Pretreatment of municipal waste activated sludge for volatile sulfur compounds control in anaerobic digestion

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<ul><li><p>dn</p><p>hlo, Lo</p><p>MercaptanPretreatment</p><p>f mdigeomizatneds chr d</p><p>ability in terms of time to lter (TTF), and decreased methyl mercaptan generation potential of the</p><p>vated she rate. Varioupre-treilizatiotters a</p><p>On the other hand, Lee and Shoda (2008) have reported that ironrich sludge can enhance anaerobic digestion. Although the combi-nation of H2O2 and iron salts (also known as Fentons reagent) hasshown signicant positive impact on sludge solubilization as wellas anaerobic digestion (Erden and Filibeli, 2010), the wastewaterto be treated must be acidic (pH 3.005.00), and therefore, the</p><p>biogas are very expensive (Ahammad et al., 2008). The commonVSCs detected in sludge are hydrogen sulde (H2S), methyl mercap-tan or methanethiol (MT), dimethyl sulde (DMS), and dimethyldisulde (DMDS) (ASCE, 1995). Recent studies have shown thatthe degradation of protein containing amino acids such as cysteine,methionine is closely related to the production of VSCs (Higginset al., 2004). Lipids (fat, oil and grease) in sludge are also known asresponsible for odor generation (Shin-Ichi et al., 1991). Based onthe extensive literature search, it can be concluded that themajorityof pretreatment studies focused primarily on sludge solubilization</p><p> Corresponding author. Tel.: +1 519 661 2111x81273; fax: +1 519 661 3498.</p><p>Bioresource Technology 102 (2011) 37763782</p><p>Contents lists availab</p><p>T</p><p>elsE-mail address: mray@eng.uwo.ca (M.B. Ray).consumption. Among various chemical treatments, although ironsalts and hydrogen peroxide have been used for sludge pretreat-ment previously, their impacts on anaerobic digestion remain con-troversial producing conicting results. For example, whileEskicioglu et al. (2008) have reported 25% reduction in methaneyield for thickened WAS treated with hydrogen peroxide (H2O2),Rivero et al. (2006) have observed a slight enhancement in biogasproduction for H2O2 treated sludge. Different studies have reportedpoor digestibility for iron dosed sludge (Smith and Carliell-Marquet, 2008; Ghyoot and Verstraete, 1997; Jack et al., 1976).</p><p>signicant impact on biogas production enhancement, the majorchallenge of using mechanical pretreatment is high energy require-ment. For example, Microsludge uses 12,000 psi pressure to sol-ubilize waste activated sludge (Stephenson et al., 2005).</p><p>The production of volatile sulfur compounds (VSCs) such ashydrogen sulde (H2S), mercaptans, etc. with low odor thresholdconcentrations is considered as the major reason behind the nui-sance odors in anaerobically digested sludges. Hydrogen sulde(H2S) in biogas is also undesirable, as it is a very toxic and corrosivegas. Physical and chemical processes used for removal of H2S fromWaste activated sludge</p><p>1. Introduction</p><p>Anaerobic digestion of waste acticompared to primary sludge due to tstep (Pavlostathis and Gosset, 1986)chemical, thermal, and mechanicalported in literature for sludge solubtion and making the organic ma0960-8524/$ - see front matter Crown Copyright 2doi:10.1016/j.biortech.2010.12.020digested sludge.Crown Copyright 2010 Published by Elsevier Ltd. All rights reserved.</p><p>ludge (WAS) is difcultlimiting cell hydrolysiss techniques includingatments have been re-n through cell disrup-vailable for microbial</p><p>pH of pretreated wastewater must be adjusted to the optimumpH of 6.57.5 before anaerobic digestion.</p><p>Mechanical pretreatment of sludge to enhance hydrolysis rate isbased on the microbial cell disruption by shear stresses. Commonlyused mechanical pretreatment techniques are ultrasound,mechanical jet, high pressure homogenizer, mechanical ball mill,etc. (Nah et al., 2000; Baier and Schmidheiny, 1997; Tiehm et al.,2001). Although different mechanical pretreatments have shownAnaerobic digestionHydrogen sulde due to the mechanical pretreatment increased total cumulative methane production by 810% after</p><p>30 days during the biochemical methane potential (BMP) test. The pretreatment also improved dewater-Pretreatment of municipal waste activatecompounds control in anaerobic digestio</p><p>Bipro Ranjan Dhar, Emhemmed Youssef, George NakDepartment of Chemical and Biochemical Engineering, The University of Western Ontari</p><p>a r t i c l e i n f o</p><p>Article history:Received 25 August 2010Received in revised form 1 December 2010Accepted 2 December 2010Available online 7 December 2010</p><p>Keywords:</p><p>a b s t r a c t</p><p>The effect of combination o(WAS) prior to anaerobicdecrease volatile sulfur cconducted using depressurat 75 1 psi, while combiperoxide (H2O2) and ferrouof H2S in biogas occurred fo</p><p>Bioresource</p><p>journal homepage: www.010 Published by Elsevier Ltd. All rsludge for volatile sulfur</p><p>a, Madhumita B. Ray ndon, Ontario, Canada N6A 5B9</p><p>echanical and chemical pretreatment of municipal waste activated sludgestion was studied using a laboratory scale system with an objective topounds in biogas and digested sludge. Mechanical pretreatment wasion of WAS through a valve from a batch pretreatment reactor pressurizedpretreatments were conducted using six different dosages of hydrogenloride (FeCl2) along with mechanical pretreatment. About 3746% removalifferent combined pretreatment conditions. Sludge solubilization achieved</p><p>le at ScienceDirect</p><p>echnology</p><p>evier .com/locate /bior techights reserved.</p></li><li><p>2.3. Biochemical methane potential (BMP) test</p><p>To assess the effect of different pretreatment conditions onanaerobic digestibility, the treated waste activated sludge wasused for biochemical methane potential (BMP) tests using300 mL serum bottles. Anaerobic digested seed was collected fromthe St. Marys wastewater treatment plant, Ontario, Canada. TheTCOD, SCOD, TSS and VSS concentrations of anaerobic seed were16,540, 1742, 12,350, and 9455 mg/L, respectively. The volumesof WAS (substrate) and anaerobic seed based on initial food (CODof substrate) to microorganism (VSS of seed) ratio (F/M) of 2(mg of CODsubstrate/mg of VSSanaerobic seed), were 140 and 110 mL,respectively. For the control, the treated WAS (substrate) was</p><p>SCOD soluble oxygen demand (mg/L)SO24 dissolved sulfate (mg/L)</p><p>SO24 S Sulfur as dissolved Sulfate (mol)T digestion time (day)TBOD total biochemical oxygen demand (mg/L)TCOD total chemical oxygen demand (mg/L)Total-S total sulfur (mol)TSS total suspended solids (mg/L)TTF time-to-lter (s)VFA volatile fatty acid (mg/L)VSS volatile suspended solids (mg/L)Yt amount of substrate removed at time t (mg of COD/L)</p><p>Table 1Characteristics of WAS.</p><p>echnology 102 (2011) 37763782 3777Waste activated sludge (WAS) samples for this study were col-lected from the Adelaide Pollution Control Plant located in London,Ontario, Canada. After thickening, the sludge was stored in a coldroom at 4 C. The characteristics of the WAS were analyzed beforethe experiments and are presented in Table 1.</p><p>2.2. Pretreatment conditions</p><p>The pretreatment of waste activated sludge was done using alaboratory scale sludge pretreatment reactor of volume 12 L. Formechanical pretreatment (MP), 10 L of sludge was pumped fromsludge feed tank to the pretreatment reactor using a meteringpump (LMI Milton Roy, Model A151-192C, Liquid Metronics Inc.,and enhancement of anaerobic digestibility, and very little effort hasgone to the fate of odor precursors and VSCs under pretreatment.</p><p>In light of the above literature, this study attempts to systemati-cally and comprehensively evaluate the impact of pretreatment onWASprior to anaerobicdigestionusinga laboratory scale systemcom-bining mechanical and chemical (H2O2 and iron salt) pretreatments.The efciency of different pretreatment conditions is evaluated interms of (a) sludge solubilization, (b) biogas production by biochem-icalmethane potential (BMP) test, (c) impact ondifferent odor precur-sors such as dissolved sulde, bound protein, and lipid afterpretreatment, (d)H2S control inbiogas, andmercaptan generationpo-tential of digested sludge, and (f) dewaterability of digested sludge.</p><p>2. Methods</p><p>2.1. Waste activated sludge (WAS)</p><p>Nomenclature</p><p>ANOVA analysis of varianceC amount of substrate (mg COD/L)F/M food to microorganism ratio (mg of CODsubstrate/mg of</p><p>VSSanaerobic seed)K anaerobic degradation rate constant (day1)LSD least signicant differenceLu ultimate biodegradable substrate (mg of COD/L)rsu substrate utilization rate of anaerobic digester (mg COD/</p><p>L-d)S2 dissolved sulde (mg/L)S2S sulfur as dissolved Sulde (mol)SBOD soluble biochemical oxygen demand (mg/L)</p><p>B.R. Dhar et al. / Bioresource TMA 01720 USA) until the pressure of the reactor reached75 1 psi. The time required to reach 75 1 psi pressure was20 min. Then after 30 min residence time the pressure of thesludge was released to atmospheric pressure (14.7 psi) throughthe sludge depressurization valve.</p><p>For combined pretreatment (CP), different dosages of hydrogenperoxide (H2O2) and iron salts were used. Hydrogen peroxide wasadded as 50 wt.% H2O2 (HX0630-1, EMD Chemicals Inc., Germany),and iron was added as Fe(II) Chloride (98% purity, Sigma Aldrich,Oakville, ON, Canada). The dosages were used based on theoreticalrequirement of the chemical dosages for dissolved sulde (S2) re-moval in untreated sludge. The theoretical requirements of H2O2and FeCl2 to remove 1 mg dissolved sulde (S2) are 0.6 and1.5 mg, respectively (Walton et al., 2003). Chemicals were addedto the sludge feed tank and allowed to mix for 30 min. After mix-ing, the chemically pretreated sludge was pumped to the pretreat-ment reactor for mechanical pretreatment. For this study, a total ofseven sets of experiments were carried out, each with duplicates.Different pretreatment conditions are summarized in Table 2.Parameter Concentration (A B)</p><p>TCOD (mg/L) 14,705 123SCOD (mg/L) 917 22TBOD (mg/L) 3819 81SBOD (mg/L) 451 24TSS (mg/L) 11,880 56VSS (mg/L) 8730 156Total VFAa (as mg COD/L) 92 3Lipid (mg/L) 195 7Dissolved Sulde (mg/L) 17.5Total Protein (mg/L) 1174 16Bound Protein (mg/L) 498 1.79Soluble Protein (mg/L) 84.5 2.98Sulfate (mg/L) 20.84 0.46Ammonia (mg/L) 68 2Total Nitrogen (mg/L) 1126 26</p><p>pH 6.16.26Alkalinity (mg/Las CaCO3) 767 19</p><p>A = Arithmetic mean of duplicate measurement.B = Absolute difference between mean and duplicate measurement.</p><p>a Summation of acetic acid, propionic, butyric, iso-butyric, valeric, and isovalericacids.</p><p>Table 2Summary of pretreatment conditions.</p><p>Set Chemical dosages</p><p>mg of H2O2/mg dissolved S2 mg of FeCl2/mg dissolved S2</p><p>Control MP CP 1 0.6 1.5CP 2 1.5 1.5CP 3 0.6 3CP 4 1.5 2.5CP 5 2 2.5CP 6 2 3</p></li><li><p>protein assay (Pierce, Rockford, USA). This method modied byLowry et al. (1951), uses standard solution of bovine serum albu-</p><p>chnmin. In order to measure various protein fractions, 50 mL sampleswere centrifuged at 10,000 rpm for 15 min at 5 C to separate thesolids in the sludge. The supernatant was ltered through a1.5 lm glass microber lter and the ltrate was analyzed forthe soluble protein fraction. Total protein and bound protein frac-tions were extracted from the suspended solids by using 1 N NaOHsolution and phosphate buffer (pH 8, 50 mM), respectively. Thesolution was mixed using a magnetic stirrer at 1500 rpm for 10and 30 min for bound and total protein, respectively, and then cen-trifuged at 10,000 rpm for 15 min at 5 C, with the centrate lteredthrough a 1.5 lm glass microber lter, prior to protein analysis.replaced by raw untreated WAS. Blank tests containing only seedand deionized water were used to determine the methane produc-tion resulting from the anaerobic seed alone. An alkalinity of5000 mg/L as CaCO3 was maintained by using 1 g of NaHCO3 ineach serum bottle. After purging with nitrogen, the serum bottleswere sealed with rubber septa and agitated in the shaker(MaxQ 4000, incubator and refrigerated shaker, Thermo Scientic,Fremont, CA) at 180 rpm, at the mesophilic temperature of37 1 C. The BMP test was conducted for about 30 days untilthe biogas production stopped. Produced biogas volume and meth-ane composition were monitored on a regular basis.</p><p>2.4. Analytical methods</p><p>All water quality parameters were analyzed according to thestandard methods (APHA, 1998). Soluble parameters were ana-lyzed after ltering the sludge sample through 0.45 lmmembranelter. HACH vials were used to measure chemical oxygen demand(COD), total nitrogen (Total-N), ammonia. As remaining H2O2 insludge sample interfere with the COD measurement (Kang et al.,1999), residual hydrogen peroxide concentrations were measuredusing Quantox peroxide test strips (Sigma Aldrich Canada,C9322) to ensure the accuracy of the COD measurement. Dewater-ability of digested sludge was measured using the time-to-lter(TTF) method (APHA, 1998).</p><p>The concentrations of volatile fatty acids (VFAs) were analyzedusing a gas chromatograph (Model Varian 8500, Varian Inc., Toron-to, Canada) with a ame ionization detector (FID) equipped with afused silica column (30 m 0.32 mm). Heliumwas used as the car-rier gas at a ow rate of 5 mL/min. The temperatures of the columnand detector were 110 and 250 C, respectively.</p><p>Total dissolved sulde (S2) was analyzed by the iodometrictitration method (APHA, 1998), and dissolved sulfate (SO24 ) wasanalyzed using ion chromatograph (Model Dionex ICS-3000). H2Sin biogas was measured using the Odalog (Model Odalog type I,App-Tek International Pty. Ltd., Brendale 4500, Australia) with adetection range of 01000 ppm. Methyl mercaptan was measuredin headspace of serum bottles using Gastec gas sampling pump(Model GV-100, GASTEC Corporation, Japan) and Gastec detectortubes (No. 70L, measuring range 0.18 ppm). The DMS was mea-sured in gas sample using gas chromatograph (GC 2010, Shimadzu)with ame photometric detector (FPD) equipped with BPX-5 col-umn (5% Phenyl Polysilphenylenesiloxane) type capillary column(30 m 0.25 m i.d. 0.25 lm thickness) obtained from SGE(Austin, TX). Helium was used as the carrier gas at a ow rate of4 mL/min. The temperatures of the column and injection were 60and 250 C, respectively. The temperature of FPD was 250 C. Theow rates of hydrogen and air were 60 and 70 mL/min, respectively.</p><p>Protein fractions were determined by micro-bicinchoninic acid</p><p>3778 B.R. Dhar et al. / Bioresource TeCell protein was calculated from the difference between total andbound protein. Lipid concentrations were measured gravimetri-cally after extraction using hexane (Bougrier et al., 2007).The biogas production was determined by injecting a gas syr-inge (Perfektum; Popper and Sons Inc., NY, USA) in the headspaceto equilibrate with the ambient pressure as recommended byOwen et al. (1979). For biogas composition analysis, 0.5 ml samplewas collected using 1 ml syringe (Hamilton, Reno, Nevada, USA),and methane composition was measured using SRI 310C GasChromatograph (Model 310, SRI Instruments, Torrance, CA)equipped with a thermal conductivity detector (TCD) and a molec-ular sieve column (Molesieve 5A, mesh 80/100, 182.88 0.3175 cm). The temperatures of the column and the TCD detectorwere 90 and 105 C, respectively. Argon was used as carrier gas at aow rate of 30 mL/min.</p><p>2.5. Kinetics of anaerobic digestion</p><p>A kinetic study was done using the BMP test results. To comparethe...</p></li></ul>

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