In May 2014 TaTEDO signed a contract with the United Nations Human Settlement Program of UN- HABITAT to implement a project for the construction of 200 m3 Biogas Plant at Manzese Secondary school in Dar es Salaam, Tanzania. The main objective of the project was to improve sanitation system at Manzese Secondary School with an environmentally friendly solution. The construction work of 200 m3 Biogas Plant at Manzese Secondary school in Dar es Salaam was completed in June 2015. During construction the following activities were undertaken
SITE CLEARANCE AND EXCAVATION WORK
Site preparations and clearance were completed in September 2014 followed by excavation of 2 pits of 100m3 twin Bio latrine. After excavation the construction of bio digesters started.
The Twin Bio Digesters each of 100m3 were constructed. The work done include:-
• Completion of the brickwork on the two digesters
• Fixing of dome gas pipes. : Fixation of the two dome gas pipes was done before carrying out inside gas tightness plasters.
• Plastering the outside upper parts of the digesters: The outer plaster protects the brickwork against roots growing into the joints. It also forms a smooth surface which reduces friction between soil and the structures and thus reduces static stress on the brickwork.
• Plastering the inside upper parts of the digesters. The plasters of the inside parts of the digesters have smooth surfaces for better gas tightness
CONSTRUCTION OF EXPANSION CHAMBERS
The construction of two expansion chambers was completed. The function of the expansion chamber is to store the displaced digested slurry from the digester (equivalent to equal volume of the gas produced), and thus developing pressure inside the plant (digester). The works carried out under this component includes:
• Construction of two expansion chambers ( one chamber for each digester)
• Inside and outside plastering of all two expansion chambers
• Constructions of five expansion chamber manholes and fabrication of its lids
SOIL BACK FILLING
Once the digesters are in use, the brickwork will be under high pressure from the inside and therefore must be supported from the outside by firmly back filling of soil. Hence soil back filling was done on the two digesters and the two expansion chambers.
REHABILITATION OF EXISTING TOILETS
The biogas plant construction of Manzese Secondary School in Dar es Salaam has been built to treat the waste from latrines. There were two existing pit toilets at the school for students and members of staff. Since human faeces are the main feed stock of the constructed plant, it was therefore necessary to convert the pit latrines into flush toilets in order to collect the feed materials. Rehabilitation of the two toilets each with twelve cubicals has been done. The toilets have been connected to a 6” PVC pipe system that feeds all the waste into the twin biogas digester via a toilet inlet chamber
CONSTRUCTION OF WASTE WATER TRANSPORTATION & SLURRY COLLECTION UNITS
Waste water transportation system was constructed as well as slurry collection and disposal units which includes filtration units. Digested substrate has almost no smell and is more liquid than undigested substrate. The volume of digester slurry is about twice as much as that of fresh substrate. Insufficient slurry disposal leads to blockage of the outlet and rising gas pressure inside the fixed dome plant. Therefore, clever and realistic planning of slurry disposal is important.
The use of a waste water treatment plant is an important design criteria concerning hygiene and safe slurry disposal. In this system, slurry is treated before being drained into a soak pit to achieve the expected sanitary conditions. The slurry disposal system constructed at Manzanse Secondary School consists of a main chamber (holding pit) waste water treatment plant and the soak pit
GAS PIPING WORK AND STOVES
Construction of gas piping system from bio digester to the kitchen was completed, one gas outlet has been provided for school laboratory, furthermore, three biogas stoves and three pots (One with capacity of 75Litres and Two with capacity of 100Litres each ) were procured and installed in the kitchen
CAPACITY BUILDING TO SCHOOL COMMUNITY ON OPERATION AND MAINTENANCE OF BIOGAS SYSTEM
TaTEDO staff conducted capacity building training to school community on operation and maintenance of biogas system. Teachers, students and cook were taken through all constructed units and detailed explanation on how to operate, use and maintain biogas system was given. The operation manual in Swahili language was distributed to teachers and students
SOME OF THE BENEFIT OF BIOGAS
Availability of Biogas Technology has the following advantages:-
1. Biogas provides the clean energy for cooking/heating and other domestic and industrial uses.
2. Reduces workload for women on firewood collection and time saved can be used for other productive activities.
3. Contributing going environmental conservation effort and Improves surrounding-health/sanitation, and thus no/ or less spread of diseases.
4. Improves socio-economic gains of the users. i.e saving of money on other fuels.
5. Alternative to traditional wood-fuel, thus protecting the on-going deforestation activities
6. Create employment opportunities, and hence contribute poverty reduction caused by use of traditional and unsustainable energy.