Improvement of Sugarcane Stillage (Vinasse) Anaerobic Digestion with Cheese Whey as its Co-substrate: Achieving High Methane Productivity and Yield

Effect of the addition of an inorganic carbon source on the degradation of sotol vinasse by Rhodopseudomonastelluris

The difficulty of the microbial conversion process for the degradation of sotol vinasse due to its high acidity and organic load makes it an effluent with high potential for environmental contamination, therefore its treatment is of special interest. Calcium carbonate is found in great abundance and has the ability to act as a neutralizing agent, maintaining the alkalinity of the fermentation medium as well as, through its dissociation, releasing CO2 molecules that can be used by phototrophic CO2-fixing bacteria. This study evaluated the use of Rhodopseudomonas telluris (OR069658) for the degradation of vinasse in different concentrations of calcium carbonate (0, 2, 4, 6, 8 and 10% m/v). The results showed that calcium carbonate concentration influenced volatile fatty acids (VFA), alkalinity and pH, which in turn influenced changes in the degradation of chemical oxygen demand (COD), phenol and sulfate. Maximum COD and phenol degradation values of 83.16 ± 0.15% and 90.16 ± 0.30%, respectively, were obtained at a calcium carbonate concentration of 4%. At the same time, the lowest COD and phenol degradation values of 52.01 ± 0.38% and 68.21 ± 0.81%, respectively, were obtained at a calcium carbonate concentration of 0%. The data obtained also revealed to us that at high calcium carbonate concentrations of 6-10%, sotol vinasse can be biosynthesized by Rhodopseudomonas telluris (OR069658) to VFA, facilitating the degradation of sulfates. The findings of this study confirmed the potential for using Rhodopseudomonas telluris (OR069658) at a calcium carbonate concentration of 4% as an appropriate alternative treatment for sotol vinasse degradation.

Two-stage biohydrogen and methane production from sugarcane-based sugar and ethanol industrial wastes: A comprehensive review

The transition to renewable energy sources is crucial to ensure a sustainable future. Although the sugar and ethanol industries benefit from this transition, there are untapped opportunities to utilize the waste generated from the sugar and ethanol process chains through two-stage anaerobic digestion (TSAD). This review comprehensively discusses the utilization of various sugarcane-based industrial wastes by TSAD for sequential biohydrogen and methane production. Factors influencing TSAD process performance, including pH, temperature, hydraulic retention time, volatile fatty acids and alkalinity, nutrient imbalance, microbial population, and inhibitors, were discussed in detail. The potential of TSAD to reduce emissions of greenhouse gases is demonstrated. Recent findings, implications, and promising future research related to TSAD, including the integration of meta-omics approaches, gene manipulation and bioaugmentation, and application of artificial intelligence, are highlighted. The review can serve as important literature for the implementation, improvement, and advancements in TSAD research.

Biomethane Production from Sugarcane Vinasse in a Circular Economy: Developments and Innovations

Sugarcane ethanol production generates about 360 billion liters of vinasse, a liquid effluent with an average chemical oxygen demand of 46,000 mg/L. Vinasse still contains about 11% of the original energy from sugarcane juice, but this chemical energy is diluted. This residue, usually discarded or applied in fertigation, is a suitable substrate for anaerobic digestion (AD). Although the technology is not yet widespread—only 3% of bioethanol plants used it in Brazil in the past, most discontinuing the process—the research continues. With a biomethane potential ranging from 215 to 324 L of methane produced by kilogram of organic matter in vinasse, AD could improve the energy output of sugarcane biorefineries. At the same time, the residual digestate could still be used as an agricultural amendment or for microalgal production for further stream valorization. This review presents the current technology for ethanol production from sugarcane and describes the state of the art in vinasse AD, including technological trends, through a recent patent evaluation. It also appraises the integration of vinasse AD in an ideal sugarcane biorefinery approach. It finally discusses bottlenecks and presents possible directions for technology development and widespread adoption of this simple yet powerful approach for bioresource recovery.

Agro-Industrial Wastewaters for Algal Biomass Production, Bio-Based Products, and Biofuels in a Circular Bioeconomy

Recycling bioresources is the only way to sustainably meet a growing world population’s food and energy needs. One of the ways to do so is by using agro-industry wastewater to cultivate microalgae. While the industrial production of microalgae requires large volumes of water, existing agro-industry processes generate large volumes of wastewater with eutrophicating nutrients and organic carbon that must be removed before recycling the water back into the environment. Coupling these two processes can benefit the flourishing microalgal industry, which requires water, and the agro-industry, which could gain extra revenue by converting a waste stream into a bioproduct. Microalgal biomass can be used to produce energy, nutritional biomass, and specialty products. However, there are challenges to establishing stable and circular processes, from microalgae selection and adaptation to pretreating and reclaiming energy from residues. This review discusses the potential of agro-industry residues for microalgal production, with a particular interest in the composition and the use of important primary (raw) and secondary (digestate) effluents generated in large volumes: sugarcane vinasse, palm oil mill effluent, cassava processing waster, abattoir wastewater, dairy processing wastewater, and aquaculture wastewater. It also overviews recent examples of microalgae production in residues and aspects of process integration and possible products, avoiding xenobiotics and heavy metal recycling. As virtually all agro-industries have boilers emitting CO2 that microalgae can use, and many industries could benefit from anaerobic digestion to reclaim energy from the effluents before microalgal cultivation, the use of gaseous effluents is also discussed in the text.

Microbial dynamics and methanogenic potential of co-digestion of sugarcane vinasse and dairy secondary effluent in an upflow anaerobic sludge blanket reactor

Co-digestion is a strategy that may prevent microbial inhibition during the anaerobic treatment of sugarcane vinasse, a substrate with highly biodegradable organic load, acidity, and toxic compound levels (e.g., sulfates, phenols). In this context, this study evaluated the microbial dynamics and methanogenic potential throughout the co-digestion of sugarcane vinasse and secondary effluent from the dairy industry in a mesophilic lab-scale upflow anaerobic sludge blanket (UASB) reactor. Periodic next-generation sequencing (NGS) analyses revealed an increase in the relative abundance of the phylum Euryarchaeota (+8.6 % after inoculation), predominating hydrogenotrophic methanogens (Methanobacterium and Methanobrevibacter) at the end of the operation. Moreover, the average methane yield was 221 mLCH₄ gCOD_rem^-1, with 69 % of organic matter removal. These results evidenced a progressive acclimation of the anaerobic microbial community to the substrate and a stable operation. Therefore, the proposed experiment demonstrates energy advantages for the agro-industrial sector by implementing a similar but full-scale treatment plant.

Co-digestion of biofuel by-products: Enhanced biofilm formation maintains high organic matter removal when methanogenesis fails

Ethanol and biodiesel industries generate large volumes of by-products, such as vinasse and glycerol, which are suitable for biogas exploitation. This paper assessed the applicability and process performance of the anaerobic structured-bed reactor (AnSTBR) for the mesophilic (30 °C) continuous (105 days) anaerobic co-digestion of sugarcane vinasse and distilled glycerol under increasing organic loading rates (OLR) (0.5-5.0 kgCOD m^-3d^-1). The highest methane yield (211 NmL g^-1COD_rem.) and volumetric production (668 NmL L^-1d^-1) occurred at an OLR of 3.5 kgCOD m^-3d^-1. The performance of the AnSTBR showed high removal efficiencies of total COD (77.1%), carbohydrates (81.9%), and glycerol content (99.7%). Biofilm growth enhancement within the reactor offset the impairment of methanogenesis activity at high organic loads. The prompt biodegradability of glycerol reinforced the importance of gradually increase the organic load to prevent the buildup of volatile acids and maintain a stable long-term co-digestion system.

Past, Present, and Future Perspectives on Whey as a Promising Feedstock for Bioethanol Production by Yeast

Concerns about fossil fuel depletion and the environmental effects of greenhouse gas emissions have led to widespread fermentation-based production of bioethanol from corn starch or sugarcane. However, competition for arable land with food production has led to the extensive investigation of lignocellulosic sources and waste products of the food industry as alternative sources of fermentable sugars. In particular, whey, a lactose-rich, inexpensive byproduct of dairy production, is available in stable, high quantities worldwide. This review summarizes strategies and specific factors essential for efficient lactose/whey fermentation to ethanol. In particular, we cover the most commonly used strains and approaches for developing high-performance strains that tolerate fermentation conditions. The relevant genes and regulatory systems controlling lactose utilization and sources of new genes are also discussed in detail. Moreover, this review covers the optimal conditions, various feedstocks that can be coupled with whey substrates, and enzyme supplements for increasing efficiency and yield. In addition to the historical advances in bioethanol production from whey, this review explores the future of yeast-based fermentation of lactose or whey products for beverage or fuel ethanol as a fertile research area for advanced, environmentally friendly uses of industrial waste products.

Anaerobic Sequencing Batch Reactors Co-digesting Whey and Glycerin as a Possible Solution for Small and Mid-size Dairy Industries: Environmental Compliance and Methane Production

A significant part of whey generated in Brazil is from small and mid-size dairy companies. Cheese whey has great potential for methane production through anaerobic biological processes but presents instabilities due to its high biodegradability. To study an alternative for the destination of this residue, the aim of this work was to investigate methane from the co-digestion of whey with glycerin and its environmental compliance at 55 °C in an anaerobic sequencing batch biofilm reactor. The best performance indicators were obtained with an influent composed of 88% cheese whey and 12% glycerin (by volume), fed-batch mode and organic loading rate of 19.3 kgCOD m^-3 day^-1 at 55 °C. This operational condition allowed us to achieve a methane productivity of 203 molCH₄ m^-3 day^-1, a methane yield close to theoretical value, and to remove 68% of all organic matter in the influent. A kinetic metabolic model was fitted to the experimental data, which indicated methanogenesis with preference for the acetoclastic route. Finally, the energy production (approximately 197 MWh month^-1) from an industrial scale reactor and its volume (three reactors of 152 m³) were assessed for a mid-size dairy industry, which could save up to US$ 22,000.00 per month in oil demand.