1- What is Biogas? 2- Advantages of biogas digestion: gas, compost, less pollution 3-How does it work

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1 1 1- What is Biogas? Biogas is produced by the anaerobic (without oxygen) fermentation of organic material (shit, leaves, anything you can compost). Production systems are relatively simple and can operate at small and large scales practically anywhere, with the gas produced (called biogas) being as versatile as natural gas (as biogas is around 60% methane CH 4 ). Biogas can be used as cooking gaz and also to substitute for diesel in engines and generators. On a big scale it can also be used in a grid and provide electricity. This is a significant technology option for Tuvalu since anaerobic digestion can make a useful contribution to disposal of domestic and agricultural wastes and thereby alleviate the severe public health and water pollution problems that they can cause. The remaining sludge can then be used as a fertiliser and actually performs better than the original manure/compost because weed seeds are destroyed in the digestion process, odours reduced and nitrogen is converted into a form that can be readily used by plants.) Biogas digestion is a tried and tested technology, is used world wide on a massive scale, and has been used in the UK, China, India and other countries for over 200 years and is still in use today. 2- Advantages of biogas digestion: gas, compost, less pollution Biogas offers great potential in meeting the household's energy needs, especially for cooking or running a diesel engine. In addition, pigs (& humans!) create waste which pollutes an already very vulnerable marine environment putting this waste in a digester will make it into something valuable and useful gas & compost!!! The compost produced by the digestion process can be used for fertilizer (either left as a liquid or died) for vegetables or other plants. It is very high in Nitrogen, Phosphorous and Potassium ( NPK - just like fertilizer you buy in the shops) and can also be used as fish feed (like the one used at De Montford Boy's school in Fiji where the "compost" is used to feed milkfish). The digested residue ("compost") is an almost odourless liquid sludge which can be piped to irrigate and fertilize plants directly or dried, bagged and sold as organic fertilizer. Gas Production: Basic digester systems will produce around 0.5 m3 of biogas per m3 of digester volume. For a family of 6 people & 10 medium sized Tuvaluan pigs, digester systems of size 4m3 can meet daily biogas requirements (about 2m3) for all residential uses this is a digester around 2/3 the size of a 6000 litre water tank. 3-How does it work Digestion process: Just like your stomach!!! It is a natural process which produces gas (when you get wind!) and compost (when you!). Just like your stomach the digester needs feeding with organic material. Please note that the process of digestion will stop if sea water or chemicals like soap, toilet cleaner, any cleaning product or bleach are swallowed (put into the digester)!! Plan of the digester at Amatuku (this is known as a Chinese Fixed Dome design very common in China with over half a billion of them in use worldwide today!!)

2 2 The process is gravity fed which means it requires no pump to run and maintain. In addition, this design uses what is known as a continuous process whereby the pig shit is continuously fed into the inlet, it naturally flows through the main digestion chamber over a period of about 5-6 weeks and then flows out as compost (liquid slurry) which can be collected from the Displacement Tank. From 10 pigs (enough to cook for a family of 6) there should be around 40kg per day fed to the digester and no more than 6 litres of washing water per day so clean out every 3 days with litres of fresh water and feed manure to the digester every day. If fed continuously, then gas and compost will be produced continuously in return The gas is piped out through a galvanised steel pipe, then into a plastic pipe for use directly in a normal domestic gas stove. Using gas piped directly into the home for cooking and lighting is the most effective way to benefit from a family-scale digester. This means that the digester has to be near the home (maximum of 10 metres away). Because the process is gravity fed, the digester is best placed underground (like in the diagram above). The proportion of fresh water used to wash the pig pen or flush the toilet has to be kept to a minimum to keep the proper parameters required to make gas. 4- Different types of digesters 4-1-THE ALOFA TUVALU AMATUKU BRICKS DIGESTOR Why : An Alofa Tuvalu project is to show and train a maximum of people in Tuvalu how to in order to reproduce and help reduce oil/gas import and expenses as well as reducing green house gas emissions, responsible for climate change. The first biogas digester at Amatuku is an 8 m3 Camartec fixed dome plant built fusing bricks and cement. The digester is running from PIG (or any type fo animal) MANURE from a 6/12 pigpen piggery for 50 or 60 pigs.

3 3 The piggery has been built for the project according to the gravity principle, i.e. piggery floor is higher than the digester and manure flushes down easily. The gas produced by the plant is for use for cooking in a community kitchen. The effluent from the digester, a very good fertilizer, is used for watering the school garden. A second Alofa Tuvalu s digester is planned in Amatuku. This one will run from the waste of the 40 Students according to the same principles. Plumbing has to allow only toilet waste to get into the digester. Shower and sink pipes cant be mixed into the digester : detergent kill the bacteria and keep the gas from forming 4-2- The NANUMEA plastic digesters : For Alofa Tuvalu second digester implementation, we chose another technique, based on designs of bio digester from China and india, made of fibreglass/plastic. A prototype was implemented by Sikeli and is in use since July Of much lower cost than the brick dome, it is made of two plastic water tanks, one is bigger than the other so that once the top of each tank is cut open, the smaller one can fit in the bigger one and move like a "telescope. The bigger tank (or drum) serves as a digester, and the smaller, placed upside down in the bigger one serves as the gas holder..

4 4 5-HOW TO BUILD A DIGESTOR : PLANNING AHEAD we advise to take all securities before starting a project and to make sure you have everything needed before starting. a) Check and chose the site b) the location of the digester compared with the piggery (if any) and kitchen stove ending gas supply. Also locate where there is going to be no water (from rain or sea) entering the digester c) the material, the equipment listing d) Tuvalu s specificities (salt water rising thru the ground, equipment not easily available) 4-HOW TO USE FEED STOCK Daily feeding can be used for continued use of plant - The digester can be fed with animal manure, waste flour, vegetable residues, waste food, waste oil, fruit peelings and rotten fruit. Oil cake, left over from oil-pressing, is another useful feedstock. Even rhizomes of banana, canna, nutgrass, non-edible seeds (e.g. Leucaena, Sesbania, tamarind, mango kernels) and spoilt grain serve as excellent feedstock material. Feedstock with large lumps should be broken up or cut into small pieces then fed into the bio digester. When compost comes out, that means there s gas in the digester. b) maintenance : If everything has been done according to plan, there should not be any need for maintenance for at least 10 years.

5 5 5-HOW TO USE THE GAS A pipe comes out of the tank and can be plugged into the gas stove. Because of the low pressure of the gas it cant be used on a LPG stove but on a special biogas stove with a bigger opening than on normal stove. 6-COSTS - Material for a brick 12m3 digester (4 to 5 households) : approx 6000 fj$, The most costly item are the bricks which represent 50% of the cost. This does not include freight, piggery constructions and workers. - Plastic digesters : For one unit implemented in Nanumea, the cost of equipment for 2 water tanks for digesters and 1 water tank for storing water calculated for a 3 month drought is around 850 Aus$ for 3 plus shipping from Fiji - Fittings and accessories : (stove, gloves, funnels, buckets) : approximately 200 Aus$. - complementary wood and other fittings for piggery and water storage grounds (from Funafuti) : approx 400Aus$ If digesters were to be developed in Tuvalu, it would be a great idea, to manufacture them in Funafuti. - Building or adapting a piggery to fit the requirements of sloping will depend on many details but minimum should not be much more than the cost of a «normal» piggery with concrete floor. 7-The TO DO list - For pig manure fed digester, prepare the grounds to insure a slight slope from the piggery to the digester - Wash pigpens with rain water. Pigs can have free access to drinking water, but don t spill it into the digester! - Estimate a maximum of 50% water for the same amount of manure or other feedstock (e.g. 10 litres of waste into the digester means you can use 5 litres of water). 8-The NOT TO DO list - No salt water : this will kill the bacteria and stop the digester - No detergents (soap, toilet cleaners etc) or petroleum products: same issue than salt - No more than 50% of water in mixed (urine, although liquid, is not water and therefore counts as manure) : if water is in excess add more waste. - If less than 50% water, then the biogas is over-fed with organic waste and the biogas plant can fail. This is a particular challenge with a plant using highly digestible organic materials. If this happens, the plant can be recovered by ceasing feeding and then building up the feed rate slowly. Or clean the system and start all over again WHAT THIS ACHIEVES Apart from personal obvious benefit, using natural/bio energy also benefits Tuvalu on a much wider scale : by reducing fossil fuel emissions into the atmosphere, we are preventing climate change and global warming. Tuvalu by doing so gives an example to the world and participates in its own way to insuring its own future. This new biodigestor technology offers a solution for domestic waste disposal and pig waste which pollute the eco system both of land and lagon waters. Plastic bio digester plant could be replicated on the islands for domestic used to supplement fire wood, Kerosine and LPG gas. A single plant produces sufficient biogas to half the use of cooking in a household, as well as a small amount of solid residue which can be used as fertiliser for the gardens.