In Gujarat, harnessing the value of dung to boost farmers’ income
No Comments
In Gujarat, harnessing the value of dung to boost farmers’ income
Subject: Science and tech
Section: Msc
Context:
- Gujarat’s dairy cooperatives are showing the way in supplementing their farmers’ income from milk by procuring dung and converting it into Bio CNG and fertilizer.
More on news:
- Deesa-Tharad highway in Gujarat’s Banaskantha district, catering to 90-100 vehicles daily, is India’s first and only gas-filling station based on dung from cattle and buffaloes.
Dung facts
- From 40 tonnes of dung, we get 2,000 cubic meters of raw biogas containing 55-60% methane, 35-45% CO2, and 1-2% hydrogen sulfide (H2S) and moisture
About Biogas plant:
- A biogas plant requires fresh dung, which contains methane along with water.
- The methane is produced by bovines inside their rumen (first of four stomach compartments), where the plant material they eat gets fermented or broken down by microorganisms before further digestion.
- Carbohydrate fermentation leads to production of carbon-dioxide (CO2) and hydrogen.
- These are used by archaea (bacteria-like microbes in the rumen) to produce methane, which the animal expels either as gas or in the dung.
- The dung left to dry in the open releases both water and methane.
- To realize its fuel value, the dung has to, therefore, be collected and delivered in fresh form at the biogas plant.
Fuel plus fertilizer:
- The raw dung unloaded at the BioCNG plant is mixed with an equal quantity of water. The resultant slurry is then pumped into an anaerobic digester.
- Anaerobic digestion is a process by which the complex organic matter in dung is broken down in the absence of oxygen to produce biogas
The digestion involves four successive stages:
- hydrolysis (break-down of organic matter into simple molecules),
- acidogenesis (their conversion into volatile fatty acids),
- acetogenesis (production of acetic acid, CO2 and hydrogen) and
- methanogenesis (biogas generation).
What is Biogas?
- It mainly comprises hydro-carbon which is combustible and can produce heat and energy when burnt.
- Biogas is produced through a biochemical process in which certain types of bacteria convert the biological wastes into useful bio-gas.
- Since the useful gas originates from a biological process, it has been termed as bio-gas.
- Methane gas is the main constituent of biogas.
Purification of Biogas:
- The raw gas is purified for removing CO2 (through vacuum pressure swing adsorption or VPSA process), H2S (using activated carbon filter) and moisture (with air dryer separator).
- The end-product, purified (to 96-97% methane, 2-3% CO2 and below 0.1% H2S and moisture) and compressed, is stored in cascades.
- This compressed biogas (CBG), conveyed through pipelines to the dispensers at the fuel station, is what’s being sold as BioCNG at Rs 72/kg.