The Production of Biogas Using Kitchen waste

The Production of Biogas Using Kitchen waste Chemical Engineering Department Andhra University

Abstract

Kitchen waste is the best alternative for biogas production in a University level Biogas Plant. It is produced when bacteria degrade organic matter in the absence of air. Biogas contains around 55-65% of methane, 30-40% carbon dioxide. The calorific value of biogas is appreciably high around 4700 Kcal. The biogas yields have been determined using batch anaerobic thermophilic digestion tests for a period of 90 days. Characteristic oscillation was observed in the rate of methane production, which may be due to the presence of methylotroph population in the activated sludge, which uses methane as a carbon source for their growth. The total biogas generated in the system over the experimental period was the sum of methane and carbon dioxide. The anaerobic digestion of kitchen waste produces biogas, a valuable energy resource Anaerobic digestion is a microbial process for production of biogas, which consist of Primarily methane (CH4) & carbon dioxide (CO2). Biogas can be used as energy source and also for numerous purposes. But, any possible applications requires knowledge & information about the composition and quantity of constituents in the biogas produced. The continuously-fed digester requires addition of sodium hydroxide (NaOH) to maintain the alkalinity and pH to 7. For this reactor we have prepared our Inoculum than we installed batch reactors, to which inoculum of previous cow dung slurry along with the kitchen waste was added to develop our own Inoculum. A combination of these mixed inoculum was used for biogas production at 37°C in laboratory(small scale) reactor.

KEYWORDS: Biogas; Kitchen waste; Anaerobic digestion, fermentation

INTRODUCTION

Due to scarcity of petroleum and coal it threatens supply of fuel throughout the world also problem of their combustion leds to research in different corners to get access the new sources of energy, like renewable energy resources. Solar energy, wind energy, different thermal and hydro sources of energy, biogas are all renewable energy resources. But, biogas is distinct from other renewable energies because of its characteristics of using, controlling and collecting organic wastes and at the same time producing fertilizer and water for use in agricultural irrigation. Biogas does not have any geographical limitations nor does it requires advanced technology for producing energy, also it is very simple to use and apply.

Anaerobic digesters also function as a waste disposal system, particularly for human waste, and can, therefore, prevent potential sources of environmental contamination and the spread of pathogens. The biogas technology is particularly valuable in agricultural residual treatment of animal excrement and kitchen residual. The anaerobic reactor has a chamber where various chemical and microbiology reactions take place; it should be air and water tight. In recent year varied modifications technological have been introduced to diminish the costs for the biogas production. Methods have been developed to increase the speed of fermentation for the bacteria gas producers, the reduction of the size of the digester, the use of materials for their production but durable, the modification of the feeding materials to ferment and the exit of the effluent for their best employment, as well as compacter the equipment to produce gas in the small housings, among others. The equipment employed in housings was developed with success

PRINCIPLES FOR PRODUCTION OF BIOGAS

Organic substances exist in wide variety from living beings to dead organisms . Organic matters are composed of Carbon (C), combined with elements such as Hydrogen (H), Oxygen (O), Nitrogen (N), Sulphur (S) to form variety of organic compounds such as carbohydrates, proteins & lipids. In nature MOs (microorganisms), through digestion process breaks the complex carbon into smaller substances. There are 2 types of digestion process : · Aerobic digestion. · Anaerobic digestion. 15 The digestion process occurring in presence of Oxygen is called Aerobic digestion and produces mixtures of gases having carbon dioxide (CO2), one of the main “green houses” responsible for global warming. The digestion process occurring without (absence) oxygen is called Anaerobic digestion which generates mixtures of gases. The gas produced which is mainly methane produces 5200-5800 KJ/m3 which when burned at normal room temperature and presents a viable environmentally friendly energy source to replace fossil fuels (non-renewable).

EXPERIMENT 1.

- A 2 liter bottle
- 50 gm kitchen waste + cow dung
- Rest water (1.5 liter)

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Result - Gas production was found but not measured.

EXPERIMENT 2.

Different sets of 1 liter & 2 liters bottles.

3 different sets with different composition are installed as below.

1. 200gm cow dung was mixed with water to make 1lit slurry which is poured in 1lit bottle.
2. 50gm grinded kitchen was mixed with 150gm cow dung and water is added to make 1lit solution which is poured in 1lit bottle.
3. 400gm cow dung was mixed with water to make 2lit slurry which is poured in 2lit bottle.

RESULTS:

In all of the 3 sets gas production occurs and gas burned with blue flame. process continues, volatile fatty acids(VFA) are produced which causes the decrease in PH of solution.

COMPOSITION OF KITCHEN WASTE OF ANDHRA UNIVERSITY

Average composition of kitchen waste was analyzed on various occasions. Over 50 % of waste was composed of uncooked vegetable & fruit waste. Eggs, raw meat, the main source of pathogens were relatively low in mass at 1.5% & 1.2% also about 15% of cooked meat was there.

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Fig. 2 Composition of kitchen waste

(A) Uncooked fruits & vegetables
(B) Cooked meat
(C) Uncooked meat
(D) Bread
(E) Teabags
(F) Eggs
(G) Cheese
(H) Paper

DISCUSSIONS :

From the result it has been seen that in set2 which contain kitchen waste produces more gas, compare to other two set. In set2 with kitchen waste produces average 250.69% more gas than set 1 (with 200gm cow dung) and 67.5% more gas than set 3 (with 400gm cow dung). Means kitchen waste produces more gas than cow dung as kitchen waste contains more nutrient than dung. So use of kitchen waste provide more efficient method of biogas production.

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From results it has been seen that pH reduces as the process going on as the bacteria produces fatty acids. Here methanogens bacteria which utilize the fatty acids, is slow reaction compare to other so it is rate limiting step in reaction. In set2 which contains kitchen waste pH decreases highly means reaction is fast, means hydrolysis and acid genesis reaction is fast as organism utilize the waste more speedily than dung. And total solid decreases more in set2.

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