Al-Khwarizmi Engineering Journal Al-Khwarizmi Engineering Journal, Vol. 6, No. 3, PP 14 -20 (2010) Biogas Production by Anaerobic Digestion of Date Palm Pulp Waste Khalidah A. Jaafar Edrici Center for Environmental & Engineering Consultation PO Box: 168, Sulaymani, IRAQ (Received 2 December 2009; Accepted 18 April 2010) Abstract The purpose of this preliminary study is to verify the possibility of using Iraqi Zahdi date palm biomass as a resource for biogas production, methane in particular using thermophilic anaerobic digestion with waste water treatment activated sludge. Moreover, is to investigate the influence of extra nutrients addition to the digestion mixture. Biogas was captured in sealed jars with remote sensing modules connected to computer with integrated program to record the gas pressure continuously. A total gas pressure with 67% Methane was produced from date pulp waste fermentation with a yield of 0.57 Lit for each gram volatile solid of substrate. Addition of 1% yeast extract solution as nutrient increased Methane yield in liters by 5.9%. This is the first time in literature to record biogas production data from Iraqi date palm biomass. Keywords: Date palm, pulp, anaerobic digestion, biogas, phoenix dactylifera L. 1. Introduction Date palm (Phoenix dactylifera L.) is one of the principal agricultural products in Middle East and North Africa region. Dates are available in huge amounts (100 million trees) yielding about 3,316,500 tons of palm secondary products per year including palm midribs, leaves, stems, fronds and coir (Taha, et al., 2006). In Iraq, nine million trees cover the middle and southern parts of the country, resulting in a surplus production of dates and other secondary biomass. Date cultivars are fruits with high sugar content (55-70% wt) (Al-Niaimi & Jaafer, 1980). Traditionally they are used for food, or to produce sweets, sweet syrup (Dibs in Arabic), vinegar and alcoholic products. In Iraq, part of the biomass waste of all these industries, is used in the blend of animal food. However, a high percentage of this waste is currently disposed to the landfill without any further treatment. The disposed biomass is mainly cellulosic compounds with some sucrose sugar, fats and minerals. This fact makes it a high potential resource for biogas or biofuel production through fermentation process. This potential has been recently considered in the Middle East and Arabic region. Very little research work has actually been done on the date palm biomass as a biofuel resource. However, there are many papers describing the dates physiochemical characteristics (Vandepopuliere, et al., 1995, Pillay, et al, 2005, Hamada, et al., 2002, Ismail, et al., 2008). To the best knowledge of the author, research data on anaerobic digestion from date palm waste is not available in literature. The aim of present work is to investigate usage of date palm biomass as a resource of bio energy. A lab research is conducted to ascertain the applicability of biogas production from small, batch scale anaerobic digestion process of date pulp biomass. Cultivars of Zahdi date variety are selected as the resource of biomass due to their abundance in Iraq representing 60% of the country production (Al- Niaimi & Jaafer, 1980), utilizing waste activated sludge at a municipal wastewater treatment plant as the inoculums. Cellulosic biomass can be converted into biofuel by catalysis with dilute acid, concentrated This page was created using Nitro PDF trial software. To purchase, go to http://www.nitropdf.com/ http://www.nitropdf.com/ Khalidah A. Jaafar Al-Khwarizmi Engineering Journal, Vol. 6, No. 3, PP 14-20 (2010) 15 acid, or enzymes known as cellulases. Anaerobic digestion of organic matter can be applied to both liquids and semi-solid wastes (Grover, et al., 2002). In the absence of oxygen and certain other exogenous inorganic electron acceptors [e.g. nitrate, Mn(IV), Fe(llI), sulfate], cellulose is decomposed by the anaerobic community into CH4, CO2 , and H2O through a complex microbial food chain (Leschine, 2008). The process can be divided into four stages, namely hydrolysis, acidogenesis, acetogenesis and methanogenesis (Mackie & Bryant, 1995). Cellulose is hydrolyzed by cellulases enzymes produced by cellulolytic bacteria into monosaccharide sugars (e.g. cellobiose and cellodextrins, and some glucose). These sugars are fermented into CO2, H2 and fatty acids (acetate, butyrate and propionate) by other cellulolytic and other saccharolytic microorganisms. In third stage, homoacetogens use H2 to reduce CO2 to acetate. In addition to syntrophic bacteria activity that ferment fatty acids such as propionate and butyrate to CO2, H2 and acetate as well. Methanogens consume H2 to reduce CO2 to CH4, and some methanogenic species convert part of the acetate produced to CH4 and CO2. Syntrophic bacteria play a key role in the decomposition of cellulose. These organisms grow very slowly, and only in the presence of H2 consuming organisms. Thus the fermentation of fatty acids is usually the rate- limiting step in the anaerobic decomposition of cellulose (Leschine, 2008). 2. Experimental Work 2.1. Substrate Preparation Biomass from Zahdi date cultivars was prepared to be in the same conditions as it is usually expelled from Syrup (Dibs) industry in Iraq. 200 g of Date fruits harvested in 2008 from the middle area of Iraq, were pitted and boiled with one liter distilled water in a beaker then cooled, filtered with fabric mesh, then rinsed with water and filtered again to get rid of as much as possible from its water soluble sugar content. The resulting biomass weight was 51% of the original pulp weight, and kept in 4 oC refrigeration for further testing. 2.2. Methodology & Procedure The Waste Management Lab/ Cornell University (USA) methodology for anaerobic digestion, was used to perform this research work. Biomass from Zahdi dates was treated with anaerobic digestion in thermophilic conditions at 55 oC. 300 ml glass jars fitted with wireless computer controlled modules from Ankom, were used as the small batch reactors. The remote sensing modules measures the total gas pressure produced during the period of fermentation experiment. In order to keep the fermentation medium close to neutral pH (7.0-7.5), which is necessary for hydrolysis of fatty acids, 50 mM BES buffer solution (N,N-bis-2-hydroxyethyl-2-amino-ethane sulphonic acid) was used to prepare incubation medium. One ml of 5 g/L yeast extract solution was added as the only external nutrient for the inoculums. No trace elements were added to the fermentation solution as the date biomass is normally rich with many minerals such as Potassium, Calcium, Boron, Iron, Manganese, Magnesium and Cobalt (Al-Niaimi & Jaafer, 1980). Blank samples of deionized water (DIW) were placed under experiment conditions to observe pressure drop/increase due to temperature variation during sampling and adding substrate. Methane yield will be normalized to the volatile solids of biomass and original carbon added to the solution. 2.3. Initial Substrate Testing Samples of substrate and inoculums were tested for Total Solid (TS) and Volatile Solid (VS) content to verify the best food/biomass ratio of mixing. Proportion of C:N was also measured with metal analyzer from CE Instruments, NC 2500 to calculate initial carbon and nitrogen added to the fermentation batch. Three grams of substrate were weighed in dried and cooled crucibles, then placed in 105 oC Fisher Isotemp oven (0-200o C) for 24 hrs, then cooled in the desiccators for 1 hr. After weighing, crucibles were placed in 550 oC Lindberg SB Muffle furnace (0-600o C) to maintain TS, VS and ash content of the substrate. 2.4. Anaerobic Digestion Procedure BES solution (50 mM) was used to prepare two groups of triplicate samples for digestion. The first group included 100 ml BES plus 5 ml of activated sludge with addition of 1% yeast extract solution as the nutrient. While the second group, was only BES solution with 5 ml of activated sludge. A third group of jars containing DIW only This page was created using Nitro PDF trial software. To purchase, go to http://www.nitropdf.com/ http://www.nitropdf.com/ Khalidah A. Jaafar Al-Khwarizmi Engineering Journal, Vol. 6, No. 3, PP 14-20 (2010) 16 were incubated as well and treated exactly as the samples. Jars were flushed with nitrogen to remove traces of oxygen from fermentation medium. After incubation for 48 hrs, to exclude any biogas produced from the activated sludge, incubation jars were opened to add 0.5 g of substrate and flushed again with nitrogen. Gas samples for GC analysis were taken every 48 hrs through the experiment period. Liquid gas chromatograph from Gow-Mac Series 580, dual detector for Methane/CO2/N2 measurement with Supleco 80/100 Porapak Q, 6’ x ¼” column was used. Helium was used as the carrier gas with 35 ml/min flow rate. While Hydrogen percentage in the total gas produced was measured with another Gow-Mac Series 580, dual detector with Hydrogen Analysis Column: Supelco 60/80 Carboxen 1000, 5’ x 1/8”. Samples from liquid phase were filtered with 0.2 µm paper filter then treated 1:1 with 2% Hydrofluoric acid and tested for VFA with Hewlett-Packard 5890 Series II (With autosampler) and VFA Column: Supelco Nukol, 15m x 0.53mm x 0.5um film thickness. The experiment took place until the total gas pressure was constant for three consecutive days, then jars were opened for final measurements of pH, VFA, and SCOD. 3. Results & Data Analysis Initial values of total solids (TS), volatile solids (VS), Carbon C and Nitrogen N of the substrate and inoculums are listed in Table 1. The volatile solids of substrate and inoculums was 39.82%, 2.37% respectively with a ratio of 16.8:1. A ratio of 10:1 inoculums to substrate by weight was selected in order to maintain approximate ratio of volatile solids substrate to volatile solids Inoculums 2:1. Also the nitrogen content of the substrate was found 2.35%, which indicates the demand for extra amount of nutrients to provide nitrogen for bacteria growth in the fermentation batch. Al-Niaimi & Jaafar (1980) have measured the protein content in Zahdi date fresh fruit. Their results showed 2.16% as nitrogen. That elucidates our results if we consider the pretreatment process of the substrate. The average of total biogas produced from nutrient added group was 9.953 psi (0.0045 gmol), while the group without nutrient addition produced 7.276 psi (0.0032 gmol). The accumulation of total gas pressures produced from the two groups of jars are illustrated in Fig. 1 Table 1, Initial Data of Substrate and Inoculums. Item TS% VS% Carbon C, wt% Nitrogen N, wt% Substrate 40.74 39.82 21.49 2.35 Inoculum 3.71 2.37 1.23 0.19 . Fig.1. Total Biogas Pressure Produced During Period of Experiment. This page was created using Nitro PDF trial software. To purchase, go to http://www.nitropdf.com/ http://www.nitropdf.com/ Khalidah A. Jaafar Al-Khwarizmi Engineering Journal, Vol. 6, No. 3, PP 14-20 (2010) 17 The influence of adding nutrient solution can be clearly observed with a 36% increase in total gas pressure. The reason for this result is that in thermophilic degradation of cellulose, propionate accumulates in higher magnitudes at temperatures higher than 53o C; this was explained by the increase of H2 concentration that results into decrease of propionate metabolism (Speece et al. 2006). Addition of a complex nutrition solution, including organic nutrients such as yeast extract will increase the growth of Syntrophic bacteria which is responsible of propionate metabolism (Leschine, 2008). GC analysis was conducted frequently to measure CH4, CO2 and H2 production. Results were adjusted to the zero point of adding substrate and the pressure variation due to temperature change and sampling. Results of total gas composition are listed in Table 2. CH4% was found in nutrient added group and substrate only group 67.43%, 67.56% respectively. It can be seen from Table 2 that the nutrient addition has given significant improvement to the total gas production but did not alter the gas composition and CH4% although it did increase the g-mol of CH4 produced. In addition, H2% was nil in both groups. The absence of H2 in the produced gas leads to the conclusion of effective methanogenation of CO2 into CH4. However, this also might indicate the demand of higher substrate/inoculums ratio in order to meet Methanogens growth. Figure 2 illustrates the mol% of methane produced in each of the two groups of jars. The highest rate of Methane production was in the first three days of fermentation and reached to the end in 14 days. The exponential curve of Methane vol.% produced explains the metabolism sequence of fermenting bacteria starting with high rates of cellulose degradation into fatty acids then metabolism by methanogens into Methane. Table 2, Total Gas Pressure and Gas Composition Produced from Date Palm Pulp Waste. Measurement 1% Nutrient Modules Substrate only Modules Total biogas pressure, psi 9.593 7.276 CH4% 67.43 67.56 CO2% 32.56 32.44 H2% 0.00 0.00 Fig.2. Mean Values of Methane Vol. % Produced From Two Groups of Mixtures, with and without Addition of Nutrients. This page was created using Nitro PDF trial software. To purchase, go to http://www.nitropdf.com/ http://www.nitropdf.com/ Khalidah A. Jaafar Al-Khwarizmi Engineering Journal, Vol. 6, No. 3, PP 14-20 (2010) 18 Methane yield calculations were referred to the VS weight of initial substrate. Results are listed in Table 3. Addition of nutrients has increased the yield of methane by approximately 39% as L/g VS substrate which is close to the increase in total gas pressure, and 5.9% as g/g VS substrate respectively. Standard deviations STDEV of total gas pressure and methane percentage readings are shown in Table 4. Table 3, Methane Yield in Two Groups of Samples, One with Addition of 1% Yeast Extract and the Second without Addition of Nutrients. Result Yeast Extract Nutrient W/O nutrient Increase % due to Nutrient addition Total biogas produced, g-mol 0.0045187 0.0032189 40.38 CH4 yield, g/ g VS substrate 0.2381 0.1716 38.78 CH4 yield, L/ g VS substrate 0.613 0.579 5.9 CH4 yield, g/ g Carbon in substrate 0.513 0.318 61.32 Fig.3. Mean Values of Methane Yield in Two Groups of Modules with and without Nutrient Addition, in g/g Volatile Solids in Substrate. Table 4, Standard Deviations (STDEV) of Total Gas Pressure, Methane Percentage and Methane Yield. Measurement 1% Nutrient Modules STDEV Substrate only Modules STDEV Total biogas P, psi 9.593 1.249 7.276 2.713 CH4% 67.43 0.013 67.56 0.010 CH4 yield, g/ g VS substrate 0.2381 0.0378 0.1716 0.0731 CH4 yield, L/ g VS substrate 0.613 0.036 0.579 0.0246 This page was created using Nitro PDF trial software. To purchase, go to http://www.nitropdf.com/ http://www.nitropdf.com/ Khalidah A. Jaafar Al-Khwarizmi Engineering Journal, Vol. 6, No. 3, PP 14-20 (2010) 19 4. Conclusions The high volatile solids content in date palm biomass compared to the inoculums indicates a high potential of biogas production from a small amount of biomass, and this is a positive factor in commercial calculations for future economic Bioenergy projects. In respect to biogas production, a ratio of 67% methane of the total gas produced and a yield of 0.6 lit/g VS substrate, in addition to the short time cycle of biogas production can be considered very promising results for date palm fruits biomass to be of a great potential. Abundance of the date palm trees in Iraq, sustainable production of the dates, and the physiochemical characteristics of the biomass in this fruit, provide the viability of producing biofuels in a commercial scale. 5. 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To purchase, go to http://www.nitropdf.com/ http://www.nitropdf.com/ ر الق جعف د الخ دة عب د خال یة المجل وارزمي الھندس ة الخ دد ٦مجل فحة3، الع 20- 14، ص )٢٠١٠( 20 انتاج الغاز الحیوي من الھضم الالھوائي لمخلفات لب التمر خالدة عبد الخالق جعفر دریسي لالستشارات الھندسیة والبیئیةمركز اال السلیمانیة العراق ١٦٨ص ب الخالصـة ا ان خصوص وي، المیث از الحی اج الغ در النت ي كمص دي العراق ر الزھ ب تم تخدام الھدف من ھذه الدراسة االولیة ھو تبیان احتمالیة استخدام مخلفات ل باس م . ة معالجة میاه المجاريالھضم الالھوائي الحراري مع الفضالت المحفزة لوحد زیج الھض ى م ة ال ذیات خارجی افة مغ أثیر اض م . باالضافة الى ذلك دراسة ت ت از جمع الغاز الحیوي بواسطة علب زجاجیة محكمة الغلق بواسطة غط الغ جیل ض وب لتس امج الحاس متحسسات الكترونیة یتم التحكم بھا عن بعد من خالل برن ة ٠.٥٧غاز المیثان بناتج مقداره % ٦٧الغاز الحیوي الناتج احتوى على نسبة . الناتج باستمرار افة . لتر غاز لكل غم مواد صلبة طیارة من المادة االولی ان اض بة ق% ١محلول خالصة الخمیرة بنسبة ن %. ٥د حسن من ناتج المیثان بنس وي م از الحی اج الغ ائج انت ر نت ث تنش ة حی اث العلمی ي االبح ى ف رة االول ي الم وھ .فضالت لب التمر العراقي This page was created using Nitro PDF trial software. 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