Henry Eastick Written by Henry Eastick

Sugar’s circular economy: transforming bagasse into citric acid

At Ragus, we have been manufacturing sugar for 94 years. During that time we have seen many exciting advances, especially in the mills that process raw pure cane sugar in countries such as India, Brazil and Thailand. One recent innovation is a potential solution to the industrial waste produced, bagasse, when processing sugar in these countries.

A recent press release by the University of York has unveiled research into using bagasse – the fibrous material left after crushing sugarcane – in citric acid production. This project is a partnership between the University of York, The International Centre for Genetic Engineering and Biotechnology (New Delhi) and Indian and UK based companies to find a use for the industrial waste generated by the sugar industry in India.

Ben Eastick shakes hands with farmer

Ragus sources cane sugar from certified suppliers around the world. Director Ben Eastick, right, visiting a cane supplier in India.

The project lead, Chair in Materials Biology Professor Simon McQueen Mason at the University of York’s Department of Biology, was kind enough to share with us his insights into this exciting new technology.

Sugar crushed into Bagasse

Crushing sugarcane at the mill, left, leaves a fibrous yet sugar rich waste stream, bagasse, right.

Using waste bagasse as a biofuel

Waste bagasse is already used as a fuel and in the production of paper. For example, in India it is a biofuel, burnt to power the mills crushing the sugarcane. Using bagasse as a biofuel is considered carbon-neutral, as the carbon dioxide produced by burning is offset by the growth of the sugarcane itself. However, despite utilising some of this waste for powering mills, this is not the most efficient use considering the many properties of polysaccharide-rich bagasse.

Before this project, in Brazil, bagasse has been used to produce second-generation bioethanol – used as a petrol substitute – with much success. Raizen, Brazil, is pioneering commercial-scale bagasse to bioethanol production. The production of bioethanol from bagasse employs fungal enzymes that digest the bagasse polysaccharides into simple sugars, which are then fermented by brewers’ yeast to convert them into ethanol (alcohol). However, brewer’s yeast cannot transform all the sugars released from bagasse, particularly xylose, which makes up one-third of bagasse. This leaves room for further improving the use of bagasse as a sustainable resource. 

Can bagasse be used in other industrial processes?

The Newton-Bhabha Fund is dedicated to funding research for the benefit of economic development and social welfare in several partner countries, including India. One of its projects is to increase the value of bagasse and reduce the impact of industrial waste. Faced with this challenge, the York-led research consortium wondered whether citric acid production might be an even more competitive use of bagasse than bioethanol.

During market research, the Indian partners in this project (Natems Sugars) discovered that citric acid was in high demand by other industries nearby a proposed sugar mill site. Furthermore, citric acid is worth more than double the value of bioethanol, with high demand in industries such as pharmaceuticals. Aspergillus- the fungus used for citric acid production, is naturally able to use all the sugars released during enzyme digestion of bagasse and convert these efficiently to citric acid.

As the project progressed, the York team isolated new strains of Aspergillus and used advanced biotechnology processes to increase the citric acid production by these strains more than ten-fold. In parallel, the team in New Delhi have developed a new strain of Penicillium (another fungus), which very effectively produces the enzymes needed to convert the bagasse into sugars for citric acid production. This allows the enzymes to be produced directly on-site at the factory for low cost, reducing the supply costs of the enzymes.

Commercialising and scaling-up citric acid production

Whilst the practicalities of this project have been extensively tested and improved upon by lab-based research scientists, the commercial viability of the process was also evaluated by engineering companies in the project. Initially, some parts of the conversion process relied on high temperature and pressure treatment of the bagasse at 160°C to facilitate its subsequent digestion with enzymes. The engineers realised that this step would make the process too expensive to be competitive. After further development, they developed a new process that works effectively at 75°C, drastically reducing both capital costs and energy use. 

The large amount of water necessary and the chemicals involved in production proved to be another challenge. Chemical disposal is an expensive process and may undermine the positives of a process because it could effectively exchange one form of industrial waste for another. However, through further process development, the consortium devised a way to convert the waste chemicals and water into a crop fertiliser, moving the process residues from being a waste problem into becoming a valuable co-product. 

Field of sugar cane

Irrigating and fertilising sugarcane crops in Cuba to optimise yield.

The future of citric acid production using bagasse

During the pandemic, the plans for a pilot scheme to further test the commercial viability of this project at larger scale were temporarily halted. The entire process would need to be executed at a larger scale and subject to a thorough techno-economic assessment to prove its commercial potential. Such a pilot factory is hoped to be built within the next few years, depending on available funding being secured, with investment into the first commercial plant to be built in India to follow. If successful, citric acid plants could be built wherever there are sugarcane mills with local demand for citric acid and other bio-chemicals.

Whilst the bioethanol market has a predicted life of only 30 years, as electrification and hydrogen fuels take over transport markets, the demand for biobased chemicals is an ever-expanding market. Citric acid, due to its high demand in the food, pharmaceutical and cosmetic industries, is a lucrative product and ideal for stimulating bagasse-processing industries other than power generation. Once commercialised, this innovative process technology could revolutionise the use of bagasse in the future, improving the business case for sugarcane farming.

Ragus has over 90 years of experience manufacturing pure sugars and syrups for specialist applications in industry. Contact a member of our customer services team at +44 (0)1753 575353 or enquiries@ragus.co.uk to find out more about how our high-quality, consistent and natural pure sugar products can enhance your application. For more sugar news and Ragus updates, follow Ragus on LinkedIn.