Design and Development of multi stage digester for waste to energy conversion
Municipal waste is an ever growing problem for Pakistan. It is estimated that approximately 48 kilo tons of waste is generated per day with an annual increase of about 3.4 %. Such a high generation rate of waste is causing many serious environmental, economic, social and health problems. A major com
2025-06-28 16:26:18 - Adil Khan
Design and Development of multi stage digester for waste to energy conversion
Project Area of Specialization Mechanical EngineeringProject SummaryMunicipal waste is an ever growing problem for Pakistan. It is estimated that approximately 48 kilo tons of waste is generated per day with an annual increase of about 3.4 %. Such a high generation rate of waste is causing many serious environmental, economic, social and health problems. A major component of municipal solid waste is food waste which comprises biodegradable organic components. Food waste is mostly suitable for treatment and energy generation. Waste to energy conversion is promising idea which not only addresses the environmental issues but also helps in solving energy problem.
Anaerobic Digestion (AD) is widely used technique for food waste treatment. Anaerobic digestion is a process of decomposition of organic waste in the anoxic and hypoxic conditions i.e. absence or lack of oxygen. Presence of different species of microorganisms play critical role in the decomposition and leads to the production of biogas and leachate as an end-product. Production of biogas as fuel and use of leachate as organic fertilizer make AD a sustainable disposal option. Anaerobic digestion reduces air pollution along with the recovery of nutrient, energy, and compost. AD is an efficient net energy producing system
In this project. a multistage digester based upon anaerobic digestion is proposed. The proposed digester will make use of slurry produced by waste grinder and will generate bio gas. The digester comprises of a plastic drum, a slurry pump, a High Density Poly Ethylene (HDPE) digester shell, slurry pipes and gas handling pipes.
As described, the digester will produce biogas and fertilizer as its products by using food waste. In this way, the proposed project offers environmental and economic benefits.
- To estimate the design parameters of the digester
- To design the multi stage digester
- To develop the multi stage digester
- To test the performance of the digester
The project implementation starts with reviewing the various available designs of AD digestors. An analytical study will be conducted to select design parameters for the proposed digester. Since the performance of digester depends upon the characteristics of waste, food waste characteristics will be studied based on literature. In third stage, some food waste samples will be collected and laboratory tests will be conducted to analyze the food waste characteristics. Theoretical and practical results of food waste characteristics will be compared to finalize the digester design parameters. After finalizing the design parameters, material selection will be done for the various components of the digester. Material selection will follow the quality and safety standards. Based upon standards, the plastic drum, slurry pump, slurry pipes, biogas pipes of prescribed specifications and standards will be obtained from appropriate vendors.
The details of design are provided in technical section. The working of digester is such that the plastic drum is inlet is to be exposed to the waste to be digested. The outlet section is to be joined through slurry pipe to the inlet of the slurry pump. The outlet of the slurry pump is to be joined to the inlet of the HDPE digester. In the direction from plastic drum to the digester the non-return valves are to be installed so to direct the waste in one direction. The biogas pipe is to be drawn from the plastic drum to the digester all the way to the cylinder.
Benefits of the ProjectOn its successful completion, the project will offer environmental, economic, social and health benefits.
- Public health improvement by reducing open dumping of food waste
- Environmental pollution control through solid waste treatment
- Clean energy generation
- Organic fertilizer production
The main components of the multi stage digester are:
- Plastic drum
- Slurry pump
- HDPE digester
- Slurry pipe
- Gas handling pipe
Plastic drum:
The first drum is the traditional water storage drum with the capacity of storing 2000 litre water.
Slurry Pump:
The pump that is used to dump the slurry from the plastic drum to the HDPE digester.
Design of HDPE digester:
• The digester cover was made of the same HDPE plastic material that could withstand harsh environmental conditions and still maintain anaerobic condition.
Volume of the Digester:
• The volume of the designed and fabricated biogas digester is 2.15 m3 size. Total digester volume took into consideration digester neck volume (Vn) where the digester cover was fixed, gas storage volume (Vgh), and the slurry or fermentation chamber volume (Vfc). For the fabrication of the biodigester, the design calculation of the digester neck, gas storage section, and slurry chamber were considered
The three shapes used in describing the different compartments of the biogas digester include the cylindrical shape that formed the neck, the spherical shape (for gas storage), and the frustum shape of the slurry chamber. The volume of each of these shapes contributed to the total volume of the biogas digester. The following parameters were used in the calculation:
• No. of sides = 12 sides
• Length of each side of the bottom stage = 0.36 m
• Length of each side of the top stage = 0.39 m
• Apothem length of the bottom and top stage = 0.65 m
• Height of the digester = 1.70 m
• Height of the hemispherical part = 0.73
| Item Name | Type | No. of Units | Per Unit Cost (in Rs) | Total (in Rs) |
|---|---|---|---|---|
| Total in (Rs) | 80000 | |||
| Plastic Drum | Equipment | 1 | 18500 | 18500 |
| Slurry pump | Equipment | 1 | 28000 | 28000 |
| HDPE digester | Equipment | 1 | 19500 | 19500 |
| Slurry pipe | Equipment | 1 | 3000 | 3000 |
| Biogas pipe | Equipment | 1 | 1000 | 1000 |
| Field visits for sample collections | Miscellaneous | 1 | 5000 | 5000 |
| Lab tests | Miscellaneous | 1 | 5000 | 5000 |