Tanzania Traditional Energy Development and Environment Organization (TaTEDO)

Cooking using biogas

BIOGAS TECHNOLOGY Construction, Utilization and Operation Manual

© TaTEDO Off Shekilango Road, Kijitonyama P.O.Box 32794 Dar Es Salaam Tanzania Tel: +255 22 2700 438 +255 22 2700 771 Fax: +255 22 2774 400 E-mail: energy@tatedo.org Website: www.tatedo.org

TABLE OF CONTENTS

CHAPETR ONE........................................................................................................................................... 3 1.0 BIOGAS TECHNOLOGY ............................................................................................................ 3 1.2 BASIC PRINCIPLES OF BIOGAS PRODUCTION.......................................................................... 3 1.3 THE ANAEROBIC ENVIRONMENT................................................................................................. 3 1.4 Factors affecting yield and production of Biogas................................................................................. 4 CHAPTER TWO.......................................................................................................................................... 7 2.0 UTILIZATION OF BIOGAS ................................................................................................................ 7 2.1 COOKING .............................................................................................................................................. 7 2.2 LIGHTING ............................................................................................................................................. 9 2.3 GENERATION OF POWER .............................................................................................................. 10 2.4 COMPRESSION OF GAS................................................................................................................... 11 2.5 COMPARISON BETWEEN DIGESTED SLURRY AND FARMYARD MANURE.................... 11 2.6 UTILITY ............................................................................................................................................... 11 CHAPTER THREE.................................................................................................................................... 14 3.0 THE VACVINA BIOGAS MODEL ................................................................................................... 14 Advantage of VACVINA BIOGAS SYSTEM.......................................................................................... 14 CHAPTER FOUR ...................................................................................................................................... 18 4.0 HOW TO CALCULATE REQUIRED DIGESTER VOLUME ............................................. 18 4.1. Preparation of Construction Materials and Appliances .................................................................. 19 4.2. Digester construction............................................................................................................................. 21 4.2.1. Digging............................................................................................................................................... 21 4.2.2. Making digester foundation................................................................................................................ 21 4.2.3. Bricklaying of the walls...................................................................................................................... 22 4.2.4. Mortar and cement liquid plastering................................................................................................... 24 4.2.5. Making digester concrete.................................................................................................................... 25 CHAPTER FIVE ........................................................................................................................................ 28 OPERATION AND MAINTENANCE..................................................................................................... 28 FEEDING OF BIODESTER ..................................................................................................................... 28 5.1 Initial cleaning and verification of the system........................................................................................ 28 5.1.1. Initial feeding of bio-digester ............................................................................................................. 28 5.1.2. Daily feeding of manure ..................................................................................................................... 28 5.2. Operation of biodigester ........................................................................................................................ 29 5.2.2. When gas burners in operation ........................................................................................................... 30 5.2.3. When whole system in use ................................................................................................................. 30 5.2.4. Warning of chemical into digester...................................................................................................... 30 CHAPTER SIX........................................................................................................................................... 31 MAINTENANCE AND TROUBLE SHOOTING................................................................................... 31 6.1.1 Common problems and Solutions........................................................................................................ 31 CHAPTER SEVEN .................................................................................................................................... 33 7.1. Practical exercise in calculation of total volume of a digester, construction materials and investment cost............................................................................................................................................ 33

CHAPETR ONE

1.0 BIOGAS TECHNOLOGY Biogas is the name given to the mixture of gases generated by the bio-degradation of organic substances under the anaerobic conditions. Sewage and agriculture waste contain organic substances with high molecular compounds. In nature, given the proper temperature and humidity conditions, these substances are broken into lower molecular compound material, inorganic matter and gases. In high concentration, this process creates pollution and adverse hygienic conditions for humans and animal. On the other hand, by properly treating the waste, useful renewable energy can be obtained as well as organic fertilizer, thus effectively “changing waste into money”. 1.2 BASIC PRINCIPLES OF BIOGAS PRODUCTION Conversion of organic Substances into Biogas Organic substances exist in wide variety of forms from living beings to dead organisms and even animal droppings. Organic matters is composed mostly of carbon(C), combined with other elements such as hydrogen (H), Oxygen (O), Nitrogen (N), Sulphur (S)… to form organic compounds such as carbohydrates, proteins and lipids. In nature Microorganisms, mainly bacteria, through a digestion process break the complex carbon into smaller substances 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 oxygen is called anaerobic digestion and generates mixtures of gases with main contents is methane (CH4) .The gas produced which is mainly methane produces 5200-5800 KJ/m3 when burned at normal temperature and thus presents a viable environmentally friendly energy source to replace a fossil fuel 1.3 THE ANAEROBIC ENVIRONMENT Anaerobic environment –also called Methanogens-are essential for the production of combustible biogas. These bacteria are very sensitive to the presence of oxygen and will effectively operate only in anaerobic conditions1. Hence the importance of designing an air tight chamber, when constructing biogas plants

1.4 FACTORS AFFECTING YIELD AND PRODUCTION OF BIOGAS Many factors affecting the fermentation process of organic substances under anaerobic condition

The quantity and nature of organic matter The temperature Acidity and alkanity (PH value) of substrate The flow and dilution of material

During the initial feeding of organic material or after adding new material, small quantities of oxygen as well as aerobic bacteria will enter the digester. These aerobic bacteria, along with some oxygen –tolerant anaerobic bacteria present in the fermented matter will burn the oxygen present and thus help restore and maintain anaerobic condition All have an important influence on the action of anaerobic bacteria responsible for the bio-degradation process. Thus it’s important to understand their effects in order to design effective man-made bio-digesters. Temperature The action of methane –producing bacteria is strongly affected by the ambient temperature. Though the biogas fermentation can occur at temperature ranging from 0 to 700C, the effective methane –producing occurs at temperature ranging from 250C to 400C with 350C as optimum temperature (see table 1) Keeping the digestion chamber at near-constant temperature is important; constructing the digester chamber underground and / or insulating it when in cold environment achieve this Table 1: Biogas yield at various temperatures

Temperature Biogas yield (m3/1 ton of dung/day)

15 0.150 20 0.300 25 0.600 30 1.000 35 2.000 40 0.700 45 0.320

The PH value Methanogenic bacteria require a neutral environment (PH values between 6.5 and 8). Higher values significantly impede the fermentation process (see table 2) Table 2: Effective of PH on methane production

From 5 6 7 8 9 10 PH value To 6 7 7 7.5 7 7

Biogas yield

12.7 14.8 22.5 24.6 17.8 10.2

Carbon to Nitrogen ratio (C/N ratio) Different organic matters contain different concentrations of carbon (C) and nitrogen (N), these two elements being the bacteria’s most important nutrients. Normally, fermentative bacteria will require thirty times more carbon than nitrogen. Therefore the optimum carbon-nitrogen ratio (C/N) ratio of the digester input is 30/1. Plant material such as weed and straw tend to have a very high C/N ratio resulting in carbon redundancy and very slow decomposition. The C/N ratio of pig and cattle manure is more suitable for biogas Using both animal dung and plant materials input for the bio digester is NOT recommended as it will reduce the fermentation process and result in incomplete decomposition of the vegetal portion Total solid Concentration Total solid concentration (TS %) is a measure of the dilution ratio of the input material. It’s calculated by dividing the weight of the remaining portion after drying at temperature of 105°C (to constant weight) by the original weight. The TS ratio is another important factor in the production of the biogas. Below an optimal value, the lower the total TS concentration, the lower the yield of biogas. On the other hand, when the total solid concentration values exceed the optimal point; the yield of the biogas also decreases and the result mixture become too dense to effectively flow through the bio-digester, the optimum dilution ratio for cattle manure is 1 part of manure for 5 parts of water. Research conducted in China has shown that temperature and the total solid concentration have an interdependent effect on the biogas yield (see table 3) Use less water during the colder months of the year to increase biogas production Table 3: interrelated effects of temperature and total solid concentration on the biogas Total yield (ml) Total solid ºconcentration (TS)-% 2 4 6 8 10 12 25-27ºC (summer and autumn)

2915 3500 6295 4090 3960 2510

18-23ºC (winter and spring)

1030 1080 1140 1380 2580 1850

The table shows that in winter months, the optimum total solid concentration is 6% and figure increase to 10% in winter time Retention time In flow – retention biogas systems (such as the VACVINA model), material is fed daily into the digester, with the fermented materials being pushed towards the system’s outlet. Retention time is defined as the total time taken by material to travel from the inlet to outlet. This represents the time allowed to the fermentation and gas –production process. Retention time is normally calculated using the total volume of the slurry in the digestion chamber and slurry volume of the input materials The higher the retention time the longer the materials stay in the digester and thus more Biogas can be extracted. Although 50 days ensures almost – complete digestion and gas extraction (97.3-99.1%) for optimal cost-benefit ratio, bio digester volumes are usually reduced to provide retention times of 40 days. Table 4: Retention time and biogas produced for different input material % of biogas extracted for different retention times Material/Days 10 20 30 40 50 60 Human excreta 40.7 81.5 94.1 98.2 98.7 100 Pig manure 46.0 78.1 93.9 97.5 99.1 100 Poultry manure 34.4 74.6 86.2 92.7 97.3 100 Table 5: Optimal values for biogas production using animal manure Factor Optimal value Temperature (ºC) 25-40 PH 7 C/N ratio 30 Total solid concentration % 6 Retention time (days) 40-50 Toxicity

Products such as pesticides, antibiotics, soap and rain water are not allowed to be fed into the digester

CHAPTER TWO

2.0 UTILIZATION OF BIOGAS Biogas is a valuable vehicle of energy containing 55 – 70% methane and 30 – 45% carbon dioxide as well as small quantities of various gases. It is almost 20% lighter than air and has an ignition temperature of 650 – 750C. Its calorific value is 20 mega joules per cubic meter (or 4700 kcal) Biogas is a cheap and clean fuel. It burns with a blue flame, which is soot-free. When it is burnt in silk mantle lamps, it illuminates better than kerosene in patrolman lantern. Biogas can replace petrol and diesel in engines. The quantity of biogas required for different application is shown below. Possible applications of biogas 2.1 COOKING The best use of biogas is for cooking. In order to get maximum heat value of the gas, it should be burnt in properly designed stove. For a typical 0.45 m3 (16 cubic feet) per hour stove, which is popular family type, the dimensions are as under: Jet size 2 mm diameter Area of jet: 3.98 mm2 Flame port size: 6.0 mm diameter Number of port: 20 Total area of ports 565 mm2 Ratio of jet area to flame port area: 1:142

4 m3 BIOGAS

5 kW Electricity

Cooking for 25 persons

Mantle lamp 25 – 28 hours

5 hp engine for one hour and thirty minutes

Length of gas mixing pipe: 20 mm It may be noted that biogas stove have large flame port diameter than stoves using liquefied petroleum gas: The procedure for the use of biogas stove is as follows:

i. Connect the stove to the gas tap by using a rubber pressure tube. ii. The air adjuster should be closed fully.

iii. Light a match and keep it near the flame ports. Then open the gas tap and place cooking vessels on the stove. The flame will be weak and long, which is an inefficient way of burning the gas.

iv Now open the air adjuster to admit air up to the point when the burning gas creates a noise. The adjuster may then be closed a little only to subside the noise and the flame will be about 25 to 30 mm high. The upper cone of flame should touch the vessels; the burner can only be adjusted for maximum efficiency when there is a cooking vessel on the burner

Precautions

i. When necessary, the flame ports should be cleaned by using a jet of water. ii. Whenever a smell emanates from the burning gas, the flow of air into the gas jet

should be checked. The smell should stop immediately if the supply of air is increased.

iii. Keep the nozzle of the burner clean. Sometimes carbon particles get deposited on the nozzle, which should be removed by erasing with sand paper. Or cleaning with soap water.

iv. In a fixed – dome type plant, when the gas pressure is high, the gas cock should not be opened full so the flame may attain a height of 25 cm and cause accidental burning of face, hair, et

2.2 LIGHTING There is a big demand for biogas lamps in unelectrified rural areas. However, the light produced is not as good as that from an electric bulb. Biogas lamps are expensive and they consume large quantities of gas. Regular servicing of lamps and good supply of mantles is required. Single mantle biogas lamps for use inside and outside houses are available in the market. Different types of biogas lamps are operated in the following manner:

i. Open the lamp and fit the clay Nozzle, also called a venturi. Make a hollow ball of the mantle and tie it to the venturi. Close the lamp.

ii. Fix the lamp at an appropriate height. Care should be taken that it is not fixed near thatched roof; otherwise there could be danger of fire.

iii. Connect the lamp with the gas tap using a rubber tube. iv. Open the gas cock fully and also the gas regulator.

V Light the mantle and allow the gas to burn. Vi The lamp should be allowed to heat up until it makes a noise. Then the gas regulator should be adjusted so that the mantle is at its brightest illumination

Vii To turn the lump, only the gas cock should be closed.

Viii To relight the lamp, first a lighted match should be held close to the mantle, through the hole in the bottom of the glass globe. Then turn on the gas immediately.

Precautions

i. Be careful that the sequence mentioned above is not reversed, otherwise there will be a minor explosion and mantle will break. Allow the lamp to heat up until it makes a noise and gives steady and good light.

ii. The clay nozzle and venture tube should be cleaned to remove dirt, carbon particles, insects, etc whenever a new mantle is fitted.

iii. The glass globe should be cleaned with soap and water whenever necessary; otherwise the glass will crack.

iv. The common reason for a lamp not working well is a defective needle in the gas regulator. The needle must be long, thin and have fine point. It must come down low enough to protrude through the jet and shut it off (Fig 8.7) If the needle doesn’t come down low enough, then file a whole (A) And make a slot so that it can come down far enough. The gas regulator lever fits into thin hole.

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2.3 GENERATION OF POWER

Biogas is an excellent and economic fuel for both petrol and diesel engine. However the power obtained is less than that obtained when liquid fuel alone is used. As engine using biogas become hotter than those on liquid fuels, their cooling has to be kept in good condition. Petrol engine can be run 100% on biogas except that little petrol is consumed for starting up. Diesel engine are modified to dual- fuel engine which use both biogas and diesel oil. Biogas is introduced in the inlet pipe after it passes through the air filter. (Fig…..) Gas inlet devices are designed to suit different engine designs and inlet pipe and in order to give the proper biogas/air mixture. Injection of a little diesel oil to ignite the gas mixture in each stroke is essential for normal running of the engine. This is because in diesel engine the temperature at the end of the compression stroke is usually not over 700oc, where as the ignition temperature of a methane/air mixture is 814oC. Dual - fuel engines are marketed as ‘gobar gas engine’. The capacities of that engines range from 3 to 96 H.P. (British Horse Power)

As the consumption of biogas in diesel is a bout 0.50 m3 gases per hour per P.H.B. or 0.65 m3 gas per hour per KW electricity, large size biogas units are required to run engine. The quantity of diesel oil saved by using biogas produced from different size of biogas unit is indicated in Table ………. Table… Quantity of diesel oil saved by running a 5 hp dual – fuel engine on biogas Table Quantity of diesel oil saved by running a 5hp dual –fuel engine on biogas Size of biogas unit (cm3)

Tie period for which a 5 H.P engine is run twice a day

Quantity of diesel oil saved (litres/day)

8 4hr 3.6 15 6hr 30 minutes 5.8 25 12hr 10.8

The monetary benefit that accrues from the use of biogas for running diesel engine is very attractive. Operational of dual – fuel is easy. After the engine has run with diesel oil for a while, the biogas valve is opened slowly. This should automatically reduce the supply of diesel oil

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through the action of the speed governor. In order to stop the engine, the biogas valve should be closed first and then the throttle valve. The gas produced from nightsoil alone or nightsoil in combination with dung contain a high concentration of hydrogen sulphide. Such a gas can be used in diesel engine only after passing it through a tube fitted with iron fillings. The iron fillings can be regenerated by open-air storage. It is important to operate the engine according to the instructions given in the manual provided by the manufacturing firm. In case there is any problem, the servicing facilities provided by the dealer or manufacturing firm should be availed of. A dual – fuel engine can be used for running an irrigation pump, flour mill, chaff cutter – thresher, etc.

Dual –fuel generators helps in the production of electricity from biogas . Generators of capacities ranging from 3.5 to 7.5 KVA are available in the market.

2.4 COMPRESSION OF GAS Methane gas is unlike commercial available bottled butane or propane gas. It liquefies at a pressure of about 47.4 kg per cm2 at a critical temperature of – 82.1oc. Further, it has to be cleaned of all hydrogen sulphide as this would corrode the storage bottles. It should be also cleaned of carbon dioxide as there is no advantage in compressing this. Considering the cost of cleaning the gas, compressing it, purchasing a special high-pressure storage bottle and transporting these heavy bottles, it is obvious that such a proposition is neither economical nor practical. 2.5 COMPARISON BETWEEN DIGESTED SLURRY AND FARMYARD MANURE The quantity of manure after processing through a biogas plant is more than farm yard manure. About 25 – 30% of organic matter is lost in open pit composting as carbon dioxide. Thus a bout 20 – 25% more quantity of manure is produced through a biogas unit. Digested slurry is better manure than farmyard manure. Its nitrogen content can be improved further by using cattle urine for dilution and preparation of dung slurry before addition to a biogas unit or nightsoil by attaching a latrine directly to biogas unit. 2.6 UTILITY Digested slurry can be used for manuring crops or fish ponds. Manuring crops Like compost and farm yard manure, the application of digested slurry to soil helps in improving soil fertility. It provides humus which is an essential component of fertile soils. It increases soil porosity and water – holdings capacity. It supports the activities of

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useful micro – organisms which facilitate the release of nutrients to crop plants. All these benefit add up to increasing crop production. Digested slurry can be used effectively in any type of soil and for any crop. The recommended application of manure is 10 tones per hectare in irrigated areas and 5 tones per hectare in dry land areas. However the response of crops would vary. The increase in crop yield is about 10 to 20%. Most responsive crops are vegetables, in particular root crops such as carrot, radish, sweet potato, fruit trees, tea, coffee, sugarcane, rice and jute. Digested slurry can use as fertilizer for crops by any one or the followings methods: Liquid form Maximum benefits are obtained when the slurry is used in liquid forms as it comes out of a plant. It can be easily distributed in the field in the slurry outlet of the plant is linked with the main irrigation channel. This would be possible only if the biogas unit is installed on the farm. Otherwise slurry can be transported in discarded oil drums or buckets, by wheelbarrow or bullock cart, which is more cumbersome. Compost Digested slurry is an excellent material for hastening the rate of composting of refuse crop wastes, garbage, etc. It also provides moisture to the compostable biomass. Two or three rectangular pits (common dimension 3m length x 2 m breadth x 1.5 m height) or circular pits are dug. First, a layer or straw, animal bedding, leaves, garbage etc. is put in the pit. Slurry is allowed to flow n to the pit. Alternate layer of refuse and slurry are made until one pit is full. It is an advantageous to place bamboo poles having holes 10 cm apart in the compost able materials for aeration. (Fig….). Finally the pit should be plastered with mud layer. This will minimizes loss of nitrogen from the pit. After about three or four months the compost will be ready for application in the fields After one pits is field up, the same procedure should be repeated for filling another pit. Composting is done in heaps, particularly in high rainfall areas. Digested slurry and refuse are first mixed in equal proportion and a pile is built about 2 – 3 m in width at the base, 1.0 m in height and 3-5 m in length. The sides are tapered so that the tip is about 0.5 m narrower in length and width than the base. Then the heap is plastered with a thin layer of soil. (Fig…..) It may be kept under a tree to protect it form rain. The compost will be ready about three or four months. If possible, the heap can be turn up side down after 15 days of initial filling and for a second time after another 15 days. During this process, water may be added if the materials look too dry. In this way, the compost will be ready in two months. Composting of slurry with other refuse is a Common practice. However, it requires availability of adequate land near the biogas plant. Semi dried The slurry may be spread in shallow pits and allowed to dry partially. It is then scraped and stored in piles which should be covered with plastic sheets or mats until applied to the field. Complete drying of slurry under the sun should be avoided.

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A slurry filter bed made near a plant can help in quick drying. The dimension of such a bed for a 4 m3 size plant would be 3m long, 1.2 m broad and 0.6 m deep with an opening at opposite end of the sloping bottom (Fig……..). The digested slurry is lead through a channel to flow and cover a 15 cm compact layer of green or dry leaves filled in the bed. Water from the slurry filters downs and flows out of the opening into a pit. This water can be reused for preparing fresh dung slurry for feeding the plant. Semi solid residue left on top of the bed has the consistency of fresh dung and can be transported easily to field for application as top dressing for crops in particular potato and sugarcane. Manuring Fish ponds Digested slurry can also be used as fertilizer for fish ponds. An ideal feed for Singi, an air breathing cat fish, may contain equal quantities of mustard oil seed cake, bran and digested slurry. This supplementary diet should be providing at a rate of 3 – 5% of the body weight of the fish. Utilization of digested slurry in pisciculture helps in the reduction of cost of supplementary fish feed.

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CHAPTER THREE 3.0 THE VACVINA BIOGAS MODEL The system consist of a flat-top rectangular underground digestion chamber with external plastic gas reservoirs, inexpensive siphons, inlet mixture tank and slurry output tank 3.1 ADVANTAGE OF VACVINA BIOGAS SYSTEM

The gas plant provides comfort and saves expenditure by supplying Clean and inexpensive renewable energy fuel for cooking and lighting

Improved hygiene and health conditions in the household compound [eliminating raw and untreated animal manure and night soil] this reduce bad smell, flies and parasites around the house.

With improved biogas stove reduce smoke from the fuel wood and leaves all family especially women from eyes problem caused by smoke

Reduction in CO2 emissions and deforestation pressure by substituting fossil fuel with biogas

Long-term improvement in the financial situation of house holds by reducing fuel and chemical fertilizer expenses

Improved of soil fertility and reduction of soil degradation by the use of the bio digester’s digested effluent as organic fertilizer

Allows for safer and cleaner animal husbandry activities especially in crowded and peri-urban areas

Reduce workload of women for fuel gathering, cleaning of pots and pans

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Fig 1: VACVINA model The digester The main digestion chamber is an underground rectangular tank made of bricks and motor fig 1. However, the shape of the tank can be adjusted to the specific configuration and meet the constraints of the family compound while retaining the sufficient volume. One of the great advantages of these models the concrete flat top of the digester can provide a clean and dry floor for the cattle stable. The inlet The inlet is a simple inexpensive off-the –shelf siphon pipe made of glazed-terra cotta

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Fig 2 the inlet siphon allows animal dung to be fed into the digestion chamber The system normally comprises two or three siphon inlets allowing the lavatory pan and the latrine to be connected in addition to cattle stable. These inlets play an important role in preventing the formation of a hardened scum layer by allowing the new material to drop on top of the liquid surface, thus wetting and breaking the top layer. As new material fed daily the surface is continuously stirred and broken. In additional siphons also act as the safety valve with 15cm of water column, they effectively ensure gas tightness of the main chamber.

2. Mixing tank

1. Digestion tank

3.Technical top

4. Slurry tank

5.Toilet

1. Digestion tank

2. Mixing tank

3. Technical top/hole

4. Slurry tank

Fig 3: VACVINA digester The outlet The outlet consist of straight pipe, normally made of PVC Ø110mm diameter and 1 meter long, at an angle of 45ºC incline in the digestion chamber. Its function is to drain the effluent (liquid form) from the digester to the slurry pit and set the level of the liquid in the digester The outlet pipe should be positioned lower than the inlet pipe, with its end opening about 35cm lower than the digester cover. To ensure gas tightness of the digester, the other end of the pipe should deep extend deep under the static surface of the liquid in the digestion chamber (see fig4)

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Fig 4: The outlet The slurry pit The slurry retention pit is constructed near the outlet of the digestion chamber and is used to store the system’s effluent for later use. The amount of effluent flowing into the slurry pit is equivalent to the input fed into the digester. However the volume of the slurry retention pit must be calculated according the intended usage of the slurry. It’s important to remember that, in order to ensure the normal functioning of the system, the slurry level must always be kept lower than the digester outlet Gas reservoir The external gas reservoirs are used to collect and store the biogas before being used as cooking fuel see fig 5. One gas reservoir should be enough for a normal family. However if the household has the larger number of animals, more gases will be generated and more gas will be required

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The bags are made of two layers of 20µc thick polythene tubing and have the storage capacity 1.5-2 cubic meters. In order to increase the gas pressure, rubber bands is tightened around the reservoir and then loosen again after finished using the burner to allow the bag to inflate it-self. Fig 5 Reservoir

CHAPTER FOUR 4.0 HOW TO CALCULATE REQUIRED DIGESTER VOLUME The size of a biogas plant which can be used for storing manures collected from husbandry activities is calculated based on the number of cattle raised by each household In general, the calculation of the volume of a bio-digester (fed with animal manure, urine…) depend closely on daily feeding of manures by each household, retention time, concentration of manure and water solution before being fed into the digester through siphon inlets, etc. For a VACVINA biogas plants, actual volumes (V) can be derived through the following formulas:

Fig 6 Digester volume V= Vgas + Vdig……………………………………………………….. (1) (See Fig. 6)

Vdm

Vgas

Gas Reservoirs

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Where Vgas: Gas volume in the digestion chamber Vdig: Slurry volume in the digestion chamber And Vdig = T x Vdm………………………………………………….. (2) Where T: retention time of the slurry in the digester (i.e. 40 days) Vdm: daily amount of water and dung (liter/day) fed in the digester And Vgas= h1S Where S: Ares of the Flat bottom slab of the digester (m2)

h1: Distance between the bottom of the cover slab and the static liquid surface in the digester (m), normally be 35-40cm

When use cattle manure Vdm can be calculated as follows Vdm= (w + nL) T……………………………………… (3) Where

W: the amount of water to dilute the dung of n cattle L: The daily average amount of dung per cattle (l/day)

The optimal dilution ratio of input material is 1:5 (one part of manure for five parts of water) Put w= 5nL into (3) and from (1), (2), and (3) we have V= Vgas + (5nL + nL) T= Vgas+ 6nLT Hence V= h1S+ 6nLT……………………………………….. (4) Where n: Regular number of Cattle L: Daily average amount of dung per animal (2litre/head/day) T: Retention time (Days) h1: Distance between the bottom of the cover slab and the static liquid surface in the digester (m), normally be 40cm (h1=0.4m) S: Ares of the Flat bottom slab of the digester (m2) For Retention time of 40 days (T=40) V= 0.4S + 240nL Fig 6. Digester volume 4.1. Preparation of Construction Materials and Appliances The materials and appliances for construction of a standard 7-m

3 biodigester –

VACVINA mode –are given in the following table: No. Description Unit Quantity 1 Solid brick small size piece 1,400 2 Cement kg 600 3 Yellow sand (not mixed with silt) m

3 1.5

4 Gravel or small stone (1 x 2 cm) m3 0.5

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5 Iron bar (diameter of 8 mm and smooth)

kg 30

6 Metal pipe piece 1 7 PVC pipe (diameter of 21 mm) m 4 8 Valve & metal connector set 15 9 Plastic gas-conducted pipe (Ø 21) m 15 10 Gas reservoir polythene bag bag 2 11 Siphon pipe set 2 12 Biogas burner set 2 13 Glue and paper tape 14 Hoe, digging hoe, shovel, pickax, ax, rotten

bucket, pounder for compacting soil, crowbar, hacksaw, saw, trowel, mortarboard for plastering, water hose, plastic bucket, mortar bucket, drum, zinc sheet, palm broom, brush for plastering mortar, water container, tent, motor rubber tube, wooden pole, torch, vibrator, jack, cow string, nail, measuring tap, metal-cutting scissors, pliers, Adjustable spanner and wooden mold.

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4.2. Digester construction Construction site selection The biodigester for every household should be constructed at the most favorable location which makes it easy for transportation of manure from animal farms to feed in the tank. The biodigester, therefore, should be placed nearby or beneath pigsty, while its shape should be designed according to the area condition or situation.

4.2.1. Digging After the selection of the construction site and design, we start digging a digester pit and its size must be a bit larger the required tank that makes us convenient for construction. In determining the size of a digester, it depends on the actual condition of the land area for construction. However, in order to smoothly run the household investment in biodigester building, it would be ideal to be pay attention to the following characteristics: the digester depth ranging from 1.5 to 5 metres, most favorably from 1.8 to 2 metres, width of less than 2 metres, and length depending on capacity desired. Remark: If the dug pit is by chance in area with low level of underground water, it is necessary another small pit be prepared to temporarily store it and then pump or remove it so as to make the foundation work convenient.

4.2.2. Making digester foundation After the digging is completed with the accurate determination of dimensions of a tank, we continue to construct its supportive foundation as following steps: Lay pieces of broken bricks or small stones (diameter of 4 x 6 cm) for 10 cm layers and then compact and spread them evenly; Apply gravel or small stone (diameter of 1 x 2 cm) for another layer of 3 cm thickness; and Make 5 cm thick concrete at ratio: 1 cement, 2 sands and 3 small stones (dia. of 1 x 2 cm).

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Fig 7 digester hole and underground

In case there is too much underground water while conducting the concrete work, it needs to be gradually pumped out of the pit, or a plastic sheet needs to be laid over the foundation area, in order to protect leakage or disturbance from the water.

4.2.3. Bricklaying of the walls While the digester foundation work is finished, we commence to lay bricks to construct the walls. In construction of the tank walls which is similar to that of high buildings with their thickness of 10 cm (i.e. thickness of single brick), high quality solid bricks are used together with cement and sand at ration of 1 cement and 4 sands. Notice: While doing the bricklaying, holes are technically determined for installing some materials such as inlets and outlet (see figure 3). Inlets are fixed at place, which is closed to the top edge of the digester wall, and the dimension of an inlet is 30 cm high and 15 cm wide. However, they can be positioned apart.

Remark: If the plant is built on soft and wet land (bad condition), iron bars should be added in the concrete to increase strength of the foundation. The iron bars should be 8 mm in diameter and cast in checked pattern with gaps of 20 cm.

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The position of an outlet is at 30 cm away from the top edge of the digester wall, and it must be 30 cm high and 15 cm wide.

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Fig 3: Position for installing inlets and outlet

4.2.4. Mortar and cement liquid plastering Mortar and cement plastering work has the most significant role in ensuring the construction quality standard by which the tank must be waterproof and airtight, thus internally plastered mortar must be firm. The sand mixed with cement for plastering the walls must be purified so that it is well mixed with the cement at ratio: 1 cement-3 sands. It is overall suggested the thickness of plastered cement and sand should be even, and the plastering should be pressed firm and smooth. At the corner of the walls, inward corns are recommended. The plastering of mortar and cement liquid should be carried out the following steps: First, the interior wall faces should be cleaned with clean water; Solution of cement (at medium rate), then, needs to be smoothly applied on the wall faces at the thickness of 1 mm (considered as the 1

st layer);

After that, one more layer of mortar (cement and sand) at 1 cm thickness should be made and then left it a bit dry on surface before it is evenly smoothed (2

nd layer); Wait for

1-2 hours after plastering of the first and second layers to let them a bit dry, and then the cement solution is additionally spread at thickness of 1 mm in which the application method is similar to that of the first layer (3

rd layer); and One hour later, cement solution

needs to be applied at thickness of 1 mm ((4th

layer). While plastering the mortar over the wall faces, 5 cm gap down from the peak of every wall is left blank to connect with the digester concrete cover later. After the top concrete is made, parts with shortage of mortar must be additionally sealed. The corners between the digester cover and the walls must be conically sealed with mortar inward to ensure airtight (figure 4).

25

39

Plastering the face of tank wall by mortar of cement & sand

2

1

2

Hole for Inlet Hole for Outlet

Fig 4: Plastering mortar inside the tank to protect leakage

4.2.5. Making digester concrete After the walls are built and plastered with mortar and cement solution, a top reinforced concrete is made to construct the digester cover. As the tank concrete has the role to serve not only as a cover to create airtight but also as a flat floor for animal rising, the concrete must be 8-10 cm thick (according to the type of animals raised). The surface of the concrete must be flat, and it must be made directly by the mold assembled at the construction site (Any reinforced concrete produced at the factory is not recommended for used in this purpose). The preparation as well as construction technique are carried out in the same way as those of constructing tall buildings or houses we are staying in (fig 5). The construction process is as follows:

26

a. How to assemble mold and install supporters of the mold to construct digester concrete The concrete mold and its supporters must be firmly and technically installed (the mold frame must have its strong supporters).

Fig 5: Assembling wooden mold and its supporters b. How to determine and make the technical hole during construction of top concrete A technical hole with the dimension of 70 x 70 cm on top must be readily made by a mold, which had already been prepared with small wooden pieces and shaped in a semi-cylinder frame with the dimension of 70 x 70 cm on top, 50 x 50 cm at bottom, and 10 cm high (Fig 6). Iron bars used to construct the technical hole should be 8 mm in diameter and cast in square pattern of 10 cm

2.

Fig 6: Technical hole Assembling wooden mold and supporters for concrete

27

To serve as a hole to go in and out of the tank to remove the wooden floor and supporters of the mold from interior digester when the concrete is, according to the determined construction technical standard (7 days), dry and firm enough. Also, it acts as a hole to enter and get out of the tank to complete the last work such as installation of the inlets and outlet, etc. To be a hole for cleaning the digester when there is blockage or after it has been operated for years (normally estimated 7-10 years). The position of the technical hole should be analytically and appropriately determined to enable convenient operation (while going in or out of the digester, ensure that it doesn’t affect the outlet and inlets …), and it must not disturb or interrupt animal raising activities.

28

CHAPTER FIVE OPERATION AND MAINTENANCE FEEDING OF BIODESTER

5.1 Initial cleaning and verification of the system Before operation is started, clean interior digester and after that recheck the installed system to ensure airtight or leakage proof. In addition all components of the system must be checked to ensure gas-tightness’, includes

Sufficient amount of water in the safety valves All siphons filled with water Lavatory pan siphon (if any) filled with water All gas valves (main gas valve, stove tap) closed

5.1.1. Initial feeding of bio-digester Once the construction of biodigester and installation of appliances are complete the bio-digesters should be operated immediately. To kick start the anaerobic process and ensure proper colonization of methanogenic bacteria, the most appropriate in put are cattle, poultry or pig manure. In order to obtain biogas faster, 800-1,000 kg of fresh manure [collected and stored not more than 7 days] should be prepared in advance as raw material for the first feeding, and water is filled together with manure until it is seen flowing out through outlet. Once the gas reservoirs start to inflate, the biogas can be used for cooking. Initially, the gas will contain some amount of air that will be flushed out as the system usedThe process of bio-degradation and biogas generation will take 5-10 days. [Slightly more days in cold temperatures].

5.1.2. Daily feeding of manure To ensure durable and sustainable operation of biodigester, it is necessary to daily feed the digester with raw materials collected from cattle shed or pigsty and toilet. Fresh material must be fed daily in the digester to sustain the cooking fuel need of the family. It’s important to ensure that the following materials are NOT fed in the digester:

- Soil, sand and stones - Branches, twigs and straws - Soaps and detergent solution, cleaning chemicals, antiseptic products and rain

water For a family of 7 persons, an average of 15-20Kg of cattle dung must be fed daily. Together with the above-mentioned manure, water is added at ratio of 1manure to 5 waters.

29

If water is overfed, then some amount of non-digested manure is flown out through outlet, since its digestion is limited, resulting in less gas production and the environment problem cannot be all solved, meaning manure still carries bad odor and diseases. In this case, water for bathing cattle during hot weather should not be directed into the digester but through canals prepared by the owner upon request in order to avoid excess water in the tank. Taking full advantages of the VAVCVINA flat-top design with multiple inlets siphons inlets, a latrine is often constructed at the same time as the bio-digester. Water used to clean latrine must be taken into account when calculating overall water-dung ratio.

5.2. Operation of biodigester 5.2.1. When reservoir is full of gas We can start to use biogas for cooking. At the beginning, if gas can’t be ignited due to the reason that it is not of high quality as it contains a lot of carbonic dioxide resulting from digestion of manure with oxygen remaining before closing the tank, first gas should be released from the reservoir, and wait until the next gas comes in which the balloon is refilled. Keep in mind to turn off gas valve soon after operation is ceased. To start fire, first ignite fire-distributing device of the burner with lighter, and then adjust gas flow and flame to the desired level by the valve. To obtain evenly distributed flame while operation, fire-distributing device made of copper should be frequently cleaned. Fig 20: Feeding manure

30

5.2.2. When gas burners in operation If biogas doesn’t supply sufficiently for cooking, rubber should be employed to tie across the reservoir to increase pressure inside the reservoir. After cooking, attention should be paid to remove rubber from the reservoir so that it can receive new biogas from the plant.

5.2.3. When whole system in use If gas reservoir is seen loose, check the pipelines and gas reservoir system itself, valves… immediately for fear that they are bent or clogged, or control water in the bottle safety valve or at siphon inlets that it could be empty. If so, repair must be done urgently.

5.2.4. Warning of chemical into digester Chemicals that are not allowed into the digester are soap, paint, and rainwater… as they interrupt reaction of bacteria in anaerobic condition. Presence of those chemicals may cause less biogas production or even stop production as a whole.

31

CHAPTER SIX

MAINTENANCE AND TROUBLE SHOOTING 6.1.0 Tips and techniques

During the first few days of operation, the biogas might contain other gas which makes it not well flammable. If this is the case, discharge entire bagful of gases and wait for a next day for a production of new biogas.

Make sue all gas valves are closed when not using biogas for cooking. When using the stove, remember first light a flame then slowly open the gas valve

and adjust the flame height and intensity according to the cooking need. To unsure a stable and clean flame, the copper regulator portion of the burner

must be cleaned at least once a week If the gas pressure is too low, use a rubber band to constrict the gas reservoir fig

21, the band must be loosen after use to allow the bag to re-inflate. The main gas should be installed out of reach of children and kept locked when

fuel is not in use

6.1.1 Common problems and Solutions Problem Cause Potential solution

Bio- degradation process has not started Wait for few days for the process to start

Insufficient bacteria content Wait for few days for the process to start

No gas or not enough gas

Feed the digester with pre-treated material

32

Gas leakage Check the gas pipe line Check the water level in the safety valve Check the water level in the digestion chamber cover, in the siphons and in the lavatory pan

Not enough feeding material Feed as per recommendation

Holes or tears in the bag Repair it with nylon bandage or replace the bag

Gas reservoir do not inflate as they should Gas is leaking from the gas pipeline Repair the gas pipeline by

welding Flush the gas reservoir and wait for it’s replacement with the new biogas

Gas does not burn properly

Too much air or co2

Add a small amount of lime solution into the digester( be very careful not to add more)

Not enough gas pressure Constrict the gas reservoir with a rubber band or install a gas extracting device

The flame often extinguishes

Water has accumulated in gas pipeline Drain water from the gas pipeline

33

CHAPTER SEVEN 7.1. Practical exercise in calculation of total volume of a digester, construction materials and investment cost TaTEDO Center Goba Mbezi beach There are 30cattle. Retention time = 30 days given, length = 3.3 m, width = 2 m, depth? Remark: 1 adult cattle quantity of manure per pig = 2 kg/day Calculate total volume of the intended digester, number of bricks, cement, sand, small stone and iron, and investment cost? Solution Steps:

1. Calculate digester volume and depth 2. Calculate the volume of foundation [Bear in mind to extended the exterior

dimension by 10 cm each] 3. Calculate the area surface of exterior walls 4. Calculate the volume of top concrete 5. Calculate the number of reinforcement steel 6. From all above you can have the quantity of cement, bricks, sand & gravel gravel

1. Digester Volume Formula: V= Vgas+ 6nLT Vdm

= 6nLT? n = (total no. of Cattle) = 30 Cattle, L (amount of manure/Cattle/day) = 2 liters = 0.002 m

3

T (retention time) = 30 days Hence, V

dm = 6 x 30 x 0.002 x 30 = 10.8 m

3

Total volume of digester V = V

gas + 10.8

But Vgas

= h1S=0.4 x 3.3 x 2 = 2.64 m3

(Length = 3.3 m and width = 2 m)

Thus, V = 2.64 + 10.8 = 13.44 m

3 ≈ 13.5 m

3

And V = 13.5 = 3.3 x 2 x Depth

Therefore, Depth = 13.5/ 6.6 ≈ 2 m Conclusion: Interior length = 3.3 m or exterior length = 3.5 m [assume a brick of 10 x9x23cm] width] Interior width = 2 m or exterior width = 2.2 m Depth = 2 m Digester volume = 13.44 m

3 ≈ 13.5 m

3

Volume of Foundation

34

For 5cm layer concrete mixture and small stone and mixture of sand and gravel Quantity of cement is found from the top layer concrete of 5cm Volume =3,6mX 2.3mx0.05 m=0.414m3 So 0.414m3 require 325 x 0.414 kg=134.55 cement=5.385 bucket [of 25litre oil/paint bucket] ≈5.5 bucket So cement: sand: gravel = 5.5: 11: 16.5 buckets For remaining layer of 15cm, Volume is 0.15mx3.6mx2.3m= 1.242m3 So quantity of gravel stone is 1.242 x 0.025m3 =0.031m3 So the quantity of gravel in bucket =0.031/0.02=1.55 bucket Cement =5.5 bucket (1), Sand=11 bucket (2) Small stone {1x2cm} Gravel = [16.5bucket] (3i) Small stone {1x2cm} Gravel=1.55 bucket (3ii) 2. Quantity of Bricks Total area of wall faces? Total area of wall faces = 2(3.5 x 2.00) + 2(2.2 x 2.00) = 22.80 m

2

Given 1m3 requires 325 kg of B200 cement And ratio is 1:2:3 cement: sand: gravel 1 sacs of 50kg cement =2 bucket of 25 litre [oil/paint bucket]

35

So, number of bricks for all wall faces = 24 bricks/m

2 x 22.80 m

2 = 550 bricks

And number of bricks for wall foundation = (1.2 x 2 + 1.2 x 2) x 24 = 116 bricks + 40 mixing tank brick= 156 bricks Therefore, total of bricks = 550 + 156= 706 bricks for both digester, mixing tanks and slurry 3. Quantity of Cement & Sand for Laying Bricks and Plastering Mortar for Walls, and Small Stone for Top Concrete a. Quantity of laying bricks & plastering mortar for walls = 22.80 m

2 x 25 kg/m

2 = 570 kg

So, 570 kg of cement for laying bricks and plastering walls = 570/ 25 =22.8 buckets b. Amount of sand for laying bricks & plastering the walls = 22.8 x 3 = 64.8 buckets Cement=22.8 bucket (4) Sand= 64.8 bucket (5) c. Quantity of cement for top concrete Assume V

1 for volume of the top concrete and size of concrete is 8cm

So, V1 = 0.08 x 3.30 x2.3 m3=0.644m3

Given 1 m3

of concrete = 322 kg of cement Therefore, quantity of cement for concrete = 0.644 m

3 x 325 kg/m

3 ≈ 209 kg

d. Quantity of sand & small stone for top concrete We know, 1 bucket of cement = 25 kg So, 276 kg of cement for concrete = 209: 25 ≈ 9 buckets (6) On the other hand, ratio of cement, sand and stone for concrete is 1: 2: 3 Then, Quantity of Sand = 9 buckets x 2 = 18 buckets (7) Small stone (1 x 2 cm) = 9 buckets x 3 = 27 buckets (8)

Given 1 m2

of wall face requires 25 kg of cement

Given 1 m2

= 24 solid bricks [SISPO] =48 KIDT=9 CEMENT BRICK Note: this depend on the size of the brick

Given 1 sack of cement = 50 kg = 2 buckets (paint bucket of 25liter)

(Given ratio of cement and sand for laying bricks and plastering walls is 1cement: 3 sands)

36

4. Total Amount of Construction Steel (D=8 mm) for Casting Concrete Distance of steel cast in length of digester = 3.3 + 0.35 = 3.65 m (interior length = 3.3 m) Distance of steel cast in width of digester = 2 + 0.35 m (interior width = 2 m)

So, Number of steels cast in width of 2.35 m = (3.65/ 0.15) + 1 ≈ 25 steels Number of steels cast in length of 3.65 m = (2.35/ 0.20) + 1 ≈ 13 steels

Therefore, total quantity of steel for casting concrete = [(25 x 2.35) + (13 x 3.65)] x 0.386 = (58.75 + 47.45) x 0.386 ≈ 41 kg) OR

Given, a gap from one steel to another cast in width = 0.15 m And 0.35 is an invariable coefficient for calculation of one length of steel

We know, 1 m of 8-mm diameter steel = 0.386 kg 1 length of 8mm diameter is 12 m long

Therefore, Total of cement = (1) + (4) + (6) =5.5 + 22.8 + 9 ≈ 37.3 buckets Total of sand = (2) + (5) + (7) = 11 + 64.8 + 18 ≈ 93.8 buckets Total small stone (1 x 2 cm) = (3i) + (8) =16.5+27 ≈44 buckets Total medium stone = (3ii) =1.55 bucket

Number of length required = [(25X 2.35) + (13X3.65)] / 12=8.85≈9 length

Conclusion Investment Cost for a Bio-digester with Volume of 13.5 m

3

1. Total volume of digester V = 13.5 m

3

2. Total number of bricks = 1,925 bricks 3. Total quantity of cement = 37.3 buckets (paint bucket) = 19 sacks of cement 4. Total quantity of sand = 94 buckets = 94 x 0.02 = 1.88 m

3 (1 bucket = 0.02 m

3)

5. Total quantity of stone (size 1 x 2 cm) = 45 buckets = 45 buckets x 0.02 = 0.9 m3

6. Total quantity of stone (size 8 x 10 cm) = 1.55x 0.02 = 0.031 m3

37

Investment cost for 13.5 m3 biogas plant.

No. Description Unit Qty Unit Price (Tshs) Total

1 Cement 50kg sacs 19 15,000 285,000

2 Steel (D = 8 mm) Length 9 11500 103,500 3 Sand m

3 1.88 18,000 33,840

4 Solid brick piece 706 250 176,500 5 Stone (size 1 x 2 cm) m

3 0.9 36,000 32,400

6 Stone (size 8 x 10 cm) m3 0.03 16,000 480

7 Biogas burner set 2 8,000 16,000 9 Plastic pipe m 15 1,600 6,000 10 Plastic valve unit 1 1,200 1,200 11 Metal valve unit 2 2,500 5,000 12 Plastic reservoir m 7 2,500 17,500 13 Glue bottle 1 1,500 1,500 14 Paper glue roll 1 1,500 1,500 15 Ring (plastic) unit 10 800 8,000

16 Zinc pipe and clip (Ø = 20 mm, L = 2.5m) set 2,5 1,000 2,500

18 Metal pipe (Ø = 20 mm, L = 1 m) and metal connector of Ø20 mm at one end and of Ø27 mm at the other

m 1.5 2,800 4,200

19 Metal connector with gear at both exterior ends

set 1 2,000 2,000

21 PVC pipe (Ø = 20 mm) 1 length 1 6,000 7,000 22 PVC L-shaped pipe (Ø =20 mm) unit 6 500 3,000 23 PVC T-shaped connector (Ø = 20 mm) unit 4 500 2,000 24 PVC siphon set 2 10,000 20,000 25 Adaptor set 1 20,000 20,000 26 Nail (L = 5 cm) kg 1 3,000 2,000 27 Nail (L = 8 cm) kg 0.5 2000 1000 28 Nail (L = 10 cm) kg 0.5 2000 1000 29 Labor cost for digging m

3 14.4 4,500 64,800

30 Labor cost for constructors and technician Digester 1 300,000 300,000

Grand Total 1,117,920Remark: US$ 1 = 1200 tshs on July 2008

38

5.1.2. Mr. George Ntenga V=7.5 m3, Number of adult Cattle = 10, retention time = 40 days, available land 2mx6m and 2m deep Notice: 1 adult Cattle (manure), amount of manure/pig/day = 2 kg. Calculate total quantity of bricks, cement, sand, small stone and construction steel and investment cost?

Solution From all above you can have the quantity of cement, bricks, sand & gravel gravel 1. Dimension of the bio-digester tank V= 0.4S + 6nLT Hence 7.5m3=0.4mxS + [6x10x0.002m3x40} S=[7.5-4.8]/0.4=6.75m2 By keeping the width at 2m length should be 3.4m Conclusion 1: Interior length = 3.4 m or exterior length = 3.6 m [assume a brick of 10 x9x23cm] width] Interior width = 2 m or exterior width = 2.2 m Depth = 2 m Digester volume = 7.5 m

3

Foundation volume calculation For 5cm layer concrete mixture and small stone and mixture of sand and gravel Quantity of cement is found from the top layer concrete of 5cm Add 10cm to the exterior dimension!!! Volume =3,7mX 2.3mx0.05 m=0.425m3 So 0.432m3 require 325 x 0.425 kg=138.2kg cement=5.5 bucket [of 25litre oil/paint bucket] ≈5.6 bucket So cement: sand: gravel = 5. 11. 16. Buckets

Given 1m3 requires 325 kg of B200 cement And ratio is 1:2:3 cement: sand: gravel 1 sacs of 50kg cement =2 bucket of 25 litre [oil/paint bucket]

Steps Calculate the dimension of the biogas keep depth at 2m Calculate the volume of foundation [Bear in mind to extended the exterior dimension by 10 cm each] Calculate the area surface of exterior walls Calculate the volume of top concrete Calculate the number of reinforcement steel

39

For remaining layer of 15cm, Volume is 0.15mx3.7mx2.3m= 1.276m3 So quantity of gravel stone is 1.276 x 0.025m3 =0.031m3 So the quantity of gravel in bucket =0.031/0.02=1.6 bucket Cement =5. Bucket (1), Sand=11 bucket (2) Small stone {1x2cm} Gravel = 16bucket (3i) Small stone {1x2cm} Gravel=1.6 bucket (3ii) 2. Quantity of Bricks Total area of wall faces? Total area of wall faces = 2(3.6 x 2.00) + 2(2.2 x 2.00) = 23.2 m

2

So, number of bricks for all wall faces = 24 bricks/m2 x 23.2 m

2 = 557bricks

And number of bricks for wall foundation = (1.2 x 2 + 1.2 x 2) m2 x 24bricks/m2= 116bricks + 40 bricks for mixing tank= 156 bricks Therefore, total of bricks = 560 + 156= 716 bricks for both digester, mixing tanks and slurry 3. Quantity of Cement & Sand for Laying Bricks and Plastering Mortar for Walls, and Small Stone for Top Concrete a. Quantity of laying bricks & plastering mortar for walls = 23.2 m

2 x 25 kg/m

2 = 580 kg

So, 580 kg of cement for laying bricks and plastering walls = 580/ 25 =23.2 buckets b. Amount of sand for laying bricks & plastering the walls = 23.2 x 3 = 69.6 buckets Cement=23.2 bucket (4)

Given 1 m2

of wall face requires 25 kg of cement for laying brick and plastering

Given 1 m2

= 24 solid bricks (SISPO) =48 KIDT=9 cement brick Note: this depend on the size of the brick

Given 1 sack of cement = 50 kg = 2 buckets (paint bucket of 25liter)

(Given ratio of cement and sand for laying bricks and plastering walls is 1cement: 3 sands)

40

Sand= 69.6 bucket (5) . Quantity of cement for top concrete Assume V

1 for volume of the top concrete and size of concrete is 8cm

So, V1 = 0.08 x 3.6 x2.2 m3=0.64m3

Given 1 m3

of concrete = 322 kg of cement Therefore, quantity of cement for concrete = 0.644 m

3 x 325 kg/m

3 ≈ 207 kg

d. Quantity of sand & small stone for top concrete We know, 1 bucket of cement = 25 kg So, 207 kg of cement for concrete = 207: 25 ≈ 9 buckets (6) On the other hand, ratio of cement, sand and stone for concrete is 1: 2: 3 Then, Quantity of Sand = 9 buckets x 2 = 18 buckets (7) Small stone (1 x 2 cm) = 9 buckets x 3 = 27 buckets (8)

4. Total Amount of Construction Steel (D=8 mm) for Casting Concrete Distance of steel cast in length of digester = 3.5 + 0.35 = 3.85 m (interior length = 3.5 m) Distance of steel cast in width of digester = 2 + 0.35 m =2.35m (interior width = 2.0 m)

So, Number of steels cast in width of 2.35 m = (3.85/ 0.15) + 1 ≈ 27 steels Number of steels cast in length of 3.85 m = (2.35/ 0.20) + 1 ≈ 13 steels

Therefore, total quantity of steel for casting concrete = [(27 x 2.35) + (13 x 3.85)] x 0.386 = (63.45 + 50.05) x 0.386 ≈ 44 kg) OR

Given, a gap from one steel to another cast in width = 0.15 m And 0.35 is an invariable coefficient for calculation of one length of steel

We know, 1 m of 8-mm diameter steel = 0.386 kg 1 length of 8mm diameter is 12 m long

Therefore, Total of cement = (1) + (4) + (6) =5 + 23.2 + 9 ≈ 37.2 buckets Total of sand = (2) + (5) + (7) = 11 + 69.64 + 18 ≈ 98.6 buckets Total small stone (1 x 2 cm) = (3i) + (8) =16+27 ≈43 buckets Total medium stone = (3ii) =1.6 bucket

Number of length required = [(27X 2.35) + (13X3.85)] / 12=9.45≈10 length

41

Conclusion Investment Cost for a Bio-digester with Volume of 7.5 m

3

1. Total volume of digester V = 7.5 m

3

2. Total number of bricks = 1,950 bricks 3. Total quantity of cement = 37.2 buckets (paint bucket) = 19 sacks of cement 4. Total quantity of sand = 98.6 buckets = 98.6 x 0.02 = 1.97 m

3 (1 bucket = 0.02 m

3)

5. Total quantity of stone (size 1 x 2 cm) = 43 buckets = 43 buckets x 0.02 = 0.9 m3

6. Total quantity of stone (size 8 x 10 cm) = 1.5x 0.02 = 0.03 m3

42

REFERENCES 1. Khandelwal, K. C. , Mahdi S.S, Biogas technology, a practical handbook. Tata McGrawhill Publishing Company Limited, New Delhi, 1986 2. Luwid Sasse, Christopher Kellner, Ainea Kimaro, Improved Biogas Unit for Developing Countries published in Germany in 1991 3. MIGESADO, Mtambo wa gesi ya samadi, maelezo na utunzaji, Ecoprint Ltd, Dar Es Salaam, 1997 4. Singh, JB, Myles, R. Dhussa, A., Manual on Deenbandhu biogas plant, Tata McGraw-Hill Publishing Company Limited, 1993 5. Thanh, Pham Van, Biogas Technology and the improved VACVINA biogas plants Social Labour Publishing House, Hanoi, 2007

43

ATTACHMENTS 1. Sample cost estimate of a 7.5 m3 biogas plant Material required for 7.5m3 biogas plant

No. Description Unit Qty Unit Price (Tshs) Total

1 Cement 50kg sacs 19 15,000 285,000

2 Steel (D = 8 mm) Length 10 11500 115,000 3 Sand m

3 1.97 18,000 35,460

4 Solid brick piece 660 250 165,0005 Stone (size 1 x 2 cm) m

3 0.9 36,000 32,400

6 Stone (size 8 x 10 cm) m3 0.03 16,000 480

7 Biogas burner set 2 8,000 16,000 9 Plastic pipe m 15 1,600 6,000 10 Plastic valve unit 1 1,200 1,200 11 Metal valve unit 2 2,500 5,000 12 Plastic reservoir m 7 2,500 17,500 13 Glue bottle 1 1,500 1,500 14 Paper glue roll 1 1,500 1,500 15 Ring (plastic) unit 10 800 8,000

16 Zinc pipe and clip (Ø = 20 mm, L = 2.5m) set 2,5 1,000 2,500

17 Metal pipe (Ø = 20 mm, L = 1 m) and metal connector of Ø20 mm at one end and of Ø27 mm at the other

m 1.5 2,800 4,200

18 Metal connector with gear at both exterior ends

set 1 2,000 2,000

19 PVC pipe (Ø = 20 mm) 1 length 1 6,000 7,000 20 PVC L-shaped pipe (Ø =20 mm) unit 6 500 3,000 21 PVC T-shaped connector (Ø = 20 mm) unit 4 500 2,000 22 PVC siphon set 2 10,000 20,000 23 Adaptor set 1 20,000 20,000 24 Nail (L = 5 cm) kg 1 3,000 2,000 25 Nail (L = 8 cm) kg 0.5 2000 1000 27 Nail (L = 10 cm) kg 0.5 2000 1000 28 Labor cost for digging m

3 14.4 4,500 64,800

29 Labor cost for constructors and technician digester 1 300,000 300,000

44

2. Technical drawings for a 9 m3 biogas plant at TaTEDO SEDC

Location: TaTEDO Center for Sustainable Energy Address : Mbezi Juu, Dar es Salaam, Tanzania

Capacity: 9m3

TECHNICAL PLAN

45

Plan for construction Steels for the top of the digestion tank

46

Category Quantity of

bar Length/Bar Total for category S1 (ǿ8) 21 3,15 66,15 m S2 (ǿ8) 11 3,65 40,15 m

S3 (ǿ8) for technical hole 16 0,50 8,00 m

Total steel ǿ8 for theTop 115 m

- Quantity of Brick: 320 units - Cement: 1.2 tons - Sand: 2.5 m, - Small Stone (2-3cm): 2 m3

POSITION OF INLET & OUTLET

47

A

A

B B

48

Plan of mixing tank integrated to Inlet Siphone

Section 1 - 1

Detail of Mixing tank Door

The Door of the mixing tank is made by wood material with the thickness of 2cm (22 x 42 x 2cm). A steel hook is placed on top for facilitating its Open/Close when needed.

49

GENERAL ILLUSTRATION OF A VACVINA BIOGAS PLANT

50

3. Technical drawings for a 12 m3 biogas plant at George Ntenga’s house at Goba VACVINA BIOGAS PLANT

Location: Family of George Ntenga

Address: Mbezi Juu, Dar es Salaam, Tanzania Capacity: 12 m3

TECHNICAL PLAN

51

The Top of the digestion Tank

52

Category Quantity of

bar Length/Bar Total for category S1 (ǿ8) 28 2,15 60,20 m S2 (ǿ8) 11 4,15 45,65 m

S3 (ǿ8) for technical hole 16 0,50 8,00 m

Total steel ǿ8 for the Top 113,85 m

- Quantity of Brick: 250 units (Dimension: 15 x 23 x 45,5cm) - Cement: 1.0 tons - Sand: 2.0 m3, - Small Stone (2-3cm): 2.0 m3