Experience with establishment and operation of reed bed treatment for small communities in the UK

Abstract

The design and development of constructed reed beds for secondary, tertiary and storm outflow treatment is described from the experience of a major water utility in the Midland region of the UK. There were only two trial sites in 1987, but 125 sites by June 1995. The problems and their resolution with the establishment ofPhragmites in gravel filled beds are described.

Two secondary treatment systems with horizontal subsurface flow beds arranged in terraces show that dilute sewage can be treated to a good secondary standard, but that nitrification is likely to be only partially complete. The example of four tertiary treatment applications showed that, for beds sized at 0.7 to 1.2 m²/pe, effluents consistently averaged better than 5 mg/l BOD₅ and 10 mg/l TSS. Three sites showed improved removal of ammonium nitrogen (N) after the first year, with better than 50% removal. One site, treating highly nitrified secondary effluent, showed a small net increase in ammonium-N even after 4 years. Samples taken by the regulatory authority from 79 sites confirm the ability of the system to meet tight standards for BOD₅. A comparison made of the performance of storm reed beds during three storm events showed relatively consistent removal of BOD, TSS, ammonia nitrogen and TON.