Comparison of the Use of Single and Multiple Oxidants on the Generation of Particulate Matter in Water Distribution Systems Derived from Groundwater Sources Containing Hydrogen Sulfide and Dissolved Organics

Due to increasingly stringent regulations, concerns about disinfection byproduct formation, and the need for improved control of distribution system water quality, there has been a shift towards the use of alternative disinfectants and oxidants in the production of drinking water. Technologies that modify water chemistry, such as hydrogen peroxide, UV irradiation, chlorine and/or chloramines may result in the generation of mineral and organic precipitates. Turbidity provides an indirect measure of the presence of particles by evaluating the light scattering properties of water. Turbidity levels are currently not monitored or regulated in treated groundwater. An important water quality parameter that influences groundwater quality is hydrogen sulfide. The control of sulfides in groundwater is of importance because its presence can cause odor and taste complaints, corrosion of pipes and other plumbing fixtures, and black-water problems in distribution systems (Levine et. al, 2004). In addition, sulfides can impose a significant oxidant demand and possibly interfere with disinfection treatments. Characteristics of particles from untreated and treated groundwater were tested as part of a field study to evaluate alternative wellhead treatment approaches for controlling hydrogen sulfide. A 1 gallon per minute (gpm) pilot-plant was used to test several groundwater treatment scenarios. The chemicals tested included chlorine, monochloramine, and hydrogen peroxide either alone or in tandem. Photochemical oxidation was evaluated using UV and advanced oxidation was evaluated using hydrogen peroxide coupled with UV. Testing was conducted either on water pumped directly from the well at ambient (7.0-7.5), or pretreated with caustic soda to evaluate the impact of elevated pH (8.2) conditions. The formation of particles was quantified using turbidity, solids (total, dissolved and suspended), and particle counts before and after oxidation. The particulate matter was characterized using a particle size analyzer in conjunction with scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). Treatment systems that rely on in-line treatment lack mechanisms for particle removal, therefore particles generated through treatment are introduced into the distribution system. It is evident from this project that treatment systems should be optimized to prevent particle formation