Analysis of the various process conditions for the production of biogas (bio-methanation)from mango peel, papaya peel and banana peel were done. Based on the analysis the process conditions were varied accordingly and the comparative study of biogas production from mangopeel, papaya peel and banana peel in terms of pH, inoculum to substrate ratio and temperature was carried out.
The major problem in the bio-methanation process was blockage and scum formation. Temperature and pH fluctuations also affect the production of biogas. High temperature(55ͦ C) causes accumulation of fatty acids which affects the process stability and influences the pH ( Nagamany and K Ramasamy, Biogas production technology: An Indian perspective). If cow dung is used as the inoculum the stability of the digester is monitored. The pH at 5 the population of microbes is lowered and the activity is reduced ( Sahota and Ajit Singh).The ratios of cow dung to peels (1:2, 1:5, 1:10) were used in different setups and the production of biogas was observed. Peels of various fruits were used in the same ratio and their production rate was measured.The C/N ratio varies for different peels and was adjusted by addition of nitrogen sources for optimization of production .
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The measurement of volume of biogas produced was done using the downward displacement technique of water. Different parameters that were considered to affect the rate of production were observed for different setups. The comparison of production from different peels aims at identifying the ideal raw material source and the optimization of the process parameters for the maximum production of the gas.
Keywords: Bio-methanation, process parameters, process stability, downward displacement of water
Introduction
The realization that the existing fuel resources are getting exhausted faster than expected and with the current developmental activities being at its high ,the situation demands more conservative action. The demand for the conventional fuel is on an all-time high and the demand can be controlled using alternative fuel sources. The extensive use of conventional sources over all these years has led to degradation in the environment. Since the global climatic stability is at stake the usage of renewable and cleaner fuel sources is being recommended. The usage of renewable fuel sources helps to conserve the existing conventional fuel and protect the environment.
Renewable sources can be direct (such as solar energy) and indirect (such as biomass): energy of the wood and the other biomass obtained from plants has solar energy fixed by the process of photosynthesis (Chang, 2003). Anaerobic digestion is a process of biodegradation which uses bacteria to convert biomass into energy. Energy is in the form of biogas which is a mixture of methane and carbon dioxide which is used for generation of power.
Fruit peels are biodegradable in nature and are a potential source for the production of biogas. The fruit peels mainly consist of cellulose, reducing sugar, non-reducing sugar, moisture etc these acts as a source of carbon and energy for the microorganism’s taking part in the bioconversion and by enzymatic hydrolysis converts the polymeric components of the peels into monomers. The monomers are converted to soluble organic acids mainly acetic acid, (methanogenic bacteria) converts it to methane and carbon-dioxide and various by products.
Maishanu and Seekimpi (1988) and Anonymous(1992) observed that microbes require neutral or mild alkaline condition for optimal biogas production. Various parameters such as pH, ratio of substrate: inoculum , temperature affects the production.
Materials and Methods
The peels of mango, papaya and banana were collected from VIT, were cut into smaller fragments and dried. The moisture content of the various peels was determined by standard method. The peels were grinded, the pulp was prepared and the slurry was prepared in the ratio in accordance to the respective moisture content of the peels. Sieve was done to obtain desired particle size and stored at room temperature.
2litre anaerobic bio-reactor was used to perform the experiment.
BMP Test
Lab Digester: Experiment was performed in 2 litre anaerobic bioreactor capped with rubber stoppers. Nine reactors were set up and each one was seeded with 20ml of inoculum. For each reactor different cow-dung to peel ratio of (1:2, 1:5, 1:10) were added. The pH was maintained by using alkali. Based on the C/N weight ratio of the peel urea was added to optimize the microbial activity. Nutrients (FeCl3 – 1g) were added for optimum growth of microbes. Water was added to the reactors after addition of substrates.
Reactors were kept at 33-37ͦC under incubation and the production of gas in each reactor was measured by water displacement method.
Analysis
The moisture content of the peels, solid content, volatile content and pH were determined by Standard method.
Total volume of gas production from various peels was measured at fixed time in each day by water displacement method.
Result and Discussion
Improper preparation of solids leads to blockage and scum formation: proper milling and dilution ratio of solid is necessary to prevent scum formation and stratification.
The C/N ratio (i.e. carbon and nitrogen sources for micro-organisms) should be 25-30:1and the loading rate is varied based on it.
The gas production depends on the pH, as a pH of 5 reduced the bacterial population and the activity. Optimum pH for methanogenic microbes was slightly acidic (7-7.2 range). pH can be maintained by removing the carbon-dioxide produced during methanation.
Higher temperature increased production but the process becomesunstable due to accumulation of fatty acids. Concentration of the volatile fatty acid in terms of acetic acid should not exceed 2000-3000 mg/l.
Stability of the digester depends on carbon-dioxide reduction (either by microbes or artificially) and the accumulation of hydrogen takes place due to the higher production rate of hydrogen than carbon-dioxide reduction rate, it inhibits methanogenesis.
Retention time of slurry depends on the dilution ratio, loading rate and digestion temperature.
Carbon-dioxide reduces the calorific value of biogas produced hence the gas is passed through lime water to remove carbon-dioxide.
Table 1. Various parameters and biogas production rate
Sno:
Fruit peel used for production
Ratio of inoculum to substrate
Loading rate of the substrate
Volume of flammable gas (stp) in litre.
Flammable gas production rate (litre/day).
1.
Mango
1:2
1:5
1:10
2.
Papaya
1:2
1:5
1:10
3.
Banana
1:2
1:5
1:10
Conclusion
The analysis of the production rate of biogas from three different fruit peels (mango, papaya, and banana) was done. The process conditions that affect the production of biogas in bioreactor were analysed.
The effect of parameters such as pH, temperature, inoculum to substrate ratio, slurry ratio was studied and the problems that occur due to the fluctuation of these parameters during the process of bio-methanation were identified.
The solutions for these problems were identified and the implementation of optimized process conditionsand the production rate of biogas from various fruit peels are to be measured and compared.
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