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Combination of Fenton oxidation and composting for the treatment of the olive solid residue and the olive mile wastewater from the olive oil industry in Cyprus
Bioresource Technology 101 (2010) 7984–7987
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Combination of Fenton oxidation and composting for the treatment of the olive solid residue and the olive mile wastewater from the olive oil industry in Cyprus Antonis A. Zorpas a,*, Costa N. Costa b a Institute of Environmental Technology and Sustainable Development, Department of Research and Development, Laboratory of Environmental Friendly Technology, P.O. Box 34073, 5309, Paralimni, Cyprus b Cyprus University of Technology, Department of Environmental Management, Cyprus
a r t i c l e
i n f o
Article history: Received 3 February 2010 Received in revised form 6 May 2010 Accepted 10 May 2010
Keywords: Fenton Compost Olive mill wastewater Olive oil solid residue
a b s t r a c t Co-composting of olive oil solid residue (OOSR) and treated wastewaters (with Fenton) from the olive oil production process has been studied as an alternative method for the treatment of wastewater containing high organic and toxic pollutants in small olive oil industry in Cyprus. The experimental results indicated that the olive mill wastewater (OMW) is detoxified at the end of Fenton Process and the COD is reduced up to 70%. The final co-composted material of OOSR with the treated olive mile wastewater (TOMW) is presented with optimum characteristics and is suitable for agricultural purpose. The final product coming out from an in-Vessel reactor seems to mature faster than the product from the windrow system and is presented with a better soil conditioner. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Olive oil production is considered one of the oldest agricultural industries in the Mediterranean countries. Approximately 1.8 106 t of olive oil is produced annually worldwide where the majority of it is produced in the Mediterranean basin. The average amount of olive mill wastewater (OMW) produced during the milling process is 1.2–1.8 m3 t1 of olives. OMW resulting from the production processes in the Mediterranean region surpasses 30 million per year (El-Gohary et al., 2009). The treatment of liquid wastes produced from olive oil production is still a major challenge facing this industry. The main problem is attributed to its dark color, high organic content and toxicity which are due to the presence of phenolic compounds. COD values of OMW may reach 150 g L1, most of which are in a particulate form while suspended solids up to 190 g L1 have been recorded (Canizares et al., 2007). Olive oil extraction is among the most traditional agricultural industries in Cyprus and it has always been, and is among the importance for the national economy. The total area under olive cultivation is about 7400–8000 ha with about 2.2– 2.7 million productive trees. It is estimated that olive trees hold 44.7% of the total agricultural area under permanent crops. This represents approximately 5.6% of the country’s cropped area
* Corresponding author. E-mail addresses: [email protected], [email protected], [email protected] (A.A. Zorpas), [email protected] (C.N. Costa). URLs: http://www.envitech.org (A.A. Zorpas), http://www.cut.ac.cy (C.N. Costa). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.05.030
and contributed 2.7–2.9% of total agricultural output. Olive mill wastewaters (OMW) constitute a serious environmental problem in the Mediterranean Sea region due to the unique features associated with this type of agro-waste, namely seasonal and localized production (typically between October and March), low flowrates (between 10 and 100 m3 d1) and high and diverse organic load (Gotsi et al., 2005). The quantity of olive oil mill vegetation and washing effluents (commonly referred to as olive mill effluents or wastewaters (OME or OMW) generated, and consequently the environmental impact, depends on the method of olive oil extraction used (Mantzavinos and Kalogerakis, 2004). In Cyprus today are based 28 small olive mills (26 are a 3-Phases Process and 2 are a 2-Phases Process) which have the ability to treat all the production of olives and to produce olive oil. The annual average olive production is about 13,500–15,500 t, equivalent to 2700–3100 t y1 of olive oil and resulting in the generation of about: 18,225–20,925 t y1 of olive mill wastewater (OMW and is equal with the water consumption) which causes serious environmental problems, mainly due to its high organic content, 9180–10,450 t y1 of olive oil solid residue (OOSR) and 1620–1860 t y1 leaves. Lagooning as physical evaporation and irrigation for the OMW and typical composting for the OOSR are the main typical and classic systems for the treatment of those waste until now in Cyprus. This study deals with a physicochemical approach for the treatment of OMW and OOSR with combination to Fenton’s Reagents, Composting system as a sustainable and cost effective method for small industries in Cyprus and other Islands under warm climate conditions.
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A.A. Zorpas, C.N. Costa / Bioresource Technology 101 (2010) 7984–7987
2. Methods
3.1. Factorial design
2.1. Methods of analysis
The aim of the experimental procedure was to determine the influence of some basic process parameters on the effectiveness of the oxidation treatment in terms of %COD removal from the OMW. These parameters are dilution of wastewater, heptahydrated ferrous sulphate concentration, hydrogen peroxide concentration, and sulphuric acid concentration. These parameters are referred to as ‘‘controlling parameters” of the system. The effect of the controlling parameters on the optimization parameter was estimated by performing a 24 factorial experiment. In general, by using a 2n factorial design, n controlling parameters interrelate to an optimization parameter through an appropriate linear model. Their significance can also be estimated and assessed (Alder et al., 1995). Then the most significant variables are altered stepwise, aiming at the determination of the optimal experimental conditions. The levels of the controlling parameters are includes: Wastewater dilution, FeSO47H2O, H2O2 (30%) and H2SO4 (98%) addition. The variation intervals include 3 Levels (+1, 0, 1). +1 Level involved zero% wastewater dilution, 4 g L1 FeSO47H2O, 2 mL L1 H2O2 (30%) and 0.5 mL L1 H2SO4 (98%). Zero Level involved zero 50% wastewater dilution, 5 g L1 FeSO47H2O, 2.5 mL L1 H2O2 (30%) and 0.25 mL L1 H2SO4 (98%). 1 Level involved zero 100% wastewater dilution, 6 g L1 FeSO47H2O, 3.5 mL L1 H2O2 (30%) and 0.75 mL L1 H2SO4 (98%). The experimental area of the factorial design was predetermined in previous preliminary trials. In the 24 factorial designs, 16 experiments were carried out. Four extra experiments in the center of the design (level 0) were also conducted for statistical purposes. Each experiment was repeated three times and the results presented are the mean values. From this data, a mathematical model was constructed. Its adequacy was checked by the Fisher criterion. According to the latter, the following ratio should follow the F-distribution with level of importance p = 5%:
The OMW and the OOSR have been collected from 3 several olive mills based in 3 different Districts of Cyprus. The District of Famagusta (DF) which is in the Eastern Part of the Island, the District of Larnaca (DL) which is about 40 km away from the olive mills of DF on the South and the District of Paphos (DP) which is about 300 km away from the olive mills of DF and 250 km from the olive mill of DL on the west. The sampling durations were for about 4 months from October–January and every second week 50 kg of OOSR and 50 L of OMW were taken and the samples were stored in the fridge at 4 °C. The two olive mills in Famagusta and Larnaca are 3-Phase process while the other one in Paphos is 2Phase process. For all the presented parameters in Table 1 and 2 a number of methods has been used as presented: in Standard Methods of Analysis (1995), by Zorpas et al., 1998), by Zorpas (2008), by Gotsi et al. (2005), by Atanassova et al. (2005), by Gaudy (1962). 3. Experimental procedure The OMW from each District (DF, DL, DP) was subjected to Fenton oxidation treatment. The oxidation was carried out batch wise at 25 °C in an agitated (200 rpm), temperature and pH controlled glass reactor of 1L capacity for 4 h. First, the wastewater sample was diluted, if necessary. Next, H2SO4 (98%) and Fenton reagent were added. As ferrous salt, FeSO47H2O was used and the hydrogen peroxide was of 30% concentration. After oxidation, vigorous stirring, neutralization with lime, coagulation with a weak anionic polyelectrolyte (2540 Praestol, 0.1%) and flocculation in a jar test apparatus, the sample was filtered and the supernatant liquid was analyzed in terms of COD. Then the treated olive mill wastewater (TOMW) from District of Famagusta were mixed with the OOSR from the same District and proceed for composting in two several compost systems according to the following scheme: CS1A (OOSRF + OMWF), CS1B (OOSRF + TOMWF), CS2A1 (OOSRF + OMWF), CS2B1 (OOSRF + TOMWF).
F¼
S2ad
ð1Þ
S2Y
S2ad ¼
PN
i¼1 ðY i
Y^ i Þ2
ð2Þ
f
Table 1 Composition of the olive mill wastewater. Characteristics
OMW–DF
OMW–DL
OMW–DP
Total solids (TS), % Total volatile solids, % of TS Total organic carbon content, % of TS Total Kjeldahl nitrogen, % of TS Total phosphorous as P2O5, % of TS Total Phenolic compounds (g L1) pH EC (mS cm1) Salinity (mg L1) CaCO3 BOD5 (g L1) COD (g L1) COD/BOD5 ratio Ash, % of TS C/N ratio C/P ratio Specific weight (gr cm3) Fats & oils mg (L1) Germination index (%) Humics (%) E4/E6 K mg L1 Ca mg L1 Mg mg L1 Na mg L1 Cl2 mg L1
6.33 ± 1.81 90.36 ± 3.31 62.71 ± 6.27 1.28 ± 0.17 0.84 ± 0.17 8.71 ± 0.51 5.66 ± 0.3 2120 ± 57 1058 ± 91 17.3 ± 5.5 70.1 ± 12.3 4.05 ± 0.91 9.71 ± 3.21 52.25 ± 5.24 74.65 ± 3.81 1.048 ± 0.033 1.46 ± 0.20 18 ± 5 0.94 ± 0.12 1.34 ± 0.03 3.1 ± 0.45 271.4 ± 14.1 32.8 ± 5.3 344.3 ± 15.1 401.4 ± 51.4
6.09 ± 1.05 91.93 ± 4.15 60.17 ± 5.99 1.31 ± 0.20 0.92 ± 0.11 9.02 ± 0.39 5.52 ± 0.4 1984 ± 33 901 ± 28 20.1 ± 9.7 57.4 ± 6.3 3.01 ± 0.87 8.99 ± 2.18 45.93 ± 4.15 65.40 ± 6.17 1.057 ± 0.029 1.45 ± 0.22 16 ± 7 1.04 ± 0.27 1.53 ± 0.05 2.87 ± 0.50 248.7 ± 16.9 28.2 ± 4.7 322.6 ± 16.9 367.8 ± 41.9
6.59 ± 0.98 88.12 ± 3.69 64.30 ± 7.12 1.25 ± 0.19 0.88 ± 0.11 490 ± 0.28 5.58 ± 0.3 1277 ± 12 645 ± 48 13.7 ± 3.4 45.9 ± 4.5 2.98 ± 0.92 9.25 ± 3.05 51.44 ± 6.02 73.68 ± 4.15 1.022 ± 0.041 6307.5 ± 279 11 ± 6 0.89 ± 0.21 1.44 ± 0.03 2.17 ± 0.21 210.6 ± 12.2 22.9 ± 6.1 209.1 ± 17.2 212.3 ± 24.7
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Table 2 Composition of the olive oil solid residue. Characteristics
OOSR–DF
OOSR–DL
OOSR–DP
Moisture Total solids (TS) (%) Total carbon content, % of TS Total Kjeldahl nitrogen, % of TS Total phosphorous as P2O5, % of TS Fats and oils, % of TS Proteins, % of TS Total sugars, % of TS Cellulose, % of TS Hemicellulose, % of TS Ash, % of TS Other extraction substances, % of TS Lignin, % of TS Potassium as K2O, % of TS Calcium content, % of TS C/N ratio C/P ratio Specific weight (gr cm3) Porosity (%) Germination index (%) Humics (%) E4/E6 ratio
48.71 ± 2.01 86.00 ± 3.33 51.45 ± 4.48 1.06 ± 0.15 0.11 ± 0.01 4.65 ± 1.09 3.29 ± 0.12 1.07 ± 0.09 22.27 ± 0.44 16.57 ± 0.94 3.65 ± 0.25 8.38 ± 0.35 11.95 ± 0.45 0.83 ± 0.11 0.72 ± 0.08 48.53 ± 5.03 467.72 ± 42.1 1.09 ± 0.02 52.4 ± 5.5 17 ± 3 1.03 ± 0.08 1.00 ± 0.05
50.12 ± 1.92 85.34 ± 4.01 46.79 ± 3.32 1.12 ± 0.07 0.13 ± 0.01 4.89 ± 1.21 3.97 ± 0.19 1.12 ± 0.11 19.31 ± 0.96 14.90 ± 0.78 4.01 ± 0.44 9.45 ± 0.59 14.41 ± 0.87 0.91 ± 0.07 0.67 ± 0.03 41.77 ± 3.97 359.92 ± 53.9 1.12 ± 0.08 49.3 ± 4.9 21 ± 5 1.18 ± 0.31 0.95 ± 0.07
62.1 ± 2.12 77.98 ± 6.71 47.12 ± 3.61 0.79 ± 0.10 0.07 ± 0.01 6.02 ± 0.93 2.43 ± 0.19 0.96 ± 0.04 16.30 ± 0.47 9.45 ± 1.02 3.12 ± 0.17 7.12 ± 0.28 9.39 ± 0.68 0.87 ± 0.11 0.65 ± 0.04 59.64 ± 4.45 673.14 ± 79.98 1.35 ± 0.04 28.6 ± 6.6 16 ± 9 0.92 ± 0.30 1.10 ± 0.13
S2 ðbj Þ ¼
S2Y N
ð3Þ
where S2Y is the standard deviation, S2a d is the adequacy deviation ^i and is calculated by the Eq. (2). Yi is the experimental i value, Y is the estimated i value from the model determined, f is the number of degrees of freedom, and N is the number of trials. As far as the determination of statistically important parameters is concerned, the procedure mentioned below was followed. The coefficient deviation is defined by Eq. (3) where N is the number of trials. The importance of the coefficient was checked by Eq. (4).
t¼
jbj j Sðbj Þ
ð4Þ
where bj is the j linear coefficient. ‘‘t” should follow the Student distribution for importance level p = 5% and degrees of freedom those of the deviation S2(Y). After the mathematical model construction and the determination of statistically important parameters, an effort to find the optimum conditions for the effectiveness of the Fenton oxidation treatment of wood-processing industry wastewater was made. This was performed through a steepest ascent method. After the treatment of OMW with Fenton treatment, the treated olive mill wastewater (TOMW) with the produced sludge’s from the Fenton Process were proceed for further treatment in two several systems: (i) in lagooning for physical evaporation and with typical red beds and (ii) with co-composting with OOSR. The amount added to the system was equal with the final moisture of 60 ± 5%. For the composting of the OOSR with the TOMW two different systems were used: (a) Compost System (CS1): A typical windrow system of 3 m length and 1.5 m, with final moisture of 60 ± 5%. The samples were aerated using an aerated air force, and (b) Compost System (CS2): An In-Vessel reactor of 1 m3 active volume (Zorpas 2008). The thermophilic phase in the reactor lasted 15 d. The temperature in the center of the reactor was about 60–65 °C and the moisture percentage between 60 ± 5%. The samples were aerated using an aerated air force (oxygen concentration range in the reactor was between 5–8%). A temperature indicator controller was controlling the operation of the fan in order to maintain the temperature at about 60 °C, according to the following principle: minimum air flow (2.3 m3 per m3 active volume) was provided at low temperature (<30 °C) and maximum air flow (28 m3 per m3 active volume was provided at high temperature (>60 °C). The
minimum airflow corresponds to the minimum oxygen demand for the microorganisms and the maximum to the necessary air for cooling. After the thermophilic period, in which the organic material was biodegraded, the compost was piled to an enclosed package where it remained for about four months to mature. The fundamental principle of a co-composting system is the biodegradation of the organic matter through exothermic aerobic bioreactions which take place in the thermophilic region with the simultaneous evaporation of the moisture of the wastewater due to the release of thermal energy (Jewell et al., 1980). As a critical parameters for the growth of microorganisms and bioreactions are the oxygen demand, the moisture (which must be in the range of 60 ± 5%) the temperature (which must be retained between 60–65 °C) and the Carbon/Nitrogen (C/N) ratio. 4. Results and discussion Tables 2 and 3 present the physicochemical characteristics of the OMW and the OOSR from the three several Olive Mills. As indicated in Table 2 the COD and the BOD5 is considering very high which causes serious environmental problems. The higher COD presented in the OMW-DL which is 127.4 ± 36.3 mg L1, follows by the OMW-DP which is at 122.9 ± 34.5 mg L1 and the OMW-DF with COD at 118.3 ± 32.1 mg L1. The total humics is considered to be very low (less than 1.4 mg L1) while the E4/E6 is below 5. The E4/E6 ratio shows the characterization of humic materials. As the E4/E6 ratio is bellow 5, the samples are characterized as Humic Acid (whereas if the ratio is above 5 the sample is characterized as Fulvic Acid), (Zorpas 1999). The COD/BOD ratio ranges from 2.98:1 to 4.05:1, which indicates the presence of poor biodegradable organic compounds and/or toxic ones El-Gohary et al. (2009). The G.I is presented to be less than 26 and the substrate is characterized as very phytotoxic both for the OMW and for the OOSR. The C/N ratio both of the substrates (OMW and OOSR) is considered to be at very satisfactory levels for composting process. The variation of the EC is due to the different quality of the water use in the production line. Similar results from the characteristic of OMW from Geece are found from Gotsi et al. (2005). El-Gohary et al. (2009) mention that the COD, TOC and BOD values, ranged from 102,900 to 207,300 mg O2 L1, from 30,000 to 93,000 and from 78,528 to 135,400 mg O2 L1, respectively from an OMW. The COD reduction is up to 65% for almost all the treated sampled
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A.A. Zorpas, C.N. Costa / Bioresource Technology 101 (2010) 7984–7987 Table 3 Physicochemical characteristics of mature compost (120 d). Parameters
Moisture (%) pH Ash, % of dry matter Organic matter, % of dry matter Total organic carbon, % of dry matter Total Kjeldahl nitrogen (%) Total phosphorous (%) C/N C/P Humic substances,% of dry matter Total phenolic compounds (mg/kg) Germination index Grow index (%)
CS1
CS2
A
A1
B
B1
32.1 ± 5.03 7.2 ± 0.05 25.85 ± 1.87 74.15 ± 3.09 40.7 ± 4.31 1.13 ± 0.16 0.45 ± 0.11 36.01 ± 3.41 90.44 ± 12.91 5.84 ± 1.09 212 ± 34 124 ± 21 73 ± 5
26.8 ± 2.35 7.7 ± 0.03 29.68 ± 1.33 70.32 ± 4.12 37.27 ± 3.16 1.33 ± 0.22 0.55 ± 0.05 28.02 ± 2.13 67.76 ± 7.01 6.35 ± 0.97 192 ± 23 138 ± 12 77 ± 6
28.2 ± 1.99 7.7 ± 0.03 28.81 ± 1.66 71.19 ± 2.99 40.58 ± 3.01 1.30 ± 0.14 0.61 ± 0.12 31.22 ± 3.04 66.52 ± 9.18 7.04 ± 1.13 188 ± 51 177 ± 19 77 ± 10
22.5 ± 2.19 7.6 ± 0.01 27.10 ± 1.51 72.90 ± 1.97 39.01 ± 2.19 1.44 ± 0.11 0.52 ± 0.07 27.09 ± 2.21 75.01 ± 5.66 7.15 ± 0.88 173 ± 19 201 ± 9 92 ± 3
(62.35 ± 8.03%). Fenton processes are suitable to treat a wide variety of effluents irrespective of their concentration and origin and are characterized by their simple and versatile operation. As olive oil manufacturing industries are usually small plants with a low, seasonal wastewater flow, a small Fenton unit would suffice to cope efficiently with the effluents produced. Rivas et al. (2001) estimated that OMW treatment (15 mg L1 of inlet COD and 80–90% COD reduction achieved in residence times between 1 and 8 h depending on the operating conditions employed) by Fenton’s reagent would cost USD 3.2 per m3 of wastewater treated and mg L1 of COD removed. This value is greater than that of the conventional biological treatment of OME by about an order of magnitude since H2O2 consumption comprises a significant fraction of the operating costs. In this respect, studies are needed to optimise the dosage of the Fenton’s components used, thus avoiding waste of costly chemicals (Mantzavinos and Kalogerakis, 2004). Table 3 shows the characterization of the final product after 120 d of maturity. It was obvious that the B1 sample of CS2 was presented with better characteristics than the other final products. Specifically, the B1 final cured compost is presented with pH at 7.6 ± 0.01, Organic Matter at 72.90 ± 1.97%, TOC at 72.9 ± 1.97%, TKN at 1.44 ± 0.11%, TP at 0.52 ± 0.07%, C/N and C/P ratio at 27.09 ± 2.21 and 75.01 ± 5.66 respectively, total humics at 7.15 ± 0.88%, total phenolic compounds at 173 ± 19 mg kg1 while the G.I is at 201 ± 9. As olive oil manufacturing industries are usually small plants with a low, seasonal wastewater flow, a small Fenton unit would suffice to cope efficiently with the effluents produced. This process proved to be effective for the reduction of wastewater pollution load and its detoxification. After this implementation, the conventional biological treatment of wastewaters is feasible and cost effective. Moreover, further wastewater treatment with reed beds could render them totally recyclable. The proposed approach towards a sustainable solution to the environmental impacts of olive oil processing includes the production of organic fertilizer/soil conditioner combined with the effective chemical and biological oxidation of wastewaters. Hence, the Fenton’s reaction appears to be useful for reducing toxic phenolic compounds consequently increases the biodegradability of OMW. Compared to other AOPs, Fenton’s reaction presents several advantages. H2O2 is environmentally friendly, since it slowly decomposes into oxygen and water. Besides, the abundance, lack of toxicity and ease of removal from water makes Fe2+ the most commonly used transition metal for Fenton’s reaction applications. The above characteristics make compost suitable for agricultural requirements and suggest that it can be used as an effective product for plant growth according to European Guidelines (European Commission, 2005). Very interesting research approaches which are not presented in this research is for the future the co-composting from the total waste
production from the olive oils industry in Cyprus. The integrated management system may include the chemical-organic sludge produced by the oxidative process, the sludge produced by the biological process, the olive tree leaves, the olive stones and the residues from the reed beds for the production of an ecological soil conditioner with very good control nutrient properties.
5. Conclusions From all the above it can be concluded regarding the pollution problems caused by olive oil production, a solution based on the principles of the clean technology concept could be the detoxification of wastewaters and the composting with the olive oil solid residues. The use of Fenton’s reaction as a primary treatment of OMW enhances the efficiency of the composted material. It is obvious that the final characteristics of the composted material presented with a very good soil conditioner. References APHA, AWWA–WPCF, 1995. Standard methods for the examination of water and wastewater. 10th Ed.. American Public Health Association, Washington, U.S.A. Alder, Y.P., Markova, E.V., Granovsky, Y.V., 1995. The Design of Experiments to Find Optimal Conditions. Mir Publisher, Moscow. Atanassova, D., Kefalas, P., Psillakis, E., 2005. Measuring the antioxidant activity of olive oil mill wastewater using chemiluminescence. Environ. Int. 31 (2), 275–280. Canizares, P., Lobato, J., Paz, R., Rodrigo, M.A., Saez, C., 2007. Advanced oxidation processes for the treatment of olive-oil mills wastewater. Chemosphere 67, 832–838. El-Gohary, F.A., Badawy, M.I., El-Khateeb, M.A., El-Kalliny, A.S., 2009. Integrated treatment of olive mill wastewater (OMW) by the combination of Fenton’s reaction and anaerobic treatment. J. Hazard. Mater. 162, 1536–1541. European Commission, 2005. Working document: Biological treatment of biowaste, 2nd draft 1, 22. Gaudy Jr., A.F., 1962. Colorimetric determination of protein and carbohydrate. Ind. Wastes Water 7, 17–22. Gotsi, M., Kalogerakis, N., Psillakis, E., Samaras, P., Mantzavinos, D., 2005. Electrochemical oxidation of olive oil mill wastewaters. Water Res. 39, 4177–4187. Jewell, J.W., Kabrick, M.R., 1980. Autoheated aerobic thermophilic digestion with aeration. J. Water Pollut. Contol Federe 52 (3), 512–523. Mantzavinos, D., Kalogerakis, N., 2004. Treatment of olive mill effluents: Part I. Organic matter degradation by chemical and biological processes: an overview. Int. J. Environ. 31, 289–295. Rivas, F.J., Beltrán, F.J., Gimeno, O., Frades, J., 2001. Treatment of olive oil mill wastewater by Fenton’s reagent. J. Agric. Food. Chem. 49, 1873–1880. Zorpas, A.A., Vlyssides, A.G., Loizidou, M., 1998. Physical and chemical characterization of anaerobically stabilized primary sewage sludge. Fresen. Environ. Bull. 7, 383–508. Zorpas, A.A., 1999. Development of a methodology for the composting of sewage sludge using zeolite. PhD thesis, National Technical University of Athens, Athens, Greece. Zorpas, A.A., 2008. Sewage sludge compost evaluation in Oats, Pepper and Eggplant cultivation. Dynam. Soil, Dynam. Plants. Global Science Book 2 (2), 103–109.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Combination of Fenton oxidation and composting for the treatment of the olive solid residue and the olive mile wastewater from the olive oil industry in Cyprus Antonis A. Zorpas a,*, Costa N. Costa b a Institute of Environmental Technology and Sustainable Development, Department of Research and Development, Laboratory of Environmental Friendly Technology, P.O. Box 34073, 5309, Paralimni, Cyprus b Cyprus University of Technology, Department of Environmental Management, Cyprus
a r t i c l e
i n f o
Article history: Received 3 February 2010 Received in revised form 6 May 2010 Accepted 10 May 2010
Keywords: Fenton Compost Olive mill wastewater Olive oil solid residue
a b s t r a c t Co-composting of olive oil solid residue (OOSR) and treated wastewaters (with Fenton) from the olive oil production process has been studied as an alternative method for the treatment of wastewater containing high organic and toxic pollutants in small olive oil industry in Cyprus. The experimental results indicated that the olive mill wastewater (OMW) is detoxified at the end of Fenton Process and the COD is reduced up to 70%. The final co-composted material of OOSR with the treated olive mile wastewater (TOMW) is presented with optimum characteristics and is suitable for agricultural purpose. The final product coming out from an in-Vessel reactor seems to mature faster than the product from the windrow system and is presented with a better soil conditioner. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Olive oil production is considered one of the oldest agricultural industries in the Mediterranean countries. Approximately 1.8 106 t of olive oil is produced annually worldwide where the majority of it is produced in the Mediterranean basin. The average amount of olive mill wastewater (OMW) produced during the milling process is 1.2–1.8 m3 t1 of olives. OMW resulting from the production processes in the Mediterranean region surpasses 30 million per year (El-Gohary et al., 2009). The treatment of liquid wastes produced from olive oil production is still a major challenge facing this industry. The main problem is attributed to its dark color, high organic content and toxicity which are due to the presence of phenolic compounds. COD values of OMW may reach 150 g L1, most of which are in a particulate form while suspended solids up to 190 g L1 have been recorded (Canizares et al., 2007). Olive oil extraction is among the most traditional agricultural industries in Cyprus and it has always been, and is among the importance for the national economy. The total area under olive cultivation is about 7400–8000 ha with about 2.2– 2.7 million productive trees. It is estimated that olive trees hold 44.7% of the total agricultural area under permanent crops. This represents approximately 5.6% of the country’s cropped area
* Corresponding author. E-mail addresses: [email protected], [email protected], [email protected] (A.A. Zorpas), [email protected] (C.N. Costa). URLs: http://www.envitech.org (A.A. Zorpas), http://www.cut.ac.cy (C.N. Costa). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.05.030
and contributed 2.7–2.9% of total agricultural output. Olive mill wastewaters (OMW) constitute a serious environmental problem in the Mediterranean Sea region due to the unique features associated with this type of agro-waste, namely seasonal and localized production (typically between October and March), low flowrates (between 10 and 100 m3 d1) and high and diverse organic load (Gotsi et al., 2005). The quantity of olive oil mill vegetation and washing effluents (commonly referred to as olive mill effluents or wastewaters (OME or OMW) generated, and consequently the environmental impact, depends on the method of olive oil extraction used (Mantzavinos and Kalogerakis, 2004). In Cyprus today are based 28 small olive mills (26 are a 3-Phases Process and 2 are a 2-Phases Process) which have the ability to treat all the production of olives and to produce olive oil. The annual average olive production is about 13,500–15,500 t, equivalent to 2700–3100 t y1 of olive oil and resulting in the generation of about: 18,225–20,925 t y1 of olive mill wastewater (OMW and is equal with the water consumption) which causes serious environmental problems, mainly due to its high organic content, 9180–10,450 t y1 of olive oil solid residue (OOSR) and 1620–1860 t y1 leaves. Lagooning as physical evaporation and irrigation for the OMW and typical composting for the OOSR are the main typical and classic systems for the treatment of those waste until now in Cyprus. This study deals with a physicochemical approach for the treatment of OMW and OOSR with combination to Fenton’s Reagents, Composting system as a sustainable and cost effective method for small industries in Cyprus and other Islands under warm climate conditions.
7985
A.A. Zorpas, C.N. Costa / Bioresource Technology 101 (2010) 7984–7987
2. Methods
3.1. Factorial design
2.1. Methods of analysis
The aim of the experimental procedure was to determine the influence of some basic process parameters on the effectiveness of the oxidation treatment in terms of %COD removal from the OMW. These parameters are dilution of wastewater, heptahydrated ferrous sulphate concentration, hydrogen peroxide concentration, and sulphuric acid concentration. These parameters are referred to as ‘‘controlling parameters” of the system. The effect of the controlling parameters on the optimization parameter was estimated by performing a 24 factorial experiment. In general, by using a 2n factorial design, n controlling parameters interrelate to an optimization parameter through an appropriate linear model. Their significance can also be estimated and assessed (Alder et al., 1995). Then the most significant variables are altered stepwise, aiming at the determination of the optimal experimental conditions. The levels of the controlling parameters are includes: Wastewater dilution, FeSO47H2O, H2O2 (30%) and H2SO4 (98%) addition. The variation intervals include 3 Levels (+1, 0, 1). +1 Level involved zero% wastewater dilution, 4 g L1 FeSO47H2O, 2 mL L1 H2O2 (30%) and 0.5 mL L1 H2SO4 (98%). Zero Level involved zero 50% wastewater dilution, 5 g L1 FeSO47H2O, 2.5 mL L1 H2O2 (30%) and 0.25 mL L1 H2SO4 (98%). 1 Level involved zero 100% wastewater dilution, 6 g L1 FeSO47H2O, 3.5 mL L1 H2O2 (30%) and 0.75 mL L1 H2SO4 (98%). The experimental area of the factorial design was predetermined in previous preliminary trials. In the 24 factorial designs, 16 experiments were carried out. Four extra experiments in the center of the design (level 0) were also conducted for statistical purposes. Each experiment was repeated three times and the results presented are the mean values. From this data, a mathematical model was constructed. Its adequacy was checked by the Fisher criterion. According to the latter, the following ratio should follow the F-distribution with level of importance p = 5%:
The OMW and the OOSR have been collected from 3 several olive mills based in 3 different Districts of Cyprus. The District of Famagusta (DF) which is in the Eastern Part of the Island, the District of Larnaca (DL) which is about 40 km away from the olive mills of DF on the South and the District of Paphos (DP) which is about 300 km away from the olive mills of DF and 250 km from the olive mill of DL on the west. The sampling durations were for about 4 months from October–January and every second week 50 kg of OOSR and 50 L of OMW were taken and the samples were stored in the fridge at 4 °C. The two olive mills in Famagusta and Larnaca are 3-Phase process while the other one in Paphos is 2Phase process. For all the presented parameters in Table 1 and 2 a number of methods has been used as presented: in Standard Methods of Analysis (1995), by Zorpas et al., 1998), by Zorpas (2008), by Gotsi et al. (2005), by Atanassova et al. (2005), by Gaudy (1962). 3. Experimental procedure The OMW from each District (DF, DL, DP) was subjected to Fenton oxidation treatment. The oxidation was carried out batch wise at 25 °C in an agitated (200 rpm), temperature and pH controlled glass reactor of 1L capacity for 4 h. First, the wastewater sample was diluted, if necessary. Next, H2SO4 (98%) and Fenton reagent were added. As ferrous salt, FeSO47H2O was used and the hydrogen peroxide was of 30% concentration. After oxidation, vigorous stirring, neutralization with lime, coagulation with a weak anionic polyelectrolyte (2540 Praestol, 0.1%) and flocculation in a jar test apparatus, the sample was filtered and the supernatant liquid was analyzed in terms of COD. Then the treated olive mill wastewater (TOMW) from District of Famagusta were mixed with the OOSR from the same District and proceed for composting in two several compost systems according to the following scheme: CS1A (OOSRF + OMWF), CS1B (OOSRF + TOMWF), CS2A1 (OOSRF + OMWF), CS2B1 (OOSRF + TOMWF).
F¼
S2ad
ð1Þ
S2Y
S2ad ¼
PN
i¼1 ðY i
Y^ i Þ2
ð2Þ
f
Table 1 Composition of the olive mill wastewater. Characteristics
OMW–DF
OMW–DL
OMW–DP
Total solids (TS), % Total volatile solids, % of TS Total organic carbon content, % of TS Total Kjeldahl nitrogen, % of TS Total phosphorous as P2O5, % of TS Total Phenolic compounds (g L1) pH EC (mS cm1) Salinity (mg L1) CaCO3 BOD5 (g L1) COD (g L1) COD/BOD5 ratio Ash, % of TS C/N ratio C/P ratio Specific weight (gr cm3) Fats & oils mg (L1) Germination index (%) Humics (%) E4/E6 K mg L1 Ca mg L1 Mg mg L1 Na mg L1 Cl2 mg L1
6.33 ± 1.81 90.36 ± 3.31 62.71 ± 6.27 1.28 ± 0.17 0.84 ± 0.17 8.71 ± 0.51 5.66 ± 0.3 2120 ± 57 1058 ± 91 17.3 ± 5.5 70.1 ± 12.3 4.05 ± 0.91 9.71 ± 3.21 52.25 ± 5.24 74.65 ± 3.81 1.048 ± 0.033 1.46 ± 0.20 18 ± 5 0.94 ± 0.12 1.34 ± 0.03 3.1 ± 0.45 271.4 ± 14.1 32.8 ± 5.3 344.3 ± 15.1 401.4 ± 51.4
6.09 ± 1.05 91.93 ± 4.15 60.17 ± 5.99 1.31 ± 0.20 0.92 ± 0.11 9.02 ± 0.39 5.52 ± 0.4 1984 ± 33 901 ± 28 20.1 ± 9.7 57.4 ± 6.3 3.01 ± 0.87 8.99 ± 2.18 45.93 ± 4.15 65.40 ± 6.17 1.057 ± 0.029 1.45 ± 0.22 16 ± 7 1.04 ± 0.27 1.53 ± 0.05 2.87 ± 0.50 248.7 ± 16.9 28.2 ± 4.7 322.6 ± 16.9 367.8 ± 41.9
6.59 ± 0.98 88.12 ± 3.69 64.30 ± 7.12 1.25 ± 0.19 0.88 ± 0.11 490 ± 0.28 5.58 ± 0.3 1277 ± 12 645 ± 48 13.7 ± 3.4 45.9 ± 4.5 2.98 ± 0.92 9.25 ± 3.05 51.44 ± 6.02 73.68 ± 4.15 1.022 ± 0.041 6307.5 ± 279 11 ± 6 0.89 ± 0.21 1.44 ± 0.03 2.17 ± 0.21 210.6 ± 12.2 22.9 ± 6.1 209.1 ± 17.2 212.3 ± 24.7
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Table 2 Composition of the olive oil solid residue. Characteristics
OOSR–DF
OOSR–DL
OOSR–DP
Moisture Total solids (TS) (%) Total carbon content, % of TS Total Kjeldahl nitrogen, % of TS Total phosphorous as P2O5, % of TS Fats and oils, % of TS Proteins, % of TS Total sugars, % of TS Cellulose, % of TS Hemicellulose, % of TS Ash, % of TS Other extraction substances, % of TS Lignin, % of TS Potassium as K2O, % of TS Calcium content, % of TS C/N ratio C/P ratio Specific weight (gr cm3) Porosity (%) Germination index (%) Humics (%) E4/E6 ratio
48.71 ± 2.01 86.00 ± 3.33 51.45 ± 4.48 1.06 ± 0.15 0.11 ± 0.01 4.65 ± 1.09 3.29 ± 0.12 1.07 ± 0.09 22.27 ± 0.44 16.57 ± 0.94 3.65 ± 0.25 8.38 ± 0.35 11.95 ± 0.45 0.83 ± 0.11 0.72 ± 0.08 48.53 ± 5.03 467.72 ± 42.1 1.09 ± 0.02 52.4 ± 5.5 17 ± 3 1.03 ± 0.08 1.00 ± 0.05
50.12 ± 1.92 85.34 ± 4.01 46.79 ± 3.32 1.12 ± 0.07 0.13 ± 0.01 4.89 ± 1.21 3.97 ± 0.19 1.12 ± 0.11 19.31 ± 0.96 14.90 ± 0.78 4.01 ± 0.44 9.45 ± 0.59 14.41 ± 0.87 0.91 ± 0.07 0.67 ± 0.03 41.77 ± 3.97 359.92 ± 53.9 1.12 ± 0.08 49.3 ± 4.9 21 ± 5 1.18 ± 0.31 0.95 ± 0.07
62.1 ± 2.12 77.98 ± 6.71 47.12 ± 3.61 0.79 ± 0.10 0.07 ± 0.01 6.02 ± 0.93 2.43 ± 0.19 0.96 ± 0.04 16.30 ± 0.47 9.45 ± 1.02 3.12 ± 0.17 7.12 ± 0.28 9.39 ± 0.68 0.87 ± 0.11 0.65 ± 0.04 59.64 ± 4.45 673.14 ± 79.98 1.35 ± 0.04 28.6 ± 6.6 16 ± 9 0.92 ± 0.30 1.10 ± 0.13
S2 ðbj Þ ¼
S2Y N
ð3Þ
where S2Y is the standard deviation, S2a d is the adequacy deviation ^i and is calculated by the Eq. (2). Yi is the experimental i value, Y is the estimated i value from the model determined, f is the number of degrees of freedom, and N is the number of trials. As far as the determination of statistically important parameters is concerned, the procedure mentioned below was followed. The coefficient deviation is defined by Eq. (3) where N is the number of trials. The importance of the coefficient was checked by Eq. (4).
t¼
jbj j Sðbj Þ
ð4Þ
where bj is the j linear coefficient. ‘‘t” should follow the Student distribution for importance level p = 5% and degrees of freedom those of the deviation S2(Y). After the mathematical model construction and the determination of statistically important parameters, an effort to find the optimum conditions for the effectiveness of the Fenton oxidation treatment of wood-processing industry wastewater was made. This was performed through a steepest ascent method. After the treatment of OMW with Fenton treatment, the treated olive mill wastewater (TOMW) with the produced sludge’s from the Fenton Process were proceed for further treatment in two several systems: (i) in lagooning for physical evaporation and with typical red beds and (ii) with co-composting with OOSR. The amount added to the system was equal with the final moisture of 60 ± 5%. For the composting of the OOSR with the TOMW two different systems were used: (a) Compost System (CS1): A typical windrow system of 3 m length and 1.5 m, with final moisture of 60 ± 5%. The samples were aerated using an aerated air force, and (b) Compost System (CS2): An In-Vessel reactor of 1 m3 active volume (Zorpas 2008). The thermophilic phase in the reactor lasted 15 d. The temperature in the center of the reactor was about 60–65 °C and the moisture percentage between 60 ± 5%. The samples were aerated using an aerated air force (oxygen concentration range in the reactor was between 5–8%). A temperature indicator controller was controlling the operation of the fan in order to maintain the temperature at about 60 °C, according to the following principle: minimum air flow (2.3 m3 per m3 active volume) was provided at low temperature (<30 °C) and maximum air flow (28 m3 per m3 active volume was provided at high temperature (>60 °C). The
minimum airflow corresponds to the minimum oxygen demand for the microorganisms and the maximum to the necessary air for cooling. After the thermophilic period, in which the organic material was biodegraded, the compost was piled to an enclosed package where it remained for about four months to mature. The fundamental principle of a co-composting system is the biodegradation of the organic matter through exothermic aerobic bioreactions which take place in the thermophilic region with the simultaneous evaporation of the moisture of the wastewater due to the release of thermal energy (Jewell et al., 1980). As a critical parameters for the growth of microorganisms and bioreactions are the oxygen demand, the moisture (which must be in the range of 60 ± 5%) the temperature (which must be retained between 60–65 °C) and the Carbon/Nitrogen (C/N) ratio. 4. Results and discussion Tables 2 and 3 present the physicochemical characteristics of the OMW and the OOSR from the three several Olive Mills. As indicated in Table 2 the COD and the BOD5 is considering very high which causes serious environmental problems. The higher COD presented in the OMW-DL which is 127.4 ± 36.3 mg L1, follows by the OMW-DP which is at 122.9 ± 34.5 mg L1 and the OMW-DF with COD at 118.3 ± 32.1 mg L1. The total humics is considered to be very low (less than 1.4 mg L1) while the E4/E6 is below 5. The E4/E6 ratio shows the characterization of humic materials. As the E4/E6 ratio is bellow 5, the samples are characterized as Humic Acid (whereas if the ratio is above 5 the sample is characterized as Fulvic Acid), (Zorpas 1999). The COD/BOD ratio ranges from 2.98:1 to 4.05:1, which indicates the presence of poor biodegradable organic compounds and/or toxic ones El-Gohary et al. (2009). The G.I is presented to be less than 26 and the substrate is characterized as very phytotoxic both for the OMW and for the OOSR. The C/N ratio both of the substrates (OMW and OOSR) is considered to be at very satisfactory levels for composting process. The variation of the EC is due to the different quality of the water use in the production line. Similar results from the characteristic of OMW from Geece are found from Gotsi et al. (2005). El-Gohary et al. (2009) mention that the COD, TOC and BOD values, ranged from 102,900 to 207,300 mg O2 L1, from 30,000 to 93,000 and from 78,528 to 135,400 mg O2 L1, respectively from an OMW. The COD reduction is up to 65% for almost all the treated sampled
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A.A. Zorpas, C.N. Costa / Bioresource Technology 101 (2010) 7984–7987 Table 3 Physicochemical characteristics of mature compost (120 d). Parameters
Moisture (%) pH Ash, % of dry matter Organic matter, % of dry matter Total organic carbon, % of dry matter Total Kjeldahl nitrogen (%) Total phosphorous (%) C/N C/P Humic substances,% of dry matter Total phenolic compounds (mg/kg) Germination index Grow index (%)
CS1
CS2
A
A1
B
B1
32.1 ± 5.03 7.2 ± 0.05 25.85 ± 1.87 74.15 ± 3.09 40.7 ± 4.31 1.13 ± 0.16 0.45 ± 0.11 36.01 ± 3.41 90.44 ± 12.91 5.84 ± 1.09 212 ± 34 124 ± 21 73 ± 5
26.8 ± 2.35 7.7 ± 0.03 29.68 ± 1.33 70.32 ± 4.12 37.27 ± 3.16 1.33 ± 0.22 0.55 ± 0.05 28.02 ± 2.13 67.76 ± 7.01 6.35 ± 0.97 192 ± 23 138 ± 12 77 ± 6
28.2 ± 1.99 7.7 ± 0.03 28.81 ± 1.66 71.19 ± 2.99 40.58 ± 3.01 1.30 ± 0.14 0.61 ± 0.12 31.22 ± 3.04 66.52 ± 9.18 7.04 ± 1.13 188 ± 51 177 ± 19 77 ± 10
22.5 ± 2.19 7.6 ± 0.01 27.10 ± 1.51 72.90 ± 1.97 39.01 ± 2.19 1.44 ± 0.11 0.52 ± 0.07 27.09 ± 2.21 75.01 ± 5.66 7.15 ± 0.88 173 ± 19 201 ± 9 92 ± 3
(62.35 ± 8.03%). Fenton processes are suitable to treat a wide variety of effluents irrespective of their concentration and origin and are characterized by their simple and versatile operation. As olive oil manufacturing industries are usually small plants with a low, seasonal wastewater flow, a small Fenton unit would suffice to cope efficiently with the effluents produced. Rivas et al. (2001) estimated that OMW treatment (15 mg L1 of inlet COD and 80–90% COD reduction achieved in residence times between 1 and 8 h depending on the operating conditions employed) by Fenton’s reagent would cost USD 3.2 per m3 of wastewater treated and mg L1 of COD removed. This value is greater than that of the conventional biological treatment of OME by about an order of magnitude since H2O2 consumption comprises a significant fraction of the operating costs. In this respect, studies are needed to optimise the dosage of the Fenton’s components used, thus avoiding waste of costly chemicals (Mantzavinos and Kalogerakis, 2004). Table 3 shows the characterization of the final product after 120 d of maturity. It was obvious that the B1 sample of CS2 was presented with better characteristics than the other final products. Specifically, the B1 final cured compost is presented with pH at 7.6 ± 0.01, Organic Matter at 72.90 ± 1.97%, TOC at 72.9 ± 1.97%, TKN at 1.44 ± 0.11%, TP at 0.52 ± 0.07%, C/N and C/P ratio at 27.09 ± 2.21 and 75.01 ± 5.66 respectively, total humics at 7.15 ± 0.88%, total phenolic compounds at 173 ± 19 mg kg1 while the G.I is at 201 ± 9. As olive oil manufacturing industries are usually small plants with a low, seasonal wastewater flow, a small Fenton unit would suffice to cope efficiently with the effluents produced. This process proved to be effective for the reduction of wastewater pollution load and its detoxification. After this implementation, the conventional biological treatment of wastewaters is feasible and cost effective. Moreover, further wastewater treatment with reed beds could render them totally recyclable. The proposed approach towards a sustainable solution to the environmental impacts of olive oil processing includes the production of organic fertilizer/soil conditioner combined with the effective chemical and biological oxidation of wastewaters. Hence, the Fenton’s reaction appears to be useful for reducing toxic phenolic compounds consequently increases the biodegradability of OMW. Compared to other AOPs, Fenton’s reaction presents several advantages. H2O2 is environmentally friendly, since it slowly decomposes into oxygen and water. Besides, the abundance, lack of toxicity and ease of removal from water makes Fe2+ the most commonly used transition metal for Fenton’s reaction applications. The above characteristics make compost suitable for agricultural requirements and suggest that it can be used as an effective product for plant growth according to European Guidelines (European Commission, 2005). Very interesting research approaches which are not presented in this research is for the future the co-composting from the total waste
production from the olive oils industry in Cyprus. The integrated management system may include the chemical-organic sludge produced by the oxidative process, the sludge produced by the biological process, the olive tree leaves, the olive stones and the residues from the reed beds for the production of an ecological soil conditioner with very good control nutrient properties.
5. Conclusions From all the above it can be concluded regarding the pollution problems caused by olive oil production, a solution based on the principles of the clean technology concept could be the detoxification of wastewaters and the composting with the olive oil solid residues. The use of Fenton’s reaction as a primary treatment of OMW enhances the efficiency of the composted material. It is obvious that the final characteristics of the composted material presented with a very good soil conditioner. References APHA, AWWA–WPCF, 1995. Standard methods for the examination of water and wastewater. 10th Ed.. American Public Health Association, Washington, U.S.A. Alder, Y.P., Markova, E.V., Granovsky, Y.V., 1995. The Design of Experiments to Find Optimal Conditions. Mir Publisher, Moscow. Atanassova, D., Kefalas, P., Psillakis, E., 2005. Measuring the antioxidant activity of olive oil mill wastewater using chemiluminescence. Environ. Int. 31 (2), 275–280. Canizares, P., Lobato, J., Paz, R., Rodrigo, M.A., Saez, C., 2007. Advanced oxidation processes for the treatment of olive-oil mills wastewater. Chemosphere 67, 832–838. El-Gohary, F.A., Badawy, M.I., El-Khateeb, M.A., El-Kalliny, A.S., 2009. Integrated treatment of olive mill wastewater (OMW) by the combination of Fenton’s reaction and anaerobic treatment. J. Hazard. Mater. 162, 1536–1541. European Commission, 2005. Working document: Biological treatment of biowaste, 2nd draft 1, 22. Gaudy Jr., A.F., 1962. Colorimetric determination of protein and carbohydrate. Ind. Wastes Water 7, 17–22. Gotsi, M., Kalogerakis, N., Psillakis, E., Samaras, P., Mantzavinos, D., 2005. Electrochemical oxidation of olive oil mill wastewaters. Water Res. 39, 4177–4187. Jewell, J.W., Kabrick, M.R., 1980. Autoheated aerobic thermophilic digestion with aeration. J. Water Pollut. Contol Federe 52 (3), 512–523. Mantzavinos, D., Kalogerakis, N., 2004. Treatment of olive mill effluents: Part I. Organic matter degradation by chemical and biological processes: an overview. Int. J. Environ. 31, 289–295. Rivas, F.J., Beltrán, F.J., Gimeno, O., Frades, J., 2001. Treatment of olive oil mill wastewater by Fenton’s reagent. J. Agric. Food. Chem. 49, 1873–1880. Zorpas, A.A., Vlyssides, A.G., Loizidou, M., 1998. Physical and chemical characterization of anaerobically stabilized primary sewage sludge. Fresen. Environ. Bull. 7, 383–508. Zorpas, A.A., 1999. Development of a methodology for the composting of sewage sludge using zeolite. PhD thesis, National Technical University of Athens, Athens, Greece. Zorpas, A.A., 2008. Sewage sludge compost evaluation in Oats, Pepper and Eggplant cultivation. Dynam. Soil, Dynam. Plants. Global Science Book 2 (2), 103–109.