Anaerobic digestion of solid slaughterhouse waste (SHW) at laboratory scale: Influence of co-digestion with the organic fraction of municipal solid waste (OFMSW)

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<ul><li><p>Biochemical Engineering Journal 40 (2008) 99106</p><p>Anaerobic digestion of solid slaughterhouseithe (a O, Unitmen193 Aember</p><p>Abstract</p><p>Mesophil on whave been ev ntinwith a hydra 1.70for co-digestion, was not successful. The second set-up was initiated with an HRT of 50 days and an OLR of 0.9 kg VS m3 day1 for digestionand 1.85 kg VS m3 day1 for co-digestion. Under these conditions, once the sludge had been acclimated to a medium with a high fat and ammoniacontent, it was possible to decrease the HRT while progressively increasing the OLR to the values used in the first set-up until an HRT of 25 daysand OLRs of 1.70 and 3.70 kg VS m3 day1, for digestion and co-digestion, respectively (the same conditions of the digesters failures previously).These digesundetected ofound to be 2007 Else</p><p>Keywords: A</p><p>1. Introdu</p><p>Anaeroba widely uwaste andsource thro</p><p>Slaughthuman con(skins, fatswastewaterproducts arorigin not iare not fit fas foodstufurated fat c</p><p> CorresponE-mail ad</p><p>1369-703X/$doi:10.1016/jters showed a highly stable performance, volatile fatty acids (VFAs) were not detected and long chain fatty acids (LCFAs) werer only trace levels were measured in the analyzed effluent. Fat removal reached values of up to 83%. Anaerobic digestion was thus</p><p>a suitable technology for efficiently treating lipid and protein waste.vier B.V. All rights reserved.</p><p>naerobic processes; Biogas; Co-digestion; Process inhibition; Solid slaughterhouse waste; Waste treatment</p><p>ction</p><p>ic digestion of organic matter has been reported assed technology in the efficient treatment of organicthe simultaneous production of a renewable energyugh the use of biogas [13].erhouses generate meat and products marketed forsumption, pollutant solid waste and other by-products, and bones), as well as substantial volumes ofas a result of cleaning operations. Animal by-</p><p>e all bodies or parts of animals and products of animalntended for human consumption, either because theyor human consumption or there is no market for themf [4]. Consumer demand for meats with a low unsat-ontent in order to reduce cholesterol has led to the</p><p>ding author. Tel.: +34 987 291841; fax: +34 987 291839.dress: (A. Moran).</p><p>expansion of the poultry industry and hence to an increase in lipidand protein waste. This waste causes important environmentalproblems as a result of organic pollution and microbial loads,and the increasing problems of its removal must be addressed asa result of legislative constraints and the cost of treatment anddisposal.</p><p>Slaughterhouse waste is an ideal substrate for anaerobicdigestion and elimination of more than 90% chemical oxygendemand (COD) can be attained [5]. Lipids represent an impor-tant fraction of the organic charge in slaughterhouse waste [6].They consist mainly of triglycerides and long chain fatty acids(LCFAs). Triglycerides may be hydrolyzed to LCFA and glyc-erol. Accumulation of LCFA may inhibit anaerobic digestion,because they are toxic for acetogens and methanogens, the twomain groups involved in LCFA degradation [79]. Another inhi-bition mechanism is the result of the adsorption of the surfaceactive acids onto the cell wall [10,11], thus affecting the pro-cesses of transportation and protection. The unionized form ofLCFA adsorbs initially to the microbial cell surface and is then</p><p> see front matter 2007 Elsevier B.V. All rights reserved..bej.2007.11.019scale: Influence of co-digestion wof municipal solid wast</p><p>Mara Jose Cuetos a, Xiomar Gomez a, Marta Institute of Natural Resources (IRENA), Avda. de Portugal 41</p><p>b Centre for Environment and Marine Studies (CESAM), DeparCampus Universitario de Santiago, 3810-</p><p>Received 26 September 2006; received in revised form 21 Nov</p><p>ic anaerobic digestion of slaughterhouse waste (SHW) and its co-digestialuated. These processes were carried out in a laboratory plant semi-coulic retention time (HRT) of 25 days and organic loading rate (OLR) ofwaste (SHW) at laboratorythe organic fraction</p><p>OFMSW)tero b, Antonio Moran a,versity of Leon, 24071 Leon, Spaint of Chemistry, University of Aveiro,veiro, Portugal2007; accepted 25 November 2007</p><p>ith the organic fraction of municipal solid waste (OFMSW)uously operated and two set-ups were run. The first set-up,kg VS m3 day1 for digestion, and 3.70 kg VS m3 day1</p></li><li><p>100 M.J. Cuetos et al. / Biochemical Engineering Journal 40 (2008) 99106</p><p>taken up into the cell [9]. LCFA are beta-oxidized to acetate,carbon dioxide and hydrogen in anaerobic digestion [12] whichare then coprocess is rLCFA andlowed by r</p><p>Inhibitioorganic cocentrationsnitrogen-riare rich inof non-digto slaughteto ammonimechanismdirectly inhbic free amare rapidlypH conditi</p><p>In studimixtures isthus improvnitrogen, wlems. Thecontent incphase digeimprovemetion of soliand the con</p><p>It shouldis another tislation wifraction [21ers presenthigh methaboth typeslems assoccompounds</p><p>The aimanization ((SHW) anorganic fraratory scaleoperationalcess were</p><p>were comption of muin lipids.</p><p>2. Materia</p><p>2.1. Exper</p><p>The inofrom the wThe slaughpoultry sla</p><p>with the contents of the stomach and intestines were collectedfrom eviscerated poultry. They were ground and frozen at</p><p> unsentcle se cotionsoredo feeed toeparfee</p><p>tageere 4terhoon r</p><p>perdig</p><p>rriedingrs ht-upnt oy digandas a</p><p>set-the fiperativelrt-ue froculuT o</p><p>the dt in aof S</p><p>bicerateer Btly,</p><p>g wahowneach</p><p>operdystat</p><p>on fois ctrati</p><p>naly</p><p>Roufolldig</p><p>alkanverted to biogas. What normally occurs during theapid hydrolysis/acidogenesis, with accumulation ofvolatile fatty acids (VFAs), removal of LCFA, fol-</p><p>emoval of VFA and methane production [7,13].n of the anaerobic digestion of waste with a high</p><p>ntent is usually also caused by high ammonia con-[1,14], produced in the degradation of proteins from</p><p>ch slaughterhouse waste [15]. Poultry by-productsnitrogen because they may contain high proportionsester material, especially if the birds are fed priorring [16]. Two different mechanisms are attributeda inhibition of methanogens. According to the first, activities of methane synthesizing enzymes areibited by free ammonia. In the second, hydropho-monia molecules diffuse passively into the cell andconverted to ammonium owing to the intracellular</p><p>ons [17].es carried out on this type of waste, co-digestion ofemployed to stabilize the feed to the reactor [18,19],ing the C/N ratio and decreasing the concentration ofhich in certain cases may produce inhibition prob-use of a co-substrate with a low nitrogen and lipidreases the production of biogas. Alternatively, two-stion systems may be employed [15,20], with whichnts are achieved in process efficiency, in the reduc-ds, the removal of chemical oxygen demand (COD)version of biogas.not be forgotten that municipal solid waste (MSW)</p><p>ype of residue that is affronting more restrictive leg-th respect to landfill disposal of the biodegradable,22]. Co-digestion of the mixtures of waste with oth-</p><p>ing a lower nitrogen and lipid content may result inne yields due to the fact that the characteristics ofof waste are complementary, thus reducing prob-</p><p>iated with the accumulation of intermediate volatileand high ammonia concentrations [23].of the present study was to carry out the biometh-</p><p>anaerobic digestion) of both slaughterhouse wasted mixtures of solid slaughterhouse waste with thection of municipal solid waste (OFMSW) at labo-in mesophilic semi-continuously fed digesters. Theconditions needed to achieve a stable digestion pro-</p><p>determined. At the same time, the results obtainedared, assessing the contribution of the organic frac-nicipal solid waste to the slaughterhouse waste rich</p><p>ls and methods</p><p>imental set-up</p><p>culum used for starting up the digesters was obtainedastewater treatment plant of the city of Leon (Spain).terhouse waste was collected at the Huevos Leonughterhouse in the same city. The entrails together</p><p>18 Ca reprea partimixturproporthen st</p><p>Twanalyzwas prdesiredpercenfeed wslaughdigestiand VS</p><p>Thewas ca</p><p>a workdigesteTwo sediffereidentifSHW,or 2) wsecond</p><p>Inwere o</p><p>respecThe staing ratthe inotial HRdue tocontenstudiesanaero</p><p>A2 opDigestsequenloadineters s</p><p>Forouslyof steaSteadyvariatiand thconcen</p><p>2.2. A</p><p>2.2.1.The</p><p>ing the(VS),til subsequent use. Given the difficulty of obtainingative sample of OFMSW, a simulated OFMSW withize of less than 3 mm was used as substrate. Thisntained fruit and vegetable waste and followed thereported in previous studies [22,24]. This waste wasat 4 C until used.ds were prepared for the study being periodicallyalways ensure the same solids content. A SHW feed</p><p>ed by diluting the sample with distilled water to thed load; the SHW:H2O ratio being 1:5 in weight. Thes of total solids (TS) and volatile solids (VS) of this.7 and 4.3%, respectively. A combined mixture withuse waste was prepared with an SHW:OFMSW co-</p><p>atio of 1:5 in weight. The mix as prepared had a TScentages of 10 and 9.3%, respectively.estion of SHW and its co-digestion with OFMSWout in two completely mixed stirred digesters, with</p><p>volume of 3 L and thermostatized at 34 1 C. Bothad a side inlet via which the systems were fed daily.s were implemented in order to run experiments underperational conditions. In the nomenclature used toestion systems letter A refers to the digester treating</p><p>letter B to the one treating the mixture. A number (1dded according to conditions imposed in the first orup.rst set-up of two reactors Digesters A1 and B1</p><p>ted at an OLR of 1.7 and 3.7 kg VS feed m3 day1,y, both at a hydraulic retention time (HRT) of 25 days.p of these digesters was performed applying this feed-m day 1 of experimentation to reactors loaded withm previously described. In the second set-up the ini-f the digesters was 50 days. This HRT was selectedifficulty of treating waste with a high lipid and proteinccordance with other successful anaerobic digestionHW, where the HRT are not as low as in the case of</p><p>digestion of other organic wastes [25,26]. Digesterd at a loading of 0.90 kg VS feed m3 day1, and2 at a loading of 1.85 kg VS feed m3 day1. Sub-the HRT was successively reduced and the organics gradually increased in accordance with the param-</p><p>in Table 1.experimental condition, the reactors were continu-</p><p>ated for two consecutive HRTs to ensure a situationstate before changing their operational conditions.e was defined as the situation where the coefficient ofr daily gas production was less than 10% [27,28]</p><p>oincides with a stable effluent volatile fatty acidson.</p><p>sis</p><p>tine analysesowing parameters were monitored periodically dur-estion process: pH, total solids (TS), volatile solidslinity, chemical oxygen demand (COD), ammonia,</p></li><li><p>M.J. Cuetos et al. / Biochemical Engineering Journal 40 (2008) 99106 101</p><p>Table 1Digester operational parameters in the second reactor set-up carried out</p><p>Digester Description Days HRT (days) Loading rate (kg VS feed m3 day1)A2 50 0.90A2 36 1.16A2 25 1.70B2 50 1.85B2 36 2.56B2 25 3.70</p><p>yield and cof volatile ftwice a wea week, and</p><p>The anaalkalinity aMethods [2</p><p>The conEqs. (1) an</p><p>FA =1 +</p><p>pKa = 0.0</p><p>where FA igen, pKa isT is the tem</p><p>The cheHanna Insthomogenizat 150 C f</p><p>Daily gawith liquid</p><p>BiogasGC gas chity detecto80/100 Meumn 13to separate(N2), hydrhelium andof 50 C. Sapparatus.</p><p>Volatilesame gastor (FID)(30 m 0.2gas was heand 250 C150 C fordetection lwas calibraSupelco (fopreviouslyfiltrated thr</p><p>Other analyses performedoriginal waste and digestates were characterized.</p><p>radability analysis was carried out, total nitrogen concen-s were determined by the Kjeldahl method [30], organicwas analyzed according to the Walkey-Black method</p><p>nd orconts su</p><p>tio.totahodhl-N</p><p>chrfattyed awithat</p><p>TheL ch</p><p>0.2oven</p><p>en iininaturlibrance</p><p>forwere</p><p>(C1.maiay</p><p>nt pr</p><p>eristic</p><p>ersSHW digestion 0100SHW digestion 101175SHW digestion 176225SHW + OFMSW co-digestion 0100SHW + OFMSW co-digestion 101175SHW + OFMSW co-digestion 176225</p><p>omposition of the biogas produced and concentrationatty acids (VFAs). All these variables were measuredek, except for ammonia, which was monitored once</p><p>gas production, which was daily measured.lyses of pH, total and volatile solids (TS and VS),nd ammonia were carried out according to Standard9].centration of free ammonia was calculated based ond (2) [1,17]:</p><p>TAN10(pKapH)</p><p>(1)</p><p>9018 + 2729.92T + 273.15 (2)</p><p>s the free ammonia, TAN is the total ammonia nitro-the dissociation constant for the ammonium ion andperature in C.</p><p>mical oxygen demand (COD) was determined using aruments Series C99 multi-parameter photometer. Theed sample was digested in the presence of dichromateor 2 h in a Hanna C9800 reactor.s production was measured using a reversible devicedisplacement with a wet-tip counter.</p><p>composition was analyzed using a Varian CP-3800romatograph equipped with a thermal conductiv-</p><p>r (TCD). A 4 m long column packed with Hayesepsh followed by a 1 m long Molecular Sieve col-80/100 Mesh (1.0 m 1/8 in. 2.0 m) were usedmethane (CH4), carbon dioxide (CO2), nitrogen</p><p>ogen (H2) and oxygen (O2). The carrier gas wasthe columns operated at 331 kPa at a temperature</p><p>tandard 234 from Supelco was used to calibrate the</p><p>fatty acids (VFAs) were determined on thechromatograph, using a flame ionization detec-</p><p>equipped with a Nukol capillary column5 mm 0.25m) from Supelco. The carrier</p><p>2.2.2.The</p><p>Biodegtrationmatter[30], amatterbon waC/N ra</p><p>Thelet metKjelda[31].</p><p>Gaschainextractmixed30 minfilters.tem X(30 m initialand thmaintatemperwas ca</p><p>with colimitlyzedstearicSigma</p><p>TheAt it mdiffere</p><p>Table 2Charact</p><p>Parametlium. Injector and detector temperatures were 220, respectively. The oven temperature was set at3 min and thereafter increased to 180 C. The</p><p>imit for VFA analysis was 5.0 mg L1. The systemted with a mixture of standard volatile acids fromr the analysis of fatty acids C2C7). Samples werecentrifuged (10 min, 3500 g) and the supernatantough 0.45m cellulose filters.</p><p>Total organicOrganic matteTotal nitrogenC/N ratioTotal fat (%)Total proteinTS (%)VS (%)NA: not analyganic carbon was determined considering an organicent/organic carbon ratio of 1.7241. The organic car-bsequently divided by the total nitrogen to obtain the</p><p>l lipid content was determined using a Standard Soxh-[29], and the protein content was calculated from thecontent using a conversion factor of 6.25 (for meat)</p><p>omatography was used for the analysis of the longacids (LCFAs). Samples for LCFA analysis were</p><p>s described by Fernandez et al. [32]. Samples weren-heptane, the solution was then centrifuged for</p><p>3500 g and filtrated through 0.45m cellulosesample was injected into a Perkin-Elmer AutoSys-</p><p>romatograph equipped with an HP Innowax column5 mm 0.25m). The carrier gas was helium. Thetemperature of 120 C was maintained for 1 min,</p><p>ncreased to 250 C, with a ramp of 8 C min1,g this temperature for 7 min. Injector and detectores were 250 and 275 C, respectively. The systemted using a mixture of LCFA from individual acids</p><p>ntrations in the range of 0100 mg L1. The detectionLCFA analysis was 5.0 mg L1. The acids ana-lauric (C12:0), myristic (C14:0), palmitic (C16:0),8:0), oleic (C18:1) and linoleic (C18:2), all from</p><p>n properties of the original waste are given in Table</p></li></ul>