Rice straw can yield clean energy rather than smog

Pakistan is the tenth largest rice producer in the world and the fourth largest exporter. According to the Pakistan Bureau of Statistics (2024-2025), Pakistan produced more than 9.8 million tonnes of rice grain, while around 13 million tonnes of rice straw was generated when harvested manually or by machines. However, rice straw is currently underutilised because of its low nutritional value and high percentage of silica, making it unsuitable for animal feed. Rice straw is burnt due to no commercial value and due to constraints in collection of straw from field because of high associated costs or time constraints issues for the next crop sowing. Rice straw is sometimes fired for household heating or for cooking in rural areas.

In recent years, straw burning has become a major environmental issue as it not only pollutes the environment but also degrades the soil ecology, affecting the nutrient availability in soil. Intensive rice straw burning occurs within 2 to 4 weeks (mid of October to mid of November) in Pakistan. The burning of rice straw creates various environmental problems, including high GHGs emissions, aerosol particles, such as coarse dust particles (PM10) and fine particles (PM2.5), and toxic gases, such as carbon monoxide, carbon dioxide, nitrogen oxides, and volatile organic compounds (VOCs). Smog formation occurs due to high amounts of VOCs and nitrogen oxides, which react in the presence of sunlight to form ground-level ozone, which can affect weather conditions. This can further exacerbates environmental conditions when there is no rain during these conditions, resulting in heavy smog.

The world is moving toward a bio circular economy, which is a closed-loop system that replaces fossil fuel-based products with renewable, bio-based materials, primarily from agricultural, forestry, and marine waste, and then cycles these materials back into the economy to minimise waste and pollution. It is a shift towards a nature-powered economy that aims to regenerate natural systems by using natural capital, thereby reducing dependence on non-renewable resources and supporting sustainable well-being.

Pakistan is burning valuable crop residues, such as rice straw, to convert them into issues such as depletion of soil organic matter, environmental pollution, human health toxic smog and fossil fuel energy import bills. According to a study on rice straw valorisation published in the Environmental Science and Pollution Research journal, raw rice straw can be challenging to convert into biogas using specialised microbes. However, this biogas can be purified by removing impurities to produce biomethane, which shares similar applications with natural gas. Biomethane can then be utilised in existing natural gas infrastructure or converted into Liquefied Natural Gas (Bio-LNG). Demand for Bio-LNG is currently soaring, especially as a maritime fuel.

However, lead researcher Muhamamad Abdul Hanan Siddhu notes that approximately 126 m³ of biomethane can be produced per tonne of rice straw through anaerobic digestion, while the biomethane yield can be significantly increased to 205 m³/tonne (63%) of rice straw by developing special techniques and emerging steam explosion pretreatment technology. A subsequent calculation showed that the use of Siddhu's steam explosion pretreatment technology to convert approximately 80% of Pakistan's burned rice straw could produce 2133 million m³ of biomethane or 1.5 million tonnes of Bio-LNG, accounting for 8532 million units of electricity, which could meet the energy demand of roughly 3.7 million households. Steam explosion pretreatment technology is chemical-free, and after harnessing the biomethane potential from rice straw, the residue can be utilised as fertiliser in agricultural production systems to reduce the dependency on expensive imported synthetic inputs and mitigate environmental problems and associated human health risks.

Therefore, the government should promote and support advanced and emerging environment-friendly technologies, such as steam explosion pretreatment, to valorise rice straw into biomethane production and simultaneously mitigate smog, reduce environmental issues and conserve Pakistan's natural resources and its foreign reserves.