Influence of the food to microorganisms (F/M) ratio and temperature on batch anaerobic digestion processes with and without zeolite addition

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  • This article was downloaded by: [McMaster University]On: 04 December 2014, At: 11:44Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

    Journal of Environmental Science and Health, PartA: Toxic/Hazardous Substances and EnvironmentalEngineeringPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lesa20

    Influence of the food to microorganisms (F/M) ratioand temperature on batch anaerobic digestionprocesses with and without zeolite additionS. Montalvo a , P. Gonzalez a , C. Mena a , L. Guerrero b & R. Borja ca Departamento de Ingeniera Qumica , Universidad de Santiago de Chile , Chileb Departamento de Ingeniera Qumica y Ambiental , Universidad Tcnica Federico SantaMara , Valparaso , Chilec Instituto de la Grasa (CSIC) , Sevilla , SpainPublished online: 04 Jul 2012.

    To cite this article: S. Montalvo , P. Gonzalez , C. Mena , L. Guerrero & R. Borja (2012) Influence of the food tomicroorganisms (F/M) ratio and temperature on batch anaerobic digestion processes with and without zeolite addition,Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 47:12,1785-1794

    To link to this article: http://dx.doi.org/10.1080/10934529.2012.689235

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  • Journal of Environmental Science and Health, Part A (2012) 47, 17851794Copyright C Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934529.2012.689235

    Influence of the food to microorganisms (F/M) ratioand temperature on batch anaerobic digestion processeswith and without zeolite addition

    S. MONTALVO1, P. GONZALEZ1, C. MENA1, L. GUERRERO2 and R. BORJA3

    1Departamento de Ingeniera Qumica, Universidad de Santiago de Chile, Chile2Departamento de Ingeniera Qumica y Ambiental, Universidad Tecnica Federico Santa Mara, Valparaso, Chile3Instituto de la Grasa (CSIC), Sevilla, Spain

    The main objective of this work was to evaluate the influence of the food to microorganisms (F/M) ratio and temperature on batchanaerobic digestion processes carried out with andwithout zeolite addition as amicrobial carrier. Three laboratory-scale experimentalruns were conducted using a synthetic substrate with a COD:N:P ratio of 500:5:1. The first run (I) was conducted at a constanttemperature of 27C, increasing the F/M ratio from 0.21 to 0.40 (g COD/g VSS). During the second run (II) the temperature andthe F/M ratio increased from 27C to 37C and from 0.21 to 0.40, respectively. Finally, in the third experimental run (III) the F/Mratio achieved high values (1.92 and 1.30) either by varying the substrate concentration at a constant biomass concentration or byincreasing the biomass concentration at a constant substrate concentration. Higher biomass growth rate, COD removal and methaneproduction were found in the reactors with zeolite, especially at the highest F/M assayed during the first run. The highest ammoniumremovals were also achieved at the highest F/M ratio (0.40) in the reactors with zeolite. Within the range studied (25C37C) inthe reactors with zeolite operating at 37C, the second run demonstrated the low influence of temperature on substrate consumptionand ammonia removal, with 93% and 70% of COD and ammonia removal efficiencies, respectively. The third run corroborated theresults previously obtained and fit the experimental results to simple kinetic models, the Monod model being the most adequate forpredicting the behavior of the systems studied. The maximum specific microorganism growth rate (max) values for the reactors withzeolite were almost twice as high as those obtained for the reactors without zeolite for similar F/M ratios.

    Keywords: Anaerobic processes, zeolite, kinetics, food/microrganisms ratio, temperature.

    Introduction

    The anaerobic treatment of medium and high-strengthwastewaters with a high biodegradable content has a num-ber of advantages:[1] quite a high degree of purificationwith high organic load feeds can be achieved, low nutri-ent requirements are sufficient, only small quantities ofexcess sludge are usually produced and, finally, a renewablecombustible biogas is generated. The production of biogasenables the process to generate or recover energy insteadof just saving it. This can significantly reduce operationalcosts compared with the high energy-consuming aerobicprocess.[2,3]

    However, one of the greatest problems in the anaero-bic processing of wastewaters is the loss of biomass in

    Address correspondence to R. Borja, Instituto de la Grasa(CSIC), Avda. Padre Garca Tejero, 4. 41012-Sevilla, Spain;E-mail: rborja@cica.esReceived February 24, 2012.

    systems with high hydraulic loading rates. To solve thisproblem, reactors have been designed with supports thatfix the biomass and result in high loading densities andlow hydraulic retention times.[14] With the increase of pop-ulation density on the given support, there is a greaterchange in cross-feeding, co-metabolism and interspecieshydrogen and proton transfer, which may further stimulatethe growth of microcolonies. The use of a porous supportsuch as zeolite enables the anaerobic reactor to retain highbiomass concentrations and thereby operate at significantlyreduced hydraulic retention times.[1,2,4,5]

    The structure and physical properties of natural zeolite[channel and pore cavities, minimum diameter of pores inthe range of 3 to 10 Angstroms, average surface area of24.9 m2/g, low bulk density, high exchange (CEC) andadsorption capacities] make it ideal for use in anaerobicdigestion processes for wastewater treatments.[6,7]

    Other researchers have demonstrated the suitabilityof the use of zeolite as microbial immobilization sup-port in batch anaerobic processes operating at mesophilic

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  • 1786 Montalvo et al.

    temperatures.[811] Although anaerobic digestion processesin batch mode are not frequently applied at full-scale, theyare useful at laboratory-scale because they can be per-formed quicklywith simple and inexpensive equipment andare helpful in assessing the extent to which a material canbe digested, providing relevant information related to themethane yield coefficient and kinetics of the process. Clayminerals such as zeolites and other surface-active materialshave been reported as influencing the microbial and enzy-matic transformation of a variety of substances, includingammonium, sulfur, carbohydrates, proteinaceous materialsand phenolic compounds.[811]

    In addition, according to previous results, zeolite hasbeen found to be a successfulmicrobial support in the batchmesophilic anaerobic digestion of different substrates, dueto the following characteristics: (i) its high capacity forimmobilization of microorganisms; (ii) its capacity for im-proving the ammonia/ammonium ion equilibrium; (iii) itsability to reduce the ammonia and ammonium ion in solu-tion.[10,11]

    On the other hand, a disadvantage of the anaerobic pro-cess is its slow start-up stage, prior to achieving the designparameters operating at steady-state conditions.[1216]Avery practical and useful tool for accelerating the start-up in anaerobic processes is to initiate the study with abatch experiment. Although this step may be sped up withthe use of zeolite,[13] it is important to consider that thesuitability of this procedure will be influenced by the food-microorganism (F/M) ratio, which will in turn determinethe different microorganisms-zeolite and substrate-zeoliteratios. In addition, it has recently been reported that theF/M ratio also influences the specific methanogenic activ-ity (SMA) test, this ratio being themost influential parame-ter for the SMA test.[17,18] Other studies have demonstratedthat F/M ratios in the range of 0.5 to 1.0 were suitablein batch anaerobic tests of different food wastes such assoup processing plants, cafeteria wastes, etc. operating atmesophilic temperature (35C) for 28 days.[19]However, other similarwastes such as fish and grease trap

    wastes took longer to digest completely at these same F/Mratios, generating higher biomass yields than the previouslymentioned wastes.[19] Optimum F/M ratios in the rangeof 0.57 to 0.68 were reported in batch bioassay tests ofsynthetically prepared complex wastewaters, achieving adecrease in the methane potential and sludge activities atincreasing F/M ratios as well as a decrease by 81% in thekinetic constant for methane production when the F/Mratio increased to 0.9.[20] Low F/M ratios (0.5) were alsoused in batch anaerobic assays of mixtures of glycerin anddairy manure containing 60% glycerin (mixture 1) and 45%glycerin (mixture 2) on the VS basis.[21] Methane yields of0.31 and 0.22 L/g VS were achieved for mixtures 1 and 2,respectively.In this context and taking the information obtained from

    the literature review into account, the aim of this work wasto assess the influence of the F/M ratio and temperature

    on batch anaerobic digestion tests carried out with andwithout zeolite addition. For this purpose, a synthetic sub-strate with sucrose as a carbon source and a COD:N:Pratio of 500:5:1 was used, evaluating organic matter andammonium removals as well as methane production underdifferent operational conditions. Finally, different simplekinetic models were used to obtain the kinetic parametersof the processes and to compare the different conditionstested.

    Materials and methods

    Characteristics of the synthetic wastewater used

    A synthetic wastewater with a COD:N:P ratio of 500:5:1was used as substrate. Sucrose was used as a carbon source,ammonia sulfate was used as a source of sulfate and nitro-gen, while potassium phosphate was used as a phosphorussource. A minimum sulfate concentration of 80 mg/L wasused in the experiments with the aim of simulating the char-acteristics of wastewaters derived from the manufacturingof pulp and paper.

    Experimental procedure

    Three experimental runs (I, II and III) were carried outto assess the influence of the F/M ratio and temperatureon batch anaerobic processes, which were conducted withand without zeolite addition. All experiments were per-formed in batch laboratory-scale reactors of 280 mL vol-ume, which were operated in triplicate. Each reactor wasinoculated with 70 mL of an anaerobic sludge, which wasobtained from a full-scale anaerobic digester treating wasteactivated sludge.During the experiments the contents of thereactors were mixed with magnetic stirrers at 120 rpm.The reactors were hermetically closed and the methane

    gas produced was measured by the displacement of a 3 MNaOH solution in order to remove the CO2 and measureonly the methane gas produced in the processes. The char-acteristics of the zeolite used are summarized in Table 1.

    Table 1. Chemical and mineralogical compositions of the zeoliteused.

    Chemical composition Mineralogical composition(%) (%)

    SiO2 66.62 Clinoptilolite 35Al2O3 12.17 Mordenite 15Fe2O3 2.08 Montmorillolite 30CaO 3.19 Others 20MgO 0.77Na2O 1.53K2O 1.20Ignition Waste 11.02

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    Table 2. Operating conditions of experimental run I.

    Experiment no. Range COD (mg/L) VSS (mg/L) F/M SO24 (mg/L)

    I-1 Low 800 3700 0.21 80I-2 Medium 1100 3700 0.29 110I-3 High 1500 3700 0.40 150

    The diameter of the zeolite particles used in all experimentswas 1 mm.In the first experimental run (I), three different assays

    were conducted with F/M ratios of 0.21, 0.29 and 0.40 (gCOD/g VSS). The temperature of the process was main-tained constant at 27C as this is the mean outlet tempera-ture of the wastewater from the manufacturing of pulp andpaper. Table 2 summarizes the main operational conditionsused in run I.During the second experimental run (II) and with the

    aim of assessing the influence of temperature, the latterwas kept constant at 27C and 37C during the first (II-1) and second (II-2) assays, respectively, whereas it wasuncontrolled (ambient temperature: 25C30C)during thethird assay (II-3). The F/M ratio also increased from 0.21to 0.29 and 0.40 (g COD/gVSS) for assays II-1, II-2 and II-3, respectively. The amount of zeolite added to the reactorswas constant (3 g) as well as the initial sulfate content(200 mg/L). The main operational conditions used in thesecond experimental run (II) are shown in Table 3.Finally, during the third experimental run (III), two sets

    of assays were conducted. The first set of experiments (III-1, III-2 and III-3) increased the F/M ratio from 0.24 to1.91 (by increasing the COD concentration from 500 to4000 mg/L and maintaining the biomass concentrationconstant at 2100 mg VSS/L). The second set of experi-ments (III-4 and III-5) saw a decrease in the F/M ratiofrom 1.33 to 0.77 (by increasing the biomass concentra-tion from 1500 to 2600 mg VSS/L and keeping the CODconcentration constant at 2000 mg/L). The temperaturewas kept constant at 37C throughout the run. Other op-erational conditions used in this third experimental runare summarized in Table 4. Different simple kinetic mod-els were applied to obtain the kinetic parameters from theexperimental data achieved in this third experimental run.

    Chemical analyses

    All chemical analyses were carried out according to therecommendations of the Standard Methods for the Ex-

    amination of Water and Wastewater.[22] Specifically, COD,VSS and sulfate were analyzed according to the StandardMet...

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