Using plants and microbes to purify polluted industrial wastewater

Wetlands are nature’s water filters. They collect water around river mouths and marshes, and whole communities of plants and micro-organisms feed off detritus in these murky depths.

Conventional chemical treatments of industrial waters consume cash, energy and time. Wetlands, by contrast, grow and clean themselves while they act as super-efficient absorbers of phosphates, nitrates and other environmental hazards.

The INDCONWET project applies these natural abilities to industrial wastewater. Toxic by-products in run-off from industrial plants can contaminate drinking water supplies and can be hazardous to health. By installing wetlands next to wastewater sources, the INDCONWET partners are growing a series of purification gardens in Slovenia, Austria and Croatia.

Danijel Vrhovsek, a researcher at Limnos, the Slovenian project partner, says “constructed wetland is inexpensive to build and easy to operate. It also has a larger buffering capacity than conventional treatments to cope with accidents.”

Boosting the filter capacity of each square metre is a key goal. Mira Shalabi, Project Co-ordinator at Bieco, the Croatian project partner, explained that “one disadvantage of constructed wetlands is that they need a bigger area than conventional treatment sites to do the same job.”

However, what they lack in space saving, constructed wetlands make up for in increased efficiency. Bieco’s pilot wetland near Zagreb has reduced concentrations of suspended solids in wastewater by up to 98%, and phosphorous and nitrogen content by 60–85% compared to the 30-40% reduction by conventional methods.

Such results meet water protection standards laid down in EU directives, and make the re-use of industrial wastewater possible.

Different industries produce different pollutants, and INDCONWET is tailoring the design of constructed wetlands to specific needs. “The efficiency of a constructed wetland depends on plant species, substrate selection and microbiological associations,” says Vrhovsek. Project partners are testing various combinations to see which will most efficiently remove pollutants from waste produced by the dairy, detergent, food and fish processing industries.

Constructed wetlands are attractive environments that also remove carbon dioxide and produce oxygen. “Wetlands are an aesthetic solution that provide valuable new habitats for wildlife, which can be used in tourist areas,” says Shalabi.

INDCONWET is a follow-up to the E! 1393 SECONWET project, which won the EUREKA Lillehammer Award for the environment in 2001. Vrhovsek says that this success played an important part in securing financial support for INDCONWET from the Slovenian and Croatian governments. “The Lillehammer prize helped local authorities accept constructed wetlands as a viable alternative to conventional wastewater treatment. As a non-bureaucratic network linking research and the private sector, EUREKA is easy to work with, and has raised the recognition of results at local and national level.”