Desorption of Organics Formed on Activated Carbon

Voudrias, Evangelos A.; Snoeyink, Vernon L.; Larson, Richard A.

doi:10.1002/j.1551-8833.1986.tb05700.x

Cited by 9 publications

(2 citation statements)

References 9 publications

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“…Some desorption incidents of TCM and BDCM were noticed during the operation of both GAC adsorbers, after a sudden drop in influent concentration or near the breakthrough point ( Figures 1-4). These incidents are expected for weakly adsorbing compounds and are usually caused by either sudden decreases in influent concentration or the presence of stronger adsorbing compounds (Thacker et al, 1983;Voudrias et al, 1986;AWWA,1990). The cumulative influent and effluent mass of the specific compounds at each sampling point was calculated from the area between the respective curves and the axis of water volume in Figures 1-6.…”

Section: Thms Removal Profiles and Calculationsmentioning

confidence: 99%

Adsorption capacity of GAC pilot filter-adsorber and postfilter- adsorber for individual THMs from drinking water, Athens

Babi

Koumenidis²,

Makri³

et al. 2013

Global NEST Journal

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Trihalomethanes are a major class of chlorination by-products in drinking water. They are formed when chlorine reacts with bromide (Br-) and natural organic matter (NOM) in source waters. Toxicology studies have shown all THMs to be carcinogenic or to cause adverse reproductive or developmental effects in laboratory animals. THMs are small volatile molecules, which are hydrophobic, non biodegradable and adsorbable on granular activated carbon (GAC). The objective of this pilot study is to evaluate the adsorption capacity for individual THMs of a GAC filter-adsorber (A) and a GAC postfilter-adsorber (B), both fed with chlorinated natural water. For this purpose, a GAC pilot plant was operated as a filter-adsorber and a postfilter-adsorber in Galatsi WTP, Athens (GTP) until the removal of individual THMs by GAC was eliminated (breakthrough). Regular sampling was performed during operation and the parameters measured were: THMs, DOC, free residual chlorine, bromide, turbidity, pH and temperature. From the experimental data, GAC bed life, GAC usage rate, GAC loading and operation time to breakthrough were calculated for most THMs. TBM was almost not detected. Some desorption of THMs, especially TCM and BDCM, was noticed during the operation of both adsorbers. Near breakthrough for THMs, equilibrium between adsorbed and dissolved THMs was considered to have been established. The GAC equilibrium loading of individual THMs was assumed to depend on the mean value of their influent concentration, which was not constant. By correlating the equilibrium data by linear regression to conform to the Freundlich isotherm, the Freundlich constants 1/n and k were determined for each of THMs. They are related to the physicochemical characteristics and background organics of water and the specific GAC used. The strength of the adsorption bond and the GAC capacity was higher for DBCM, lower for BDCM and even lower for TCM for both adsorbers. In addition, the GAC(B) capacity for BDCM and DBCM was higher than that of GAC(A), probably due to larger surface area and surface chemistry of GAC(B). Also, the lower particle size and the higher uniformity coefficient of GAC(B), along with the lower flow rate may have attributed to that by enhancing GAC equilibration. However, TCM was less adsorbed by GAC(B), probably due to the stronger competition effect by BDCM and DBCM, being in much higher mean influent concentration. The DOC content of influent water seems also to reduce significantly the adsorption of THMs (especially of TCM), as the comparison of our results with the isotherm results with distilleddeionized water by other researchers showed.

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Section: Thms Removal Profiles and Calculationsmentioning

confidence: 99%

Adsorption capacity of GAC pilot filter-adsorber and postfilter- adsorber for individual THMs from drinking water, Athens

Babi

Koumenidis²,

Makri³

et al. 2013

Global NEST Journal

View full text Add to dashboard Cite

show abstract

“…Some desorption incidents of TCM and BDCM were also noticed, when a sudden drop in influent concentration occurred or near the breakthrough point (Figure 1). These incidents are expected for weakly adsorbing compounds and are usually caused by either sudden decreases in influent concentration or the presence of stronger adsorbing compounds (Thacker et al, 1983;Voudrias et al, 1986;AWWA,1990).…”

Section: Thmsmentioning

confidence: 99%

Removal of Specific DBP by GAC in Galatsi (Athens) WTP

2013

Global NEST Journal

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The objective of this pilot-study is to evaluate the Granular Activated Carbon (GAC) performance for the removal of specific disinfection by-products (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), from Athens drinking water. For this purpose, a GAC pilot filter-adsorber was operated in Galatsi WTP, Athens, for 235 days, until the GAC removal efficiency for individual THMs, HAAs and DOC was almost eliminated (breakthrough). From the experimental results, GAC bed life, GAC loading, carbon usage rate, and operation time to breakthrough for most THMs and HAAs were calculated. The average influent concentrations of the more chlorinated THMs and HAAs were higher than those of less chlorinated and more brominated species and their mass adsorbed on the GAC column was also higher, as expected according to Freundlich isotherm. TCA, TCM and DCA had the highest influent concentrations and they seemed to be better adsorbed than the rest. TBM, TBA and DBCA were almost not detected in feed water. Comparison of the GAC loading at breakthough for pairs of compounds with similar average influent concentration showed that TCA is better adsorbed than TCM and that BDCA is better adsorbed than MCA, BDCM and DBCM. Desorption phenomena of some THMs and HAAs, probably caused by a sudden drop in influent concentration, were also noticed. The above findings represent real operation conditions for Athens drinking water. Further research is recommended on methods to reduce desorption from carbon beds.

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Halogenated Biphenyls

Mukerjee¹

2001

Patty's Toxicology

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Polyhalogenated biphenyls are a family of compounds based on biphenyl as the parent compound. Chlorinated and brominated biphenyls have been manufactured for commercial purposes. There are 209 possible structural congeners of polychlorinated biphenyl (PCB) and for polybrominated biphenyls (PBBs) the same number of congeners can exist. A listing of all PCB congeners is given along with their Chemical Abstract Services (CAS) Registry numbers an identifying numbering system are given. PCBs used commercially are complex mixtures consisting of various PCB congeners and isomers. It has been estimated that in the United States a total of 1400 million pounds of PCBs were manufactured of which 150 million pounds were exported, and 3 million pounds were imported. Because of their nonflammability, thermal stability, outstanding dielectric properties, and resistance to chemical reactivity, PCBs have been used extensively as dielectric fluids in liquid‐cooled electric motors, transformers, capacitors; electromagnets, vacuum pumps, gas turbines, hydraulic fluids; heat‐transfer systems; voltage regulators, liquid‐filled cable, fluorescent light ballasts, electronic equipment; as plasticizers in synthetic resins, adhesives, surface coatings, sealants, printing and carbonless coping papers, pesticide extenders, inks, lubricants, and cutting oils. PCBs have also been used in slide mounting medium for oil immersion lens microscopy. Although PCBs are no longer produced and their use has been discontinued in most countries, many old equipment filled with PCBs are still in service today. World wide approximately 800,00 tons of PCBs are still in use. These equipments are the new sources of environmental contamination when PCBs start leaking or when the equipments are disposed of. Commercial production of polybrominated biphenyls in the United States began in 1970 and was discontinued in early 1977. The general population may be exposed to PCBs from a variety of sources, including food, ambient air, occupational settings, and consumer products. The major exposure routes to humans are through food. Accidental oral exposures to PCBs have been reported. In all cases, total PCB levels must be based on specific congener analysis or direct perchlorination rather than in terms of Aroclors because the congener patterns in environmental media and biological tissues usually do not match those in Aroclor fluids unless massive contamination has occurred (typical of spills and some occupational situations). Thus predictive models based on specific congener data must also be utilized. The less chlorinated congeners predominate in air samples from known contaminated areas and in water and wet deposition samples with temperature and the amount of sediment in river and water samples being important covariables. In contrast, the more highly chlorinated isomers with substituents at the 2,4,5 or 2′,4′,5′ positions tend to bioaccumulate in some crop vegetables, game animals, fish, and human tissue samples. PCBs in contaminated soils can be absorbed by plants and vegetables with shallow‐root systems to PCB contamination, although volatilization in this situation is also favored; erosion of such soils will also cause contamination of sediments. The more chlorinated congeners dominate in soils and sediments and the resident biota (cash crops, vegetables, fish, aquatic life). The absolute levels in any situation depend on which of the competing processes dominates. PCB mixtures produce low to moderate acute toxicity in mammalian species, but produce pronounced subacute and chronic toxicity. In contrast, invertebrates exhibit greater acute toxicity to PCBs (LC 50 s<1 mg/L). In addition, as reported for other halogenated aromatic hydrocarbons, PCBs exhibit significant interspecies variability in toxicity. In considering the health effects of PCBs in animals, it is important to consider the isomer and congener composition of the PCBs, potential impurities, the length of exposure, and the species under investigation.

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Desorption of Organics Formed on Activated Carbon

Cited by 9 publications

References 9 publications

Adsorption capacity of GAC pilot filter-adsorber and postfilter- adsorber for individual THMs from drinking water, Athens

Adsorption capacity of GAC pilot filter-adsorber and postfilter- adsorber for individual THMs from drinking water, Athens

Removal of Specific DBP by GAC in Galatsi (Athens) WTP

Halogenated Biphenyls

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