Nanofiltration concentrate disposal: experiences in The Netherlands

• Published in: Desalination 2005-07, Vol.178 (1), p.303-312
• Main Authors: Nederlof, M.M., van Paassen, J.A.M., Jong, R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Biological and physicochemical phenomena; Chemical engineering; Continental surface waters; Exact sciences and technology; General purification processes; Membrane concentrate disposal; Membrane separation (reverse osmosis, dialysis...); Nanofiltration; Natural water pollution; Pollution; Wastewaters; Water treatment and pollution
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2004.11.041

Vitens has six full-scale nanofiltration plants running successfully. Another one is under construction. Five of these plants are fed with anaerobic ground water with high levels of hardness, colour and/or sulphate. One plant treats bank filtrated IJssel River water, which is hard and contains organic micropollutants. A full-scale reverse osmosis plant is under construction for a water treatment plant where hard groundwater with organic micropollutants is to be treated. In all of these cases disposal of the resulting concentrate is a serious problem, especially in those cases where no large surface water is present. In general, the concentrate disposal as such is not the problem, but the discussion is focused on a limited number of parameters such as sulphate, chloride, phosphate, iron and anti-scalant. For different reasons the water authorities put restrictions on the disposal of these compounds. Iron is a problem because it will cause a brown (visible) plume in the surface water. Most water authorities have quality objectives for sulphate and chloride in their surface water. The anti-scalant contributes to the total-P content in the case of polyphosphonates, and is considered to be a compound that promotes algae growth and which is not present in a natural environment and is therefore not acceptable. It is necessary to discuss disposal options with the water authority before engineering the installation. It is important to explain why a specific membrane filtration concept is chosen instead of conventional techniques. In the past, several solutions for concentrate disposal were developed by Vitens: treatment of the concentrate before discharging by rapid sand filtration or continuous filtration; selection of a nanofiltration membrane with a lower rejection for sulphate; selection of less contaminated groundwater wells that are used as feed water; discharging the concentrate in the influent or near the effluent of a wastewater treatment plant; transport over several kilometers in order to discharge the concentrate in a larger surface water. Despite these creative solutions it is expected that concentrate disposal will become more difficult. Water authorities use the stand-still principle (concentrations may not be increased), and European legislation may result in more severe restrictions. Therefore, there is a need for technologies that either remove specific compounds from the concentrate before discharge or technologies that make concentrate disposal