Aerobic Biodegradability

The ultimate aerobic biodegradability of plastic materials in an aqueous medium can be controlled by measuring the oxygen demand in a closed respirometer (84). 

The standard ASTM D6954-04 is used for the exposure of plastics that can degrade by a combination of oxidation and biodegradation (87). This standard should permit the comparison and ranking of the overall rate of the environmental degradation of plastics in the course of thermal or photo oxidation. Each degradation stage is independently evaluated to allow a combined evaluation of a polymer s environmental performance. 

The ISO standards 14852 and 14855 (88,89) have been recently revised in the form of ISO 14855-1 2012 (90). This standards describes a method for the determination of the ultimate aerobic biodegradability of organic plastics materials imder controlled composting conditions by the measurement of carbon dioxide evolved and the degree of disintegration of the plastic at the end of the test. 

This method is designed to simulate the typical aerobic composting conditions for the organic fraction of solid mixed mimicipal waste. The test material is exposed to an inoculum which is derived from compost. The composting takes place in an environment wherein temperature, aeration and humidity are closely monitored and controlled. The test method is designed to yield the percentage conversion of the carbon in the test material to evolved carbon dioxide as well as the rate of conversion. 

A variant of this method, uses a mineral bed, i.e., vermiculite inoculated with thermophilic microorganisms obtained from compost with a specific activation phase, instead of a mature compost. This variant is designed to yield the percentage of carbon in the test substance converted to carbon dioxide and the rate of conversion. 

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Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

API, Modeling Aerobic Biodegradation of Dissolved Hydrocarbons in Heterogenous Geologic Formations, Pubhcation No. 848-00200, American Petroleum Institute, Washington, D.C., 1995. 

Stasinakis AS, Thomaidis NS, Nikoiaou A, Kantifes A (2005) Aerobic biodegradation of organotin compounds in activated siudge batch reactors. Environmental Pollution, 134(3) 431-438. 

Aerobic biodegradation of trichloroethylene occurs by cometabolism with aromatie eompounds (Ensley 1991) and thus requires a cosubstrate such as phenol (Nelson et al. 1987, 1988) or toluene (Fan and Scow 1993). Trichloroethylene degradation by toluene-degrading baeteria has been demonstrated in the presence, but not absence, of toluene (Mu and Scow 1994). Isoprene, a structural analog of trichloroethylene, has also been used as a cosubstrate for triehloroethylene oxidation by some bacteria (Ewers et al. 1990). One source of inhibition of degradation in the absence of cosubstrate may be the toxieity of triehloroethylene itself to indigenous bacteria. 

The aerobic biodegradation of monocyclic azaarenes frequently involves reduction (Chapter 10, Part 1), but purely chemical reduction may take place under highly anaerobic conditions. This has been encountered with the substituted l,2,4-triazolo[l,5a]pyrimidine (Flumetsulam) (Wolt et al. 1992) (Figure 1.27). 

Taylor BF, DC Gilchrist (1991) New routes for aerobic biodegradation of dimethylsulfoniopropionate. Appl Environ Microbiol 57 3581-3584. 

Rnss R, C Muller, H-J Knackmuss, A Stolz (1994) Aerobic biodegradation of 3-aminobenzoate by Gram-negative bacteria involves intermediate formation of 5-aminosalicylate as ring-cleavage substrate. FEMS Microbiol Lett 122 137-144. 

Danko AS, M Luo, CE Bagwell, RL Brigmon, DL Freedman (2004) Involvement of linear plasmids in aerobic biodegradation of vinyl chloride. Appl Environ Microbiol 70 6092-6097. 

Barth JAC, G Slater, C Schiith, M Bill, A Downey, M Larkin, RM Kalin (2002) Carbon isotope fractionation during aerobic biodegradation of trichloroethene by Burkholderia cepacia G4 a tool to map degradation mechanisms. Appl Environ Microbiol 68 1728-1734. 

Hirschorn SK, Ml Dinglasan, M Eisner, SA Mancini, G Lacrampe-Couloume, EA Edwards, BS Lollar (2004) Pathway dependent isotopic fractionation during aerobic biodegradation of 1,2-dichloroethane. Environ Sci Technol 38 4775-4781. 

Hunkeler D, N Andersen, R Aravena, SM Bernasconi, BJ Butler (2001) Hydrogen and carbon isotope fractionation during aerobic biodegradation of benzene. Environ Sci Technol 35 3462-3467. 

Clemente IS, MD Mackinnon, PM Fedorak (2004) Aerobic biodegradation of two commercial naphthanic acids preparations. Environ Sci Technol 38 1009-1016. 

The pathways for the aerobic biodegradation of alkylated benzenes have been elncidated in extensive investigations and have been discussed in Chapter 8, Part 1, so that only salient featnres are briefly snmmarized here. The genes for the degradation of toluene may be either chromosomal or... 

Calmon-Deeriaud, A. Bellon-Maurel, V, Silvestre, K Standard Methods for Testing the Aerobic Biodegradation of Polymeric Materials, Vol 135, pp. 207-226. 

Tetrachoroethylene (perchloroethylene, PCE) is the only chlorinated ethene that resists aerobic biodegradation. This compound can be dechlorinated to less- or nonchlorinated ethenes only under anaerobic conditions. This process, known as reductive dehalogenation, was initially thought to be a co-metabolic activity. Recently, however, it was shown that some bacteria species can use PCE as terminal electron acceptor in their basic metabolism i.e., they couple their growth with the reductive dechlorination of PCE.35 Reductive dehalogenation is a promising method for the remediation of PCE-contaminated sites, provided that the process is well controlled to prevent the buildup of even more toxic intermediates, such as the vinyl chloride, a proven carcinogen. 

Calculation of the Requirements in Oxygen and Macronutrients (N, P) for the Aerobic Biodegradation of Toluene... 

An 02 flow must be maintained through the contaminated zone at a level sufficient for the aerobic biodegradation of contaminants. Note that during bioventing the main aim is the maximum utilization of 02 by the microbial cultures. For this reason, air flow rate is usually an order of magnitude lower than that applied in simple SVE systems. A simple empirical rule is that the mean residence time of air in the contaminated soil pore volume should be between 1 and 2 days. 

Mills and colleagues58 describe the use of these formulations to predict aerobic biodegradation in surface waters and present methods of adjusting for temperature and nutrient limitations. This approach to predicting biodegradation is problematic because it is difficult to obtain empirical coefficients in the deep-well setting. 

Addition of oxygen to die subsurface may enhance aerobic biodegradation... 

A full-scale cleanup was performed using in situ bioremediation to treat MTBE and BTEX at a service station in Massachusetts. Soil at the site consists of a layer of sand and gravel underlain by peat, silt, and clay. The in situ bioremediation system consisted of 12 injection wells and two butane injection panels used to stimulate cometabolic aerobic biodegradation of the contaminants in groundwater. The system was operated between October 2000 and January 2001. MTBE concentrations were reduced from 370 to 12 pg/L and BTEX contamination in groundwater was reduced by approximately two orders of magnitude during the 4-month period.74... 

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