Sugarcane Bagasse: A Sustainable Feedstock for Biorefinery Portfolios in South Africa

Abstract

Rising global populations, infrastructural development, and rapid urbanization have heightened the reliance on a linear economy, resulting in severe environmental and human impacts. This crisis has triggered an urgent quest for sustainable and ecologically benign innovations, as outlined in the United Nations’ Sustainable Development Goals (SDGs). This review investigates the potential of sugarcane bagasse (SCB) as a promising feedstock for advancing circular bioeconomy initiatives in South Africa. It shows how this copious bioresource can be utilized to enhance the country’s biobased value chains by producing bio-commodities, such as biofuels and platform chemicals. The review also identifies the driving forces behind the circular bioeconomy model within the South African sugarcane industry. To achieve the circular bioeconomy, it outlines essential technological prerequisites, including critical pretreatment strategies and emerging bio-innovations necessary for the effective valorization of SCB. Furthermore, it showcases the R&D and commercial strides that have been achieved in South Africa. Finally, the study covers techno-economic studies that corroborate the economic viability of this domain. In conclusion, harnessing SCB not only presents a viable biorefinery pathway towards sustainable economic growth but also contributes to environmental preservation and social well-being, aligning with global sustainability imperatives. The successful integration of these innovative approaches could play a pivotal role in transforming the South African sugarcane industry into a continental leader in circular bioeconomy innovations.

1. Introduction

1.1. Revitalizing South Africa’s Sugarcane Industry: A Strategic Need

The demand for limited resources like land, water, food, and energy has surged due to high population growth and rapid urbanization [1]. By 2050, it is estimated that 90% of the global population will reside in developing countries [2]. This will, in turn, have severe ramifications, including the fast depletion of natural resources and a sporadic increase in waste accumulation [3,4,5]. In response, scientists and policymakers are developing sustainable technologies such as “Green Biorefineries” to combat these issues. These innovations are aimed at producing a diverse portfolio of biobased products while eradicating the high dependency on the cumbersome fossil-based linear economy [6].

The global need for carbon-neutral technologies, coupled with the depletion of fossil reserves, is the main reason for the promotion of biorefinery innovations [7,8]. Several countries have committed to reducing their greenhouse gas emissions by integrating renewable and sustainable technological innovations in their value chains [9]. The legal frameworks that allow the use of bioenergy and biofuel blends to meet their transportation needs, reduce dependency on traditional petroleum imports, and assist in reducing the escalating oil prices and carbon emissions have already been established [10].

Interest in producing fuels from biomass is increasing owing to the growing energy demand [11,12]. Biomass fulfills several important functions, including the generation of electricity, the fueling of vehicles, and the provision of process heat for industrial processes [12]. Among a variety of potential bio-based resources, lignocellulosic biomass, also known as second-generation or 2G biomass, is a promising feedstock for the production of bio-based fuels and platform chemicals due to its high abundance, affordability, and it does not compete with edible crops, unlike 1G feedstocks. Second-generation feedstocks include agro-processing residues such as sugarcane bagasse [13]. Sugarcane bagasse is a fibrous remnant of cane stalks left after the sugarcane processing step [14,15].

A total of 90% of sugarcane content is bagasse, and only 5% is sugar [16]. In the context of South African sugar mills, approximately 270–280 kg of bagasse is generated for every ton of sugarcane that is harvested [13,17]. Thus, sugarcane bagasse can be beneficiated and used as a lignocellulosic feedstock to produce biofuels, bioproducts, and biochemicals in a biorefinery concept [18]. In the next two decades, it is envisioned that South Africa and its BRICS counterparts will be the major players in the global bioeconomy markets. The BRICS nations currently dominate the global sugar industry [15].

Over the last two decades, the South African sugarcane industry has experienced multifaceted challenges characterized by unstable climatic variations, an influx of inexpensive sugar imports, diminishing profit margins, and a decline in cultivable land. These issues have led to significant declines in the sector, necessitating urgent interventions. In response, local stakeholders, including scientists, policymakers, and sugarcane producers, have collaboratively developed the “South African Sugarcane Master Plan 2030.” This comprehensive framework aims to revitalize the local sugarcane sector by promoting the adoption of innovative, scalable, and commercially viable biorefinery portfolios.

The significance of this initiative lies not only in its potential to rejuvenate the nation’s struggling sugarcane industry but also in its economically viable approach within the South African bioeconomy context. This review, the first of its kind, demonstrates how the principles of the circular bioeconomy could be effectively integrated and leveraged through sugarcane-centric waste streams in South Africa. By unlocking these biobased value chains, this strategy could enhance sustainability, increase resource efficiency, and ultimately transform the economic landscape for local sugarcane stakeholders. It is hoped that this study will not only contribute to the scholarly discourse but also inform practical strategies for achieving a resilient and thriving sugarcane sector in South Africa.

Ultimately, it aims to bridge the gap between fundamental research and practical applications of biorefinery development within the South African context.

1.2. The Hurdles Faced by the South African Sugarcane Industry

South Africa has historically been a leading producer of sugarcane, significantly contributing to the national economy [19]. The industry spans three provinces, i.e., Mpumalanga, KwaZulu-Natal, and the Eastern Cape, making it the largest sugar industry on the African continent [20]. It is estimated that the sugarcane sector generates around USD 736 million annually, representing about 0.6% of the nation’s GDP [21]. It plays a vital role in promoting socioeconomic development in rural areas by allocating resources, creating jobs, providing income, and establishing transport and communication networks [22].

However, the South African sugarcane industry currently faces considerable challenges that threaten approximately 85,000 direct and 350,000 indirect jobs [23]. Biotic and abiotic stressors, including drought, salinity, pests, and disease outbreaks, exacerbate these issues. Further complicating the situation are high input costs, insufficient technological advancements, unstable global economies, inadequate infrastructure, social challenges, and market fluctuations, such as low prices on the foreign market and high operating costs [19,24]. The implementation of a new tax law on 1 April 2018, aimed at reducing non-communicable diseases (NCDs) associated with high sugar consumption, has also led to a decrease in demand for sugar-based products, further threatening the profitability of the local sugar industry [25]. Ongoing land redistribution initiatives and the resulting skewed land distribution remain critical issues, causing pressure on land demand and raising uncertainties about farm viability.

Climate change is impacting South Africa’s rainfall patterns and temperature, with the surface temperature in Southern Africa rising twice as fast as the global average [26].

Regions such as KwaZulu-Natal and Mpumalanga, which are the leading sugarcane producers, have been severely affected by droughts and floods, resulting in a decline in the number of small-scale sugarcane farmers [27,28,29].

To address these challenges, it is essential to diversify the product range by efficiently upcycling sugarcane residues such as bagasse. These agricultural byproducts can be converted into high-value products through fractionation, extracting valuable components such as cellulose, hemicellulose, and lignin, which serve as key chemical precursors.

1.3. The South African Sugarcane Master Plan 2030

In 2019, the South African government, in collaboration with local sugarcane industries, developed a strategic roadmap aimed at revitalizing the country’s declining sugarcane sector, which faces numerous challenges, including cheap imports, unfavorable climate variations, ongoing droughts, financial losses, and unusable land [19]. As a result, specific actionable interventions were proposed, including (i) developing technologies to produce a wide range of globally competitive sugarcane-based products such as biofuels, platform chemicals, and biopolymers; (ii) forming a joint task team of government and private stakeholders to oversee key tasks and responsibilities; (iii) involving academia, science councils, and private companies to establish research consortiums focused on sugarcane biorefineries; (iv) commercializing R&D efforts to boost the national economy and create jobs; and (v) reducing environmental impacts associated with the country’s sugar mills. The task involved the Department of Land Reform and Rural Development; the Department of Trade, Industry, and Competition; the Council for Scientific and Industrial Research; local academic institutions; the Department of Agriculture; the National Treasury; the Industrial Development Corporation; the Department of Health; the South African Sugar Association; the South African Sugar Millers Association; the South African Cane Growers Association; the South African Farmers Development Association; the Beverage Association of South Africa; the Coca-Cola Beverages Africa; the Consumer Goods Council of South Africa; the South African Sugar Converters Association; the South African Revenue Services; and the National Bargaining Council for Sugar Manufacturing and Refining Industry [19].

To date, several technological milestones have been achieved, with notable biorefinery projects such as the Sustainable Aviation Fuel Project, Polylactic Acid Project, and Polyethylene Project—these are now conducted at TRL 6–8. Additionally, this approach has reduced the burden on local sugar mills, as they can now sell their waste streams to start-ups, SMMEs, and companies specializing in biorefinery portfolios.

2. Biorefineries Driving South Africa’s Sugarcane Revival

Biorefineries are innovative technological methods that convert biomass into valuable biobased products, including chemicals, fuels, and polymers, similar to how petroleum refineries operate but without the associated environmental pollution of petroleum (see Figure 1 and Figure 2) [11,21]. A significant advantage of biorefineries lies in their ability to produce biofuels and chemicals from low-cost lignocellulosic biomass, which comprises cellulose, hemicellulose, and lignin [30]. This biomass is abundant, renewable, inexpensive, and does not compete with food sources, making it an attractive alternative to fossil fuels [31,32]. The output of biorefinery scenarios can be categorized into two main types: energy products, which provide heat, electricity, or transportation services, and material products, which are valued for their chemical or physical properties rather than for energy generation. In the context of sugarcane, which is primarily a food crop, several countries are exploring energy-related options, particularly in Brazil [32,33].

Revitalizing the South African sugarcane industry could involve integrating biorefinery processes with existing sugar mills to support regional and rural development and diversification [34]. By transforming sugar processing facilities into biorefineries that produce food, biofuels, animal feed, and other bioproducts, the industry could enhance revenue streams while promoting sustainable practices in sugarcane cultivation. Current economic evaluations of biofuel production from 2G waste biomass utilize thermochemical and biochemical processes, highlighting the potential of this technological route [13].

South Africa produces approximately 20 million tons of sugarcane annually, equivalent to 1.75 million tons of coal in biomass energy, with the potential to generate 1600 MW of electricity [34]. Notably, the Illovo Group in South Africa manufactures high-value-added products such as furfural and furfuryl alcohol from sugarcane bagasse, which are marketed globally [35,36]. A typical South African sugar mill valorizes sugarcane using five critical steps: (1) milling, juice extraction, and disposing of the sugarcane bagasse after pressing; (2) clarifying the juice to remove impurities; (3) evaporating to concentrate the syrup; (4) crystallizing to form sugar crystals; and (5) separating the blend of sugar crystals and syrup, resulting in molasses and raw sugar [37,38,39].

Sugarcane bagasse, the fibrous residue from crushed cane, is a promising lignocellulosic biomass source for biorefineries due to its high cellulose and hemicellulose content. Although bagasse is burned to generate electricity and heat for the sugar mills, significant quantities remain due to limitations in incineration processes, with South Africa generating around 7.6 million tons of bagasse annually [13]. This byproduct can be converted into biofuels, chemicals, and other valuable products. Various chemicals, metabolites like alcohol and alkaloids, protein-enriched animal feed, mushrooms, and enzymes have been derived from bagasse [40,41,42,43]. However, the utilization of bagasse as feedstock is limited by its high pentose fraction and complex chemical structure, which complicate enzymatic pretreatment processes. Enhancing the delignification of bagasse can improve enzymatic digestibility and yield sustainable products such as enzymes, pigments, biochar, and biofuels. The lack of cost-effective technology to address the recalcitrance of biomass structures remains a barrier to the extensive production of energy from this feedstock [44].

3. Extraction of Sugars from Sugarcane Bagasse

3.1. Pretreatment Strategies Used in Sugarcane Bagasse

Sugarcane bagasse (SCB) comprises approximately 45–50% cellulose, 25–30% hemicellulose, 25% lignin, and 2.4–9% ash [37]. The composition varies due to different factors such as location, soil chemical composition, crop variety, climate conditions, fertilizers, and physical factors [37]. The low ash content offers several benefits for microbial bioconversion compared to biomass such as wheat straw and rice straw [45]. However, the chemical structure contributes to its recalcitrant nature; it cannot be easily separated into usable components [30,37]. Most of the glucose in lignocellulose is trapped in highly crystalline cellulose polymers (Figure 3) [46]. To make cellulose more available to the enzymes that transform carbohydrate polymers into fermentable sugars, pretreatment is vital to change the structure of cellulosic biomass [47]. In the biorefinery process, pretreatment is the most expensive step, contributing 20–50% of the total cost. When paired with enzymatic synthesis and hydrolysis, it accounts for roughly 40% of the total costs [4]. However, this is a critical step in the use of lignocellulosic biomass if a high conversion value is sought [16].

Selecting a pretreatment method is not simple and requires consideration of each pretreatment’s solid concentrations and sugar-release patterns, as well as how well it works with the feedstock, enzymes, microorganisms, and the technological process (Table 1) [48]. When selecting an appropriate pretreatment regime, the following factors should be considered; however, they are not the only ones: cost and energy efficiency, ecological and environmental consequences, and the composition of the lignocellulosic waste [40]. Additionally, pretreatment strategies need to (i) enhance sugar recovery, (ii) prevent losses of carbohydrates, (iii) prevent the development of inhibitors that hinder the future fermentation and hydrolysis processes, and (iv) be economical [49]. Available strategies typically have drawbacks when it comes to achieving production that is environmentally friendly, economical, and scalable [50,51]. Pretreatment strategies are classified into biological, physical, chemical, or physicochemical methods [45,52].

This topic has been thoroughly addressed in the academic literature, particularly in the review articles by Karp et al. [2] and Mankar et al. [16]. These articles discuss the various fractionation regimes that researchers can use to recover fermentable sugars. Consequently, Section 3.1.1, Section 3.1.2, Section 3.1.3 and Section 3.1.4 will provide a quick guide to avoid unnecessary repetition.

3.1.1. Biological Pretreatment Strategies

Biological pretreatment removes lignin from biomass using microorganisms such as fungi (white-rot, brown-rot, and soft-rot fungi), actinomycetes, bacteria, and enzymatic systems. While there are several techniques for removing lignin from lignocellulosic biomass, they are hindered by the need for solvents, high energy costs, and the production of harmful inhibitors [53]. Enzymatic or microbial delignification dramatically increases the accessibility of polysaccharides in this environmentally friendly method [4]. In addition to their environmental merits, biological pretreatment strategies are inexpensive, safer, and less energy-consuming [54]. The breakdown of the hemicellulose and lignin in sugarcane bagasse is typically attributed to white-rot, soft-rot, and brown-rot fungi [45].

3.1.2. Physical Pretreatment Strategies

There are different types of physical processes, such as milling (e.g., ball milling, two-roll milling, hammer milling, colloid milling, and vibratory milling) and irradiation (e.g., by gamma rays, electron beams, or microwaves), that can be employed to improve the enzymatic hydrolysis or biodegradability of lignocellulosic waste materials [55]. The most common type of physical pretreatment is comminution, which entails grinding the substance to the desired particle size [4]. Cellulose crystallinity and the degree of polymerization can be reduced, increasing the accessible surface area and pore size through physical pretreatments [49]. Increased surface area and reduced cellulose crystallinity work together to improve enzymatic hydrolysis, which increases saccharification rates and yields [4]. Physical pretreatments, like the comminution of biomass, e.g., milling, have low performances along with high costs [48].

3.1.3. Chemical Pretreatment Strategies

Chemical pretreatment incorporates oxidants, solvents, alkalis, acids, etc. These substances react with the biomass and break the bonds between them [38]. Under mild temperature conditions, chemical agents such as acids (H₂SO₄, HCl, H₃PO₄, HNO₃, etc.) disrupt the hemicellulose chemical bonds, increasing the recovery of monomeric sugars from the biomass [56]. Maintaining an optimal temperature is a requirement for this type of strategy; this in turn, enhances the glucose yield for further processes [9].

3.1.4. Physicochemical Pretreatment Strategies

Both physical and chemical strategies, with the help of steam explosion, ammonia method, carbon dioxide explosion, wet oxidation, and liquid hot water, pretreat biomass in the physicochemical strategy [56]. This strategy is also known as the thermo-chemical pretreatment strategy; it addresses the drawbacks of alternative pretreatment methods [4].

Table 1. The significant advantages and drawbacks of pretreatment strategies.

Pretreatment	Advantages	Drawbacks	References
Biological	- Low energy requirements - Improves fermentation efficiency - Degrades lignin hemicellulose - Low amounts of inhibitors produced	- Time-consuming - Costly for commercial use - Stringent bioprocess - Low hydrolysis	[4,9,38,49,51,57]
Physical	- Reduces crystallinity of cellulose - Reduced pretreatment time - Enhanced saccharification rate and yield due to reduced particle size and increased surface area	- Labor-intensive - High costs and low performance associated with physical pretreatments	[4,48,51]
Chemical	- Enzymes are recyclable - Alters lignin structure - Hydrolyses hemicellulose	- Reagents cannot be separated - Could corrode the reactors - Enzymes increase the costs	[4,49,51]
Physicochemical	- Efficient lignin removal - Causes hemicellulose degradation and lignin transformation	- Generates toxic compounds - Results in costly processes	[49,51]

Table 1. The significant advantages and drawbacks of pretreatment strategies.

Pretreatment	Advantages	Drawbacks	References
Biological	- Low energy requirements - Improves fermentation efficiency - Degrades lignin hemicellulose - Low amounts of inhibitors produced	- Time-consuming - Costly for commercial use - Stringent bioprocess - Low hydrolysis	[4,9,38,49,51,57]
Physical	- Reduces crystallinity of cellulose - Reduced pretreatment time - Enhanced saccharification rate and yield due to reduced particle size and increased surface area	- Labor-intensive - High costs and low performance associated with physical pretreatments	[4,48,51]
Chemical	- Enzymes are recyclable - Alters lignin structure - Hydrolyses hemicellulose	- Reagents cannot be separated - Could corrode the reactors - Enzymes increase the costs	[4,49,51]
Physicochemical	- Efficient lignin removal - Causes hemicellulose degradation and lignin transformation	- Generates toxic compounds - Results in costly processes	[49,51]

4. Biorefinery Portfolios from Sugarcane Bagasse

Sugarcane bagasse is viewed as a sustainable alternative feedstock for producing electricity, animal feed, organic acids, sugars, enzymes, metabolites, and second-generation biofuels such as ethanol and other value-added products [45,58,59]. This section summarizes the various biorefinery routes that could be used to upcycle the sugarcane bagasse, leading to the generation of a wide array of high-value-added products.

4.1. Biofuels

There has been a significant increase in the production of second-generation fuels, especially those derived from agricultural residues [60]. Global interest in developing biofuels as an alternative to fossil fuels has risen due to the ongoing energy and economic crises [61]. Biofuel is a sustainable energy source obtained by processing various feedstocks, such as algae, animal waste, and plants [62]. One valuable feedstock for the biofuel industry is sugarcane bagasse, which is abundant and rich in cellulose and hemicellulose. Currently, South Africa contributes only 0.01% to global biofuel production. The growth of the biofuels sector is hindered by a lack of incentives and supportive policies [63]. The objective of South Africa’s biofuels policy is to enhance the incorporation of clean energy sources, stimulate the rural economy, and create jobs by achieving a 2% market share for liquid biofuels [13]. So far, investments in biofuels have been relatively low due to insufficient funding. However, it is estimated that 24% of South Africa’s liquid fuel needs could be met with bioethanol, given the high availability of biomass [27]. Additionally, Figure 4 illustrates the various biorefinery products that can be produced using sugarcane bagasse.

4.1.1. Biogas

There is a global increase in the generation of biogas from a variety of lignocellulosic biomass [49]. Biogas is produced through anaerobic digestion of various feedstocks, including bagasse. Methane is the principal constituent of this gas; it is also known as biomethane [65]. Biogas primarily comprises 60–70% methane and 20–30% carbon dioxide with traces of propane, hydrogen sulfides, and other impurities [17,66]. The typical composition of biogas differs depending on the feedstock composition and the conditions of the anaerobic digester [67]. Anaerobic digestion can convert organic materials, such as sewage sludge, animal waste, and industrial effluents, into a mixture of carbon dioxide and methane [8]. The digestate obtained as effluent from the anaerobic digestion of organic materials can be beneficiated as a biofertilizer, thus improving the economic gains. It is used as a soil amendment and compost material [66]. Due to a high energy output/input ratio (28/1), anaerobic digestion technology has a higher efficiency in energy generation from biomass in comparison to thermo-chemical and other biological processes [68]. Technoeconomic studies have demonstrated that sugarcane plants can generate biomethane through a cascading biorefinery scenario, which facilitates the valorization of bagasse for bioenergy production. This procedure enhances both the efficiency and economic viability of the process [3,15]. However, further large-scale studies are required to evaluate the practical and commercial feasibility of biogas production from this feedstock.

4.1.2. Bioethanol

In several countries, cellulosic ethanol production is a significant alternative energy source that helps reduce reliance on fossil fuels. Ethanol is traditionally produced from fermenting 1G-derived sugars and starch-based feedstock, like sugarcane, corn, and cassava, which affect the food supply [43]. The availability of sugarcane bagasse as waste generated during the sugar mill production process can be utilized for the production of bioethanol. Thus, competition with the food supply is alleviated. The use of sugarcane bagasse in the production of bioethanol has a major advantage: it is less carbon-intensive than fossil fuels, resulting in reduced levels of air pollution [69]. The generation of bioethanol is among the most promising alternatives to fossil fuels [70]. Bioethanol, the most widely used biofuel product from a biochemical pathway, has the most significant market (USD 58 billion annually) [71]. It is produced from the valorization of sugars obtained in sugarcane bagasse, using yeast cultures such as Saccharomyces cerevisiae [65]. Countries like the United States, Brazil, China, India, and members of the EU are advancing industrial-scale 2G bioethanol production using lignocellulosic biomass. This sustainable process uses agricultural residues and non-food plant materials, reducing competition with edible feedstocks. These technologies focus on efficient enzymatic hydrolysis and fermentation to convert complex carbohydrates into fermentable sugars for biofuels [1]. This biofuel is also produced in South Africa, with several bioethanol producers that use bagasse.

4.1.3. Biohydrogen

Hydrogen is a viable substitute for fossil fuels as it is a sustainable energy source. It burns clean and generates water rather than greenhouse gases, making it an environmentally friendly fuel [72]. Additionally, its energy output of 122 kJ/g is high (about 2.75 times higher than that of hydrocarbon fuels), and it is applicable in fuel cells to generate electricity [73]. There are several methods for producing hydrogen, such as electrolysis with solar energy or combusting fossil fuels. These methods are costly, as they require a lot of energy. However, biological hydrogen production may be more appealing, mainly if wastewater or other biomass could be utilized as the source material [74]. In contrast to thermo-chemical and electro-chemical processes, photosynthetic and fermentative processes are more sustainable and require less energy to produce hydrogen naturally [72]. The bioprocess of biohydrogen is mainly mediated by potent inocula such as Clostridium sp. and Bacillus sp., found in various ecosystems such as sludge, wastewater, soils, compost, etc. [19]. In comparison to other fermentative bacteria like Enterobacter sp., yielding 1 mol hydrogen/mol glucose, these potent spore-forming biocatalysts can convert glucose to hydrogen with a yield of up to 2 mol of hydrogen/mol glucose [72]. Most studies in this field are pursued at lower technology readiness levels (TRLs) as the biohydrogen economy is still hampered by the low H₂ yields, making this biorefinery route less appealing.

4.1.4. Biobutanol

Ajala et al. [65] showed that biobutanol production is economically feasible from the hydrolysates of starch and lignocellulosic feedstocks. Biobutanol, commonly referred to as next-generation liquid biofuel, is typically produced during the acetone–butanol–ethanol (ABE) fermentation process by fermentative bacteria [45]. It has been utilized in industrial processes involving plastic, flavoring, and food [60]. Butanol, with characteristics similar to gasoline, is used as a dye solvent and fuel in industries [45]. Production of biobutanol from sugarcane bagasse is a viable biorefinery route for generating biofuels. Compared to ethanol, butanol has a higher energy value and is less hygroscopic. Additional elements like pretreatment and detoxification also affect the viability of turning sugarcane bagasse into biobutanol. Due to the fact that traditional pretreatment methods, such as acid hydrolysis, typically produce hazardous inhibitors such as furfural and 5-hydroxymethylfurfural that significantly impede bacterial growth, these procedures are crucial [75]. Recent innovations in this area are now bio-augmenting the process performance using innovative scientific tools such as metabolic engineering, consolidated processing, the use of bio-additives, and optimization of bioprocess yields using multivariate tools [60].

4.2. Platform Chemicals

The manufacturing of platform chemicals from renewable materials aligns with the South African government’s framework of transitioning to a greener economy or bioeconomy, as shown in recent policy documents such as the National Development Plan 2030 [36]. Numerous platform chemicals, including lactic acid, citric acid, furfural, succinic acid, and xylitol, may be produced using this feedstock, as elucidated in this section.

4.2.1. Lactic Acid

Lactic acid is an organic acid with several applications in the food, pharmaceutical, and cosmetics industry sectors and for the synthesis of specific chemical intermediates, oxygenated compounds, and plant growth regulators [76,77]. Chemical synthesis and microbial fermentation are the routes used to produce lactic acid [78]. Lactic acid is manufactured using a commercial strain of Lactobacillus, which possesses a strong tolerance to acids, and it can be genetically engineered to produce selectively optically pure isomers [79]. This acid may be produced on a large scale from sugarcane bagasse hydrolysate, a renewable, easily accessible raw material primarily consisting of fermentable sugars such as glucose and xylose [33]. Over the years, interest in the use of lactic acid in the production of poly-lactic acid (PLA) has grown significantly [80]. PLA is a biobased polymer with properties of a thermoplastic; it is a biodegradable, biocompatible, and environmentally friendly alternative to plastics derived from petrochemicals [77,80]. A review by Agrawal and Kumar [43] showed that the commercialization of 2G lactic acid fermentation is progressing rapidly, as most technologies have reached TRL 8. Several companies, particularly in Asia, are investing in this technological domain, driven by its market potential.

4.2.2. Citric Acid

Today, citric acid (2-hydroxypropane-1, 2, 3-tricarboxylic acid) is one of the most significant organic acids obtained via fermentation, which is extensively used in the food, beverage, chemical, and metallurgical sectors [81]. The annual production of citric acid exceeds millions of tons globally [82]. Özüdoğru et al. [25] reported that in 2018, the global demand for citric acid was estimated to be around 2 million tons per annum with an annual growth of 4%. This is expected to rise to about 3 million tons by 2026. Citric acid is mainly produced using fermentation processes of Aspergillus niger and Candida sp. [82,83]. Similarly to other biobased products, the commercial production of citric acid is primarily achieved using 1G feedstocks. However, due to sustainability and food-versus-fuel concerns, an emphasis is put on 2G and 3G feedstocks for large-scale citric acid processes.

4.2.3. Furfural

Furfural is a key green chemical produced through lignocellulosic-based biorefinery processes [84]. It is a naturally occurring precursor to furan-based chemicals and plays an essential role in generating biofuels and biochemicals [85]. This chemical attracts interest due to its physical strength, corrosion resistance, and thermosetting properties [86]. It has a wide range of uses in making plastics, agrochemical products, pharmaceuticals, and various chemicals derived from saccharides rather than petroleum [87]. According to the literature [88], furfural is generated from sugarcane bagasse, Eucalyptus wood, and corn stalks using different concentrations of mineral acids. Sugarcane bagasse is considered one of the best feedstocks for furfural production because of its high xylan content [7]. Initially, mineral acids break down C5 polysaccharides in biomass into monosaccharides, mainly xylose, which are then converted into furfural via acid-catalyzed dehydration [89]. South Africa ranks among the top producers of biobased furfural globally. Illovo Sugar Africa is a major producer, making about 20 kt/year, primarily from sugarcane bagasse [76,84]. To boost revenues, the company also produces furfural derivatives and other byproducts.

4.2.4. Succinic Acid

Succinic acid is a dicarboxylic acid (C₄H₆O₄). It was included in the United States Department of Energy’s list of the top 12 value-added chemicals that can be produced from biomass in 2004 and 2010 [18]. Maleic anhydride is catalytically hydrogenated to succinic anhydride and then hydrated, or maleic acid is directly hydrogenated to produce succinic acid from crude oil [90]. Due to an urgent need to reduce pollution and the requirement to shift from a fossil-based linear economy to a circular bio-based economy, research in green technology is gaining increasing attention [91]. Manufacturing succinic acid from renewable agricultural feedstock expands a biorefinery’s potential product range by decreasing reliance on finite oil resources [90]. Most naturally occurring succinic acid producers are bacteria found in the rumen of cows. In this environment, succinic acid is produced and used to generate propionic acid, which provides energy and essential components for biosynthesis through oxidation [78]. Many researchers utilize microbial strains such as Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens, Corynebacterium glutamicum, and recombinant Escherichia coli to develop industrial processes for succinic acid fermentation [90]. In the literature, most of these processes remain at low technology readiness levels (TRLs), with only a few progressing to higher levels, highlighting the early stage of this field [92].

4.2.5. Xylitol

Xylitol, chemically known as pentahydroxy pentane (C₅H₁₂O₅), is a sugar-derived alcohol known for its versatile applications across various sectors, i.e., food and pharmaceutical industries [93]. Industrially, xylitol is synthesized from xylan, a hemicellulose derived from hardwoods or corncobs, through the hydrolysis process to yield xylose, followed by hydrogenation into xylitol in the presence of a suitable catalyst [93]. An alternative process through the microbial conversion of xylose to xylitol has garnered significant interest, particularly due to the “natural” appeal of the resultant products. This interest is further fueled by the demand for xylitol as a sweetener for diabetic consumers, driving research and development towards its production from biomass. Notable feedstocks that have been explored for the xylitol production process include corn cobs, sugarcane bagasse, and rice straw, with additional investigations into oil palm, Eucalyptus wood, and corn leaves [93]. Despite the advancements made in engineering the potent microbial strains applicable in xylitol production, technological barriers persist concerning the biodegradability of lignocellulosic substrates and the expensive separation of xylitol from the fermentation broth, which is an area that necessitates continued research and innovation.

5. Biorefinery Development in South Africa

R&D and Commercialization Initiatives

As shown in

Table 2. Biorefinery research and commercialization in South Africa.

University/Company Name	Sector	Products	Publications
Agricultural Research Council	Science council	Biofuels	[94,95]
Biorefinery Industry Development Facility—Council for Scientific and Industrial Research	Science council	Biofuels and platform chemicals	[96,97]
Stellenbosch University	Academia	Platform chemicals—lactic acid, succinic acid, furfural, citric acid	[98,99]
Cape Peninsula University of Technology	Academia	Biofuels	[100]
University of KwaZulu-Natal	Academia	Biofuels and platform chemicals	[101,102]
University of South Africa	Academia	Biofuels	[103]
North-West University	Academia	Biofuels, biochar, hydrochar	[104,105]
Durban University of Technology	Academia	Biobased products	[106,107]
University of the Western Cape	Academia	Biobased products	[108,109]
Ziziba	SMME	Protein	N/A
MycoSure	SMME	Protein	[110]
Bio2Watt	Company	Biogas	[111]
OptimusBío	Company	Fertilizers, skincare products, platform chemicals	[112]
Selokong Sa Dimelana	SMME	Castor oil, biodiesel	[113]
Adsorb Technologies	SMME	Biochar, activated carbon	[114]
Energy Phambili	Company	Biochar, activated carbon, bio-oil, wood vinegar	N/A

, biorefinery research and its commercialization are gaining significant momentum in South Africa. This approach is seen as an effective way to promote the country’s green economy initiatives while reducing socioeconomic challenges linked to the fossil-based linear economy. Local universities, SMMEs, and large corporations are actively engaged in various biorefinery platforms, producing a range of biobased products like biofuels, biochemicals, and biofertilizers. University research and science councils aim to implement the “stage-gate technology approach”, which assesses biorefinery solutions through realistic R&D results, enabling progression to higher TRLs and eventual commercialization. These R&D efforts are often licensed to startups, SMMEs, and companies to foster economic growth through innovation and enterprise. Furthermore, several local businesses, including OptimusBio, MycoSure, and Energy Phambili, are already pioneering the biorefinery market in South Africa. While these initiatives are not yet on par with those of South Africa’s BRICS partners and those from the Global North, their presence highlights the country’s dedication to shifting towards carbon-neutral solutions.

In addition to these initiatives, several government funding programs, such as the Biofuel Grant of the Technology Innovation Hub, the DSI’s Circular Economy Demonstration Fund, the Forestry Bioeconomy Innovation Cluster of the Technology Innovation Hub, the DSI’s Industrial Biocatalysis Hub, the DSI’s Circular Bioeconomy, and the DSI’s Strategic Industrial Bioinnovation Partnership Programme, have been implemented over the past decade, as a strategic approach of advancing the country’s biorefinery landscape. This funding is aimed at funding innovations that have the potential for industrialization.

6. Techno-Economic Viability of Valorizing Bagasse in South Africa

Techno-economic analysis (TEA) provides essential R&D insights that guide the evaluation of innovative bioeconomy initiatives. By utilizing simulation tools, TEA enables a thorough examination of technical and economic factors without the need for expensive and labor-intensive experimental work. This analytical approach is integral to the stage-gate methodology, which rigorously assesses each production scale before progression to subsequent stages.

A techno-economic analysis of the combined torrefaction and gasification of sugarcane bagasse for methanol and electricity production evaluated four scenarios (S1–S4), finding that the co-production route (S1) offered the best performance [115]. In this setup, methanol output was about 0.48 kg per kilogram of bagasse, and syngas had a lower heating value of 9.25 MJ/Nm³, both better than non-torrefaction scenarios. S1 was identified as the most viable option based on favorable economic indicators, including net present value and return on investment [115]. Key factors affecting profitability included revenue from methanol and electricity sales and raw material costs. Overall, torrefaction improved product yield and syngas quality, enhancing the economic viability of this process [115].

In a comprehensive study by Petersen et al. [116], a techno-economic model was developed to evaluate the production of ethanol and electricity from sugarcane bagasse. In this study, six scenarios were examined, ranging from electricity production alone to electricity and ethanol coproduction schemes. They found that the coproduction of ethanol and electricity was more economically viable than a single biorefinery scenario. This approach also yielded a 30% internal rate of return. Economies of scale could be realized by processing larger quantities of sugarcane bagasse, thus enhancing overall profitability.

Pachón et al. [36] developed two integrated biorefinery models associated with an existing sugar mill in South Africa, utilizing bagasse and molasses as raw materials: (1) SM LE, which produces both sugar and lactic acid, and (2) SM LF, which produces sugar, lactic acid, and furfural. Both setups generated excess electricity for sale. The techno-economic analysis results indicated that both models are financially viable, surpassing the current sugar-only operations under the conditions examined. Among the two, SM LF (lactic acid + furfural) exhibited better economic results, featuring a more favorable net present value (NPV) and internal rate of return (IRR) when compared to SM LE. While specific details on payback period and profitability metrics were not included in the summary, the research still establishes that integrated biorefineries provide significant economic advantages and improved sustainability outcomes (reduced climate, ecotoxicity, and fossil fuel impacts) within the context of South Africa.

An assessment by Nieder-Heitmann et al. [117] looked at the life cycle costs associated with converting sugarcane bagasse into itaconic acid, succinic acid, and electricity. The findings showed that this is the most sustainable scenario due to the sequential biorefinery units, resulting in minimal environmental burden. The profitability was measured based using the present net value, the net present value, the internal rate of return, total capital investment, production costs, and the technology readiness levels [117]. It was revealed that the co-production of succinic acid and itaconic acid has negligible environmental impacts compared to their fossil reference products.

In addition, Louw et al. [118] showed that the generation of 1G biorefinery portfolios, especially platform chemicals, is more financially viable than 2G feedstocks, as these require robust pretreatment steps, which are often expensive. Therefore, retrofitting the sugar mills with cascading biorefinery routes will improve the income of sugar mills. In conclusion, it can be shown that the upcycling of this feedstock is financially viable, as shown by these local studies. This also implies that further pilot or demonstration processes can be pursued, with manageable technical and financial risks. However, this might be a viable R&D approach in South Africa, given the “fuel vs. food” conundrum.

In South Africa, there is currently no substantial research focus on the production of amino acids, antibiotics, or enzymes from sugarcane bagasse, with existing efforts largely centered on bioenergy, platform chemicals, and low- to mid-value materials. This gap reflects limited specialized infrastructure, scarce targeted funding, and a lack of established value chains for these high-purity bioproducts within the national biorefinery landscape.

7. Conclusions and Future Outlooks

This review highlights the utilization of sugarcane bagasse (SCB) as a sustainable feedstock for circular biorefineries in South Africa by reviewing its potential in the biomanufacturing of diverse commercial biorefinery portfolios such as biofuels and chemicals. Fossil fuels are a finite energy resource that South Africans overly rely on; however, their combustion emits substantial amounts of greenhouse gases that cause adverse effects on the environment and the population. This has prompted the adoption of “Green technologies”. The depletion of fossil fuels and the constraints of 1G feedstocks emphasize the need to valorize 2G feedstocks such as SCB. Adopting integrated circular biorefinery strategies can address the hurdles faced by the local sugarcane industry. These strategies will not only increase profitability within this sector but also promote sustainable practices. Unlocking the full potential of lignocellulosic biomass requires pretreatment strategies, which are often cost-intensive, accounting for approximately 40% of the cost when paired with enzymatic hydrolysis. However, they are crucial for the diverse applications of SCB. The full potential of sugarcane bagasse may be harnessed to propel the transition towards a bio-based circular economy in the following ways: (i) continued research on pretreatment strategies to develop technologies that are cost-effective, energy-efficient, accessible, minimize inhibitory by-products, and enhance sugar recovery; (ii) supportive government policies, which include tax incentives, subsidies, and infrastructure development, are essential to accelerate the adoption of biorefineries and expand their operations; (iii) collaborations among academic institutions, industry stakeholders, and policymakers can stimulate innovation, mitigate risks, and improve the commercialization of biorefinery technologies; (iv) increasing the number of high-value chemicals and biofuels derived from SCB can help biorefineries become more economically sustainable; (v) implementation of measurement systems, such as life cycle assessments, which assess the social and environmental effects, will ensure the reliable development of biorefinery systems; and (vi) developing a viable market will promote the commercialization of biorefinery products.