[Advances in Chemistry] Aquatic Humic Substances Volume 219 (Influence on Fate and Treatment of Pollutants) || Trihalomethane Precursor and Total Organic Carbon Removal by Conventional Treatment and Carbon

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<ul><li><p>34 Trihalomethane Precursor and Total Organic Carbon Removal by Conventional Treatment and Carbon </p><p>Benjamin W. Lykins, Jr., and Robert M . Clark </p><p>Drinking Water Research Division, Risk Reduction Engineering Laboratory, U.S. Environmental Protection Agency, Cincinnati, O H 45268 </p><p>Data from four water-treatment plants were used to describe the performance of conventional treatment and granular activated carbon for removing trihalomethane precursors to meet various treatment goals. Also presented are data for total organic carbon removal, which has been suggested as an organic surrogate for measuring the effectiveness of water treatment. Conventional treatment, as used in the four water-treatment plants evaluated, substantially reduced total organic carbon and trihalomethane precursor concentrations. Granular activated carbon may be a treatment alternative to consider for meeting trihalomethane standards as low as 50 g/L.</p><p>DlSINFECTION BYPRODUCTS ARE BEING CONSIDERED FOR REGULATION under the Safe Drinking Water Act Amendments of 1986 (J). One of the most significant disinfection byproducts for utilities that use chlorine is total trihalomethanes (TTHMs). Pressure is growing to reconsider the existing T T H M standard of 0.1 mg/L (100 g/L) and to lower it to some as yet unspecified level. Trihalomethane levels as low as 10-50 g / L may be considered. Utilities may be forced to investigate disinfectants other than chlorine and to evaluate treatment modifications. New options might range from improved conventional treatment to granular-activated-carbon (GAC) adsorption. </p><p>0065-2393/89/0219-0597$07.25/0 1989 American Chemical Society </p><p>Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>CSF</p><p> LIB</p><p> CK</p><p>M R</p><p>SCS </p><p>MG</p><p>MT</p><p> on </p><p>Sept</p><p>embe</p><p>r 4,</p><p> 201</p><p>4 | h</p><p>ttp://</p><p>pubs</p><p>.acs</p><p>.org</p><p> P</p><p>ublic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 15</p><p>, 198</p><p>8 | d</p><p>oi: 1</p><p>0.10</p><p>21/b</p><p>a-19</p><p>88-0</p><p>219.</p><p>ch03</p><p>4</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>598 AQUATIC HUMIC SUBSTANCES </p><p>Most water utilities are able to meet a T T H M level of 0.10 m g / L (100 g/L) by using properly operated conventional treatment. However, if the standard is reduced substantially, adding G A C to conventional treatment may be an acceptable option. The length of time during which G A C can remove T H M s to meet a 10-, 25-, 50-, or 1 0 0 ^ g / L standard wil l determine its efficacy as a viable treatment option. </p><p>The U.S. Environmental Protection Agency's Drinking Water Research Division has collected extensive treatment data for removal of organic substances, including T T H M , their precursors, total organic carbon (TOC), and total organic halide (TOX) at several water utilities under actual operating conditions. In these studies G A C was used at some sitesincluding Cin cinnati, Ohio; Jefferson Parish, Louisiana; Manchester, New Hampshire; and Evansville, Indianato determine its ability to remove those organic compounds present after conventional treatment. </p><p>Literature Survey Conventional Treatment. T T H M precursors can be reduced by </p><p>proper conventional treatment (coagulation, flocculation, sedimentation, and filtration). The extent of reduction can depend on several factors, such as type of coagulant, p H , and temperature. The effects of pretreatment processes for removal of humic substances are site-specific because of raw water quality variables, treatment-plant operating conditions, and treatment-plant design (2, 3). The literature shows some diversity of findings that make it difficult to understand the THM-precursor removal process during coagulation. </p><p>Reckhow and Singer (4) reported that alum coagulation of aquatic fulvic acid removed T O C and T H M formation potential proportionately. Jodellah and Weber (5) observed that high levels of T O C removal may yield no selective removal of T H M precursors. Just as there were differences in the findings of investigators during bench studies, water-treatment plants also showed varying removals for T O C and T H M precursors (6). Under slightly acidic p H conditions, Edzwald and co-workers (2) reported that similar T O C and THM-precursor removals were achieved despite differences in raw water quality. </p><p>GAC Treatment. The specific coagulation process influences both the amount and the T H M reactivity of the residual organic matter remaining after treatment prior to chlorination (7). Higher-molecular-weight organic compounds were most effectively removed during pretreatment, and lower-molecular-weight organic materials were effectively reduced by G A C (7, 8). Jodellah and Weber (5) indicated that increased T O C removal by activated-carbon treatment resulted in decreased T H M formation in treated water. </p><p>Proper pretreatment appears to benefit activated-carbon adsorption. Randtke and Jepsen (9) reported significant increases in the adsorption ca-</p><p>Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>CSF</p><p> LIB</p><p> CK</p><p>M R</p><p>SCS </p><p>MG</p><p>MT</p><p> on </p><p>Sept</p><p>embe</p><p>r 4,</p><p> 201</p><p>4 | h</p><p>ttp://</p><p>pubs</p><p>.acs</p><p>.org</p><p> P</p><p>ublic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 15</p><p>, 198</p><p>8 | d</p><p>oi: 1</p><p>0.10</p><p>21/b</p><p>a-19</p><p>88-0</p><p>219.</p><p>ch03</p><p>4</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>34. LYKINS &amp; CLARK Removal by Conventional Treatment and Carbon 599 </p><p>parity of organic substances after alum coagulation. Lee and co-workers (10) showed that alum coagulation enhanced both carbon adsorption capacity and the rate of uptake. Semmens and co-workers (II) observed improved G A C performance with greater levels of pretreatment. Weber and Jodellah (3) noted that alum coagulation improved overall adsorbability of T O C . </p><p>Treatment at Research Locations </p><p>Various conventional treatment methods were used at the research sites to remove or reduce the mix of compounds present in the source water. The type of treatment (conventional and GAC) used at these utilities is as follows. </p><p>Cincinnati, Ohio. The primary source water for the Cincinnati Water Works is the Ohio River. To aid settling, 17 mg/L of alum was added to the raw water. Prior to flocculation and clarification, 17 mg/L of lime, ferric sulfate (8.6 mg /L for high turbidity and 3.4 mg/L for low turbidity), and chlorine (plant effluent concentration 1.8 mg/L of free chlorine) were added. Postfiltration adsorption was evaluated by deep-bed G A C contactors with an ultimate empty-bed contact time (EBCT) of 15.2 min. </p><p>Jefferson Parish, Louisiana. The Mississippi River provides source water to the Jefferson Parish treatment plant. Potassium permanganate (0.5-1.0 mg/L) was added for taste and odor control. A cationic polyelec-trolyte (diallyldimethyl diammonium chloride; 0.5-8.0 mg/L) was added as the primary coagulant, with lime (7-10 mg/L) fed for p H adjustment to 8.0-8.3. Chlorine and ammonia (3:1 ratio) were added for chloramine disinfection (1.4-1.7 mg /L residual after filtration). A sand filter was converted to a postfilter G A C adsorber with about 20 min E B C T . In addition, four G A C pilot columns were operated in series, providing 11.6, 23.2, 34.7, and 46.3 min E B C T . </p><p>Manchester, New Hampshire. The principal water source for the Manchester Water Works is Lake Massabesic. Alum and sodium aluminate were added for coagulation, p H adjustment, and alkalinity control at dosage levels averaging about 12 and 8 mg/L, respectively. Chlorine was added prior to sand filtration at an average dose of 1 mg/L. At the clearwell, chlorine was again added in the range of 2-3 mg/L to produce an average-distribution free chlorine residual of 0.5 mg/L. A G A C filter normally used for taste and odor control was used for postfiltration adsorption with 23 min E B C T . </p><p>Evansville, Indiana. The Evansville Water Works uses Ohio River water as its source. Chlorine and alum were added before primary settling, with average concentrations of 6 and 28 mg/L, respectively. A free chlorine residual of 1.5-2.0 mg /L was maintained after sand filtration. Approximately </p><p>Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>CSF</p><p> LIB</p><p> CK</p><p>M R</p><p>SCS </p><p>MG</p><p>MT</p><p> on </p><p>Sept</p><p>embe</p><p>r 4,</p><p> 201</p><p>4 | h</p><p>ttp://</p><p>pubs</p><p>.acs</p><p>.org</p><p> P</p><p>ublic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 15</p><p>, 198</p><p>8 | d</p><p>oi: 1</p><p>0.10</p><p>21/b</p><p>a-19</p><p>88-0</p><p>219.</p><p>ch03</p><p>4</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>600 AQUATIC HUMIC SUBSTANCES </p><p>12 m g / L of lime was added after primary settling for p H control to 8.0. A pilot plant operating parallel with the full-scale plant used chlorine dioxide for disinfection. Average alum and polymer (anionic high molecular weight) dosages of 12 and 0.8 mg/L, respectively, were added to the raw water of the pilot plant. An average lime dose of about 6 m g / L was used for p H control to 8.0. Post-pilot-plant G A C contactors had an E B C T of 9.6 min. </p><p>Results </p><p>T O C removal has been suggested as a means of measuring treatment performance. Although T O C is relatively easy to analyze and incorporates all organic compounds, it does not relate to any specific regulatory requirements. In the following evaluation, however, T O C was used as a general surrogate parameter to determine the performance of conventional treatment and G A C adsorption. </p><p>Removal of instantaneous trihalomethanes and their precursors to meet a T T H M standard was also evaluated by using the terminal trihalomethane (terminal T H M ) parameter. Because the utilities studied used various disinfectants that affected the trihalomethane concentrations, terminal T H M (instantaneous T H M plus T H M formation potential) allows a comparison among utilities by indicating the maximum trihalomethane in the distribution system at a given time. In this evaluation, ambient p H and temperature were maintained. Chlorine dosages were chosen to ensure a chlorine residual after a storage time that simulated the time from the treatment plant to the farthest point in the distribution system. </p><p>Conventional Treatment. The T O C raw water concentration at Evansville, Indiana, varied from 2.8 to 3.6 mg /L during one 85-day operational phase. Average raw water T O C concentration was 3.0 mg/L. Average T O C removal was 37% with full-scale conventional treatment and 40% for the pilot plant. Average sand filter T O C concentration was 1.9 and 1.8 m g / L for the full-scale and pilot plant, respectively. Evansville's 3-day raw water terminal T H M concentrations ranged from 95 to 178 pg/L, for an average of 140 g /L . After conventional treatment the average concentration was 82 g / L for the full-scale plant (an average reduction of 41%) and 34 g / L for the pilot plant (a 76% reduction). More efficient T H M precusor removal in the pilot plant for this operational phase was attributed to the addition of a polymer (anionic high molecular weight) for effective turbidity removal. </p><p>The initial raw water T O C concentration at Manchester was 4.6 mg/L. It varied from 3.8 to 4.8 mg/L, with an average concentration of 4.5 m g / L for 130 days of operation. The raw water T O C concentration was reduced about 47% to an average of 2.4 mg/L. Three-day terminal T H M concentrations for Manchester's raw water at ambient temperature ranged from 104 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>CSF</p><p> LIB</p><p> CK</p><p>M R</p><p>SCS </p><p>MG</p><p>MT</p><p> on </p><p>Sept</p><p>embe</p><p>r 4,</p><p> 201</p><p>4 | h</p><p>ttp://</p><p>pubs</p><p>.acs</p><p>.org</p><p> P</p><p>ublic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 15</p><p>, 198</p><p>8 | d</p><p>oi: 1</p><p>0.10</p><p>21/b</p><p>a-19</p><p>88-0</p><p>219.</p><p>ch03</p><p>4</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>34. LYKINS &amp; CLARK Removal by Conventional Treatment and Carbon 601 </p><p>to 191 g / L (an average of 151 g/L) . Precursor removal through conventional treatment reduced the 3-day terminal T H M to an average of 70 g /L , a 54% reduction. </p><p>In Cincinnati, where ferric sulfate was used as the primary coagulant, a 41% reduction in the T O C concentration was seen through conventional treatment. Raw water T O C concentrations ranged from 1.9 to 5.9 mg/L, for an average of 3.4 mg/L. After conventional treatment the T O C concentrations ranged from 1.1 to 3.4 mg/L, for an average of 2.0 mg/L. The average reduction through conventional treatment was 41%. Three-day terminal T H M concentrations for the raw water ranged from 64 to 211 g /L , for an average of 146 g /L . After conventional treatment, the terminal T H M concentrations ranged from 39 to 181 g /L , for an average of 89 g /L , producing an average terminal T H M reduction of 39%. </p><p>At Jefferson Parish, polymers were used as the primary coagulant. The raw water (Mississippi River) T O C concentration ranged from 2.9 to 5.9 mg/L, with an average of 4.0 mg/L. After conventional treatment the T O C concentrations ranged from 2.3 to 3.8 mg/L, with an average of 2.9 mg/L, for a reduction of 27.5%. Five-day terminal T H M concentrations for the raw water ranged from 133 to 511 g /L , with an average of 281 g /L . After conventional treatment the range was 82 to 364 g /L , for an average of 175 g /L . Average 5-day terminal T H M reduction through conventional treatment was 37.7%. </p><p>Table I summarizes the removal of the T O C through conventional treatment. Table II shows removal of terminal trihalomethanes through various steps in the treatment process. In this case, terminal trihalomethanes are used because they represent the formation potential of T T H M in the dis-</p><p>Table I. Average Total Organic Carbon Removal During Conventional Treatment </p><p>Raw Water Sand Filter Percent Water Utility (mg/L) Effluent (mg/L) Removal Cincinnati, O H 3.4 2.0 41 Jefferson Parish, LA 4.0 2.9 28 Manchester, N H 4.5 2.4 47 Evansville, IN 3.0 1.9 37 </p><p>Table II. Average Terminal Trihalomethane Removal During Conventional Treatment Terminal Raw Water Sand Filter Percent </p><p>Water Utility Day ^g /L) Effluent (g/L) Removal Cincinnati, O H 3 146 89 39 Jefferson Parish, LA 5 281 175 38 Manchester, N H 3 151 70 54 Evansville, IN 3 140 82 41 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>CSF</p><p> LIB</p><p> CK</p><p>M R</p><p>SCS </p><p>MG</p><p>MT</p><p> on </p><p>Sept</p><p>embe</p><p>r 4,</p><p> 201</p><p>4 | h</p><p>ttp://</p><p>pubs</p><p>.acs</p><p>.org</p><p> P</p><p>ublic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 15</p><p>, 198</p><p>8 | d</p><p>oi: 1</p><p>0.10</p><p>21/b</p><p>a-19</p><p>88-0</p><p>219.</p><p>ch03</p><p>4</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>602 AQUATIC HUMIC SUBSTANCES </p><p>tribution system itself. The time to the most distant customer in the distribution system is represented by the terminal day. </p><p>As can be seen from Tables I and II, the utilities examined experienced variable performance in average percent removal of both T O C and terminal T H M . This variability may be due in part to source water quality. For example, Cincinnati, Jefferson Parish, and Evansville (with a river water source) had lower percent removal efficiency for terminal T H M than did Manchester (with a lake source). </p><p>Granular Activated Carbon Treatment. G A C performance for removing both T O C and terminal T H M also varied for the different utilities evaluated. For instance, at Evansville, Indiana, after conventional treatment, G A C further reduced the T O C concentration during about 30 days of operation, after which the G A C effluent...</p></li></ul>

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