Sonication for advanced drinking water treatment

Journal of Harbin Insitute of Technology (New Series), Vol. 16, No.1, 2009Sonication for advanced drinking water treatmentZHANG Guang-ming, WEI Xi-zhu, L Xiang-kun, ZHANG Jie, DOU Zi-bo张光明，魏希柱,李相昆，张杰，豆子波.(State Key Lab of Urban Water Reoure Enionment, Harbin Institute of Technology, Harbin 150090 ,China, gmgwen@ gmail. com)Abstract: This paper investigated the feasibility of sonication as an advanced treatment method for drinking w陆ter production and used comprehensive indexes of water quality to examine its eficience. Results show that som-ication significantly reduces the toxicity of water. Sonicationith5 W/L at 90 kHz lating for 30 min decreasesthe water SUVA and the disinfection byproduct formation potential ( DBPFP) by 38. 7% and 27. 2% respective-ly. Sonication also decreases the UV254 by more than 50% through destroying unsaturated chemical bonds.Higher sound intensity and higher frquency benefit the reduction of TOC and UV254. Besides, sonication sig-nificantly increases the afinity of organics with granular activated carbon (GAC), and thus the hybrid sonica-tion-CAC method reduces the water T0C, COD, UV254, and DBPFP by 78.3%，69.4%，75.7%，and70. 0% respectively. Therefore, sorication and the hybrid sonication-GAC method are proposed as advancedtreatment methods for drinking water.Key words: sonication; drinking water; advanced treatment; DBPFPCLC oumber: TU991Document code; AArticle ID: 1005-9113(2009)01 0016-05Surface water pollution is a serious problem in de-chanically attack sludge flocs. Sonication also gener-veloping countries. In 2006, 50% of surface water inates hydroxyl free radical that is a very active oxidantChina was polluted and failed to meet the national sur~and may react with almost all chemicals. These extremeface water quality standard. Hundreds of persistentconditions and active radicals provide unique environ-chemicals including endocrine disruptors ( EDCs) werements to convert organic matters in water into CO2,found at unsafe levels in 14 major rivers including Son-H2O，inorganie ions， and simple organic acids.ghujiang River , Zhujiang River, and Xiangjiang Riv-Hundreds of studies show that sonication can rapidlyerl. The prevailing pollution of surface waler meansdegrade CCI4，CFC 11, CFC 113， phenols, benzenethat hundreds of water supply plants are forced to useand substituted benzenes, pesticides, and polychlori-unqualified source water, which cannot be purified ef-nated biphenyl ( PCBs), and can effectively deactivatefectively using conventional water treatment process ofbacteria-”。 These researches showed that sonicationcoagulation, sedimentation, filration， and disinfee-quickly degraded many pollutants butmineralizationtion. As a result, many water supply plants use or planwas less effective, the products were often more benignto use advanced treatment after filtration to further puri-than the mother compounds. Since sonication is knownfy the water. The established advanced treatment meth-effcient to remove so many pollutants, it is natural toods include ozone oxidation, granular activated carbontest the feasibility of the technique for advanced drink-(GAC) absorption, ozone-GAC, and membrane filtra-ing water trealment. However, researches focus on sin-tion， Many new technologies have been proposed andgle pollutant degradation and no experiment using com-intensively studied, in which an important group is ad-prehensive indexes is reported,vanced oxidation processes ( AOPs) characterized byhydroxyl free radical oxidation (2-. This paper inves-1 Experimentaltigates one AOP method, sonication, for advanced pur-ification of drinking water from polluted source waler.1.1 Equipments and MaterialsSonication, ultrasonic irradiation, has been stud-Four ultrasonic reactors of the same dimensiongied for water and wastewater treatment for many years.were used for sonication. The sound frequency was 25When applied to liquids, powerful ultrasound causes akHz, 40 kHz, 60 kHz, and 90 kHz respectively. Thecoustic cavitation in which millions of small bubblesreactors were of stainless steel and the volume was 13collapse to produce very high temperature (5000 K)," 中国煤化工granular activatedpressure (500 bar) , and extreme shear forces that me-carbollumn diameter wasReeived 2008 -05 - 29.TYHCNMHGSponsored by the National High Technology Research and Development Program of China( Gront No. 2007 A062339) and the National Science Foundation for Post-doctoral Scientists of China( Grant No. 2006AA06Z306).●16.Joumal of Harbin Insiue of Tchnology (New Series), Vol. 16, No. 1, 200910 cm, and was flled with 1.2 m wood based GAC.chlorination. These DBPs were measured using an Agi-The empty bed retention time ( EBRT) was 30 min.lent 6890 N gas chromalography (GC) with a 30 m xAll experiments were performned using filtraled wa-0.32 mm x0.25 μm HP-5 column and ECD detector.ter collected from a local water supply plant. The waterCHC], and CHBr, were extracted with n-pentane ac-plant used river water as source water and had a stand-cording to standard methods[ method 6322B,ard treatment process of screening, coagulation, sedi-APHA]. The extract was then analyzed using a CC in-mentation, filtration, and chlorine disinfection. Thelet temperature of 220C， detector temperature offiltrated water was kept at4 C before use. For trials U-300C，column pressure of 15 psi, and column flowsing 100 W/L power density, 5 L of water was usedrate of 0.7 mL/ min. The column temperature programeach trial since the maximum power was 500 w. Forwas as following: kept at 35 C for 4 min , increased toall other trials, 10 L of water was used each time.120 at the rate of 20 C/min, and then maintainedDisinfection by-products ( DBPs ) standards were0.5 min. For haloacetic acids analysis, samples werepurchased from Aldrich. All chemicals were used with-pretreated using a micro-extraction procedure without further purification. Homemade de-ioned water wasmethyl tertbutyl ether and esterified with diazomethaneused for all measurements.[ method 6251B，APHA ] before GC measurement.1.2 Selection of Water Quality IndexesThe GC inlet temperature was 220 C, detector temper-Important comprehensive indexes for water includeature was 300 C , column pressure was 23.7 kPa, andchemical oxygen demand ( COD)，total organic carboncolumn flow rate was 0.7 mL/min. The column tem-(TOC), and absorbance of ultraviolet light at 254 nmperature program was as fllows: kept at 40 C for(UV254) , among which COD is traditionally the key.5 min, increased to 140 C at the rate of 10 C/min,However, COD is measured using oxidant of KMnO%and then increased to 240 C at the rate of 40 C/ min.that cannot fully oxidize persistent organics. As a re-sult, the measured COD value may be far below the re-2 Results and Discussional value ( TCOD). Therefore, TOC is used more andmore to measure the organic conteht in water. The2.1 Filtrated Water CharacteristicsCOD/TOC value presents the liability of the water toThe experiments lasted from April to October inoxidation. UV254 emphasizes the structural factor.2007. Filtrated water was collected from a local waterUnsaturated bonds absorb UV lights stronger and con-treatment plant and Tab. 1 reports the basic character-tribute more to UV254 than saturated bonds do. SUVAistics of the filtrated water. The source water qualityis defined as UV254/TOC * 100. SUVA evaluates thefluctuated with the season, but the filtrated water qual-extent of unsaturated chemical bonds and is an index ofity was relatively stable.water toxicity. Another key toxicity index is the disin-fection by-products formation potential ( DBPFP).Tab. 1 Characteristics of filtrate used1.3 Analysis ProceduresndexRangeAverageImportant chemical index for water quality inclu-COD (mg.L)3.2-4.23.6ding COD, UV254, TOC, NH4*-N, NO2~ -N, pH,and turbidity were monitored. The water COD wasUV254(cm-')0.05 -0. 080.07measured using a WTW COD meter, TOC was meas-TOC(mg.L"l)3.7-5.64.2ured using an Oi 1010 TOC analyzer, UV254 wasTubidiy( NTU)0.4-1.31.0measured using a HITACHI U-3010 UV-visible spec-Ammonia- nitrogen(mg.L-1)0.06-0. 230.14trometer，turbidity was monitored using a HACH2100P meter, and pH was measured using a HACH pHNirie mirogen(mg.LI)0-0.0030.0020meler.Nitnte nirogen(mg.L-")0.5-1.10.9Bacteria in water samples were measured by enu-'Alkalinity in CO3'*(mg.L-"I)85 -136112merating the colony forming unit (CFU) of heterogene-ous plate count ( HPC) bacteria fllowing the APHAH7.6-7.97.7standard method using membrane filtration.HPC(/100 mL)108 -294145DBPFP was measured by chlorination of the sam-ples with a 7-day incubation period following the intro-The source water was from a river that everydayduction of the NaOCl solution and phosphate bufferreceives million tons of industrial and municipal(pH 7.0). The applied chlorine concentration was awaste中国煤化工' The poor qualitybout 5 mg/L, which was determined from the prelimi-of soCOD and TOC ofnary studies. Typical hazardous disinfection byprod-theYHC N M H Gneed of advanceducts, CHCl, CHBr, dichloroacetic acid ( DCAA),treatment. The TCOD/TOC is 2.7, but the measuredand trichloroacetic acid (TCAA), were analyzed afterCOD/TOC of filtrated water was less than 1, showing, 17.Journal of Harbin Institute of Technology (Nen Series), Vol. 16, No. 1, 2009that majority organics in the filtrate was resistant to oxi-free radical and other oxidants generated by acousticdation.cavitation continuously oxidized ammonia-nitrogen toThe filtrated water has an average SUVA of 1.73;NO2 -N or NO3 - -N. The overall result was that am-such a high SUVA is expected because of the sourcemonia-nitrogen increased rapidly in the first 30 min ofwater pollution.sonication and then decreased. Further extension ofNote that the average total alkalinity was 112 mg/Lsonication time after 60 min could reduce ammonia-ni-Since both carbonate and bicarbonate are effective freetrogen to below the initial value but is quiet unnecessa-radical scavengers, their existence weakens the oxida-ry since the low level of ammonia-nitrogen in the filtra-tive effects of sonication.ted water was acceptable for drinking water.2.2 Water Characteristics Changes2.3 Impacts of Important ParametersThe changes of water UV254， COD, TOC andThe most important operational parameters in s0~NH4*-N by sonication were reported in Fig. 1. Theno-chemistry are frequency, power density and dura-ultrasonic frequency was 40 kHz and the power densityion. Though researches generally found that longerwas 50 W/L. Both COD and TOC represent the organ-sonication benefits degradation of single pollutants,ic compounds in water but have different meanings.Fig. 1 showed clearly that longer sonication unnecessa-TOC measures the absolute content of organics whilerily decreases the comprehensive indexes values. TheCOD evaluates the amount of organics liable tosonication duration of 30 min was used for following ex-KMnO2. The maximum TOC removal was 14. 98% af-periments.ter 1 h. In general, AOPs quickly attack the organicThe filtrated water was treated using various ultra-pollutants via free radical reaction to form small mole-sonic power densities for 30 min and the sound fre-cules such as short-chain acids and acetates (9.14.quency was 40 kHz. The results were summarized inFurther mineralization is inefficient, and thus the TOCFig. 2. Clearly higher ultrasonic power density benefi-removal is low. Those small intermediates are readilyted TOC and UV254 reduction, and increased the CODto KMnO, oxidation and contribute more to COD thanmore. When the power density increased from 5 W/Ltheir mother compounds do. Therefore, the COD valueto 100 W/L, the TOC reduction increased from 4. 6%increased after 20 min sonication. Ozonation, anotherto 19. 1% and the UV254 reduction increased fromimportant advanced oxidation method and well-esti-37% to 54%. It is generally agreed that high ultrason-mated AOP, is also known to increase COD and be in-ic power facilities pollutant degradation but certain lim-efficient for TOC reduction'2]its, energy saturation plateau , exist. Considering ener-gy consumption, lower power density is much pre-ferred, and thus following experiments were performedusing the power density of5 W/L.600.8-400.6退30... TOC0.4"+.. TOC--UV254一UV254COD-*- NH4-N0t&020-10t/minFig. 1 Water charaterstics change by sonication( 40 kHz,-250 W/L)5030 100Power density/ (Wol")On the other hand, sonication reduced the UV254Fig.2 Impact of ultrasound intensity(40 kHz, 30 min)very quickly and achieved 38% reduction within 5min, showing that sonication destroyed aromaticSound frequency defines the sound field and influ-rings9 and double and triple bonds that strongly ab-ences the sono-degradation of pollutants. Reports havesorbed ultraviolet lights at 254 nm. Longer sonicationshown that different pollutants had various optimal son-did not help in UV254 reduction, indicating certainication frequencies. For example , microcystin-LR de-limits. .grad中国煤化工odide had highestThe initial rapid increase of ammonia nitrogen wasrate .ide range (13.14].due to the conversion of organic-nitrogen to inorganicHowe:MYHCNMHGond100kHzarenitrogen, a normal phenomenon in oxidation of waterexpensive and, thus, improper for water treatment. Wwith high organic contents. At the same time , hydroxyllimited the choice to frequencies below 100 kHz. The●18.Jounal of Harbin Insiue of Technology (New Series), Vol. 16, No. 1, 2009filtrated water samples were treated using ultrasound of2. 5 Hybrid Sonication-GAC Method25 kHz, 40 kHz, 60 kHz, and 90 kHz, the powerThe source water was seriously polluted and thusdensity was 5 W/L and the sonication duration was 30sonication could not reduce TOC and COD to accepta-min. The results were summarized in Fig. 3. Higherble levels. The same problem exists in the well-esti-sound frequency clearly worked better for TOC reduc-mated method of ozonation， and hybrid ozone-GACtion; sound frequency increase from 15 kHz to 90 kHzmethod is used as the solution. Accordingly, we pro-led to TOC reduction increased from 4. 2% to 17%.posed a hybrid sonication-CAC method and tested itsThe UV254 reduction also benefited from higher soundefficiency. The results were reported in Fig. 4 andfrequency but to a much less extent. On the otherTab. 2.hand , the COD change showed no connection with thesound frequency, showing that COD is not a sensible口Sonirationindex to evaluate the water treatment process. General-口GAC■Sunieation-GACly , higher sound frequencies favor hydroxyl free radicalproduction and promote chemical reactions, thus accel-erate pollutant degradation. However, too high fre-quency increases may hampen cavitation and decreasethe treatment efficiency. Within the frequency rangestudied, 90 kHz was the best and, thus, was used forfollowing experiments.50 ITOC。CODTOCUV25.t oUV254Fig.4 EfTect of hybrid sonication-GAC(90 kHz, 5 W/L,30 min, EBRT 30 min)20↑Clearly, sonication enhanced the eficiency of0tGAC adsorption. The COD and TOC removal ratios bysonication-CAC were much higher than the sum of2409(COD and TOCremoval ratios by sonication and byCAC alone. For example , sonication alone reduced on-Sound frequency/kHzly 3% COD, GAC alone reduced 17% COD, and 90n-Fig.3 Impact of ultrasound frequency(5 W/L, 30 min)ication-GAC reduced 63% COD. This could be ex-plained by the fact that sonication changed the compo-2.4 SUVA and DBPFP Reduction by SonicationThe water toxicity was evaluated using two inde-sition of organics in water by cleaving large moleculesxes, namely the SUVA and the DBPFP. The sonicationand oxidizing compounds, thus significantly increasedconitions were as fllowing: frequency of 90 kHz,the afinity of the degraded compounds with the CAC.power density of 5 W/L, and duration of 30 min. TheThe water mutagenic rate and DBPFP were also greatlySUVA value decreased from 1.73 to 1. 07, showing areduced by the hybrid method. The efluent from thereduction of 38.7%. The DBPFP results were reportedsonication-GAC process was of high quality with a CODin Tab.2. Clearly, sonication could reduce the waterof1.1 mg/L, TOC of0.91 mg/L, UV254 of 0.017,NO2-N of 0.074 mg/L, DBPFP of 168.53 mg/L, andmutagen potential and disinfection byproducts formationHPC of 350/100 mL.potential. The results showed that sonication was effi-cient in toxicity reduction.3 ConclusionsTab.2 DBPFP of water, 90 kHz, 5 W/L, 30 min, EBRT=Sonication has been reported effective for pollutant30 min鸣/Ldegradation, and this study shows that sonication is aIndex Filrated waterAfter sonicationAfter sonication-CACviable advanced treatment method for drinking water.CHCI204.1150.263.4Sonication significantly reduced the toxicity of water,CHBr;137.0108.443.3destroyed complex large molecules and oxidized unsatu-DCAA51.732.513.2rated中国煤化工onic power densityimprcof 25 -90 kHz,TCAA110.273.643.5higheMHCNMHGater treatment sigTotal503.2364. 8163.5nificantly. Hybrid sonication-GAC was very effective inCOD and TOC removal, and the eficiency was much, 19.Joumnal of Harbin Institule of Technology (Nev Sries), Vol. 16, No. 1, 2009higher than the addition of sonication alone and GACnitrophenols by means o[ advanced oxidation processes in aalone. Therefore, sonication and sonication-CAC arehomogeneous phase: Photolysis in the presence of hydrogenperoxide versus the Fenton reaction. Chemosphere, 1992,feasible advanced treatment methods for drinking water24: 1369 - 1380.production and sonication-GAC is prefered if the[8] Dewil R, Baeyens J, Goutvrind R. Ultrasonic treatment ofsource water is heavily polluted.waste activated sludge. Environmental Progress, 2006 ,25: 121 - 128.References:[9] Okuno H, Yima B, Mizukoshi Y, et al. Sonolytie degrada-[1 ] Chinese Environmental Protection Bureau. 2005 Chinesetion of hazardous organic compounds in aqueous solution.Environmental Report. 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