Standard nitrate treatment processes are expensive and create their own effluent disposal problems because of eutrophication directly caused by high nitrate discharges into the environment. In the widely used ion exchange process, polluted water is passed through a resin bed which binds nitrate while releasing chloride ions. Eventually, the resin has to be regenerated with brine, producing a concentrated nitrate effluent that has to be pumped or carried in road tankers to a sewage treatment works.
So when the regional water supplier Yorkshire Water heard about research being carried out by Ionex, a small technology company based near Gloucester, it quickly realised its potential for creating more efficient water treatment processes. Together with the UK Government's Environment Agency, Yorkshire Water funded research on a large-scale pilot plant to process water from a bore hole at Kilham, near Bridlington.
"Eureka opened doors that allowed us to talk to the people who really make the decisions"
Ionex Ltd., UK
The Ionex process involves two main advances on conventional systems. It has modified the ion exchange columns and resin regeneration process to produce smaller quantities of more concentrated nitrate effluent. More importantly, it has developed a catalyst technology to allow the effluent to be treated in an electrochemical cell. Current passed through the solution converts nitrate into harmless nitrogen and oxygen, and as an added bonus breaks down the smaller quantities of organic compounds released from the soil. The salt used to regenerate the resin can be easily collected and recycled.
Yorkshire Water is about to decide whether to go ahead with building a full operational plant supplying fresh water to homes and businesses throughout the region. Trials have shown that the capital costs are ~30% higher than conventional processes, but savings in effluent disposal costs reduce the operational costs by a factor of 10 - 20, which gives a very rapid payback."ELIMINATE is a big opportunity for the company to save money and meet its environmental targets," says Derek Wilson, senior project manager for Yorkshire Water.
Other water companies in the UK, the Netherlands and as far afield as Brazil have shown interest in the project and are thinking of installing ELIMINATE technology in their own water treatment plants. Moreover, water utilities are not the only organizations examining the economics of the new technology in their area. The process is of potential value in a wide range of sectors, particularly the steel industry, which spends huge sums of money treating nitrates produced from the action of nitric acid used to clean and polish sheet metal.