The treatment capacity of the wastewater treatment plant for Huttwil, Lotzwil, Langenthal and Aarwangen was inadequate during the 90s, and some of the partially treated wastewater was discharged into small and fragile streams. A total of 18 municipalities established a public limited company (ZALA AG) in 2000, and in 2004 a new, modern wastewater treatment plant was put into operation in Aarwangen, which is constantly kept up to date with the latest technology. TBF was responsible for general project management of the new building and has since advised the managing board and operating staff of the wastewater treatment plant on all pending matters.

Today, the treatment performance of the plant, which operates at a very moderate cost, is higher than that of almost any other plant in the canton of Bern - a success story for the local population and water protection.