The use of gravity aerators for the prevention of hydrogen sulphide problems in sewer systems
Hydrogen sulphide (H2S) causes odours and concrete corrosion even in very small concentrations. Con-crete corrosion of 5 cm in 5 years has been observed when the hydrogen sulphide content has been 20 ppm. Unavoidable hydrogen sulphide formation in pressure sewers begins when wastewater is put under anaerobic conditions. Anaerobic conditions begin after 0.5 – 2 hours in the pressure sewer. Chemicals, oxygen feed, corrosion resistant materials, biological methods, aeration etc. can be used to prevent problems caused by hydrogen sulphide. A drawback of the use of these methods is that it can be quite expensive. In addition, it is not recommended to have aerobic conditions in the entire sewer system to avoid the sewer acting as a wastewater treatment plant using 0 – 20 mgO2/l/h of oxygen. Using gravity aeration as part of the sewer system, hydrogen sulphide problems can be solved efficiently and cost-effectively, especially when considered in the planning phase. Gravity aerators have proved to be nearly maintenance free only the filters in ventilation require some maintenance.