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S m e l l T e s t : Smell Test: A C o m p a r i s o n A n d R a n k i n g A Comparison And Ranking O f H y d r o g e n S u l f i d e E m i s s i o n F a c t o r s Of Hydrogen Sulfide Emission Factors How bad does your wastewater treatment plant (WWTP) really smell? Researchers provide a new perspective on headworks odor control and measurement. By Amitdyuti Sengupta with Linda Daly and Bhaskar Kura F ormation and release of hydrogen sulfide (H 2 S) gas from municipal wastewater is a well-recognized problem that has significant impacts on wastewater infrastructure. Impacts of generation and emission of H 2 S from wastewater include corrosion and reduction in the service life of wastewater infrastructure, odor nuisance in the community, and health impacts of wastewater operations and maintenance personnel (Neilsen, et al. WEFTEC 2006). Section 522 of Water Quality Act, 1987 mandates the U.S. EPA to study and document corrosion level in wastewater systems in the U.S. The EPA's study "Hydrogen Sulfide Corrosion: Its Consequences, Detection and Control," conducted on 89 municipalities in September 1991, revealed that 80 percent of the municipalities reported accelerated corrosion and collapse of the wastewater infrastructure. Health Impacts: H 2 S exposure is possible through various routes such as inhalation, oral, and dermal. In a wastewater treatment plant setup, operators face a high risk of H 2 S exposure. Table 1 lists the potential health impacts in humans from the Agency for Toxic Substances and Disease Registry (ATSDR). Table 1: Exposure Routes And Associated Health Impacts Heath Impact Exposure Routes Death Systemic Effect Immunological Effect Neurological Effect Reproductive Effect Development Effect Cancer Inhalation yes yes none yes limited data none none Oral none none none none none none none Dermal none none none none none none none Source: Compiled from ATSDR (Note: "None" indicates no database found on ATSDR website.) Economic and Social Impact: Water Infrastructure Network (WIN) reported in the year 2000 that 50 percent of the $23.5 billion spent nationally for replacement, repair, and addition to wastewater infrastructure all over the U.S. was due to hydrogen sulfide-related corrosion. Consistent H 2 S odor in a neighborhood has the potential to impact the quality of life and negatively influence property prices in the area. Strict air quality regulations and greater public concerns have led to an increased social focus on odor-related issues (Kim et al. 2007). Figure 1 shows corrosion on a sluice gate valve and bar screen at the headworks. Figure 1. Corroded valve and bar screen at monitoring site headworks Need For Research Conventional odor control studies performed by municipalities to design their individual odor/corrosion control strategies largely depend on establishing a dilution to detection threshold (D/T) ratio and ascertaining the recognition threshold (R/T) for air samples collected from the study area. Often these samples for R/T and D/T are collected using a few grab samples (instantaneous samples using tedlar bags) over a period of a few days. Continuous sampling is rarely done since it is cost-prohibitive and time-consuming. These conventional odor studies based on R/T and D/T have a number of limitations and lead to inaccurate conclusions. Therefore, there is a demand for rapidly and economically identifying and forecasting H 2 S emissions from various wastewater infrastructures. Methodology To reduce detrimental health, social, and economic impacts, air quality management tools such as emission factor (EF) for estimating H 2 S emissions from a wide variety of sources including wastewater facilities are very useful. Per the EPA, "an air quality emission factor is the relationship between the amount of pollution released and the amount of raw material processed, or amount (number) of product (units) produced, or amount of work done." Examples of emission factors include: mass of CO 2 emitted per distance driven by a vehicle (kg-CO 2 /km-driven), mass of SO 2 produced per unit amount of electricity produced (kg-SO 2 /KWH- electricity produced), and others. Determining EF is considered an important step in assessing air pollution and subsequent control. 18 wateronline.com ■ Water Innovations