Earning in place of burning

Paddy straw burning is considered a contributing factor to the dense haze that envelops the national capital and neighbouring states of Punjab, Haryana and Uttar Pradesh during October and November each year.

In recent years, the Union as well as state governments have imposed multiple rules and regulations to dissuade farmers from stubble burning. Measures such as subsidies have also been introduced to promote crop residue management machines like Happy Seeder. Yet, these have had little impact on the farm fire cases. This shows an urgent need to identify alternative utilisation of rice straw and thereby increase the value of the crop waste for farmers.

Here are some technologies that can help farmers, industries and government gain from paddy straw, while mitigating the problem of stubble burning.

Large-scale technologies

Direct combustion: This facility burns the rice straw in particular conditions to eliminate the massive piles of rice straw, while at the same time making the generated heat available for cooking and other purposes. Although the calorific value of rice straw (15 MJ / kg) is comparably less than that of petrol (45.8 MJ / kg) and diesel (54.5 MJ / kg), it is higher than the other agricultural waste. Currently, such facilities have not gained much attention in India.

Pyrolysis and gasification: These two technologies involve the burning of rice straw for its conversion into fuel in the form of a gas with high heating value. In pyrolysis, rice straw is placed in a system with a temperature range of 200-760 degrees Celsius where it is processed in the absence of oxygen. In the case of gasification, the temperature could range between 480-1,650 degrees Celsius along with some restricted supply of oxygen.

At present, the major problems linked with the use of gasification and pyrolysis techniques are low gas production and the presence of a large amount of tar in the gas, resulting in corroding the gas collection system. However, studies suggest that it is possible to generate high-quality syngas with high heating value through the gasification and pyrolysis process.

Biochar production: Biochar is produced as the final product after the incineration of rice straw at a lower temperature. The generated byproduct consists of 50 per cent of carbon content and is usually used as a soil conditioner (at optimum content of 20 tonnes per hectare), which helps improve the water retention capacity, crop yield, increases types of helpful microbes in the soil and reduces the emission of greenhouse gases (CO2 and CH4).

The biochar works similar to activated carbon as it does not need any specific condition for its activation as compared to activated carbon.

Power generation: The generation of power from rice straw is one of the most reliable methods to make the most out of agricultural waste. A biomass-based power plant could use 15-30 tonnes of rice straw in a day during its continuous working.

At present, biomass-based powerplants of different capacities have been established in Punjab, Haryana and Uttar Pradesh and are working efficiently. These states are also planning to increase the number of such facilities to upsurge the power production rate.

Pellet production: Rice straw, in its original form, possesses lower energy and high volume, which makes it inefficient for combustion and transportation as compared to wood-based biomass. But its volume can be reduced by converting rice straw into a small-sized pellet (2-5 cm).

During its production, the rice straw is subjected to pass through a machine having a massive compressive capacity and compressed material is allowed to come out of a smaller sized orifice in the form of a cylindrical-shaped pellet.

Last year, the Council on Energy Environment and Water proposed to use rice straw pellets to replace the 25 per cent of coal used during the power generation. Adopting this approach, approximately 1.3 million tonnes of crop residue, particularly rice straw, could be used to get benefits.

Biofuels: It is a valuable approach to extract biofuels from rice straw in the form of iso-propanol, iso-butanol, ethanol and biogas to save the fossil fuels for the upcoming generations. In addition, the overall quality and quantity of the produced fuel depend upon the pretreatment processes, skilled labour, physical properties and species of rice straw.

Paper production: The presence of high cellulose and low lignin content in rice straw makes it a suitable raw material for the paper and pulp industries instead of hardwood.

In addition to this, the chemicals used throughout the production processes have lesser toxicity towards human health and the environment and have a high affinity to get recycled in comparison to the conventional chemicals used during the paper production through wood.

Small-scale technologies

Composting: The production of rice straw-based compost is one of the easiest ways to get rid of the biomass left in the fields. For an optimised output, one needs to maintain the parameters such as 40-60 degrees Celsius temperature, pH of 6.9-8.3, carbon-nitrogen ratio of 25-30, and moisture content of 50-65 per cent.

Mushroom cultivation: The rice straw-based mushrooms are produced in tropical and sub-tropical regions. Volvariella volvacea is one of the straw mushroom species, which is cultivated and consumed in the Asian region, and is known for its pleasant taste and high nutritional value. The optimal temperature for growing rice straw-based mushrooms are around the temperature range of 28-35 degrees Celsius and a pH of six to seven and humidity level of 70-90 per cent.

Though it is essential to have a better quality of rice straw to produce good quality of mushrooms, scientists suggest that using rice straw is a cost-effective approach of mushroom cultivation because of low initial cost of production.

Silica extraction: Studies have already established that rice straw contains a high amount of silica (70-80 per cent of the total mass), which indicates the possibility of synthesizing silica particles from this crop waste. Researchers have conducted several experimental studies for the extraction and found that silica particles having a size of around 200 nm can be extracted by allowing the samples to cook at 450°C in a basic solution followed by its addition to the acidic solution where heating is provided to remove the excessive solvents.

Feed for ruminants: Farmers usually report a lower preference for using paddy straw as fodder because of the comparatively high silica content, which decreases the digestibility of it. But abundance and cheap accessibility of rice straw have given rise to a new option for its application as a source of feedstock for the milch animals such as cows, goats and buffaloes.

Studies suggest the addition of rice straw along with the original feed in small proportions — less than 2 per cent of the body weight of the animal — could help enhance muscle strength and milk production.

In addition, the overall digestibility and softness of rice straw can be significantly improved through certain pre-treatment.

However, there is still a lack of awareness, adaptation and poor management techniques that deter farmers from using paddy straw as fodder.

As an adsorbent: A few studies have demonstrated the capability of rice straw as an adsorbent to remove the various pollutants, such as heavy metals and toxic compounds like phenols, present in the contaminated waters.

Soil incorporation: As suggested by the scientists working in the field of soil and agriculture, the addition of rice straw into the soil not only manages the huge quantity of waste but also increases soil fertility, water retention capacity, aeration process and the overall yield of the next crop, for instance, wheat.

Right after the harvesting of rice, the standing straw stems can be mixed with the soil through the application of conventional or subsidised machinery. Farmers of Punjab and Haryana, commonly adopt this practice to avoid the expenditure associated with the collection, baling and transportation of rice straw.

Some of the above-mentioned technologies are working efficiently on the ground level but a few of them require essential promotions through the newspaper, hoarding boards, social media and other means of the information transfer.

The participation of farmers, stakeholders and government and non-government organisations in promoting these technologies can impart a notable contribution towards the sustainable management of rice straw, and the gains can be felt both at the local and regional levels.

Views expressed are personal