The role of pH on sewer corrosion processes and control methods: A review.

The production and emission of hydrogen sulfide (H2S) in sewer systems is associated with the corrosion of sewer structures and harmful odour. Numerous studies have been conducted to find the best solution to overcome this issue. The pH plays a critical role not only on microbial and chemical processes that are responsible for all processes of corrosion but also on the efficiency of several control methods. This paper first critically reviews the literature on the interplay between pH and various chemical and microbial in-sewer processes, followed by a review of the control methods that depend on pH or indirectly alter pH. The paper argues that proper evaluation of each method should include the impact the control method has on downstream processes. This paper concludes the raising of pH has several benefits but is operationally difficult to implement. It also emphasises single control method may not be as efficient as combination of one or two methods in controlling the production and emission of H2S. Finally, the research requirements and future directions in relation to emerging and potential methods that are not heavily reliant on pH control are discussed.

Hydrogen sulphide control in sewers by catalysing the reaction with oxygen.

This work for the first time shows possible advantage of using ferrous as a catalyst to selectively oxidise hydrogen sulphide in sewer water where biological activity is present. Ferrous catalysed the oxidation reaction in all conditions, but the oxygen requirement for the chemical oxidation of sulphide varied depending on the initial conditions (pH, concentrations of sulphide and oxygen). For initial concentrations of O2 and S2- exceeding 2 mg/L, and a pH between 7.3 and 8.3, approximately 1 mg-O2 was required to oxidise 1 mg-S2-. For the typical conditions experienced in a sewer (pH < 8.0 and O2 and S2- < 2.0 mg/L), approximately 2.0 mg-O2 is required to oxidise 1 mg-S2-. The most efficient O2 usage of 0.25-0.5 mg-O2 was observed with initial O2 and S2- concentrations below 2.0 mg/L and a pH >8.1. The developed mathematical model described the experimental results over a wide range using only three coefficients. The catalytic effect of ferrous selectively increased the oxidation rate of S2- in sewer water samples in which biochemical oxygen utilisation competes for oxygen. Further trials are needed to optimise the method for application in sewer systems where biofilm is present and varying conditions (temperature, H2S concentration, oxygen consumption rate) exist.