Anaerobic digestion challenge of raw olive mill wastewater

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<ul><li><p>eLum</p><p>W)5 kics.ovarveMWdaycoferecre</p><p>worldtries mich larill waal., 2</p><p>oblemstrializts of Oseaso</p><p>The adopted solution in many countries is the evaporation inopen ponds which requires large areas and generates several prob-lems such as bad odour, methane emissions, inltration into thesoil and insect proliferation (Roig et al., 2006; Jarboui et al.,2010). This means that common cost-effective practices appliedto OMW management are not an operative solution to solve thisproblem.</p><p>tions 204400 times higher than the ordinary urban wastewater(Azbar et al., 2009; Xing et al., 2000) and, consequently, it repre-sents a signicant energy potential (Gelegenis et al., 2007). Apartfrom the renewable energy generation in the form of biogas, anaer-obic digestion presents some other appealing advantages since itallows small amounts of sludge generation, low nutrient require-ments, reduction of greenhouse gases emissions and productionof a liquid fertilizer. However, several OMW characteristics suchas the acid pH, low alkalinity, low nitrogen content and the pres-ence of a lipidic fraction and phenolic compounds derived fromthe olive stones and pulp, make this wastewater a potential toxic</p><p> Corresponding author. Tel.: +351 210924600; fax: +351 217127195.E-mail addresses: (M.A. Sampaio), marta.goncal</p><p>Bioresource Technology 102 (2011) 1081010818</p><p>Contents lists available at</p><p>T</p><p> (M.R. Gonalves), (I.P. Marques).production did not contribute to nd a solution in order to properlymanage the resulting efuent (McNamara et al., 2008). OMWcannotbe treated in a domestic wastewater treatment plant due totechnical limitations (Rozzi and Malpei, 1996). On the other hand,the application of untreated OMW on soils and crops causesphytotoxic and biotoxic effects whichmake it unsuitable for furtheruse as fertilizer or as irrigation water (Niaounakis and Halvadakis,2006).</p><p>this situation. Biological processes are considered environmentallyfriendly and, in many cases, a cost-effective procedure (McNamaraet al., 2008).</p><p>Anaerobic digestion has been reported as one of the most prom-ising technologies for the disposal of OMW (Paraskeva andDiamadopoulos, 2006; Marques, 2000). Comprising a high organiccontent (45220 g COD L1), this efuent is classied among thestrongest industrial liquid wastes that corresponds to concentra-1. Introduction</p><p>Olive oil production is expandinghealth-promoting effects. Most counphase centrifugation system, fromwhreddish-brown liquid called olive m(Morillo et al., 2009; McNamara etbecome a serious environmental proil increasing production and induprocess that generates larger amoun2006). Moreover, the scattered and0960-8524/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.biortech.2011.09.001wide as a result of itsake use of the three-</p><p>ge quantities of a strongstewater are obtained008). This efuent hasas a result of the oliveation of the extractionMW (Kapellakis et al.,nal nature of olive oil</p><p>OMW has been the subject of many waste treatment studiesinvolving chemical and physical treatment (coagulation/occula-tion and chemical oxidation), biochemical treatment (fermentation,aerobic process, composting) and combined processes/techniques(Roig et al., 2006; El-Gohary et al., 2009; Sarika et al., 2005). How-ever, no satisfactory solution has yet been found for the safe OMWdisposal mainly due to technical and economical limitations(Morillo et al., 2009). As a result, signicant OMW volumes in Med-iterranean area are discharged directly into watercourses (Azbaret al., 2009; El-Gohary et al., 2009) and it is urgent to adopt technol-ogies that allow maximizing the benet/price ratio and overcomeAnaerobic digestion challenge of raw oliv</p><p>M.A. Sampaio, M.R. Gonalves, I.P. Marques Bioenergy Unit, National Laboratory of Energy and Geology I.P. (LNEG), Estrada Pao do</p><p>a r t i c l e i n f o</p><p>Article history:Received 30 May 2011Received in revised form 26 August 2011Accepted 1 September 2011Available online 10 September 2011</p><p>Keywords:Raw olive mill efuentBiogasAnaerobic hybrid digesterPhenolic compoundsOrganic shocks operation</p><p>a b s t r a c t</p><p>Olive mill wastewater (OMHigh concentrations (545OMW adverse characteristCH4) and 8182% COD remperformance was also obseing piggery efuent and ODeveloped biomass (350</p><p>efuents complementarityobtained. Unlike what is reexpenses to correct it or d</p><p>Bioresource</p><p>journal homepage: www.ll rights reserved.mill wastewater</p><p>iar 22, 1649-038 Lisboa, Portugal</p><p>was digested in its original composition (100% v/v) in an anaerobic hybrid.g COD m3), acid pH (5.0) and lack of alkalinity and nitrogen are someLoads of 8 kg COD m3 d1 provided 3.73.8 m3 biogas m3 d1 (6364%l. An efuent with basic pH (8.1) and high alkalinity was obtained. A goodd with weekly load shocks (2.74.1, 8.410.4 kg CODm3 d1) by introduc-alternately. Biogas of 3.03.4 m3 m3 d1 (6369% CH4) was reached.s) was neither affected by raw OMW nor by organic shocks. Through thencept, a stable process able of degrading the original OMW alone wasred, OMW is an energy resource through anaerobiosis without additionalase its concentration/toxicity.</p><p> 2011 Elsevier Ltd. All rights reserved.</p><p>SciVerse ScienceDirect</p><p>echnology</p><p>evier .com/locate /bior tech</p></li><li><p>2. Methods</p><p>2.1. Substrates: agro-livestock and industrial efuents</p><p>The OMW tested in this study resulted from the olive oil cam-paign of 2010. It was collected in an olive oil production plantequipped with a three-phase olive oil extraction process, locatedin Rio Maior (Portugal). The unit is characterized by an averageolive oil production capacity of 42 m3 year1. Piggery efuentwas obtained from a pig farming facility located in the vicinity ofthe olive oil mill, also in Rio Maior. Both substrates were character-ized (Table 1) and stored at 4 C. They were digested in their origi-nal form; which means that they were not subjected to anyalteration.</p><p>2.2. Analytical and chromatograph methods</p><p>Characterization of the efuents used in the hybrid feed.</p><p>echnology 102 (2011) 1081010818 10811substrate and not suitable for anaerobiosis. To overcome theseproblems several synthetic nutrient, chemical additions and pre-treatments (chemical and biochemical) have been reported toenable OMW anaerobic digestion (Dareioti et al., 2009; El-Goharyet al., 2009; Martinez-Garcia et al., 2009; Azbar et al., 2009,Gelegenis et al., 2007). But again, these pre-treatments involveinputs which raise the cost-benet ratio and also lead to organicload reductions and, consequently, to a decrease of the availablemethanogenic potential for energy production.</p><p>This work is part of a broader plan that aims to make the ener-getic valorisation of the raw OMW, by anaerobiosis, simpler, moreexible and cheaper. So, the concept of OMW complementaryefuent was applied in order to reduce the treatment processingsteps by elimination of the operational phases related with OMWcorrections and/or pre-treatments. This feeding approach wastested by combining progressive increases of OMW volumes witha complementary efuent during the experimental period. The rstresults have showed to be possible to treat anaerobically the rawOMW using another efuent and digesting them simultaneously(Marques et al., 1997, 1998).It was also proved that the piggeryefuent can work as a good complementary efuent of OMW.Afterwards, the strategy of combining OMW with other wasteswas used by different authors. A study about the effect of differentsubstrates (manure, household waste and sewage sludge) revealedthat OMWandmanure were the best co-digestion option (Angelidakiand Ahring, 1997). More recently, a combination of OMW anddiluted poultry manure was degraded in a cylindrical down owanaerobic reactor with 18 days of hydraulic retention time (HTR)(Gelegenis et al., 2007). However, under a critical OMW percentageof 28% (v/v) the methane production rate dropped rapidly and1 m3 m3 d1 was registered as a maximum. In a two-stage CSTRanaerobic reactor, Dareioti et al. (2009) used a mixture of 55%OMW and 40% cheese whey and 5% (v/v) liquid cow manure. Efu-ent was successfully degraded and a methane production rate ofabout 1.35 m3 m3 d1 was obtained using a HTR of 19 days. Othermixture (75% OMW plus 25% pig slurry) was pre-treated byCandida tropicalis and digested in a xed bed reactor (HTR of11 days) to give 1.61 m3 m3 d1 of biogas (Martinez-Garciaet al., 2009). The up-ow xed bed digester (anaerobic lter), pre-viously studied by Marques (2001), was also tested with severalfeed mixtures but without recourse to any operational action be-fore the anaerobic digestion phase (pre-treatments, chemical cor-rections or supplementations). Working with 83% OMW and 17%piggery efuent (v/v) and about 6 days of HTR, a production rateof 1.31 m3 CH4 m3 d1 was registered. Following the work per-formed and aiming to make the process even simpler and cheaper,it was decided to test other up-ow digester type. An anaerobichybrid digester was used instead of the anaerobic lter (Gonalveset al., 2009). Similar feed mixtures were provided and amounts of83% OMW (v/v) were treated without any inhibition (HRT = 6 days)providing a methane production rate of 1.96 m3 m3 d1 (Gonalveset al., submitted for publication).</p><p>Based on the team results a biogas plant working all year withthe complementary substrate can advantageously receive increas-ing amounts of OMW without affecting the system stability. Bear-ing in mind the seasonality of the OMW production (three or fourmonths a year) and the large volumes of efuents that are gener-ated (730 million m3 every year: Niaounakis and Halvadakis,2006), the present work aims to test the ability of the anaerobicunit to digest a single substrate. In order to reduce the storage timeof OMW, a feeding consisting only of the original OMW was pro-vided to study its effect in the digester behaviour. Being possibleand advantageous to operate the reactor with two substrates</p><p>M.A. Sampaio et al. / Bioresource T(OMW and the complementary efuent), the other goal of thisstudy is to evaluate the conditions of process stability when so dif-ferent efuents are alternately introduced.OMW PE</p><p>pH 4.96(0.08) 6.99(0.01)Partial alkalinity (kg CaCO3 m3) 0 4.85(0.14)Total alkalinity (kg CaCO3 m3) 2.40(0.07) 8.63(0.39)COD (kg O2 m3) 55.28(2.3) 30.71(0.00)CODS (kg O2 m3) 50.81(0.57) 12.12(0.12)NH3 (kg N m3) 0 1.83(0.04)Total N (kg N m3) 0.21(0.02) 2.35(0.53)TSS (kg m3) 3.18(0.07) 19.60(1.65)TS (kg m3) 28.23(0.36) 23.31(0.05)VSS (kg m3) 0.53(0.00) 4.80(0.38)VS (kg m3) 15.85(3.22) 15.70(0.01)VFA (kg acetic acid m3) 2.64(0.38) 3.43(0.27)TPh (kg caffeic acid m3) 3.59(0.01) 0.38(0.00)Colour [390 nm] 22.42(0.68) 2.23(0.00)Aromatic compounds [254 nm] 128.12(1.93) 17.82(0.00)Total and soluble chemical oxygen demand (COD and CODS),total solids (TS), volatile solids (VS), total suspended solids (TSS),volatile suspended solids (VSS) and total ammonium nitrogen(TNH4 -N) concentrations were determined according to StandardMethods (APHA, 1998). The proportion of ammonium concentra-tions and free ammonia (NH4 versus NH3) were estimated accord-ing to Eq. (1) (El-Mashad et al., 2004), where T is the absolutetemperature (273373 K).</p><p>NH3 N THN4 N 1 10pH=10 0:1075 2725=T </p><p>1</p><p>pH measurements were performed in a WTW pH meter andprobe. Alkalinity was evaluated as partial alkalinity (PA) and totalalkalinity (TA) by titration to pH 5.75 and 4.50 with normalized0.1 N HCl, respectively. Total nitrogen (TN) was quantied viaMerck Nitrogen cell tests (10150 mg NL1). Colour and aromaticcompounds measurements were assayed by measurement of theabsorbance at 390 and 254 nm, respectively, using a HitachiU-2000 Spectrophotometer. Total phenolic compounds (TPh) con-centration values as caffeic acid were determined via a modiedFolinCiocalteu method (Singleton and Rossi, 1965). Volatile fattyacids (VFA: acetate, propionate, butyrate, iso-butyrate, iso-valerateand valerate) were analysed using a gas chromatograph (HewlettPackard 5890) equipped with a ame ionization detector and a2 m 2 mm Carbopack B-DA/4% Carbowax 20 M (80120 mesh)column. Nitrogen was used as carrier gas (30 mL mn1). Tempera-ture of the column, injector and detector was 170, 175 and 250 C,respectively. Total VFA concentrations were expressed as acetic</p><p>Table 1OMW, olive mill wastewater; PE, piggery efuent; 0, below detection limit.Values are the averages of determinations. Values in brackets show standarddeviations.</p></li><li><p>acid. Soluble sampleswere obtained by centrifugation at 10000 rpmfor 10 min using a VWR Galaxy 7D Microcentrifuge and were usedfor CODS, colour, aromatic compounds, total phenolic compoundsand VFAs determination.</p><p>The methane content of biogas collected in the digester head-space was measured by the injection of 0.5-mL bioreactor gassample into a gas chromatograph (Varian CP 38000) equipped witha thermal conductivity detector and a Porapack S column of1/8 3 m. Column, injector and detector temperatures were 50,60 and 100 C, respectively. Nitrogen was utilized as the carriergas (20 mL mn1).</p><p>2.3. Reactor operation</p><p>Experiments were carried out by using an up-ow anaerobichybrid digester that was previously used and described elsewhere(Gonalves et al., submitted for publication). It was initiallyremoved from the cold chamber at 4 C and then kept under mes-ophilic conditions of temperature (37 1 C) by using a water jack-et. It was fed in a semi continuous manner by means of a peristalticpump in order to obtain a HRT of about six days. The inuent con-sisted of a blend of the raw OMW and its complementary substrate(piggery efuent, PE) obtained by an increase of OMW contentalong the experimental time (Marques, 2001). Gas production</p><p>(B) Digester feeding with the original OMW (from day 233 to287, Raw OMW feed). The hybrid reactor was fed with100% OMW and any kind of supplementation, correction ordilutions of the olive oil mill efuent were performed (Table2). On day 288 of the experiment, an interruption of thedigester operation took place. During a period of 11 days,the unit was preserved at mesophilic conditions of temper-ature and no feed was provided.</p><p>(C) Feeding the digester by applying alternate pulses of each ofthe substrates (from day 300 to 350 days, Raw OMW or PE,alternated feed) (Table 2). The unchanged OMW wasdigested during the initial two weeks (C0) of this phase. Afterthat, ve weekly cycles were performed by using alternatelyeach substrate. During each cycle, 17% and 83% of the oper-ational time corresponded to PE and OMW supplies,respectively.</p><p>3. Results and discussion</p><p>The load applied to the hybrid unit was efciently convertedinto biogas. The hybrid stability and its capacity in convertingthe potential toxic matters of the inuent are documented by theremoval ability and methane production of the digester biomassover the 350 days of experiment.</p><p>10812 M.A. Sampaio et al. / Bioresource Technology 102 (2011) 1081010818was evaluated by a wet gas meter and corrected to standard con-ditions for pressure and temperature (1 atm, 0 C). Volume ofdige...</p></li></ul>