BIOFILTRATION OF POTW ODORS: PROBLEMS AND SOLUTIONS

Control of odorous emissions is one of the problems that nearly every wastewater treatment plant must face. The major component of these odors is often hydrogen sulfide (H2S) and other organo-sulfur gases such as sulfides, disulfides, and mercaptans. Biofiltration is proven as an effective treatment option for sulfur-containing odors. In recent years, more and more biofilters have been installed worldwide. Properly designed and operated, greater than 99% of contaminant removal efficiency for both H2S and other organo-sulfur compounds has been widely reported.However, the longevity of improperly designed biofilter systems as well as consistent performance with high removal efficiency during long-term operation is sometimes problematic. Performance deterioration and even biofilter failure have been reported.During the biofiltration process, H2S and other sulfur-containing compounds are used by sulfuroxidizing bacteria as energy sources and are converted to odorless compounds such as elemental sulfur and sulfuric acid. The acid produced during the biological reaction can cause corrosion, clogging, channeling, and system failure. The performance of the biofilter can deteriorate quickly within a few months at high sulfur loadings.Based on 200 days of laboratory testing and years of field biofilter data, this paper discusses the major causes of biofilter performance deterioration. Among the many reasons, most biofilter failures are caused by media acidification either directly or indirectly. A pH profile along a biofilter treating H2S shows that the media pH changes quickly from 7.0 to as low as 0.8. Media amendment with calcium carbonate is not effective and causes other problems. Formation of elemental sulfur is an indication of system overloading and short-circulation. Nutrient addition is often ignored by most biofilter users. The authors discuss solutions to these problems from both the design and operational perspectives. The paper indicates that biofilters can provide effective, long-term odor removal operation when designed and operated properly.