Lakshmi C. Associate Professor, Civil Engineering Department, SJBIT
ABSTRACT
Energy is one of the most important factors for human development and to global prosperity. Present study deals with recovery of energy from anaerobically digested biomass resources such as cattle dung and hostel kitchen organic waste. In this regard anaerobic digester at lab level is fabricated to utilize the institute canteen waste for producing the biogas. Biogas production is a Clean, low carbon technology, useful for the efficient management and conversion of organic waste into clean renewable biogas and organic manure/fertilizers. It will give extensive knowledge of Design aspects of Biogas reactor and maintenance of reactor during the process. It has the potential for leveraging sustain-able livelihood development as well as tackling local and global land, air and water pollution. Also decomposed slurry/waste used as manure for gardening purpose. The amount of methane present in biogas is found to be 65%.To segregate methane from other gases such as H2S and Co2 purification by lime treatment is adopted. Further from the experimental work it was observed that bio methane is best alternative compared to LPG in respect of calorific value biogas and emission study. The present work will be worthy for academicians and people dealing with bio-energy, environmental pollution.
Key words : Anaerobic digestion, biomass.
INTRODUCTION
Improper solid waste management leads to substantial negative environmental impacts for example, pollution of air, soil and water, and gene- ration of greenhouse gases from landfills, and health and safety problems due to diseases spread by insects and rodents attracted by garbage heaps, and diseases associated with different forms of pollution. Municipal authorities charged with responsibility of providing municipal solid waste management services have found it increasingly difficult to play this role. The difficulty has been aggravated by lack of effective legislation, inade- quate funds, and services, and inability of municipal authorities to provide the services cost-efficiently. The upshot is that an increasing proportion of
because organic carbon can serve both as a source of energy and cell carbon, more carbon is required than for Eg. Nitrogen.
Activity has essentially ceased as a humus material commonly known as compost.
This paper was presented in the National Seminar on "Swatchh Bharat Drive for Solid Waste Management" held at Bangalore on 23rd September 2016
urban dwellers in developing countries, particularly the urban poor, will lack access to municipal solid waste management services and, consequently, suffer from pollution-related environmental and health problems. Fortunately, there are ways of dealing with or, at least, minimizing this problem.
MATERIALS ANDMETHODOLOGY
Solid waste management is the discipline associated with the control of generation, storage, collection, transfer and transport, processing and disposal of solid waste in a manner in accordance with best principles of public health, economics, engineering, conservation, aesthetics and other environmental considerations that is also responsive to public attitudes. This study also includes administrative, financial, legal, planning, and engineering functions involved in solution to all problems of solid waste. All the waste from human and animal activity that are normally solids and that are discarded as useless or unwanted. It refers to heterogeneous mass throw away from the urban community as well as the more homogeneous accumulation of agriculture, industrial and mineral waste. Some other common terms applied to solid waste are refuges, garbage and rubbish. The term refuse and solid waste are used more or less unanimously although the later term is preferred.
Aerobic Composting Microbiology
Fusing the aerobic composting process a succession of facultative and obligate aerobic micro organisms is active. In the beginning shares of composting rite, thermophilic bacteria predominate leading to thermophilic fungi, which appear after 5-10 days. In the final stages or caring period as it is sometimes known actinomycetes and molds appear because significant concentration of their micro-organisms may not be present. Critical parameters in the control of aerobic composting process include moisture content, C/N ratio, and temperature for most biodegradable organic waste once the moisture content is brought to a suitable level (50 to 60%) and the mass aerated microbial metabolism speeds up. The aerobic micro organic matter develop bell tissue from nitrogen, phos- phorus, some of the carbon and the other required nutrients. Much of carbon serves as a source of energy for the organisms and is burnt up and respired as CO
2
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Lakshmi C.
Aerobic Deposition Technology
Anaerobic composition is the putrefactive breakdown of the organic matter by reduction the absence of oxygen, leading to the production of methane (CH4) and carbon dioxide (CO2).In recent years there has been a great interest in applying the anaerobic digestion process for the processing of the organic fraction of MSW because of opportunity to recover the methane and the fact that digested material is similar to compost produce aerobically.
PROCESS DESCRIPTION
There are 3 basic steps involved in the process of producing the methane from organic fraction of MSW. The first step involves the preparation of organic fraction of the MSW. It also receives sorting and preparation and size reduction at the source level. The second step involves the addition of moisture and nutrients blending pH adjustment to about 6.8 and maintain a temperature of 550C. The anaerobic digestion is carried out in continuous flow reactor so that the contents are mixed completely. In the third step the mixed content after digestion as it out flow from the reactor it as to be reintroduce so that the microbial activity is kept continuously in progress.
PROCESS MICROBIOLOGY:
In the anaerobic composting of wastes, a number of anaerobic organisms work together to bring about the conversion of organic portion of the wastes to a stable end product. In anaerobic fermentation, the formation of methane takes place by. 1. The conversion of methane and water.
The picture below shows different types of food waste introduced into the pilot
CO
2
and hydrogen to
2. The conversion of formate and acetate to
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Proteins Amino acids Lipids + O2+ Carbohydrates Nutrients Cellulose + Microorganisms ⎯→
Compost + New cells (Facultative and obligate aerobic thermophilic
⏐ ↓ Lignin Dead cells+
Ash CO2+
methane, carbon dioxide and water The methanogens and acidogens form a syntrophic (mutually beneficial) relationship in which the methanogens convert fermentation end products such as hydrogen, formate and acetate to methane and carbon dioxide and water.The methanogens are able to utilize the hydrogen produced by acidogens. The utilisation of hydrogen, produced by the acidogens and other anaerobes by the methanogens is termed as interspecies hydrogen transfer. In effect the methanogenic bacteria remove compounds that would inhibit the growth of acidogens.
Anaerobic transformation of solid waste can be described Organic matter New cell + + resistant by H
2
O + following Nutrients equation.
→ + Organic Matter + CO
2
+ CH
4
+ NH
3
+ H
2
S + Heat
METHODOLOGY; Aerobic Decomposition
For the purpose of aerobic composting a tank of dimension 3x.75x.5 m was constructed. The volume of the tank is 1.125m3. The materials used for constructing the tank were solid blocks, rapid hardening cement, fine aggregates and weather proof course. The tank was provided with the required slope in order to collect the leachate from one end of the tank. The pilot model built was cured for the required period and then the waste was introduced. For the purpose of composting a part of the total waste was chosen amounting to 280kgs. This was segregated from the starchy foods like roties, chapaties as also, oils, fats, meat, and bones. The food waste included for composting were only vegetable peals fruits green vegetables and also cooked food like rice grams and cereals.
Since the model was built next to sewage treatment plant, there was a constant production of slurry from the plant. The slurry obtained was collected and dried. The food waste of 50 kgs was introduced into the tank uniformly spread across the length and breadth of the tank every day. The dried slurry of 10 Kgs was laid over the food waste and 2 such layers were prepared every day. The moisture content of the food waste was determined before introducing into the tank. Test on moisture content were conducted and the moisture content was found to be 61 percent when the food was introduced into the tank. After introducing food waste temperature was recorded. The temperature varied between 35 degrees to 40 degrees. This was created by the windrows. Turning used to be done once in a week. The process was carried for 3 weeks with food waste introducing 50 Kgs each day 4 times.
There was a rapid rise in the temperature in the initial stages due to the biological activity. The temperature variation due to aeration system was recorded upto 5 degrees in two weeks .Temperature started falling as the biodegradable organic carbon is decreased. The lechate collected during the process was as little as one litre .This was reintroduced into waste water treatment plant.
Parameters Values (mg/L)
This study
1st 2nd 3rd 4th Sample Sample Sample Sample
Average pH 4.42 4.24 4.66 4.68
Volume reduction with time Time (weeks) Volume reduced (Litres approx)
1 500
2 380
3 295
4 180
5 110
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1st Test Sample
PROCESS OF DECOMPOSITION
It was noticed that several microorganisms had developed in the tank for bringing out the decomposition of food waste into organic matter.
Screening
In the process of screening 350 micron sieve was used to carry out screening. By screening the large lumps of organic matter could be broken into a fine medium. The product resulted out of the process is in the form of coarse grain powder having large surface area with different particle sizes. Decrease in size of the particle indicates the size reduction.
Compost
The compost obtained is of total quantity of 110 kgs. This serves as a fertilizer and also as manure for the greeneries distributed across the campus. The compost obtained out of the food waste when tested for its nutrient values was found to include carbon, nitrogen, phosphorous,potassium and results are tabulated.
Parametres Values
pH (1:5) 6.43
EC (1:100) 0.86
N (%) 0.77
P (%) 0.45
K (%) 0.41
ANAEROBIC DECOMPOSITION
Anaerobic decomposition of organic matter is brought about by putrefactive bacteria. These organisms will make use of nitrogen, phosphorous and other nutrients to live and to develop cell protoplasm, and they reduce the organic nitrogen to organic acids and ammonia. The carbon from the organic compounds which is not utilized in the cell protein is liberated mainly in the reduced form of
Lakshmi C.
The Picture below shows the final product as fertilizer or manure produced out of the food waste generated from the college canteens
methane. A small portion of carbon maybe respired as carbon di-oxide.
For anaerobic decomposition a pilot digester was fabricated out of mild steel. The digester is of floating type which does not allow the atmospheric air to interact within the food particles introduced to the outer cylinder.
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Anaerobic Digester.
Compressor
Lakshmi C.
ANAEROBIC DIGESTION IN DIGESTER
The material chosen for fabricating the equipment was mild steel. This model includes several parts to be welded and screwed.(Such as introducing inlets and outlets separately into the system). The model was painted with primer coating of 1mm in order to avoid rusting. In order to make sure that the model was leak proof, it was completely filled with water and let for 48 hours noting the initial height of the inner cylinder on the central pipe. After 48 hours it was noted that there was no drop in the rise of the inner cylinder. This ensured us that the tank was leak proof for water or air. Introduction of Food Waste and Slurry: In order to initiate the microbial activity in the food waste, cow dung was introduced in to the outer cylinder by mixing it with water on a proportion of 1:2. All the food waste which was collected from all the canteens of the campus was found to be of larger amount for which the pilot model was not sufficient to accommodate. Hence only 4 kg of food waste was introduced initially.since the inlet of the model was restricted by size. Either food particles below 30 mm sizes or by reducing the size to 30mm were introduced. The food waste mainly consisted of vegetable and fruit peel and cooked food excluding other hard food. The food waste was added for 5 days continuously. During each days process the introduced food consisting of carbohydrates, fats and proteins was getting converted into sugars, fatty acids, amino acids in the process of hydrolysis. In converting these acids into carbonic acids, alcohols, hydrogen, carbon dioxide and ammonia, acedogens or acid formers play a vital role. A third group of microorganisms known as methane formers convert the hydrogen, acetic acid and the carbon dioxide into methane gas and co2. These bacteria are strictly anaerobic and are responsible for conversion. The food waste was slowly increased by quantity up to 8 kgs in due course of 15 days. With the rise in the inner cylinder over the central pipe it
was noticed that the biogas was collected within the inner cylinder. Since the decomposed food waste rises to the top it covers the daily introduced food at the bottom of the tank.
The biogas consisted of methane, carbon dioxide and other gases quantity of gas obtained, mainly it was when H
2
S. tested In the total found to be consisting of 65 – 70 percent methane. The volume of gas produced was found to be 0.5 to 0.75m3 per kg of volatile solids destroyed. The pressure of this gas produced within the inner cylinder when measured was determined to be about 5- 7 kg per cm2.
As the pressure which was delivered by the pilot model was not sufficient enough for the gas to be utilized in various applications, the gas needed to be compressed in order to develop a better pressure. A manually operated pressure pump was designed and fabricated in order to compress the gas. The pump so designed has an inlet,an outlet& a well fabricated enclosed cylinder with a piston. A lever had to be used for pumping the gas. The compressor had a capacity of 0.150ft3 for every cycle (to and fro movement of lever). The pilot model delivered a pressure of 5-7kg/cm2 where as when the gas had been compressed into a gas cylinder a pressure of about 15 kg/cm2 was obtained.
RESULTS
The compost and the biogas produced out of the food waste generated from the college messes and the canteens have various applications. The compost produced out of the waste will be used as manure for the greeneries in and around the campus. As the compost consists of good nutrients it finds the use as fertilizer for plants. This reduces the cost of chemical fertilizer used to maintain the flora around the college campus. The process is environmental friendly by reducing the cost on transport, labor and saves the land nutrition.
Biogasification
The biogas was utilized in uncompressed and compressed form and found to have many applica- tions which could be used for different applications in the campus.
Uncompressed Gas
This gas can be used to burn mantel lamp. An attempt was made to burn a lamp over 2 hours spending 10 cubic ft.
The same uncompressed gas was tested for flame by burning the Bunsen burner. The blue flame indicated the presence of methane.
Compressed Gas
The gas was compressed mechanically using a
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crude compressor designed for this project. The compressed gas when filled into the commercial cylinder finds its applications in cooking. The biogas was compressed to a pressure of 15 kg per cm2 into a commercial cylinder and was connected to the canteen gas pipeline for cooking food.
The gas was compressed mechanically using a crude compressor designed for this project. The compressed gas when filled into the commercial cylinder finds its applications in cooking. The biogas was compressed to a pressure of 15 kg per cm2 into a commercial cylinder and was connected to the canteen gas pipeline for cooking food.
The gas demand can also be defined using the daily cooking times. The gas consumption per person and meal lies between 150 and 300 litres biogas. For 1 litre of water to be cooked 30-40 litres of biogas, for half kg rice 120 – 140 litres of gas are required.
Biogas Lamps
The compressed gas has an application in illuminating mantle lamps. The bright light of a mantel lamp is the result of incandescence. The intense heat induced luminosity of special metals, so called rare earth like thorium, cerium are 1000 – 2000 centigrade. The light output is comparable with normal 40 watt bulb. One lamp consumes 120 – 150 litres biogas per day.
Automobiles
The compressed gas can be used for running automobiles for commuting within the campus. To demonstrate this, the gas was compressed into a commercial cylinder and when connected to automobile like the auto rickshaw with slight changes in the combustion engine was found to be useful in commuting short distances within the campus.
Biogas-fueled Gen Set
If the output of a biogas system is to be used for fueling engines, the plant must produce at least 10 m3 biogas per day. For example, to generate 1 KWH electricity with a generator, about 1m3 biogas is required. Small-scale systems are therefore unsuitable as energy suppliers for engines.
CONCLUSIONS
The institution is spread over an area of 29 acres and houses about 4 canteens including a student's mess. The college produces on an average 550Kgs of food waste every day. This waste can be used as the input to the system. The system generates bio-gas using anaerobic decomposition
and organic compost using aerobic decomposition. A separate compression unit also has been developed for compressing the bio-gas generated. The system is one of the very few attempts to use food waste as input. The pilot bio-gas plant can take an input of about 500 liters of food waste while the composting plant can take an input of about 1000 liters of food waste. The results obtained included: ➢ Production of 110 kilos of compost using food
waste of about 270 kilos ➢ Generation of about 3 cubic meters of gas for
an input of 200 kilos of food waste The applications demonstrated by the pilot are: ➢ Use of the bio-gas generated for cooking food
in the canteen ➢ Illumination of mantel lamps ➢ Running of an automobile using compressed
gas The canteen produces about 500 kilos of food waste every day comprising vegetable peels and cooked food. The system when implemented in a larger scale would provide the following benefits:
Generation of Compost ➢ Meet the gardening requirements in the
campus ➢ Saving of money on transport, labour, ➢ Stop ill-effects of disposing unprocessed food
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waste directly to the environment. Ill-effects include health hazards, foul smell, generation of leachate gases, etc.
REFERENCES 1. J. Walter Fitts& Jerry B. Fitts, "Under- standing Composting", ISBN: 0-86619-207- 7[C] 1984. 2. Experimental Studies of Anaerobic Digestion of Organic Fraction of Municipal Solid Waste Using a Bioreactor with Integral Flow Features1Charles N. Agulanna, 1Goddy N. Onuoha, 2Emmanuel E. Anyanwu,1Projects Development Institute (PRODA) Enugu,PMB 01609, Enugu State, Nigeria2Federal University of Technology 3. Characteristics of municipal solid waste and a proposed management plan for Kharagpur, West Bengal, India. Resource conservation and Recycling 5, pp 166-174, 2009. 4. R.M.Espinosaet. al., Integrated urban solid waste management programme in Mexican University. Waste Management, 28, pp 527- 532, 2008. 5. Veronica Ebot Manga et. al., Waste management in Cameroon – A new policy perspective. Resource conservation and Recycling. 52, pp 592-600, 2008
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