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Microbes can deal with surfactants

A wide variety of surfactants are used in industry and need to be removed from wastewater, but a similar variety of bacteria can be applied to the task

Global production of surfactants (“surface active agents”) now exceeds 15 million tonnes per year and these compounds find extensive use in household cleaners, personal care products, paints, pesticides, textiles, petroleum recovery, polymers and the pulp and paper industry. Hence it is not surprising that significant quantities of surfactant may end up in the wastewater treatment plant, where they must be removed as part of the treatment process.

Most surfactants in significant use today are readily biodegradable by a range of microbial species but high levels can cause effluent toxicity, disruption of the microbial floc, increased growth of filament formers and excessive foaming. This means that breakdown may not happen to the required degree in the treatment plant and partially degraded surfactants can pass through to discharge, elevating BOD and COD and risking breach of consent limits, as well as the clearly undesirable result of releasing them into the environment. The addition of suitable bacteria can greatly enhance surfactant breakdown in the wastewater treatment plant and helps to avoid these problems.

Surfactants are amphiphilic molecules meaning that they consist of both hydrophilic (“water-loving”) and hydrophobic (“water-hating”) portions. This enables them to adsorb at liquid/liquid, solid/liquid and gas/liquid interfaces, lowering liquid surface tension and endowing them with their cleaning, emulsifying, dispersing and wetting properties. According to the charge carried by the hydrophilic head portion of the molecule, surfactants may be non-ionic (e.g. alcohol ethoxylate), anionic (e.g. sodium lauryl sulphate), cationic, (e.g. quaternary ammonium compounds) or amphoteric (e.g. cocamidopropyl betaine).

This gives rise to a wide variety of surfactants with different properties, and microbial breakdown of these complex molecules tends to occur in stages. For example, a typical breakdown pathway for the anionic surfactant linear alkylbenzene sulphonate would be: ω- and β-oxidation of the straight alkyl chain; removal of the sulphonate group by desulphonation; and then breakdown of the remaining benzene ring, e.g. oxidation of phenylacetic acid.

As for other complex molecules, it is therefore essential to select bacteria with suitable metabolic abilities and a consortium of organisms is often required for complete biodegradation as a particular species or strain can only carry out one step of the breakdown pathway. This synergism between members of the microbial population is very important for surfactant breakdown.

Biological Preparations supplies consortia of bacteria that are capable of breaking down non-ionic, anionic, cationic and amphoteric surfactants.

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