ABSTRACT
Bioaugmentation, or the use of commercially grown micro-organisms to supplement or replace naturally occurring microbes, is now widely practiced in water and wastewater
treatment (Huban and Plowman, 1997). The micro-organisms used are usually naturally occurring species collected from special sites where natural selection has already favoured microbes adapted to unusual conditions. For example, up to half the microorganisms in coastal waters can degrade hydrocarbons, while meat-processing plants and even septic tanks can yield microbes capable of degrading fats and proteins. These organisms are collected and grown in the laboratory, being cultured on a medium rich in the pollutant they are required to degrade. From this the best strains can be isolated and grown. This enrichment technique can be developed by using mutagenesis to find the most efficient degraders or by producing new custom-built microbes by gene manipulation (Powledge, 1983). In practice, only organisms selected from the environment are used, with mutation or gene manipulation only used for enhanced industrial processes (e.g. the production of enzymes), so that there are no problems about releasing new genetically engineered species into the environment. The microbial culture that is eventually produced is grown in special reactors in order to produce the large quantities needed, then freeze-dried and packaged ready for sale. Most companies market their microbes as a powder that also contains important additives, such as wetting agents, emulsifiers to aid dispersion, and nutrients to aid reactivation and growth. To activate the microbes all that is required is to add warm water and stir. Bioaugmentation is used for the following key applications:
(a) improve removal efficiencies in terms of biochemical oxygen demand (BOD) or chemical oxygen demand (COD) removal;
(b) to improve the degradation of target substances that are often recalcitrant or cause operational problems;
(c) to reduce process instability often caused by fluctuation in the organic loading; (d) to restart or commission treatment plants; (e) to reduce the inhibitory effects of toxic compounds in wastewaters; (f) to improve mixed liquor flocculation and separation; (g) to induce and enhance nitrification; (h) to reduce the accumulation of sludge and scum from aerobic and anaerobic
digesters and lagoons by ensuring complete stabilization.
