MICROBIALLY INDUCED CONCRETE CORROSION IN SEWERS.

摘要

Microbially Induced Concrete Corrosion (MICC) damages sewage collection systemsrnthroughout the world. The theoretical basis of MICC has been under examination for atrnleast 50 years by many researchers worldwide. Researchers at the University ofrnHouston are engaged in a re-examination and advancement of the basic tenets of thisrntheory. Several studies have been performed with the objectives of providing new andrnmore useful information that will allow a fuller understanding of the rate and extent ofrnMICC under different environmental conditions. The objectives of the overall studyrnare: 1) determine the type and number of organisms present in sewage that causernMICC; 2) determine the kinetics of growth and acid production of these organisms; 3)rndetermine the kinetics of the reaction of microbially produced acid with the concreternand 4) use the information obtained in objectives 1, 2, and 3 to develop a processbasedrnmodel that can be used to describe and predict the rates of concrete corrosionrnunder various environmental conditions. This paper summarizes some of the resultsrnobtained during the pursuit of the first three objectives. The numbers of sulfuroxidizingrnmicroorganisms present in sewage have been determined to be as low as 12rnMPN/100 mL to as many as 5 million MPN/100 mL sewage. Studies performed torndetermine the growth kinetics of two sulfur-oxidizing isolates from samples ofrncorroding concrete from Houston sewers have shown that the organisms are inhibitedrnby high concentrations of thiosulfate and that acid production takes place in twornstages. At low pH the reduction of the surface pH of the three types of concrete testedrnin contact with sulfuric acid followed saturation kinetics. First order kinetic modelsrncould be used to describe the mass lost from both Portland and Microsilica cementrnwhen exposed to higher concentrations of sulfuric acid.