The treatment of waste water in decentralised plant will remain an important component in waste-water management in Europe. Long term it is expected that the number of small-scale waste-water treatment plants in the EU will reach around ten million. The international environmental fair IFAT 2008 brings together the users and suppliers of this technology and these services. In Germany, for example, centralised waste-water treatment facilities operated by local authorities serve around 92 percent of the population. This figure is not expected to exceed 95 percent, even in the long term. Which means that as many as four million people in Germany will remain without access to municipal waste-water treatment facilities, says Dr Elmar Dorgeloh of ‘Abwasser dezentral', a newly created independent consultation and information centre on decentralised waste-water treatment, based at the development and testing institute for waste-water treatment technology at the Rheinisch-Westfälische Technische Hochschule in Aachen (www.abwasser-dezentral.de). Currently the waste water from this sector of the population is being treated in around two million small-scale facilities with four to 50 population equivalents. By 2015, according to Dorgeloh, over half these facilities need to be completely rebuilt, or at least brought up to modern standards.

The same picture is seen in many other European countries. "France, Italy, Poland and Spain also have potential for at least one million small-scale treatment plants each. In the long term we could easily be looking at around ten million mini waste-water treatment plants in the European Union," affirms the waste-water expert.

Significant progress in technology has led to a considerable improvement in the cleaning performance of such decentralised mini facilities, in some cases matching that of larger-scale plant. In particular performance has been boosted by the use of activated sludge processes based on membrane technology for phase separation. As the membrane captures all the solids, the effluent concentrations of all parameters are reduced by the proportions of the filtered materials. In addition, depending on the cut-off of the membranes used, germs can also be captured, thus enabling hygienisation of the effluent.

Planning and building these mini plants has become much easier in recent years, thanks to a largely module-based system and the use of officially authorised building products.

Proper construction is one key requirement of mini treatment plants, but of equal importance in ensuring consistent cleaning performance is proper management and professional maintenance. A recently launched pilot project in the Unna district in Westphalia, Germany, shows how this can be an interesting new business opportunity for large municipal waste-water treatment organisations. Here, for 21 private homes, the local authorities have replaced old treatment facilities, mainly three-chamber pits, with modern small-scale treatment plant based on membrane filter modules. A contract was signed with the site owners, under the terms of which the waste-water treatment company undertakes full responsibility for operation and maintenance of the system, for a period of ten years.

The environmental trade fair IFAT 2008 taking place next year, the most important trade event in the world for environmental technology, recycling and the treatment of water, waste water and sewage, offers a superb opportunity for trade visitors to compare the various technical and economic concepts for decentralised waste-water treatment. At the last IFAT in 2005, over 50 companies involved in this segment came along to exhibit in Munich.