Preliminary Research On Cast Iron Microbiologically-influenced Corrosion Characteristics And Evaluation Index In Reclaimed Water

With the growth in demand for water, wastwater reclamation and reuse becomesincreasingly important to enhance water supply reliability. Reclaimed water provides anutrient-rich condition to microbial growth, which promotes the microbiologically-influnenced corrosion (MIC). In this research, reclaimed water static cultureexperiments were implemented to probe the mechanisms and characteristics of MIC inreclaimed water environment. And water quality regulating experiments wereimplemented to find out key factors to promote MIC. At last, response surfacemethodology was used to fit the relationship formula between MIC rate and key factorsconcentration, and a method was established to evaluate the MIC ability based on thisformula.From the15-day static culture experiments, microorganisms in unsterilized systempromoted the cast iron corrosion before biofilm formed and inhibit it after. Theimmature biofilm promotes the anode and cathode reaction to accelerate iron corrosionin the early stage, while the mature biofilm increases the iron surface diffusionresistance to2.381015/cm2, inhibiting the cast iron corrosion in the later stage.Besides, the biofilm of unsterilized system coupon surface hold up more35.03%of Pthan inorganic product film, which further inhibit the cast iron corrosion after biofilmformed. According to water quality regulating experiments, COD, NH4+-N and total Fecan promote the MIC rate of reclaimed water pipe line significantly. When the CODincreased from15mg/L to120mg/L, the MIC rate increases from0.0060mm/a to0.0457mm/a. When the NH4+-N increased from0mg/L to8mg/L, the MIC rateincreases from-0.0017mm/a to0.0293mm/a. When the total Fe increased from0.2mg/L to1.4mg/L, the MIC rate increases from0.0082mm/a to0.0313mm/a. Thesethree factors enhance the promoting role of microorganisms to cathodic corrosionreaction.Design-Expert8.0.0.5software was used to multiple regression simulation theformula of these three factors concentration to MIC rate (MR). For this formula, F is63.8,“Prob> F”is lower than0.0001, and predictive average absolute percentage erroris9.233%. Based on the formula, an evaluation index of MIC in reclaimed waterenvironment is build up. The evaluation criteria of this index are: if the index less than0,microorganisms can inhibit pipe line corrosion, then the integrity of the biofilm should be preserved. If the index in the range of0-0.025mm/a, microorganisms can corrodepipe line slightly, then measures should be taken to inhibit MIC according to specificcircumstances. If the index greater than0.025mm/a, the MIC must be controlled. Atlast, by using this classification evaluation criteria, existing reclaimed water MIC abilitywere evaluated. The result is: reclaimed water used to surface recharge has slight levelMIC ability, and to deep recharge is protection level, the total Fe<0.8mg/L ornamentalriver reclaimed water and total Fe<1.0mg/L landscape reclaimed water is slightly level,the rest are all control level.