Reduction of hydrogen sulfide gas in a small wastewater collection system using sodium hydroxide

The Kennebunk Sewer District collection system experienced H₂ S-induced corrosion downstream of terminus manholes for the Wells Road and Boothby Road pumping stations. An automated odor control system using sodium hydroxide (NaOH) was developed to mitigate further corrosion. System performance was quantified by recording the [H₂ S] in the terminus manholes before and after NaOH treatment. Preliminary evaluation at the Wells Road facility demonstrated significant (p < 0.001) reduction in the average [H₂ S] between the treatment (4.8 ± 0.3 ppm) and control (67 ± 1.5 ppm). Permanent systems installed at both facilities in 2017 yielded similar positive results. The average [H₂ S] in the Wells and Boothby Road terminus manholes reduced from 89.4 ± 1.0 to 8.0 ± 0.1 ppm and from 7.9 ± 0.2 to 0.82 ± 0.06 ppm, respectively. This work demonstrates the ability of the NaOH system presented here to minimize emission of corrosive H₂ S gas in small collection systems. PRACTITIONER POINTS: Biologically-produced hydrogen sulfide (H₂ S) gas corrodes sewer collection system components and results in premature asset failure. Maintaining wastewater pH above 8.5 by injecting sodium hydroxide (NaOH) minimizes H₂ S emission by shifting the molar distribution of sulfur species and partially inhibiting the anaerobes that produce H₂ S. The practical application of this approach may be limited to small wastewater collection systems.