Granular Activated Carbon Adsorption of Organic Micropollutants: Scale-Up and Effect of Background Dissolved Organic Matter

Conventional drinking water treatment does not effectively reduce the concentrations of many common emerging trace organic contaminants or micropollutants (MPs), thus advanced treatment processes like granular activated carbon (GAC) are being evaluated for potential use in controlling MPs. However, adsorption by GAC is not selective for MPs as background dissolved organic matter (DOM), which is ubiquitous in all natural waters derived from both natural and anthropogenic sources, is also removed. Background DOM irreversibly reduces both adsorption capacity and kinetics for MPs, termed fouling, and varies in magnitude with GAC particle size thereby complicating valuable performance predictions. The objectives of this research are to (a) expand the database of MP breakthrough at environmentally relevant concentrations with full-scale and small-scale GAC media in several waters with different background DOM concentrations and types and (b) develop relationships that allow the breakthrough to be related to compound and system properties, and (c) better understand the effects of DOM type on MP breakthrough.Adsorption of 30 environmentally relevant MPs using full- and small-scale GAC media was investigated using several different surface waters with different DOM, measured as dissolved organic carbon (DOC). For coagulated waters, MPs broke through earlier on average with increasing DOC and 52% later on average by doubling the EBCT based on the bed volumes to 10% MP breakthrough. Several predictive relationships were presented for predicting the bed volumes to 10% MP breakthrough at the full-scale based influent DOC concentrations, MP pH-dependent octanol-water partition coefficients, MP polarizabilities, MP molar volumes, and bed volumes to 10% MP breakthrough using the proportional diffusivity design of the rapid small-scale column test (PD-RSSCT). On average, the PD-RSSCT over predicts MP adsorption capacity by a factor of 3.0±1.2. Relationships for adjusting the PD-RSSCT to predict full-scale MP breakthrough using a fouling factor were based on the ratios of the influent MP concentration to the influent DOC concentration, bed volumes to 10% MP breakthrough in the PD-RSSCT, and MP pH-dependent octanol-water partition coefficients. Smaller molecular weight DOM fouled GAC more than unfractionated and large molecular weight DOM, whereas large molecular weight slowed adsorption kinetics. Environmentally relevant background MP concentrations of about 3 μg/L had a small to negligible effect on target MP breakthrough.