Sugarcane byproduct pressmud can be a sweet spot for India’s compressed biogas sector

India has assumed a key position in the worldwide sugar economy, emerging as the foremost sugar producer since 2021-22, surpassing Brazil. Additionally, it stands as the second-largest sugar exporter globally. The expansion of the ethanol biofuel sector over the past five years has not only strengthened the sugar industry but also contributed to the improved financial standing of sugar mills.

Pressmud, a residual byproduct in the sugar industry often known as filter cake or press cake, has been acknowledged as a valuable resource for green energy production. The byproduct can help Indian sugar mills generate extra revenue by utilising it as a feedstock for biogas production through anaerobic digestion and subsequent purification to create compressed biogas (CBG). 

Usually, the yield of pressmud falls within the range of 3-4 per cent weight by weight with the input sugarcane processed in a unit.

The use of pressmud as a feedstock for CBG offers several advantages. Firstly, it eliminates the complexities associated with the feedstock supply chain, as found in the case of agricultural residue, where biomass harvesting machinery is required for harvesting and aggregation. 

Secondly, the feedstock is sourced from one or two producers or sugar mills, as opposed to agricultural residue, which involves multiple producers / farmers within a narrow window of 45 days per year. Thirdly, pressmud’s quality is not a concern, unlike municipal solid waste, where the presence of inorganic material can damage anaerobic digesters, leading to lower gas output. 

Fourthly, it eliminates pretreatment costs as it lacks the organic polymer lignin, unlike agriresidue. Lastly, in terms of conversion efficiency, approximately 25 tonnes of pressmud are needed to produce a tonne of CBG. In comparison, cattle dung requires 50 tonnes for the same gas output. Furthermore, its cost (Rs 0.4-0.6 per kilogramme) makes it more economical than other feedstocks like agricultural residue (Rs 1.5-2/kg) and cattle dung (Rs 1-2/kg).

Nevertheless, pressmud also has specific challenges. While once considered a disposal issue for sugar mills, owners have now recognised its potential for revenue generation. This realisation has resulted in a substantial increase in pressmud prices over the last two years, rising from Rs 100 per tonne to Rs 500-600 per tonne. 

Pressmud faces competition for use as fertiliser and in bio-composting, contending with spent wash and being used as fuel in brick kilns. The lack of long-term agreements with sugar mills and the involvement of mediators in procurement further compound the challenges. Another challenge arises from the need for CBG plants to store feedstock for the entire year, given that sugar mills operate for a specific period. 

Storing pressmud proves challenging as it undergoes gradual decomposition, resulting in the breakdown of organic compounds. This complicates long-term storage and raises production costs.

Regarding regional production, Uttar Pradesh and Maharashtra, the primary sugarcane-growing states, contribute to approximately 65 per cent of the total sugarcane cultivation area. Key sugarcane-producing states are Uttar Pradesh (225.2 million tonnes), Maharashtra (123.9 million tonnes), Karnataka (62.5 million tonnes), Tamil Nadu (16.9 million tonnes) and Bihar (12.1 million tonnes). Collectively, this is around 440 million tonnes out of India’s overall sugarcane production, which reached about 495 million tonnes in 2022-23.

In the 2022-23 timeframe, among the 531 operational sugar mills in India, 330 were privately owned, 190 were cooperative and 11 were public. India’s sugar production for the fiscal year 2022-23 amounted to 32.74 million tonnes, along with approximately 11.4 million tonnes of pressmud.

This quantity has the potential to generate 460,000 tonnes of CBG valued at Rs 2,484 crore, considering the minimum guaranteed price of Rs 54/kg under the central government’s Sustainable Alternative Towards Affordable Transportation scheme.

However, to fully unlock the potential of this resource, certain interventions are necessary at the earliest. Firstly, states with the highest CBG potential from pressmud should implement bioenergy policies that streamline the approval process for projects. This can provide a unified solution and a variety of incentives, both monetary and non-monetary. 

Two examples of states taking progressive steps are Uttar Pradesh and Bihar, which have introduced supportive bioenergy policies for CBG plants.

Secondly, to prevent long-term economic instability in CBG plants resulting from unsustainable feedstock costs, the government should establish a mechanism to control pressmud prices below a specified threshold. Encouraging sugar mills to commit to extended agreements (10-15 years) with CBG plants, featuring an annual rate increase of 5-10 per cent, will ensure economic viability.

Thirdly, comprehensive research is essential to developing technologies for pressmud storage that prevent methane emissions into the environment and minimise gas loss from the feedstock. In addition, state renewable energy nodal agencies and biogas development and training centres should conduct periodic training sessions to educate operators on the functioning of CBG plants, handling scientific equipment and feedstock characterisation.

Pressmud is a low-hanging fruit for the CBG industry and it should be harnessed promptly to address waste management issues in sugar mills, create a sustainable energy source and supply organic fertiliser to our soils.

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