Energy & Fuels 2005, 19, 1179-1185
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Thermochemical Treatment of Solid and Wastewater Effluents Originating from the Olive Oil Food Industry Georgios Taralas* and Michael G. Kontominas Laboratory of Food Chemistry and Technology, Department of Chemistry, University of Ioannina, GR-45 110, Ioannina, Greece Received August 21, 2004. Revised Manuscript Received January 12, 2005
Thermochemical treatment of waste effluents originating from the olive oil food industry was investigated at total pressure conditions slightly above atmospheric pressure (103-104 kPa) and temperatures of 700-855 °C. The experimental data were obtained in a laboratory-scale reactor. Wastewater that was concentrated by means of evaporation/drying (denoted as cww), with a biomass formula of CH1.3O0.5, mixed with olive husks (kernels) was used here as a sample fuel (i.e., a mixture of olive husks (kernels) and cww (95%/5%, as determined from the low heating value, LHV)). Pretreatment of the specific solid waste effluent by washing (leaching) and fractionation was studied. The particle size (dp) class of the olive husks (kernels) varied between 0.35 mm < dp < 0.50 mm (with a biomass formula of CH2.2O0.7) and 0.50 mm < dp < 1.0 mm (with a biomass formula of CH2.2O0.6). For H2O-vapor thermal treatment of the evolved gas obtained during pyrolysis of the biofuel used here, the composition products were analyzed. Gas compositions (viz., CO, CO2, O2, CH4, and C2+), along with the amounts of benzene and toluene, tar/liquid phase, and char total yields are given. In thermal treatment experiments in air, the major gas was CO2. The effect of the moisture content and the particle size class of the biofuel samples on the variation of the devolatilization rate, relative to devolatilization time, was determined at a given furnace temperature regime.
Introduction Recently, specific attention has been given to the exploitation of renewable energy resources and also to the minimization and treatment of effluents from the olive oil food industry (olive husks and wastewater).1-5 During the production of olive oil, with the help of continuous centrifugal three-phase technology and the traditional batch process (the olives are ground, and the olive oil is separated by pressure), three products result: olive oil, solid waste, and olive mill wastewater (denoted hereafter as omww). Nevertheless, the terms that are related to olive wastes are neither standardized nor country-specific.1,2 * Author to whom correspondence should be addressed. E-mail address:
[email protected]. (1) Taralas, G.; Kontominas, M. G. Energetic Valorization of Solid Residues. Pyrolysis of Olive Husks. Presented at the International Conference of Science in Thermal and Chemical Biomass Conversion, August 30-September 2, 2004, Victoria, Vancouver Island, BC, Canada. (Conference proceedings to be published in March 2005.) (2) Taralas, G. Energy Saving and Treatment Applications of Vegetation Water and Solid Waste from Olive Oil Mill Industries in Greece (in Gr.). ESCOR Co., 2002. (3) Buttiglieri, M. The Energy Use of the Olive-Husks in Southern Italy. A Feasibility Study of Low Cost Production and Distribution. In Biomass for Energy and the Environment; Chartier, P., Ferrero, G. L., Henius, U. M., Hultberg, S., Sachau, J., Wiinblad, M., Eds.; Pergamon and Elsevier Science, Ltd.: London, 1996; pp 1894-1899. (4) Gukierman, A. L.; Della Rocca, O. A.; Horowitz, G. I.; Bonelli, P.; Casanello, M. C. An Integral Characterization Study on Olive Stones Pyrolysis. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic & Professional: London, 1997; pp 176-190. (5) Armesto, L.; Bahillo, A.; Cabanillas, A.; Veijonen, K.; Otero, J.; Plumed, A.; Salvador, L. Co-Combustion of Coal and Olive Oil Industry Residues in Fluidized Bed. Fuel 2003, 82, 993-1000.
The activities in the olive oil food industry produce a huge amount of omww residue, the treatment of which has recently become a subject of interest, particularly for Mediterranean countries.1,6,7 The omww material represents a considerable ecological problem in the Mediterranean basin, because of its high organic load and unsatisfactory method of disposal.8 Different chemical characteristics of omww, including high chemical oxygen demand (COD) and polyphenols, can be found in the literature.9-12 For the omww material, the possible deposition methods, applied either individually (6) Carbera, F. The Problem of the Olive Oil Wastes in Spain: Treatment or Recycling? In Proceedings of the 7th Mediterranean Conference on Organic Wastes Recycling in Soils; Land, E., Dumonet, S., Eds.; Ordine Nazionale dei Biologi: Vieste, Italy, 1996; pp 11171125. (7) Iconomou, D.; Diamantitis, G.; Zanganas, P.; Theochari, I.; Israilides, K.; Kouloumbis, P. Reduction of Phenolic Concentration in Olive-Oil Mill Wastewater by Biotechnological Means. In Proceedings of the International Conference on Production and Restoration of the Environment; Tsihrintzis, V. A., Korfiatis, G. P., Katsifarakis, K. L., Demetracopoulos, A. C., Eds.; Publisher Bouris: Thessaloniki, Greece, 2000; pp 569-572. (8) Boari, G.; Brunetti, A.; Passino, R.; Rozzi, A. Anaerobic Digestion of Olive Oil Mill Wastewaters. Agric. Wastes 1984, 10 (3), 161-175. (9) Gonza´lez-Lo´pez, J.; Bellido, E.; Benı´tez, C. Reduction of Total Polyphenols in Olive Mill Wastewater by Physico-Chemical Purification. J. Environ. Sci. Health 1994, 29 (5), 851-865. (10) Tsonis, S. P.; Grigoropoulos, S. G. Anaerobic Treatment of Wastewater from Olive Oil Mills. In Advances in Modelling, Planning, Decision and Control of Energy, Power and Environmental Systems; Tzafestas, S. G., Hamza, M. H., Eds.; ACTA Press: Anaheim, CA, 1983; pp 282-285. (11) Curi, K.; Veliogˆlu, S. G.; Diyanmandogˆlu, V. Treatment of Olive Oil Production Wastes. Treatment and Disposal of Liquid and Solid Industrial Wastes. In Proceedings of the 3rd Turkish-German Environmental Engineering Symposium; Curi, K., Ed.; Pergamon Press: Oxford, U.K., 1980; pp 189-205.
10.1021/ef040078r CCC: $30.25 © 2005 American Chemical Society Published on Web 04/02/2005
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or in some combination, include aerobic treatment (bioremediation), lagooning, anaerobic treatment, filtration, ultrafiltration, membrane filtration, wet oxidation, precipitation/flocculation, adsorption, concentration by drying/evaporation (i.e., concentrated wastewater, cww), electrolysis, and co-composting.2 However, in this framework, advanced thermochemical conversion technologies are needed to minimize both solid and omww residues from olive oil production and, at the same time, recover the remaining energy.1 Advanced thermochemical technologies such as devolatilization (or pyrolysis), combustion, and gasification at atmospheric pressure have been proposed for the conversion of biofuels to useful energy products.3 Obviously, these technologies must also follow strict environmental regulations.2 The olive milling process results in a low-entropy desired product and higher-entropy unwanted effluents. Adequate criteria for combustion, pyrolysis, and gasification can be considered as technologies to recover energy from effluents that originate from the olive oil milling industry.2 Thus, a mixture of olive husks (kernels) and cww (95%/5%, as determined from the low heating value (LHV)) was used here as a sample fuel. The thermochemical treatment of solid residues and omww is necessary, not only to recover the heat of different boilers and exhaust gases to use them as concentrated omww, by means of evaporation/drying systems,13-15 but also for the design of combustors/ pyrolyzers and/or gasifiers.1,2,16-20 The implementation of advanced thermochemical processes is dependent on the reliable design of largescale power plants, in which the catalytic system for tar abatement phenomena, hot-gas conditioning, and the reduction of alkalis and/or minerals of the biofuels has an important role in combined heat and power generation.21-29 The alkalis (e.g., sodium, potassium, etc.) of (12) Paredes, C.; Bernal, M. P.; Cegarra, J.; Roig, A. Bio-Degradation of Olive Mill Wastewater Sludge by its Co-Composting with Agricultural Wastes. Bioresource Technol. 2002, 85 (1), 1-8. (13) Annesini, M. C.; Gironi, F. Olive Oil Mill Effluent. Aging Effects on Evaporation Behaviour. Water Res. 1991, 25 (9), 1157-1160. (14) Ballester Diaz, L.; Carcı´a Vinao, A. F.; Perez Amer, J. P. Installation for the Integral Purification of Olive Mill Wastewater (in Sp.), European Patent ES 202 11 91, Fabrica de San Carlos, SA, Spain, priority ES 19900000486, 1991. (15) Ollero de Castro, P. Equipment for Evaporating-Concentrating Olive Mill Wastewater (in Sp.), European Patent ES 204 35 07 A, Spain, priority ES 19910001437, 1991. (16) Guanxing, C.; Sjo¨stro¨m, K.; Bjo¨rnbom, E. Pyrolysis/Gasification of Wood in a Pressurized Fluidized Bed Reactor. Ind. Eng. Chem. Res. 1992, 31, 2764-2768. (17) Guanxing, C.; Qizhuang, Yu.; Sjo¨stro¨m, K.; Bjo¨rnbom, E. Pyrolysis/Gasification of Biomass in the Presence of Dolomite in a Pressurized Bed. In Advances in Thermochemical Biomass Conversion; Bridgwater, A. V., Ed.; Blackie Academic & Professional: London, 1994; pp 1197-1204. (18) Corella, J.; Aznar, M. P.; Delgado, J.; Aldea, E. Steam Gasification of Cellulosic Wastes in a Fluidized Bed with Downstream Vessels. Ind. Eng. Chem. Res. 1991, 30, 2252-2262. (19) Gil, J.; Caballero, M. A.; Aznar, M. P.; Corella, J. Biomass Gasification with Air in a Fluidized Bed: Effect of the In-Bed Use of Dolomite under Different Operation Conditions. Ind. Eng. Chem. Res. 1999, 38, 4226-4235. (20) Corella, J.; Toledo, J. M.; Aznar, M. P. Improving the Modeling of the Kinetics of the Catalytic Tar Elimination in Biomass Gasification. Ind. Eng. Chem. Res. 2002, 41, 3351-3356. (21) Taralas, G. Effects of MgO, CaO and Calcined Dolomites on Model Substance Cracking and Conversion of Tar from Biomass Gasification/Pyrolysis Gas. Lic. of Engineering Dissertation, Royal Institute of Technology (KTH), Department of Chemical Engineering and Technology, Stockholm, Sweden, 1990. (ISBN 91-7170-043-9). (22) Taralas, G.; Vassilatos, V.; Delgado, J.; Sjo¨stro¨m, K. Thermal and Catalytic Cracking of n-Heptane in the Presence of CaO, MgO, and Calcined Dolomites. Can. J. Chem. Eng. 1991, 69, 1413-1419.
Taralas and Kontominas
the solid agroresidues (such as husks, Spanish “orujillo”, straw, cobs, rice husks, etc.) may influence the thermochemical conversion processes and char devolatilization.30-35 Moreover, alkalis and/or minerals can accumulate in the gasification reactor and may condense on particles, eventually causing agglomeration and sintering in the fluidized beds.2,36-38 Pretreatment of the biofuels may be one way to reduce the alkali, ash, and mineral contents of the biomass. Two possible pretreatment methods are washing and fractionation of a sample, in which a large portion of the minerals and alkalis of the biofuel sample hopefully will be removed.1,2 The objective of this work was to gather information about (a) the thermochemical treatment of olive husks (kernels) and cww compounds with different moisture content and particle size, using H2O vapor, air, or N2 as the processing and/or carrier gases, (b) and the influence from the application of selected pretreatment techniques such as washing (leaching) and fractionation of the olive husks (kernels) on the physical and chemical parameters. This research has been conducted as a contribution to the development of advanced thermochemical processes. Experimental Section The Samples. The investigated effluents were Greek olive husks (kernels) and omww that originated from the olive milling industry (via the continuous three-phase extraction (23) Taralas, G.; Sjo¨stro¨m, K.; Bjo¨rnbom, E. Dolomite Catalysed Cracking of n-Heptane in the Presence of Steam. In Advances in Thermochemical Biomass Conversion; Bridgwater, A. V., Ed.; Blackie Academic & Professional: London, 1994; pp 233-245. (24) Taralas, G. Catalytic Steam Cracking of n-Heptane with Special Reference to the Effect of Calcined Dolomite. Ind. Eng. Chem. Res. 1996, 35, 2121-2126. (25) Taralas, G. Cyclohexane-Steam Cracking Catalysed by Calcined Dolomite. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic & Professional: London, 1997; Vol. 2, pp 1086-1100. (26) Taralas, G. Catalytic Steam Pyrolysis of a Selected Saturated Hydrocarbon on Calcined Mineral Particles. Can. J. Chem. Eng. 1998, 76, 1093-1101. (27) Taralas, G. Modeling the Influence of Mineral Rocks, Active in Different Hot Gas Conditioning Systems and Technologies on the Production of Light R-Olefins. Can. J. Chem. Eng. 1999, 77, 12051214. (28) Taralas, G.; Kontominas, M. G.; Kakatsios, X. Modelling the Thermal Destruction of Toluene (C7H8) as Tar-Related Species for Fuel Gas Cleanup. Energy Fuels 2003, 17, 329-337. (29) Taralas, G.; Kontominas, M. G. Kinetic Modelling of VOC Catalytic Steam Pyrolysis for Tar Abatement Phenomena in Gasification/Pyrolysis Technologies. Fuel 2004, 83, 1235-1245. (30) Ergudenler, A.; Ghaly, A. E. A. Agglomeration of Silica Sand in a Fluidized Bed Gasifier Operating on Wheat Straw. Biomass Bioenergy 1993, 4, 135-147. (31) Salour, D.; Jeckins, B. M.; Vafaei, M.; Kayhanian, M. Control of In-Bed Agglomeration by Fuel Blending in a Pilot Scale Straw and Wood Fuelled AFBC. Biomass Bioenergy 1993, 4, 117-133. (32) Corella, J.; Toledo, J. M.; Padilla, R. Olivine or Dolomite as InBed Additive in Biomass Gasification with Air in a Fluidized Bed: Which is Better? Energy Fuels 2004, 18, 713-720. (33) Real, C.; Alcala, M. D.; Criado, J. M.; Preparation of Silica from Rice Husks. J. Am. Ceram. Soc. 1996, 79 (8), 2012-2016. (34) Jensen, A.; Dam-Johansen, K.; Wo´jtowics, M. A.; Serio, M. A. A TG-FTIR Study of the Influence of Potassium Chloride on Wheat Straw Pyrolysis. Energy Fuels 1997, 12, 929-938. (35) Werther, J.; Saenger, M.; Hartge, E.-U.; Ogada, T.; Siagi, Z. Combustion of Agricultural Residues. Prog. Energy Comb. Sci. 2000, 26, 1-27. (36) Skifvars, B.-J.; Sfiris, G.; Backman, R.; Widegren-Dagfard, K.; Hupa, M. Ash Behavior in a CFB Boiler during Combustion of Salix. Energy Fuels 1997, 11, 843-848. (37) Skifvars, B.-J.; Hupa, M.; Beckman, R.; Hiltunen, M. Sintering Mechanisms of FBC Ashes. Fuel 1994, 73, 171-176. (38) Manzoori, A. R.; Agarwal, P. K. Agglomeration and Defluidization under Simulated Circulating Fluidized-Bed Combustion Conditions. Fuel 1994, 73, 563-568.
Solid and Wastewater Effluents from Olive Oil Table 1. Characteristics of the Oil Mill Wastewater (omww) Samples from the Continuous Extraction Process parameter
value
Seasonal Variations of omww Materiala pH 4.5-6.0 COD 40.0-130.0 g/L suspended solids 30.0-40.0 g/L water content 83%-92% sluggish matter1 15.0 g/L residual oil 0.3%-30.0% Studied omww Sample Material pH 5.0 COD 58.0 g/L total solids 35.0 g/L density 1100 g/L a Seasonable variations occurring over a brief period of the year (November through March).
process), such as that processed in Achaia Prefecture.1,2 Table 1 shows typical and specific characteristics of the omww. The omww is normally dark in color (gray), because of oxidation of the polyphenols.13 The test method that offers organic contamination information of the industrial process water is COD.39,40 The COD values of the omww were determined using a spectrophotometer (Hach, model DR/3000) after digestion of the sample by a Hach digestion reagent. However, additional information about the COD analysis procedures can be found elsewhere.41,42 The omww effluent samples were concentrated via evaporation with a rotating evaporator (EMITECH, model K950) at atmospheric pressure to an concentrated remainder that could then be dried to a residue in which >95% of the organic load was concentrated. The effluent samples were condensed and collected periodically as the evaporation proceeded.2,41 On the other hand, the olive husk (kernel) samples with a particle size of dp > 3.5 mm were dried to reduce their moisture content to ∼9%; controlled milling, using a 0.25-mdiameter hammer mill, with four rotating hammers operating at 2800 rpm, was performed and then particle size was then classified.1 The mesh sizes of the sieves are 1.5 mm for the top sieve and 1.0, 0.5, and 0.35 mm for the bottom sieve (1880 U.S. standard mesh).1 The elemental composition of the samples used here is depicted in Table 2. The ultimate analysis, which determined the carbon, hydrogen, oxygen, and nitrogen composition in the fuel, was performed according to the ASTM standard test methods.1,43 Analysis of the volatile matter in the samples was performed in a LECO model MAC 400 system.43 The moisture and sulfur contents was determined following Swedish Standard Institution (SIS) methods SS-18717044 and SS-187114,45 respectively. All analyses were performed twice. The biomass (39) Turano, E.; Curcio, S.; Paola, M. G.; Calabro´, V.; Iorio, G. An Integrated Centrifugation-Ultrafiltration System in the Treatment of Olive Mill Wastewater. J. Membr. Sci. 2002, 109, 519-531. (40) Vitolo, S.; Petarca, L.; Bresci, B. Treatment of Olive Oil Industry Wastes. Bioresource Technol. 1999, 67, 129-137. (41) Di Giacomo, G.; Brandani, V.; Del Re, G. Evaporation of Olive Oil Mill Vegetation Waters. Presented at The 12th International Symposium on Desalination and Water Reuse, Malta, Valletta, April 15-18, 1991. (42) Beccari, M.; Majone, M.; Carucci, G.; Lanz, A. M.; Petrangeli, P. M. Removal of Molecular Weight Fractions of COD and Phenolic Compounds in an Integrated Treatment of Olive Oil Mill Effluent. Biodegradation 2002, 13 (6), 401-410. (43) Taralas, G.; Arvelakis, S.; Koullas, D. P.; Koukios, E. G. The Feasibility of Biomass Gasification for Electricity Production from Agricultural Biomass: The Vision of a Southern European Utility. In Biomass for Energy and the Environment, Proceedings of the 9th European Bioenergy Conference; Chartier, P., Ferrero, G. L., Henius, U. M., Hultberg, S., Sachau, J., Wiinblad, M., Eds.; Pergamon: Oxford, U.K., 1997; pp 1376-1381. (44) Biobra¨nslen och Torv-Besta¨mning av Total Fukthalt, Swedish Standard Institution, SS 187170, 1997. (45) Biobra¨nslen och Torv-Provberedning, Swedish Standard Institution, SS 187114, 1992.
Energy & Fuels, Vol. 19, No. 3, 2005 1181 formula (CH1.3O0.5) of the cww was estimated to be the composition, in terms of the atomic fractions of H, C and O. Fractionation of Sample. After sieving, three particle size classes are obtained: class I, 0.35-0.5 mm; class II, 0.5-1.0 mm; and class III, 1.0-1.5 mm. The effect of fractionation on several olive husk (kernel) properties, and typical proximate, ultimate, and chemical analyses (including moisture and ash content, calorific value, etc.), is also presented in Table 2. In regard to the high heating value (HHV), the small size (0.35 mm < dp < 0.50 mm) offers a value of 20.7 MJ/kg. The determination of the HHV and the ash content was measured following SS-ISO1928 (www.sis.se) and SS-187171.46 The LHV (18.7 MJ/kg for a particle size of dp >1.0 mm and 11.8 MJ/kg for the cww samples) was determined using the HHV and the percentage of hydrogen in the sample.1,47 The cww samples have a much higher ash content than the olive husks. The lignin and cellulose contents shown in Table 2 were determined according to the ANSI standard method D-1103 on samples that were obtained by drying the olive husk (0.35 mm < dp < 0.50 mm) at a temperature of e40 °C.2,48 For the analysis of the extractives content, the sample (1.0 g) was extracted with 55 mL of acetone in a Soxhtec extractor (temperature of ∼90 °C) at residence times equal to stages of 90 min (boiling) and 20 min (rising), respectively.2 The species present in the ash samples were determined and calculated semiquantitatively by means of X-ray fluorescence (XRF) (UniQuant).21 The composition (here, K2O, Na2O, CaO, MgO, SiO2, Al2O3, SO3, and Cl), which is depicted in Table 3, is assumed to be oxides. Ash from both materials, but especially the cww sample, exhibited a very high potassium content. The biomass formulas were also estimated as a composition in terms of the atomic fractions of H, C, and O. Two particle sizessnamely, 0.35 mm < dp < 0.50 mm (with a biomass formula of CH2.2O0.7) and 0.50 mm < dp < 1.0 mm (with a biomass formula of CH2.2O0.6)swere chosen for experimentation. Finally, the samples were stored in a desiccator. Washing of Sample. The fractionated olive husks (kernels) samples were washed to partially remove possible alkalis and minerals. Despite the fact that silica and alumina separately have melting points well above 2000 °C, they may be mixed in certain ratios with a potassium melt at temperatures of 1.0 mm
concentrated wastewater, cww
8.4 6.1 74.1 11.4
9.0 4.4 76.2 10.5
8.8 2.0 77.9 11.3
16.2 N/Ab N/Ab
47.2 2.4 6.0 0.10 44.4
51.1 2.1 6.6 0.2 39.9
N/Ab N/Ab N/Ab
54.5 2.1 4.3
N/Ab
39.1
N/Ab N/Ab N/Ab 20.7
23.5 38.3 28.1 20.5
N/Ab N/Ab N/Ab 19.8
12.5
b
For various particle size (dp) classes. Not analyzed. Table 3. Ash Analysis of Olive Husks (Kernels) and Concentrated Wastewater Samples Composition (%, ash basis) component
K2O
Na2O
CaO
MgO
SiO2
Al2O3
SO3
Cl
olive husks (kernels)a dp < 0.5 mm 0.5 < dp < 1.0 mm dp > 1.0 mm concentrated wastewater, cww
22.3 19.9 41.8 46.8
4.9 2.2 3.9 2.1
13.1 9.1 9.8 2.8
8.6 6.1 3.3 3.2
31.6 30.8 18.9 3.3
3.3 2.9 2.5 1.0
3.2 2.8 0.68 N/Ab
0.92 N/Ab 1.4 N/Ab
a
For various particle size (dp) classes. b Not analyzed. Table 4. Moisture, Ash, and Volatiles Content, and High Heating Value, in the Solid Residue due to Washinga treatment conditions 300 mL of deionized water stir time ) 6 h stir time ) 12 h stir time ) 24 h 500 mL of deionized water stir time ) 6 h stir time ) 12 h stir time ) 24 h
a
moisture
Content (%, db) ash content
volatiles
high heating value, HHV (MJ/kg)
11.3 11.9 10.5
2.2 2.1 2.3
78.7 79.8 81.0
21.4 21.4 21.1
13.4 10.7 10.6
2.2 1.7 2.1
78.7 79.1 80.3
21.1 21.1 20.7
For a particle size class of dp < 0.5 mm. For a description of the analytical methods, see Table 2. Table 5. Mineral, Alkali, and Chlorine Contents of Solid Residue due to Treatmenta Content (%, ash basis) treatment conditions
300 mL of deionized water stir time ) 6 h stir time ) 12 h stir time ) 24 h 500 mL of deionized water stir time ) 6 h stir time ) 12 h stir time ) 24 h a
K2O
Na2O
CaO
MgO
SiO2
Al2O3
SO3
Cl
11.2 5.89 4.85
3.84 1.44 0.79
21.2 20.9 19.7
5.47 4.13 2.54
18.4 22.7 19.1
3.97 3.70 3.97
N/Ab N/Ab N/Ab
0.41
