Research On The Distribution Of Microorganism In Secondary Water-supply Systems

The problem of water quality pollution in secondary water supply systems (SWSS) is very common in China, and People have given more attentions to the microbiological water quality. An area with SWSS in a campus was chosen for this study. By monitoring the water quality, this paper studied the rules of bacterial regrowth and distributing in SWSS, established a bacterial predicting model, and then pointed out measures to prevent regrowth of bacteria.6 monitoring sites were set and 17 water quality parameters were analyzed. A great deal of water quality data was gained. With this data, we analyzed the changes of water quality in SWSS, and the reasons how cistern affected on HPC. In this article R2A culture medium was used for the plate count instead of plate count agar (PCA), in order to solve the problem that HPC is under the real number using PCA. It was studied that the rules of bacteria distributing in SWSS, and how other parameters affected HPC. In addition, we set 3 monitoring sites at different floors aiming for studying water quality in this building. Dense water sampling was made to study how the water quality changes along with time in the chosen area.Based on the relativity of these parameters, we chose total residual chlorine, turbidity, Fe, UV254 and NH3-N as input, HPC as output. A BP neural network model with 3 layers was established to predict HPC. We used this model to predict HPC with other parameters, predict HPC of a site with the data of other sites, and predict HPC of the monitoring sites with the data of the cistern entry. This model can simulate the trend of water quality variation well. Neural network could get into partly minimum easily, so HPC was predicted as qualification or disqualification according to water quality criterion (100CFU/ml). The result showed that the prediction effect of BP neural network model is good and the precision is satisfying.Based on the analyse of water quality variation and the rules of bacteria growth, some measures were brought forward for preventing bacteria regrowth in SWSS, which involved enhancing water treatment, the choice of pipe diameter and material, and the choice, alteration and management of secondary water supply systems.