Removal Effectiveness of Reduced Sulfur Compounds In Multi-Stage Biotrickling Filter For Biosolids Handling Processes

The application of biotrickling filters (BTF) has become commonplace for the removal of hydrogen sulfide and for the reduction of odors from air emissions in wastewater treatment facilities. Operation at a low pH of 1.5-2.0 provides an environment for rapid reproduction of thiooxidans bacteria and metabolism of hydrogen sulfide (H2S). An elimination capacity in excess of 90 gm of H2S per cubic meter of media per hour can be achieved. However, a family of organic sulfur compounds (OSCs) that contributes significantly to nuisance odors often co-exist in air emissions. Some of these OSCs are highly resistant to removal in a biotrickling filter due to their low water solubility as expressed by the Henry's Law Coefficient. Solubility is further depressed in a low pH environment. Low removal efficiencies impact the odor removal performance of a biotrickling filter.To address this problem, a dual train biotrickling filter operating at MSD's 120 MGD Morris Forman Water Quality Treatment Center (MFWQTC) was modified from a three stage neutral pH process to a multi functional three stage BTF. The modifications provided the flexibility to operate one or two of the three stages at neutral pH to improve OSC removal with the first stage or stages always recirculated to maintain a low pH. Each stage has a different type of media designed for a specific function and duty, and includes polyurethane cubes and a combination of advanced, inorganic granular media with high surface area. This study traces the removal path of some common OSCs at three stages of operation in the 9,200 cfm multi-stage biotrickling filter system at both acidic and neutral pH levels. Significant data on H2S and OSC compound removal efficiencies has been collected and will be presented.A performance test conducted on August 14, 2008, showed a 99.2% removal efficiency for H2S with inlet H2S ranging between 50 and 100 ppm and an 83% reduction of total RSCs with the bottom two stages at low pH and the top stage at neutral pH. A test was also conducted in the summer of 2009 to compare an Alpha mode (recirculate bottom two stages for low pH and third stage as neutral pH with surface irrigation) on one vessel to a Beta mode on the other vessel (recirculate one bottom stage only). The objective is to increase OSC removal and not sacrifice H2S removal efficiencies. Odalog data has been collected continuously since the spring of 2008 on the inlet and outlet (each vessel) for H2S performance monitoring.