Bioresource Technology 166 (2014)592-595Contents lists available at ScienceDirectRIOREOURCEBioresource Technology雪ANELSEVIERjournalhomepage:www.elsevier.com/locate/biortechShortCommunicationAdvanced treatment of biologically pretreated coal gasificationCrossMarkwastewater by a novel integration of heterogeneous catalytic ozonationandbiologicalprocessHaifeng Zhuang, Hongjun Han*, Shengyong Jia, Baolin Hou, Qian ZhaoState Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology.Harbin 150090. ChinHIGHLIGHTS.Sewagesludgewasconverted intosludgebasedactivatedcarbon(SBAC). MnOx were loaded on SBAC to serve as catalyst (MnOx/SBAC) for catalytic ozonation..MnOx/SBACsignificantlyimprovedtheperformanceofpollutantsremovalinozonation. The catalytic ozonation process (COP) efluent was more biodegradable and less toxic. The integration of COP and ANMBBR-BAF had efficient capacity of pollutants removal.ARTICLEINFOABSTRACTArticle history:Advanced treatment of biologically pretreated coal gasification wastewater(CGW)was investigatedReceived 16 March 2014employing heterogeneous catalytic ozonation integrated with anoxic moving bed biofilm reactorReceived in revised form 5 May 2014(ANMBBR) and biological aerated filter (BAF) process. The results indicated that catalytic ozonation withAccepted 7May2014the prepared catalyst (i.e. MnOx/SBAC, sewage sludge was converted into sludge based activated carbonAvailable online 23 May 2014(SBAC) which loaded manganese oxides) significantly enhanced performance of pollutants removal bygenerated hydroxyl radicals.The effluent of catalytic ozonation process was more biodegradable and lessKeywords:toxic than that in ozonation alone. Meanwhile, ANMBBR-BAF showed efficient capacity of pollutantsBiologically pretreated coal gasificationremoval in treatment of the effluent of catalytic ozonation at a shorter reaction time, allowing thewastewaterdischarge limits to be met, Therefore, the integrated process with efficient, economical and sustainableHeterogeneous catalyticozonationadvantageswas suitableforadvanced treatment of real biologicallypretreated CGWCatalyst@ 2014 Elsevier Ltd. All rights reserved.Mechanism discussionBiological process1. Introductioncost-effective process for advanced treatment of biologicallypretreated CGW.The biologically pretreated coal gasification wastewater (CGW)Heterogeneous catalytic ozonation process has attracted morecontains a large number of toxic and refractory compounds, suchand more attentions in recent years due to its efficient capacityasphenoliccompounds,polynucleararomatichydrocarbonsandin the degradation and mineralization of toxic and refractorycompounds (Kasprzyk-Hordern et al.,2003).It was developed tonitrogenousheterocyclic compounds,long-chainhydrocarbons,ammonia,andsoonalongwithlowbiodegradabilityandunsatis-overcomethelimitationsofozonationprocessbycatalystswhichfactory effluent quality (Zhuang etal.,2014).This wastewater con-can promote the decomposition of aqueous ozone to generatetrol task has become a bottleneck for the development of coalhydroxyl radicals (-OH). However, these efficient catalysts all havegasification industry in China which has played a key role in newchallenges in the technical complexity and high cost of productionclean and renewable energy market in recent years (Wangwhich limit their full-scale practical application. Meanwhile, theand Han, 2012).Thus,itis very urgent tofind an efficient andprevious studies showed sewage sludge based activated carbon(SBAC) as a efficient catalyst for catalytic wet air oxidation ofphenoliccompoundsand ozonationof oxalicacid (Marquesetal.,* Corresponding author. Address: School of Municipal and Environmental2011: Wen et al., 2012). which was not only a environmentallyEngineering. Harbin Institute of Technology. Harbin 150090, China. Tel.: +86 451beneficial and sustainable sewage sludge disposal method but also87649777: fax: +86 451 86283082.reducedthecostofproductionof catalyst.Furthermore,thereisaE-mail address: han13946003379@163.com (H. Han).http://dx.doi.org/10.1016/j.biortech.2014.05.0610960-8524/ 2014 Elsevier Ltd. All rights reserved
Short Communication Advanced treatment of biologically pretreated coal gasification wastewater by a novel integration of heterogeneous catalytic ozonation and biological process Haifeng Zhuang, Hongjun Han ⇑ , Shengyong Jia, Baolin Hou, Qian Zhao State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China highlights Sewage sludge was converted into sludge based activated carbon (SBAC). MnOx were loaded on SBAC to serve as catalyst (MnOx/SBAC) for catalytic ozonation. MnOx/SBAC significantly improved the performance of pollutants removal in ozonation. The catalytic ozonation process (COP) effluent was more biodegradable and less toxic. The integration of COP and ANMBBR–BAF had efficient capacity of pollutants removal. article info Article history: Received 16 March 2014 Received in revised form 5 May 2014 Accepted 7 May 2014 Available online 23 May 2014 Keywords: Biologically pretreated coal gasification wastewater Heterogeneous catalytic ozonation Catalyst Mechanism discussion Biological process abstract Advanced treatment of biologically pretreated coal gasification wastewater (CGW) was investigated employing heterogeneous catalytic ozonation integrated with anoxic moving bed biofilm reactor (ANMBBR) and biological aerated filter (BAF) process. The results indicated that catalytic ozonation with the prepared catalyst (i.e. MnOx/SBAC, sewage sludge was converted into sludge based activated carbon (SBAC) which loaded manganese oxides) significantly enhanced performance of pollutants removal by generated hydroxyl radicals. The effluent of catalytic ozonation process was more biodegradable and less toxic than that in ozonation alone. Meanwhile, ANMBBR–BAF showed efficient capacity of pollutants removal in treatment of the effluent of catalytic ozonation at a shorter reaction time, allowing the discharge limits to be met. Therefore, the integrated process with efficient, economical and sustainable advantages was suitable for advanced treatment of real biologically pretreated CGW. 2014 Elsevier Ltd. All rights reserved. 1. Introduction The biologically pretreated coal gasification wastewater (CGW) contains a large number of toxic and refractory compounds, such as phenolic compounds, polynuclear aromatic hydrocarbons and nitrogenous heterocyclic compounds, long-chain hydrocarbons, ammonia, and so on along with low biodegradability and unsatisfactory effluent quality (Zhuang et al., 2014). This wastewater control task has become a bottleneck for the development of coal gasification industry in China which has played a key role in new clean and renewable energy market in recent years (Wang and Han, 2012). Thus, it is very urgent to find an efficient and cost-effective process for advanced treatment of biologically pretreated CGW. Heterogeneous catalytic ozonation process has attracted more and more attentions in recent years due to its efficient capacity in the degradation and mineralization of toxic and refractory compounds (Kasprzyk-Hordern et al., 2003). It was developed to overcome the limitations of ozonation process by catalysts which can promote the decomposition of aqueous ozone to generate hydroxyl radicals ( OH). However, these efficient catalysts all have challenges in the technical complexity and high cost of production which limit their full-scale practical application. Meanwhile, the previous studies showed sewage sludge based activated carbon (SBAC) as a efficient catalyst for catalytic wet air oxidation of phenolic compounds and ozonation of oxalic acid (Marques et al., 2011; Wen et al., 2012), which was not only a environmentally beneficial and sustainable sewage sludge disposal method but also reduced the cost of production of catalyst. Furthermore, there is a http://dx.doi.org/10.1016/j.biortech.2014.05.061 0960-8524/ 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China. Tel.: +86 451 87649777; fax: +86 451 86283082. E-mail address: han13946003379@163.com (H. Han). Bioresource Technology 166 (2014) 592–595 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
593H.Zhuang et al./Bioresource Technology 166 (2014) 592-595high expectation on SBAC modification by loaded Mn oxides(Faria etal.,2009).An amountof SBAC was immersed inMnnitrate(MnOx, the most reactive metal oxides catalyst)for furthersolutions with a desired concentration and thesuspension was stir-improving the catalytic activity and stability of SBAC, However,red with 200 rpm for 24 h, and then evaporated in a rotary evapo-few studies on using this type of catalyst to enhance the catalyticrator at 105 °C for 12 h. After that the MnOx/SBAC was calcined atactivity in ozonation of real industrial wastewater have been pub-600 °Cfor 3h in a mufflefurnace in the absence of oxygen conditionlished.Itisnoteworthythatcatalyticozonationprocess(COP)fortoobtaintherequiredcatalyst,andthenwashedwithMilli-Qwatercomplete eliminating pollutants is expensive because the oxida-toremovethelooselybondedmetal ironsanddriedandstored.Thetion intermediatesformedduringtreatmenttendtobemoreandmain characteristics of MnOx/SBAC were as follows: 327.5 m/g ofmore resistant to their chemical degradation (Munoz et al.,BETarea,0.122cm*/gofmicroporesvolume,0.204cm*/gofmacro2005).However,theoxidationintermediates aregenerallymoreandmesoporesvolumes,3.318nm of averagepore size,15.23%ofbiodegradable than the original molecules. Therefore, there is aMn,1.12% of Zn,0.47%of Fe,1.54%of Al and 6.58of pHpzc-greatadvantageous of integrating COP with biological process toattain a more efficient and cost-effective process for treating low2.2.Experimental proceduresbiodegradability and high toxicity wastewater. Especially, nitrogencompounds, which were difficult to remove in coP, even the con-Theraw wastewater was first added into CoP reactor (1.2L ofcentration increased by oxidation intermediates formed (Yangthe effective volume) followed by a continuous input of ozoneetal.,2011).weremoresuitableforbiological treatment.Itwasgas.Ozone was generated using a corona discharge ozone genera-reported that anoxic moving bed biofilm reactor (ANMBBR) andtor with pure oxygen as feed gas (DHX-I, Harbin Jiujiu Electro-biological aerated filter (BAF) process (ANMBBR-BAF) with short-chemistryTechnology Co.,Ltd., China).Theflowrate of ozonegascut biological nitrogen removal (SBNR) was successfully appliedwas500ml/min and ozonegas concentration was 15mg/L.Theto advanced treatment of real biologically pretreated CGWoff-gas was absorbed by KI solution. In the adsorption test, air,(Zhuang et al.,2014).But, the system still had several problemsinstead of ozonewas introduced into thereactorwith all othertobesolved,suchasoverlonghydraulicresidencetimes(12hofreaction conditions kept identical. Additionally,the added concen-HRT) and interference of toxic compounds (total phenols in excesstration of tert-butanol (TBA) as scavenger for -OH was 100 mg/L.of 100 mg/L restricted the biodegradation). Thus, the novel integra-The COP effluent was poured into a sparger equipped for aerationtionofCOPandANMBBR-BAFhassubstantialadvantagesto solve1h to remove the remaining ozone and further treated inthe difficult problems between them. In the present study. theANMBBR-BAF system.The composition of bioreactors, start-upcatalytic activity of MnOx/SBAC in ozonation of raw wastewaterand operational strategies of ANMBBR-BAF system were describedwas investigated, and then MnOx/SBAC dose and reaction timeby Zhuang et al. (2014).The pH was controlled by added NaOHwere optimized. Meanwhile, effects of initial pH and tert-butanol(1 mol/L) and HCI (1 mol/L).on pollutants removal were examined during cop.Furthermore,the performance of pollutants removal of the integrated coP with2.3. Analytical methodsANMBBR-BAFprocess was evaluated.BET surface area and pore volume of MnOx/SBAC weremeasured using a surface area and porosity analyzer (ASAP 2020,2. MethodsMicromeritics). The pH at the point of zero charge (pHpzc) wasmeasured with a mass titration method. Samples were gold-coated2.1.Materialsand observed under a scanning electron microscope(SEM, HITACHIS4800 HSD,Japan).The percentage content of major elements wasReal biologically pretreated CGW was obtained from thedeterminedbyX-rayfluorescence(XRF)withX-rayspectrometereffluent of an upflow anaerobic sludge bed reactor followed by(AXIOS-PW4400, Holland). COD, BODs,TP and NH-N were mea-anoxic-aerobic process after ammonia stripping and phenols sol-suredbyStandardMethods(APHA,1998).TOCandTNweredeter-ventextractionintheLurgicoalgasificationwastewatertreatmentmined with a total organic carbon analyzer (Toc-V, Shimadzuplant (China Coal Longhua Harbin Coal Chemical Industry Co., Ltd).Corporation, Japan).PH values were determined with a pH meterThe concentrations of the main pollutants of raw wastewater were(pHS-3C, Leici, China). The ozone gaseous concentration wasasfollows:300-350mg/L of cOD,0.05-0.07of BODs/COD value,measured using the iodometric titration method. Throughout120-180 mg/L of total phenols (TP), 100-140 mg/Lof total organicexperiments, the withdrawn samples were filtered using 0.45 μmcarbon (TOC),60-80mg/Loftotal nitrogen(TN)and30-50mg/Lofacetic acid fiber filters to separate the catalyst particles priorNH-N. The pH ranged between 6.5 and 7.5. The dewatered sewageto analysis and the results were average of at least threesludge was collected from the biological wastewater treatmentmeasurementswithanaccuracyof5%.plant (Harbin, China).Thepreparationprocessof SBACfollowed themethoddevelopedby Wen et al.(2012).Briefly.the sewage sludge was dried at 105C3.Results and discussionfor24hthengroundandsievedintoauniformsizeof<0.1mm.Then, a 10 g of sample was impregnated into a 75 ml of 3mol/L3.1.Effects of catalyston ozonation of biologicallypretreated CGWZnCl2 solution as an activation agentfor 24 h at room temperature.When the supernatant liquid was completely removed, the sampleThe addition of MnOx/SBAC significantly enhanced the TPwas dried at i05 °C and subsequently was pyrolyzed in a muffle fur-removal and biodegradability of treated wastewater in cop.nace where high pure N2 was in-poured for producing the absenceFig.1 shows 83.5% of TP was degraded with ozonation alone inof oxygen condition.The furnace temperature was gradually60 min, the corresponding BODs/COD value was improved toincreased at a rate of 18C/min and the final temperature of0.152. With 1.0 g/L of MnOx/SBAC, the same removal efficiency700 C maintained for 1 h, prior to cooling in nitrogen gas. Afterand BODs/COD value in COP reached within 3O min. When dosingbeing pyrolyzed, the products were washed with 3.0 mol/L HCI toMnOx/SBAC in the range from 0.0 to 1.0 g/L, the removal efficiencyremoveinorganicimpurities,thentheproductswerewashed withandBODs/CODvalueincreasedfasterthanthatwhendosingintheMilli-Q water until constant pH and dried.MnOx/SBAC wasrange of 1.0-5.0 g/L. The removal efficiency and BODs/COD value atprepared by a simple wet impregnation improved technique1.0g/LofMnOx/SBACwere13.4%and286.8%higherthanthatin
high expectation on SBAC modification by loaded Mn oxides (MnOx, the most reactive metal oxides catalyst) for further improving the catalytic activity and stability of SBAC. However, few studies on using this type of catalyst to enhance the catalytic activity in ozonation of real industrial wastewater have been published. It is noteworthy that catalytic ozonation process (COP) for complete eliminating pollutants is expensive because the oxidation intermediates formed during treatment tend to be more and more resistant to their chemical degradation (Muñoz et al., 2005). However, the oxidation intermediates are generally more biodegradable than the original molecules. Therefore, there is a great advantageous of integrating COP with biological process to attain a more efficient and cost-effective process for treating low biodegradability and high toxicity wastewater. Especially, nitrogen compounds, which were difficult to remove in COP, even the concentration increased by oxidation intermediates formed (Yang et al., 2011), were more suitable for biological treatment. It was reported that anoxic moving bed biofilm reactor (ANMBBR) and biological aerated filter (BAF) process (ANMBBR–BAF) with shortcut biological nitrogen removal (SBNR) was successfully applied to advanced treatment of real biologically pretreated CGW (Zhuang et al., 2014). But, the system still had several problems to be solved, such as overlong hydraulic residence times (12 h of HRT) and interference of toxic compounds (total phenols in excess of 100 mg/L restricted the biodegradation). Thus, the novel integration of COP and ANMBBR–BAF has substantial advantages to solve the difficult problems between them. In the present study, the catalytic activity of MnOx/SBAC in ozonation of raw wastewater was investigated, and then MnOx/SBAC dose and reaction time were optimized. Meanwhile, effects of initial pH and tert-butanol on pollutants removal were examined during COP. Furthermore, the performance of pollutants removal of the integrated COP with ANMBBR–BAF process was evaluated. 2. Methods 2.1. Materials Real biologically pretreated CGW was obtained from the effluent of an upflow anaerobic sludge bed reactor followed by anoxic–aerobic process after ammonia stripping and phenols solvent extraction in the Lurgi coal gasification wastewater treatment plant (China Coal Longhua Harbin Coal Chemical Industry Co., Ltd). The concentrations of the main pollutants of raw wastewater were as follows: 300–350 mg/L of COD, 0.05–0.07 of BOD5/COD value, 120–180 mg/L of total phenols (TP), 100–140 mg/L of total organic carbon (TOC), 60–80 mg/L of total nitrogen (TN) and 30–50 mg/L of NH4 + -N. The pH ranged between 6.5 and 7.5. The dewatered sewage sludge was collected from the biological wastewater treatment plant (Harbin, China). The preparation process of SBAC followed the method developed by Wen et al. (2012). Briefly, the sewage sludge was dried at 105 C for 24 h then ground and sieved into a uniform size of <0.1 mm. Then, a 10 g of sample was impregnated into a 75 ml of 3 mol/L ZnCl2 solution as an activation agent for 24 h at room temperature. When the supernatant liquid was completely removed, the sample was dried at 105 C and subsequently was pyrolyzed in a muffle furnace where high pure N2 was in-poured for producing the absence of oxygen condition. The furnace temperature was gradually increased at a rate of 18 C/min and the final temperature of 700 C maintained for 1 h, prior to cooling in nitrogen gas. After being pyrolyzed, the products were washed with 3.0 mol/L HCl to remove inorganic impurities, then the products were washed with Milli-Q water until constant pH and dried. MnOx/SBAC was prepared by a simple wet impregnation improved technique (Faria et al., 2009). An amount of SBAC was immersed in Mn nitrate solutions with a desired concentration and the suspension was stirred with 200 rpm for 24 h, and then evaporated in a rotary evaporator at 105 C for 12 h. After that the MnOx/SBAC was calcined at 600 C for 3 h in a muffle furnace in the absence of oxygen condition to obtain the required catalyst, and then washed with Milli-Q water to remove the loosely bonded metal irons and dried and stored. The main characteristics of MnOx/SBAC were as follows: 327.5 m2 /g of BET area, 0.122 cm3 /g of micropores volume, 0.204 cm3 /g of macro and mesopores volumes, 3.318 nm of average pore size, 15.23% of Mn, 1.12% of Zn, 0.47% of Fe, 1.54% of Al and 6.58 of pHpzc. 2.2. Experimental procedures The raw wastewater was first added into COP reactor (1.2 L of the effective volume) followed by a continuous input of ozone gas. Ozone was generated using a corona discharge ozone generator with pure oxygen as feed gas (DHX-I, Harbin Jiujiu Electrochemistry Technology Co., Ltd., China). The flow rate of ozone gas was 500 ml/min and ozone gas concentration was 15 mg/L. The off-gas was absorbed by KI solution. In the adsorption test, air, instead of ozone, was introduced into the reactor with all other reaction conditions kept identical. Additionally, the added concentration of tert-butanol (TBA) as scavenger for OH was 100 mg/L. The COP effluent was poured into a sparger equipped for aeration 1 h to remove the remaining ozone and further treated in ANMBBR–BAF system. The composition of bioreactors, start-up and operational strategies of ANMBBR–BAF system were described by Zhuang et al. (2014). The pH was controlled by added NaOH (1 mol/L) and HCl (1 mol/L). 2.3. Analytical methods BET surface area and pore volume of MnOx/SBAC were measured using a surface area and porosity analyzer (ASAP 2020, Micromeritics). The pH at the point of zero charge (pHpzc) was measured with a mass titration method. Samples were gold-coated and observed under a scanning electron microscope (SEM, HITACHI S4800 HSD, Japan). The percentage content of major elements was determined by X-ray fluorescence (XRF) with X-ray spectrometer (AXIOS-PW4400, Holland). COD, BOD5, TP and NH4 + -N were measured by Standard Methods (APHA, 1998). TOC and TN were determined with a total organic carbon analyzer (TOC-V, Shimadzu Corporation, Japan). PH values were determined with a pH meter (pHS-3C, Leici, China). The ozone gaseous concentration was measured using the iodometric titration method. Throughout experiments, the withdrawn samples were filtered using 0.45 lm acetic acid fiber filters to separate the catalyst particles prior to analysis and the results were average of at least three measurements with an accuracy of ±5%. 3. Results and discussion 3.1. Effects of catalyst on ozonation of biologically pretreated CGW The addition of MnOx/SBAC significantly enhanced the TP removal and biodegradability of treated wastewater in COP. Fig. 1 shows 83.5% of TP was degraded with ozonation alone in 60 min, the corresponding BOD5/COD value was improved to 0.152. With 1.0 g/L of MnOx/SBAC, the same removal efficiency and BOD5/COD value in COP reached within 30 min. When dosing MnOx/SBAC in the range from 0.0 to 1.0 g/L, the removal efficiency and BOD5/COD value increased faster than that when dosing in the range of 1.0–5.0 g/L. The removal efficiency and BOD5/COD value at 1.0 g/L of MnOx/SBAC were 13.4% and 286.8% higher than that in H. Zhuang et al. / Bioresource Technology 166 (2014) 592–595 593
594H.Zhuang et al/Bioresource Technology 166 (2014) 592-595100a10003alone￥03+MnOx/SBAC—SBAC8r80MnOx/SBAC(ee(%) Kee eoel d6060404o0.0g/L-+0.5 g/L—1.0g/L2020×2.0g/L5.0g/Lo24710119102030405060700Initial pHReaction time (min)70b0.703aloneD 03 +TBA0.0g/LoO3+MnOx/SBAC0.5g/L0.6(%)Kouepe ealO3+MnOx/SBAC+TBA1.0g/L50*2.0g/L0.55.0g/L40Oo3050.320OO0.210C.151015202530350.0010203040506070Reactiontime (min)Reaction time (min)Fig. 2. Effects of initial pH and TBA on the performance of COD and TOC removalFig.1. Effects of catalyst (MnOx/SBAC) on the TP removal and BODs/CODError bars represent standard deviation of triplicate tests.improvement,(a)TPremoval,(b)BODs/COD improvement.Errorbars representstandard deviation of triplicate tests.nosignificant differencesMnOx/SBAC dropped (around 15.0%).Especially,at pH higher thanozonationalone.However,wereobservedwhenthedoseofMnOx/SBACincreasedfrom1.oto7.obothcatalystandmostofpollutantsofrawwastewaterwere5.0 g/LThus,the optimal amount of catalyst of 1.0 g/L was a trade-negatively charged (catalyst pHpze was 6.28 and raw wastewateroff between efficient catalytic activity and cost.pHwasapproximately7)occurringrepulsiveforcesbetweenthemMeanwhile,phenolic compounds had high toxicity over biodeg-which would inhibit adsorption. In raw wastewater pH, coDradation which acted as the dominant toxic pollutants in real bio-removal efficiency was 62.8% with coP in 30 min. In contrast, thelogically pretreated CGW (around 51.6% of COD). It had beenadsorption of COD on MnOx/SBAC only accounted for 33.7% ofreported thatTP concentrationbelow 100mg/Lwas selectedasCOD.Thus, the improvement of cOD removal was attributed tooptimum conditionsthat organiccompoundswas commonlystronger decomposition of ozone intoOH rather than adsorptionacceptable for biological treatmentprocess (Zhuang et al.,2014).by the catalyst at alkaline conditions (Moussavi and KhosraviThis level achieved within 30 min in CoP. The corresponding2012).However,the effect of initial pH on catalytic activity wasBODs/COD was 0.42 which was considered totally biodegradablelimited,and coD removal slightly improved in coP(around(Esplugas et al,2004).Under met requirements of the subsequent12.6%) when pH increased from 7to 11.biological process,the reaction timewas shortened to 30minInordertofurtherinvestigationtheinterventionof'OHinCOPwhich saved 50% of energy consumption.Therefore,CoPwiththeeffectofTBAasradicalscavengeronTOCremovalwasper-MnOx/SBAChadadual benefitinthatitreducedthetoxicpollu-formed. Fig.2 exhibits the presence of TBA affected negativelythe catalytic activity of catalyst. Toc removal efficiency wastantsand enhanced biodegradabilityin shorterreactiontimedecreased from26.1% (ozonation alone)and 52.5% (MnOx/SBAC)3.2.Mechanism discussionin 30 min without TBA to 15.2% and 27.8%, respectively. when100mg/Lof TBA wereadded under raw wastewater pH.The resultsAs illustrated in Fig. 2, the catalytic activity of MnOx/SBAC sig-indicated the main reaction pathways of cOP involved the partici-nificantly was improved with pH increased. When pH increasedpation of the highly reactive-OH. Compared to COP with SBACfrom2to11,COD removal efficiency was improved by32.4%and(1g/L)as catalyst achieved around 30.2% reduction of TOC (data40.1% in ozonation without and with MnOx/SBAC(1g/L)innot shown) in raw wastewater, the high dispersion of Mn oxides30 min,respectively.Meanwhile, CoD removal by adsorption ofonthe SBAC (Fig.Si)andthemultivalenceoxidation states were
ozonation alone. However, no significant differences were observed when the dose of MnOx/SBAC increased from 1.0 to 5.0 g/L. Thus, the optimal amount of catalyst of 1.0 g/L was a tradeoff between efficient catalytic activity and cost. Meanwhile, phenolic compounds had high toxicity over biodegradation which acted as the dominant toxic pollutants in real biologically pretreated CGW (around 51.6% of COD). It had been reported that TP concentration below 100 mg/L was selected as optimum conditions that organic compounds was commonly acceptable for biological treatment process (Zhuang et al., 2014). This level achieved within 30 min in COP. The corresponding BOD5/COD was 0.42 which was considered totally biodegradable (Esplugas et al., 2004). Under met requirements of the subsequent biological process, the reaction time was shortened to 30 min which saved 50% of energy consumption. Therefore, COP with MnOx/SBAC had a dual benefit in that it reduced the toxic pollutants and enhanced biodegradability in shorter reaction time. 3.2. Mechanism discussion As illustrated in Fig. 2, the catalytic activity of MnOx/SBAC significantly was improved with pH increased. When pH increased from 2 to 11, COD removal efficiency was improved by 32.4% and 40.1% in ozonation without and with MnOx/SBAC(1 g/L) in 30 min, respectively. Meanwhile, COD removal by adsorption of MnOx/SBAC dropped (around 15.0%). Especially, at pH higher than 7.0 both catalyst and most of pollutants of raw wastewater were negatively charged (catalyst pHpzc was 6.28 and raw wastewater pH was approximately 7) occurring repulsive forces between them which would inhibit adsorption. In raw wastewater pH, COD removal efficiency was 62.8% with COP in 30 min. In contrast, the adsorption of COD on MnOx/SBAC only accounted for 33.7% of COD. Thus, the improvement of COD removal was attributed to stronger decomposition of ozone into OH rather than adsorption by the catalyst at alkaline conditions (Moussavi and Khosravi, 2012). However, the effect of initial pH on catalytic activity was limited, and COD removal slightly improved in COP (around 12.6%) when pH increased from 7 to 11. In order to further investigation the intervention of OH in COP, the effect of TBA as radical scavenger on TOC removal was performed. Fig. 2 exhibits the presence of TBA affected negatively the catalytic activity of catalyst. TOC removal efficiency was decreased from 26.1% (ozonation alone) and 52.5% (MnOx/SBAC) in 30 min without TBA to 15.2% and 27.8%, respectively, when 100 mg/L of TBA were added under raw wastewater pH. The results indicated the main reaction pathways of COP involved the participation of the highly reactive OH. Compared to COP with SBAC (1 g/L) as catalyst achieved around 30.2% reduction of TOC (data not shown) in raw wastewater, the high dispersion of Mn oxides on the SBAC (Fig. S1) and the multivalence oxidation states were 0 10 20 30 40 50 60 70 0 20 40 60 80 100 TP removal efficiency (%) Reaction time (min) 0.0 g/L 0.5 g/L 1.0 g/L 2.0 g/L 5.0 g/L a 0 10 20 30 40 50 60 70 0.0 0.1 0.2 0.3 0.4 0.5 0.6 b 0.7 BOD5/COD Reaction time (min) 0.0g/L 0.5 g/L 1.0 g/L 2.0 g/L 5.0 g/L Fig. 1. Effects of catalyst (MnOx/SBAC) on the TP removal and BOD5/COD improvement, (a) TP removal, (b) BOD5/COD improvement. Error bars represent standard deviation of triplicate tests. 0 20 40 60 80 100 COD removal efficiency (%) Initial pH O3 alone O3+MnOx/SBAC SBAC MnOx/SBAC 2 4 7 9 10 11 0 5 10 15 20 25 30 35 0 10 20 30 40 50 60 70 TOC removal efficiency (%) Reaction time (min) O3 alone O3 +TBA O3+MnOx/SBAC O3+MnOx/SBAC+TBA Fig. 2. Effects of initial pH and TBA on the performance of COD and TOC removal. Error bars represent standard deviation of triplicate tests. 594 H. Zhuang et al. / Bioresource Technology 166 (2014) 592–595
595H.Zhuang et al./Bioresource Technology 166 (2014) 592-595suggested to be responsible for the higher catalytic activity ofwhich all met class-l criteria of the Integrated WastewaterMnOx/SBAC.Suchas cobaltoxides enhancedmineralization ofher-Discharge Standard (GB18918-2002, China). The results showedbicide 2,4-D by generated -OH with electron transferred, which hadthat integration of COP and ANMBBR-BAF was an efficient, cost-multivalence oxidation states of cobalt (Hu et al., 2008). Similarly.effectively and sustainable process for treating real biologicallyMn oxides also existed in mixed valence (+2 and +3 valences). Itpretreated CGW withashortretentiontime.can be assumed that the presence of such species had a catalyticeffect to the generation of -OH by electron transferred between4.Conclusionsloaded Mn oxides and ozone molecules in COP. As regards 1.12%of Znwas found in thebulk of MnOx/SBAC,Wen etal.(2012)A novel integration of COP and ANMBBR-BAF was successfullyhadconfirmedZnOandZnClhadnocatalyticactivityinozonationapplied to advanced treatment of biologically pretreated CGW.oforganicmatter.Additionally.thereweredifferencesbetweentheThe results indicated COP with MnOx/SBAC significantly improvedTP (81.2%) and TOC (52.5%) removal trend, which indicated theperformance of pollutants removal by generated 'OH and the efflu-most of phenolic compounds were converted into intermediatesentweremorebiodegradableand lesstoxicthanthatinozonationrather than completely eliminated.alone.Meanwhile,ANMBBR-BAF showed efficient capacity of pol-lutants removal in COP effluent at short reaction time.The resultsshowed the integrated process with efficient and economical3.3.Biological treatment of theCoP effluentadvantages was beneficial to engineering application.The real biologically pretreated CGW consists considerableAcknowledgementsamountsoftoxicandinhibitorycompoundswithlowbiodegrad-ability (around 0.06 of BODs/COD value). which are the most diffi-This work was supported by Sino-Dutch Research Programculttobreakdownbymicroorganisms(Padoleyetal.,2oo8).(SDRP: 2012-2016) and the independent subject sponsored byFig.3 shows it took about 12 h for the TN to be reduced to belowState Key Laboratory of Urban Water Resource and Environment,15 mg/L with raw wastewater in ANMBBR-BAF, which had efficientHarbin Institute of Technology (No.2013DX10).performance ofTN removal with SBNR process, especially under thehigh toxic loading (around 160 mg/L of TP). But, it was difficult toAppendixA.Supplementarydatadecrease the TOC tobelow 20mg/L in 24 h.In contrast, after pre-treating of raw wastewater with COP in 30 min,the biological pro-Supplementary data associated with this article can be found, incessreducedremainingTOC(around57.0mg/L)oftheCOPeffluentthe online version,at http://dx.doi.org/10.1016/j.biortech.2014.05.to 17.4 mg/L at a much shorter time of 5.5 h, the corresponding TN061.decreased to 13.6mg/L.Moreover,most of the TN(77.3%)wasremoved in the ANMBBR-BAF which consumed around 25.6% ofReferencesCOD and 17.8%of TP as carbon resource fordenitrification.Theseobservations clearly depicted that, CoP could degrade the toxicAPHA,1998.Standard Methods for the Examination of Waterand Wastewaterand inhibitory compounds into simple intermediates or completely20th ed. American Public Health Association,American Water Workseliminate,thereby overcoming raw wastewater negative impactonAssociation,WaterEnvironmentFederation Washington,DCEsplugas,S,Contreras,S,llis,D.,2004:Engineeringaspectsoftheintegrationofthe metabolism of microorganisms.Additionally,the optimum HRTchemical and biological oxidation:simplemechanisticmodels for.the oxidationofintegrated process was 6 h, further prolonged time did not signif-treatment.JEnviron.Eng.130,967-974icantly enhanced pollutants removal. Table S1 summarizes theFariaP.C.Co.JJ.M_PreiraM.F.R209.ctivatedcarbonandceriaatalyapplied to the catalytic ozonation ofdyes and textile efluents.Appl. Catal.B:average removal efficiencies of COD, TOC, NH-N, TN and TP wereEnviron.88.341-35087.5%,85.5%,90.9%,80.6%and 98.7%, the corresponding effluentHu,C.Xing.S.,Qu.J.,He.H.,208.Catalyticozonationofherbicide2.4-Dovercobaltconcentrations of 37.5, 17.4, 3.9,13.6 and 1.7mg/L, respectively.oxidesupportedon-mesoporouszirconia.J.Phys.Chem.C112,5978-5983.Kasprzyk-Hordern,B.,Ziolek,M.Nawrocki,J2003.Catalyticozonation andmethods of enhancing molecular ozone reactions in water treatment. ApplCatal.B:Environ.46.639-669140Marques.R.R.N.Staber.F.Smith.KM.FabregatABengoa,C.Font.JFortunyTOCinANMBBR-BAFPullket,S.Fowler,G.D.,GrahamNJD211.Sewagesudgebased catalytsfoD-TOC in integrated process120catalytic wet air oxidation of phenol:preparation,characterization and catalytic+TN in ANMBBR-BAFperformance.Appl.Catal.B:Environ.101,306-316Moussavi,GKhosravi,R,2012.PreparationandcharacterizationofabiocharfromTN in integrated process100pistachio hull biomass and its catalytic potential for ozonation of waterXrecalcitrant contaminants.Bioresour.Technol.119,66-71.Munoz.RieradevallJ.TorradesFPeral.J,Domenech,,205.nvironmenta80assessment ofdifferent solar driven advancedoxidation processes.Sol.Energy79,369-375TPadoley,K.V.,Mudliar,S.N.,Pandey,R.A.,20o8.Heterocyclicnitrogenouspollutants60in the environment and their treatment options -an overview. Bioresour.R政Technol.99.4029-4043Wang.W.Han,HJ.2012.Recoverystrategiesfor tacklingtheimpactof phenolic40 compounds in a UASB reactor treating coal gasification wastewater,Bioresour.3?Technol.103.95-100.Wen.anZHMa.JLiuZ.QZhaoiJJ22eusefsewagesludgea20catalyst in ozonation-efficiencyforthe removal of oxalic acid and the control1894ofbromateformation.J.Hazard.Mater.239-240,381-388.Yang,S.,Wang,Q.H.,Zhang.T.,Li,P,Wu,CF.,2011.Biologicalnitrogen.removal0using the supernatant of ozonized sludge as extra carbon source.Ozone Sci. Eng61200.5U9182433,410-416Reaction time(h)Zhuang.H.F.Han,HJ.Jia,S.Y.Zhao,Q.,Hou,B.L,2014.Advanced treatmentofbiologically pretreated coal gasification wastewater using a novel anoxicFig.3.Time-evolution profile of TOC and TN concentrations in the integratedmoving bed biofilm reactor (ANMBBR)-biological aerated filter (BAF) system.Bioresour.Technol.157,223-230heterogeneous catalytic ozonation with ANMBBR-BAF process. Error bars representstandard deviation of triplicate tests
suggested to be responsible for the higher catalytic activity of MnOx/SBAC. Such as cobalt oxides enhanced mineralization of herbicide 2,4-D by generated OH with electron transferred, which had multivalence oxidation states of cobalt (Hu et al., 2008). Similarly, Mn oxides also existed in mixed valence (+2 and +3 valences). It can be assumed that the presence of such species had a catalytic effect to the generation of OH by electron transferred between loaded Mn oxides and ozone molecules in COP. As regards 1.12% of Zn was found in the bulk of MnOx/SBAC, Wen et al. (2012) had confirmed ZnO and ZnCl2 had no catalytic activity in ozonation of organic matter. Additionally, there were differences between the TP (81.2%) and TOC (52.5%) removal trend, which indicated the most of phenolic compounds were converted into intermediates rather than completely eliminated. 3.3. Biological treatment of the COP effluent The real biologically pretreated CGW consists considerable amounts of toxic and inhibitory compounds with low biodegradability (around 0.06 of BOD5/COD value), which are the most diffi- cult to break down by microorganisms (Padoley et al., 2008). Fig. 3 shows it took about 12 h for the TN to be reduced to below 15 mg/L with raw wastewater in ANMBBR–BAF, which had efficient performance of TN removal with SBNR process, especially under the high toxic loading (around 160 mg/L of TP). But, it was difficult to decrease the TOC to below 20 mg/L in 24 h. In contrast, after pretreating of raw wastewater with COP in 30 min, the biological process reduced remaining TOC (around 57.0 mg/L) of the COP effluent to 17.4 mg/L at a much shorter time of 5.5 h, the corresponding TN decreased to 13.6 mg/L. Moreover, most of the TN (77.3%) was removed in the ANMBBR–BAF which consumed around 25.6% of COD and 17.8% of TP as carbon resource for denitrification. These observations clearly depicted that, COP could degrade the toxic and inhibitory compounds into simple intermediates or completely eliminate, thereby overcoming raw wastewater negative impact on the metabolism of microorganisms. Additionally, the optimum HRT of integrated process was 6 h, further prolonged time did not significantly enhanced pollutants removal. Table S1 summarizes the average removal efficiencies of COD, TOC, NH4 + -N, TN and TP were 87.5%, 85.5%, 90.9%, 80.6% and 98.7%, the corresponding effluent concentrations of 37.5, 17.4, 3.9, 13.6 and 1.7 mg/L, respectively, which all met class-I criteria of the Integrated Wastewater Discharge Standard (GB18918-2002, China). The results showed that integration of COP and ANMBBR–BAF was an efficient, costeffectively and sustainable process for treating real biologically pretreated CGW with a short retention time. 4. Conclusions A novel integration of COP and ANMBBR–BAF was successfully applied to advanced treatment of biologically pretreated CGW. The results indicated COP with MnOx/SBAC significantly improved performance of pollutants removal by generated OH and the effluent were more biodegradable and less toxic than that in ozonation alone. Meanwhile, ANMBBR–BAF showed efficient capacity of pollutants removal in COP effluent at short reaction time. The results showed the integrated process with efficient and economical advantages was beneficial to engineering application. Acknowledgements This work was supported by Sino-Dutch Research Program (SDRP: 2012–2016) and the independent subject sponsored by State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (No. 2013DX10). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2014.05. 061. 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Technol. 157, 223–230. 0 0.5 3 6 9 12 18 24 0 20 40 60 80 100 120 140 TOC and TN concentrations (mg/L) Reaction time(h) TOC in ANMBBR-BAF TOC in integrated process TN in ANMBBR-BAF TN in integrated process Fig. 3. Time-evolution profile of TOC and TN concentrations in the integrated heterogeneous catalytic ozonation with ANMBBR–BAF process. Error bars represent standard deviation of triplicate tests. H. Zhuang et al. / Bioresource Technology 166 (2014) 592–595 595