Cellulosic 2G Ethanol from agro-waste can prevent stubble burning

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Author – Nikita Nandakumar

Crop stubble burning has been the biggest environmental issue in India that hogged the media spotlight during winters over the last few years. There is an urgent need to reduce this burning and utilize this agricultural waste for producing biofuel or eco-friendly packaging material.

Why stubble burning?

Farmers in North India tend to burn their remaining crop residue of paddy, sugarcane and wheat during the post-harvest period in November-December. While the wheat crop residue is typically used as fodder, rice straw and other crop residues are considered waste. Recent trends indicate that crop residue burning is happening across India in summer, since some farmers are burning wheat residues as well.

Why is this happening? Getting the crop stubble removed and using it as fodder requires labor resources and time. Due to the steady migration of laborers to cities, the farm labor cost has risen steadily. So farmers prefer to use combine harvester machines, but these affordable devices are capable of only harvesting the top edge of the crops, leaving behind the stubble. For every hectare of wheat crop, the cost of renting a combine harvester is around INR1,600-2,000, whereas the cost of removing the stubble is INR3,500/ha. Considering the extremely low value of stubble fodder, it is more economical for farmers to just burn and clear the fields.

This crop stubble burning practice has come at a heavy price now. A Down to Earth study estimates that crop residue burning released 149.24 million tons of carbon dioxide, 250,000 tons of oxides of sulfur, 9 million tons of carbon monoxide and 1.28 million tons of tiny particulate matter, contributing to massive air pollution in cities such as Delhi while melting Himalayan glaciers.

Further, the heat from burning paddy straw penetrates 1cm into the soil, elevating the ground temperature, killing good bacteria, microbes and harming soil nutrients like nitrogen, phosphorus, potassium, sulfur. This has deteriorated the quality of crop and made them more prone to disease.

Initiatives to avoid stubble burning

Fortunately, there is an interesting solution to handle this menace of stubble burning and extract energy from it as well. Indian scientists have innovated a simple process of producing ethyl alcohol (ethanol) from cellulose of crop stubble, which can prevent stubble burning and provide a good local energy source to power plants.

Nowadays, various agricultural machines like Happy Seeder, Rotavator, Paddy Straw Chopper, have been developed so that farmers can manage crops and crop residue with ease. The state governments have put a subsidy now of 50-80% on crop machines and should continue to provide the support so that farmers can afford these machines. The use of farming residues as a biofuel for transportation or industry can, in turn, significantly reduce GHG emissions as compared to fossil fuels.

India’s first cellulosic 2G ethanol generation unit

India got its first second-generation (2G) ethanol plant named the Centre for Energy Biosciences set up at Kashipur in Uttarakhand. The Department of Biotechnology (DBT) and the Institute of Chemical Technology (ICT) Mumbai put up a pilot demonstration plant-based in the premises of India Glycols Limited.

The pilot plant has been operational since March 2016, converting and processing 10 tons of waste daily, capable of generating 300 liters of alcohol for every 1000 kilograms of agricultural waste such as bagasse, rice, wheat straw, cotton stalk, bamboo and wood chips. The plant yields bioethanol in less than 24 hours, as compared to 4-5 days taken by other plants. It recycles 90% of enzymes and water used, which brings down the operational cost significantly.

According to Arvind Lalli, the chemical engineering professor who heads the Centre for Energy Biosciences, a liter of 2G bioethanol can be produced and sold at INR25 per liter. As of 2014, 1G ethanol cost up to INR50. The plant features advanced reactor design and separation technologies with rapid reaction regime operations. The DBT-ICT Centre for Energy Biosciences, along with industrial partners, Bharat Petroleum Corporation and Hindustan Petroleum Corporation, is on the way to design and scale-up the technology to 450 tons per day by the end of 2020.

2G ethanol conversion technology

The 2G ethanol conversion is carried out in two methods – thermochemical and biochemical methods. In the thermochemical route, the biomass containing lignocellulosic feedstock is treated with non-biological catalysts (e.g. heat), temperature and chemicals to form an intermediate stage (synthesis gas). This gas is then purified to produce methanol, ethanol, other alcohols and hydrogen.

The Kashipur bioethanol plant set up by the DBT-ICT Centre for Energy Biosciences follows the biochemical conversion route. A series of large bioreactors are set up and the technology features more than 90% yield of sugars from biomass. Wheat and bagasse-based agricultural waste is used in its pilot operation round. They use imported enzymes that are recovered after the process and recycled back for the next batch process.

Why 2G Ethanol wins over 1G

Ethanol production from cellulose is not new but the second-generation ethanol process differs from the first generation one in terms of feedstock and the production process. You can check the detailed bioethanol production process from agri-waste here in this video on Bioethanol Production from Rice Straw – https://www.youtube.com/watch?v=A9BB-A2uc0I

1G Ethanol from sugar or molasses:
♦  Conflicts with the food chain
♦  Total installed capacity of only 2.5 billion liters currently
♦  Increased capacity will impact the sugar market and encroach on fertile land for sugarcane production

Cellulosic 2G Ethanol from agricultural waste:
♦  Prevents pollution from burning
♦  Recycles, adds value to farm waste
♦  Utilizes 500 million tons of farm waste available per year
♦  Can produce up to 100 billion liters of alcohol

Commercial feasibility

The National Biofuels Policy formulated in 2018 seeks to widen the range of feedstock for ethanol production from the present sugar-based molasses to other waste such as rural-urban garbage, cellulosic and lingo-cellulosic biomass including sorghum, sugar-beet, cassava, decaying potatoes, damaged grain including maize, cane trash, cotton stalk, bagasse, wheat, rice, and other crop residues allowing farmers to sell their agricultural residues while reducing the open-air burning of waste.

Around 12 public sector units are setting up cellulosic 2G ethanol bio-refineries across 11 states in India to produce around 35-40 crore liters of ethanol annually.

  • Indian Oil Corp has set up a 2G ethanol plant at its Panipat refinery. The proposed plant will utilize non-food biomass, mainly rice straw and other lignocellulosic feedstock, consuming around 473 tons of raw material to produce 100-kilo liters of biofuel per day.
  • Bharat Petroleum Corporation is setting up India’s first dedicated 2G ethanol bio-refinery at Baulasingha village in Bargarh district in Odisha. The Bargarh Bio-Refinery will utilize about 200,000 tons of rice straw annually as feedstock to produce 3 crore liters per annum of ethanol. The refinery will be based on zero-liquid discharge plant technology, where water will be recycled back into the plant.
  • Hindustan Petroleum Corp Ltd has installed a bio-refinery at Bhatinda in Punjab, utilizing agricultural residues to produce 3.20 crore liters per annum of ethanol. The unit is set to use around 400 tons of agriculture residue per day to produce the fuel.

We have a massive amount of agricultural waste sources available in India. However, the technology for converting cellulosic biomass into biofuels is still in the evolving stage, which needs to be upgraded and refined for commercial operation. If successfully operated and scaled-up, this cellulosic 2G ethanol conversion can establish India as a significant global technology provider, contribute to a reduction in carbon emissions, and reduced oil imports.

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