Study On Bio-stability And Its Influencing Factors In Water Distribution System

Drinking water is closely linked to human health, and the water source's pollution has become a common focus in the drinking water research field all around world with the development of industrialization production and people's living level. At the same time, people's demand to drinking water quality is increasing. Although output water has accorded with drinking water criterion, but drinking water stays in the water distribution system for some time, and water quality could deteriorate. Corrosion scales could form on the pipe wall that serving for long time. Drinking water can suffered from secondary pollution, and hygeian situation directly influences supply water quality. The work took biodegradable dissolved organic carbon (BDOC) as an evaluating indicator to study biological stability change in water distribution system, and to provide some basis for water plants in improving water quality.Traditional water quality indexes and BDOC change in water distribution system was studied by taking experimental network as an objective. The correlation between traditional water quality indexes and BDOC was analyzed, free residual chlorine shows a negative correlation with BDOC, and turbidity presents a positive correlation with BDOC. Total iron presents a positive correlation with BDOC.The measurement BDOC year-round in city water distribution system shows that BDOC concentration was 0.17~1.46 mg/L, and BDOC in water distribution system slowly declined in winter, and then ascended along with the pipes. Residual chlorine decayed fast in summer for the temperature was high, and BDOC declined evidently. BDOC ascended and declined in spring and autumn, the difference of two seasons was not big because the temperature was close. TOC concentration declined through water distribution system.16SrRNA was applied to study the biodiversity in water distribution system in order to find the relationship and population structure in whole water distribution system. The amplified fragment length of 9 water samples was 100~300 bp. 17 sequences were gained by sequencing the recovery fragments. The sequence length was 192~227bp. Phylogenetic tree was constructed according to sequence analysis of special bands. The phylogenetic relationships of special bands were determined.BDOC forecasting models in water distribution system were constructed through multivariate linear stepwise regression and neural networks. In order to find the first-rate model, 6 netwrok were tested, and finally the network with 1 hidder layer and 25 neurones was determined. Through the comparison, the way of neural networks was found that had the highest accuracy in forecasting BDOC change in water distribution system, and the accuracy of it was 82.86%, which was higher than multivariate linear stepwise regression(17.14).The effect of BDOC on the growth ring was studyed in static pipe and dynamic modelling network. BDOC showed a positive correlation with adsorptive bacteria on the growth ring and dissociative bacteria in water. Organic matters characteristic peak of growth ring was got by infrared spectroscopy, meaning that some organic matters deposited on the growth ring. Thermo gravimetric analysis of the growth ring indicated that BDOC showed a positive correlation with organic matters in the growth ring. The growth ring tends to form in water distribution system that has a high concentration of BDOC.Corrosion scales were analyzed in physical structure, chemical composition, and microbiology by several methods. Specific surface area of 3 corrosion scales were big with the value in the range of 47~115m2/g. Total pore volume of Corrosion scales were 0.03~0.21 cm3/g, and this showed that there were a lot of holes in the corrosion scales. Microcosmic shape of corrosion scales were analyzed by Scanning electron microscope, corrosion scale stratified clearly, which consisted of surface biofilms, stratum compactum and tectorium. Corrosion scale was composed of predominantly goethite (α-FeOOH), lepidocrocite (γ-FeOOH) and FeS according to XRD analysis. Iron bacteria and sulphate reducing bacteria were found in corrosion scale by microbial measurement. The analysis mechanism of the growth ring showed that microbial corrosion didn't exist alone, it also happened together with electrochemical corrosion. And the action of microbe accelerated the formation of corrosion scale in water distribution system.