Published December 2008
With increasing pressure on water resources worldwide, increasing numbers of facilities are now recycling water within their own boundaries. Rising costs of raw water and discharge permits, plus more-stringent rules on the quantity and quality of treated effluent, make water reuse and recycling increasingly attractive.
At present, the trend is largely limited to recycling selected water streams within the plant boundaries, and to re-using treated municipal wastewater as a source of process water. “Zero liquid discharge” (ZLD) and re-use of plants’ own treated effluent remain generally uneconomic, though they will increasingly be required in dry or environmentally-sensitive locations.
Key to this convergence between process water and wastewater are the various membrane-based treatment processes, especially reverse osmosis (RO). Thanks in large part to their ability to desalinate seawater at reasonable cost, large-scale RO systems are forecast to see sales growth of up to 50% over the next four years. The resulting fall in costs will further encourage the use of RO in wastewater recycling. Membrane technologies have also significantly improved the economics of water treatment for demanding uses such as boiler feed, semiconductor manufacturing, and pharmaceuticals.
A landmark water re-use project is at Dow Chemical’s Terneuzen site in the Netherlands, where 30,000 m3 /d, representing half the water used on site, now comes from recycled process water, rainwater and household wastewater. Dow claims to have reduced its overall consumption of process water by 35% in 13 years, and the company’s external water business proposes to cut the cost of water re-use by 35% by 2015.
All water and wastewater treatment processes are sensitive to site conditions, and this is especially true of membranes. Done correctly, however, water re-use and recycling brings significant economic, environmental, and social benefits.