Renewable energy from industrial effluents: A scalable model for the circular economy

Transform industrial effluents into renewable energy in India, promoting circular economy, biogas, bio-CNG, and sustainable growth.

Industrial effluent, the liquid waste or by-products discharged from industrial processes, is not a liability if treated responsibly and innovatively. Containing a substantial amount of organic and inorganic substances, effluent discharged from industries such as food processing, pharmaceuticals, distilleries, dairy, sugar, paper & pulp, and others could be a potential source of renewable energy, paving the way for a cleaner and greener future.

In our experience with industrial clients, the textile sector processes approximately 5,625–5,720 m³/day of effluent, petrochemical sectors process up to 3,000–4,000 m³/day, and food & beverages up to 350 m³/day of high-strength wastewater is generated, with industry-average COD values ranging from 4,000-5000 mg/L and BOD between 2,000 and 3,000 mg/L, reflecting very high energy conversion potential for biogas and bio-CNG applications.

Indian industrial effluent scenario

Every year, the manufacturing clusters in India produce approximately 13,500 million litres per day (MLD) of industrial wastewater. A large amount of this is disposed of irresponsibly, polluting the land and water. In 2024, the Union Government informed the Lok Sabha that about 402.67 million litres per day (MLD) of industrial effluents from 3,186 grossly polluting industries (GPI) are discharged into the Ganga and Yamuna and their tributaries, flowing across the country. With India going through rapid industrialisation and new sectors emerging and evolving at a fast pace, industrial discharge is expected to increase, necessitating better effluent treatment infrastructure and stricter compliance to protect the environment and public health.

Turning waste into energy

The Indian food and beverage sector is among the largest in the world, and drug and pharmaceutical production ranks third globally by volume. It is also the third-largest spirits market worldwide, with its distillery industry consistently ranking among the top internationally.

Textile effluents can produce biogas yields of up to 0.35 m³ methane per kg COD removed, with modern plants in sugar, distilleries, and paper sectors recovering 75% of organics as biogas, typically converting 1 MLD of effluent into 1,000–2,500 kWh/day of energy. In well-optimised operations, energy recovery can substitute 30–50% of grid electricity and state-of-the-art water recovery processes can reclaim 70–95% of influent water. Textile and paper plants now achieve water reuse rates of 50–73%, supporting dramatic carbon footprint reduction and grid substitution.

These data are not just an indication of India’s industrial scale but also the volume of waste generated that can be utilised efficiently to meet the growing energy needs of the country sustainably.

Sectors such as textiles, paper, sugar, pharmaceuticals and others, where key raw materials are sourced directly from plants, animals, and the earth, produce a massive amount of organic and inorganic waste that can be turned into biogas, bio-CNG, biochar and more with the help of advanced technology. This approach would not only reduce the environmental burden of untreated discharge but also provide industries with a sustainable energy alternative, thereby reducing their dependency on fossil fuels.

A fine example of waste-to-energy production in India is the sugar mills of Uttar Pradesh and Maharashtra, which have deployed anaerobic digesters to process molasses-rich wastewater to produce energy. Studies suggest that with every 10% increase in renewable energy, carbon emissions are reduced by 1.6%.

Closing the loop

Beyond energy production, using industrial effluent is also about building a circular economy, where nothing goes to waste. Contrary to the traditional linear ‘take-make-waste’ model of economy, a circular economy is designed to maintain the value of products and materials by creating closed-loop systems that regenerate natural resources and reduce pollution. It also strengthens business viability by reducing costs, enabling carbon credit revenues, and aligning the business’s operation with ESG targets and SDGs.

From the effluent discharged, an advanced treatment system can enable the recovery of 80-95% of water, which can further be reused in the industrial process, significantly reducing the need for freshwater. The remaining effluent may support 70-85% recovery of nutrients like nitrogen and phosphorus for fertiliser with the help of biological nutrient removal (BNR), ammonia stripping, struvite precipitation, or a bio-based recovery system.

Technologies such as Zero Liquid Discharge (ZLD) systems, which treat and recycle wastewater leaving no discharge, and Biological Nutrient Removal (BNR) technologies, which effectively remove nitrogen and phosphorus from wastewater, can help industries enhance operational efficiency. Embedding these solutions also supports India’s decarbonisation and net-zero 2070 commitments, contributing to sustainable growth.

Innovative sustainable energy technologies

When it comes to converting organic waste to energy, anaerobic digestion is the most widely adopted route. The system can generate around 0.35 m³ of methane per kg of Chemical Oxygen Demand (COD) removed. Up to 75% of the organic waste can be converted into biogas, with an approximate thermal value of about 22 MJ m⁻³, offering reliable onsite energy recovery. Membrane bioreactors (MBR) and reverse osmosis (RO) can complement anaerobic digestion for treating wastewater to produce high-quality water.

Fermentation, Thermochemical processes, Mechanical Biological Treatment (MBT), and Gasification are other advanced technologies that treat waste and convert it into useful products such as energy, fuel, or compost. With distinct processes, mechanisms, and end products, they are suitable for different types of waste and industries. For example, in distilleries, anaerobic digestion and biogas cogeneration are particularly effective, while in pharmaceuticals, membranes and oxidation play a critical role.

Government policies and challenges

The conversion of industrial effluent to energy in India is supported by progressive policies, including the National Bio-Energy Mission, initiatives by the Ministry of New and Renewable Energy (MNRE), and guidelines from the Central Pollution Control Board (CPCB) promoting zero liquid discharge and anaerobic treatment technologies. Despite these, challenges exist in terms of widespread implementation due to high capital costs, technological gaps, lack of skilled manpower, and other factors. Addressing these issues through better incentives, advanced technologies, and supportive regulatory frameworks is crucial to unlock the potential of industrial effluent as a sustainable energy source in India.

Not all industrial effluent or wastewater discharge from industries is the same, nor can it be treated the same way. But in any case, it is necessary to handle them responsibly for sustainable development. As India strives to increase the share of renewable energy in the energy mix of the country, treating industrial effluent presents an opportunity not only to generate green energy but also to promote a circular economy, thereby reducing the burden on the planet.