Biodegradability anaerobic digestion

The major part of the biosphere is aerobic and consequently priority has been given to the study and assessment of biodegradability under aerobic conditions. Nevertheless, there are environmental compartments that can be permanently (e.g. anaerobic digesters) or temporarily anaerobic (e.g. river sediments and soils) and surfactants do reach these. The majority of surfactants entering the environment is exposed to and degraded under aerobic conditions. This is the predominant mechanism of removal even in cases of absence of wastewater treatment practices (direct discharge) and it is estimated that less than 20% of the total surfactant mass will potentially reach anaerobic environmental compartments [1]. Only in a few cases, however, will the presence of surfactants in these compartments be permanent. The presence of surfactants in anaerobic zones is not exclusively due to the lack of anaerobic degradation. Physico-chemical factors such as adsorption or precipitation play an important role as well as the poor bioavailability of surfactant derivatives (chemical speciation) in these situations. 

Surfactants such as LAS and NPEO have been found in compartments with low oxygen content, such as anaerobic sludge digesters or anaerobic continental and marine sediments [14,15,18-25]. One of the possible causes of this persistence is the inhibition of the anaerobic digestion [17,26,27]. Battersby and Wilson [27] observed inhibitory effects of NP at 50 mg CL-1 on methane formation in a survey of the anaerobic biodegradation potential of organic chemicals in digesting... 

During anaerobic biodegradation, the H2 concentration is reduced to a much lower level than that of acetate. The acetate concentration in an anaerobic digester tends to... 

Biogas can be used after appropriate gas cleanup as a fuel for engines, gas turbines, fuel cells, boilers, industrial heaters, other processes, or for the manufacturing of chemicals. Before landfilling, treatment or stabihzation of biodegradable materials can be accomplished by a combination of anaerobic digestion followed by aerobic composting. 

Biological. Vinyl chloride was reported to be a biodegradation product from an anaerobic digester at a wastewater treatment facility (Howard, 1990). Under aerobic conditions. Pseudomonas putida oxidized 1,1,2-trichloroethane to chloroacetic and glyoxylic acids. Simultaneously, 1,1,2-trichloroethane is reduced to vinyl chloride exclusively (Castro and Belser,... 

In addition, anaerobic biodegradation of PEGs with Mns up to 20,000 was reported approximately at the same time in 1983 by three groups (10-12), Anaerobic digestion is also a useful process in sewage disposal systems and the studies on anaerobic metabolism of PEG are important to learning the fate of this compound in ecosystem. Research on this field is in its early stage, and further extensive studies remain to be done in the future. 

Cresols are widely distributed natural compounds. As discussed above, they are formed as metabolites of microbial activity and are excreted in the urine of mammals (Fiege and Bayer 1987) and humans (Needham et al. 1984). Cresols from human urine are probably biodegraded at municipal sewage treatment facilities prior to release to ambient waters. However, for combined septic and storm sewage systems, cresols may be released to surface waters during periods of precipitation when influent volumes exceed treatment plant capacities. Also, in rural and suburban areas where septic tanks are used (o- and m-cresols can resist anaerobic digestion), human excrement may be a nonpoint source release of cresols to groundwater. 

Ballapragada, B.S., Magar, V. S., Puhakka, J. A., Stensel, H. D. Ferguson, J. F. (1994). Fate and biodegradation of tetrachloroethene and pentachlorophenol in anaerobic digesters. In Proceedings of the Water Environment federation 67 th Annual Conference Exposition. Chicago, IL, October 16-20, pp. 265-76. 

Biodegradation aqueous aerobic t,/2 = 168-240 h, based on aerobic soil grab sample data (Kirkland Fryer 1972 Smith Hayden 1981 quoted, Howard et al. 1991) aqueous anaerobic t,/2 = 672 1320 h, based on anaerobic digest or sludge data (Battersby Wilson 1989 quoted, Howard et al. 1991) aerobic rate constant, k = 2.89 x 10 3 Ir1 (Armbrust 2000). 

Biodegradation anaerobic degradation decreased by 30% within 238 d corresponding to a pseudo-first-order k = 1 X 10 d by sewage sludge collected from a mesophilic digester (Gerecke et al. 2005)... 

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