Biogas Production of Selected Animal Wastes

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1 Biogas Production of Selected Animal Wastes Abstract Anaerobic process of digesting animal wastes is traditionally used for achieving biogas for energy production. The impact of this biogas technology leads to this investigation using different animal waste treatments in order to produce useful gas for cooking in the kitchen. Carabao manure and chicken dung at different volumetric ratio were used in this study to measure the gas production of the different treatments. The mixing ratio of chicken dung to carabao manure used in the study were 100:0, 75:25, 50:50, 25:75 and 0:100 mixing of treatments within the dextrose bottle as digester. Water was 25% volume mixed to the slurry. The mixture of animal wastes produced significant volume of biogas. The carabao manure and chicken dung were determined on a weekly basis. The volume ratio of 25% chicken dung and 75% manure yield the highest biogas production during the 4th, 5th and 6th week of decomposition having value of 6,390 ml, 8,817.50ml and 10,815ml, respectively. The weekly biogas yield was influenced by carbon/nitrogen ratio and ph level affecting the decomposition stage of the wastes mixture. The ph values of the different treatments ranged from 6.32 to 7.15 and it had least effect of decomposition during initial stage. The wastes mixture had mesophilic temperature of 35 0 C. Decomposition of animal wastes inside the digester is recommended for a longer period to really ferment the wastes and to maximize gas production. Keywords: Biomass, anaerobic fermentation, decomposition, slurry mixture, biogas yield, digester 1.0 Introduction The interest in biogas technology escalated around the world because of the increasing demand for renewable energy production, the use of alternative materials and the reduction of destructive gas emitted from the use of fossil fuel. The development of anaerobic digesters for livestock manure treatment and energy production accelerated at a fast pace over the past few years. Rural small-

2 scale biogas technology is fascinating. Biogas is a gas produced by the anaerobic fermentation of organic matter or any biodegradable materials such as biomass, manure or sewage, municipal waste, green waste and energy crops (Normak and Menind, 2010). Molinuevo et al. (2008) point out that anaerobic digestion is an excellent method in reducing the foul odor of decomposing organic matter and at the same time in producing methane gas. It can be considered as a biological substitute system to other traditional methods of organic matter decomposition. Biogas technology is a biological method for degrading and stabilizing organic, biodegradable raw materials in special plants in a controlled manner through the microbial activity in oxygen-free conditions, and results in two endproducts: energy rich biogas and nutrient-rich digestion residue (Luostarinen S, Normak A and Edström M, 2011). The anaerobic digestion of organic wastes is primarily used for energy production to produce a biogas. According to Vindis et al., (2009) as cited by Chukwuma (2009), the anaerobic fermentation significantly reduces the total mass of wastes, generates solid or liquid fertilizer and yields energy. 173 There is an increasing awareness of the technology in recent years. The anaerobic digesters that can help control the disposal and odor of animal waste has stimulated renewed interest in the technology (PAES, 2003). Dairy farmers faced with increasing federal and state regulation of the wastes their animals produce are looking for ways to comply. Nowadays, new digesters are built because they effectively eliminate the environmental hazards of dairy farms and other animal feedlots. It is often the environmental reasons rather than the digester s electrical and thermal energy generation potential that motivate farmers to use digester technology. Separation of the solids during the digester process removes about 25 percent of the nutrients from manure, and the solids can be sold out of the drainage basin where nutrient loading may be a problem. In addition, the digester s ability to produce and capture methane from the manure reduces the amount of methane that otherwise would enter the atmosphere. Scientists stated that methane gas in the atmosphere is one contributor to global climate change. (Lund et al., 1996). PAES (2003) stated that people in the rural areas are raising animals for their

3 174 livelihood and for additional income purposes. 2.0 Methodology plastic hose with regulator valve in between to facilitate the flame testing of the gas that was produced inside the bottle. Carabao manure and chicken dung were used in this study. Fresh carabao manure were collected from the Auxiliary Project of the Philippine Carabao Center, Visayas State University. It was collected in the vicinity of the carabao ranch and placed in a container and then transported to the experimental site. The chicken dung was also collected at the Animal Science Auxiliary Project and then transported to the experimental site. The chicken dung and carabao manure were collected and placed in the plastic containers. Other plastic containers like basin and small empty gallons were used to mix the wastes and water and to make several treatments. Dextrose Bottles The study used the dextrose bottles for biogas fermentation (Figure 1a) and served as the digester. There were three bottles used in every set-up (see Figure 1b). Using the dextrose bottles allowed the researcher in determining the daily biogas production in volume basis (milligram). The three bottles were connected using the transparent Figure 1. Dextrose bottles for biogas production. Experimental Set-up The experimental set-up was categorically based on laboratory design using dextrose bottles and its accessories. Three bottles were used and interconnected with plastic tubing to facilitate the fermentation process. The first bottle labeled as A

4 was considered the digester or the fermentation chamber; the second bottle labeled as B is the gas collector and third one labeled as C is known as the water overflow collector. The digester was filled with slurry and water with a ratio of 75:25. The bottle was filled with 750 milligrams of slurry to make an allowance of 25 milligrams for gas chamber. Bottle B was initially filled with 500 milligrams of water and served as the gas collector or the gasholder. During the fermentation process, gas was produced at the digester and naturally escaped to the gas collector. The gas transferred to the gasholder and the amount of water displaced into the third bottle through its pressing pressure was the equivalent volume of gas produced. The digester and the gasholder were sealed and closed tightly with a rubber stopper and with the aid of a sealer so that gas could not escape. Figure 2 shows the actual experimental set-up of the digester, gas collector and the waterflow collector. This was the sample of the experimental set-up during the fermentation process of the different treatments. Experimental Design and Lay-out The experimental design and lay-out used in this study was Figure 2. Experimental set-up for biogas. 175 Complete Randomized Design (CRD) to enable randomization of the placement of the several replications of the different treatments. The assignment of the different treatments were randomly picked and placed in its corresponding assignment to see to it that the effect of different factors that may affect the biogas production were evenly distributed to all the different treatments. The readings for all the treatments were made equal to enable to qualify the presumption of homogeneity (Gomez and Gomez, 1984). There were five different treatments with 4 replications in each treatment. The placement of the different treatments was drawn by lots as it was the necessary point to consider in the real experimental setup.

5 176 Table 1. Experimental design of the different treatments of selected animal wastes. T 4 R 2 T 5 R 2 T 2 R 1 T 1 R 3 T 3 R 3 T 1 R 4 T 2 R 3 T 5 R 4 T 3 R 1 T 4 R 4 T 2 R 4 T 3 R 4 T 2 R 2 T 3 R 2 T 5 R 1 T 1 R 1 T 4 R 3 T 1 R 2 T 5 R 3 T 4 R 1 Figure 3. The complete random arrangement of the experimental set-up. Data Gathering The data gathering was done every 6 o clock in the morning and in the afternoon during the first two days. But beginning on the third day of the experiment until last day of gathering data the recording was done once a day only and it was done every 6 o clock in the afternoon because it was found out that biogas production during night time is very minimal. In recording the amount of biogas produced in a day, different treatments were quantified through the volume of water displaced to the gas collector. The water that was displaced to the overflow collector was equivalent to the gas that was produced in the digester. Once the gas collector was almost empty with water, it was refilled with water immediately in order to have enough water that can be displaced in the coming days. The gas production data were

6 177 collected instantaneously every day. Table 4 shows the data sheet where the cumulative data represented the summation of the data from the very beginning of the experiment. However, the ph level and the initial temperature of the different treatments were determined at the beginning of the experiment to identify factors that may affect the gas production. The data collection and the experiment were terminated after forty four cumulative days. test was an option to the data analysis because the numbers of observations were equal to all the different treatments. Nevertheless, Levene s Test of Equality of Error Variance was used in the analysis of the data in this experiment just to show that data of the researcher qualified the presumption of homogeneity. 3.0 Results and Discussion The Statistical Analysis For appropriate analysis of data, homogeneity test or the Levene s Test of Equality of Error Variances was done before proceeding to the proper analysis of variance of the data to evaluate whether the data is homogenous or heterogeneous It is further stated that assumption of data normality in the analysis of variance can be frequently violated but usually with minor effects. According to David C. Howell, a known Statistician, if the population distributions tend to be symmetric, or at least similarly shaped or uni-directionally skewed, the consequence of variance of heterogeneity, when sample sizes are equal, is not very serious (Gomez and Gomez, 1984). In this study, homogeneity Different raw materials will produce different amounts of biogas and methane depending on their content of carbohydrates, fats and proteins (Luostarinen et al., 2011). The biogas produced out of different treatments was quantified based on the daily production (see Table 4). The first day of biogas production was irregular because there were digesters that leaked due to pressure of gas produced as a result of the reaction of the substrates. The leaked digesters were mostly from treatments 1 and 2 having higher percentage of chicken dung which reacted easily to the heat of the sun and formed bubbles. However, the leaked bottles were sealed again for the continuity of the experiment. At the beginning, the reading of biogas production was done twice a day, 6 o clock in the morning and

7 afternoon, respectively. However, noticeably gas production during the night was very minimal, thus reading was made once a day at 6 o clock in the afternoon. The instantaneous data was recorded. The ph level of the different treatments was determined on the first day of biogas production. The ph level of the different treatments was very close to each other. Replication 2 of treatment 1 had the lowest value of about 6.32 and replication 4 of treatment 5 had the highest value of about Luostarinen et al. (2011) stated that ph affects the degradation directly through the microbes but also indirectly via the chemical equilibria of possible ammonia. However, in this experiment the ph level below 6.5 was just the value at initial time of fermentation and it could be normalized as the digestion process continues because concentration of NH4 increases due to digestion of nitrogen which normally increases the ph value of the substrates. Furthermore, the temperature of the different treatments was also determined. The mesophilic temperature 35 degree Celsius is a condition that is favorable to biogas production (Chukwuma, 2009). The climatic condition could also affect the biogas production. Sunny day favors the production of the biogas 178 compared during the night because in the gas production aspect, better gas production is achieved with higher temperature. The biogas production of the different treatments is progressive with respect to the duration of fermentation. The gas production during the first week is quite minimal compared to the preceding weeks of fermentation. The complete picture of the biogas production of the different treatments at the different weeks of fermentation is in Figure 4. Significant Differences of the Biogas Production of the Different Treatments The daily cumulative data of biogas production was summarized on a weekly basis for statistical analysis purposes. The duration of the experiment lasted for six consecutive weeks and the mean value of the replications of the different treatments were analyzed through regression and the analysis of variance. The computed P-value of weekly biogas production from week 1 to week 6 is highly significant based on the set value of 0.01 level of significance. The computed F-value on the first week of biogas production was ; the second week of the biogas

8 179 Figure 4. Graph of weekly mean increment of biogas production. production was also significant at 0.01 level but the F-value was quite smaller compared to the other because it was the week where transition was made from the acidification stage to the start of the methanization stage. At the third week and fourth week the calculated F-value increased to but its increment was quite small because it was the stage where different gases were already produced. However, the production of methane was still low. Meanwhile, on the fifth and sixth week of fermentation the computed F-value were high which are about and The significance of the result has something to do with the volume of carabao manure and chicken dung at different ratios as discussed in PAES (2003). Table 2. Analysis of variance of the weekly biogas production.

9 180 Table 3. The Duncan s Multiple Range Test on the weekly biogas production. The Increment Biogas Production of the Different Treatments On the first week of biogas production, treatment 1 had a very high mean value which was about 1,576.25ml compared to the other treatments. It was followed by treatments 3 and 2 which had 1, ml and 1, ml, respectively. Treatments 4 and 5 had lower amounts of about ml and ml, respectively, as shown in Table 3. During the second week of the experiment, the mean biogas production of all treatments increased with small increments of biogas production from the first week as shown in the graph in Figure 4. But their differences of increment was just small. The second week of fermentation was the hydrolysis and acidification stages. But still treatment 1 had the highest mean biogas production of 2, ml and had the lowest mean biogas production of ml. The mean biogas production of Treatment 4 increased to 1, ml which had the highest increment biogas production of 875 ml. Meanwhile, at the third week of biogas production there was a transition of gas produced between the different treatments. Treatment 4 had the highest mean biogas production of 2, with the mean of 4, ml. And the increment biogas production of Treatment 1 was just ml with the mean of 2, ml; this was the leading treatment during the second week. The second highest increment biogas produced was treatment 5 and 3 which had 2,210.00ml and 1,685 ml, respectively. This happened due to

10 181 the different stages of fermentation. However, at the fourth week of biogas production, treatment 3 had the highest increment biogas production of 2, ml followed by Treatments 4 and 5 which had an increment biogas production of 2, ml and 2, ml, respectively. Moreover, week 5 and week 6 had the same growth pattern of the increment of biogas production with week 4 because they were under the methanization stage. 4.0 Conclusion 5.0 References Cited Gomez KA, Gomez AA Statistical Procedures for Agricultural Research.2nd Edition.An International Rice Research Institute Book. Wiley-Interscience Publication. Canada. Luostarinen S, Normak A, Edström M Overview of Biogas Technology. Baltic Forum for Innovative Technologies for Sustainable Manure Management. WP6 Energy potentials. Based on the results of the study, the following conclusions can be drawn: a.) the weekly biogas production of the different treatments of selected animal manure differ significantly from each other due to Carbon/Nitrogen (C/N) ratio as one of the factors affecting the fermentation process of the different treatments, b.) there is significant difference of growth pattern of the weekly biogas production of the different treatments due to C/N ratio. Treatments 1 and 2 increased slowly during the process while treatments 3, 4 and 5 increases rapidly from the first week to last week of fermentation process. Molinuevo B, Garcia M, Leon C, Ecitores M Anaerobic Co-digestion of Animal Wastes (Poultry Litter and Pig Manure) with Vegetable Processing Wastes. Agricultural Technological Institute of Castilla and Leon, Finca Zamaduenas, Valladolid, Castilla and Leon, Spain. Normak A, Menind A Animal Wastes and Energy Production: Manure, Biogas, Compost. Estonian University of Life Sciences, Kreutzwaldi 1, Tartu. www. Emu.ee.

11 182 Philippine Agricultural Engineering Standards Biogas Technology: Its Technical Aspects and Importance. Enhancing the Implementation of Agriculture and Fisheries Modernization Act. Developed Standards for Year II. UP Los Baños, Bureau of Agricultural Research-Department of Agriculture. Vindis P, Mursec B, Janzekovic M, Cus F. (2009). The Impact of Mesophilic and Thermophilic Anaerobic Digestion on Biogas Production.Journal of Achievements in Materials and Manufacturing Engineering. 38 (2): Chukwuma E Comparative Study of Biogas Yield from Different Animal Waste Mixture. Faculty of Engineering. Nnamdi Azikiwe University, Awka