The biogeochemical origin of sewage gases and control of their generation
2022
Namour, Philippe
The review discusses the ″sewer gases″ emitted from wastewater systems, namely hydrogen (H₂), methane (CH₄,), ammonia (NH₃), carbon monoxide (CO), phosphine (PH₃,), hydrogen sulphide (H₂S), carbon dioxide (CO₂) and nitrous oxide (N₂O). Sewer gases are naturally occurring gases resulting from internal biogeochemical processes in sewers due to the natural biodegradation of organic matter (OM). Since they are irritating (NH₃ and PH₃), asphyxiating (H₂, CO₂, CH₄), explosive (H₂, PH₃, H₂S, CH₄) and have a greenhouse effect (CH₄, N₂O, CO₂), they threaten human health and the sustainability of the sanitation system. This is due to H₂S-induced corrosion that can lead to the collapse of large sewer sections. Controlling the production of sewer gas is therefore critical and requires a thorough understanding of the biogeochemical processes in sewers that drive gas production. This is the subject of the first section of the review. The review then describes the biocorrosion mechanisms for concrete and iron rebar in sewer structures, and finally designs new cost-effective mitigation methods based on electron flux management using the redox mechanisms described in the first section. All sewer gases are gaseous by-products of major biogeochemical cycles of carbon (H₂, CO, CO₂, CH₄), nitrogen (NH₃ and N₂O), sulphur (H₂S) and phosphorus (PH₃). Electron exchange is the common denominator in all these gas-producing reactions. In addition, it is through redox reactions that this review presents the sewer gas production processes and looks for control methods. In particular, the review highlights the central role played by the Fe²⁺/Fe³⁺ redox couple, as both electron acceptor and donor in sewer gas production. The two key parameters of physical and chemical control are on the one hand the redox potential, and on the other hand, the temperature, due to Q₁₀ ≈3 of sewer gas-producing reactions.
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