Surfactants are an indispensable ingredient of relevant products used in households for cleaning of surfaces, garment, as well as personal hygiene. Typically, surfactants after being used are discharged of via waste water. The technology for public sanitation systems for the collection, transportation, and treatment of (municipal) waste water is technically well developed and has been established in many countries. Collected waste water is generally purified in biological waste water treatment plants [WWTPs]. Biological WWTPs are designed to eliminate biodegradable organic matter from waste water, preferably by microbial degradation it to carbon dioxide (CO2) and water (H2O).
The proper treatment of domestic waste water is especially relevant for surfactants since virtually all surfactants exercise a pronounced eco-toxicological effect on aquatic organisms, due to their surface activity. To ensure effective elimination of surfactants, minimum requirements on the (aerobic) biodegradability of surfactants have been established in national and international regulations for detergents (e.g. Regulation (EC) No 648/2004 in the European Union).
The treatment process generates considerable amounts of activated sludge (bacterial biomass) that needs further processing in so-called digesters under anaerobic conditions. Digested sludge can be either disposed or incinerated. Since digested sludge contains important nutrients application as a fertilizer on agricultural areas is the method of choice, if the terrestrial toxicity is well controlled and mitigated.
In Europe, requirements aimed at protecting the aquatic environment from the adverse effects of urban waste water are laid down in the Urban Waste Water Directive (Council Directive 91/271/EEC). Since the effort to construct, operate, and maintain a public sanitation system is considerable, solutions for decentralized sewage treatment, serving smaller communities, should be considered to avoid that untreated sewage is entering the environment.