Showing papers on "Microbial biodegradation published in 1983"

Microbial degradation of synthetic organochlorine compounds.

Abstract: Although pesticides are designed to be selective, that is, more toxic to harmful organisms than to man and beneficial organisms, their selectivity is not always complete. Most pesticides are degraded chemically and biologically in nature. Their chemical degradation in water and soil is influenced by several factors such as pH, temperature, sunlight, moisture and coexisting inorganic and organic compounds. Examples of organochlorine compounds that have been used as pesticides are shown in figure 1. Because of their persistence in the environment, the use of organochlorine pesticides has been minimized in developed countries. For four decades, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and its derivatives have been widely used as herbicides, especially for the control of brush, jungle and aquatic weeds. The 1968 annual production of these compounds exceeded 60 million pounds in USA 5~ and residues of the substances have been detected in crops, soil, the atmosphere, rainwater and surface water. Technical 2,4,5-T contains traces of the highly toxic compound 2,3,7,8-terachlorodibenzo-pdioxin (TCDD) as an impurity 2. In addition, about 0.0002% of 2,4,5-T is converted to TCDD when wood or brush containing 2,4,5-T is burned. The spraying of the herbicide Orange (butyl esters of 2,4-D and 2,4,5-T in an equal amount) over jungle in Southeast Asia has resulted in the accumulation of TCDD in soil at a mean level of 1.9 ppm with maximum levels of 47 ppm. Pollution by TCDD has developed into a cause of continuing public anxiety throughout the world t~ As summarized in two recent reviews ]4,28, the toxity of organochlorine pesticides and their effects on microorganisms have been studied extensively. Organochlorine compounds used in industry and as pesticides are often found in drinking water. Approximately 80 different organic halogen compounds have been demonstrated in drinking water in the United States 49. Several of these are listed in table 1. Trihalomethanes such as bromodichloromethane, chlorodibromomethane and chloroform, which have been demonstrated ubiquitously in chlorinated water and which are suspected as carcinogens 13, are found even in drinking water. Chlorination of water is used widely for disinfecting water since it is the most effective method for killing waterborne pathogens

Comparison of biodegradation rates in laboratory screening studies with rates in natural waters.

Abstract: Microbial degradation (biodegradation) of organic chemicals is generally recognized as an important removal mechanism in natural systems. For chemicals which reach the aquatic environment in significant quantities, estimates of biodegradability are key in assessing the overall hazard associated with the use of a particular chemical (Larson 1980). Estimates of biodegradability are often generated in the laboratory via biodegradability screening studies (Larson 1979). In screening studies, compounds are tested as sole carbon and energy sources at relatively high (mg/L) concentrations with a dilute synthetic salts solution as the test medium. Degradation is measured nonspecifically by following the amount of carbon dioxide produced or oxygen consumed during microbial metabolism, and soil or sewage are typically used as the source of degradative microorganisms. These experimental conditions do not accurately simulate natural aquatic environments, where chemical concentrations are low (μg/L) and a variety of nutrient conditions and microbial species exist. As a result, legitimate questions have been raised about the reliability of biodegradability screening tests, and the ability of such tests to predict fate of compounds in the “real world” (Alexander 1981).

Microbial degradation of crude oil in sea water in continuous culture

Abstract: The degradation of crude oil in continuous culture of a mixed bacteria population has been studied. The degradation percentage reaches 83 % with a 0.05 h-1 dilution rate and a 6 g 1-1 crude oil concentration. The different crude oil compounds : saturated, aromatic, polar hydrocarbons and asphaltenes are degraded at 97 %, 81 %, 52 % and 74 % respectively.

Large-scale microbial degradation of refractory organic compounds

Abstract: Landfarming is a technique which utilizes microorganisms in soils to biodegrade municipal and industrial wastes and sludges. Many examples of large-scale landfarming of industrial wastes are known in the oil refining, petrochemicals, woodtreating chemicals, and tannery industries in the United States. Biodegradation processes for refractory (environmentally persistent) organic compounds are generally regarded as being limited by the inherent resistance of these compounds to attack by naturally occurring microorganisms, insolubility, and other factors. This research describes the successful biodegradation of an apparently refractory organic compound, 2,4,6-trichlorophenol (TCP), in large-scale lysimeters containing agricultural soils amended with sewage sludge. Thus, within 2 months the levels of TCP in certain agricultural soils contained in lysimeters decreased from an initial 1,000 ppm to 100-10 ppm and the inorganic chloride concentration in the leachate increased from a nominal 50 ppm to 300-700 ppm. In one soil sample the concentration of TCP decreased to 0.5 ppm after 7 months elapsed time.