Study Of Corrosion In Drinking Water Distribution System Under Water Source Switch

In this paper, water source switch in South-to-North Water diversion project asthe object of study, which will cause the deterioration of the water quality of thepipes. Analysising the adjustment of composition of the biofilm on the pipe scale,with adjusting influent chlorine concentration and dissolved oxygen concentration.It control the deterioration of water quality caused by switching the water sourceeffectively, the microbial corrosion mechanism of the pipes has a certain study.Firstly, Two pilot-scale pipe lines were used to study the controlling ironrelease in drinking water distribution system under water source switch. Groundwater was used as the initial water source, DO and chlorine concentration werecontrolled at7-8mg/L and1.0-1.1mg/L, respectively. After40days, α-FeOOH andFe₃O₄were the primary crystals in the scale layer. When the ground water waschanged to surface water, the oxidation and reduction of iron could reach a newbalance quickly because of the new composition of the corrosion products and themicroorganisms on the biofilm. This could reduce the iron release from corrodedcast iron pipes and maintain the water chemical stability of drinking waterdistribution system.Experiments used four kinds of typical water: groundwater, surface water,water from Danjiangkou and recycled water. It found that, biofilm cultivated steadywith controlling DO and chlorine concentration after50days.When changing thewater resource with Larsen index, iron releasing is not clearly, the effluent is clear，and the turbidity meets the standard．After comparison of XRD, α-FeOOH were theprimary crystals in the cast iron sheets, and the crystal type became better, strengthbecame larger. Verifying the further conclusion that the biofilm cultivated steady.The simulation experiment carried out in the laboratory was to research themechanism of corrosion from molecular biology at the water source switch.PCR-DGGE and real-time PCR were used to investigate that the diversity ofmicroorganism on the biofilm was richer than intial stage, biofim scale increasedtolerance to the surrounding environment after cultivating stability. Therefore,microbial populations did not change obviously when switching the water source inthe laster stage. These results suggested that because of IOB and SRB existed on thebiofilm, iron-oxidizing was the primary reaction, water source switch can not changethe populations of microorganism on the biofilm when it cultivated stability.Stabilityof biofilm may control the phenomenon of iron release when the water sourceswitch,especially Larsen index was changed. Biofilms populations was change byDO and chlorine concentration, iron reducing bacteria became the dominant bacteria.The synergistic interactions between the metal surface, abiotic corrosion products,and bacterial cells and their metabolites, which can effectively inhibit pipecorrosion and sustain the stability of water quality.