Study On Characteristics And Improvement Technologies Of Cistern Water Quality In Weibei Semi-arid Loss Plateau

Weibei Semi-arid Loss Plateau is located in the south of Northern Shaanxi loesshilly region and the northern part of the Guanzhong Plain. It belongs to semi-arid-regionwhich suffer extremely shortage of water resource, so rainwater harvesting by cisternappears to be one of the main forms for supplying fresh water in rural areas of the LoessPlateau. Even though collecting cistern water is a good way to solve the problem ofscanty drinking water resource for domestics and livestock demands, sediment andpollutant were carried the rainwater flow into the cistern during runoff. Because therainfall mainly focus on June to August, rainwater needs remain in the cistern for amuch longer time. This conditions encourage the growth of bacteria and lead to thewater quality deteriorate Taking cistern water as drinking water may lead toinflammatory bowel disease after long-term ingestion.This paper is conducted to study the cistern water quality of typical village,efficiency and kinetics characteristics of different materials ion release during runoffprocess and pollution control of early rainfall in order to improve the cistern waterquality of Weibei Semi-arid Loss Plateau. The research result shows:(1) Detecting the water quality of three different circumstance cisterns the resultshows that parts of water quality indices are not eligible. The cistern water pH is7.89~8.63, the turbidity value is1.07~20.10NTU, coliforms and total bacteria are30~390CFU/100ml and800~2800CFU/100ml respectively, other routine water qualityindexes are not exceeded.(2) According to the electric conductivity and ion release rate, the release amount of different meterials from big to small was: concrete> mechanism red tile> red brick>grey tile> local soil. Regarding to ion release rate the maximum is concrete, theminimum is local Under different pH values, the total released ion quantity of differentmaterials increased with increasing rainfall acidity, but the average rate of conductivitychange was no significant difference, and ion release rate decreased significantly after10s and tends to zero value after30s except concrete. From the point of improvingcistern water quality, the contribution of concrete is most significant,(3)Using SWMM model to simulate the change of water quality in a singlerainwater-harvesting, and the results show that the changing of pollutants concentrationin early rain is consistent with the test result. In the early five minutes of the storm, thepollutants concentration increases firstly and then decreases with the delay of rainfall.Simulation of the whole village shows: pollutants concentration increases firstly, thendecreases with the delay of rainfall, peak concentration appeared after about16minutes,and the peak concentration appear time increase with increment of rain frequency.Greening the rainwater-harvesting can reduce pollutants amount obviously. When thewhole catchments have been greened, the amount of TSS and TN reduce by68%and22%respectively.