied effects of vegetation-filtration chamber system designed by our research group and water cellar on water quality through both indoor experiment and filed experiment for high-efficiency use of water and soil resources.The indoor experiment studied the effects of slop and intermittent rain on runoff and nutrients trapping efficiency of vegetation filter strips;the field experiment studied the purification effect of small gravel channel,gravel chamber and water cellar on water quality.(1)We designed three slopes for the indoor soil-bin test: 5°,10°and 15°,with 0.8 mm/min rainfall intensity and 72 mm rainfall.The results showed that the trapping efficiency of switchgrass filter strip(1 m)for surface runoff and non-adsorptive nutrient-NO3-N declined with the increase of slope.However,adsorptive nutrients-NH3-N and TP did not have this characteristic.In 5°,10°and 15°slopes,the runoff trapping efficiency of switchgrass filter strip were 33.0%,28.7% and 25.2%,respectively;the NO3-N trapping efficiency were 42.6%,36.1% and 29.1%,respectively;the NH3-N trapping efficiency were 42.5%,44.0% and 51%,respectively;the TP trapping efficiency were 43.3%,61.5% and 44.2%,respectively?(2)In the intermittent rain event,we designed three artificial rainfall intensity with 24-hour intervals: 0.8 mm/min,1.2 mm/min and1.8 mm/min,with 72 mm rainfall for each experiment.The results showed that the trapping efficiency of switchgrass for surface runoff,mineral nitrogen(NH3-N + NO3-N)and TP decreased with the increase of rainfall experiments.Specifically,the surface runoff trapping efficiency were 25.2%,15.7% and 12.0% respectively in the three rainfall experiments;the NO3-N trapping efficiency were 29.1%,25.0% and 15.3%,respectively;the NH3-N trapping efficiency were 51.0%,55.9% and 32.4%,respectively;TP trapping efficiency were 44.2%,36.0% and 27.8%,respectively.Moreover,in the last rainfall experiment,the trapping efficiency of switchgrass filter strip for mineral nitrogen and TP decreased most quickly.(3)The laboratory experiments showed that switchgrass filter strip increased water and nutrients infiltration so that nutrients can be trapped in soil,reducing surface nutrients loss.In 5°,10°and 15°slopes,the average water infiltration rate of switchgrass filter strip were 1.3 times,1.5 times and 1.7 times the bare slopes,respectively.NO3-N of switchgrass filter strip in soil water were 1.6 to 2.4 times bare slope;NH3-N of filter 2.2 to 3.8 times bare slopes;TP of filter 3.3 times bare slope.Nutrients of the switchgrass filter strip cumulated in the soil water with a certain pattern.NO3-N and TP cumulative process in the middle rainfall experiment was a transitional event between the initial rainfall event and the last rainfall event,containing the characteristics of both: NO3-N and TP cumulative curves occurred temporal turning point after the rainfall event lasted for 50 min;before the 50 min,the cumulative curves of NO3-N and TP were similar to the initial rainfall event;after 50 min,similar to the last rainfall event.The infiltration volume was the decisive factor for this pattern.(4)In the field experiment,we monitored water quality in the small gravel channel,gravel chambers and water cellars.The results showed that gravel channel and chambers can reduce turbidity,COD,nitrogen and sulfate.Meanwhile,they can reduce the peak value of the pHysio-chemical parameters and make them reach stable quickly.The concentration values of turbidity,COD and NO2-N were lowest at the 19 m of Grave channel;concentration values of TN and SO42-kept stable between 10 m and 19 m of the grave channel and declined between 19 m and 28 m.For water cellars,materials had effects on water quality: with the same catchments,the water cellar with cement mortar on the wall and red clay on the bottom had a better water quality that the water cellar with cement mortar on the wall and the bottom.It is suggested that road should not be used as a catchment to collect rainfall for drinking;if possible,it is better to adopt pave a layer of red clay on the bottom of cement mortar cellar in order to adsorb and deposit impurities more effectively,and finally increase the water purification efficiency.