Researches On The Interaction Between Biofilm And Corrosion Characteristics Of Ductile Iron/PE Pipes Based On Reclaimed Water

The supply of water resources is related to the beneficial to the people's livelihood.To some extent recycled water as a new renewable resource can alleviate the shortage of drinking water resources in China also related to the water supply crisis.Network system is the last link of water contact with residents,landscape,factories and other areas,plays a very important role in water supply system.Whether it is considered from the historical or the economy factors,China has 50% of the pipes are used in ductile iron pipe.This pipe is seriously aging that rust corrosion caused serious pathogen retention.So it is reduce the pipeline water capacity and pipeline secondary pollution,affecting the safety of water.Due to the rapid development of research and application of PE pipe,PE pipe of the global consumption in 2010 amounted to 500×10~4 tons.There is lack of nutrients in the recycled water pipe,pipe surface due to the adhesion of bacteria can form biofilms.The addition of different pipes and different disinfectants will affect the growth of the biofilm.In order to ensure the biological stability of the reclaimed water pipe network,it is very important to study the biofilm colony properties and its influencing factors in the pipeline.It is less study on the current situation of the actual water pipe network,the distribution of biofilm in different pipeline.This paper is writing by homemade device simulation of biofilm reactor to imitate actual pipe network of recycled water,research of the difference of nodular cast iron pipe and PE pipe between,such as water quality change,biofilm community structure characteristics and the pipe wall corrosion situation.(1)The reactor is running for 4 days,microbial biofilm began to gather and formation on thel surface of the wall.At 28 days,the biofilm biomass of PE pipe reached the maximum and the maximum value of ductile iron was formed in 35 days,and then both of the biomass is constantly decreasing.After reaching a certain thickness of the biofilm in the CDC reactors,caused them to fall off their own by the action of shearing force.The total number of bacteria in the pipe network is the largest,up to 6.31×106cfu/cm2.Mixed disinfectant was added in reclaimed water.On the one hand,a good control of the breeding of bacteria in the water,on the other hand also increased the COD and TOC content in the wall of water and,the content of both of them are increasing along with the pipe network.With the regression equation of TOC and COD,the correlation coefficient is greater than 0.9 and almost equal to 1,which shows that the linear relationship between them is significant.Under the unit area,the EPS protein and polysaccharide in the biofilm showed a trend of increasing first and then decreasing.The combined EPS protein and polysaccharide showed a clear trend along the trend.(2)The microbial diversity and community structure of the biofilm were studied by the combination of traditional biology and molecular biology methods.Scanning electron microscopy was used to observe the biofilm,the surface distribution of the bacteria were mostly aureus and Coli.There are gating two dominant species respectively Proteobacteria and intends to the phylum Bacteroidetes,class level gamma-deformation Proteobacteria was the dominant species in reclaimed water.Pipe has a great influence on the biodiversity and community structure,in terms of biological diversity,Ductile iron > PE pipe;in addition,together with two kinds of pipe bacteria only has Sphingomonas.The concentration of residual chlorine on biofilm of biological was diversity,and the effects of community structure varies was depending on the tube,the concentration of residual chlorine of PE pipe has little effect.It has significantly effect of residual chlorine concentration on nodular cast iron pipe.It has different factors to effects of reclaimed water pipe wall biofilm microbial community structure.At the phylum level,the pipe is the main influencing factor;the concentration of disinfectant is the main influencing factor.(3)At the same time,the corrosion of nodular cast iron pipe wall in the C1 device without adding disinfectant is more serious than that of the C2,C3 and C4 devices with disinfectant.Under the same conditions,residual chlorine concentration in mg / L of C1 device,with the increase of the use of a pipeline,pipe wall corrosion surface more and more serious.The pipeline is always containing plenty of residual chlorine case,the corrosion of pipeline is not serious,some regions is pitting.The composition of corrosion products on the surface of nodular graphite cast iron is mainly composed of Fe,O and C,which indicate that the corrosion products are mainly carbon and oxygen compounds and iron oxide compounds.Under the condition of chlorine resistant bacteria,the microorganism was distributed in the corrosion products,and the products were composed of the biological membrane.The corrosion layer formed by the biological film has stronger inhibition on the corrosion of nodular cast iron.In the environment of reclaimed water,the biofilm can promote the corrosion of nodular cast iron in the early stage,and the stable growth of the biofilm can protect the surface of nodular cast iron.