Biotreatment of H2S- and NH3-containing waste gases by co-immobilized cells biofilter

Gas mixture of H2S and NH3 in this study has been the focus in the research area concerning gases generated from the animal husbandry and the anaerobi c wastewater lagoons used for their treatment. A specific microflora (mixtu re of Thiobacillus thioparus CH11 for H2S and Nitrosomonas europaea for NH3 ) was immobilized with Ca-alginate and packed inside a glass column to deco mpose H2S and NH3. The biofilter packed with co-immobilized cells was conti nuously supplied with H2S and NH3 gas mixtures of various ratios, and the r emoval efficiency, removal kinetics, and pressure drop in the biofilter was monitored. The results showed that the efficiency remained above 95% regar dless of the ratios of H2S and NH3 used. The NH3 concentration has little e ffect on H2S removal efficiency, however, both high NH3 and H2S concentrati ons significantly suppress the NH3 removal. Through product analysis, we fo und that controlling the inlet ratio of the H2S/NH3 could prevent the biofi lter from acidification, and, therefore, enhance the operational stability. Conclusions from bioaerosol analysis and pressure drop in the biofilter su ggest that the immobilized cell technique creates less environmental impact and improves pure culture operational stability. The criteria for the biof ilter operation to meet the current H2S and NH3 emission standards were als o established. To reach Taiwan's current ambient air standards of H2S and N H3 (0.1 and 1 ppm, respectively), the maximum inlet concentrations should n ot exceed 58 ppm for H2S and 164 ppm for NH3, and the residence time be kep t at 72 s. (C) 2000 Elsevier Science Ltd. All rights reserved.