New method for efficient control of hydrogen sulfide and methane in gravity sewers: Combination of NaOH and Nitrite

An innovative treatment method by the combination of NaOH and nitrite is proposed for controlling hydrogen sulfide and methane in gravity sewers and overcome the drawbacks of the conventional single chemical treatment. Four reactors simulating gravity sewers were set up to assess the effectiveness of the proposed method. Findings demonstrated hydrogen sulfide and methane reductions of about 96.01% and 91.49%, respectively, by the combined addition of NaOH and nitrite. The consumption of NaNO2 decreased by 42.90%, and the consumption rate of NaOH also showed a downward trend. Compared with a single application of NaNO2, the C/N ratio of wastewater was increased to about 0.61 mg COD/mg N. The greenhouse effect of intermediate N2O and residual methane was about 48.80 gCO2/m3, which is far lower than that of methane without control (260 gCO2/m3). Biofilm was destroyed to prevent it from entering the sewage by the chemical additives, which reduced the biomass and inhibited the recovery of biofilm activity to prolong the control time. The sulfide production rate and sulfate reduction rate were reduced by 92.32% and 85.28%, respectively. Compared with conventional control methods, the cost of this new method was only 3.92 × 10−3 $/m3, which is potentially a cost-effective strategy for sulfide and methane control in gravity sewers.