Removal of Organic Matter in Water Treatment

The performance of several types of water treatment plants in removing various molecular weight (MW) fractions of naturally occurring aquatic organic matter and humic substances is described. An assessment was made of the performance of direct filtration, conventional treatment, and softening in removing trihalomethane (THM) precursors from a diverse array of water sources. In addition, a comparison was made between conventional treatment and direct filtration in removing THM precursors from a common water source, the Colorado River. As a general rule, THM reactivity (μg THM/mg C) increased with MW although the $<10\text{,}000\mathrm{MW}$ range was found to be the most consistently reactive fraction of aquatic organic matter. All of the various treatments preferentially removed the most reactive fraction of precursor present in each molecular weight range. None of the various treatments proved to be very effective in removing precursor material below a MW of $<500\text{.}$ The ability to remove THM precursors appears to be related to both the source of humic substances as well as the type of treatment employed.