anaerobic digestion of organic wastewater from chemical fiber manufacturing plant: lab and...

Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx

G Model

JIEC-1517; No. of Pages 5

Anaerobic digestion of organic wastewater from chemical fibermanufacturing plant: Lab and pilot-scale experiments

Jae-Ho Lee a, Jeung-Jin Park b, Im-Gyu Byun c, Tae-Joo Park a, Tae-Ho Lee a,*a Department of Civil and Environmental Engineering, Pusan National University, Busan 609-735, Republic of Koreab Enco Co. Ltd., Chilgok, Gyeongbuk 718-814, Republic of Koreac Institute for Environmental Technology and Industry, Pusan National University, Busan 609-735, Republic of Korea

A R T I C L E I N F O

Article history:

Received 11 March 2013

Accepted 17 August 2013

Available online xxx

Keywords:

Anaerobic digestion

Chemical fiber manufacturing wastewater

Biogas

Anaerobic contact reactor

1,4-Dioxane

A B S T R A C T

Chemical fiber manufacturing wastewater (CFMW) usually contains high levels of organic materials.

Anaerobic digestion of CFMW was evaluated by the lab and pilot scale experiments in the study. The

CFMW used in the experiment characterized an inappropriate C/N ratio and acid pH for anaerobic

digestion. The COD removal efficiency, pH and the methane yield were significantly decreased with

5.00 g COD/L day of OLR in the lab scale experiment. These results were thought to be due to the

inappropriate C/N ratio and acid pH of CFMW. Thus, the addition of nutrients and neutralization for

CFMW were conducted in the pilot scale experiment. Accordingly, the significant decreases in COD

removal efficiency and pH were not observed although the OLR increased to 5.00 g COD/L day. The

methane yield also increased above 25% compared to that of the lab scale experiment. In the case of 1,4-

dioxane, the removal efficiency was not improved significantly at the higher HRT. It was considered that

constant proportion of acetic acid was used in the degradation of 1,4-dioxane as a cosubstrate regardless

of HRT.

� 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

1. Introduction

In the chemical fiber manufacturing process, a large amount ofwater is used for the various steps of the chemical fiber production.The two primary raw materials, terephthalic acid (TPA) andethylene glycol (EG), are converted by a polycondensation reactionto polyethylene terephthalate (PET) resins or fibers. The waterconsumed in the manufacturing process is finally discharged as thewastewater which needs to be treated. Lin et al. [1] reported thatover 5000 tons of wastewater could occur daily in a typical largechemical fiber plant. The wastewaters generated by chemical fiberplants are mainly characterized by their high chemical oxygendemand (COD). Some of the wastewaters also contain 1,4-dioxaneproduced from the polyester manufacturing process.

In order to treat these wastewaters, chemical fiber plants firstuse physicochemical treatment methods like neutralization andcoagulation, followed by traditional activated sludge process as asecondary treatment. However, due to the expensive handlingcosts and production of secondary environmental pollutants such

* Corresponding author at: School of Civil and Environmental Engineering, Pusan

National University, 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735, Republic of

Korea. Tel.: +82 51 510 2465.

E-mail address: [email protected] (T.-H. Lee).

Please cite this article in press as: J.-H. Lee, et al., J. Ind. Eng. Chem.

1226-086X/$ – see front matter � 2013 The Korean Society of Industrial and Engineer

http://dx.doi.org/10.1016/j.jiec.2013.08.024

as chemical sludge, a better alternative for pre-treatment oforganic wastewater before aerobic biological treatment is re-quired.

Anaerobic digestion has been widely employed by manyindustries as their primary treatment of wastewater [2,3].Anaerobic digestion is a complex biological process regulated bya bacteria consortium in which complex compounds are degradedinto methane, carbon and other gases. Anaerobes are sensitive tothe type of substrate, which is hydrolyzed to sugars, amino acidsand fatty acids [4]. They are also degraded by acetogens intoacetate, hydrogen and carbon dioxide, which are consumed readilyby methanogens. Thus, anaerobic digestion of organic wastewatersenables not only the removal of pollutants regarding wastewaterstreams but also the production of renewable energy in the form ofmethane [5].

There are several types of reactors used in the field of anaerobictreatment processes such as a continuous stirred tank reactor, up-flow anaerobic sludge blanket reactor, up-flow anaerobic filtration,fluidized bed reactor and up-flow anaerobic sludge fixed-filmreactor. An anaerobic contact digester is one of them. This processconsists of a contact digester and a sedimentation tank wheresludge from digester effluent is settled and the settled sludge isrecycled into the contact digester. The anaerobic contact process iscapable of reaching a steady-state quickly due to mixing. Wardet al. [6] reported that mixing enhances contact efficiency between

(2013), http://dx.doi.org/10.1016/j.jiec.2013.08.024

ing Chemistry. Published by Elsevier B.V. All rights reserved.


mailto:[email protected]


http://www.sciencedirect.com/science/journal/1226086X


Table 1Characteristics of organic wastewater used in this study.

Item CFMW

pH 4.51 � 0.8a

SS (mg/L) 18.5 � 3.3

CODCr (mg/L) 11,480 � 820

BOD5 (mg/L) 415 � 25

TN (mg/L) 13.4 � 1.5

TP (mg/L) 1.2 � 0.2

1,4-Dioxane (mg/L) 252 � 35

a Mean value � standard deviation.

J.-H. Lee et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx2

G Model


the microorganisms and the substrate, reducing resistance to masstransfer and accumulation of inhibitory intermediates. In addition,the anaerobic contact process generally requires short hydraulicretention times and enables relatively high effluent quality. Thesuccessful study using this process includes ice-cream wastewaterand fermented olive mill wastewater treatment [7,8]. Thus, organicwastewaters from a chemical fiber manufacturing plant can betreated by anaerobic contact digestion.

The aim of the study was therefore to evaluate the feasibility ofanaerobic digestion for organic wastewater from a chemical fibermanufacturing plant. For this purpose, the lab and pilot scaleexperiments were conducted. Organic wastewater from thepolyester manufacturing process was used and operated withthe anaerobic contact process. In the lab scale experiment, theprocess was operated at four different phases with an organicloading rate of 0.63�5.00 g COD/L day. Through the result of thelab scale experiment, we found better conditions for anaerobicdigestion of organic wastewater and reflected them in the pilotscale experiment. The treatment performance of the reactor wasmonitored and evaluated in terms of pH, alkalinity, COD and biogasproduction. In addition, organic wastewater contained a highconcentration of 1,4-dioxane and thus the removal efficiency of itwas also evaluated.

2. Experimental

2.1. Characteristics of organic wastewater

The characteristics of chemical fiber manufacturing wastewater(CFMW) used in this study are presented in Table 1. The organicwastewater was collected from a chemical fiber manufacturingplant located at the city of Ulsan in Korea. The CFMW representedlow pH, TN and TP concentrations, but it showed a high CODconcentration. The optimum pH and COD:N:P ratio of anaerobicdigestion for the enhanced yield of methane has been reported tobe 7 and 100:2.5:0.5, respectively [9]. Thus, nutrients supplemen-tation and neutralization for CFMW were considered for the stableanaerobic digestion treatment. CFMW also contains 1,4-dioxaneand then removal efficiency of 1,4-dioxane was evaluated.

2.2. Anaerobic contact reactor

Experiments for the anaerobic digestion of CFMW wereconducted by the lab and pilot scale anaerobic contact process,which consisted of an anaerobic contact reactor, sedimentationtank and gas holder as shown in Fig. 1. The contact digester and allthe other tanks of the lab and pilot reactors were made of acryl and

Anaerobic contact r

Gas holder

Influent storage tank

M

P

Fig. 1. Schematic diagram


stainless, respectively. The contact digester was completely closedand mixed continuously with 80 rpm. The influent was fed into theanaerobic digester continuously with a peristaltic pump. Thevolumes of the lab and pilot scale contact reactor were 18 L and3 m3, respectively. Temperature of digester was maintained with35 8C by a thermostatically controlled system. The sedimentationtank allows the flocculated solids to be settled and the sludgerecycling was carried out continuously from the sedimentationtank to the anaerobic digester, ensuring a constant biomassconcentration in the contact reactor.

2.3. Operating condition

The operating conditions were separated based on the organicloading rate (OLR) and were given in Table 2. In the lab scaleexperiment (Run 1), the process was operated at four differentphases with an organic loading rate of 0.63–5.00 g COD/L day.Through the result of the lab scale experiment, we concludedbetter conditions for anaerobic digestion of organic wastewaterand reflected them in the pilot scale experiment (Run 2). In Run 2,the process was operated with an organic loading rate of 1.25–7.50 g COD/L day. In addition, nutrients supplementation andneutralization of CFMW were conducted. The addition of nutrientswas carried out in order to achieve a COD:N:P ratio of 100:2.5:0.5and thus the concentration of TN and TP in CFMW increased toabout 300 and 60 mg/L, respectively. The pH of CFMW wasneutralized by NaOH which caused the increase in alkalinity ofCFMW about 800 mg CaCO3/L. The OLR increased after reactorsreached steady-state conditions.

2.4. Analytical methods

All samples under each set of conditions were tested within 7days of sampling. For each sample, the CODCr, BOD5, alkalinity,suspended solids, TN and TP concentrations were measured

eactor

Sedimentation tank

M

P

Sludge recycling

Effluent

of the reactor setup.



Table 2Operating conditions.

Condition Run 1 Run 2

I II III IV I II III IV

OLR (g COD/L day) 0.63 1.25 2.50 5.00 1.25 2.50 5.00 7.50

HRT (days) 18.4 9.2 4.6 2.3 9.2 4.6 2.3 1.5

SRT (days) 15 15

Temp. (8C) 35 35

MLSS (mg/L) 14,480 � 980a 14,150 � 1100

a Mean value � standard deviation.

J.-H. Lee et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx 3

G Model


according to the standard methods [10]. Filtration of the samplewas carried out through a 1.2 mm of glass microfiber filter. The pHwas measured using an Orion Research pH meter (Model 230A,USA). Methane was determined using a 2 m � 1/800 stainless steelcolumn of Porapak Q 80/100 mesh in a Hewlett-Packard 5890Series II gas chromatograph (GC) equipped with a thermalconductivity detector. 1,4-Dioxane was measured by Hewlett-Packard 6890N Series GC/MSD and column was Ultra-2(0.2 mm � 25 m � 0.33 mm). The stored samples were kept in arefrigerator at 4 8C until analysis.

3. Results and discussion

3.1. Variation of pH and alkalinity

Anaerobes are highly pH dependent and methanogens areaffected to a greater extent [11]. Beccari et al. [12] confirmed thatmethanogenesis is strongly affected by pH and optimum pH formost microbial growth is between 6.8 and 7.2 while acidogenicbacteria is more in favor of acid pH. Activity of methanogensgenerally decreases when pH in the digester is out of from theoptimum value [13].

As shown in Fig. 2(a), pH of anaerobic digester in conditions I, II,III in Run 1 was maintained with above 6.5 although the mean pHof influent was 4.5. However, as the OLR increased, continuouslyslow decrease in pH of the anaerobic digester occurred and pHeventually dropped to below 5 in condition IV. The resistance tosignificant changes in pH of the anaerobic digester depends on itsbuffering capacity. Buffer capacity is often known as alkalinity inthe anaerobic digestion process, which is the equilibrium of carbondioxide and bicarbonate ions [6]. As presented in Fig. 2(a),alkalinity continuously decreased as the OLR increased. Thedecrease of alkalinity continued until it was below500 mg CaCO3/L in condition IV. In fact, the production of alkalinityin the anaerobic digestion process was normally caused by theactivity of the methanogens, which could increase alkalinity in theform of ammonia and bicarbonate [14]. In the experiment, an

Fig. 2. The variation of pH (*) and alkalinity (*


increase in the OLR decreased HRT to 2.3 day in condition IV. Insuch a short HRT, changes from acidogenesis to methanogenesishardly occurred, resulting in an increase in organic acids and adecrease in the production of alkalinity. In this scenario, acontinuous injection of influent having low pH was thought tohave accelerated the pH drop. These results demonstrate thatneutralization of influent or supplementation of alkalinity isneeded to optimize pH in the system.

In the pilot scale experiment, although the OLR increased to5.00 g COD/L day, a sharp decrease in pH was not observed(Fig. 2(b)). This was the reason why pH of the influent wasneutralized by NaOH. Supplementation of nutrients was alsothought to have contributed to the stability of pH. The presence ofammonia in the anaerobic digester increases alkalinity because itcan produce another buffer system by reacting with bicarbonate[15]. Thus, the addition of nutrients to influent would have apositive effect on increasing the buffering capacity with theproduction of ammonium bicarbonate (NH4HCO3). However, adecrease in pH was observed when the OLR was 7.50 g COD/L day,indicating that a significant pH drop might occur at such short HRTdespite neutralization of pH due to the accumulation of organicacids.

3.2. COD removal

In an anaerobic digestion process, the removal of COD is mainlyachieved by the conversion of reaction intermediates to methaneby the methanogens and the good performance of the process isindicated by the lower effluent COD concentration [16]. As it can beseen from Fig. 3, the COD removal efficiencies in conditions I, II, IIIand IV in Run 1 were 90.6, 88.5, 86.3 and 68.4%, respectively. Theincrease of the OLR generally leads to the higher COD concentra-tion in effluent. Various studies proved that higher OLR reducedCOD removal efficiency in the anaerobic digestion system [17,18].In the lab scale experiment, although higher OLR also decreasedCOD removal efficiency, the system adapted to the increase of OLRwithout a significant decrease in the COD removal efficiency while

) in anaerobic digester in each condition.



60

70

80

90

100

0.63 1.25 2.50 5.00 7.50

OLR [ g COD/ L·day]

Re

mo

va

l e

ffic

ien

cy

[%

]

Fig. 3. The COD removal efficiency of each OLR in Run 1 (*) and Run 2 (&)

experiments.

J.-H. Lee et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx4

G Model


the OLR was between 0.63 and 2.50 g COD/L day. The main reasonfor this was thought to be the low suspended solid concentration ofCFMW, which requires a short hydrolysis period. Thus, methano-genesis is the rate limiting phase in the anaerobic digestion processof CFMW. The use of a continuously mixed reactor might be alsoadvantageous for COD removal because of higher substrate–cellsurface interaction and higher microorganism activity [19,20].However, after the OLR reached 5.00 g COD/L day, the significantdecrease in the efficiency of COD removal was observed. In ananaerobic system where acidogenesis was dominant, organiccompounds were converted to liquid intermediates and remainedin the system, making the COD removal efficiency in theacidogenesis lower than that in the methanogenesis [21]. Incondition IV in Run 1, the anaerobic digestion process did notproperly proceed to the methanogenic phase because of short HRT.This caused the accumulation of organic acids by acidogenesis anda sharp decrease in pH, thus the removal efficiency of COD wassignificantly decreased.

In Run 2, a decrease in COD removal efficiency was alsoobserved as the OLR increased. Contrary to Run 1, a significantdecrease in the removal of COD did not occur when the OLR was5.00 g COD/L day. This result explained that the stable C/N ratiowith supplementation of nutrients and neutralization of influentby NaOH had facilitated an effective methanogenesis. It could bealso proved through the comparison of COD removal efficiencybetween Run 1 and Run 2 when the OLRs were 1.25 and2.50 g COD/L day. However, in condition IV in Run 2, the removalefficiency of COD was significantly decreased. This result showedthat a high OLR above 5.00 g COD/L day may be harmful toward the

Fig. 4. Methane production (*) and met


anaerobic digestion of CFMW although it was reformed bynutrients and NaOH.

3.3. Methane production

The volume of the methane produced per day increased withthe increased OLR over the range tested except condition IV in Run1. However, as shown in Fig. 4(a), methane yields of CFMW inconditions I, II and III in Run 1 were approximately 0.26, 0.23 and0.21 L CH4/g CODremoved, respectively. The relation between themethane yield and the OLR has been widely observed in anaerobicdigestion. Chiang and Dague [22] reported that the methane yieldof 0.30 L CH4/g CODremoved at the low OLR was obtained, while itwas 0.26 CH4/g CODremoved at the higher OLR. The decrease in themethane yield with the increasing OLR might be attributed to adecline in the activity of methanogens at the higher OLR whichcaused the accumulation of organic acids in the system. Theanaerobic digestion of CFMW also presented a much lowermethane yield than the theoretical methane yield (0.34 L CH4/g CODremoved). The low methane yield might be caused by low pHof CFMW with 4.5, which made the favor condition for the growthof acidogenic bacteria over methanogenic bacteria. In this result,the higher production rate of carbon dioxide may reduce themethane ratio of the biogas. Thus, the biogas did not containsufficient methane content and it decreased from 59% to 54% whenthe OLR increased from 0.63 to 2.50 g COD/L day.

In the pilot scale experiment, methane yields of CFMW inconditions I, II, III and IV were about 0.29, 0.27, 0.26 and 0.22 L CH4/g CODremoved, respectively (Fig. 4(b)). Compared to the methaneyields of the lab scale digester, those of the pilot scale digesterincreased above 25%. The methane content also increased from54% to 57% when the OLR was 2.50 g COD/L day in Run 1 and Run 2.In the anaerobic digestion process, the C/N ratio is an importantfactor because carbon offers the energy source for anaerobes andnitrogen enhances microbial growth. When the amount ofnitrogen is limiting, microbial populations remain small and ittakes longer to decompose the available carbon [23]. Therefore,supplementation of nutrients and neutralization of CFMW werelikely to have exerted a positive effect on improvement of themethane yield and methane content.

3.4. 1,4-Dioxane removal

1,4-Dioxane which is used as a stabilizer for chlorinatedsolvents can cause harmful effects on the environment because ofits higher toxicity and carcinogenic. A discharge limit of 1,4-dioxane to the water system was regulated at 5 mg/L by theMinistry of Environment Republic of Korea as of 2011. In the study,CFMW contains 1,4-dioxane from the polyester manufacturing

hane content (*) in each condition.



Fig. 5. The removal efficiency of 1,4-dioxane in each condition in Run 2.

J.-H. Lee et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx 5

G Model


process. Thus, the degradation of 1,4-dioxane by anaerobicdigestion was needed to be properly achieved. Burback and Perry[24] reported that the mixed culture was unable to degrade 1,4-dioxane because none of the bacteria in the mixed communitywere able to grow in the presence of it. However, biodegradation of1,4-dioxane has been reported for both pure and mixed cultures ofmicroorganisms. Shen et al. [25] evaluated the capability ofanaerobic biodegradation of 1,4-dioxane by iron-reducing micro-organisms. Mixed cultures of bacteria could also degrade 1,4-dioxane in the presence of not only the cosubstrate tetrahydrofu-ran [26], but also acetic acid [27].

In Run 2, the removal efficiencies of 1,4-dioxane were 50.5,53.2, 48.7 and 42.8% in conditions I, II III and IV, respectively(Fig. 5). In the step of acidogenesis of anaerobic digestion,acidogenic bacteria degrades sugar, fatty acids and amino acidsinto organic acids which mainly consist of acetic acid. Thus, mixedcultures of bacteria were thought to have exhibited the ability todegrade 1,4-dioxane using acetic acid as a cosubstrate. However,the removal efficiency of 1,4-dioxane was not significantlyimproved at the higher HRT. Since acetic acid was mainly usedby methanogenesis and was converted into methane, theproportion of acetic acid used in the degradation of 1,4-dioxaneas a cosubstrate was thought to have been maintained constantlyregardless of HRT. In the chemical fiber plant, effluent of theanaerobic digestion process would be treated by secondary aerobicsludge treatment with other wastewaters. Although 1,4-dioxaneconcentration of anaerobic digestion effluent was still high, itwould be diluted with other wastewaters and be treated effectivelyby the aerobic treatment process because it was first degraded byanaerobic digestion.

4. Conclusions

A chemical fiber manufacturing plant discharges a large amountof organic wastewater, which is mainly treated by physicochemi-cal treatment methods that cause the expensive handling costs and


secondary environmental pollutants. Therefore, anaerobic diges-tion of organic wastewater was evaluated by the lab and pilotscale experiments. In the lab scale experiment, the decrease ofCOD removal efficiency and the methane yield with the higherOLR of CFMW were observed. These results were attributed to aninappropriate proceeding to methanogenesis with deficiency innutrients and acid pH of CFMW, resulting in the accumulation oforganic acids and significant pH drop in OLR condition of5.00 g COD/L day. CFMW was thus supplemented with nutrientsby nitrogen and phosphorus and neutralized by NaOH in the pilotscale experiment. Through reformation of CFMW, a sharpdecrease in pH was not observed with the higher OLR. Themethane yield was also increased above 25% compared to that ofthe lab scale experiment. These results indicated that the additionof nutrients and neutralization were appropriate for the stableanaerobic digestion of CFMW. In the case of 1,4-dioxane, theremoval efficiency was not improved significantly at the higherHRT. It was considered that constant proportion of acetic acid wasused in the degradation of 1,4-dioxane as a cosubstrate regardlessof HRT.

Acknowledgements

This research was supported by the Program for the Construc-tion of Eco Industrial Park (EIP) which was conducted by the KoreaIndustrial Complex Corporation (KICOX) and the Ministry ofKnowledge Economy (MKE).

References

[1] S.H. Lin, Desalination 120 (1998) 185.[2] S. Sakinkaya, M.F. Sevinli, J. Ind. Eng. Chem. 19 (2013) 197.[3] L. Singh, M.F. Siddiqui, A. Ahmad, M.H.A. Rahim, M. Sakinah, Z.A. Wahid, J. Ind. Eng.

Chem. 19 (2013) 659.[4] E. Senturk, M. Ince, G. Onkal Engin, Bioresour. Technol 101 (2010) 3970.[5] L. Maya-Altamira, A. Baun, I. Angelidaki, J.E. Schmidt, Water Res. 42 (2008) 2195.[6] A.J. Ward, P.J. Hobbs, P.J. Holliman, D.L. Jones, Bioresour. Technol. 99 (2008) 7928.[7] M. Hamdi, J.L. Garcia, Bioresour. Technol. 38 (1991) 23.[8] A. Vlissidis, A.I. Zoubolis, Bioresour. Technol. 43 (1993) 114.[9] D. Somayaji, University of Gulbarga, 1992 (Ph.D. thesis).

[10] APHA, American Public Health Association, Washington DC, 2005.[11] C.P. Leslie Grady Jr., G.T. Daigger, H.C. Lim, Biological Wastewater Treatment, 2nd

ed., CRC Press, 1999 (Revised & Expanded).[12] M. Beccari, F. Bonemazzi, M. Majone, C. Riccardi, Water Res. 30 (1996) 183.[13] M.H. Gerardi, Wastewater Bacteria, Wiley-Interscience, New Jersey, 2006.[14] I.S. Turovskiy, P.K. Mathai, Wastewater Sludge Processing, Wiley, New York, 2006.[15] F. Cecchi, P. Traverso, P. Pavan, D. Bolzonella, L. Innocenti, ChemInform 34 (2003)

141.[16] M. Hutnan, L. Mrafkova, M. Drtil, J. Derco, Chem. Pap. 53 (1999) 374.[17] A. Torkian, A. Eqbali, S.J. Hashemian, Resour. Conserv. Recy. 40 (2003) 1.[18] H. Patel, D. Madamwar, Bioresour. Technol. 82 (2002) 65.[19] P.J. Meynell, Methane Planning a Digester, Prism Press, London, 1976.[20] P. Kaparaju, I. Buendia, L. Ellegaard, I. Angelidakia, Bioresour. Technol. 99 (2008)

4919.[21] P. Thanwised, W. Wirojanagud, A. Reungsang, Int. J. Hydrogen Energy 37 (2012)

15503.[22] C.F. Chiang, R.R. Dague, Water Environ. Res. 64 (1992) 141.[23] A. Hilkiah Igoni, M.J. Ayotamuno, C.L. Eze, S.O.T. Ogaji, S.D. Probert, Appl. Energy

85 (2008) 430.[24] B.L. Burback, J.J. Perry, Appl. Environ. Microbiol. 59 (1993) 1025.[25] W.R. Shen, H. Chen, S. Pan, Bioresour. Technol. 99 (2008) 2483.[26] M.J. Zenker, R.C. Borden, M.A. Barlaz, Environ. Eng. Sci. 20 (2003) 423.[27] C.C.C. Raj, N. Ramkumar, H.J. Siraj, S. Chidambaram, Process Saf. Environ. 75

(1997) 245.


http://refhub.elsevier.com/S1226-086X(13)00387-0/sbref0005



































anaerobic digestion of organic wastewater from chemical fiber manufacturing plant: lab and...

Documents