Treatment of RO concentrate by means of a combination of a willow field and electrodialysis

The increasing demand for recycled water has led to the use of reverse osmosis (RO) in numerous applications. This purification process produces a concentrate with a high salinity, containing nutrients and organic compounds. This RO concentrate is generally considered as a waste stream, causing a major impact on the ecosystem when discharged. This paper explores the potential of treatment of this concentrate by a biological pretreatment using a willow field followed by electrodialysis (ED). Due to the high salinity of the RO concentrate various willow species were initially examined in a salt tolerance test. A dense willow plantation of 28.33 m(2), composed of the most suitable species, was developed and used to reduce the nutrient and organic load of the RO concentrate. The removal rate of COD, total nitrogen and total phosphorus in the willow test field was 20%, 32% and 32%, respectively. Subsequently, an ED pilot scale plant was used for the production of an adequate effluent with a satisfying salt concentration, which can he re-inserted into the biological unit of the WWTP. This results in the indirect increase of the overall water recovery and minimization of the waste fraction. It was concluded that the coupling of a willow field and electrodialysis is a sustainable and environmentally friendly solution for treating saline wastewaters such as RO concentrates. (C) 2012 Elsevier B.V. All rights reserved.