Sugarcane wastes into commercial products: Processing methods, production optimization and challenges
Sugarcane is a cash crop that has been a significant source of revenue in many countries around the world. In the last few decades, sugarcane mills that were only intended for sugar production were converted into biorefineries. Biorefinery enables the co-production of useful products from the sugarcane wastes such as bagasse, molasses, cane trash, filter mud and vinasse. In certain applications like disposable plates, fly ash, and as reinforcement in polymer composites, bagasse can be directly employed without the need for secondary processing while applications like paper, biochemical, lignosulfonate, vanillin, etc., require secondary processing through the biochemical route involving pre-treatment, acid hydrolysis, and fermentation. Other sugarcane wastes can also be mixed with bagasse to obtain biomethane, bioethanol, and bioelectricity. This article focuses on the recent advancements in such pre-treatment and processing methods employed by the researchers. It also outlines the strategies to co-generate two different products and ways to maximize the product yield and highlights various parameters influencing the process. The challenges that are critical to the sustainability of the sugarcane biorefineries and their mitigations were also discussed.
Sugarcane, commonly found in many countries around the world, is a cash crop that generates revenue and holds a significant share in the economy of individual countries. Fig. 1 shows the illustration of the sugarcane plant. It is a perennial grass belonging to genesis Saccharum. A total of 124 countries are involved in producing sugarcane out of 195 countries. Fig. 2 shows the summarized list of the top ten countries based on the amount of sugar they produce in 2020 (“Sugar Producing Chen et al., 2020,” 2020). In the United States of America (USA), 17 states generate jobs for the people within the sugar industries. Further, Minnesota (an US state) produced about 28,021 jobs from the sugarcane industries and revenue of $3.36 billion. Likewise, New York is responsible for producing over 1000 jobs and generate a revenue of about $292 million from the sugarcane industry.
Once the sugarcane is planted, it utilizes soil nutrients to grow and be harvested like the other budding plants. Usually, between 5 and 9 months, the sugarcane is harvested from the soil. The green top or sugarcane tops are usually cut, and the stem is sent to the sugar mills. A typical sugar mill, referred to as a first-generation sugar mill, consists of facilities for the extraction of sugar juice, which is then converted into crystal sugar through the centrifuging process. The produced sugar is then dried, sorted out, packed, and distributed.
From the harvest to the final processing, there are four main sugarcane wastes produced: (i) sugarcane bagasse, (ii) dry leaves and sugarcane tops, (iii) sugarcane press mud, and (iv) molasses.Table 1 shows the lists of the chemical composition of by-product from sugarcane.
In recent years, many traditional sugar mills have been converted into bio-refineries or second-generation sugar mills, where several by-products can be produced from the generated wastes. Conversion of input feedstock into multiple products and by-products in an integrated sugarcane processing facility is referred to as biorefinery (Sindhu et al., 2016). Fig. 3 shows the products synthesized from the sugarcane wastes in the sugarcane biorefineries.
This article addresses the recent advancements in the processing methods to convert sugarcane wastes to useful products and product optimization strategies that can be followed by sugarcane biorefinery to maximize benefits such as revenue generation, improve product yield, reduce wastes and to produce goods according to the market demand for certain products such as bioethanol, biochemicals, etc. It also provides a detailed discussion on the challenges awaiting sugarcane biorefineries and mitigations. The content is organized in the following way: direct use of bagasse in applications such as composites, cement, disposable plates, and individual/combined use of the bagasse and other sugarcane wastes that require processing to be converted into useful products.
Bagasse is the fibrous material that remains after the extraction of sugar juice and constitutes about 30–40 wt % of the sugarcane. Around 280 kg of bagasse is generated from every ton of the sugarcane. Bantacut et al. (2018) and Guerra et al. (2020) reported that the quantity of bagasse generated depends on many factors: (i) harvest time, (ii) agronomic practices, (iii) soil condition, and (iv) the extent of crushing and milling operations carried out on the sugarcane in the sugar mill.
Arshad and Ahmed (2016) and Silalertruksa et al. (2015) reviewed the power co-generation using bagasse. They reported that the thermal energy from the combustion of 1 tonne of bagasse in the grate boiler is used to produce 2.2 tonnes of steam at a pressure of 20–22 bars and a temperature of 350 °C. Cane trash is usually left in the field as residue can also be added to the boiler along with the bagasse for the steam production. The generated steam is then used to run the backpressure steam
Filter mud, also known as press mud, is the residue remaining after clarification and filtration of the sugarcane juice. It is of solid as well as fibrous nature. Filter mud is rich in soil nutrients such that they are suitable for use as fertilizer. However, the transportation cost of piles of filter mud from the sugarcane mill is expensive. Thus, these residues are often unused or let into the water bodies, resulting in water contamination and pollution. Christofoletti et al. (2013)
Sugarcane biorefineries have emerged as the primary source of revenue in many developing countries and underdeveloped countries worldwide. Initially, sugar was the only main product that was generated from the sugar mills. Over the years, the sugarcane mills were converted into biorefinery, an integrated facility to co-produce ethanol, bio-chemical, bio-electricity, bio-gas, etc. Despite the advantages such as increased income and processing of the generated waste into useful commercial
Sugarcane is a cash crop usually planted in various countries for its crystal sugar. Since the sugarcane harvest is seasonal, the sugar mills can benefit all around the year by converting itself into a biorefineryor as a second-generation sugar mill. Biorefinery encompasses additional facilities to synthesize useful products from the wastes generated after extracting the sugarcane juice.
