Hidrológiai Közlöny 1999 (79. évfolyam)
4. szám - A Magyar Hidrológiai Társaság XVII. Országos Vándorgyűlése, Miskolc, 1999. július 7–8.
381 Emission of volatile reduced sulfiir compounds from natural and anthropogenic sources A gázhalmazállapotú, redukált kénvegyületek emmissziójának természetes és antropogén forrásai István Dévai 1, Ronald. D. DeLaune 1, William H. Patrick, Jr. 1 and György Dévai 2 1 Wetland Biogeochemistry Institute, Louisiana State University, Baton Rouge, LA 70808, U.S.A. 2Department of Ecology, L. Kossuth University, Debrecen, H-4010, Hungary Abstract: The interest and research in volatile reduced sulfur oompounds have increased iapidly during the last dccade because of their influence on air pollution, climatic effects and precipitation chemistiy. Recent estimates of natural sulfur emission have ídentifíed the importance of biogenic sources of volatile reduced sulfur compounds. Anthropogenic sulfur emissions are comparable to but probably somewhat larger than natural emissions. In this paper highlights of the following laboratory and field experiments are presented (1) the production of volatile reduced sulfur compounds (hydrogen sulfide, carbonyl sulfide, methanethiol, dimethyl sulfide and carbon disulfide) in salt marsh sediment in laboratory microcosms as influenced by soil redox conditions (2) the seasonal and diumal field sulfiir gas emissions from wetlands along a salinity gradient in Louisiana Gulf Coast (salt, brackish and freshwater marshes) (3) the quantity and composition of reduced malodorous sulfur gases emitted to the atmosphere at sewage treatment plants of Baton Rouge (Louisiana, U.S. A.) at various steps of the treatment process (4) the quantity and composition of reduced malodorous sulfur gases being produced in wastewater sludge as influenced by redox conditions. Key words: sulfur emission, wetlands, sewage treatment plants, redox conditions, malodorous sulfur gases Introduction The increase in the sulfur emission from anthropogenic sources (such as coal, oil and natural gas buming) has resulted a growing interest in the atmospheric sulfiir budgct because of the potential role volatile sulfur compounds play in the acidic deposition, global climate changes and photochemical reactions in the atmosphere mcluding smog formation Recent estimates of natural sulfur emission have alsó identified the importance of biogenic sources of volatile reduced sulfur compounds. Coastal manne environments such as salt, brackish and freshwater marshes, swamps and intertidal zones are major sources of sulfur gases but reported rates of sulfur gas emission can vary by orders of magnitude, creating uncertainties in wetlands contribution to the global atmospheric sulfur budget. Despite the wide-ranging research on this subject, our knowledge about production of different reduced sulfur gases as aflected by soil and sediment conditions (redox, pH, temperature, etc.) is alsó extremely limited. Oxidation-reduction (redox) processes play a major role in the microbial degradation of organic carbon and nutrient chemistry and on the mobility and fáte of environmental contaminants such as toxic metals, pesticides, synthetic organics and petróleum hydrocarbons. Anthropogenic sulfur emissions are comparable to but probably somewhat larger than natural emissions. Although the combustion of fossil fuels accounts for 80 to 85 % of the totál but other industnal sources are alsó important During transportation of sewage to treatment facilities the resultant anaerobic conditions produce a large amount of malodorous gases at manholes and terminals. Sulfur-bearing gases represent compounds with the lowest odor detection threshold. Emission of these compounds to the atmosphere from wastewater collection and treatment facilities is a growing maintenance and environmental problem. The presence of these malodorous gases is of concem because of potential health hazards and corrosive attack on concrete. An increasing public intolerance alsó is conceming odors emitted to the atmosphere from sewage and wastewater treatment facilities. Redox conditions and available electron acceptors are alsó important in wastewater purification determining the rate of organic matter decomposition in aerobic/anaerobic environments Due to the wide rangé of oxidation states and the variety of sulfur compounds with carbon and oxygen we are a long way from understanding sulfur chemistry in natural and man-operated systems. Objectives Our main goal was to dctermine in laboratory and field expenmcnts: (1) the production of volatile reduced sulfur compounds (hydrogpn sulfide, carbonyl sulfide, methanethiol, dimethyl sulfide and carbon disulfide) in salt marsh sediment in laboratory microcosms as influenced by soil redox conditions (2) the seasonal and diumal field sulfur gas emissions from wetlands along a salinity gradient in Louisiana Gulf Coast (salt, brackish and freshwater marshes) (3) the quantity and composition of reduced malodorous sulfur gases emitted to the atmosphere at sewage treatment plants of Baton Rouge (Louisiana, U S A.) at various steps of the treatment process (4) the quantity and composition of reduced malodorous sulfur gases being produced in wastewater sludge as influenced by redox oonditions (representing a rangé from anaerobiosis to the borderline of aerobiosis). Methods In the field measurements solid adsorbent preconcentration was used to trap reduced gaseous sulfur compounds using emission flux chambers. With the aid of portable air samplers tnplicate samples were collected along a salinity gradient in Louisiana Gulf Coast (from salt, brackish and freshwater marshes) and at sewage treatment plants of Baton Rouge (Louisiana, U S A.) In the laboratory experiments salt marsh sediment and sewage sludge suspensions were equilibrated (at 25±2 OC) in laboratory microcosms at various redox conditions using a modification of the redox controlled system developed by Patrick and co-workers. The suspensions' redox potential in microcosms was maintained at a preselected level within ± 20 mV. Suspensions were continuously purged with compressed gases with a flow rate of 20 ml/min. Oxygen free nitrogén, compressed air and pure oxygen or their combinations were used depending to the desired redox level. To monitor and determine the production of reduced volatile sulfur compounds samples were collected from the purge gas stream exiting the microcosm using solid adsorbent preconcentration technique. Following the trapping procedure the adsorption tubes were thermally desorbed and trapped sulfur gases were analyzed using a gas chromatographic method. The desorption apparatus (Dynatherm Thermal Desorption Unit Model 890) was connected directly to the gas chromatograph. The valve compartment and the transfer Íme temperature were maintained at 110 °C, the desorptron chamber temperature 310 °C, desorption time was 2 .0 min. Separation of the sulfur gases (hydrogen sulfide, carbonyl sulfide, methanethiol, dimethyl sulfide and carbon disulfide) was conducted on a gas chromatograph (Perkin Elmer Model 8700) equipped with a 1.4 m x 1/8" OD Teflon (FEP) column packed with 40/60 Carbopack B HT 100 and flame photometric detector. The carrier gas (nitrogén of high punty) flow-rate was 20 ml/min, the detector temperature was 150 °C, the column temperature was programmed from -20 °C to 75 °C at 30 °C/min rate (using a liquid carbon dioxidé subambient accessory). Working standards consisted of different sulfur gases (above) diluted in nitrogén gas (Scot Specialty Gases). Excellent recoveries, adequate separation, resolution, calibration and stable retention times of analyzed volatile sulfur compounds were obtained using this optimalized thermal desorption and gas chromatographic method Results Following presented the brief deseription of main results associated with goals above:
