[Advances in Chemistry] Aquatic Humic Substances Volume 219 (Influence on Fate and Treatment of Pollutants) || Characteristics of Humic Substances and Their Removal Behavior in Water Treatment

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<ul><li><p>29 Characteristics of Humic Substances and Their Removal Behavior in Water Treatment </p><p>J. S. Kim1, E . S. K. Chian, F. M. Saunders, E . Michael Perdue2, and M . F. Giabbai1 </p><p>School of Civil Engineering, Georgia Institute of Technology, Atlanta, GA 30332 </p><p>The characteristics of naturally occurring aquatic humic substances and their removal behavior in water treatment were investigated in a plant operation and in alum coagulation with conventional labo-ratory jar-test experiments. Specific characteristics of humic sub-stances affected the performance of alum coagulation in removing both humic substances and turbidity. Up to 50% of the humic sub-stances were removed in both the treatment plant and alum coagu-lation. High-molecular-weight humic substances were preferentially removed. This preference resulted in substantial decreases in color intensity and trihalomethane formation potential per unit mass of humic substances. The characteristics and removal behavior by alum coagulation of commercial humic acid were significantly different from those of the source-water humic substances. </p><p>REMOVAL OF HUMIC SUBSTANCES has long been of concern in water treatment because of their abundance in natural waters and their potential adverse effects on public health and esthetics. They impart color to water and are able to form complexes with other inorganic and organic species (1-4) that frequently prevent the removal of these pollutants in treatment processes. More importantly, humic substances are major precursors in the formation </p><p>1Current address: HazWaste Industries, Inc., 2264 Northwest Parkway, Suite F, Marietta, GA 30067 </p><p>2Current address: School of Geophysical Sciences, Georgia Institute of Technology, Atlanta, GA 30332 </p><p>0065-2393/89/0219-0473$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>ch02</p><p>9</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>474 AQUATIC HUMIC SUBSTANCES </p><p>of trihalomethanes (THM) upon chlorination (5, 6). The ubiquity of T H M s in drinking water (7), together with their potential carcinogenic activity (8), prompted the U.S . Environmental Protection Agency (EPA) to promulgate the maximum contaminant level of 100 g / L of total T H M s in water systems serving more than 10,000 persons (9). </p><p>Most traditional water-treatment plants have been designed and operated to maximize removal of turbidity and pathogens through the use of coagulation-flocculation-sedimentation, filtration, and chlorination processes. Now that humic substances can be removed in water treatment, a considerable amount of effort has been focused on the optimization of existing treatment processes, especially coagulation, for effective removal of humic substances (10-17). However, there are still questions relating to the performance of these processes in removing humic substances because the nature of humic substances is not fully understood. Because the nature of humic substances can be an important factor influencing the performance of the water-treatment processes and the formation of T H M s upon chlorination, this study was initiated to investigate the specific characteristics of humic substances in natural water sources and their removal behavior in water treatment. </p><p>Humic substances in natural waters are unresolvably complex mixtures of organic matter; their physical and chemical properties are difficult to characterize. They are generally described as yellow, acidic, chemically complex, and polyelectrolytelike materials that range in molecular weight from a few hundred to several thousands (18). Recent studies (19-21) have indicated that humic substances in natural waters from different sources are relatively similar to each other in nature, but are significantly different from the commercial model humic substances commonly used in laboratory studies. </p><p>Most information on the removal ofhumic substances in water treatment and their impact on water quality has been obtained from studies with model humic substances (11, 13, 14). A clear distinction should be made between data acquired from model humic substances and those from natural water sources. </p><p>In order to address this concern, the characteristics ofhumic substances and their removal behavior in water treatment were investigated at a full-scale operating plant and in alum coagulation with conventional laboratory jar tests. The Chattahoochee Water Treatment Plant (CWTP) of Atlanta, G A , was selected for this study. </p><p>C W T P is a conventional plant that uses the Chattahoochee River as its source of raw water. The treatment sequences are coagulation-flocculation-sedimentation, filtration, and chlorination. Humic substances isolated from the C W T P source water and the model Aldrich humic acid were used in alum coagulation. The specific objectives of this study were to characterize the humic substances isolated from the source water and from </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>ch02</p><p>9</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>29. KIM ET AL. Humic-Substance Removal Behavior in Water Treatment 475 </p><p>the treated effluents of each subsequent treatment process of the C W T P ; to evaluate the removal behavior ofhumic substances by alum coagulation with conventional jar-test procedures; and to compare the nature of both types of humic substances and their removal behavior by alum coagulation. </p><p>Experimental Materials and Methods CWTP and Water Sampling. The CWTP is a conventional plant that employs </p><p>coagulation-flocculation-sedimentation, filtration, and chlorination (Figure 1). Alum is used as a coagulant in coagulation-flocculation after pH adjustment with lime. Prechlorination is practiced in both plant-intake and rapid-mix units. The supernate from the sedimentation basins is filtered through a dual-media filter (anthracite and sand); this process is followed by postchlorination. The sludge produced is chemically conditioned and dewatered with a filter press. The resulting sludge cakes are disposed of in a sanitary landfill. </p><p>The CWTP, designed to treat 230 106 L/day, was treating an average of 150 X 106 L/day. It uses the Chattahoochee River as a water source; general water characteristics are shown in Table I. The average color and turbidity values were 28 Pt-Co units and 27 nephelometric turbidity units (NTU), respectively. These values represent relatively low color and high turbidity, compared to many surface waters (22). </p><p>The water-sampling points, selected for the isolation of humic substances and investigation of their characteristics and removal behavior in the CWTP, included the source water (SW), effluent from coagulation-flocculation-sedimentation (ACFS), filtration effluent (AF), and the clear well (CW). The water volumes and sampling dates taken for the isolation ofhumic substances from each sampling point are shown in Table II, along with the amount of humic substances isolated. Because a large volume of water from each sampling point was required to isolate sufficient quantities of humic substances for subsequent laboratory experiments, water samples were taken during several periods of time rather than at intervals chosen according to the hydraulic retention time of each unit process. Approximately 200-700 L of water samples per day were taken from a sampling point. </p><p>The source-water quality and the performance of the CWTP were considered to influence the removal behavior of humic substances in the treatment processes. Therefore, various water-quality parameters were measured at each sampling point according to the hydraulic retention time of each unit process during the water-sampling period, as shown in Table II. </p><p>Figure 2 illustrates the results of the water-quality parameters for the four sampling points at the CWTP. Instantaneous THMs were produced after prechlorination and increased to 29.1 g/L in CW. Trihalomethane formation potential (THMFP) is a measure of the maximum amount of THMs that can be formed by the reaction of free residual chlorine with humic substances. A comparison of SW THMFP (228.5 g/L) with CW THMFP (95.2 g/L) shows a 69% reduction of THM precursors. The nonvolatile TOC (NVTOC) was reduced by 50% (i.e., from 4.3 to 2.1 mg/L), whereas UV absorbance at 254 nm and color were removed by 71 and 100%, respectively, through the treatment processes. </p><p>All water-quality parameters for humic substances decrease significantly during the treatment processes (Figure 2), especially after alum coagulation-flocculation-sedimentation. NVTOC decreased to a lesser extent than THMFP and humic substances (as measured by color). This preferential removal of THMFP and humic substances corroborates the results of Babcock and Singer (23), who observed </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>ch02</p><p>9</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>SW </p><p>I*-</p><p>Sam</p><p>plin</p><p>g po</p><p>ints</p><p> A</p><p>CT</p><p>S A</p><p>F C</p><p>W </p><p> 1.</p><p>5 p</p><p>pm C</p><p>Xj </p><p>. L</p><p>- 8.</p><p>0 pp</p><p>m a</p><p>lum</p><p> L </p><p>Lim</p><p>e to</p><p> pH</p><p> 7 </p><p>0.3</p><p> ppm</p><p>15 m</p><p>in </p><p>4-6 </p><p>h </p><p>1 </p><p>Rap</p><p>id </p><p>Floc</p><p>cula</p><p>tion </p><p>Sedi</p><p>men</p><p>tatio</p><p>n Fi</p><p>ltrat</p><p>ion </p><p>Cle</p><p>ar </p><p>wel</p><p>l m</p><p>ixin</p><p>g </p><p>Floc</p><p>cula</p><p>tion </p><p>Sedi</p><p>men</p><p>tatio</p><p>n Fi</p><p>ltrat</p><p>ion </p><p>Cle</p><p>ar </p><p>wel</p><p>l </p><p>1.5p</p><p>pmC</p><p>l 2 </p><p>&gt;|&lt; </p><p>Proc</p><p>ess </p><p>hydr</p><p>aulic</p><p> det</p><p>entio</p><p>n ti</p><p>me </p><p>15 m</p><p>in </p><p>Figu</p><p>re 1</p><p>. F/</p><p>ou; d</p><p>iagr</p><p>am a</p><p>nd </p><p>oper</p><p>atio</p><p>nal</p><p> con</p><p>diti</p><p>ons </p><p>of th</p><p>e C</p><p>hat</p><p>tah</p><p>ooch</p><p>ee W</p><p>ater</p><p> Tre</p><p>atm</p><p>ent </p><p>fian</p><p>t, a</p><p>lon</p><p>g w</p><p>ith</p><p> th</p><p>e fo</p><p>ur </p><p>sam</p><p>plin</p><p>g po</p><p>ints</p><p> for </p><p>the </p><p>isol</p><p>atio</p><p>n o</p><p>f hu</p><p>mic</p><p> su</p><p>bsta</p><p>nce</p><p>s. C</p><p>hem</p><p>ical</p><p> dose</p><p>s an</p><p>d pr</p><p>oces</p><p>s de</p><p>ten</p><p>tion</p><p> tim</p><p>e ar</p><p>e ap</p><p>prox</p><p>imat</p><p>e an</p><p>nu</p><p>al a</p><p>vera</p><p>ges </p><p>for </p><p>a fl</p><p>ow o</p><p>f app</p><p>roxi</p><p>mat</p><p>ely </p><p>15</p><p>0 x</p><p> 10</p><p>6 L</p><p>/day</p><p>. </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>ch02</p><p>9</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>29. KIM ET AL. Humic-Substance Removal Behavior in Water Treatment 477 </p><p>Table I. General Characteristics of CWTP Source Water Parameters Concentrations0 </p><p>Dissolved oxygen 8.6 Color (Pt-Co unit) 28.0 pH 6.8 Alkalinity (mg/L as CaC0 3) 12.0 Hardness (mg/L as CaC0 3) 10.8 Turbidity (NTU) 27.0 Suspended solids 17.6 Dissolved solids 37.5 Fluoride 0.1 Sulfate 5.4 Phosphate 0.2 Nitrate 0.04 Aluminum 0.6 Iron 0.4 Calcium 2.5 Magnesium 0.9 Sodium 2.2 Potassium 1.4 Aldrin NF f c Chlordane NF DDT NF Dieldrin NF Endrin NF Heptachlor NF Heptachlor epoxide NF Lindane NF Methoxychlor NF Toxaphene NF NOTE: Data were obtained from plant records. Values presented are averages of two determinations sampled on October 5 and No-vember 5, 1984. 'In milligrams per liter. fcNot found. </p><p>Table H . Humic Substances in CWTP Water Water Vol. of Water Humic Sampling </p><p>Sampling Sampled Substances Dates Points (L) Isolated (g) (1984) </p><p>SW 3102 3.99 Nov. 4-Nov. 15 ACFS 3143 2.92 Oct. 25-Nov. 3 AF 6467 4.79 Oct. 1-Oct. 14 CW 7164 4.94 Oct. 15-Oct. 24 </p><p>that alum coagulation selectively removed those portions of organic matter most responsible for T H M production. These observations allowed us to investigate more closely the types of humic substances removed by alum coagulation. The humic substances remaining after alum coagulation are ultimately chlorinated, and chlorination results in the formation of THMs. </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>ch02</p><p>9</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>478 AQUATIC HUMIC SUBSTANCES </p><p>CO J &lt; 5 g. 2 </p><p>in CM g &lt; 3 </p><p>1 1 Q: W </p><p>200 </p><p> 0. 06 </p><p>0.03 </p><p>0.016 CN </p><p> ^ CJ </p><p>0.008 </p><p>228. 5 (55.7) </p><p>1W8.6 !(*3.1) </p><p>(2.2) </p><p>THKfT Inet. THM* </p><p>116. 1 (23.7) 22. 0 (3.9) </p><p>t.26 0.6*) 3. 38 </p><p>(0.60) </p><p>0.061 (0.022) </p><p>I 0.023 | (0.008) </p><p>0.013 (0.006) </p><p>0.016 (0.013) </p><p>0.003 </p><p>IK*001? </p><p>(0.08) </p><p>0.93 (0.17) </p><p>SW ACFS AF </p><p>^ ^ 5 . 2 </p><p>2. 30 (0.39) </p><p>2.11 1(0.2 6). </p><p>0.018 |(0.0 0 5J </p><p>1. 1 (0. 32)1 </p><p>CW </p><p>Figure 2. Monitoring the water-quality parameters of the CWTP during the water-sampling period. Values presented are daily averages and those in pa</p><p>rentheses are standard deviations. </p><p>Isolation of Humic Substances. The humic substances in water samples from the four CWTP sampling points were isolated as a hydrophobic acid fraction of dissolved organic matter by methyl methacrylate resin (XAD-8) adsorption procedures (24) from the concentrate of reverse osmosis (RO). The overall scheme for the isolation ofhumic substances from water samples is depicted in Figure 3. The organic matter in water samples was concentrated at the plant by using the membrane process facility shown in Figure 4, which was equipped with a spiral-wound composite membrane module for seawater desalination (FT-30, FilmTec Corp., Minneapolis, MN). </p><p>Water samples were continuously pumped to the sample reservoir at the same flow rate as the RO permeate, and the result was a concentration of organic matter in the sample reservoir. The operating pressure and feed flow rate of the RO module were maintained at 4140-4830 kPa and 910 L/h, respectively. Sodium azide (0.5 mg/L) was added to the water samples to prevent algal and microbial growth, and a stoichiometrically determined amount of sodium sulfite was added to prevent possible oxidation of organic matter by residual chlorine. The initial sample, even-</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>ch02</p><p>9</p><p>In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988. </p></li><li><p>29. KIM ET AL. Humic-Substance Removal Behavior in Water Treatment 479 </p><p>Water Samples </p><p>\ </p><p>RO Concentrt ion of Organics </p><p>tPermeates </p><p>Aqueous Triethylamine S o l u t i o n (0.15 U) </p><p>S o l u t i o n </p><p>RO Concentrates </p><p>V * </p><p>F i l t r a t i o n on 0.45 um F i l t e r s </p><p>J.PH 1.8 with conc-HCl </p><p>XAD-8 Columns </p><p>E f f l u e n t s </p><p>Desorbed Humics </p><p>I Vacuum Evaporation 1 and Desalting </p><p>Glass F i l t e r </p><p>L y o p h i l i z a t i o n </p><p>Hur.ic Substanc </p><p>Resin + ppt 10.15 NaOH </p><p>V. 71. S o l u t i o n Resm Reapply t o XAD-8 </p><p>Column </p><p>Figure 3. Overall scheme for isolation of humic substances from water samples. </p><p>tually concentrated from approximately 3000-7000 L to 20-40 L, was transferred to an 80-L Pyr...</p></li></ul>

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