Enhanced anaerobic biodegradability of real coal gasification wastewater with methanol addition

Availableonlineatwww.sciencedirect.comSciencedirectN11-2629/xJoumal of Environmental Sciences 2010, 22(12)1868-1874Enhanced anaerobic biodegradability of real coal gasification wastewaterwith methanol additionWei Wang, Hongjun Han:, Min Yuan, Huiqiang LiState Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology. Harbin 150090, China. E-mail: whir@ 126.6Received 21 January 2010: revised 26 April 2010; accepted 28 April 2010AbstractCoal gasification effluent is a typical refractory industrial wastewater with a very poor anaerobic biodegradability due to its toxicityMethanol was introduced to improve anaerobic biodegradability of real coal gasification wastewater, and the effect of methanol additionon the performance was investigated in a mesophilic upflow anaerobic sludge bed reactor with a hydraulic retention time of 24 hr.Experimental results indicated that anaerobic treatment of coal gasification wastewater was feasible with the addition of methanol. Thecorresponding maximum COD and phenol removal rates were 71% and 75%, respectively, with methanol concentration of 500 mgCoD/L for a total organic loading rate of 3. 5 kg COD/(m-day)and a phenol loading rate of 0.6 kg/(m-day). The phenol removalate was not improved with a higher methanol concentration of 1000 mg COD/L Substrate utilization rate(SUR)tests indicated thatthe SURs of phenol were 106, 132, and 83 mg phenol/(g VSS-day)at methanol concentrations of 250, 500, and 1000 mg COD/Lrespectively, and only 45 mg phenol/(g VSS day) in the control reactor. The presence of methanol could reduce the toxicity of coalgasification wastewater and increase the biodegradation of phenolic compounds.Key words coal gasification wastewater; anaerobic; biodegradability; phenol; methanolDOI:10.1016/S1001-0742(09)60327-2Introductionhibited and has low efficiency. The use of the anaerobicprocess in COD removal in coal conversion wastewaterCoal gasification is one of the best methods for acquiring treatment only contributes 25% to the removal of theclean coal energy to meet the rising demand in China(Li anaerobic-anoxic-oxic system(Wang et al., 2002). In thiset al., 2009). However, a coal gasification plant consumes a type of wastewater, recalcitrant organics and inhibitoryrge amount of water during its manufacturing processes. compounds are the most difficult compounds for theCoal gasification wastewater is discharged mainly from anaerobic treatment to break down. For example, phethe gas washing and condensing operations of the coal nolic compounds, cyanide, and long chain alkenes aregasifier. Considering its complex composition and the tox. the inhibitors of methanogenic bacteria( Chakraborty andic pollutants contained in it, coal gasification wastewater Veeramani, 2006: Hernandez and Edyvean, 2008). Thisis regarded as a serious problem in the world(Zhu et toxicity causes the anaerobic treatment of real coal conver-al., 2009). Although raw coal gasification wastewater is sion wastewater to require a large volume of clean waterpretreated through solvent extraction and steam stripping as diluents or granular activated carbon as absorber, whichto remove phenols and ammonia, the effluent still contains would be very costly on an industrial scale(Kindzierski ethigh concentrations of phenolic compounds as well as al., 1991; Nakhla and Suidan, 1995). Recently, anaerobicrefractory and inhibitory compounds(Gai et al., 2008). co-digestion has been developed for treating refractoryConventional anoxic-oxic treatment methods provide cost- wastewater(Youngster et al., 2008; Zhang et al., 2008)effective and efficient techniques for coal gasification Some publications in the field of industrial wastewaterwastewater treatment. However, reducing effluent COD to treatment described the anaerobic digestion of recalcitrantless than 200 mg/L remains difficult(Wang et al., 2002 ) wastewater with the addition of an easily biodegradableIn recent years, there have been numerous attempts to treat substrate(Perez et al. 2006: Yang et al., 2008). Anaer-coal gasification wastewater under anaerobic conditions obic中国煤化工 onsiderable growthto improve its biodegradability( Ramakrishnan and Gupta, rately( Brandt et al2006: Kuschk et al 2010).CN MHGbiodegradability ofAnaerobic process is suitable for the treatment of coal the wastewater by increasing the toxic and recalcitrantasification wastewater, but the process is seriously in- compounds of degraders, as well as by increasing theabsorption capacity of the system( Chen et al., 2008)CorrespondingauthorE-mail:hanl3946003379@163.comNo.12Enhanced anaerobic biodegradability of real coal gasification wastewater with methanol additionMethanol, as an easily biodegradable substrate, is an Table I Main characteristics of the real coal gasification wastewateravailable and inexpensive product in the coal gasificationParameterfeasible to improve the anaerobic biodegradability of coal COD (mg/L)addition of methanol700-l100450-700In the present study, anaerobic treatment of real coal volatile phenols (mgL)gasification wastewater both unsupplemented and supple- Volatile acids(mmol/L)mented with methanol were investigated in two upflow NH3-N(mg/L)00-150anaerobic sludge bed(UASB)reactors. The effect of Bicarbonate alkalinity(mmolL)methanol concentration on COD and phenol removal was Sulfide(mg/L)studied to acquire the optimum dose of methanol. The Thiocyanate(mg/L)20-50purpose of the work was to test whether the addition of Cyanide(mg/L)methanol could enhance anaerobic biodegradability of realTemperature(C)65-8.0coal gasification wastewater and to supply a technicallyfeasible and cost-effective way for anaerobic treatment ofrecalcitrant wastewaterZnCl2 0.5, CuCl2 0.5, (NH4)2MoO4 4H2O 0.5, AlCl3 0.5CoCl2.2H20 0.5, NaBO2.10H20 0.3, and NiClz2H2O1 Materials and methods0.5. The supplemented methanol used for this study wasan analytical reagent. Because the influent pH was in1.1 Experimental setupthe range of 7.0 to 8.0, no alkalinity was needed toTwo UASB reactors were comprised of plexiglass add to the wastewater. During the start-up period, thecolumns with an internal diameter of 10 cm, a height of infuent COD(1500 mg/L)and total phenols concentra-120 mm, and a working volume of 7 L. The reactors were tions(300 mg/L), were controlled by diluting the realoperated at(37±1)°Cwastewater. Methanol was added into the reactor (calledthe supplemented reactor )to keep the initial methanol1.2 Inoculumconcentration at 500 mg COD/L. Although this amountAnaerobic digested sludge was obtained from full-scale provided 25% of the total influent COD(2000 mg/L).anaerobic reactors which were used for the treatment of the addition also encouraged the growth of methanogeniccoal gasification wastewater of the China Coal Longhua bacteria. The coal gasification wastewater concentrationHarbin Coal Chemical Industry Co, Ltd. The sludge and phenol loading rate were gradually increased fromas grey-black with good settlement characteristics. To- 2500 mg COD/L and 0.5 kg/(m day)on day 68 to 3000suspended solid(TSS)was 45.8 g/L and volatile mg COD/L and 0.6 kg/(m-day)on day 143, respectivelysuspended solid (VSS)was 33 g/L in both reactors. The amount of methanol added was kept at 500 mg COD/LMethanogenic activity of the seed sludge was 0.12 g COD. to maintain the stable amount of co-substrate. Meanwhile,CHa/(g vSs-day)another UASB reactor was operated without methanoladdition as a control(called the control reactor). when1.3 Coal gasification wastewaterthe supplemented reactor reached stable operation, theRaw coal gasification wastewater was obtained from effect of methanol concentration on the performance wasthe lurgi gasifier at China Coal Longhua Harbin Coal investigated to obtain the optimum amount of methanolChemical Industry Co, Ltd. Since the raw wastewater was During the entire experimental period, the reactors weresubjected to a series of physico-chemical pretreatments operated continuously at constant hydraulic retention time(such as sour gas stripping, extraction with disopropyl (HRT) of 24 hr with the upflow liquid velocity of 0.375ether and ammonia stripping) to reduce the concentra- m/hr. The operational conditions of the supplementedtions of solids, greases, phenols, and ammonium, the reactor are shown in Table 2wastewater could be treated with the biological process.1.5 Analytical methodsTable I shows the main characteristics of the real coalgasification wastewater. Predominant pollutants in coalCOD, BOD, SS, VSS, sulfide, long chain alkenes, thio-gasification wastewater include phenolic compounds, het- cyanate, cyanide and NH3-N were determined accordingerocyclic compounds, polycyclic aromatic hydrocarbons, to standard methods. The concentrations of total phenolslong chain alkenes, amine compounds, ammonia, sulfide, and volatile phenols were measured by the titration methodiocyanate, and cyanide. Phenolic compounds are the (Wei et al, 2002). Bicarbonate alkalinity and volatile fattynain organic pollutants in the wastewater and comprise acids(VFA)were analyzed by the distillation method(an-40%6-50% of the total CODdenson and Yang, 1992). Effluent methanol was measuredtngranhv ac decrrihad by Weijma et al.1.4 Start-up(day 1-227)and operation( day 228-359)(2000中国煤化工 actor was measuredThe feed nutrients consisted of the followinntent of the biogastrients(in mg/L): K2HPO4 20, KH2PO4 10, CaCl22H2O WaCNMHment system with20, FeSO4 7H2O 15, and MgSO47H2O 50; micro- 3 molL NaOH solution. In addition, substrate utilizationnutrients(in mg/L): FeCl3-3H20 1, MnCl2-4H20 0.5. rates(SUR) of phenol and methanol were used to assess1870Wei Wang et alVoL 22Table 2 Operational conditions employed in the anaerobic treatment of real coal gasification wastewater in the supplemented reactorMethanolMethanolTOLLLRHRT VUmg COD/L) (mg COD/L) ( of total COD) (mg/L) (kg COD/(m-day)) (kg/(m-day)) (hr)1-670375143-2270002330375293-359002503.250.6.375CGWin: influent coal gasification wastewater; methanol influent methanol concentration; TPin: total phenols; TOLR: total influent organic loadingrate: PLR: phenols loading rate; HRT: hydraulic retention time; Vu: upflow velocitythe biodegradability using the seed sludge and biomass 3000 and 500 mg/L, respectively, during day 68-142 Onfrom the UASB reactors. SUR tests were carried out in day 72, COD removal was reduced to 31% and 19.7%140 mL sealed vials with a working volume of 100 mL. in the supplemented and control reactors, respectivelThe test substrates controlled phenol concentration of 500 On the other hand, phenols concentration in the effluentmg/L and methanol concentration of 500 mg COD/L. The increased to 324.9 and 451 mg/L in the supplementedSUR values of phenol and methanol were expressed as and control reactor, respectively(Fig. le, f). The con-the rates of phenol depletion(mg phenol/(g VSS.day ))and trol reactor without methanol addition was shown to bemethanol depletion(mg COD/g VSS day), respectively. ineffective in the biodegradation of phenol compoundsand it restricted COD removal by 20%0-35%. However,2 Resultsin the supplemented reactor, COD and phenols removalrecovered to 69% and 55%(Fig. Id, h), respectively on2.1 Efect of methanol addition on start-up perfor- day 84 and reached stable values of 72% and 70% on daymance(day 1-227)122, respectively. Methane production achieved 3. 2 L/dayat methanol concentrations of 500 mg COD/L, which farInfluent COD of 1500 mg/ and total phenols concentra- exceeded the value of 0.12 L/day in the control reactortion of 300 mg/L with influent organic loading rate (OLR)(Table 3). Subsequently, during day 143-227, total influent1.5 kg COD/(m-day)and phenol loading rate(PLR)of Cod and total phenols increased to around 3500 and0.3 kg/(m-day)were applied in the two UASB reactors. In 600 mg/L, respectively. Although the acclimation extendedthe supplemented reactor, the amount of methanol addition over 200 days, the coal gasification wastewater still had aremained at 500 mg COD/L as co-substrate during start- serious effect on anaerobic microorganisms, such that theup periods. Figure I shows the comparison of anaerobic anaerobic treatment efficiency was lower than 40%in thetreatment of the real coal gasification wastewater in the control reactor(Fig. ld). with the addition of methanol,supplemented and control reactors. In the control reactor COD and phenols removal increased to 71% and 75%(Fig. Id and h), the COd and total phenols removal were respectively, on day 219(Fig. Ic, g). Effluent of pH andaround 28% and 25% after 67 days of operation. Although vFa were 8.0 and 1.5 mmol/L in the reactor( Fig. lk, o);inoculums in the full-scale anaerobic devices had acclimat- these values did not vary much during the operation stageed for the real coal gasification wastewater for over halfa year, the treatment efficiency of the organic pollutants 2.2 Efect of methanol concentrations on the perforwas still low because of the toxicity. In the supplementedce(day228359)reactor, COD and phenols removal could reach up to Figure 2 shows the effect of methanol concentration on70% and 60%, respectively, on day 67( Fig. Ic, g). The COD and total phenols removal in the supplemented reac-addition of methanol altered the metabolic environment tor. The stimulative effect of the 500 mg COD/L methanoland resulted in changes in the effiuent. Figure I(i and J) added as external carbon source in the start-up periodillustrates the decrease of effluent volatile phenols. The was observed. The effects of methanol concentrations ofincrease in effluent alkalinity was more prominent in the 1000 and 250 mg COD/L on the performance of thesupplemented reactor than that in the control reactor, supplemented reactor were also investigated. On day 228(Fig. Im, n)CoD/L resulted in an increase in the influent total Cod toInfluent total COD and phenols increased to around 4000 mg/L and TOLR to 4 kg COD/(m-day)influent PLRTable 3 Main parameters of the stable process at different methanol additionsPLR (ke COD removal TP removal Residual methandCOD/(m-day) (m-day)) (g COD/day)中国煤化(/day) (g VSS/L)43-2270(bank)303662143-2273.531747CN MHG.20 35.00228-2921000293-35925012062.47TP: total phenols; SS: suspension sludge; ND: not detected12Enhanced anaerobic biodegradability of real coal gasification wastewater with methanol addition1871InfluentEmRemoval efficiencysupplemented reactorControl reactor( Methanol: 500 mg COD/L)( Methanol: 0 mg COD/L)ustr20++4600eacne e ?init。”乱6°a:·,,·808Dassn,…"n200220016018020022中国煤化工Fig. 1 Comparison on anaerobic treatment of the real coal gasification wasCNMHGe control reactor.1872Wei Wang et alremained at 0.6 kg/(m-day)(Table 2). COD and phenolsTable 4 Substrate(phenol and methanol)utilization rates for theremoval rates decreased to 40%-45% and 30%-35% frombiomass in the different periods70%0-72% and 74%0-76%, respectively. Figure 2 clearly Time MethanolSURshows that increased methanol concentration resulted in (day)Phenol (mgMethanol (mga poor performance of the reactor both in terms of CoD(mg COD/L) phenol/(g vSS-day)COD/gvsS-day))and phenols removal From day 260 to 292, effluent COD 0and phenols concentrations were about 1800 and 320 mg/L 143-227along with the removal efficiency in the range of 50%- 143-22760% and 40%-50%, respectively. On day 293, the amount00293-359of methanol addition was decreased to 250 mg CODLMeanwhile, the influent total COD and told decreased to3250 mg/L and 3.25 kg CoD/(m -day), respectively, and 3 Discussionthe influent PLR remained stable. Although there was asignificant decline in the amount of methanol added, CODPhenolic compounds are dominant organic contamiand phenols removal rates still reached 55% and 60%, on nants in coal gasification wastewater(Yang et al., 2006)day 359 while effluent COD and phenols concentrations and generally comprise 40%0-80% of the total CODwere about 1500 and 230 mg/L. The above amounts were (Kindzierski et al, 1991). Biodegradation of phenoliclower than the effluent concentrations in the previous compounds represent the treatment efficiency of the realperiod (day 228-292)coal gasification wastewater in an anaerobic reactor. Ac-Performance and operational parameters with the cording to some studies, wastewaters containing even lowmethanol addition of 0, 250, 500, and 1000 mg COD/L concentrations of cyanide, thiocyanate, and pyridine haveare shown in Table 3. The maximum COD and phenols toxic and inhibitory effects on the anaerobic digestion ofremoval were found to be 17.47 g COD/day and 3.03 phenolic compounds( Gijzen et al., 2000; Chakraborty andg/day, respectively, for total organic loading rate of 3. 53 kg Veeramani, 2006). The initial feed of 50% strength(1500COD/(m-day)and phenol loading rate of 0.6 kg/(m -day) mg CoD/)was intended to reduce the inhibitory effectswith the methanol addition of 500 mg COD/L. On the of these toxic compounds in the control reactor.Howeverother hand, in the control reactor these amounts were onlyin Fig. 1b and d, the results illustrated that the dilution didaround 6.62 and 1.36 g/day. The methanol concentration not improve the removal efficiencies of COD and phenolsof 1000 mg CoD/L did not improve the phenols removal Sludge acclimation in the control reactor did not sequesterefficiency of the system further. While, when methanol the strong toxic effect of the wastewater on methanogenicconcentration decreased to 250 mg COD/L, total phenols microorganisms. Little methane production and low SURremoval was 2.47 g/day, which was higher than 1.89 g/day were observed in the control reactor. This phenomenon hadwith methanol addition of 1000 mg COD/. The methanol also been reported by Suidan et al.(1983)addition from 0 to 1000 mg COD/L increased methaneMethanol is an easily biodegradable substrate( Sung andproduction from 0. 12 to 3. 35 L/day. In addition, methanol Liu, 2003), and its addition to the real coal gasificationas an easily biodegradable substrate was utilized as a wastewater could change the organic composition.Thepriority in coal gasification wastewater. It was not difficult addition of methanol clearly caused some improvement onto determine that almost all the methanol was degraded total phenols removal and methane production comparedand the residual methanol in effluent was less than 10 mgCOD/L, even was not detectedproduction was observed to increase with the increasein the amount of methanol added. In the supplemented reactor, COD and phenol removal reached maximumvalues with the addition of 500 mg COD/L methanolMethanolMethanolThus. methanol addition did result in increased methane500 mg COD/L 1000 mg COD/L 250 mg COD/Lproduction and phenols degradation in the treatment ofreal coal gasification wastewater. Co-digestion of real coalgasification wastewater with methanol could significantlyefficiency; however, this efficnot positively correlated with the addition of methanolAlthough the phenol SURs were 132 and 106 mg phe-nol/(g VSs-day)with the methanol addition of 500 and50 mg COD/L, respectively, the value decreased to83 mg phenol(g VSS day)when methanol concentrationas increased to 1000 mg COD/L (Table 4). anaerobicg%80200024026028030320340360poun中国煤化工 ited by toxic com--ater High methanolCN MHgnal metabolic equiFig 2 Efect of methanol concentrations on COD and total phenols librium and cause the degradation of phenolic compounds,removal in the supplemented reactor.making these compounds competitively inferiorEnhanced anaerobic biodegradability of real coal gasification wastewater with methanol additionWe hypothesized that the degradation of methanol could of Technology(No. 2010DX05)and the National Highenhance the bacterial detoxification of toxic compounds Technology Research and Development Program(863)ofand strengthen the digestion activity of recalcitrant com- China(No. 2007AA06A411)pounds. Adding the appropriate amount of methanol mightchange the predominant species of methanogens or shiftthe methanogenic population to encourage initial methane Referencesproduction and sequester toxicity. The methanol additionof 500 mg COD/L represented the optimum condition for Anderson G K, Yang G, 1992. Determination of bicarbonate andmaximum COD and phenol removal in the real coal gasitotal volatile acid concentration in anaerobic digesters usingfication wastewater in this study. Moreover, the synergistic a simple titration. Water Environment Research, 64( 1): 53-addition to the objective wastewater. Once adapted, the Brandt B w. van Leeuwen I MM, Kooijman SA L M, 2003anaerobic bacteria could retain viability and activity atconcentrations that far exceed the initial inhibitory concen-Application to co-metabolism of structurally non-analogouscompounds. Water Research, 37(20): 4843-4854trations. The effective removal of COD and total phenols Chakraborty S, Veeramani H, 2006. Effect of HRT and recyclecould be completed with the decreased ratio of methanolratio on removal of cyanide,cyanate and am-CoD to total influent Cod from 25% to 8.3% The initialmona In anco-substrate concentration played an important role inProcess Biochemistry, 41(1): 96-105.improving the activity of methanogenic and acetogenic Chen Y, Cheng JJ, Creamer K S, 2008. Inhibition of anaerobic di-bacteria and in enhancing the removal of toxic and recalcgestion process: A review, Bioresource Technology, 99(10):trant substances during acclimation periods. The addition0444064of excessive or insufficient amounts of methanol might Cheng Suidan MT, Venosa A D, 1998. Anaerobic biotransformake it difficult to obtain satisfactory results within a shortmation of 2, 4-dinitrotoluene with ethanol. methanol, aceticperiodand hydrogen32(10):2921-2930Methanol can be easily obtained from the coal gasi- Gai H J, Jiang Y B, Qian Y, Kraslawski A, 2008. Conceptualfication industry (Kumabe et aL., 2008),making theco-digestion of coal gasification wastewater with methanoldesign and retrofitting of the coal-gasification wastewatertreatment process. Chemical Engineering Journal, 138(substrate or its manufacturing wastewater a feasible option3):8494In fact, the co-substrate is not unique and other easily Gijzen H J, Bernal E, Ferrer H, 2000. Cyanide toxicity andbiodegradable substrates have been observed in laborato-ry scale studies( Cheng et aL, 1998; Ramakrishnan andGupta, 2006). Thus, co-digestion is a promising method Hernandez JE, Edyvean RG J, 2008. Inhibition of biogasto enhance the anaerobic biodegradability of coal gasifi-production and biodegradability by substituted phenoliccation wastewater. Our findings also suggest the potentialcompounds in anaerobic sludge. Journal of Hazardousapplication of the method specifically for phenols removal Kindzierski W B. Fedorak PM. Hrudey S E,1991.Anaerobicin real wastewater. Furthethe optimum conditions for co-digestion treatment of coaltreatability of a phenolic coal conversion wastewater afterpropyl ether extraction. Water Research, 25(4): 479-Kumabe K, Fujimoto S, Yanagida T, Ogata M, Fukuda T,4 Conclusions2008. Environmental and economic analysis of methanolproduction process via biomass gasification. Fuel, 87(7)gasification1422-1427wastewater, anaerobic treatment with the addition of Li k z, Zhang R, Bi JC, 2009. Experimental study on syngasmethanol was performed in UASB reactors. Resultsoduction by co-gasification of coal and biomass in aindicated that anaerobic biodegradability of the coal gasi-uidized bed. International Journal of Hydrogen Energy,35(7):2722-2726fication wastewater studied improved greatly upon the Kuschk P. Stottmeister U Liu Y J. Wiessner A. Kastner Maddition of 500 mg COD/L methanol with the influentMuller R A, 2010. Batch methanogenic fermentation exper-total COD 3500 mg/L and phenol concentration 600 mg/L.iments of wastewater from a brown coal low-temperatureThe requirement of methanol addition ratio to the coalcoke plant. Journal of Emvironmental Sciences,gasification wastewater was not fixed and the addition ofexcessive or insufficient amounts of methanol might make Nakhla g F, Suidan MT, 1995. Anaerobic toxic wastes treatment:it difficult to obtain satisfactory results within a short pe-dilution effects. Journal of Hazardous Materials, 42(1): 71riod. Anaerobic treatment of coal gasification wastewaterith other co-substrates, such as volatile acids and phenol,L I. Sales D. 2006also offers a viable option in terms of cost and efficiency.中国煤化工 cutting oil wastewaterAcknowledgmentsCNMHG Ineering JournalRamakrishnan A, Gupta S K, 2006. Anaerobic biogranulationThis work was supported by the State Key Laboratory ofin a hybrid reactor treating phenolic waste. JoumalUrban Water Resource and Environment, Harbin InstituteHazardous Materials B, 137(3): 1488-1495et alSuidan MT, Siekerka G L, Kao S W, Pfeffer J T, 1983. Anaerobicremoval from industrial coal-gasification wastewater.filters for the treatment of coal gasification wastewater.Chemical Engineering Journal, 117(2): 179-185Biotechnology and Bioengineering, 25(6): 1581-1596Q, Shang H, Li H, Xi H, Wang J L, 2008. Biodegrada-Sung S w, Liu T, 2003. Ammonia inhibition on thermophiliction of tetrachlorothylene using methanol as co-metabolicanaerobic digestion. Chemosphere, 53(1): 43-52.substrate. Biomedical and Environmental Sciences, 21(2):Wang JL, Quan X C, Wu L B, Qian Y, Hegemann w,2002. Bioaugmentation as a tool to enhance the removal Youngster L K G, Somsamak P, Haggblom MM, 2008.of refractory compound in coke plant wastewater. ProcessEffects of co-substrates and inhibitors on the anaerobic o-Biochemistry, 38(5): 777-78demethylation of methyl tert-butyl ether(MTBE). AppliedWei Fs, Qi wQ, Sun ZG, Huang Y R, Shen Y w, 2002.WaterMicrobiology and Biotechnology, 80(6): 1113-1120and Wastewater Monitoring and Analysis Method (4th ed. ) Zhang B, He P J, Li F, Shao L M, 2008. Enhancement ofChina Environmental Science Press, Beijinganaerobic biodegradability of flower stem wastes with veg-Weijma J, Stams A J M, Hulshoff Pol L w, Lettinga G, 2000etable wastes by co-hydrolysis. Journal of EmvironmentalThermophilic sulfate reduction and methanogenesis withSciences,20(3):297-303methanol in a high rate anaerobic reactor. Biotechnology Zhu XP, Ni JR, Lai P, 2009. Advanced treatment of biologicallypretreated coking wastewater by electrochemical oxidationYang C. Qian Y, Zhang L J, Feng J Z, 2006. Solvent extractionusing boron-doped diamond electrodes. Water Research,process development and on-site trial-plant for phenol43(17):4347-4355中国煤化工CNMHG