Microbial monitoring and performance evaluation for H₂S biological air emissions control at a wastewater lift station in South Texas, USA

Abstract

A pilot-scale biological sequential treatment system consisting of a biotrickling filter and two biofilters was installed at Waste Water Lift Station # 64 in Brownsville, Texas, USA to evaluate the performance of the system being loaded with variable concentrations of wastewater hydrogen sulfide (H₂S) emissions. In this study, the effectiveness of sulfur oxidizing bacteria along with the distribution of various sulfur species and their correlation with the performance of the biofilters was evaluated. The biofilters were packed with engineered media consisting of plastic cylinders with compacted organic material which was supplied by Met-Pro Environmental Air Solutions (formerly Bio·Reaction Industries). The overall performance of the pilot-scale biological sequential treatment system with an Empty Bed Residence Time (EBRT) of 60s and the overall performance of the biofilter unit with an EBRT of 35s developed a removal efficiency of > 99% at H₂S levels up to 500 ppm. A decrease in performance over time was observed in the first and second sections of the first biofilter unit with the third section of the biofilter unit ultimately becoming the most robust unit removing most of the pollutant. The second biofilter unit was not needed and subsequently removed from the system. The number of CFUs in sulfur oxidizing T.thioparus selective media grew significantly in all four sections of the biofilter over the two months of pilot operation of the biological unit. The sulfur oxidizer growth rates appeared to be highest at low total sulfur content and at slightly acidic pH levels. This study has implications for improving the understanding of the distribution of sulfur oxidizing bacteria throughout the length of the biofilter columns, which can be used to further optimize performance and estimate breakthrough at these very high H₂S input loadings.

Keywords:

• Biofiltration
• sulfur oxidizers
• air emissions treatment
• biofilter
• wastewater lift station emissions

Acknowledgments

Portions of this project were supported by the National Science Foundation sponsored Center for Research Excellence in Science and Technology (CREST) RESSACA and the Institute for Sustainable Energy and the Environment at Texas A&M University-Kingsville. The work represents the findings and opinions of the authors and does not necessarily reflect those of the National Science Foundation. The authors would also like to acknowledge the contributions of Dr. James Boswell and Paul John of Met-Pro Environmental Solutions (formerly Bio·Reaction Industries LLC). Significant contributions and assistance from personnel of the Public Utilities Board (PUB) of Brownsville, Texas are also recognized. Dr. Paca was supported by the Ministry of Education in the Czech Republic, Project AMVIS ME09031.