Constructed wetlands for sludge dewatering

Helophytes such as the common reed can be used for removing excess water from sludges from different sources such as municipal and industrial wastewaters and from dredging. Several pilot and full-scale studies indicate that the original dry-weight content of municipal wastewater sludge can be increased from about 1% to 40%. Reeds can grow in substrates polluted by several heavy metals without taking up and concentrating excessive amounts of these elements in their above-ground parts. In contrast with terrestrial plants and similar woody plants (willows) reeds can be at the origin of food-chains and so constitute a safe species for dumping sites. Sludge drying by reeds constitutes a sustainable procedure since it does not make use of manmade energy nor chemicals. Being atmosphere driven it is a reliable procedure but, in the short-term, of low predictability. (C) 1997 IAWQ. Published by Elsevier Science Ltd.