Environmentally Friendly Waste System

The aim of the prototype is to provide a smaller system where we can run the digester and use proportionality to confirm our results. To proceed with our prototype, we first have to calculate the theoretical amount of biogas produced and the amount of carbon dioxide and hydrogen sulphide that we have to remove.




Taking the basis to be 432kg of waste in the original digester

Total amount of biogas produced: 33.36 m3.

Total amount of carbon dioxide produced: 12.57 m3

Total amount of methane produced: 21.063m3



Taking the basis to be 4.32kg of waste in the prototype

Total amount of biogas produced: 0.3363 m3

Total amount of carbon dioxide produced: 0.1257 m3

Total amount of methane produced 0.21063m3



Hence concentration of CO2 present in Biogas would be 37.377%vol

Hence concentration of CH4 present in Biogas would be 62.63%vol

Therefore maximum composition of H2S in biogas produced: 1%vol (est 10-40ppm)



Composition of CO2 in head space: 0-0.03%

Initially there will be atmospheric air in the system. In this air, there is a 0.03%vol of CO2 in the system which can be negligible. The air is consumed by the bacteria as time goes on.



Composition of CH4 in head space: 0%

There is no methane gas in the atmosphere



Composition of H2S in head space: 0%

There is no hydrogen sulphide in the atmosphere

Since our large scale digester has the restriction of requiring a large amount of sludge, we have decided to focus on making the prototype which will enable us to put in more features at a lower cost with a more practical outlook. The prototype will give us many other advantages like demonstrating the wetland system using the prototype, proving the presence of methane from the digester prototype, and the addition of features which can be tested and proved through the prototype as well as measurements of gas contents and parameters via the prototype itself.


Required to prove the amount of gases produced
- CO2
- H2S
- CH4



To do this, Dr Han has suggested a closed system where the initial composition air of the closed environment is measured and compared to the final composition of air in the closed environment after anaerobic digestion is done(anaerobic is digestion is where all the gases are produced) Throughout the run, the system is air-tight and no air can enter in or escape.



Prototype designs:

Another alternative is that dragger tubes can be used for composition measurement of these gases. Dragger tubes are a cheaper alternative to meters. To use this method, we need a canister. It is made of acrylic tubes (low chemical strength) and we will incorporate drain valves, rubber seal etc. The dragger tubes can then be inserted into these openings to draw out the gases.



It was also discussed that the carbon dioxide produce is useful for marine plants growth (absorb CO2, release O2)this way, it reduces the amount of CO2 to the atmosphere (decrease in global warming effects as well). In return, the O2 produced by the plants can be used to grow fishes. However, there is a problem of Methane gas capture. It would be hard to capture it. Although it is not soluble in water, it would be hard to capture.



At the moment, these are the things we need to do:
1) Find out the range of dragger tubes
2) Calculation on sizing of canister


Following that, we can progress more on our small scale prototype and make the necessary changes from there.