Biological Hydrogen Production from Industrial Wastewaters
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th Proceedings of the 5 International Workshop on Hydrogen and Fuel Cells October 26 –29, 2010 Campinas, SP, Brazil ISSN 2179-5029 BIOLOGICAL HYDROGEN PRODUCTION FROM INDUSTRIAL WASTEWATERS (1) GUILHERME PEIXOTO (1) JORGE LUIS RODRIGUES PANTOJA FILHO (1) MARCELO ZAIAT (1) Department of Hydraulics and Sanitation, São Carlos School of Engineering (EESC), University of São Paulo (USP), São Carlos, São Paulo State, Brazil ABSTRACT This research evaluates the potential for producing hydrogen in anaerobic reactors using industrial wastewaters (glycerol from biodiesel production, wastewater from the parboilization of rice, and vinasse from ethanol production). In a complementary experiment the soluble products formed during hydrogen production were evaluated for methane generation. The assays were performed in batch reactors with 2 liters volume, and sucrose was used as a control substrate. The acidogenic inoculum was taken from a packed-bed reactor used to produce hydrogen from a sucrose-based synthetic substrate. The methanogenic inoculum was taken from an upflow anaerobic sludge blanket reactor treating poultry slaughterhouse wastewater. Hydrogen was -1 -1 produced from rice parboilization wastewater (24.27 mL H 2 g COD) vinasse (22.75 mL H 2 g -1 COD) and sucrose (25.60 mL H 2 g COD), while glycerol only showed potential for methane generation. KEY WORDS Hydrogen; biological process; wastewaters; 1. INTRODUCTION The bioproduction of hydrogen is an interesting option because organic waste can be used as feedstock for the process. The fermentative process could be another way of generating hydrogen besides electrolysis and methane steam reforming, which are the most common processes used for hydrogen production nowadays. Hydrogen generation using the fermentation process is possible with various types of wastewater using either mixed or pure cultures [1]. The use of various effluents, mainly wastewater containing cellulose, pentose, and xylose [2] [3], glycerol, residues from biodiesel production [4], effluent from cheese processing [5], dairy wastewater [6], by-products of wheat flour processing [7], molasses [8], solid food wastes [9], effluent from paper production [10] and domestic sewage [11], among others, has been reported. Industrial effluents are potential energy sources readily found in many communities. Thus, hydrogen generation from these wastewaters could be carried out using local feedstock, reducing the costs involved in transportation and storage. It is worth mentioning that vinasse and glycerol are by-products of ethanol and biodiesel plants, respectively. Both are renewable fuels that would have theirs sustainability increased if hydrogen could be produced using by-products of these processes. 1 Correspondence should be addressed to Guilherme Peixoto: Phone: +55 (16) 3373-8360; fax: (16) 3373-9550; e-mail: [email protected] 26 th Proceedings of the 5 International Workshop on Hydrogen and Fuel Cells October 26 –29, 2010 Campinas, SP, Brazil ISSN 2179-5029 Glycerol and vinasse were chosen due to the Brazilian industrial expansion on the production of renewable fuels, such as biodiesel and ethanol. The rice parboilization wastewater was chosen due to the high content of carbohydrates in its composition. According to Hawkes et al. [12] they are the main precursors of hydrogen production. Current glycerol generation in Brazil is about 17.6 million liters per year considering the study realized by Silva et al. [13], which estimates that biodiesel production generates 10% (weight/weight) of glycerol. Vinasse generation is usually 14 times the volume of ethanol produced. Data from UNICA (Sugarcane Agroindustry Union of São Paulo State) show that it was produced 15 million cubic meters of ethanol in the 2004–2005 harvest, thus resulting in a 210 million cubic meter generation of vinasse. According to researches realized in 2005 by EPAGRI (Rural Extension and Agropecuary Research Business), to parboil 1 kg of rice it is generated around 1 liter of effluent. Thus, it is estimated that in Brazil, where 24% of the rice is parboiled [14], it was generated around 2.8 million cubic meters of rice parboilization wastewater in 2006. The production of methane can be easily carried out using the organic acids generated in the hydrogen production process. According to Mohan et al. [15] the utilization of effluents for the production of hydrogen followed by posterior methanization of the soluble products generated in the acidogenic systems offers a solution for the problem of the renewable fuels and reduces significantly the pollution impact of the wastewaters used in the process. 2. OBJECTIVE The objective of this paper is to evaluate the potential of industrial residues for hydrogen generation through simple assays in bench-scale batch reactors with sucrose as the control substrate. 3. METHODOLOGY 3.1. BATCH REACTORS The reactors were composed of 2 liters glass flasks, consisting of 1 liter of liquid volume and 1 liter of headspace . 3.2. WASTEWATERS Three effluents were tested (vinasse; glycerol; rice parboilization wastewater), and sucrose was used as a control substrate. Vinasse was obtained from an ethanol production plant (Usina Nova Era, Ibaté, SP, Brazil), and glycerol was obtained as a by-product after the esterification reaction of vegetable oil in a biodiesel production plant (Granol, Anápolis, GO, Brazil). The rice parboilization wastewater was obtained as a residue of the parboiled rice production process by a food production plant (Nelson Wendt Alimentos, Pelotas, RS, Brazil). The sucrose-based synthetic wastewater was prepared with organic demerara sugar (Native Natural Products, São Francisco S/A, Sertãozinho, SP, Brazil). Basic characterizations of the wastewaters are presented in Table 1. 27 th Proceedings of the 5 International Workshop on Hydrogen and Fuel Cells October 26 –29, 2010 Campinas, SP, Brazil ISSN 2179-5029 Table 1 . Characterization of the wastewaters. Parameters Vinasse Glycerin Rice WW Sucrose COD (mg L -1) 20731 1108230* 5354 364 pH 3.8 ND 4.6 5.5 -1 Alkalnity (mg L CaCO 3) 0 ND 0 0 TS (mg L -1) 18170 ND 657 0 VSS (mg L -1) 14440 ND 537.5 0 FS (mg L -1) 3270 ND 119.6 0 Total N (mg L -1 N) 187.5 0 104.6 0 -1 3- Total P (mg L PO 4 ) 133 0 124.5 0 *For aqueous solution of 1g L -1 glicerol; COD – Chemical Oxygen Demand; TS – Total Solids; VSS – Volatile Suspended Solids; FS – Fixed Solids; N – Nitrogen; P – Phosphorous; ND – Not Determined. 3.3. Nutritional medium The reactors were filled with filtered wastewater (1.2 µm membrane) diluted with tap water to reach a chemical oxygen demand (COD) of approximately 300 mg L -1 in each flask. A -1 nutritional medium containing (in mg L ): CH 4N2O (6), NiSO 4.6H 2O (0.15), FeSO 4.7H 2O (0.75), FeCl 3.6H 2O (0.075), CoCl 2.2H 2O (0.012), CaCl 2.6H 2O (0.618), SeO 2 (0.0108), KH 2PO 4 (1.608), KHPO 4 (0.39) and Na 2HPO 4.2H 2O (0.828) was added to all reactors. Sodium bicarbonate (500 mg L -1) and chloridric acid (10 mol L -1) were added to each reactor to maintain the pH level of approximately 5.5. 3.4. Inoculum The acidogenic inoculum with around 30 g L -1 VSS was obtained from fixed-bed anaerobic reactors used for hydrogen production from sucrose-based synthetic wastewater [16].These reactors were filled with low density polyethylene as a support material for the attachment of biomass and kept at 25 ºC for 0.5 h of hydraulic detention time. The metanogenic inoculum used in the complementary experiment had around 37 g L -1 VSS and was obtained from a UASB (Upflow Anaerobic Sludge Blanket Reactor) treating poultry slaughterhouse wastewater [17]. The granular sludge was taken directly from the middle of the reactor blanket zone. 3.5. Experimental procedure The duration of the experiment was 36 h. The complementary evaluation took about 156 h. The tests were performed in 4 batch reactors (in duplicate). Argon was fluxed for 20 min to guarantee an anaerobic environment in each reactor before closing them. The reactors were placed in a thermostatic chamber at 25.0±0.9ºC without agitation. Gas and liquid samples were taken periodically from the reactors for analysis. Internal pressure of the flask was measured using a pressure gauge with detection range of 0 to 500 mbar. Less than 10% of the overall bulk liquid volume was taken throughout the experiment. In the acidogenic step (0 to 36 h) the liquid phase (1 liter) consisted of the diluted effluent, the nutritional medium utilized by Fernandes et al. [18] and around 400 mg L -1 VSS of inoculum taken from a packed-bed reactor used to produce hydrogen from a sucrose-based synthetic substrate [16]. In the complementary experiment (48 to 224 h), the reactors from the first step were opened and their products were filtered with a 0.45 µm membrane to remove the acidogenic biomass. After this procedure they were complemented with the same nutritional medium of the acidogenic step, inoculated with around 500 mg L -1 VSS of the methanogenic inoculum taken from an UASB [17], adjusted for pH 7.0 and fluxed with Argon. 28 th Proceedings of the 5 International Workshop on Hydrogen and Fuel Cells October 26 –29, 2010 Campinas, SP, Brazil ISSN 2179-5029 3.6. Analytical methods The composition of the biogas (hydrogen, carbon dioxide, and methane) was analyzed via gas chromatography (Shimadzu GC/TCD) [18]. Organic acids were measured using gas chromatography (HP GC 6890/FID), following the procedures described in [19]. Ethanol concentration was determined using gas chromatography (Shimadzu GC/FID) with an automatic injector (COMBI-PAL, AOC 5000, headspace mode) equipped with an HP-INNOWAX column. Chemical oxygen demand (COD), pH, alkalinity, total solids (TS), volatile suspended solids (VSS), fixed solids (FS), nitrogen and phosphorous were analyzed according to the Standard Methods [20].