Assessment of optimum dilution ratio for biohydrogen production by anaerobic co-digestion of press mud with sewage and water

Download Assessment of optimum dilution ratio for biohydrogen production by anaerobic co-digestion of press mud with sewage and water

Post on 26-Jun-2016

214 views

Category:

Documents

2 download

Embed Size (px)

TRANSCRIPT

  • r bnd

    , Indngin

    Sewage

    presd Udrotionuctint t

    2010 Elsevier Ltd. All rights reserved.

    ive tohas aresentwaterl proc

    and Radjaram, 1998). In contrast, hydrogen production is favoredat an acid pH (Gomez et al., 2006; Mohanakrishna et al., 2010).

    As a semi-solid material, press mud cannot be fermented unlesswater or sewage is added. Fermentation can be carried out in an

    Seed sludge was collected from a municipal wastewatertreatment plant maintained by the Public Works Department,Pondicherry, India. It was sieved through a wire mesh of 0.5 mm to remove solid materials that may block the ow in thepump. Cow dung was mixed with water at a 1:2 ratio and digestedunder anaerobic conditions for 30 days at a pH between 5 and 6 byadding HCl/NaOH as needed. The digest was ltered through wiremesh ( 0.5 mm) to remove brous materials, mixed with seedsludge at 4:1 ratio, and heated to 70 C for 1 h to inhibit themethanogens, and used as seed. The characteristics of the seed(fermented cow dung diluted with sludge) are given in Table 1.

    Corresponding author. Tel.: +91 413 2643007, mobile: +91 94437 48471;fax: +91 413 2643008.

    E-mail addresses: radjaram@rediffmail.com (B. Radjaram), saravananae@gmail.com (R. Saravanane).

    Bioresource Technology 102 (2011) 27732780

    Contents lists availab

    Bioresource T

    els1 Tel.: +91 413 2655281x210, mobile: +91 93451 56037; fax: +91 413 2655101.gen fermentation which can utilize highly concentrated organicwastewater and biomass, such as municipal solid wastes and sew-age sludge as raw material (Das and Veziroglu, 2001). Press mud isanother potential waste source for hydrogen production. About 4%of crushed sugar cane is converted to press mud, and annuallyabout 4.2 million tons of press mud is available from the sugarindustry in India (Saravanane and Radjaram, 1998). It is an acidic,thus mildly corrosive, compressed brous waste that contains515% sugar (Partha and Sivasubramanium, 2006) and 84% is bio-degradable. Earlier studies on press mud examined the feasibilityof methane production by methanogenesis at pH of 8 (Saravanane

    parameter in anaerobic fermentation as low dilution leads to prod-uct inhibition and high dilution leads to wash out of biomass inreactor (Han and Shin, 2004). In the present study water and sew-age were used to dilute press mud to allow efcient fermentation.

    2. Methods

    2.1. SeedUASBBiohydrogenCo-digestion

    1. Introduction

    Hydrogen is a promising alternatcause it is clean, renewable and122 kJ/g (Chang and Lin, 2004). At pmainly from fossil fuels, biomass andlogical processes. One such biologica0960-8524/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.biortech.2010.11.075carbon-based fuels be-high energy yield of, hydrogen is producedusing chemical or bio-ess is anaerobic hydro-

    upow anaerobic sludge blanket (UASB) process since this anaero-bic treatment system has a high treatment efciency and a shorthydraulic retention time (HRT) (Chang and Lin, 2004). Fermenta-tion in a continuous stirred tank reactor does not seem practicalsince this type of reactor was unable to maintain high level of fer-mentative biomass for hydrogen production and its specic hydro-gen production rate was low (Yu et al., 2002). Dilution is a keyKeywords:Press mud

    acidic press mud with sewage controlled pH for fermentation. Hence press mud can be exploited for bio-hydrogen production.Assessment of optimum dilution ratio foco-digestion of press mud with sewage a

    B. Radjaram a,, R. Saravanane b,1aDepartment of Civil Engineering, Pondicherry Engineering College, Puducherry 605 014b Environmental Engineering Laboratory, Department of Civil Engineering, Pondicherry E

    a r t i c l e i n f o

    Article history:Received 21 March 2010Received in revised form 16 November 2010Accepted 17 November 2010Available online 26 November 2010

    a b s t r a c t

    Anaerobic co-digestion offormed in continuously fetime of 30 h, the specic hyimum biohydrogen producdemand (COD) and VS red56 was suitable at ambie

    journal homepage: www.ll rights reserved.iaeering College, Puducherry 605 014, India

    s mud with water or sewage at ratios of 1:7.5, 1:10 and 1:12.5 were per-ASB reactors for hydrogen production. At a constant hydraulic retentiongen production rate was 187 mL/g volatile solids (VS) reduced during max-of 7960 mL/day at a 1:10 ratio of press mud to sewage. Chemical oxygen

    ons of 61% and 59% were noted on peak biohydrogen yield. A pH range ofemperature for entire process; a lower pH was inhibitory. Co-digestion ofiohydrogen production by anaerobicwater

    le at ScienceDirect

    echnology

    evier .com/locate /bior tech

  • 2.2. Feed substrate

    Table 1Characteristics of seed and feeds of R1 and R2 for dilutions of 1:7.5, 1:10 and 1:12.5.

    Substrate pH TS TDS TSS TVS

    Seed 6.76 10.9 2.05 8.85 6.8Reactor R11:7.5 6.46 7.7 2.25 5.45 4.651:10 5.01 7.7 2.45 5.25 5.51:12.5 5.65 15.4 2.2 13.2 4.2

    Reactor R21:7.5 5.2 9.9 7.6 2.3 4.251:10 5.18 7.2 1.5 5.7 3.91:12.5 6.12 6.6 5.62 0.98 3.2

    All units are in g/L except pH.

    2774 B. Radjaram, R. Saravanane / BioresourceTwo UASB reactors of volume 20 L each were used in this study.The cylindrical plexiglas reactors had an internal diameter 10 cmand a height of 190 cm (H/D > 10) with a gas liquid separator atthe top (diameter, 20 cm; height, 20 cm) with an efuent port at15 cm from the bottom of the gas liquid separator. Seven samplingports were evenly xed over the entire height of the column at25-cm interval. The gas liquid separator housed an inverted funnelconnected to a wet gas meter through a exible tube for measuringthe gas ow rate. The reactor had provisions for feeding from thebottom and removal of efuent from the top. The reactor receivedfeed from a feed tank through a peristaltic pump (Ravel RH P 100 L)as shown in the schematic diagram (Fig. 1). The feed substrate inthe feed tank was stirred at every 20 min for 3 min with a mechan-ical stirrer tted in the tank to prevent settlement of solids.The characteristics of pressmud and sewage are given in Table 2.In preliminary experiments it was determined that a minimumdilution of 1:7.5 of press mud and water was necessary to obtaina hydrogen fermentation substrate that can be ltered and ulti-mately used in a continuous ow system. Therefore, feeds for reac-tor R1 were prepared for three series of experiments by diluting4 kg press mud with 30, 40 and 50 L of water to obtain dilutionratios of 1:7.5, 1:10, and 1:12.5, respectively. Feeds for reactor R2were prepared at the same dilution ratios by adding sewage insteadof water. The press mud/sewage and press mud/water mixtureswere allowed to soak for 4 h, ltered through wire mesh( 0.5 mm) to remove bers and the ltrate was fed into the reac-tors. The characteristics of the feed substrate are given in Table 1.

    2.3. Bioreactor systemTable 2Characteristics of press mud and sewage.

    Parametersa Press mud Sewage

    pH 4.55 7.2COD (%) 117.6 13.6C/N ratio 24.04 17.5Total solids (%) 29 7.4Moisture content (%) 71 Total volatile solid (%) 84 5.8Organic carbon (%) 48.80 6.1Nitrogen (%) 2.05 1.96Phosphorous (%) 0.65 Potassium (%) 0.28 Sodium (%) 0.18 Calcium (%) 2.7 Sulphate (%) 1.07 Sugar (%) 3 Wax (%) 1

    a Average values.2.4. Operation

    Reactors R1 and R2 were operated with press mud diluted withwater and sewage, respectively. HRT was xed at 30 h since a high-er HRT does not lift the particulate substrate in the reactor column.The experiments were started in R1 and R2 with a 1:7.5 dilutionand performance was observed till steady state was reached inboth reactors. The operation was continued at steady state for 30additional days. Then, the dilution was changed to 1:10 and theperformance was monitored for 30 days. Finally the dilution waschanged to 1:12.5 for another 3034 days. The pH of the reactorswas between 5 and 6, by adding HCl/NaOH as needed with the feedand the reactors were operated at ambient temperatures(3038 C) without heating or cooling.

    2.5. Analytical methods

    Temperature, pH and biohydrogen production were measureddaily with a thermometer, pH probe and wet gas meter, whilethe gas composition was analyzed using a gas chromatograph(Nucon GC). The total volatile solids (VS), chemical oxygen demand(COD), volatile fatty acid (VFA), alkalinity, etc. were estimated oncea week by standard methods (APHA, 1995).

    3. Results and discussion

    3.1. Start-up of UASB reactor

    During the start-up period, the UASB system was fed continu-ously with diluted substrate at a concentration starting from2500 to 10,000 mg COD/L to reach an organic loading rate (OLR)of 820 g/L/day. The pH in the reactor decreased from 6.5 to 5.5during the start-up period, while hydrogen production (Fig. 2b)and COD removal efciency (Fig. 2c) gradually increased. Biohy-

    TVDS TVSS Total COD Alkalinity VFA

    1 5.8 10.40 19.03 1.82

    1 3.65 12.48 12.68 1.502.4 3.1 17.88 15.85 5.220.8 3.4 29.95 6.34 1.68

    2.27 1.98 10.56 27.36 2.040.5 3.4 32.03 47.55 0.342.48 0.72 8.32 19.03 5.52

    Technology 102 (2011) 27732780drogen production started on day 29 in R1, with an uneven outputfor 76 days. After 76 days, both biohydrogen production and CODremoval efciency stabilized in the system, reaching approxi-mately 1600 mL/day and 70%, respectively (Fig. 2b and c). Hydro-gen production started on day 34 in R2 with an unsteady outputup to day 60. After 60 days both hydrogen yield and COD removalefciency stabilized. These results revealed that anaerobic acti-vated sludge of reactors R2 and R1 possessed good acid-toleranceand stable hydrogen production ability, which indicated goodacclimatization.

    3.2. Continuous hydrogen production

    R1 reached steady-state conditions, dened as consistenthydrogen production with a variation of less than 10%, after90 days (Fig. 2b). The hydrogen production was 1900 mL/day witha 1:7.5 diluted feed. When, the dilution was changed to 1:10 on

  • 0urceFeed tank

    200 L

    Timer

    Gas liquid separator

    190

    200

    Feed

    B. Radjaram, R. Saravanane / Bioresoday 120, production gradually reached 50006000 mL/day by day136. After 144 days it reached 7210 mL/day and nally attained amaximum of 7820 mL/day during days 145150 (Fig. 2b). Whenthe dilution was changed to 1:12.5 on day 150, gas production de-clined and did not stabilize (Fig. 2b). Maximum hydrogen produc-tion was 4.887 L/kg press mud at 1:10 dilution in R1. Reactor R2took 60 days to reach steady-state conditions. At a 1:7.5 pressmud:sewage ratio, maximum hydrogen production was 1990 mL/day on day 89. When the dilution was changed to 1:10 on day90, the gas yield dropped below 1000 mL/day for 1 week time,but increased thereafter (Fig. 4b). The highest hydrogen productionof 7960 mL/day occurred on day 115. At a dilution of 1:12.5, max-imum hydrogen production was 3880 mL/day (Fig. 4b). Maximumhydrogen of 4.990 L/kg press mud added was evaluated at a 1:10dilution in R2. These yields are lower than those obtained withwheat feed and sweet sorghum fermentations which were 56 L/kg feed at HRT of 15 h (Hawkes et al., 2008) and 10.41 L/kg feed(Georgia et al., 2008), respectively; however, the use of such sub-strates for hydrogen production is questionable since they are alsoused as animal feed. The yields were higher than those achievedwith Rhodobacter sphaeroides RV which reached only 1.41.6 L/Lreactor volume/day (Fascetti and Todini, 1995) and 1.3 mL/mL por-ous glass media/h (Tsygankov et al., 1994) and required input oflight. Earlier studies had demonstrated that sewage sludge diges-tion can produce hydrogen at the rate of 3.75 mL/min (Nicolauet al., 2008) and that acclimatized anaerobic activated sludge hada hydrogen producing ability as high as 10.4 m3 H2/m3 reactor/day in a continuous reactor with an available volume of 9.6 L(Ren et al., 1995. The co-digestion experiments with press mudand sewage demonstrated that sewage was able to support

    Peristaltic pump

    Fig. 1. Schematic arrangement of UASB100

    Sampling ports

    Effluent port

    Gas meter 200

    150

    250

    Technology 102 (2011) 27732780 2775hydrogen production since it yields 4.99 L/kg press mud feed, i.e.0.5 m3/m3 reactor volume/day.

    H2 % gradually increased with experiment days and reached amaximum of 5055% during consistency periods of study in reac-tors 1 and 2 (Figs. 2 and 4b).

    3.3. Assessment of COD loading rate, % reduction and specic hydrogenproduction rate

    COD removal uctuated in the initial start-up stage and laterstabilized after 80 days of operation in R1 (Fig. 2c). COD reduc-tion was 6077%, 70% and 86% at 1:7.5, 1:10, and 1:12.5 dilu-tions, respectively (Fig. 2c). The high COD reduction waspossible due to the large column height (H/D > 10) which pro-vided a long mixing path during substrate ow from inlet tooutlet. Filling the column to about one third its heights withbiomass allowed maintenance of adequate numbers of hydro-gen-producing bacteria in the reactor. Specic biohydrogen pro-duction rates (SBPR) were 10.98, 40.6 mL, and 2.58 mL/g CODreduced/day at maximum hydrogen production at 1:7.5, 1:10,and 1:12.5 dilution, respectively (Fig. 3a). In R2, COD loadingrates varied between 6 and 25 g/L/day (Fig. 4c) and COD reduc-tions were 3641%, 5561%, and 4041% at the 1:7.5, 1:10, and1:12.5 dilutions, respectively (Fig. 4c). Anaerobic fermentation offood waste in leaching bed reactor gave biohydrogen yield of21.241.5 mL/g COD at an HRT of 25 h (Kim et al., 2004). Biohy-drogen yield was 26.13 mol/kg COD reduced in molasses fer-mentation (Ren et al., 2006) and 1.82.3 mM/g COD fed incheese processing waste water (Yang et al., 2007) whereas inour study 41 mL/g COD reduced was achieved from a waste

    DrainAll dim in mm

    reactor for biohydrogen production.

  • urce2776 B. Radjaram, R. Saravanane / Bioresosubstrate by co-digestion. SBPR in R2 was 2037, 3541, and3951 mL/g COD reduced/day at 1:7.5, 1:10, and 1:12.5 dilu-tions, respectively (Fig. 5a). With a decrease in the dilution ra-tio, substrate becomes dense and product inhibition occurs

    Fig. 2. (a) Duration of experiments, (b) biohydrogen yield and % H2, (c) COD loading ratmud and water.Technology 102 (2011) 27732780due to excess VFA accumulation in the reactor, but higher dilu-tion led to wash out of bacteria and decreased biohydrogen pro-duction. Han and Shin (2004) observed a similar outcome intheir study.

    e and % reduction, (d) VS loading rate and % reduction of reactor R1 digesting press

  • urceB. Radjaram, R. Saravanane / Bioreso3.4. Appraisal of Volatile solid loading rate, % reduction and SBPR

    Volatile solid (VS) loading rates reached a maximum of 13 g/L/day in R1 (Fig. 2d). VS reduction was 55%, 90%, and 69% at 1:7.5,

    Fig. 3. Proles of various operating parameters (a) SPBR, (b) VSS/TSS and VFA/alkalinityexperiments in reactor R1 digesting press mud and water.Technology 102 (2011) 27732780 27771:10, and 1:12.5 dilutions, respectively (Fig. 2d). Hydrogen yieldgradually increased after 75 days and was consistently around1600 150 mL/day at a 1:7.5 dilution with a SBPR of 12.77 mL/gVS reduced/day on peak output. Though the SPBR was as high as

    ratios, (c) VFA and (d) alkalinity monitored during steady state and three series of

  • urce2778 B....

Recommended

View more >