Effects of pH on the simultaneous removal of hydrogen sulfide and ammonia in a combined absorption and electro-oxidation system

• Published in: Journal of hazardous materials 2020-01, Vol.382, p.121011-121011, Article 121011
• Main Authors: Kang, Jeong-Hee, Yoon, Yeojoon, Song, JiHyeon
• Format: Article
• Language: English
• Subjects: Absorption; Ammonia; Electro-oxidation; Hydrogen sulfide; pH effect
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2019.121011

[Display omitted] •We investigated a combined absorption and electro-oxidation process for the pretreatment of biogas containing H2S and NH3.•Two main reactions of the combined system were carried out; simultaneous absorption and competitive oxidation of H2S and NH3.•The mass transfer of H2S increased with increasing pH, whereas that of NH3 was not changed because of high solubility.•The oxidation rate and end-products by the reaction with reactive chlorine species were strongly influenced by pH variation.•In the combined system operation, a neutral pH was appropriate because absorption and oxidation rate could be balanced. Biogas commonly contains both H2S and NH3, and these impurities need to be removed before use. In this study, a combined system consisting of an absorption column and an electro-oxidation reactor was developed to simultaneously treat H2S and NH3. In particular, the effect of the pH (6, 8, and 10) on the system performance was investigated. The mass transfer rate of H2S from the gas to liquid phases was sensitive to pH because of its relatively low solubility at low pHs, while more than 99% of the introduced NH3 was steadily absorbed. Therefore, a pH higher than 8 was favorable for the simultaneous removal of both gases. In the electro-oxidation reactor, H2S was primarily oxidized, while the NH3 oxidation started after H2S was completely eliminated. Furthermore, the oxidation rate and current efficiency of both H2S and NH3 increased with decreasing pH value. The results showed that a low pH was advantageous for the electro-oxidation. In conclusion, the mass transfer rate and oxidation kinetics should be balanced to increase the simultaneous removal of H2S and NH3. Therefore, among the tested pH values, the best performance in the combined system was achieved using a pH of 8.