Ind. Eng. Chem. Res. 2007, 46, 6737-6743
6737
Mesophilic and Thermophilic Anaerobic Co-digestion of Olive Mill Wastewaters and Abattoir Wastewaters in an Upflow Anaerobic Filter Hana Gannoun, Nada Ben Othman, Hassib Bouallagui, and Hamdi Moktar* Laboratory of Microbial Ecology and Technology, Department of Biological and Chemical Engineering, National Institute of Applied Sciences and Technology, BP 676, 1080, Tunisia
The mixture of olive mill wastewater (OMW) with abattoir wastewater (AW) induced the precipitation of OMW phenolic compounds with AW proteins and the removal of chemical oxygen demand (COD). Anaerobic batch experiments with different proportions of OMW:AW (v:v) (10:90; 20:80; 40:60; 60:40) showed that the 40:60 mixture can be co-digested in a continuous system because it improves the C/N ratio and reduces the inhibition of methanogenic bacteria by phenolic compounds. The continuous co-digestion of this mixture was tested under mesophilic (37 °C) and thermophilic (55 °C) conditions using an upflow anaerobic filter (UAF). The organic loading rates (OLRs) which could be achieved during the co-digestion were higher than those obtained during the anaerobic treatment of OMW alone. The change from a mesophilic to a thermophilic environment in the UAF was carried out with a short start-up of thermophilic condition. A higher discoloration, higher COD removal (80%), and biogas yield (0.52 L/g of COD removal) were obtained at 55 °C and the performance of the reactor was maintained even at an OLR as high as 12 g of COD/L‚d. The reduction of faecal coliforms achieved after digesting the influent was important in mesophilic (11-21 MPN/mL) and thermophilic conditions (0-11 MPN/mL) and influenced by the combined effect of the antimicrobial activity of OMW and thermophilic operating conditions. The enhanced performance obtained with the UAF treating OMW:AW (40:60) could be attributed to the dilution of OMW with AW, which reduces the toxicity, and the thermophilic conditions, which improves the biodegradability. Introduction Olive oil and abattoir factories produce vast amounts of liquid and solid waste. In Mediterranean countries, treatment of OMW is becoming a serious environmental problem due to its high content of phenolic compounds, suspended solids, and its resistance to biodegradation.1 Several methods have been proposed for treating OMW such as physical and chemical treatment, coagulation, filtration, and evaporation in lagoons. However, the proposed treatments only partially solve the problem.2-4 Therefore, great interest has been focused on biological treatment of OMW as an alternative to the conventional treatment processes. The aerobic biodegradation of OMW is limited by auto-oxidation of phenolic compounds into recalcitrant polyphenolic compounds with high molecular weight.4 Anaerobic treatment of OMW is considered to be feasible, but several difficulties were noted, due to the inhibitory effects toward methanogenic bacteria of the high concentration of aromatic compounds and the lack of ammonia needed as nitrogen source for synthesis of bacterial biomass.5 Erguder et al.6 concluded that an anaerobic reactor treating OMW must be supplied with NH4Cl and KCl in addition to alkalinity (NaHCO3) in required amounts. Many anaerobic processes such as anaerobic contact, “UASB reactor”, and anaerobic filters have been applied to treat diluted OMW but problems arose due to the toxicity and biodegradability of this effluent and the acidification of reactors.7 Moreover, the dilution that is required in order to reduce OMW toxicity is not compatible with the water resources scarcity in most Mediterranean countries. Co-digestion of OMW with animal waste has been studied.5,8,9 It is one way to dilute toxicants and to supply missing nutrients. Several studies demonstrated that co-digestion of different * Corresponding author. E-mail address:
[email protected]. Tel : 0021671703627. Fax: 0021671704329.
organic wastes showed a distinct increase in methane yield and that individual waste streams could be combined as a substrate for more efficient treatment.10 AW contains a high concentration of biodegradable organics mostly in the form of fats and proteins, sufficient alkalinity, adequate nitrogen, and micronutrients for bacterial growth. Then OMW could be mixed with AW in order to decrease the toxicity of phenol compounds and provide a source of nitrogen needed to achieve a favorable COD/N ratio. Indeed, preliminary work of mesophilic anaerobic co-digestion of OMW:AW in batch reactors showed that dilution of OMW with AW reduced the toxicity and improved the anaerobic digestion.11 Performance of anaerobic biodegradation of the mixture of OMW:AW should be improved in thermophilic conditions. Compared to a mesophilic anaerobic digestion (30-40 °C) thermophilic anaerobic digestion (50-60 °C) usually brings an acceleration of biochemical reactions, higher efficiency in the degradation of organic matter, and the production of a lower amount and better quality of digested sludge.12 Moreover, most often a higher destruction of pathogenic organisms can be achieved at these temperatures.13,14 The aim of the present work was to investigate the anaerobic co-digestion of OMW and AW under mesophilic and thermophilic conditions in order to evaluate the stability and the performance of the upflow anaerobic filter (UAF). Experimental Section OMW and AW Sampling. Fresh OMW used in the present study was obtained from an olive oil production plant located in the north of Tunisia, which uses a continuous process for extraction of olive oil. Because of the seasonal production and the instability of the waste, it was stored at -20 °C. The AW was collected from an abattoir factory (El Ouardia City, Tunis). Analysis of raw OMW and AW were carried out and the average composition is shown in Table 1.
10.1021/ie061676r CCC: $37.00 © 2007 American Chemical Society Published on Web 08/07/2007
6738
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007
Table 1. Characteristics of Olive Mill Wastewaters (OMW), Abattoir Wastewaters (AW), and OMW:AW 40:60 Mixture after Settling parameter pH conductivity (ms/cm) TS (g/L) TSS (g/L) COD (g/L) total Kjeldhal nitrogen (g/L) COD/N absorbance at 280 µm absorbance at 390 µm faecal coliforms (MPN/mL)
olive mill wastewater
abattoir wastewater
OMW:AW 40:60
5.16 ( 0.09 15.33 ( 3.5 48 ( 2.5 6.5 ( 0.3 110 ( 5 0.1 ( 0.02 50:0.045 234 ( 9 37.3 ( 2.5
7.5 ( 0.05 7.26 ( 2 5.44 ( 1.5 0.5 ( 0.1 6 ( 1.5 0.81 ( 0.04 50:6.75
6.5 ( 0.3 11.71 ( 1 28 ( 3 1.8 ( 0.2 41 ( 2 0.69 ( 0.01 50:0.84 94 15 230
45.104
Experimental Setup. (1) Anaerobic Batch Reactors. Different proportions of OMW:AW (v/v) (10:90; 20:80; 40:60; 60: 40) were digested in 1 L batch reactors to study their anaerobic biodegradability and toxicity under mesophilic conditions (37 °C). The inoculum used (pH ) 6.93; TS ) 4.15% w/v) was taken from an active mesophilic digester treating OMW. (2) Continuous System. The anaerobic digestion of the OMW:AW 40:60 was carried out in a UAF (Figure 1). It consisted of a vertical cylindrical glass column (60 cm length and 10 cm in diameter). The active liquid volume was 2 L. The digester was filled with Flocor (Φ3L3, porosity 95%, specific surface 230 m2‚m-3) as media support entities for the growth of microorganisms. The sludge issued from the batch test (40:60) was used to inoculate the UAF. Sodium hydroxide (NaOH) solution was used for pH adjustment of the feed in batch and continuous reactors to neutral value. Feed was supplied by a peristaltic pump connected to a programmable timer. Different OLRs were applied by varying HRT from 13.66 to 3.33 days under mesophilic and thermophilic conditions. Analytical Methods. Chemical oxygen demand (COD) was measured spectrophotometrically.15 Total solids (TS), total
suspended solids (TSS), and total nitrogen were determined according to the procedure listed in Standards Methods for the Examination of Water and Wastewater.16 The biogas produced was collected daily in plastic bags at room temperature. The total volume was later determined with a wet gas meter and time to time the methane content was estimated using an ORSAT apparatus. In this way the biogas volume productions of mesophilic and thermophilic reactors were directly comparable. Volatile fatty acids (VFA) were measured by HPLC (Waters) equipped with a polypore H column (250 mm × 7.8 mm [inside diameter]) connected to a differential refractometer (RI-401 Wates) and a CR-6A Shimadzu integrator. The mobile phase was 0.02 N H2SO4 at a flow rate of 0.6 mL‚min-1. It was centrifuged for 15 min at 13000 rpm and filtered through a 0.22 µm filter (Millipore) before use. The volume of injection was 20 µL. Discoloration was assayed by the measurement of absorbance at 390 nm (Jenway UV-visible spectrophotometer). Total polyphenol content was determined using the FolinCiocalteu method.17 To a 3.6 mL of sample appropriately diluted, 200 µL of Folin-Ciocalteu reagent was added and vortexed. After exactly 3 min, 800 µL of sodium carbonate (20% w/v) was added, and the mixture was vortexed and allowed to stand at 100 °C for 1 min. The absorbance was read at 750 nm, and the total polyphenol concentration was calculated from a calibration curve, using gallic acid as standard. The most probable number technique (MPN) was used to determine faecal coliforms.18 Based on dilutions down to nearly 1 remaining bacterium per test tube (3-fold setups repeated two times), the exit concentration can be estimated statistically. Results and Discussion Effect of Pretreatment Assay on the Anaerobic Batch Reactor Performances. The precipitation of phenolic compounds of OMW with the proteins of AW was studied after mixing both effluents at different proportions of OMW:AW (10:
Figure 1. Schematic diagram of the pretreatment unit and the upflow anaerobic filter used for mesophilic and thermophilic anaerobic digestion of OMW: AW (40:60) in a continuous system.
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007 6739
Figure 2. Total suspended solids (TSS) and soluble COD contents of OMW:AW mixture after precipitation but without TSS removal (9) and after precipitation and TSS removal by sedimentation (0). Table 2. Characteristics of OMW:AW Mixture before and after Precipitation Sedimentationa 10:90
20:80
40:60
60:40
Different Mixtures of (OMW:AW) 7.02 6.5 6 21 34 41 0.51 1.02 2.04 50:2.5 50:1.27 50:0.55
5.38 73 3.06 50:0.28
After Precipitation, Sedimentation COD removal (%) 26.6 20 13.5 total phenol removal (%) 22 17 12 COD:N 50:1.67 50:0.67
9 5.23 50:0.31
pH COD (g/L) total phenol (g/L) COD:N
a
Mesophilic anaerobic digestion of OMW:AW in UAF.
Table 3. Performance Data of Mesophilic Anaerobic Batch Reactors of Different Mixtures of OMW:AW after 10 days of Digestion OMW:AW final pH conductivity (mS/cm) COD removal (%) discoloration (%) total phenol removal (%) Y (L biogas/g of COD removal)
0:100
10:90
20:80
40:60
60:40
100:0
7.2
7.5 4.8 28 34.6 52.5 0.125
7.3 5.18 43 55.3 35.4 0.201
7.01 9.78 66 29.5 29 0.189
6.4 9.01 58 41.8 30.5 0.04
4.6
30 0.112
12
90; 20:80; 40:60; 60:40). The total suspended solids (TSS) formed by precipitation increased with the increase of OMW proportion (Figure 2). Different mechanisms of interaction between phenolic compounds and proteins may be involved such as hydrogen bonding,19 covalent bonding,20 hydrophobic interactions,21 and ionic bonding in aqueous media.22 The removal of TSS by settling improved the water quality for all OMW: AW mixtures and in some cases a favorable COD:N ratio (COD/ N, 50:1)23 could be obtained (Table 2). The results with anaerobic batch tests (Table 3) showed that final pH, biogas yield, and COD removal increased with dilution of OMW by AW up to 40:60. The mixture of AW and OMW can improve the anaerobic digestion because of the reduction of toxicity of OMW by dilution24 and the removal of phenol compounds.4-25 COD removal obtained with the 0:100 and 10: 90 mixture was lower than those obtained with 20:80, 40:60, and 60:40 mixtures probably as a result of the inhibitory effect of the initial nitrogen content of AW.26 The maximum COD removal efficiency of 66% was obtained with the batch reactor
Figure 3. Effect of loading rate by varying HRT on pH variation of the influent (9) and effluent (0); the CODinlet (O), the CODoutlet (b), and the biogas production rate (2) during anaerobic digestion of the mixture of OMW:AW in UAF at mesophilic temperature.
fed with the 40:60 mixture of OMW:AW for which the biogas yield remained stable compared to the 20:80 mixture. In addition, TSS removal and phenol reduction obtained after settling for this proportion (40:60) indicate that it can also enhance the stability process (Figure 2, Table 2). According to the results obtained with pretreatment assay and batch reactors, it could be concluded that the co-digestion of these two wastes is more advantageous than processing each one separately. The 40:60 mixture was selected for the experiments with continuous reactors because it provides the necessary nutrients and buffer capacity. Mesophilic Anaerobic Digestion of OMW:AW in UAF. The UAF was fed initially with an organic loading rate (OLR) of 3 g COD/L‚d corresponding to a hydraulic retention time (HRT) of 13.66 days. The OLR was increased gradually by varying the HRT, from this value to 4.5 days (OLR ) 9 g COD/ L‚d) (Figure 3). The influent pH remained in a range of 5.86.8 during all of the process. At the HRT of 13.66 days, a COD
6740
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007
Table 4. Decolorization Removal, Faecal Coliform, and Total VFA Obtained with Mesophilic and Thermophilic Anaerobic Co-digestion of OMW:AW at Different OLRs Different Organic Loading Rates (OLRs: g/L‚d) Mesophilic 3
4.1
6
Thermophilic 9
4.1
6
8.2
10
12
faecal coliform 21 20 16 11 10 8 5 0 0 (MPN/mL) discoloration (%) 40 43 42 43 45 49 50 66 62 total VFA (mg/L) 3000 3200 3260 5000 1500 1800 2040 2300 3700
removal of 75% was obtained. COD removal remained stable between 70 and 75% when HRT was reduced to 10 days (OLR ) 4.1 g COD/L‚d). This indicates that the mesophilic digester showed initially stable conditions, although it presented a VFA concentration of 3000 mg/L (Table 4). Despite this VFA amount, no pH drop was observed thanks to the ammonium coming from AW. Evidence of process upset due to an organic overloading was observed when the VFA concentration rose to 5000 mg/L at an OLR of 9 g COD/L‚d (Table 4) and biogas production decreased (Figure 3). The anaerobic process was overloaded and the VFAs were built up due to the faster growth rate of the mesophilic VFA producers compared to the mesophilic VFA consumers. In addition, the acetogenic and methanogenic bacteria may be more inhibited by phenolic compounds than the acidogenic bacteria.24 The OLR reached with anaerobic codigestion of the mixture OMW:AW was higher than that obtained with OMW alone.4 This is probably due to the toxic effect of undiluted OMW.27 It has been well-established that phenolic compounds are major contributors to the toxicity and that their antibacterial activity limits the anaerobic biodegradability.24,28 Biogas production rate was improved by the increase of the OLR up to 6 g COD/L‚d; it averaged 1.5 (70% of CH4) to 4.8 L/d (67% of CH4) at an HRT of 13.66 and 6.7 days, respectively. The increase in biogas production was in some way compensated by a lower methane percentage. Thermophilic Anaerobic Digestion of OMW:AW in UAF. The temperature was increased in one step from 37 to 55 °C with a simultaneous decrease of the OLR from 9 to 4.1 g COD/ L‚d in order to have a fast start-up of the process. The digester stability was reached after a week, and the OLR was then increased gradually from 4.1 g COD/L‚d to 12 g COD/L‚d (Figure 4). The reactor effluent pH remained between 7.2 and 8.4 during all of the study. The increase of pH from the influent to the effluent can be due to the degradation of protidic compounds. In fact, changing from mesophilic to thermophilic conditions usually results in an increase in protein hydrolysis which in turns leads to an increase in the buffer capacity of the system. This result is in agreement with previous studies.29-31 For all OLR applied, the COD removal efficiencies were quite high. Indeed, a COD removal of 80% was obtained at organic loads of 8.2 g COD/L‚d and remained constant at both OLRs of 10 and 12 g COD/L‚d. The one-step increment of the reactor temperature was followed by an increase of the biogas production rate which averaged 2.75, 3, 4.15, and 3.9 L biogas/L‚d at an OLR of 6, 8.2, 10, and 12 g COD/L‚d, respectively. The anaerobic filter showed a little sensitivity to the increase of the OLR under thermophilic conditions. These results are in accordance with those reported by van Lier32 and Kim et al.33 The biogas production rate obtained in thermophilic conditions was satisfactory and the performance of the reactor was shown to be stable, but the methane content decreased from 75 to 70% with the increase of the OLR from 4.1 g COD/L‚d to 12 g COD/L‚d, respectively. This is thought to be due to the
Figure 4. Effect of loading rate by varying the HRT on pH variation of the influent (9) and effluent (0); the CODinlet (O), the CODoutlet (b), and the biogas production rate (2) during anaerobic digestion of the mixture of OMW:AW in UAF at thermophilic temperature.
increase of inhibitory effect of the recalcitrant phenolic compounds on methanogenic bacteria.34 Evolution of Performances of a UAF Treating a Mixture of OMW:AW (40:60) from Mesophilic to Thermophilic Conditions. The mesophilic and thermophilic anaerobic digestion are characterized by an optimal temperature range and overpassing the upper limit would cause an immediate death of the considered group of bacteria.35 Since the thermophilic microorganisms are the main interest in the thermophilic anaerobic digestion, the transition from mesophilic to thermophilic temperature may therefore require a long acclimation period. Different strategies of adapting mesophilic reactors to thermophilic temperature have been described in the literature at constant HRT and OLR: one-step36,37 or a stepwise temperature increase.38 Nevertheless, there is a lack of studies where the adaptation of stable mesophilic reactor to thermophilic temperature is applied in a one-step increase of temperature at different OLR and HRT in order to establish the best digesting capacity with the shortest adaptation time to thermophilic operation. According to Bousˇkova´ et al.,35 a one-step increasing temperature from mesophilic to thermophilic is the best strategy
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007 6741
Figure 5. COD removal, biogas production rate, and biogas yield obtained with the upflow anaerobic filter treating AW:OMW in mesophilic (9) and thermophilic (0) conditions at various HRTs.
in changing operational temperature in anaerobic digestion. The fast adaptation of the mesophilic sludge to the thermophilic conditions indicates the presence of thermophilic microorganisms in the mesophilic inoculum. In a study on characterization of the microbial community during the start-up of a thermophilic anaerobic digester, Chachkhiani et al.39 concluded that the dominant species taking part in the anaerobic thermophilic digestion were not adapted mesophiles but the thermophiles already present in the inoculum at a subdominant level which quickly became dominant under thermophilic anaerobic conditions. As expected from the previous reports and also confirming them, the one-step increase of temperature coupled to a reduction of OLR was very efficient in our case since it allowed us to reach good and stable performances in only 1 week after the shifts. COD removal, biogas production, and biogas yield obtained with anaerobic co-digestion of OMW:AW under mesophilic and thermophilic conditions in UAF are used to evaluate the process efficiencies (Figure 5). The COD removal efficiency of the thermophilic anaerobic filter was greater than the mesophilic anaerobic filter treating the mixture of OMW:AW for the HRT varying from 4.5 to 6.8 days. Maximum COD removal was obtained at an HRT of 10 days for the mesophilic anaerobic filter while the thermophilic anaerobic filter presented only slight
changes for the different HRT studied. The COD efficiencies obtained with mesophilic and thermophilic anaerobic codigestion showed that at high HRT (13.66, 10, and 6.8 days), COD removal was limited to 80%. As could be expected, this is probably the result of the presence of recalcitrant compounds like pseudolignin and condensed tannins in OMW.24 The highest biogas production rate (4 L/L‚d) was obtained with thermophilic temperature at an HRT of 4 days (Figures 4 and 5). It has been shown that biogas production rates are higher under thermophilic conditions than under mesophilic conditions. This is mainly due to a higher maximum specific growth rate (2-3 times) of thermophilic microorganisms compared to mesophilic analogues.40 The biogas yield presented stable behavior at mesophilic temperature at a level varying from 0.3 to 0.35 L/g COD removed following the perturbation of HRT from 13.66 to 4.5 days (Figure 5). The thermophilic anaerobic digestion induced a little increase of the biogas yield from 0.5 to 0.52 L/g COD removed at an HRT of 5 and 4 days, respectively. The thermophilic digester remained stable at an HRT of 3.33 days (OLR ) 12 g COD/L‚d) and still presented a biogas with a methane content of 70%. In contrast, the mesophilic digester was already overloaded at an HRT of 4.5 days. At this HRT, the biogas production had a lag phase, and the methane content was less than 65%. This is in agreement with several works in the literature which have shown that thermophilic systems are capable of achieving higher organic loadings compared to their mesophilic counterparts.41,42 Table 4 summarizes the color removal, the faecal coliform reduction, and the VFAs of the mesophilic and thermophilic anaerobic co-digestion of OMW:AW. The coliform removal obtained under mesophilic conditions did not present significant differences at the different OLRs tested. The thermophilic process was apparently more efficient in the destruction of coliforms at the high OLR (10 and 12 g COD/L‚d) (MPN/mL ) 0). The important faecal coliform reduction achieved could be attributed to the combined effect of the anaerobic environment, temperature,43 and the antimicrobial activity of OMW.44 The digester VFA levels were higher at 37 °C than at 55 °C. This seems to suggest that methanogenic bacteria with higher affinity for VFA were selected and dominated in the thermophilic digester after the temperature increase. The high buffering capacity in the thermophilic digester was attributable to the enhanced degradation of nitrogenous compounds. This is supported by previously reported comparative studies of mesophilic and thermophilic co-phase anaerobic digestion.31 The discoloration correlated to the removal of phenolic compounds was improved at the higher OLR in thermophilic conditions (Table 4). Converti et al.45 suggest that the thermophilic microflora have the capacity to use more carbon sources than the mesophilic and psychrophilic microflora. Moreover, with higher OLR, biodegradation of several compounds can be improved thanks to cosubstrate assimilation.46 The dark effluent from the anaerobic co-digestion of OMW: AW still contained a significant concentration of COD, due to the non-degraded residual phenolic compounds as mentioned by Hamdi.4 Previous works on the anaerobic treatment of OMW have shown that a chemical47 or a biological48 post-treatment is capable of removing if not degrading these residual aromatics. Conclusions and Practical Strategy for the Management of Olive Mill and Abattoir Wastewaters. This investigation has shown that the anaerobic co-digestion of OMW and AW is a technically viable solution for these wastes since their mixing reduces the main problems encountered during their separate
6742
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007
anaerobic treatment: polyphenol toxicity for OMW and ammonium toxicity resulting from protein hydrolysis for AW. Moreover, co-digestion gives more energy thanks to the increase of the COD:N ratio which depends on the OMW:AW ratio. The OMW:AW ratio, which allows an optimal precipitation of phenolic compounds and proteins, must be adjusted as a function of the amount of phenolic compounds and proteins present in OMW and AW, respectively. This OMW and AW treatment solution will be possible at the condition to have a strategy of constructing olive mills and slaughterhouses in the same industrial complex in order to reduce transport costs. Presently, OMW, which is produced in large quantities over a short period of the year (3-5 months), is stored in evaporation basins, a practice with a lot of negative impacts for the environment. The mixing of AW produced all over the year with stored OMW will allow detoxification of OMW and implementation of an efficient and stable anaerobic co-digestion. Thanks to the organic carbon provided by OMW the co-digestion of these two wastes should produce enough energy to operate the installation and this both under mesophilic and thermophilic conditions. From a sanitary point of view, in addition to the effect of the precipitation step, anaerobic co-digestion will contribute to the disinfection of AW particularly when performed under thermophilic conditions. The solids generated during the precipitation and recovered by settling represent an organic waste which can be discharged in sanitary landfills with a minimum of biological risks due to the fact that the precipitated bacteria are killed by the OMW phenols. The quality of this solid could be improved by aerobic composting or anaerobic digestion after mixing it or not with other solid wastes. Acknowledgment The authors thank Prof. Sami Sayadi for his help in HPLC analysis and the anonymous reviewers of this paper for their constructive criticism which allowed them to improve the original manuscript and lead to the proposal of some advice for the management of OMW and AW. Literature Cited (1) Ramos-Comenzana, A.; Monteolica-Sanchez, M.; Lopez, M. J. Bioremediation of alpechin. Int. Biodeterior. Biodegrad. 1995, 35, 249268. (2) Saglik, S. L.; Ersoy, S. Imre. Oil recovery from lime treated wastewater of olive mills. Eur. J. Lipid Sci. Technol. 2002, 104, 212-215. (3) Beccari, M.; Majone, M.; Riccardi, C.; Savarese, F.; Torrisi, L. Integrated treatment of olive oil mill effluents: effect of chemical and physical pretreatment on anaerobic treatability. Water Sci. Technol. 1999, 40 (1), 347-355. (4) Hamdi, M. Anaerobic digestion of Olive Mill Wastewater. Process Biochem. 1996, 31, 105-110. (5) Angelidaki, I.; Ellegaard, L.; Ahring, B. K. Modelling anaerobic codigestion of manure with olive oil mill effluent. Water Sci. Technol. 1997, 36 (6-7), 263-270. (6) Erguder, T. H.; Guven, E.; Demirer, G. N. Anaerobic treatment of olive mill wastes in batch reactors. Process Biochem. 2000, 36, 243-248. (7) Hamdi, M. Future prospects and contraints of olive oil mill wastewater use and treatment. Bioprocess Eng. 1993, 8, 208-214. (8) Marques, I. P. Anaerobic digestion treatment of olive mill wastewater for effluent re-use in irrigation. Desalination 2001, 137, 233-239. (9) Lyberatos, G.; Gavala, H. N.; Stamatelatou, A. An integrated approach for management of agricultural industries wastewaters. Nonlinear Anal. Theory Methods Appl. 1997, 30 (4), 2341-2351. (10) Del Borghi, A.; Converti, A.; Pallazi, E.; Del Borghi, M. Hydrolysis and thermophilic anaerobic digestion of sewage sludge and organic fraction of municipal solid waste. Bioprocess Eng. 1999, 20, 553-560.
(11) Gannoun, H.; Ben Othman, N.; Bouallagui, H.; Hamdi, M. Anaerobic co-digestion of olive mill wastewaters and abattoir wastewaters. In Third European Bioremediation Conference; Kalogerakis, N., Ed.; Department of Environmental Engineering, Technical University of Crete: Greece, Chania, 2005; p 167. (12) Bouallagui, H.; Haouari, O.; Touhami, Y.; Ben Cheikh, R.; Marouani, L.; Hamdi, M. Effect of temperature on the performance of an anaerobic tubular reactor treating fruit and vegetable waste. Process Biochem. 2004, 39, 2143-2148. (13) Buhr, H. O.; Andrews, J. F. The thermophilic anaerobic digestion process. Water Res. 1977, 11, 129-143. (14) Rimkus, R. R.; Ryan, J. M.; Cook, E. J. Full-scale thermophilic digestion at the West-Southwest sewage Treatment Works, Chicago, Illinois. J. Water Pollut. Control. Fed. 1982, 54 (11), 1447-1457. (15) Knetchel, R. J. A more economical method for the determination of chemical oxygen demand. Water Pollut. Control 1978, 50, 25-29. (16) Standard Methods for the Examination of Water and Wastewater, 19th ed.; American Public Health Association/American Water Works Association/Water Environment Federation: Washington DC, 1995. (17) Waterman, P. G.; Mole, S. Analysis of Phenolic Plant Metabolites; Blackwell Scientific Publ.: Oxford, UK, 1994; pp 83-91. (18) Koch, A. L. Growth measurement. In Manual of Methods For General Bacteriology; Gerhardt, P., Ed. in chief; ASM: Washington, DC, 1981; 197-217, ISBN 0-914826-30-1. (19) Loomis, W. D.; Battaile, J. Plant Phenolic compounds and the isolation of plant enzymes. Phytochemistry 1966, 5, 423-438. (20) Rawel, H. M.; Czajka, D.; Rohn, S.; Kroll, J. Interactions of different phenolic acids and flavonoids with soy proteins. Int. J. Biol. Macromol. 2002, 30, 137-150. (21) Hagerman, A. E.; Butler, L. G. Protein precipitation method for the quantification of tannins. J. Agric. Food Chem. 1978, 26, 809-812. (22) Rubino, M. I.; Arntfield, S. D.; Nadon, C. A.; Bernatsky, A. Phenolic protein interactions in relation to the gelation properties of canola protein. Food Res. Int. 1996, 29, 653-659. (23) Hamdi, M.; Festino, C.; Aubart, C. Anaerobic digestion of olive mill wastewaters in fully mixed reactor and in fixed film reactors. Process Biochem. 1992, 27, 37-42. (24) Boari, G.; Brunetti, A.; Passino, R.; Rozzi, A. Anaerobic digestion of olive oil mill wastewaters; Agric. Wastes 1984, 10, 161-175. (25) Sabbah, I.; Marsook, T.; Basheer, S. The effect of pretreatment on anaerobic activity of olive mill wastewater using batch and continous systems. Process Biochem. 2004, 39, 1947-1951. (26) Banks, C. J. Anaerobic digestion of solid and high nitrogen content fractions of slaughterhouse wastes. AIChE Symp. Ser. (EnViron. Responsible Food Process.) 1994, 90, 103-109. (27) Mechichi, T.; Sayadi, S. Evaluating process imbalance of anaerobic digestion of olive mill wastewaters. Process Biochem. 2005, 40, 139-145. (28) Borja, R.; Alba, J.; Blanks, C. J. Impact of the main phenolic compounds of olive mill wastewater (OMW) on the kinetics of acetoclastic methanogenesis. Process Biochem. 1997, 32, 121-133. (29) Poggi-Varaldo, H. M.; Alzate-Gaviria, L. M.; Perez-Hernandez, A.; Nevarez-Morillon, V. G.; Rinderknecht-Seijas, N. A side-by-side comparison of two systems of sequencing coupled reactors for anaerobic digestion of the organic fraction of municipal solid waste. Waste Manage. Res. 2005, 23 (3), 270-280. (30) Yu, H. Q.; Fang, H. H. P.; Gu, G. W. Comparative performance of mesophilic and thermophilic acidogenic upflow reactor. Process Biochem. 2002, 38, 447-454. (31) Song, Y.-C.; Kwon, S.-J.; Woo, J.-H. Mesophilic and thermophilic temperature co-phase anaerobic digestion compared with single-stage mesophilic and thermophilic digestion of sewage sludge. Water Res. 2004, 38, 1653-1662. (32) van Lier, J. B. Limitation of thermophilic anaerobic wastewater treatment and the consequences for process design. Antonie Van Leeuwenhoek 1996, 69, 1-14. (33) Kim, M.; Ahn, Y. H.; Speece, R. E. Comparative process stability and efficiency of anaerobic digestion; mesophilic vs. thermophilic. Water Res. 2002, 36, 4369-4385. (34) Sayadi, S.; Allouche, N.; Jaoua, M.; Aloui, F. Detrimental effects of high molecular-mass polyphenols on olive mill wastewater biotreatment. Process Biochem. 2000, 35, 725-735. (35) Bousˇkova´, A.; Doha´nyos, M.; Schmidt, J. E.; Angelidaki, I. Strategies for changing temperature from mesophilic to thermophilic conditions in anaerobic CSTR reactors treating sewage sludge. Water Res. 2005, 39, 1481-1488. (36) van Lier, J. B.; Grolle, K. C. F.; Stams, A. J. M.; de Macario, E. C.; Lettinga, G. Start up of a thermophilic UASB reactor with mesophilic granular sludge. Appl. Microbiol. Biotechnol. 1992, 37, 130-135.
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007 6743 (37) Fang, H. H. P.; Lau, I. W. C. Start-up of thermophilic (55 °C) UASB reactors using different mesophilic seed sludge. Water Sci. Technol. 1996, 34 (5-6), 445-452. (38) Zabranka, J.; Dohanyos, M.; Jenicek, P.; Zaplatilkova, P.; Kutil, J. The contribution of thermophilic anaerobic digestion to the stable operation of wastewater Sludge treatment. Water Sci. Technol. 2002, 46 (4-5), 447453. (39) Chachkhiani, M.; Dabert, P.; Abzianidze, T.; Partskhaladze, G.; Tsiklauri, L.; Dudauri, T.; Godon, J. J. 16S rDNA characterization of bacterial and archaeal communities during start-up of anaerobic thermophilic digestion of cattle manure. Bioresour. Technol. 2004, 93, 227-232. (40) Mladenovska, Z.; Ahring, B. K. Growth kinetics of Methanosarcina ssp. isolated from full scale biogas plants treating animal manure. FEMS Microbiol. Ecol. 2000, 31, 225-229. (41) Harris, W. L.; Dague, R. R. Comparative performance of anaerobic filters at mesophilic and thermophilic temperatures. Water EnViron. Res. 1993, 65 (6), 764-771. (42) Zinder, S. H.; Anguish, T.; Cardwell, S. C. Effects of temperature on methanogenesis in a thermophilic (58 °C) anaerobic digester. Appl. EnViron. Microbiol. 1984, 47 (4), 808-813. (43) Bendixen, H. J. Hygiene and sanitation requirements in Danish biogas plants. In Biomass for Energy & EnVironment; Ninth European Bioenergy Conference, Copenhagen; Chartier, P., Ferrero, G. L., Henius, U. M., Hultberg, S., Sachau, J., Iinblad, M., Eds.; Pergamon: London, UK, 1996; Vol. 1, pp 296-301.
(44) Ramos-Cormenzana, A.; Juarez-Jime´nez, B.; Garcia-Pareja, M. P. Antimicrobial activity of olive mill wastewaters (alpechin) and biotransformed olive oil mill wastewater. Int. Biodeterior. Biodegrad. 1996, 38 (34), 283-290. (45) Converti, A.; DelBorghui, A.; Zilli, M.; Arni, S.; DelBorghui, M. Anaerobic digestion of the vegetable fraction of municipal refuses: mesophilic versus thermophilic conditions. Bioprocess Eng. 1999, 21, 371376. (46) Perez, M.; Rodriguez-Cano, R.; Romero, L. I.; Sales, D. Anaerobic thermophilic digestion of cutting oil wastewater: Effect of co-substrate. Biochem. Eng. 2006, 29, 250-257. (47) Beccari, M.; Carucci, G.; Majone, M.; Petrangeli Papini, M. Removal of molecular weight fractions of COD and phenolic compounds in an integrated treatment of olive oil mill effluents. Biodegradation 2002, 13 (6), 401-410. (48) Bertin, L.; Majone, M.; Di Gioia, D.; Fava, F. An aerobic fixedphase biofilm reactor system for the degradation of the low-molecular weight aromatic compounds occurring in the effluents of anaerobic digestors treating olive mill wastewaters. J. Biotechnol. 2001, 87 (2), 161-177.
ReceiVed for reView December 27, 2006 ReVised manuscript receiVed June 9, 2007 Accepted June 12, 2007 IE061676R
