Water Quality Variation In Micro-storage Facilities And Its Influence On Safety Of Drinking Water In The Loess Plateau

Under the press of globle water resource shortage, harvested rainwater has beenwidely used to provide not only process water but also domestic water consumption inChina and many other coutries. It is an important issue to investigate water qualityvariation of harvested rainwater as drinking water source in micro-storage facilities and itsinfluence on safety of drinking water. Aiming at a number of problems with water qualityissue during rainwater utilization, the paper took some typical water quality parametersclosely related to human health as researcher object, studied characteristics and mechanismof the spatio-temporal variability of the referred pollutants, by means of indoor andoutdoor experiment and theoretical analysis. The main conclusions are listed as follows:1. Simulation and analysis of temporal variation of typical pollutants concentration inharvested rainwater. During storage process, the concentration of pollutants graduallyreduced with time, and reached a stable trend in20~30days, which agreed with effect ofself-purification. According to the measured results of temporal variation in pollutantsconcentration, the temporal migration process changes of pollutants could be dividend intothree stages, viz. the early settlement-dominant period, the transition period and thediffusion-dominant period. A numerical model was established for describing the temporalchanges of pollutants in small and micro-rainwater utilization engineering, validated andevaluated. And turbidity and COD werer verified well by the monitoring results; nitrogencompounds had a certain deviation, but a rational trend.20-30days after storage wasrecommended as suitable time for utilization.2. Simulation and analysis of vertical distribution of typical pollutants concentrationin rainwater. Turbidity and COD contents are high at two ends and low in the middle alongthe vertical line, due to sediment at the bottom and floating debris at the surface andbiological activities. Sediment and floating debris are two main pollution sources. Alongthe vertical line, the measured relative pollutant content was positively correlated to thepower function of relative distance from the pollution source. Several types of vertical distribution were given based on the measured data. So low pollutant content appears inthe middle, and cleanness of surface and bottom could improve harvested rainwater quality.A numerical model was established for describing the vertical distribution of pollutants insmall and micro-rainwater utilization engineering, validated and evaluated, and wasverified by the monitoring results, which had certain deviation, but credible usage. Arelative depth of0.4-0.6h was was recommended as suitable zone for utilization.3. The effect of MBER soil stabilizer, compared with cement material, as constructionmaterials on water quality was studied. With the effect of soil stabilizer, during storagetime, the pollutants concentration decreased about15~20%; as for the vertical distribution,the relative concentration decreased about8~12%. The effect of solidified soil usingMBER soil stabilizer was due to the hydrate reaction of solidified soil and reactionproducts. Soil stabilizer could strengthen self-purification of water to some extent, whichcould reduce the amount of turbidity, COD and some ions such as nitrate and nitrite.Results showed that the water quality did not exceed the standard for drinking water inChina for distribute water supply. Results in this research were valuable for popularizationand application of MBER soil stabilizer in rainwater utilization from point view of waterquality issue.4. A suitable water quality assessment method was given. Turbidity, COD, ions (suchas nitrate) and pH were chosen as the main factors or indicators for describing thecharacterization of rainwater quality using statistics analysis method. The rainwater qualityassessment method was presented as a result to security drinking water quality. Throughdata analysis and comparison, the method is intuitive, reliable and targeted.5. The suitability of different spatial scales of rainwater utilization was investigated.Harvested rainwater utilization in the rural single family courtyard, small watershed wasinvestigated and evaluated. Results showed that: rainwater utilization had great potentialin solving the rural household in dingbian. Rational utilization of rainwater resources is asuitable strategy to alleviate the problem of drinking water safety in rural area.