SREL employs a tested-and-proven technology called anaerobic digestion to cleanly convert organic waste into biogas, a form of renewable energy, and organic fertilizer. Biogas is a renewable gas consisting primarily of methane and carbon dioxide, and can be used as natural gas, converted into electricity, or further processed into compressed natural gas (CNG) for use in motor vehicles.
Step 1: Conversion of Organic Waste into Biogas
Organic, biodegradable waste, or feedstock (pressmud), enters the system for digestion where an anaerobic process using bacteria ferments the wastes and produces biogas as a gaseous bi-product. Several times a day, waste, fresh water and recycled water (over 30% water is reused during plant operations) is fed into digesters, which serve to treat the feedstock, eventually turning it into biogas consisting of mostly methane, as well as carbon dioxide and hydrogen sulfide.
Step 2: Biogas Conversion into Bio-CNG
The biogas produced at our plant will contain approximately 60% to 70% methane, 30% to 40% carbon dioxide and trace amounts of hydrogen sulfide.
This biogas produced is further processed so that the carbon dioxide and hydrogen sulfide gases are removed. The result is a gas consisting of mostly methane. This is very similar to natural gas obtained from the oil & gas fields.
By using compressors in our bottling plant, the methane and carbon dioxide gases will be stored under high pressures in cylinders. These gases can then be utilized in industrial applications, for fuel in vehicles, electrical power generators and for other heating purposes.
With an onsite combined heat and power (CHP) unit, electrical power generation is also viable. The Warana Bio-CNG project will be using a portion of the gas for auxiliary power consumption to run the plant. The waste heat from the CHP unit will also be used to maintain the temperature of the digesters.
Step 3: Organic Fertilizer Use and Storage
The remaining non-digestible solids exit the digester in the form of a liquid slurry. The liquid slurry is further processed into a semi-liquid slurry (pressmud digestate) and pumped into trucks for further use by local farmers. The effluent from the slurry processing is stored in an adjacent storage lagoon and eventually recirculated back into the digesters with the feedstock at the beginning of the anaerobic digestion process.