Gas Test Checking
Before conducting the aerobic digestion run, we had to do a gas check first.
1. Close V7 to prevent any more gas from entering the methane capture system.
2. Insert the Drager tube into the gas test socket.
3. Ensure V4 is open.
4. Open V5 to allow the gas to fill up the gas test socket.
5. Drag the tube using the Drager pump to measure the concentration of gases inside
6. Close V5 after measurement is obtained.
Fig 1: Far right: Drager Pump, Far left: the gas test socket.
Fig2: Carbon Dioxide Drager Tube
We observed changes in colour near the tip of the drager tube as observed
Fig 3: Hydrogen Sulphide Drager Tube. There is a very dark noticeable colour change observed.
Fig 4: Qualitative testing of methane using Drager tube and pump
Fig 5: There is some colour change (greenish faint colour) Methane presence is proven
After the gas test checking, we proceeded to conduct the Aerobic Digestion. The procedures performed by us are as follows
Aerobic Digestion
Before conducting the aerobic stage, We ensured that the valves leading to the 1st chamber (Anaerobic stage) are closed. They are V1, V2, V4, V5, V6, V7, and V8.
1. Crack open vent valve V9 to allow natural atmospheric balance for digesting, the close it. Open V10 slightly then fully to measure the pressure of the system.
2. Open V11 and run Fish Tank Pump to allow aeration.
3. Start Heating Coil and maintain at 60oC by Thermostat control
4. Manually stir the sludge in the 2nd chamber
5. Leave sludge for approximately 10 days
6. After the completion of the process, collect sample by opening V3 and closing it after all the sludge has dropped into the bottom containment.
7. Stop Fish tank pump, Heating Coil, thermostat control.
8. Close all valves and perform housekeeping
Fig 1: The transferrence of the sludge from the 1st stage to the 2nd stage
Figure 2: leaking methane capture system
As observed, the waste had become more liquid, and the solids have disintegrated into the surrounding liquid. The colour of the waste mixture had also changed from a darker brown to a lighter brown. Even though still rather smelly, the smell seemed less pungent.
For this run, it was much better than the loading as all the waste had been contained. But problems on the digester prototype started to appear to us during our transferrence of sludge to the 2nd chamber below. As seen from Fig 6, there is leakages at the middle tube between the two chambers. The side and bottom of the 2nd chamber also started to leak as the level of the waste in the 2nd chamber increased. Immediately, we asked for some of the technicians to come down to rectify the problem. The problem was assumed recitified for that day after the technicians had sealed it with a different silicon, and the leaks seemed to have stopped.
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