Many surface drinking water supplies are highly coloured. The bulk of soluble organics present in natural water supplies consist of humic materials. These compounds are relatively large molecular weight polar organics that contribute the yellow to brown colour in some surface supplies.

Figure 1 - Schematic of Zenon's Nanofiltration System.

Many small communities in Northern Ontario and Quebec which draw water from coloured surface supplies often have serious problems when chlorinating. In fact, after chlorination, trihalomethane (THM) concentrations in these drinking waters can be elevated above the federal guideline of 350 mg/L. Health officials are concerned over the implications of these elevated concentrations of THMs in drinking waters.

Providing high quality water to remote communities has often meant using small package plants staffed by skilled operators who must regularly adjust chemical dosages in response to changing feed conditions. Further complicating the process is that the removal of disinfection by-product precursors (DBPs) under these conditions is often difficult. It is necessary to identify and develop technologies which are suitable for small communities and can achieve THM levels at the lowest cost possible.

Zenon's membrane technology offers a potential solution by removing trihalomethane precursors prior to chlorination. The process train is shown schematically in Figure 1. This technology has been widely used for removal of colour from groundwater sources, and this new nanofiltration module has now expanded the application of this advanced technology to surface waters.

Nanofiltration technology exhibits very high removal of disinfection byproduct precursors. With the low operator interface required with a membrane based solution as opposed to conventional chemical addition technologies, nanofiltration offers considerable advantages.

The nanofiltration system removes from 50-90% of the THMFP (Trihalomethane Formation Potential) from the surface water. High removals are also achieved for colour, TOC and turbidity.