The Study And Simulation Of Microorganism In Drinking Water Distribution

With the improvement of people’s material life level promoted by the rapid development of China’s economy, people pay more and more attention to the safety of drinking water. In the latest 2006 version of drinking water health standards, microbiological indicators ranked first in the table of conventional water quality indicators and limit values. Making efforts to ensure that the biological safety of drinking water is becoming very important in water supply management. Therefore, it is of great significance to study the changes of microorganism in water supply networks.In this paper, the rule of microorganisms varying in water supply network and its main factors was studied and analyzed through static experiments using two tanks produced by different materials. And the varying rule of bacteria under different regimes of flow in networks by simulative pipe loop experiments. According related literatures and the results of the experiments, a mathematic model of microorganism in drinking water networks was established. Then the microorganism in demonstration project network was simulated by programming in EPANET2.0 and EPANET-MSX. The main conclusions and results are as follows:①The static experiments showed that microbial regrowth is relatively slow, the increase of the concentration of microorganisms is not obvious in the 30 hours experimental period. The materials of tanks and the quality of the water are both factors affecting the decay of residual chlorine. The smother the tanks and higher the organic matter content in the water, the faster the residual chlorine decay rate, then the easier the microorganism growth.②Because of the redox reaction between residual chlorine and organic pollutants in the water, a part of AOC is generated, which induced that the concentration of residual chlorine decreases, while at the same time, the concentration of assimilable organic carbon(AOC) increases in the early stage of the experiment.③It seems that adding chlorine in drinking water has double effects: on the one hand, because of the existence of residual chlorine, the microbial growth was inhibited in the early stage, while on the other hand, the AOC produced by the decay of residual chlorine provides a more organic substrate for microbial growth which accelerates microbial regrowth rate. Taking a long pipeline for example and using Matlab tools for the simulation calculation, the calculation results showed that, there may be an economically optimal chlorine dosage which can let the concentration of microorganisms at the end of the pipe just meet the requirements of the water quality standard limit value.④The results of simulative pipe experiment showed that the higher the flow velocity, the more the biomass of biofilm. The biofilms formed under different flow velocity have different characteristics that have some influence on the desorption process of bacteria from biofilm to bulk water. For the same biofilm, the desorption rate increased with flow velocity above the biofilm. In addition, comparing with the static experiment data, the flow velocity in the pipeline have no obvious influence on the growth of bacteria in bulk water, when the flow velocity is low.⑤Considering the organic carbon and chlorine as the key factors affecting changes of microorganisms in the water supply network, a microorganism model in water distribution system was established on the base of multi-species reaction. According to the least squares principle, the parameters of the model were checked using Matlab to call function file in EPANET2.0 and EPANET-MSX. Generally, it can meet the accuracy requirement to predict microorganism distribution in water supply network using the checked model.