Pretreatment and in Situ Fly Ash Systems for Improving the

Jun 12, 2017 - Pretreatment and in Situ Fly Ash Systems for Improving the Performance of Sequencing Batch Reactor in Treating Thermomechanical Pulping...
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Research Article pubs.acs.org/journal/ascecg

Pretreatment and in Situ Fly Ash Systems for Improving the Performance of Sequencing Batch Reactor in Treating Thermomechanical Pulping Effluent Xiaoqian Chen,†,‡ Chuanling Si,*,†,§ and Pedram Fatehi*,‡ †

Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science & Technology, 1038 South Dagu Road, Hexi District, Tianjin 300222, China ‡ Chemical Engineering Department, Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1, Canada § State Key Laboratory of Tree Genetics and Breeding, Chinese Academy of Forestry, Beijing 100091, China S Supporting Information *

ABSTRACT: In this work, two methods were applied for improving the performance of activated sludge in treating the effluent of the thermomechanical pulping process. In one attempt, the effluent of the pulping process was pretreated with 0.2 wt % of fly ash (FA) at room temperature and 100 rpm for 1 h, and the FApretreated samples were further processed by a sequencing batch reactor (SBR) system. In another work, FA (0.2 wt %) and activated sludge were mixed with the effluent simultaneously in an in situ system. The results showed that FA assimilation would benefit the removal of nonbiodegradable substances and thus facilitate the decomposition of contaminants by activated sludge in both systems, especially in the in situ system. The removal efficiencies of 96.1%, 99.1%, 95.2%, 90.51%, and 99.5% were achieved for COD, BOD, TOC, lignin, and sugar from the effluent, respectively. In addition, the sludge volume index (SVI) of the FA-pretreated and in situ systems decreased to 100.7 and 75.5 mL/g and the effluent suspended solids (ESS) decreased to 67.9 and 55.5 mg/L, respectively, indicating that the use of FA improved activated sludge settling and flocculation affinity. These results are attributed to the adsorption of lignocelluloses on fly ash and decomposition of lignocelluloses by activated sludge. Moreover, as undervalued biomass-based fly ash was utilized as an efficient adsorbent, the developed technique is green and promising for application in wastewater treatment systems. KEYWORDS: Biomass fly ash, Sustainable chemistry, In situ system, Pulping wastewater, Activated sludge

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INTRODUCTION Wastewater treatment in the pulp and paper industry is typically processed using biological treatment systems. Compared with physicochemical processes, biological methods are considered to be more cost effective for treating wastewater.1 However, most biological methods are ineffective in degrading the recalcitrant compounds such as lignin mainly because of the size and complex structure of the compounds.2 Therefore, a more effective treatment system needs to be developed for removing recalcitrant pollutants and improving the efficiency of biological treatment systems. Some adsorbents, such as activated carbon and silica, have been previously assessed for removing pollutants from wastewater of the pulp and paper industry.3 In one study, the application of activated carbon in the effluent of a pulp and paper company resulted in 80.6% reduction in chemical oxygen demand (COD) with the use of 4% activated carbon in the adsorption process.4 However, the use of activated carbon is limited by its high price.5 Therefore, it is desirable to find an alternative carbon-containing adsorbent. Biomass-based fly ash © 2017 American Chemical Society

(FA) contains carbon and has a porous structure. Thus, it can be used as an inexpensive adsorbent for removing refractory pollutants.6−8 FA is a solid waste generated as a byproduct of boilers, specifically wood-based boilers. Approximately 40% of fly ash is used for beneficial purposes, and the rest is handled as a solid waste, which introduces environmental concerns if landfilled.9,10 However, studies on the treatment of pulping effluent with fly ash is limited. The first objective of this study was to investigate the impact of FA on the properties of pulping effluents. The application of FA in the effluent of the pulping industry is a promising approach to utilize this waste, which is in agreement with the general concept of forest biorefining that covers the generation of value-added products from underutilized biomass. Moreover, a combination of physical and biological treatments has been considered as a method for treating industrial Received: April 12, 2017 Revised: June 9, 2017 Published: June 12, 2017 6932

DOI: 10.1021/acssuschemeng.7b01131 ACS Sustainable Chem. Eng. 2017, 5, 6932−6939

Research Article

ACS Sustainable Chemistry & Engineering effluents.11−14 In the past, two treatment options were considered: (i) pretreatment of the wastewater with adsorbents prior to a biological treatment or (ii) simultaneous physical and biological treatments of effluents in in situ systems.11−14 The presence of adsorbents (e.g., activated carbon) in biological systems provides an opportunity for organic materials to be removed from effluent via adsorbing on the adsorbents.15 Ç eçen reported that the addition of 1000 mg/L of activated carbon to an activated sludge system improved the COD removal from the bleaching effluent of a pulp mill by 20%.16 Martin and co-workers claimed that the addition of 1000 mg/L of activated carbon to activated sludge enhanced the COD removal from 87% to 93% when operated on synthetic wastewater containing 2500 mg/L COD.17 In the study conducted by Sirianuntapiboon, the removals of COD and BOD from a synthetic textile effluent was increased from 95.9% and 93.9% to 97.2% and 94.6%, respectively, when 1000 mg/L of activated carbon was present in a sequencing batch reactor (SBR) system.18 However, no information is available on the impact of fly ash (FA) on biological systems. The second objective of this work was to investigate how the in situ system of FA and activated sludge would process the effluent of a thermomechanical pulping process. In this study, a combination of FA and activated sludge was applied to treat the effluent of a thermomechanical pulping process under two scenarios of FA as a pretreatment step for an activated sludge system and an in situ FA−activated sludge system. For the first time, FA was introduced in an in situ system for treating pulping effluents. Another novelty of this work was the comparison between the performance of FA pretreatment and FA in the in situ system.

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wastewater, and operating process. All of the experiments were operated at 25 °C for about 3 months under steady state conditions. The aeration process was controlled using air pumps (TOPFIN AIR500, USA) with a magnetic stirring bar at the agitation intensity of 500 rpm to prevent settling of sludge and fly ash. The dissolved oxygen (DO) concentration was maintained higher than 1 mg/L using a DO meter (Model HQ40d, USA), and pH was controlled between 7 and 8 by adding NaOH.19 The system was filled with 1 L of influent daily and was operated in the following sequence of filling, reacting, settling, and drawing with respective time intervals of 10 min, 23 h, 40 min, and 10 min, respectively. The concentration of mixed liquor suspended solids (MLSS) was adjusted to around 5000 mg/L by withdrawing a certain amount of mixed liquor per day at the end of the reaction period. After settling, effluent samples were collected and analyzed for COD, BOD, TOC, sugar, and lignin. Analytical Methods. The chemical oxygen demand (COD) of the samples were determined by colorimetric methods according to Standard Method 5220 D.20,21 This analysis was carried out using a COD kit via mixing 2 mL of samples with premixed chemicals and then incubating in a block digester at 150 °C for 2 h. Afterward, the absorbency of the sample was measured at 620 nm and then converted to a COD concentration using a standard calibration curve.22 The biological oxygen demand (BOD) analysis was performed in 300 mL incubation bottles, in which 5 mL of samples was mixed with buffered solutions containing microorganisms. The samples were stored in an incubator at 20 °C for 5 days. The DO concentrations in the samples for the BOD assessment were determined before and after the incubation period.23 The total organic carbon (TOC) of the samples was analyzed using a Vario TOC Cube instrument (Elementar Analysensysteme GmbH, Germany), which is based on the oxidation of organic compounds to carbon dioxide. Wastewater samples are combusted at 1200 °C in an oxygen-rich atmosphere. All carbon present converts to carbon dioxide, and the carbon dioxide is measured using a nondispersive infrared (NDIR) detector. The total suspended solids (TSS), mixed liquor suspended solids (MLSS), and effluent suspended solids (ESS) of wastewater samples were determined by filtering the wastewater samples through glass fiber filters with a pore size of 1.2 μm.24 Sludge volume index (SVI) was calculated according to Standard Method 2710 D.20,21 In this test, 100 mL of reactors’ constituents were transferred to graduated cylinders at the end of each cyclic operation and settled for 30 min. The SVI (g/L) was calculated by dividing the measured volume of the settled sludge (mL/L of settled sludge/total volume of the sludge mixture) by the dry weight concentration of MLSS. Sugar and Lignin analyses. The concentration of total sugars in the samples was determined using an ion chromatography unit equipped with a CarboPac SA10 column (Dionex Corporation, Canada) and a Thermo Scientific Electrochemical detector with 1.00 mM of KOH as eluent at a flow rate of 1.2 mL/min and 30 °C. Samples were hydrolyzed with 4 wt % sulfuric acid at 121 °C in oil bath (AC200, Thermo Fisher Scientific, Inc., USA) prior to testing.25 The lignin content of the samples was determined by UV/vis spectrophotometry (Genesys 10S, Thermo Scientific, Inc., USA) at the wavelength of 205 nm using a calibration standard curve.26 Elemental Analysis. The organic compounds of the wastewater and FA were determined using a Vario EL cube instrument (Germany). Initially, wastewater and FA samples were dried at 105 °C overnight and ground into powder. Then, approximately 0.02 g of dried samples were transferred into the carousel chamber of the elemental analyzer and combusted at 1200 °C, and the generated gases were reduced to analyze carbon, hydrogen, oxygen, and nitrogen contents of the samples. The metal elements of the wastewater samples were measured directly by an inductively coupled plasma emission spectrometer (ICP), a Varian Vista Pro CCD (Canada) equipped with CETAC ASX-510 autosampler, a cyclonic spray chamber, and a Seaspray nebulizer according to the method established in the past.25,27 The sludge samples were taken out from the reactors directly and dried at 105 °C overnight and ground into powders before the metal element detection.

MATERIALS AND METHODS

Materials. Sodium hydroxide (>99.0%) was obtained from SigmaAldrich Company and diluted to 1 mol/L prior to use. Potassium dihydrogen phosphate (KH2PO4), ammonium chloride (NH4Cl), sodium nitrate (NaNO3), and poly(ethylene oxide) were purchased from Sigma-Aldrich Company. The chemical oxygen demand (COD) kits (K-7365) were obtained from CHEMetrics Inc., USA. Fly Ash, Sludge, and Wastewater. Fly ash (FA) was collected from a bark boiler of a pulp mill located in Northern Ontario, Canada, which was dried at 105 °C prior to use. A combination of wastewater sludges, sawdust, and barks from softwood and hardwood species was used as feed in the boiler. Activated sludge with 12,000 mg/L of mixed liquor suspended solids (MLSS) was obtained from the secondary wastewater treatment system of the same pulp mill and seeded into the reactor. A thermomechanical pulping effluent (denoted as TMP in this work) was obtained from the same mill. Samples were kept in a refrigerator at 4 °C in closed plastic barrels for analysis to avoid decomposition. Experimental Procedure. To evaluate the effect of FA on the activated sludge system, three processes were evaluated in parallel. One unit was operated as a conventional activated sludge using TMP. The second unit contained FA-pretreated TMP in the activated sludge system, and the third unit contained an in situ FA−activated sludge system of TMP. The dosages of FA in the second and third units were the same (0.2 wt %). Initially, TMP was pretreated with FA (0.2 wt %) for 10 h at room temperature and then filtered using a Whatman filter (No. 5), and FA-pretreated TMP was obtained. The biological treatment of TMP was studied in a sequencing batch activated sludge reactor under aerobic conditions. To investigate the effect of FA on the biological treatment efficiency, three different runs were operated in parallel in 2-L reactors. In this in situ system, FA was added manually to the reactor in every operating cycle to compensate for FA withdrawal with sludge waste. In each comparative run, the initial conditions were identical with the same seed sludge, influent 6933

DOI: 10.1021/acssuschemeng.7b01131 ACS Sustainable Chem. Eng. 2017, 5, 6932−6939

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ACS Sustainable Chemistry & Engineering Particle Size Distribution (PSD). The particle size distributions of influents, effluents, and sludge were measured by using a Malvern Mastersizer 2000 instrument (Worcestershire, UK) in the detection range of 0.02−2000 μm. In this study, 200 mL of TMP samples were added to 1-L beakers and diluted to 800 mL with distilled water prior to analysis. For sludge samples, 1 mL of mixed sludge samples was directly taken out from reactors while stirring and then diluted to 800 mL with distilled water. During the particle size analysis, samples were stirred at 2400 rpm to avoid settling of particles, and data were recorded at room temperature. Each sample was analyzed three times, and the average values were reported. Statistical Analysis. A t test statistical analysis was used for determining the significance of generated data. The significance of correlation was established at a 95% confidence level (p-value 3500 >1000 >2500 − −

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DOI: 10.1021/acssuschemeng.7b01131 ACS Sustainable Chem. Eng. 2017, 5, 6932−6939

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(13) Aktaş, Ö .; Ç eçen, F. Addition of activated carbon to batch activated sludge reactors in the treatment of landfill leachate and domestic wastewater. J. Chem. Technol. Biotechnol. 2001, 76 (8), 793− 802. (14) Muhamad, M. H.; Abdullah, S. R. S.; Mohamad, A. B.; Rahman, R. A.; Kadhum, A. A. H. Application of response surface methodology (RSM) for optimization of COD, NH3-N and 2, 4-DCP removal from recycled paper wastewater in a pilot-scale granular activated carbon sequencing batch biofilm reactor (GAC-SBBR). J. Environ. Manage. 2013, 121, 179−190. (15) Ç eçen, F., Aktas, Ö . Activated Carbon for Water and Wastewater Treatment: Integration of Adsorption and Biological Treatment; Wiley: New York, 2011. (16) Ç eçen, F. Activated carbon addition to activated sludge in the treatment of kraft pulp bleaching wastes. Water Sci. Technol. 1994, 30 (3), 183−192. (17) Martin, M. J.; Serra, E.; Ros, A.; Balaguer, M. D.; Rigola, M. Carbonaceous adsorbents from sewage sludge and their application in a combined activated sludge-powdered activated carbon (AS-PAC) treatment. Carbon 2004, 42 (7), 1389−1394. (18) Sirianuntapiboon, S.; Sadahiro, O.; Salee, P. Some properties of a granular activated carbon-sequencing batch reactor (GAC-SBR) system for treatment of textile wastewater containing direct dyes. J. Environ. Manage. 2007, 85 (1), 162−170. (19) Dong, W. Y.; Wang, H. J.; Li, W. G.; Ying, W. C.; Gan, G. H.; Yang, Y. Effect of DO on simultaneous removal of carbon and nitrogen by a membrane aeration/filtration combined bioreactor. J. Membr. Sci. 2009, 344 (1), 219−224. (20) Standard Methods for the Examination of Water and Wastewater, 20th ed.; American Public Health Association: Washington, DC, 2005. (21) Cassidy, D. P.; Belia, E. Nitrogen and phosphorus removal from an abattoir wastewater in a SBR with aerobic granular sludge. Water Res. 2005, 39 (19), 4817−4823. (22) Oveissi, F.; Sitter, T.; Fatehi, P. PDADMAC as a flocculant for lignosulfonate of NSSC pulping process. Biotechnol. Prog. 2016, 32 (3), 686−691. (23) Latif, U.; et al. Biochemical oxygen demand (BOD). In Environmental Analysis by Electrochemical Sensors and Biosensors; Moretto, L. M., Kalcher, K., Eds.; Springer: New York, 2015. (24) Gao, W.; Han, M.; Qu, X.; Xu, C.; Liao, B. Characteristics of wastewater and mixed liquor and their role in membrane fouling. Bioresour. Technol. 2013, 128, 207−214. (25) Fatehi, P.; Gao, W.; Sun, Y.; Dashtban, M. Acidification of prehydrolysis liquor and spent liquor of neutral sulfite semichemical pulping process. Bioresour. Technol. 2016, 218, 518−525. (26) Fatehi, P.; Ryan, J.; Ni, Y. Adsorption of lignocelluloses of model pre-hydrolysis liquor on activated carbon. Bioresour. Technol. 2013, 131, 308−314. (27) Gupta, V. K.; Jain, C. K.; Ali, I.; Sharma, M.; Saini, V. K. Removal of cadmium and nickel from wastewater using bagasse fly ash-a sugar industry waste. Water Res. 2003, 37 (16), 4038−4044. (28) Liao, B. Q.; Allen, D. G.; Droppo, I. G.; Leppard, G. G.; Liss, S. N. Surface properties of sludge and their role in bioflocculation and settleability. Water Res. 2001, 35 (2), 339−350. (29) Yang, S. F.; Li, X. Y. Influences of extracellular polymeric substances (EPS) on the characteristics of activated sludge under nonsteady-state conditions. Process Biochem. 2009, 44 (1), 91−96. (30) Chun, H.; Yizhong, W. Decolorization and biodegradability of photocatalytic treated azo dyes and wool textile wastewater. Chemosphere 1999, 39 (12), 2107−2115. (31) Urbain, V.; Block, J. C.; Manem, J. Bioflocculation in activated sludge: an analytic approach. Water Res. 1993, 27 (5), 829−838. (32) Ç eçen, F.; Erdinçler, A.; Kiliç, E. Effect of powdered activated carbon addition on sludge dewaterability and substrate removal in landfill leachate treatment. Adv. Environ. Res. 2003, 7 (3), 707−713. (33) Environment Standards for Common Effluent Treatment Plants, Central Pollution Control Board, India Ministry of Environment, Forest and Climate Change Notification, 2016. www.cpcb.nic. in/Industry-Specific-Standards/Effluent/CETP.pdf.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b01131. Images of influent and effluents for control, FApretreated and in situ systems. (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel: 807-343-8697. Fax: 807-3467943 (C. Si). *E-mail: [email protected]. Tel: 807-343-8697. Fax: 807346-7943 (P. Fatehi). ORCID

Pedram Fatehi: 0000-0002-3874-5089 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank NSERC, CRC, CRIBE, and NOHFC programs and Open Fund of State Key Laboratory of Tree Genetics and Breeding (Chinese Academy of Forestry) (Grant No. TGB2016002) for supporting this research.

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REFERENCES

(1) Kamali, M.; Khodaparast, Z. Review on recent developments on pulp and paper mill wastewater treatment. Ecotoxicol. Environ. Saf. 2015, 114, 326−342. (2) Leiviskä, T.; Rämö, J.; Nurmesniemi, H.; Pöykiö, R.; Kuokkanen, T. Size fractionation of wood extractives, lignin and trace elements in pulp and paper mill wastewater before and after biological treatment. Water Res. 2009, 43 (13), 3199−3206. (3) Pokhrel, D.; Viraraghavan, T. Treatment of pulp and paper mill wastewater-a review. Sci. Total Environ. 2004, 333 (1), 37−58. (4) Boonpoke, A. Study on preparation of water hyacinth-based activated carbon for pulp and paper mill wastewater treatment. J. Environ. Biol. 2015, 36 (5), 1143−1148. (5) Aksu, Z.; Yener, J. A comparative adsorption/biosorption study of monochlorinated phenols onto various sorbents. Waste Manage. 2001, 21 (8), 695−702. (6) Andersson, K. I.; Eriksson, M.; Norgren, M. Removal of lignin from wastewater generated by mechanical pulping using activated charcoal and fly ash: Adsorption isotherms and thermodynamics. Ind. Eng. Chem. Res. 2011, 50 (13), 7722−7732. (7) Srivastava, V. C.; Mall, I. D.; Mishra, I. M. Treatment of pulp and paper mill wastewaters with poly aluminium chloride and bagasse fly ash. Colloids Surf., A 2005, 260 (1), 17−28. (8) Oveissi, F.; Fatehi, P. Process for treating spent liquor of the TMP process with biomass-based fly ash. Ind. Eng. Chem. Res. 2015, 54 (29), 7301−7308. (9) Sharma, R.; Shaw, R.; Tiwari, S.; Tiwari, S. Nano-Titania decorated fly ash as self-cleaning antibacterial cool pigment. ACS Sustainable Chem. Eng. 2015, 3 (11), 2796−2803. (10) Ahmed, Z. T.; Hand, D. W.; Watkins, M. K.; Sutter, L. L. Combined adsorption isotherms for measuring the adsorption capacity of fly ash in concrete. ACS Sustainable Chem. Eng. 2014, 2 (4), 614− 620. (11) Kargi, F.; Pamukoglu, M. Y. Simultaneous adsorption and biological treatment of pre-treated landfill leachate by fed-batch operation. Process Biochem. 2003, 38 (10), 1413−1420. (12) Satyawali, Y.; Balakrishnan, M. Effect of PAC addition on sludge properties in an MBR treating high strength wastewater. Water Res. 2009, 43 (6), 1577−1588. 6938

DOI: 10.1021/acssuschemeng.7b01131 ACS Sustainable Chem. Eng. 2017, 5, 6932−6939

Research Article

ACS Sustainable Chemistry & Engineering (34) H.A.T. Directive.. Council Directive of 21 May 1991 concerning urban waste water treatment. Regulation (EC) 2003, 50, 1−16. (35) Kreetachat, T.; Damrongsri, M.; Punsuwon, V.; Vaithanomsat, P.; Chiemchaisri, C.; Chomsurin, C. Effects of ozonation process on lignin-derived compounds in pulp and paper mill effluents. J. Hazard. Mater. 2007, 142 (1), 250−257. (36) Pessala, P.; et al. Lignin as the Cause of Acute Toxicity in Pulp and Paper Mill Effluents. In Environmental Fate and Effects of Pulp and Paper Mill Effluent; Dennis, L., Borton, T. H., Robert, F., Jill, T., Eds.; CRC Press: Boca Raton, 2004. (37) Del Rio, J. C.; Speranza, M.; Gutiérrez, A.; Martınez, M. J.; Martınez, A. T. Lignin attack during eucalypt wood decay by selected basidiomycetes: a Py-GC/MS study. J. Anal. Appl. Pyrolysis 2002, 64 (2), 421−431. (38) Lin, H. J.; Xie, K.; Mahendran, B.; Bagley, D. M.; Leung, K. T.; Liss, S. N.; Liao, B. Q. Sludge properties and their effects on membrane fouling in submerged anaerobic membrane bioreactors (SAnMBRs). Water Res. 2009, 43 (15), 3827−3837. (39) Agridiotis, V.; Forster, C. F.; Carliell-Marquet, C. Addition of Al and Fe salts during treatment of paper mill effluents to improve activated sludge settlement characteristics. Bioresour. Technol. 2007, 98 (15), 2926−2934. (40) Kim, J. S.; Lee, C. H.; Chun, H. D. Comparison of ultrafiltration characteristics between activated sludge and BAC sludge. Water Res. 1998, 32 (11), 3443−3451. (41) He, S. B.; Xue, G.; Kong, H. N.; Li, X. Improving the performance of sequencing batch reactor (SBR) by the addition of zeolite powder. J. Hazard. Mater. 2007, 142 (1), 493−499. (42) Hong, S.; Elimelech, M. Chemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes. J. Membr. Sci. 1997, 132 (2), 159−181. (43) Tsang, Y. F.; Sin, S. N.; Chua, H. Nocardia foaming control in activated sludge process treating domestic wastewater. Bioresour. Technol. 2008, 99 (9), 3381−3388. (44) Kannan, N.; Karthikeyan, G.; Tamilselvan, N. Comparison of treatment potential of electrocoagulation of distillery effluent with and without activated areca catechu nut carbon. J. Hazard. Mater. 2006, 137 (3), 1803−1809. (45) Guan, B.; Yu, J.; Fu, H.; Guo, M.; Xu, X. Improvement of activated sludge dewaterability by mild thermal treatment in CaCl2 solution. Water Res. 2012, 46 (2), 425−432. (46) Duan, J.; Gregory, J. Coagulation by hydrolysing metal salts. Adv. Colloid Interface Sci. 2003, 100-102, 475−502. (47) Murthy, S. N.; Novak, J. T.; De Haas, R. D. Monitoring cations to predict and improve activated sludge settling and dewatering properties of industrial wastewaters. Water Sci. Technol. 1998, 38 (3), 119−126. (48) Lesage, N.; Sperandio, M.; Cabassud, C. Study of a hybrid process: Adsorption on activated carbon/membrane bioreactor for the treatment of an industrial wastewater. Chem. Eng. Process. 2008, 47 (3), 303−307. (49) Zhang, S.; Zhang, P.; Zhang, G.; Fan, J.; Zhang, Y. Enhancement of anaerobic sludge digestion by high-pressure homogenization. Bioresour. Technol. 2012, 118, 496−501. (50) Kugelman, I. J.; McCarty, P. L. Cation toxicity and stimulation in anaerobic waste treatment. J. Water Pollut Control Fed. 1965, 37 (1), 97−116. (51) McCarty, P. L. Anaerobic waste treatment fundamentals. Public works 1964, 95 (11), 91−94. (52) McCarty, P. L. Anaerobic waste treatment fundamentals. Public works 1964, 95 (10), 123−126.

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