Experimental Investigation of Biogas Production from

Experimental Investigation of Biogas Production from Food Waste and Analysis for the Waste Energy Recovery and Utilization from Institutions of State of Tamil Nadu in India G. Ramesh

D. Palaniswamy, M.R. Veerendran, S. Vignesh 2 i 3 Kumar , D. Vinoth and R. Deepak Raj

Department of Mechanical Engineering, Srikrishna

Department of Mechanical Engineering, Adithya Institute of

Engineering College, Coimbatore, Tamil Nadu, India

Technology, Coimbatore, Tamil Nadu, India l E-mail: [email protected]; [email protected]; 2 3 [email protected]; [email protected]

Abstract-Biogas refers to a gas made from anaerobic digestion of kitchen waste. Methane is a clean energy one of the constituent of biogas which has a great potential to be an alternative fuel. Abundant biomass from various institutions could be a source for Methane production where combination of waste treatment and energy production would be an advantage. In state of Tamil Nadu around of 2944 educational institutions are there, from those institutions a large amount of waste is produced but those waste are not utilized. Objective of this study is to utilize the kitchen waste in an bio digester to produce biogas which will be the alternative fuel for their kitchen energy need. This work was carried out to produce biogas in a Compact Water Plastic Tank with a fIXed type, using different kitchen waste from the kitchen, hostel, and canteen in Adithya Institute of Technology. It was realized through the Observation and Experimental Test using 5 liter bottles, the gas produced within 21 days. In the experimental pilot and scale up tank, the formula was fermented and the 5 different types of digesters were tested. If this system is implemented in all institutions of state of Tamil Nadu the energy that can be recovered is discussed.

running out of space [2]. Montreal, Canada, has a contract to send 1.3 million tonnes of waste each year to a landfill located 40 km away with permits that extend only to 2012 [3]. In 2006, nearly a million tonnes of the waste generated in Toronto, Canada, was trucked to landfills across the U.S. border into Michigan. As a solution, the City of Toronto has purchased a landfill site that is over 200 km away from the downtown area that opened January, 2011 [4]. Mexico City produces 12,500 tonnes of trash per day and sends it to a sprawling, polluted landfill that is running out of space [5]. As of 2011, two thirds of China's cities are overrun with garbage and millions of tonnes of waste are sent to non­ sanitary landfills with one quarter of cities having no place to dispose of trash [6]. There is no simple solution to this waste problem. This is a pressing global issue that requires design and consumption paradigm shifts as well as new waste management solutions.

B. Energy Recovered from Waste Management Biogas is about 20% lighter than air and has an ignition temperature in the range of 650°C to 750°C. It is an

Keywords: Food Waste, Bacteria, Anaerobic Digestion,

odorless and colorless gas that burns with clear blue flame

Fermentation, Energy Recovery, Biogas.

similar to that of LPG gas. Its calorific value is 20 Mega Joules (MJ)-m when methane content ranges from 60 to 70%[7].

I. INTRODUCTION

Biogas refers to a gas made from anaerobic digestion of agricultural and animal through synergistic

A. The Problem with Landfills The waste generated by this increasing urbanization of humans and industries will have to be sorted and processed. The most common waste management solution is land filling. The main problem with this is that landfills around the world are running out of space. The last landfill in the greater New York City area closed in 2001 and now 12,500 tonnes of garbage are transported daily outside the state by truck, barge, and train [1]. London currently sends 20 million tonnes of annual waste to 18 different landfills that are 978-1-4673-4603-0/12/$31.00 ©20121EEE

dung, human

sewage

[8], [9],

metabolic activities of consortia of

hydrolytic, acetogenic and methanogenic bacteria on organic materials [10]. The gas is a mixture of methane (CH) 60-70%, carbon dioxide 30-40%; hydrogen 5-10%, nitrogen 1-2%, hydrogen

sulphide

(trace),

water

vapor

0.3%.

Biogas

systems also provide a residue of organic waste, after anaerobic digestion that has superior nutrient qualities over the usual organic fertilizer, cattle dung, as it is in the fonn of ammonia. The biogas technology is particularly valuable in agricultural residual and kitchen residual. Anaerobic digesters also function as a waste disposal system, particularly for

Proceedings of7'h International Conference onIntelligent Systems and Control (ISCO 2013)

518

kitchen waste, and can, therefore, prevent potential sources

anaerobic bacteria are the most common class of bacteria

of environmental contamination and the spread of pathogens

that produced methane, mesophilically or thermophilically

[11]. The anaerobic reactor has a chamber where various

within pH 4-7. However, a few facultative bacteria have

chemical and microbiology reactions take place; it should

been identified as methane producers when the hydrogenase

be air tight. In recent year various modifications have been

enzyme was found in these bacteria. Even though the

introduced to reduce the costs for the biogas production.

production rate of methane was lower than in strictly

Methods have been developed to increase the speed of

anaerobic bacteria, the issue of sensitivity to oxygen did not

fermentation for the bacteria gas producers, the reduction of

raised here. Recently, methane production was found to be

the size of the digester, the use of materials for their

possible by aerobic bacteria.

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 [12]. In countries like UK and Australia particular temperature has to be maintained by external source but here Tamil Nadu our atmospheric temperature is suitable for production of biogas without any external source. A substrate of kitchen waste with cow manure was used to achieve a yield increase of 44% [13]. The co-digestion of fruit and vegetable wastes, cattle slurry and chicken manure or sewage sludge for biogas production have also been tried [14], [15].

To date, most of the research on methane production involved anaerobic bacteria due to its high production rate and the ability to use a wide range of carbohydrates. Clostridium sp. is a typical acid and methane producer which ferments carbohydrate to acetate, butyrate, carbon dioxide and organic solvent. Clostridium butyricum [16], Clostridium acetobutyricum [17], Clostridium beijerinckii [17], C. thermolacticum [18], C. saccharoperbutylacetonicum [19], Clostridium tyrobutyricum [20], C. thermocellum [21] and

Clostridium

paraputrificum

[22]

are

examples

of

anaerobic and spore forming methane producer.

C. Food Waste Available for Anaerobic Digestion

II. MECHANISM OF BIO DIGESTION

A study of global food waste published in 2011 by the Food

A. Anaerobic Digestion

and Agriculture Organization of the UN found that roughly

Biogas technology is concerned to micro organism. These

year goes to waste totaling 1.3 billion tonnes [23]. This

are living creatures which are microscopic in size and are in visible to unaided eyes. They are called bacteria, fungi, virus etc. Bacteria can be dividing into two major groups based on their oxygen requirement. Those which grow in the presence of oxygen are called aerobic while the other grow in the absence of gaseous oxygen are called anaerobic. When organic matter undergoes fermentation (process of chemical change in organic matter brought about by living organisms) through anaerobic digestion, gas is generated. This gas is known as Biogas. Biogas is generated through Fermentation or bio digestion of various waste is by a variety of anaerobic and facultative- organisms. Facultative bacteria are capable of growing both in presence and absence of air or oxygen. Aerobic and anaerobic fermentation can be used to decompose

one third of all food produced for human consumption each waste is distributed fairly evenly between developing and industrialized nations with 40% of the food waste in the developing nations occurring in the production and processing phases of consumption while in the industrialized nations, 40%

occurs

at

the

retail

and

consumer

levels

of

consumption [23]. Applying anaerobic digestion (AD) to this amount of food waste has the potential to generate 367 m3 of biogas per dry tonne at about 65% methane [24] with an energy content of 6.25 kWh/m3 of biogas [25] yielding 894 TWh annually. This represents almost 5% of the total global electrical energy utilization of 20,181 TWh in 2008 [26]. In addition, where anaerobic digestion technology is applied, food waste would not be sent to landfills reducing transportation costs and greenhouse gas emissions.

organic matter. Normally the aerobic fermentation produces Co2, NH3 and small amount of the other gases along with the decomposed mess and evolution of heat. Anaerobic fermentation produces CO2, CH4, H2 and trace of other gases

along

with

the

decomposed

mass.

Aerobic

fermentation is used when the main aim is to render the material hygienic and to recover the plant nutrients for the reuse in the fields. The residue is rich in C2, N2, P, K and other nutrients. In biogas plants the main aim is to produce the Methane and hence the anaerobic digestion is used.

B. Bacteria Involved There are numerous types of microorganisms that are found to produce methane during anaerobic condition. Strictly

D. Temperature Effect The optimal temperature ranges are the mesophilic, namely 30°C to 38°C, and the thermophilic 44°C to 57°C [27], respectively. The rate of decomposition and gas production is sensitive to temperature, and, in general, the process becomes more rapid at high temperatures [28]. Despite this 'thermophilic

benefit',

the

digestion

process

becomes

increasingly unstable with rising temperature, and requires higher rates of heat inputs, and produces poorer-quality supernatant containing larger quantities of dissolved solids [27]. However, Kiely [29] insists that most digesters now operate at mesophilic temperatures, for which good stability and gas production occur. In addition, Tchobanoglous et al.

519

Experimentalinvestigation ofBiogasProductionfromFood Waste andAnalysis for the WasteEnergy Recovery... [30] posited that reactor temperatures between 25°C and

water content in the substrate decreases, the density of the

support

substrate decreases. This is an important factor to note when

stable

converting from tons of input material to a volumetric

treatment. However, according to Viessman and Hammer

measurement of cubic meters. The relationship between

35°C

are

biological-

generally

the

reaction

rates

preferred yet

optima

provide

a

to more

[31], the rate of biological activity in the range between 5°C

dryness and volume can be determined by the following set

and 35°C doubles for every lOoC tol5°C temperature rise.

of inequalities:

This is possibly why Kiely [29] and Viessman and Hammer [31]

agree

that

thermophilic

digestion

has

not

been

successful in practice because thermophilic bacteria are very sensitive to small temperature-changes. Eckenfelder [32] added to this by stating that the maintenance of higher temperatures is usually not economically justifiable, so corroborating the view of Mattocks [33], who, after noting that at

an

elevated

temperature

minor

changes

in

D= 1 for b:S0:15 D= l-e

(-031b-OI)

for b >0.15

where: D 14 Density in dry tons/m3, b 14 Dryness (%).

C. Digester Sizing Considerations

system

In order to figure out the size of the tank needed to digest

conditions could reduce digester efficiency or productivity,

the waste, several related parameters are needed: input flow

stressed that an additional source of energy will likely be

rate, dryness, total solids, volatile solids, organic loading rate,

required to maintain the digester contents at a constant

and hydraulic retention time. The size of the reactor can be

higher-temperature. It is important to state that psychrophilic

calculated by a modified version of the organic loading rate

temperature ranges

equation:

(say at 20°C)

are not suitable for

anaerobic digestion, as, according to Tchobanoglous et al. [30], the degradation of long-chain fatty-acids is often rate

3 3 Volume m = Flow rate (m /day)

x Volatile solid Concentration (kg/day) 3 Organ anic loading rate (m /day)

limiting. If long-chain fatty-acids accumulate, foaming may occur in the reactor and so inhibit process continuity.

From the estimate of annual tonnage, the amount of dry material can be calculated. Once the amount of dry material is known and the density, then a flow rate can be calculated

III. DESIGN OF SMALL-SCALE ANAEROBIC DIGESTION SYSTEM FOR FOOD WASTE

after the tonnage is converted to cubic meters and divided by the number of days in a year. Next, the amount of volatile

to consider when

solids (VS) needs to be measured or taken from literature. This

discussing the feasibility of designing an anaerobic digestion

can be done in a laboratory by taking a sample, weighing it,

There are several

important

factors

system to operate with food waste as the predominant input

drying it in an oven at 550

substrate. Food

input

weight (24 h) and then comparing the two eights. In the case

substrate but it is also prone to over acidification and lower

of food waste, literature shows volatile solids are usually

pH levels due to the amount of fatty acids produced. A

90e95% of the total solids (dry material) or 28e29% of the

waste

is

considered

a

desirable

_

C until it maintains a stable

review of important considerations for digesting food waste

substrate's wet weight [17,37,36]. Once the VS percentage

follows.

is known, the concentration of organic material in kg/m3 can be obtained by multiplying VS by the weight of the

A. Amount of Waste Available An estimation of the total tonnage of input substrate is a

substrate per cubic meter (derived from density). From here, it becomes necessary to have a desired organic loading rate for the substrate. Studies of the mesophilic digestion of food

very important first step in the design process. Often this

waste show that the organic loading rate can be much higher

amount is not directly known and needs to be estimated

than typical wastewater treatment or farm waste systems

through a waste audit. A total amount of waste can be

while remaining stable. For wastewater treatment and farm

estimated from a weekly, monthly, or annual audit.

waste, OLRs (organic loading rate) can range from 1 to 5 3 kgVS/m [38,39]. The Environmental Protection Agency's

B. Dryness of Input One of the more important parameters for AD systems is the

yearlong

study

of

food

waste

AD

in

California

ran

successfully at an OLR of 7 kgVS/m3 [17]. Other studies have shown that the OLR for food waste can go as high as 10

dryness of the input material. Before an accurate size of the

kgVS/m3 while remaining stable and producing biogas [36,

digestion tank or a prediction of biogas content can be

40, 41]. Once flow rate, concentration, and possible OLR

made, the amount of dry solids present in the input ubstrate is

ranges have been determined, a design choice becomes

necessary. In agricultural manure waste, there is only a

necessary. Due to the fact that OLR (organic loading rate)

2e12% solid content meaning the input slurry is mostly

and HRT (hydraulic retention time) depend on each other

water. The potential biogas comes from the solids content;

and can both be used to size the system, one or the other

so accordingly, manure has a very low biogas yield per ton.

must be fixed in order to determine the appropriate reactor

According to a literature review of waste taken from

size. This process should leave an amount of eligible play

cafeterias, Public cafe and in Hostel mess, food waste is

for the parameter that has been fixed once the system has

approximately 30% dry material [17, 34, 35, 36]. As the

been sized. Once in operation, changing HRT (hydraulic

Proceedings of7'h International Conference onIntelligent Systems and Control (ISCO 2013)

520

retention time) and OLR have different effects on the

25:75

25% Cooked foods and 75% cow dung

system and the possible consequences need to be considered

0:100

0% cooked foods and 100% cow dung

before sizing can occur. If the concentration of VS is increased by increasing the OLR while keeping the HRT (hydraulic retention time) constant, then the viscosity of the slurry changes and subsequently the pump ability of the

C. Climatic Condition of the State Fortunately, the average ambient temperature at Coimbatore

substrate changes. There is a usually an upper limit of 15%

(which was the considered region), at the time of this study,

on pumps used to transport the slurry, so the system could

was 31°C, so leading easily to the adoption of the optimal

experience mechanical failure if the OLR (organic loading

mesophilic temperature of 35°C in the digester. Tamil Nadu

rate) was already close to the upper limit [42]. In contrast, if

is suitable for the production of biogas without any external

the OLR (organic loading rate) is held constant and the HRT

heat treatment except the month of December and January due

is changed, then the system could experience undesirable

to winter season, so the bio gas produced will be slightly

biochemical effects such as the organic matter not breaking

reduced in those months, past 70 years climatic condition of

down as much and subsequent methane production would

the state is studied and it is found that Tamil Nadu climatic

decrease. Using the

condition is suitable for bio gas production[43].

prominent

design

OLR

(organic loading rate) as

criterion

does

not

appear

often

a in

literature, it is the HRT(hydraulic retention time) of a system that is varied.

D. Experimental Setup It was ensured that foreign materials like earth, sand, gravel,

IV. PROPOSED PLANT OF SCALE DOWN SET-UP

sawdust, soap, detergents, etc. do not enter the digester Tap water was added to the Waste inside the 5 L bottles. The digester was fully stirred manually with a piece of wood

A. Sources of Waste

until there were no lumps. As shown in fig 2. Five tanks of 5 L

The wastes use in this study was the peelings and food

capacity (5 L capacity bottle is choosed because for testing.

refuse from Adithya Institute of Technology, Mess, Public

It is as per the requirement) were grouped into 2 systems,

cafe and in Hostel mess. In Adithya institute of technology

with combined inlet and out let but with different L shaped

around of 2000 students are studying, in them 500 students

glass tubes. The systems have gas storage tanks in order to

are hostellers so the waste obtained from mess and cafeteria

obtain the Biogas running in the continuous process. The

is approximately 1000 kg/week is shown in below Table 1.

Digester was prepared in 5 different Compositions 100:0, 75:25, 50:50, 25:75, and 0:100 of 2kg to check which

TABLE 1: TABULATION OF FOOD WASTE ON DAILY BASIS

S.I No. Week

Morning Afternoon kg-week kg-week

Night kgweek

Total kgweek

composition yield maximum amount of gas with food

Average (kg-day)

1

1

3 50

3 57

336

1043

149

2

2

38 5

364

378

1127

161

3

3

343

378

378

1099

1 57

4

4

3 57

371

3 57

108 5

1 55

5

5

378

343

364

108 5

1 55

waste. The design of the digesters was based on a full-scale anaerobic digester with its own internal heating system and gas mixing system to ensure a constant homogeneous mixture and temperature. After 21 days gas is produced [11], [44]. Each digester system was completely independent.

B. Food Waste Preparation for Anaerobic Digestion Evaluation of the individual waste (in the batch system) were selected. 1. Cooked Food: Tamarind Rice, Lemon Rice, Tomato Rice,

Coconut

Rice,

Coriander

Rice,

Curd

Rice,

gas measuring beaker with scale

Parota, Noodles, Dosa, Idly, Poori, Chapatthi etc ...

51t digester tank

FIG. 1: EXPERIMENTAL SETUP

2. Cow dung (To initiate the process) 3. Fruit peelings: sweet banana, pineapple, papaya etc ... Evaluation of the mixed waste in the batch system According to the Experiment 100: 0

All the Cooked foods and 0% of cow dung.

75:25

75% cooked foods and 25% cow dung

50:50

50% Cooked foods and 50% cow dung

V. RESULTS AND DISCUSSION A. Biogas Measurement Daily

biogas

measurement

was

done

through

water

displacement method [45]. This gasometrical method is used

Experimentalinvestigation ofBiogasProductionfromFood Waste andAnalysis for the WasteEnergy Recovery...

521

for general laboratory-based volwne measurement because

warming and economical compared to other fuels with help

it is inexpensive, easy to set up, robust, capable of working

of waste materials. If all the institutions of Tamil Nadu

for long periods without maintenance. The total volume of biogas produced over 45 days was recorded, and the sum of

follow this 75:25 composition to produce biogas approximately 9 x 10 ml/week can be recovered.

5.692

biogas generated for the best producing fifteen days was considered as the performance index of the digester. A pH

ACKNOWLEDGEMENT

tape was used to measure the pH before the food refuse was added into the bottles and after the digestion period. It

We wish to express our appreciation to our Adithya Institute

ranged from 6 -8. The process pH was also monitored daily,

of Technology for us to provide a great opportunity to make

but not controlled. The highest volume for given day of the d experiment was 3100 mm on the 3r week.

this state of art and by motivating us in a perfect path to reshape our knowledge

B. Quantity of Biogas Generation

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Figure

2

below.

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Figure 2

shows

that

75:25

compositions can yield large amount of gas than the rest of the compositions.

3 500 3 000 2500 2000 1500

v-

I-

I-

-

l-

1000

V-

I--

I--

-

I--

500

V-

I--

I--

-

I--

• WIIKI • WIiKi .WI!K3

a

FIG. 2: THE COLLECTION OF GAS ON WEEKLY BASIS

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