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The presence of atmospheric H₂S (hydrogen sulfide) is always an indicator of underlying deterioration of concrete and metals caused by what is referred to as H₂S induced corrosion. The gaseous H₂S that is released into the atmosphere is converted to H₂S0₄ (sulfuric acid) by aerobic bacteria that are found in the head space above the wastewater. Since 1979 V&A has been actively involved in the evaluation of the impacts of H₂S on sanitary sewer collection systems and wastewater treatment plants. The following is a brief listing of projects completed by the firm along with a description of the key elements of the projects.

H₂S Corrosion and Odor Control Project Experience

V&A was the prime consultant for Orange County Sanitation District’s Evaluation of Sulfides Treatment in Main Interceptors. This project included the evaluation of existing chemical addition practices, and monitoring of flow rates, temperature, sulfides concentrations, and pH at several locations in four interceptors and through the treatment plant. Analysis included correlation of chemical addition volumes and times with the atmospheric and dissolved sulfide kill results, as well as the impacts to the treatment plant effluent, especially through the activated sludge process. Report recommendations included optimizing chemical dosing to maximize slime-layer kill while minimizing costs and minimizing negative effects on the treatment plant biological systems.
As a subconsultant to Nasland Engineering for the City of San Diego La Jolla-Pacific Beach Manhole Rehabilitation 1998-1999 project, V&A provided an internal inspection of 160 manholes. Manholes varied in design: several coated with a polyurethane or epoxy coating, or lined with T-Lock PVC liner. Several of the manholes had hydrogen sulfide related damage. The final report included a summary of all inspection results, rehabilitation recommendations on a site-by-site basis, and then specifications and a construction cost estimate for rehabilitation of the manholes.
As a subconsultant to Brown and Caldwell, V&A provided field services for the flow monitoring and wastewater sampling of numerous locations throughout the East Bay Municipal Utility District (EBMUD) collection system as part of the Wood Street Interceptor Damage Assessment Project in 1997. V&A personnel conducted laboratory testing of the wastewater samples for dissolved sulfides during the pilot study and provided corrosion expertise and assistance to Brown and Caldwell in the preparation of the final report.
V&A completed a hydrogen sulfide study as a prime consultant for the City of Foster City, California. The work involved the evaluation of 53 pump stations and four force mains. The hydrogen sulfide levels were measured and the extent of damage to the piping and wet wells was determined. A 10-year capital improvement budget was developed to assist the City in planning for the rehabilitation of the pump station wet wells and for a hydrogen sulfide control plan. Of several chemicals which were tested, sodium hypochlorite was found to be the most effective. A Bio Filter was designed and built in 1989, and a second one was built in 1995. The Bio Filters remove odors caused by hydrogen sulfide in the wastewater. Both filters have worked successfully, with a minimal amount of maintenance, since their installation.
As a subconsultant to Camp Dresser & McKee, V&A conducted a pilot study for the Union Sanitary District to determine the effectiveness of sodium hypochlorite, ferric chloride, ferrous chloride, and liquid oxygen to treat approximately 2.2 million gallons per day of raw wastewater. All of the chemicals were found to be effective to a certain extent. However, after evaluating shock dosing with sodium hypochlorite, it was found that for this particular sewer system, sodium hypochlorite was the least costly means of sulfide control. Along with the levels of dissolved hydrogen sulfide, the atmospheric levels of H₂S were also measured to determine if there was a reduction related to the chemical treatment used.
V&A conducted field testing in conjunction with excavation of selected sites along a cement mortar lined sewer force main as a prime consultant to the West County Sanitation District. The objective of the investigation was to determine the remaining wall thickness and the extent of hydrogen sulfide damage along the force main, with particular attention to the line at the transition to gravity flow and at high points along the force main. An H₂S gas sampling meter was installed at the manhole where the force main transitions into a gravity sewer. The meter recorded H₂S levels every 15 minutes for two weeks. The data indicated a diurnal pattern to the sulfide levels which appeared to have the highest levels at night. The report to the District included recommendations for replacement, rehabilitation and chemical treatment of the water to reduce the generation of sulfides in the wastewater flow.

In a subsequent investigation, V&A performed testing of wastewater samples at a pump station to determine the levels of hydrogen sulfide in the flow stream. This information was then used to analyze the possible chemical treatment options. Further testing was performed to evaluate the effectiveness of sodium hypochlorite under various flow conditions.

Some agencies have covered their sedimentation basins and have sealed manholes as a means of odor control however the sealing or covering of facilities almost always results in corrosion due to the concentration of H₂S and resultant H₂SO₄. For example, a pH between 2 and 3 was recorded on the interior surfaces of a primary sedimentation cover. At these pH levels, it does not take long for significant damage to occur on concrete or metallic surfaces.

V&A’s Role in H₂S Corrosion and Odor Control

V&A has extensive experience in conducting condition assessments of H₂S damaged structures and V&A employees are OSHA-required confined space trained. We share these case histories in the hope that the reader may benefit from our past experience. Readers should contact V&A at the number below if any further information or guidance is needed with respect to these services.


Vol 3 No 2 March 2005 *Case History*		for previous articles, visit the Infrastructure Preservation News archives and V&A's web site at www.vaengr.com
V&A's Experience with H₂S in Wastewater Collection Systems By Jose L. Villalobos, P.E. The presence of atmospheric H₂S (hydrogen sulfide) is always an indicator of underlying deterioration of concrete and metals caused by what is referred to as H₂S induced corrosion. The gaseous H₂S that is released into the atmosphere is converted to H₂S0₄ (sulfuric acid) by aerobic bacteria that are found in the head space above the wastewater. Since 1979 V&A has been actively involved in the evaluation of the impacts of H₂S on sanitary sewer collection systems and wastewater treatment plants. The following is a brief listing of projects completed by the firm along with a description of the key elements of the projects. H₂S Corrosion and Odor Control Project Experience V&A was the prime consultant for Orange County Sanitation District’s Evaluation of Sulfides Treatment in Main Interceptors. This project included the evaluation of existing chemical addition practices, and monitoring of flow rates, temperature, sulfides concentrations, and pH at several locations in four interceptors and through the treatment plant. Analysis included correlation of chemical addition volumes and times with the atmospheric and dissolved sulfide kill results, as well as the impacts to the treatment plant effluent, especially through the activated sludge process. Report recommendations included optimizing chemical dosing to maximize slime-layer kill while minimizing costs and minimizing negative effects on the treatment plant biological systems. As a subconsultant to Nasland Engineering for the City of San Diego La Jolla-Pacific Beach Manhole Rehabilitation 1998-1999 project, V&A provided an internal inspection of 160 manholes. Manholes varied in design: several coated with a polyurethane or epoxy coating, or lined with T-Lock PVC liner. Several of the manholes had hydrogen sulfide related damage. The final report included a summary of all inspection results, rehabilitation recommendations on a site-by-site basis, and then specifications and a construction cost estimate for rehabilitation of the manholes. As a subconsultant to Brown and Caldwell, V&A provided field services for the flow monitoring and wastewater sampling of numerous locations throughout the East Bay Municipal Utility District (EBMUD) collection system as part of the Wood Street Interceptor Damage Assessment Project in 1997. V&A personnel conducted laboratory testing of the wastewater samples for dissolved sulfides during the pilot study and provided corrosion expertise and assistance to Brown and Caldwell in the preparation of the final report. V&A completed a hydrogen sulfide study as a prime consultant for the City of Foster City, California. The work involved the evaluation of 53 pump stations and four force mains. The hydrogen sulfide levels were measured and the extent of damage to the piping and wet wells was determined. A 10-year capital improvement budget was developed to assist the City in planning for the rehabilitation of the pump station wet wells and for a hydrogen sulfide control plan. Of several chemicals which were tested, sodium hypochlorite was found to be the most effective. A Bio Filter was designed and built in 1989, and a second one was built in 1995. The Bio Filters remove odors caused by hydrogen sulfide in the wastewater. Both filters have worked successfully, with a minimal amount of maintenance, since their installation. As a subconsultant to Camp Dresser & McKee, V&A conducted a pilot study for the Union Sanitary District to determine the effectiveness of sodium hypochlorite, ferric chloride, ferrous chloride, and liquid oxygen to treat approximately 2.2 million gallons per day of raw wastewater. All of the chemicals were found to be effective to a certain extent. However, after evaluating shock dosing with sodium hypochlorite, it was found that for this particular sewer system, sodium hypochlorite was the least costly means of sulfide control. Along with the levels of dissolved hydrogen sulfide, the atmospheric levels of H₂S were also measured to determine if there was a reduction related to the chemical treatment used. V&A conducted field testing in conjunction with excavation of selected sites along a cement mortar lined sewer force main as a prime consultant to the West County Sanitation District. The objective of the investigation was to determine the remaining wall thickness and the extent of hydrogen sulfide damage along the force main, with particular attention to the line at the transition to gravity flow and at high points along the force main. An H₂S gas sampling meter was installed at the manhole where the force main transitions into a gravity sewer. The meter recorded H₂S levels every 15 minutes for two weeks. The data indicated a diurnal pattern to the sulfide levels which appeared to have the highest levels at night. The report to the District included recommendations for replacement, rehabilitation and chemical treatment of the water to reduce the generation of sulfides in the wastewater flow. In a subsequent investigation, V&A performed testing of wastewater samples at a pump station to determine the levels of hydrogen sulfide in the flow stream. This information was then used to analyze the possible chemical treatment options. Further testing was performed to evaluate the effectiveness of sodium hypochlorite under various flow conditions. Some agencies have covered their sedimentation basins and have sealed manholes as a means of odor control however the sealing or covering of facilities almost always results in corrosion due to the concentration of H₂S and resultant H₂SO₄. For example, a pH between 2 and 3 was recorded on the interior surfaces of a primary sedimentation cover. At these pH levels, it does not take long for significant damage to occur on concrete or metallic surfaces. V&A’s Role in H₂S Corrosion and Odor Control V&A has extensive experience in conducting condition assessments of H₂S damaged structures and V&A employees are OSHA-required confined space trained. We share these case histories in the hope that the reader may benefit from our past experience. Readers should contact V&A at the number below if any further information or guidance is needed with respect to these services. V&A Consulting Engineers 1999 Harrison Street, Suite 975, Oakland, CA 94612 Tel. (510) 903-6600, Fax (510) 903-6601 www.vaengr.com Copyright 2005