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StagedCoagulationforTreatmentofRefractoryOrganics

ArticleinJournalofEnvironmentalEngineering·September2004

DOI:10.1061/(ASCE)0733-9372(2004)130:9(975)

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Staged Coagulation for Treatment of Refractory OrganicsDavid A. Fearing1; Emma H. Goslan2; Jenny Banks3; Derek Wilson4; Peter Hillis5;

Andrew T. Campbell6; and Simon A. Parsons7

Abstract: Seasonal periods of high rainfall have been shown to cause elevated natural organic matter~NOM! loadings at treatmeworks. These high levels lead to difficulties in removing sufficient NOM to meet trihalomethane standards, and hence bettertreatments are required. Here the removal of NOM was investigated by conventional coagulation treatment using both bulk anated NOM. Initial experiments showed that over 70% removal of the hydrophobic and hydrophilic acid fractions was achievworks, while only 16% of the hydrophilic nonacid fraction was being removed. Bench scale jar testing of the isolated NOMdemonstrated that high removals of the hydrophobic fractions were achieved and that optimized conditions increased remhydrophilic fractions, indicating that staged coagulation could be of benefit in the removal of the recalcitrant fractions. Experimeoptimized staged coagulation indicated that a small increase in the removal of the total NOM of this water was possible whento conventional treatment.

DOI: 10.1061/~ASCE!0733-9372~2004!130:9~975!

CE Database subject headings: Organic matter; Coagulation; Water treatment; Seasonal variation; Rainfall.

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Introduction

Natural organic matter~NOM! is described as an intricate mixtuof organic compounds that occurs universally in ground andface waters. Natural organic matter can cause major problethe treatment of water as it is converted into disinfection bypucts when chlorine is used during water treatment~Krasner et al1989!. These byproducts can be in the form of trihalometha~THMs!, haloacetic acids and many other halogenated cpounds, some of which are of major concern to the water tment industry, as tests have shown links between cancer inratory animals and THMs~Singer 1999; Rodriguez et al. 200!.To control the risk, United States and United Kingdom legislahas tightened in recent years to dictate the amount of THM

1School of Water Sciences, Cranfield Univ., CranfiBedfordshire MK43 OAL, UK.

2School of Water Sciences, Cranfield Univ., CranfiBedfordshire MK43 OAL, UK.

3Yorkshire Water, Research and Process Development, WesternHalifax Rd., Bradford BD6 2LZ, UK.

4Yorkshire Water, Research and Process Development, WesternHalifax Rd., Bradford BD6 2LZ, UK.

5United Utilities Service Delivery, Asset Creation-Task TeThirlmere House, Lingley Mere, Lingley Green AWarrington WA5 3LP, UK.

6United Utilities Service Delivery, Asset Creation-Task TeThirlmere House, Lingley Mere, Lingley Green AWarrington WA5 3LP, UK.

7School of Water Sciences, Cranfield Univ., CranfiBedfordshire MK43 OAL, UK. ~corresponding author! E-mail:s.a.parsons@cranfield.ac.uk

Note. Associate Editor: Wendell P. Ela. Discussion open until Feary 1, 2005. Separate discussions must be submitted for individupers. To extend the closing date by one month, a written request mfiled with the ASCE Managing Editor. The manuscript for this papersubmitted for review and possible publication on April 16, 2002;proved on June 27, 2003. This paper is part of theJournal of Environ-mental Engineering, Vol. 130, No. 9, September 1, 2004. ©ASCE, IS

0733-9372/2004/9-975–982/$18.00.

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lowed in drinking water. The current consent in the United Kdom is 100mg/L for total THMs and 80mg/L in the United State@Drinking Water Inspectorate UK 1998; US Environmental Ptection Agency~EPA! 1998#.

Most studies on NOM treatability have focused on bulkganic matter but more recently isolation of aquatic organic mhas been used to study the character and treatability of the dent organic molecules in NOM. This has shown considerableefits in the characterization of a water when compared tostudy of collected bulk organics. Generally the NOM is initiafractionated by the removal of colloidal matter by filtratthrough 0.45mm pore filters followed by the concentration afractionation of the resultant dissolved matter. Malcolm and MCarthy ~1992! and Aiken et al.~1992! both developed a methofor the resin fractionation of NOM using a two column adsorptechnique. The columns contained XAD-8 and XAD-4 Ambenonfunctional uncharged macroporous resins and the methlows for the isolation and separation of both the hydrophobicfraction and the hydrophilic acid fraction. The four fractionstained by using this method are hydrophobic acid~HPO-A!, con-sisting of humic and fulvic acids, humic acid fraction~HAF! andfulvic acid fraction~FAF! respectively, a hydrophilic acid fractio~HPI-A! and a hydrophilic nonacid fraction~HPI-NA!. TheHPO-A is further separated into its HAF and FAF by precipitaof the HAF at pH 1. The HPI-NA passes through both columTypical dissolved organic carbon~DOC! removals observed feach of the four fractions by coagulation are 87, 55 and 52%HAF, FAF, and HPI-A, respectively~Croueet al. 1999! and 44%DOC removal for HPI-NA. The remainder of the DOC is madefrom the hydrophobic neutrals and hydrophilic neutrals thanot eluted from the XAD-8 column and XAD-4 columns, resptively.

The treatment of water is traditionally focussed on the remof either color or turbidity. Recently some water treatment faties have started to optimize their works purely on the removnatural organic matter~Chow et al. 2000!. As most NOM is an

ionic at the pH of natural water~pH 4–8! it has a strong affinity

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to cationic additives such as metal coagulants and cationicelectrolytes. Consequently, coagulation is regarded as a esunit process when treating a water source for the removorganic matter~Lind 1995; Volk et al. 2000!. The definition ocoagulation as a process varies but three definitions include1. a process for combining small particles into larger ag

gates~Amirtharajah and O’Melia 1990!;2. coagulation involves the addition of chemicals into a w

to produce chemical species that act to destabilize connants and improve their removal~Dennett et al. 1995!; and

3. coagulation is a process for combining colloid materialssmall particles into larger aggregates and for adsorbingsolved organic matter on to these aggregates, therebytating their removal in subsequent sedimentation/flotaand filtration stages~Jiang and Graham 1998!.

While there are several mechanisms proposed for coaguwith metal salts it is likely that a combination of~1! charge neutralization and~2! adsorption onto hydroxide species occur duthe coagulation of NOM~Cheng et al. 1995; Dennet et al. 19Gregor et al. 1997; Bell-Ajy et al. 2000!.

It has been shown that typical removals for single stageagulation of high specific ultraviolet absorbance~SUVA! watersare .50% for both DOC and UV254. Specific ultraviolet absobance (m21 L mg21) is defined as the ratio of ultraviolet~UV!absorbance at 254 nm (m21) to DOC (mg L21) ~Edzwald andTobiason 1999!. However for waters that have high DOC conctrations~i.e., .10 mg/L) this may not be sufficient for satisfyithe THM removal requirement~Chow et al. 1999; Bell-Ajy et a2000; Volk et al. 2000!. Carlson and Gregory~2000! reported thasingle-stage coagulation on a highly colored, low turbidity wsource following annual snow melt was ineffective. An alternato single-stage coagulation is multiple-stage coagulation wcan include both sequential and independently optimized mustage coagulation~Wahlroos 1991; Chow et al. 1999; Billica aGertig 2000; Carlson and Gregory 2000!

Chow et al. ~1999! investigated the removal of DOC frothree raw waters using sequential alum coagulation. A seriestests at pH 6 were performed and dosed repeatedly with thealum dose five times. The results showed DOC removal for wwith an initial total organic carbon~TOC! of 9 mg/L increasefrom 50 to 60% after the second dose. Subsequent alumshowed no additional removal. The data did show an increremoval of UV absorbing compounds after each dose, alththis was only significant for the high TOC, high SUVA watested, and was correlated with an increased removal of highlecular weight organics.

Alternatively, a number of researchers have looked atstage coagulation where each stage is optimized independWahlroos~1991! used two-stage coagulation with iron coagulato improve chemical oxygen demand removal from 50 to 9using an initial dose at pH 4.8–5.0 followed by a secondary

Table 1. Raw Water Quality~Albert Water Treatment Works!

Parameter UnitsWater quality~June–July!

Water quality~November–December!

DOCa mg/L 7.12–8.36 10.9–12.1Color Hazen 59–80 88–105UV-Abs L/m 39.5–40.6 58.7pH — 6.3–6.6 6.4–6.8Turbidity NTU 2.7–3.2 3.3–4.1aDissolved organic carbon.

at a pH of 8.0. Carlson and Gregory~2000! reported similar ex-

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periments on snow melt water using sequential coagulation.reported that the first stage was conducted at a pH of 4.8intended for the removal of humic substances and the sestage was at pH 8.0–8.5 and was intended for particulatmoval. They identified that current treatment efficiency wasduced at elevated TOC levels that was primarily thought to beto NOM restabilizing the alum flocs. Two-stage coagulationshown to improve the treatability of the source water, especwhen it contained high levels of humic material.

Billica and Gertig~2000! following on from the work by Carson and Gregory looked at the impact of this sequential coation on filter performance. The use of single-stage coagulwith alum during periods of elevated TOC, breakthrough ofticles would be observed after 5 h and would rise from 5 to 4particle counts/mL after 9 h. With two-stage coagulation noticle breakthrough was observed.

The purpose of this research was to investigate coagulatia high SUVA, high DOC raw water which is difficult to treHere we have investigated and optimized coagulation of fracisolated from both the raw water and treated waters. The remdata for each fraction was compared and used to optimizmoval of DOC from the bulk water by way of a multistageagulation process.

Experimental Materials and Methods

Works Overview

Albert Water Treatment Works~WTW! is a three-stage pla~33–55 ML/day! on the western side of Halifax, England. Trement consists of ferric coagulation, clarification, primary filtion, and manganese removal. Clarification is via six dissolveflotation units; primary filtration is via six rapid gravity filteand manganese removal is through eight pressure filterssource water quality varies significantly from season to se~Table 1!. An extensive seasonal sampling and fractionationgram has been undertaken at Albert WTW and details of seachanges in DOC, THMFP of raw, filtered, and individual fractiare reported in Goslan et al.~2002!. During November and December the raw water DOC and color increase substantially,ing to difficult to treat water.

Fractionation

Raw inlet water~75 L! and treated water collected after prim

Table 2. Volume of Fraction Added to Simulate Water Sources

Fraction

Amountof fraction

added~mL!

Dissolvedorganiccarbon

concentration~mg/L!

Raw FAF 424.7 9.24Raw HAF 57.2 3.38Raw HPI-A 338.0 2.63Raw HPI-NA Neat 1.53Treated FAF 7.8 2.95Treated HAF 2.2 1.83Treated HPI-A 7.4 2.05Treated HPI-NA Neat 1.26

Note: FAF5fulvic acid fraction; HAF5humic acid fraction; HPI-A5hydrophilic acid fraction; and HPI-NA5hydrophilic nonacid fraction

filtration ~300 L! from Albert Reservoir was passed through a

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Whatman 1mm prefilter capsule and a Whatman 0.45mm filtercapsule and acidified to pH 2 using hydrochloric acid~HCl!. Allof the acidified filtered water was put through the XAD-7HXAD-4 column pair ~total resin volume was 1200 mL in eacolumn!. XAD-7HP resin was used in place of XAD-8 resin asmanufacture was discontinued. The effluent from both colucontained the nonacid hydrophilic fraction~HPI-NA!. The XAD-7HP column was back eluted with sodium hydroxide~NaOH, 0.1M, 1800 mL!. The eluate was acidified to pH 2 and pasthrough a 60 mL XAD-7HP column to further concentrateHPO-A The HPO-A was desorbed from this column using Na~0.1 M, 250 mL!. This was the hydrophobic acid fraction~HPO-A!. The XAD-4 column was back eluted in the same way as

Fig. 1. Isolated fraction dissolved organic c

Fig. 2. Isolated fraction trihalomethane~

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XAD-7HP column with NaOH~0.1 M, 1800 mL!. The eluate waacidified to pH 2 and passed through a 60 mL XAD-4 columconcentrate further. The hydrophilic acid fraction~HPI-A! wasdesorbed from this column using NaOH~0.1 M, 250 mL!. The pHof the HPO-A was adjusted to 1 by adding concentrated HClleft to settle for 24 h and centrifuged. The supernatant~FAF! wasdecanted. The residual~HAF! was dissolved in the minimum rquired volume of NaOH~0.1 M, ;50 mL). The HAF was hydrogen saturated by passing it through a 5 mLcolumn of Bio-RadAG-MP-50 resin in the hydrogen saturated state and therinsed with reverse osmosis~RO! water~5 mL to ensure compleelution of the HAF!. The FAF was further concentrated on amL column of XAD-7HP and rinsed with RO water~20 mL!, and

OC! distribution of raw and coagulated water

distribution of raw and coagulated water

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desorbed with NaOH~0.1 M, 50 mL!. The FAF was hydrogesaturated in the same way as the HAF eluate and was pthrough a 5 mLcolumn of Bio-Rad AG-MP-50 resin and rinswith RO water~5 mL!. The HPI-A was further concentratedbeing pumped through a 20 mL column of XAD-4 resin, rinwith RO water ~20 mL! and desorbed with NaOH~0.1 M, 50mL!. The HPI-A was hydrogen saturated in the same way aHAF eluate and was pumped through a 5 mLcolumn of Bio-RadAG-MP-50 resin and rinsed with RO water~5 mL!. The fractionswere stored at,5°C. The recovery of the DOC was quantifiby measuring the influent DOC of the water and the DOCvolume of the fractions produced. Recoveries were in the ran87–110%.

Bench Scale Jar Testing

Solutions of water containing both the raw and treated fracfrom the water collected in November 2000 were preparesimulate the source water in terms of FAF, HAF, HPI-A,HPI-NA concentration. This was achieved by dosing a predmined amount of the raw or filtered fraction into de-ionized w~13 L! while stirring using a magnetic stirrer~Table 2!. The DOCconcentration of the fractions containing less than 3 mg/L wincreased in order that any removal during coagulation coumeasured accurately in terms of DOC and ultraviolet absor~UV-Abs! at 254 nm. The pH of the stock solutions was t

Fig. 3. Variation in coagulant dose

Table 3. Specific Ultraviolet Absorbance~SUVA! and Trihalometha

Fraction

Raw

SUVA (m21 L mg21 C) THM-FP (mg m

HAF 4.9 118.9FAF 6.1 186.5HPI-A 3.7 171.3HPI-NA 1.6 85.4

Note: HAF5humic acid fraction; FAF5fulvic acid fraction; HPI-A5hyd

978 / JOURNAL OF ENVIRONMENTAL ENGINEERING © ASCE / SEPTEMB

measured and the pH adjusted to pH 6 with NaOH~0.1 M! andHCl ~0.1 M!. To the stock solutions, NaHCO3 ~20 mg/L! wasadded to achieve approximately 10 mg/L of alkalinity as CaC3 ,which was approximately the concentration found in the nawater sources, and the pH was measured again.

The coagulation and flocculation experiments were carrieusing a Phipps & Bird PB-900 six-paddle jar tester. Six aliqof the solution~1 L! prepared previously were taken from the fsolution. While stirring at 200 rpm for 1 min, ferric sulph~Mistrale-600, EA West! coagulant was dosed to five of the jaleaving the first one as a blank, and the required amount ofto adjust the pH to 6 was added; once again the pH was recof the aliquots. The jars were then stirred for 15 min at 30before settling for an additional 15 min before sampling. Samof each of the jars were taken by filtering through 0.45mm glassfiber filter paper to remove any solids and each sample waslyzed for DOC and UV-Abs.

Analytical Techniques

The DOC~mg/L! was measured using a TOC analyzer~ShimadzuTOC-5000A!, and UV-Abs at 254 nm~L/m! was measured usina Jenway 6505 UV/Vis spectrophotometer with a 4 cmquartzcell. A blank using RO water was run in an optically matchedbefore the sample analysis, and SUVA~L/mg m! was calculateas a ratio of the UV-Abs to DOC. The THM-FP was carried

red for optimum color removal~pH 4.5!

ormation Potential~THM-FP! of Raw and Filtered Fractions

Filtered

SUVA (m21 L mg21 C) THM-FP (mg mg21 C)

6.5 154.02.9 92.02.0 43.91.3 70.2

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using a method adapted from procedure 5710B in ‘‘Stanmethods for the treatment and examination of water and wwater’’ ~American Public Health Association 1992!. The methodinvolved buffering samples at pH 7, chlorinating samplesexcess free chlorine, and storing the sample at 20°C for 7 daallow the reaction to reach completion. The concentration ofTHM ~chloroform, bromodichloromethane, dibromochromethane and bromoform! was measured using a SRI 9300Achromatograph. The THM-FP was the mass sum of theTHMs.

Fig. 4. Coagulant optimized at works inlet pH removals of isolateas Fe, pH 6.3!

Fig. 5. pH and coagulant optimized removals of isolated naturacoagulant doses and pHs!

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Experimental Results and Discussion

Fractionation

The results of the organic matter fractionation are shown in1 and 2, which outline the removals achieved by coagulatioboth the DOC and the THM-FP for each of the individual orgfractions. The principal fraction in terms of DOC and reactivitthe FAF~6.24 mg/L and 1,164.2mg/L, respectively! followed bythe HAF ~1.81 mg/L and 215.1mg/L, respectively!. It should be

ural organic matter fractions with and without staged coagulation~14 mg/L

nic matter fractions with and without staged coagulation~see Table 4 fo

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noted that the THM-FP of the individual fractions totaled mthan the bulk water~1,638.1 and 907.5mg/L, respectively!. Thishas been observed for another study~Owen et al. 1993! wherefractionated substances had a combined reactivity of 100mg/mgC compared with a raw water reactivity of 38mg/mg C. The samstudy also looked at ultrafiltration fractions of the same waterhad a combined reactivity of 219mg/mg C. This was attributedsynergistic effects in chlorine substitution or oxidation reactin the presence of NOM fractions compared to bulk NOM.heterogeneous nature of NOM as well as its fractions is liresponsible for this behavior~Owen et al. 1993! and can be explained in that the fractionation procedure has the effect of dturing the fractions compared to when they are combined inbulk water and the relative reactivity of the isolated fractionstherefore be different compared to those in the bulk water~Peu-ravuori and Pihlaja 1997!.

The treatment conditions employed at Albert WTW at the tof this study are able to achieve high removals of DOC for HFAF, and HPI-A ~98, 89, and 71%, respectively!, while theTHM-FP removal for those fractions is equally high~97, 94, and93%, respectively!. Removal of the HPI-NA is poor with on16% of the DOC and 31% of the THM-FP being removedcoagulation. In addition, the removal of FAF, which althoughpreviously stated is high, is still a cause for concern due to

Fig. 6. Maximum dissolved organic carbon~DOC!

Table 4. Summary of Optimum Coagulation Conditions

Fraction Optimum dose~mg/L as Fe! Optimum pH

Raw FAF 12 4.8Raw HAF 8 4.8Raw HPI-A 8 4.2Raw HPI-NA 15 4.2Treated FAF 8 4.2Treated HAF 8 4.0Treated HPI-A 8 4.0Treated HPI-NA 15 3.5

Note: FAF5fulvic acid fraction; HAF5humic acid fraction; HPI-A

5hydrophilic acid fraction; and HPI-NA5hydrophilic nonacid fraction.

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high remaining DOC and reactivity in terms of THM-FP perof carbon~0.7 mg/L and 92mg/mg C, respectively!. Table 3 compares the SUVA and THMFP of both raw and filtered fractio

Coagulation

The treatment at Albert WTW currently employs ferric sulphas the coagulant. This is constantly reviewed so that maxicolor removal is achieved. Data supplied by Yorkshire Watershows how the coagulant dose varies throughout the yeahow the average coagulant dose is increased by up to 50% dlate summer and autumn~Fig. 3!.

The removal of DOC and THM-FP from the raw water durautumn 2001 was 79 and 93%, respectively. This leaves a reTHM of approximately 70mg/L, which means that there is velittle room for error or sudden deterioration in the raw wquality. There is therefore a need to further reduce the DOC iprechlorinated water. It was previously shown that double colation improves the overall removal of DOC and it is with thismind that optimizing the coagulation of both the raw andpreviously treated fractions was carried out. The works inletwater as shown in Table 1 was approximately pH 6. It was thfore decided to compare the maximum DOC removal at thiswith the removals achieved when each of the fractions ismized for both coagulant dose and pH to show the effecoptimization has on removal efficiency. The removals for thelated fractions at the works inlet pH~6.3! are shown in Fig. 4.can be seen that the secondary coagulant dose significancreases DOC removal for all four fractions, with the FAF showthe largest improvement~34% increase!.

The results of the dual optimization compared with thshown at works inlet pH show a major improvement in Dremoval for all the fractions studied. The hydrophobic fract~i.e., HAF and FAF! show an additional 19 and 5% DOCmoval, respectively. This increases the overall removal to incess of 80% compared with approximately 70% when the pnot optimized. An even greater improvement in DOC remov

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removal being obtained for the HPI-A and HPI-NA fractions,spectively, compared with that seen for the non-pH optimtreatment~Fig. 5!.

Following on from the improved removals for the isolafractions the raw source water was doubly coagulated usinoptimum conditions from the optimization of the fractions. Tmethods were adopted to coagulate the model water. Methinvolved coagulation and pH adjustment followed by a 30 s dbefore addition of the second coagulant dose and anotheadjustment, the remaining coagulation was allowed to contindescribed previously. Method 2, although similar, did not increoptimization of the pH after the second coagulant dose hadadded. The results of the two methods applied show that thoptimization of pH after the second coagulant dose, althoshowing no great increase in DOC removal, had a signifieffect on the UV-Abs removal with an additional 26% remobeing achieved~Fig. 6!.

Currently single-stage optimized coagulation achievesDOC removal at Albert WTW. The employment of optimiztwo-stage coagulation is capable of achieving 80% removalpared to a theoretical removal of 82% based on the optimizof the isolated fractions. It is not clear from the results if a greproportion of the hydrophilic fractions are removed from thestage coagulation by the SUVA values alone and a full fracation would be required to establish this. High UV-Abs remorates are observed for method 1~91%! suggesting high removaof HAF and FAF that are known to cause high color and hehigh UV-Abs, however only 65% is seen when the second stanot pH optimized. This suggests that Method 2 is in fact oacting as a single staged optimized coagulation~see Table 4!.

It is known that metal oxides are more selective to ceisolated fractions. For example Bose and Reckhow~1998!showed how fractions had differing affinities to aluminumdroxide surfaces. Where the HAF and FAF have a greater afthan the other acidic fractions, neutrals and bases show a ‘‘l

Fig. 7. Correlation between specific ultraviolet absorbance~SUVA!matter fractions by ferric coagulation

extent of adsorption’’ than hydrophobic fractions. This may pro-

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vide an explanation as to why there appears to be an abmaximum of approximately 80% DOC removal which equatethe concentration of hydrophobic material in the raw waterthat as expected the more highly charged HAF and FAF aretralized or adsorbed preferentially. Once all the hydrophobicterial has been coagulated there remains very few sites fohydrophilic fractions and hence very low removals are obsein conventional coagulation. In addition they showed howmoval was affected by hydrophobicity and showed a clear clation of DOC removal with SUVA. This correlation was evaated for the fractions tested here.~The SUVA data for the treateHAF, FAF, and HPI-A were not considered due to the measvalues for UV-Abs being lower than the level of detection ofinstrument! and as expected a linear relationship exists betwSUVA and DOC removal which confirms the greater DOCmoval seen of more hydrophobic organic compounds compathose more hydrophilic in nature~Fig. 7!. Here the graph showhigher removal for the fraction by coagulation than that showBose and Reckhow when absorbing onto preformed ferricdroxide flocs. This is to be expected as the flocs formed dcoagulation are fresher than preformed flocs and will hahigher specific surface area and reactivity~Bose and Rekho1998!.

Conclusions

The treatment of water at certain times of the year during peof high rainfall can be problematic due to increased levelNOM. Current treatment processes although achieving~79%! removals of DOC from the bulk water still leave higreactive organic compounds in the resultant water. Optimizeagulation of both the raw and treated fractions can lead toproved removal of the most recalcitrant compounds. Two-scoagulation using optimum conditions obtained from the i

dissolved organic carbon~DOC! removal of isolated natural organ

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ment of the water source. Although the results presented dshow a significant improvement or deterioration in treated wquality this is a significant area for exploratory study as prevwork has shown that the floc produced by two stage coagulare less likely to breakthrough filtration processes~Carlson andGregory 2000! a common problem linked to raised levelsNOM.

Acknowledgments

The writers would like to thank Yorkshire Water Plc, United Utties Plc, and EPSRC for funding this research. The opinionpressed are those of the writers and do not necessarily refleviews of Yorkshire Water or United Utilities.

References

Aiken, G. R., McKnight, D. M., Thorn, K. A., and Thurman, E.~1992!. ‘‘Isolation of hydrophilic organic acids from water using noionic macroporous resins.’’Org. Geochem.,18~4!, 567–573.

American Public Health Association/American Water Works AssociaWater Environment Federation.~1992!. Standard methods for the eamination of water and wastewater, 18th Ed., Washington, D.C.

Amirtharajah, A., and O’Melia, C. R.~1990!. Coagulation processedestabilization, mixing, and flocculation, McGraw-Hill, New York,269–365.

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