Small wastewater treatment plants in Flanders (Belgium): standard approachand experiences with constructed reed beds

In Flanders (Belgium) an estimated 15% of the population will never be conn ected to a central wastewater treatment plant (WWTP). Small WWTPs can be a valuable option. Aquafin bases the decision to build SWWTPs on a drainage a rea study. To realise an accelerated construction the process choice is mad e accordingly to a standard matrix, which represents the different technolo gies in function of the size and the effluent consents. A pilot scale const ructed two-stage reed bed is used to optimise the concept of the reed beds. The concept consists of a primary clarifier, two parallel vertical flow re ed beds followed by a subsurface flow reed bed. The removal efficiency of o rganic pollutants is high (COD: 89%, BOD: 98%). Phosphorus removal is high at the start-up but diminishes throughout the testing period (from 100% to 71% retention after 7 months). Nitrogen removal amounts to 53% on average. Nitrification is complete in summer. Denitrification appears to be the limi ting factor. In autumn leakage of nitrogen is assumed. Removal efficiency o f pathogens amounts to almost 99%. Clogging forms a substantial constraint of the vertical flow reed bed. Problems appear to be related with presettle ment, feed interval and geotextile.