SOME CORROSION PROBLEMS IN MUNICIPAL WASTE WATER COLLECTION SYSTEM OF GALATI

The system for collecting municipal wastewater effluent collects outside the city population and waste water from several industrial units located in the municipality of Galati. The wastewater comes from unit's related industry such as: edible oil plant, Arcelor Mittal steel mill plant, furniture factory, etc. Wastewater treatment plants handle some of the most corrosive and aggressive liquids and solids known to process engineering. Pipes, tanks, pumps, and all the instrumentation that measures flow, level, pressure, temperature and other parameters are exposed to high concentrations of organic and inorganic compounds, sewage and industrial waste, corrosive chemicals, solids and microbiological organisms of all forms, as well as various gases. Over the last decade the increase in municipal wastewater treatment activities has been confronted with a dramatic increase of sewage sludge amount. Municipal sewage sludge contains complex organic material mainly consisting of carbohydrates (similar to 14%), proteins (similar to 40%), lipids (similar to 10%), lignin (similar to 17%) and ash (30 - 50%). It also contains heavy metal, viruses, bacteria and other microorganisms. This leads to microbiologically induced corrosion (MIC) and severe corrosion problems in equipment and sewage installation plant for waste water treatment. Even though holding, aeration, and sedimentation tanks are constructed of concrete, they inevitably suffer the damaging effects of corrosion and microbiological attack. New waste treatment plants making use of extensive fabrication of carbon steel offer a solution to the infrastructure corrosion problems, although at extremely high cost. The research work presents some results of corrosion resistance evaluation of carbon steel S355JR in different artificial wastewaters which simulate the wastewater collected by Galati sewerage.