ABSTRACT
Biodegradation can generally be defined as an elimination of an organic compound from the ecosystem through the enzymic action of ambient microorganisms. These include predominantly bacteria and, to a certain extent, also fungi. Higher organisms such as algae, protozoans and plants play only a marginal role in biodegradability. The rate and extent of biodegradation depend on the microbial count and species, chemical structure of the organic compound and on the environment in which the degradation takes place. The degradation can proceed both aerobically and anaerobically.1−4
Degradation can in principle be ultimate or partial:
(i) Complete degradation denotes the transformation of the organic compound to carbon dioxide and water, with a concomitant formation of fresh microbial biomass; and
(ii) Partial degradation involves either a partial decomposition of the molecule (eg degradation of an aliphatic chain up to a quaternary carbon atom) or the formation of new, more complex compounds which are biologically stable (eg formation of polyphenols from simple phenols), ie biotransformation. Partial degradation is often associated with primary degradation. This term derives from the study of surfactants; in this field, primary degradation denotes a minimum transformation of a molecule which leads to the disappearance of some of its characteristic properties. For instance, a substantial shortening of the hydrophobic aliphatic chain in surfactants leads to a loss of surface activity and thereby to a loss of the foaming ability. The term primary degradation was adopted in a period when detergent legislation were being promulgated, and has been losing its dominance with the advent of legislation on chemicals. Partial degradation cannot be considered environmentally sufficient since any ensuing stable metabolites may be accumulated in the environment.
