Environmentally Friendly Waste System

Throughout the past weeks, we have been doing some literature research. I'll summarise our findings below:

Anaerobic Digestion:

1. The product of the anaerobic digestion is methane, CO2 and biomass
2. Requires no oxygen for the digestion
3. Most of the methane (70%) is produced in the final stage of the anaerobic digestion
4. There are three stages to anaerobic digestion

• Hydrolysis
• Acetogenesis
• Methanogenesis

In Acetogenesis, organic acids and alcohols are converted to acetic acid by acetogenic bacteria. Only with the production of the acetic acid can methane be formed in the last stage, Methanogenesis. In other words, acetogenesis is the limiting stage of methane production.
Aerobic Digestion:

1. The product of Aerobic digestion is water, CO2 and biomass
2. Bacteria consuming organic matter in the presence of air (oxygen)
3. The fastest rate of breakdown occurs at the start of the process so retention time of 2-6 days can achieve the desired results
4. Majority of the energy in the starting material is released as heat by their oxidisation into carbon dioxide and water

One apart from capturing Methane gas, in this project, we are also trying to cut down on the number of days for the two stage (aerobic & anaerobic) digestion to be completed. From what we found, we can reduce the aerobic stage of the process from the current standard of 10 days to somewhere between 2-6 days.
Initially, the whole process took 20 days, 10 days for aerobic and another 10 for the anaerobic digestion. So by shortening the time taken for aerobic digestion, it gives us room to play around the retention time of the anaerobic digestion. As such, we can optimise the production of methane gas as well.

Thermophilic MO:

1. Heat loving
2. Two types : True thermophilic and Facultative thermophilic
3. True Thermophiles: Optimum growth temperature of 60 oC-70 oC and no growth or feeble growth at 40-45 oC.
4. Facultative Thermophiles: Develop at about 20 oC, have their optimum temperature at about 50oC and their maximum is 60 oC
5. There are extremely thermophilic MO that can work at over a 100 oC.

Mesophilic MO:

1. Optimum working conditions: 20 oC (or lower) to 45 oC

There is still more research to be done on Mesophilic MO. To date, we have not found any substantial research that would add value to our project.

Methane Capture:
Used to indirectly measure the performance of the digester.
Ranges from 810 to 120L of digester gas per kg of volatile solids (13-18 ft3)
Proper operation can yield approximately:
-65-69% methane
-31-35% CO2
-if composition of gas contains more than 35% CO2 gas, the digester has problem

Carbon dioxide Reduction is where most of the remaining methane are being formed.
CO2 +8H ->CH4 + 2H2O
Methane formers are strictly anaerobic. They are more fastidous as compared to acid forming bacteria and have slower metabolism.
The ultimate oxygen demand of the waste being degraded is equal to the ultimate oxygen demand of the methane gas produced
-End of Research-
Note: There are certain formulas and diagrams that cannot be uploaded here on Blogger. Due to the formatting.
Apart from this research, we have met up during the first week of the holidays. We have came up with an equipment list and a softcopy of the datasheet on the parameters that need to be taken down during the run.

List of equipments needed:
1. pH and DO probe (from Mdm Tan – 10th June 09)
2. RTD and Data logger (Mr Kon)
3. Containers, beakers and test tube (Uncle Chris)
4. Tools – spanner, coupling
5. Stirrer
6. Pressure gauge indicator

Others (to check with Uncle Chris):
Glass bottles: use to contain the human manure to be digested
Water bath: to generate heat of 60 oC to the manure
Air divider to reduce the amount of air inlet to manure depending on the weight
Tubing: use as connector to transfer air to manure
Ensure all parts of the digester are in working condition
We have also found the ratio of H2S in the product to be insignificant. As such, removal may be secondary for the time being.

Compound Vol %
Methane 50-75
Carbon dioxide 25-50
Nitrogen < 7 Oxygen < 2 Hydrogen sulfide < 1 Ammonia <>
Lastly, Denise and Jianwei have spoken to Mr Desmond Lim on a suitable prototype for our project. The updates on that would be up next week. 

Plan for Holiday 2nd Week:

1. Call uncle Chris to confirm schedule for testing
2. Research on CO2 removal
3. Finalising on the procedures
4. 19th June : Actual first run of digester.
5. Discussion on the prototype

In our final year project, we will be working to extend on the project of an environmentally friendly system to handle waste recovery. In this project, the main idea would be to use human waste and convert it into a suitable manure to be used in plant growth.


This would be done using a 2 stage digester in which the waste would be loaded into the top and it would be process through an anaerobic process and later dropped to the bottom stage where it would undergo an aerobic process. The final product would be a fertilizer that can be used to grow crops in farms.

As a continuation of this project, we are planning to harvest the methane gas for usage as fuel in the third world countries. Methane gas is the byproduct in the anaerobic stage. In order to harvest the pure methane, we would be required to extract all other gases produced by the anaerobic process. This includes carbon dioxide and hydrogen sulphide. The most basic method would be to use water to absorb the other gases which are more soluble than methane.

This project can be traced back to the needs of the third world countries. This system is crucial because at the current moment, the waste in the third world countries are not being properly treated and thus, the living conditions are extremely unhygienic. In addition, by providing methane as a source of fuel for these third world nations, it would lower the burden of paying to buy fuel gas for daily usage.

We would be conducting most of our experimental runs at Singapore Vision Farm located in Chua Chu Kang and the testing of samples would be done in Ensure Engineering’s lab in Tuas.

This blog is to act as our logbook for our FYP.
We do welcome feedback.

Big Big Thanks to everyone who will be involved (: