Character and Treatment of Organic Colloids in Challenging and Impacted Drinking Water Sources

Abstract

Aquatic colloids are ubiquitous in nature and are composed of inorganic and organic material. During treatment of drinking water they foul granular filters, membranes, and granular activated carbon and are likely to hinder oxidation processes. The organic fraction of aquatic colloids was isolated from 14 samples (three wastewaters, five reservoirs, three rivers, two biological laboratory reactors, and one treated reservoir water). Transmission electron microscopy revealed nanoscale cellular debris and fibrous material. On the basis of advanced spectroscopic techniques (Fourier transform infrared spectroscopy, C13 nuclear magnetic resonance, and transmission electron microscopy) organic colloids were found to contain peptidoglycan, lipids, carbohydrates, and proteins. Saccharides and hydrolysable amino acids accounted for 44 to 81% of organic carbon. The reactivity of these colloids toward chlorine was also evaluated. Disinfection by-product yields were comparable to other organic matter fractions. During simulation of conventional water treatment, organic colloids were well-removed (42% or 0.41 mg-C/L), and the organic colloid disinfection by-product yield was reduced by 32% for trihalomethanes and 25% for haloacetic acids, illustrating that conventional treatment was highly effective at physical removal. The composition of organic colloids relates to aquatic biological activity and is likely to pose treatment challenges when biologically active waters (e.g., wastewater reuse, algae-impacted surface water) enter drinking water treatment plants.