Biofilters and Biotowers for Treating Odors and Volatile Organic Compounds
Abstract:This paper provides information related to odor control design criteria used in sizing and selecting biotechnology-based odor control technologies and performance data obtained from various biotechnology-based odor control systems applied in full scale at wastewater treatment plants (WWTPs) across the U.S. It includes data for specific odor-causing compounds and overall odor reduction in terms of odor concentrations as measured by odor panel analysis. The paper also includes performance data for removal of volatile organic compounds.
Biofilters typically are sized to provide sufficient contact time (known as the empty bed residence time, or EBRT) for odorous compounds to be absorbed, adsorbed, and biodegraded. The odorous compounds of concern in WWTP applications typically include relatively high levels of hydrogen sulfide and lower levels of reduced sulfur organic species, such as methyl mercaptan, dimethyl sulfide, and carbonyl sulfide. EBRTs for odorous compounds typically found in wastewater collection and treatment systems vary with the type of system and media selected. For in-ground, open vessel biofilters, EBRTs of 30 to 120 seconds are common, with a nominal EBRT of 60 seconds for organic-based media systems and 60 to 120 seconds for soil-based systems. For enclosed vessels with propriety “high rate” media, EBRTs of 30 to 45 seconds are fairly common. The data presented in this paper suggest that biofilter system EBRTs below 45 seconds may cut into required safety factors in order to maintain reliable odor treatment in typical wastewater treatment applications. Biotower systems typically are operated at significantly lower EBRTs than biofilters, with EBRTs in the range of 10 to 30 seconds being common, but even lower EBRTs have been achieved in the field.
Performance data were collected from 39 operating biotechnology-based odor control systems. EBRTs for the various systems range from 1.8 to 177 seconds. All systems tested were treating foul air collected from WWTP process units. Sources of odorous air loads included collection system lift station wet wells, plant headworks facilities, primary clarifiers, trickling filters, sludge dewatering, and sludge or sludge cake storage facilities.
The performance data are for both total odor and compound-specific removal efficiencies. Laboratory analysis for odor used the odor panel method and followed ASTM E-679-91, “Determination of Odor and Taste Threshold by a Forced-Choice Ascending Concentration Series Method of Limits”. Reduced sulfur compound speciation and quantification was completed using laboratory procedures adhering to ASTM D5504-01 GC/SCD. VOC analysis followed modified EPA Method TO-14A/15 analysis for 68 VOC compounds. Onsite field measurements of H2S were performed using an Arizona Instrument Jerome 631-X H2S analyzer.
Document Type: Research Article
Publication date: January 1, 2006
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