NOM's the word

摘要

There is a growing problem facing the UK water industry - this problem being the elevation of organic carbon levels in raw water. Many of the utilities that draw water down from upland moorland catchments are seeing year on year increases in colour and dissolved natural organic matter (NOM). One such works in the Severn Trent Water region has seen increases in colour rise from a value of always below 50° hazen to seasonal peaks of around 150° hazen. While the current treatment technologies can treat and remove colour, the problem is the effect the residual NOM can have on process performance, and on formation of disinfection by products such as trihalomethane (THM's). All chemical disinfectants (chlorine, ozone and chlorine dioxide) are known to form various types of disinfection by-products (DBP's). The primary precursors for THMs are NOM where it has been shown that 1 mg of organic carbon (measured as DOC) can react to form between 1 and 190 mg THM dependent on its source. The standard for THMs in the UK moves from a three-month average of 100μg/l to a limit of 100μg/l by 2003. The removal of NOM and hence the reduction in THMs is therefore a major goal in the treatment of any water source.