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Powdered or granular activated carbon adsorption has been widely used in drinking water treatment plants primarily for taste, odor, and synthetic organic contaminant (SOC) removal. However, carbon adsorption has not been widely used for controlling DOM due to the low equilibrium capacities and slow adsorption kinetics. The main reason for these drawbacks is that the majority of commercial activated carbons have been developed primarily to remove small molecular weight hydrophobic SOCs from water. As a result, many commercial carbons do not provide feasible engineering solutions for removing large molecular weight and heterogeneous mixtures of DBP precursors. This research was undertaken to develop a fundamental understanding of tailoring activated carbons for DBP control. The main objectives of this project were to (1) conduct a systematic investigation for developing a fundamental understanding of how activated carbons should be tailored for enhanced removal of dissolved organic matter (DOM) from natural waters; and (2) investigate the effectiveness of some carbon tailoring approaches for disinfection by-products (DBP) formation control at typical drinking water treatment conditions. This project showed that the removal of DBP precursor by GAC adsorption can be significantly improved. GAC adsorption, using modified GACs, can provide another alternative to some water utilities for meeting the Stage 2 requirements of the Disinfectant/Disinfection By-Products Rule.
The addition of chlorine disinfectant to drinking water during the treatment process results in the formation of disinfection by-products (DBPs). The United States and several other nations regulate for DBPs in drinking water because studies have linked exposure to these compounds to increased incidence of cancers as well as birth and developmental defects. Incorporation of activated carbon(AC) into the drinking water treatment process may reduce the formation of DBPs through the adsorption of natural organic matter (NOM) precursors and formed DBPs. The goal of this research project is to investigate how AC can be better used by small-scale drinking water plants as a feasible option for reducing the DBPs formed in their systems, which would allow them to consistently achieve compliance with the Environmental Protection Agency’s latest regulation Stage 2 D/DBP Rule. This research compared the factors of AC particle size, carbon source material, and concurrent coagulant addition in NOM sorption experiments. Although concurrent chemical addition and carbon source had no significant differences on AC performance, the performance of powdered activated carbon (PAC) was notably greater than granular activated carbon(GAC). Characterization of NOM in source water showed preferential adsorption of hydrophilic NOM compounds onto the AC. Finally, a pilot studied was designed to investigate the potential of granular activated carbon (GAC) to adsorb formed DBPs before entering the distribution system.
Many water treatment plants need to remove objectionable trace organic compounds, and activated carbon adsorption is often the best available technology. Utilities face the challenge of having to choose from a large variety of activated carbons, and iodine number or BET surface area values are often utilized in the selection process. Although neither parameter correlates well with adsorption capacities, alternative activated carbon selection criteria based on fundamental adsorbent and adsorbate properties are lacking to date. The first objective of this research was to systematically evaluate the effects of activated carbon pore structure and surface chemistry on the adsorption of two common drinking water contaminants: the relatively polar fuel oxygenate methyl tertiary-butyl ether (MTBE) and the relatively nonpolar solvent trichloroethene (TCE). The second objective was to develop simple descriptors of activated carbon characteristics that facilitate the selection of suitable adsorbents for the removal of organic contaminants from drinking water.Originally published by AwwaRF for its subscribers in 2003 This publication can also be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below
This monograph provides comprehensive coverage of technologies which integrate adsorption and biological processes in water and wastewater treatment. The authors provide both an introduction to the topic as well as a detailed discussion of theoretical and practical considerations. After a review of the basics involved in the chemistry, biology and technology of integrated adsorption and biological removal, they discuss the setup of pilot- and full-scale treatment facilities, covering powdered as well as granular activated carbon. They elucidate the factors that influence the successful operation of integrated systems. Their discussion on integrated systems expands from the effects of environmental to the removal of various pollutants, to regeneration of activated carbon, and to the analysis of such systems in mathematical terms. The authors conclude with a look at future needs for research and develoment. A truly valuable resource for environmental engineers, environmental and water chemists, as well as professionals working in water and wastewater treatment.
Powdered activated carbon (PAC) is commonly used in drinking water treatment plants to control taste and odor, and it is available to remove synthetic organic chemicals (SOCs) that must be controlled to meet drinking water standards. The objective of this study was to show how the adsorptive properties of PAC could more effectively be used in both conventional and unconventional treatment processes to control organic compounds. A major finding of this study involved the competitive effect of natural organic matter (NOM) on the the adsorption of organic compounds on activated carbon. Isotherm data show that the adsorption capacity of a compound is highly dependent on the initial compound concentration due to the competition of NOM for adsorption sites on the surface of the carbon. The equilibrium carbon capacity at a certain aqueous concentration decreases with decreasing initial organic compound concentration in the isotherm test when the initial NOM concentration is constant. An easy-to-use method was developed in this study to determine the isotherm of an organic compound when present in natural water at any initial concentration. The method approximates the complex mixture of NOM as a single compound referred to as the equivalent background compound (EBC). The initial concentration and single solute isotherm constants of the EBC are solved for based on the NOM's competitive effect on the adsorption of the organic compound on activated carbon, and these data can be used to accurately predict the adsorption capacity for conditions of relevance in operating plants. The performance of PAC in a floc-blanket reactor (FBR) for the adsorption of TCP, NOM and trichloroethylene (TCE) from natural water was investigated. Laboratory and field data were collected. PAC residence times as high as 30 hrs can be achieved in the floc blanket under laboratory conditions. Comparison of the PAC adsorption capacity in the reactor to the equilibrium adsorption capacity of TCP, TCE, and NOM in central Illinois groundwater and surface water showed that full utilization of the adsorption capacity of the carbon can be achieved with such high residence times. However, the PAC performance has to be compared to an isotherm conducted with an initial SOC concentration comparable to the SOC concentration in the influent to the reactor. This is due to the finding of decreasing isotherm capacity with decreasing initial concentration.
The objective of this research was to investigate NOM removal with activated carbon and MIEX®. Hydrophilic (HPI), hydrophobic (HPO), and transphilic (TPI) NOM was fractionated and subsequent DBP formation from these fractions was studied. Several new adsorptive materials (greensand, carbon nanotubes, iron impregnated activated carbon) were tested for DBP reduction potential. Reductions by the materials were poor and therefore the materials were not investigated further. Activated carbons, although similar in structure, perform differently from each other. Aqua Nuchar® and Hawkins Sabre Series® had greater than 30% difference in TTHM FP reduction under the same test conditions. None of the activated carbons investigated were found to have potential for brominated DBP precursor removal. When MIEX® (magnetic ion exchange) was compared to activated carbon with respect to NOM fraction removal, it was found that MIEX® removed more of the HPI and TPI fractions. This was represented well in DBP FP reductions specifically derived from reactions with NOM in these fractions. In particular, MIEX® decreased NOM in the HPI fraction only 10% more than activated carbon but decreased TTHM FP 34% greater than activated carbon. This suggests that MIEX® preferentially removes DBP precursors to a greater extent than activated carbon. MIEX® was also found to decrease formation of brominated DBPs. SUVA, UV254, DOC, and chlorine demand were all investigated as surrogate parameters for DBPs. UV254 was found to correlate best with DBP formation with 0.56