COMPARATIVE STUDY OF DIGESTIBILITY OF CRUDE GLYCEROL IN ANAEROBIC DIGESTION OF COW DUNG AND MUNICIPAL SOLID WASTE

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1 Journal of Engineering Science and Technology Special Issue on 4th International Technical Conference 2014, June (2015) School of Engineering, Taylor s University COMPARATIVE STUDY OF DIGESTIBILITY OF CRUDE GLYCEROL IN ANAEROBIC DIGESTION OF COW DUNG AND MUNICIPAL SOLID WASTE M. ANITHA, S. K. KAMARUDIN*, N. A. GHAZALI Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, UKM Bangi, Selangor, Malaysia Fuel Cell Institute, Universiti Kebangsaan Malaysia, UKM Bangi, Selangor, Malaysia *Corresponding Author: ctie@eng.ukm.my Abstract The digestibility of crude glycerin in anaerobic digestion was investigated in this present study. 2 sets of experiment were carried out at room temperature of C for 28 days using lab-scaled reactor to determine biogas and methanol yield. Relationship between the methanol and biogas yield were studied and it was discovered that methanol, the intermediate product of anaerobic digestion, consumed by the microbes to further converted into biogas. Anaerobic digestion of solid wastes without the addition of crude glycerin resulted in higher biogas and methanol yield compared to digestion with the addition of crude glycerin. Banana peels was resulted in higher cumulative biogas production of 1670 ml and methanol yield was highest (0.51g/L, 1.05 vol.%) in digestion of cornhusk without addition of crude glycerin. Banana peels and cornhusk were identified as the best potential substrate for anaerobic digestion in this study. Keywords: Cow dung, Crude glycerin, Biogas production, Methanol yield. 1. Introduction Biodiesel is an emerging, renewable liquid biofuel produced from natural fats such as vegetable oil and animal wastes via transesterification. Unique characteristics of biodiesel in terms of environmental, economic, and social factors had convinced many developing countries to use biodiesel as an alternative for gasoline. However, the excessively produced by-product (crude glycerin) of biodiesel plant been a threat for this development and implementation. Utilization of crude glycerin to many other valuable end products would be a viable option. The hygroscopic glycerin is well known for its versatility, renewability, and environmental value. 62

2 Comparative Study of Digestibility of Crude Glycerol in Anaerobic Digestion Anaerobic digestion is a biological process at where a biodegradable compound decomposes into biogas. If burned, this gas burn cleanly as liquefied petroleum gas (LPG). Methanol is a biofuel, which has higher heat efficiency and releases less contaminants than gasoline when burned. There are many researches are being conducted on the anaerobic digestion of crude glycerol for the production of biogas and methane [1-6]. The objective of this research is to study on the potential of crude glycerol digestibility in anaerobic digestion of cow dung and municipal solid wastes as well as to determine biogas and methanol yield. 2. Materials and Methods 2.1. Wastes and inoculum Crude glycerin used as co-substrate was obtained from a fatty alcohol production plant, Emery Oleochemicals (M) Sdn Bhd located at Telok Panglima Garang, Selangor. The crude glycerin was stored at room temperature away from heat and sunlight. The samples used in the experimental studies are municipal solid waste which are boiled rice, cornhusk and banana peels. The samples are collected at a night market at Seksyen 16, Bandar Baru Bangi, Selangor. Fresh cow manure was collected from a cow farm at Kajang, Selangor and it was stored under refrigeration at 4 C until its utilization. The cow manure was used as inoculum in this study Preparation of samples Preparation of samples was carried out in two parts that are moisture removal and reduction of particle size. All the solid waste, which are boiled rice, cornhusk and banana peels, were dried in an air oven (model Froilabo AC240, France) at 40 C for 4 days till the end moisture content is less than 10 wt.%. The samples were then grinded using electrical kitchen grinder (model MK-C300N, Japan) to reduce the particles sizes. In the experiments, the cow dung was diluted at 1:1 ratio using distilled water and stirred manually until obtain a consistent uniformity. Table 1 shows the ratio of mixtures of samples in each reactor. The crude glycerol was diluted 100 times to reduce viscosity before fed into reactors. Table 1. Composition of feedstocks in each reactor. Composition of feedstocks Experiment g Cow dung + 15g Corn husk g Cow dung + 15g Banana peels g Cow dung + 15g Boiled rice Experiment g Cow dung + 15g Corn husk + 4.5g Crude glycerin g Cow dung + 15g Banana peels + 4.5g Crude glycerin g Cow dung + 15g Boiled rice + 4.5g Crude glycerin

3 64 M. Anitha et al Reactor experiments 250 ml Erlenmeyer flask was used a lab-scale reactor for this experiment. 2 sets of experiment were conducted and the samples were prepared at respective mixing ratio as tabulated in Table 2 and were fed into each reactor. Nitrogen gas was purged into each reactor for 10 minutes before the experiment begin to form an anaerobic state. Every day each reactor was manually agitated to mix the suspended solids at the bottom of the reactors. The experiments were run at room temperature in the range of 25 to 30 o C for 28 days Analytical procedure and methods The proximate analysis of samples was done to identify total solids, volatile solids, moisture content, and ash content of the solid wastes according to National Renewable Energy Laboratory (NREL) procedures. The elemental compositions of the wastes were determined using instrument CHNS-O (model EA1112, ThermoFinnigan, Italy) by dynamic flash combustion at 1800 o C according to manufacturer s standard procedure. The Fourier Transform Infrared Spectroscopy (FTIR) (model Thermoscientific NICOLET6700, cm -1 region) testing was conducted to determine functional groups in the samples. By comparing and interpreting the spectra with known library spectra, the unknown compounds in the samples were identified. The reactors performances were monitored continuously in terms of ph, volumetric biogas yield and analyses on the digestate. ph of reactors was monitored each week and 1M of sodium hydroxide (NaOH) and 1M hydrochloric acid (HCl) was used to regulate the ph in the range of 6.5 to 7.5. The biogas produced was recorded on daily basis. For the analysis of digestate, the samples were centrifuged at 8000 rpm for 10 minutes and then the supernatants were analysed for methanol composition using analytical high-pressure liquid chromatography (HPLC) method. This was conducted on a Rezex ROA-Organic Acid H+ column run at 60 o C in water mobile phase at 0.6 ml/min. 3. Results and Discussions 3.1. Proximate analysis Table 2 displays proximate analysis results of the substrate. The total solid content of cornhusk (95 wt.%) is higher than banana peels and boiled rice. The volatile matter was the lowest on banana peels (86.3 wt.%) and the highest on cornhusk (92 wt.%). It is noted that the moisture content of banana peels was the highest (10 wt.%) followed by boiled rice (9.5 wt.%) and cornhusk (5.0 wt.%). Boiled rice showed the highest ash content (13.3 wt.%) whereas, banana peels had the lowest ash content (3.0 wt.%).

4 Comparative Study of Digestibility of Crude Glycerol in Anaerobic Digestion Samples Table 2. Proximate analysis of substrate. Total Solid (wt.%) Volatile Matter (wt.%) Moisture content (wt.%) Ash (wt.%) Corn husk Banana peels Boiled rice Elemental composition analysis Table 3 shows results from elemental compositional analysis. Carbon content was the lowest in cow dung (11.93 wt.%), however higher carbon content was observed in all other samples. Cornhusk had the highest carbon content of 41.63%. Cow dung showed the lowest carbon to nitrogen (C/N) ratio of 5.81 whereas; crude glycerin had the highest C/N ratio of This implies that, addition of substrates and crude glycerin enhances the C/N ratio in the reactor and thus supplies a source of nourishments for microorganisms during anaerobic digestion process. Table 3. Elemental composition analysis. Hydrogen, H Carbon, C Nitrogen, N C/N Samples (%) (%) (%) ratio Corn husk Banana peels Boiled rice Cow dung Crude glycerin Note: Sulphur and oxygen content not determined 3.3. Identification of functional group Table 4 displays functional group of the samples using FT-IR instrument. Based on the results, alcohol functional group was detected in crude glycerin. Carboxylic acid, amines, and alkyne group were observed to present in cornhusk, banana peels and boiled rice samples. Samples Corn husk Banana peels Boiled rice Crude glycerin Cow dung *ND=Not determined Table 4. FT-IR analysis. Functional group Amines, carboxylic acid, alkyl halide, alkyne Amines, carboxylic acid, alkyl halide, alkyne Amides, alkanes, alkenes, carboxylic acid, alkyne Amines, alcohol, aromatic, aliphatic amines, carboxylic acid, alkyl halide ND

5 66 M. Anitha et al ph variation Figure 1 shows the variation in the ph values of reactor during the experiments. The ph of reactors was adjusted in the range of at the beginning of the experiments. It is well observed in Fig. 1 that the ph fluctuates throughout the hydraulic retention time (HRT). 1M of NaOH were used to adjust the ph of the reactors to prevent inhibition of methanogenesis. Anaerobic microbes particularly, methanogens are very sensitive to the acid concentration in the digester that could inhibit the methanogenesis process. The rapid decrease in the ph value at week 2 to 3 in Fig. 1 shows the formation of volatile fatty acids (VFAs). The VFAs were then consumed by the methanogen, which increases the ph of the reactors. The optimum ph value for anaerobic digestion is in the range of 5.5 to 8.5. Fig. 1. ph values of reactors for (a) Experiment 1 (b) Experiment Biogas yield Figure 2 presents the volumetric biogas yield for experiment 1 and 2. The biogas produced from digestion was unstable and fluctuates throughout the experiment and it requires a longer duration to achieve a steady state. The cumulative biogas produced during the hydraulic retention time of 28 days was the highest on banana peels (1620mL), followed by cornhusk (880mL) and boiled rice (810mL) in Experiment 1. Similarly, in Experiment 2, banana peels recorded the highest cumulative yield of biogas, which is 700mL and followed by cornhusk (640mL) and boiled rice (620mL). In both the experiments, similar trend of biogas production can be observed in all three reactors disregard, with or without addition of crude glycerin Relationship of crude glycerin and biogas yield Figure 3 shows the comparison of biogas yield in Experiment 1 and 2. At overall, all three reactors without addition of crude glycerin in Experiment 1 produced higher quantity of biogas compared to Experiment 2 with crude glycerin. Castrillón et al. [7] stated that, thermophilic anaerobic digestion of crude glycerin enhances the production of biogas and methane gas. This indicates that anaerobic digestion of crude glycerin at room temperature quite unfavorable and lowers the process efficiency.

6 Comparative Study of Digestibility of Crude Glycerol in Anaerobic Digestion Methanol yield Figure 4 shows methanol yield for experiment 1. The methanol percentages and concentrations were determined by analytical HPLC. The methanol yield was at the highest on the first week for cornhusk (2.76 g/l) and completed diminished in the subsequent weeks. However, boiled rice showed a slight increase in the methanol yield from week 1 to week 3. Banana peels recorded only 0.06 g/l of methanol concentration and 0.16 vol.% of methanol in the 4 th week of experiment. Fig. 2. Biogas yield for (a) Experiment 1 (b) Experiment 2. Methanol yield for Experiment 2 for 4 weeks of experiment displayed on Fig. 5. Cornhusk showed a fluctuate trend in the accumulation of methanol. The highest yield of methanol was noticed on week 2, which are 1.04 vol.% and 0.51 g/l of methanol. Boiled rice produced significant amount of methanol on week 1 (0.75 vol.%, 0.66 g/l) and 4 (0.94 vol.%, 0.48 g/l). However, banana peels did not produce any methanol or the methanol produced at small quantity and it was used up by methanogen for the conversion to biogas.

7 68 M. Anitha et al. Fig. 3. Comparison of biogas yield for Experiments 1 and 2 (a) Cornhusk (b) Banana peels (c) Boiled rice. Fig. 4. Methanol yield for Experiment 1. Fig. 5. Methanol yield for Experiment Relationship between biogas and methanol yield Figures 6 and 7 show relationship between biogas production and methanol yield for cornhusk, boiled rice and banana peels for Experiment 1 and Experiment 2. From Fig. 6(a) and Fig. 7(a) for cornhusk, it can be observed that cumulative biogas yield increases per week as methanol yield decreases. This shows the accumulated methanol converted into biogas and being consumed by microbes.

8 Comparative Study of Digestibility of Crude Glycerol in Anaerobic Digestion Similar trend can be seen for boiled rice in Fig. 6(b) and Fig. 7(b). However, banana peels of Experiment 1 shows opposite trend where methanol yields slightly increases as biogas being produced, Fig. 6(c), whereas, in Experiment 2, Fig. 7(c) biogas yield increases each week without the conversion of methanol to biogas. There is other unknown conversion of compounds takes place, which produces biogas. The relationship between methanol and biogas could not be derived clearly due to the fluctuations of results for each sample. In summary, anaerobic digestion of cow dung and municipal solid wastes (Experiment 1) resulted in higher biogas and methane yield than anaerobic digestion of crude glycerin, cow dung and municipal solid wastes (Experiment 2). In Experiment 1, banana peels recorded biogas yield of 1670 ml and cornhusk had produced high methanol yield of (2.76 g/l, 6.48 vol.%). Then in Experiment 2, banana peels had produced high biogas yield (700 ml), cornhusk had produced high methanol yield of (0.51 g/l, 1.05 vol.%). Hence, banana peels and cornhusk are very potential substrates for anaerobic digestion process. Fig. 6. Comparison of biogas and methanol yield trend for (a) Corn husk (b) Boiled rice (c) Banana peels in Experiment 1. Fig. 6. Comparison of biogas and methanol yield trend for (a) Corn husk (b) Boiled rice (c) Banana Peels in Experiment 2.

9 70 M. Anitha et al. 4. Conclusion The results from this study show the potential conversion of crude glycerin to methanol and biogas via anaerobic digestion of municipal solid waste and cow dung. These wastes are abundantly available in the environment and can be utilized as a viable feedstock for anaerobic digestion process. This study revealed that anaerobic digestion of crude glycerin at room temperature resulted in lower yield of biogas and methanol compared to anaerobic digestion without crude glycerol. Although, methanol and biogas yield is lower than previously reported work, improvisation in experimental conditions will improve the yield. Acknowledgement The authors are privilege to acknowledge the financial support provided by Ministry of Education of Malaysia (MOHE) under research grant (FRGS/2/2013/TK/UKM/01/1 and Universiti Kebangsaan Malaysia for research grant (UKM-GUP ). References 1. Siles, J.A.; Martin, M.A.; Chica, A.F.; and Martin, A. (2010). Anaerobic codigestion of glycerol and wastewater derived from biodiesel manufacturing. Bioresource Technology, 101(16), Astals, S.; Nolla-Ardevol, V.; and Mata-Alvarez, J. (2012). Anaerobic codigestion of pig manure and crude glycerol at mesophilic conditions: biogas and digestate. Bioresource Technology, 110, Nuchdang, S.; and Phalakornkule, C. (2012). Anaerobic digestion of glycerol and co-digestion of glycerol and pig manure. Journal of Environmental Management, 101, Astals, S.; Nolla-Ardevol, V.; and Mata-Alvarez, J. (2013). Thermophilic codigestion of pig manure and crude glycerol: Process performance and digestate stability. Journal of Biotechnology, 166(3), Castrillón, L.; Fernandez-Nava, Y.; Ormaechea, P.; and Maranon, E. (2013). Methane production from cattle manure supplemented with crude glycerin from the biodiesel industry in CSTR and IBR. Bioresource Technology, 127, Athanasoulia, E.; Melidis, P.; and Aivasidis, A. (2014). Co-digestion of sewage sludge and crude glycerol from biodiesel production. Renewable Energy, 62, Castrillón, L.; Maranon, E.; Fernandez-Nava, Y.; Ormaechea, P.; and Quiroga, G. (2013). Thermophilic co-digestion of cattle manure and food waste supplemented with crude glycerin in induced bed reactor (IBR). Bioresource Technology, 136,