Seasonal characterization of sugarcane vinasse: Assessing environmental impacts from fertirrigation and the bioenergy recovery potential through biodigestion

Simultaneous Optimization and Integration of Multiple Process Heat Cascade and Site Utility Selection for the Design of a New Generation of Sugarcane Biorefinery

Biorefinery plays a crucial role in the decarbonization of the current economic model, but its high investments and costs make its products less competitive. Identifying the best technological route to maximize operational synergies is crucial for its viability. This study presents a new superstructure model based on mixed integer linear programming to identify an ideal biorefinery configuration. The proposed formulation considers the selection and process scale adjustment, utility selection, and heat integration by heat cascade integration from different processes. The formulation is tested by a study where the impact of new technologies on energy efficiency and the total annualized cost of a sugarcane biorefinery is evaluated. As a result, the energy efficiency of biorefinery increased from 50.25% to 74.5% with methanol production through bagasse gasification, mainly due to its high heat availability that can be transferred to the distillery, which made it possible to shift the bagasse flow from the cogeneration to gasification process. Additionally, the production of DME yields outcomes comparable to methanol production. However, CO2 hydrogenation negatively impacts profitability and energy efficiency due to the significant consumption and electricity cost. Nonetheless, it is advantageous for surface power density as it increases biofuel production without expanding the biomass area.

Environmental assessment and durability performance of cement mortar incorporating sugarcane vinasse in replacement of water

Sugarcane vinasse wastewater (SVW) is one of the most voluminous waste generated in the ethanol industry and usually applied in fertigation. It is characterized by presenting high COD and BOD; thus, continued disposal of vinasse results in negative environmental impacts. In this paper, we investigated the potential of SVW in replacement of water in mortar, rethinking about reuse of effluent, reduction of pollutants in the environment, and water consumption in civil construction. Mortar composites with 0, 20, 40, 60, 80, and 100% of water replaced by SVW were studied in order to determine the optimum content. Mortars with 60 to 100% of SVW result in improved workability and reduction in water demand. The mortars with 20, 40, and 60% SVW resulted in satisfactory mechanical properties, i.e., similar to the control mortar. However, XRD analysis of cement pastes showed that the SVW causes a delay in CH formation, reaching mechanical strength after 28 days. Durability tests results showed that SVW contributes to the mortar becoming more impermeable; therefore, less susceptible to weathering. This study provides an important evaluation of the potential of SVW for application in civil construction, indicating relevant results for replacement of water by liquid wastes in cementitious composites and reduction the use of natural resources.

Carbon and Nutrients from Organic Residues Modulate the Dynamics of Prokaryotic and Fungal Communities

Inputs of carbon (C) and nutrients from organic residues may select specific microbes and shape the soil microbial community. However, little is known about the abiotic filtering of the same residues with different nutrient concentrations applied to the soil. In our study, we explored how applying organic residue, vinasse, as fertilizer in its natural state (V) versus its concentrated form (CV) impacts soil microbiota. We conducted two field experiments, evaluating soil prokaryotic and fungal communities over 24 and 45 days with vinasse (V or CV) plus N fertilizer. We used 16S rRNA gene and ITS amplicon sequencing. Inorganic N had no significant impact on bacterial and fungal diversity compared to the control. However, the varying concentrations of organic C and nutrients in vinasse significantly influenced the soil microbiome structure, with smaller effects observed for V compared to CV. Prokaryotic and fungal communities were not correlated (co-inertia: RV coefficient = 0.1517, p = 0.9708). Vinasse did not change the total bacterial but increased the total fungal abundance. A higher C input enhanced the prokaryotic but reduced the fungal diversity. Our findings highlight vinasse's role as an abiotic filter shaping soil microbial communities, with distinct effects on prokaryotic and fungal communities. Vinasse primarily selects fast-growing microorganisms, shedding light on the intricate dynamics between organic residues, nutrient concentrations, and soil microbes.

Technical and economical assessment of the treatment of vinasse from Pisco production using the advanced oxidation process

The removal of organic matter from Pisco production wastewater was evaluated using coagulation/flocculation, filtration as a pre-treatment, and solar photo-Fenton, with the use of two types of photoreactors: compound parabolic collectors (CPC) and flat plate (FP), with and without utilizing the ozonation process. The overall removal efficiency for chemical oxygen demand (COD) was 63% and 15% using FP and CPC, respectively. Also, for the overall removal efficiency of polyphenols, a percentage of 73% and 43% were obtained using FP and CPC, respectively. When ozone was used in the solar photoreactors, the resulting trends were similar. COD and polyphenol removal, using an FP photoreactor in the solar photo-Fenton/O₃ process, resulted in values of 98.8% and 86.2% after the process. COD and polyphenol removal, using solar photo-Fenton/O₃ process in a CPC, resulted in values of 49.5% and 72.4%, respectively. The economic indicators of annual worth and economic treatment capacity established that FP reactors represent lower costs than CPCs. These results were corroborated by the economic analyses of the evolution of costs versus COD removed as well as by the cash flow diagrams projected for 5, 10, and 15 years.

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.

Microbial Behavior and Influencing Factors in the Anaerobic Digestion of Distiller: A Comprehensive Review

Anaerobic digestion technology is regarded as the most ideal technology for the treatment of a distiller in terms of environmental protection, resource utilization, and cost. However, there are some limitations to this process, the most prominent of which is microbial activity. The purpose of this paper is to provide a critical review of the microorganisms involved in the anaerobic digestion process of a distiller, with emphasis on the archaea community. The effects of operating parameters on microbial activity and process, such as pH, temperature, TAN, etc., are discussed. By understanding the activity of microorganisms, the anaerobic treatment technology of a distiller can be more mature. Aiming at the problem that anaerobic treatment of a distiller alone is not effective, the synergistic effect of different substrates is briefly discussed. In addition, the recent literature on the use of microorganisms to purify a distiller was collected in order to better purify the distiller and reduce harm. In the future, more studies are needed to elucidate the interactions between microorganisms and establish the mechanisms of microbial interactions in different environments.

Pristina longiseta reproduction test: chronic exposure to environmental contaminants

Aquatic worms are considered a suitable group to evaluate the effects of contaminants on the environment, although one of the main challenges is to use the species of local occurrence. Recently, Pristina longiseta was suggested to be used in acute bioassays. In this context, this study aimed to establish a chronic exposure for ecotoxicological bioassays using the cosmopolitan species of occurrence in Brazilian freshwater P. longiseta. Firstly, we tested three exposure times (4, 7, and 10 days) under the presence or absence of aeration for reproduction outputs. After determining the best configuration (7 days without aeration), we assessed the effects of the chronic exposures using the standardized reference substance potassium chloride (KCl), the antibiotic sulfamethoxazole (SMX), the flame retardant tetrabromobisphenol A (TBBPA), and the sugarcane vinasse. Our results showed suitability for applying the chronic exposure using P. longiseta and indicated the sensitivity of the offspring to KCl (EC50-7d = 0.51 g/L). Sulfamethoxazole and TBBPA caused a significant decrease in the offspring of P. longiseta (EC50-7d = 59.9 µg/L and < 62.5 µg/L, respectively). Sugarcane vinasse showed high toxicity for the species, and 4.26% of vinasse was calculated as EC50-7d. Therefore, the described protocol was successfully applied as an ecotoxicological bioassay to evaluate the effects of environmental contaminants on the reproduction rate of the freshwater worm P. longiseta.

Strategies to control pH in the dark fermentation of sugarcane vinasse: Impacts on sulfate reduction, biohydrogen production and metabolite distribution

pH is notably known as the main variable defining distinct metabolic pathways during sugarcane vinasse dark fermentation. However, different alkalinizing (e.g. sodium bicarbonate; NaHCO₃) and/or neutralizing (e.g. sodium hydroxide; NaOH) approaches were never directly compared to understand the associated impacts on metabolite profiles. Three anaerobic structured-bed reactors (AnSTBR) were operated in parallel and subjected to equivalent operational parameters, except for the pH control: an acidogenic-sulfidogenic (R1; NaOH + NaHCO₃) designed to remove sulfur compounds (sulfate and sulfide), a hydrogenogenic (R2; NaOH) aimed to optimize biohydrogen (bioH₂) production, and a strictly fermentative system without pH adjustment (R3) to mainly evaluate lactic acid (HLa) production and other soluble metabolites. NaHCO₃ dosing triggered advantages not only for sulfate reduction (up to 56%), but also to enhance the stripping of sulfide to the gas phase (75-96% of the theoretical sulfide produced) by the high and constant biogas flow resulting from the CO₂ released during NaHCO₃ dissociation. Meanwhile, molasses-based vinasse presented higher potential for bioH₂ (up to 4545 mL-H₂ L^-1 d^-1) and HLa (up to 4800 mg L^-1) production by butyric-type and capnophilic lactic fermentation pathways. Finally, heterolactic fermentation was the main metabolic route established when no pH control was provided (R3), as indicated by the high production of both HLa (up to 4315 mg L^-1) and ethanol (1987 mg L^-1). Hence, one single substrate (from which one single source of inoculum was originated) offers a wide range of metabolic possibilities to be exploited, providing substantial versatility to the application of anaerobic digestion in sugarcane biorefineries.

Study of Technological Process of Fermentation of Molasses Vinasse in Biogas Plants

The volume of ethanol production waste—molasses waste in Ukraine—reaches up to 4 million m3 per year. It is not easy to dispose of and is polluting the environment. Currently, the development of an effective technology for using molasses in biogas plants to obtain energy gas—biogas—is an urgent problem. The purpose of our work is to determine the rational volume of loading molasses bard into the methane tank in a quasi-continuous mode to obtain the maximum volume of biogas. To achieve this goal, the following experimental studies were carried out: mono-fermentation of molasses and combined fermentation of cattle manure and molasses on a laboratory biogas plant in a periodic mode; on the basis of the obtained laboratory studies, a special simulation model of biogas output during the quasi-continuous fermentation of substrates was established and the amount of molasses added to obtain the maximum biogas output was determined. The maximum output of biogas under the periodic system of loading the methane tank when adding 10.5% molasses to cattle manure is 1.462 l/(h kg DOM); when adding 26.1% molasses to cattle manure, it is 3.594 l/(h kg DOM). In order to increase the yield of biogas, it is advisable to add molasses in the amount of 30% of the volume of the substrate to the substrate based on cattle manure, which allows the discounted payback period of the biogas plant to be reduced to 1.2 years.

Sugarcane vinasse as organo-mineral fertilizers feedstock: Opportunities and environmental risks

Fertigation using sugarcane vinasse is expected in the sugar and alcohol industries; however, its indiscriminate practice can trigger soil salinization and contamination of water sources. This review article appraises the vinasse use as a precursor material in producing organo-mineral fertilizers. Vinasse use could be an alternative for the increased demand for organo-mineral fertilizers. In that case, the vinasse reuse would be maintained but through controlled practices and lower environmental impact. The state-of-art points to possible advantages associated with the vinasse conversion into organo-mineral fertilizers, such as ease of transport and handling, low variability in its composition, and lower risks of soil and water resources contamination. It has been summarized and critically discussed the past ten years (2011-2021, total number papers revised: 175) of research data about vinasse composition, along with the limitations to be overcome in the near future to enable the application of organo-mineral fertilizers. Possible nutrients supplementation beyond those already present in vinasse composition would depend on the crop requirement, and the impact on the soil biota and integrity should be better understood. The aspects discussed along the manuscript would be aligned with circular economy principles, converting a residue (vinasse) into a potential resource for agricultural activities, including sugar and alcohol industries. After all, although promising, obtaining organo-mineral fertilizers from vinasse must be empirically validated and its feasibility proven by comparative studies between fertigation and the use of organo-mineral fertilizers.

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.

Irrigation with Water Contaminated by Sugarcane Pesticides and Vinasse Can Inhibit Seed Germination and Crops Initial Growth

Sugarcane crops are dependent on chemicals for maintaining plantations. Therefore, environmental consequences concern adjacent areas that can be affected by contaminants in common use, including pesticides and vinasse (i.e., a by-product from the ethanol industry). This study aimed to evaluate phytotoxicity through two plant bioassays with water from mesocosms contaminated with the herbicide 2,4-D (447.0 μg L^-1), the insecticide fipronil (63.5 μg L^-1), and sugarcane vinasse (1.3%). First, the germination test (4 d) with Eruca sativa L. assessed water samples collected three times after the contamination (2 h, 14 d, and 30 d), considering germination, shoot, and root growth. The results from this bioassay indicated higher phytotoxicity for 2,4-D as it fully inhibited the shoot and root growth even in low concentrations (0.2 μg L^-1). However, no significant effect was reported for fipronil and vinasse. Also, the 2,4-D effects drastically decreased due to an expressive concentration reduction (99.4% after 30 d in mixture with vinasse). Second, the irrigation test with Phaseolus vulgaris L. and Zea mays L. considered shoot and root growth and biomass under 21 days after plants emergence. The herbicide 2,4-D inhibited the initial growth of tested species, especially the roots (up to 45% inhibition). Furthermore, sugarcane vinasse caused harmful effects on plant growth (up to 31% inhibition). Therefore, our data showed that these contaminants could inhibit plant germination and initial growth under our tested conditions. These evaluations can endorse risk assessments and water management in sugarcane crops surrounding areas.

Resource recovery from sugarcane vinasse by anaerobic digestion - A review

The increase in biofuel production by 2030, driven by the targets set at the 21st United Nations Framework Convention on Climate Change (COP21), will promote an increase in ethanol production, and consequently more vinasse generation. Sugarcane vinasse, despite having a high polluting potential due to its high concentration of organic matter and nutrients, has the potential to produce value-added resources such as volatile fatty acids (VFA), biohydrogen (bioH₂) and biomethane (bioCH₄) from anaerobic digestion. The objective of this paper is to present a critical review on the vinasse treatment by anaerobic digestion focusing on the final products. Effects of operational parameters on production and recovery of these resources, such as pH, temperature, retention time and type of inoculum were addressed. Given the importance of treating sugarcane vinasse due to its complex composition and high volume generated in the ethanol production process, this is the first review that evaluates the production of VFAs, bioH₂ and bioCH₄ in the treatment of this organic residue. Also, the challenges of the simultaneous production of VFA, bioH₂ and bioCH₄ and resources recovery in the wastewater streams generated in flex-fuel plants, using sugarcane and corn as raw material in ethanol production, are presented. The installation of flex-fuel plants was briefly discussed, with the main impacts on the treatment process of these effluents either jointly or simultaneously, depending on the harvest season.

A spatially explicit assessment of sugarcane vinasse as a sustainable by-product

This study evaluates the benefits of mineral fertilizers replacement for biodigested vinasse. Data from experimental anaerobic digestion (AD) of vinasse were applied to support the analysis. Based on previous experiments, this assessment assumed that vinasse production could reach 2.38 × 107 m3/year generating around 66,585 MWh/year of electric energy from biogas burning in the Administrative Region of Campinas (ARC). This amount of energy could supply more than 103,000 inhabitants and avoid 35,892 tCO2eq/year (from electric energy replacement). The biodigested vinasse might also reduce the total N, P, and K mineral fertilizers demand per hectare of sugarcane crop in 30%, 1%, and 46%, respectively, avoiding additional greenhouse gas emissions of 111,877 tCO2eq/year. There is no biodigested vinasse surplus for a moderate fertigation rate of 100 m3/ha, complying with local environmental laws related to nutrients excess side effects in areas destined to sugarcane crop. Notwithstanding, a Geographic Information System analysis for a small adjacent area to ARC indicated nine different fertigation rates, ranging from 50 to 100 m3/ha. Even though the general analysis for ARC shows high NPK replacement levels, the fertigation practices should be subsidized for robust soil analysis and adequate to safe environmental levels. A management tool can be designed using the results here presented to subsidize investments for AD widespread adoption by the sugarcane industry to catch a reasonable practice from the economic and environmental perspectives.

Physicochemical properties of konjac glucomannan/alginate films enriched with sugarcane vinasse intended for mulching applications

Biodegradable films are a promising strategy to reduce the environmental impact caused by conventional plastics commonly used in agriculture. This study focused on the production and characterization of Konjac glucomannan (KGM) and alginate (ALG) based films enriched with sugarcane vinasse (VIN), a nutrient-rich wastewater generated in large volumes by the sugar-ethanol producing industries. ALG, KGM and ALG/KGM blended (50:50) films were produced by casting and treated with calcium ions (Ca²⁺) (ALG films) and a combination of Ca²⁺, alkali, and ethanol (KGM and ALG/KGM films). Vinasse addition tended to reduce transparency and water resistance of the films and had less effect on their mechanical properties. Crosslinking of ALG films resulted in enhanced mechanical properties and reduced moisture content, water solubility, swelling, water vapor permeability, and flexibility. KGM films were less impacted by crosslinking/deacetylation but showed improved water resistance while maintain a high degree of swelling (290% and 185% for KGM and KGM/VIN films respectively). Blended films exhibited characteristic properties of the two biopolymers and adequate compatibility indicated by Fourier transform infrared spectroscopy (FTIR) and morphologies. Vinasse-added ALG/KGM films represent a novel nutrient-enriched, bio-based material for agricultural applications and could help to face the environmental challenges imposed by vinasse disposal.

Biochemical conversion of sugarcane bagasse into the alcohol fuel mixture of isopropanol-butanol-ethanol (IBE): Is it economically competitive with cellulosic ethanol?

This work presents a techno-economic analysis of the production of isopropanol, butanol, and ethanol (IBE) from sugarcane bagasse using clostridia and compares IBE with cellulosic ethanol for the minimum selling price (MSP) and sustainability aspects. The MSPs of the fuels are similar (15 USD/GJ) provided that glucose and xylose are effectively utilized in both processes, and the IBE process is equipped with a genetically-modified Clostridium species with enhanced IBE yield and a highly productive continuous bioreactor with integrated product recovery. Notably, these technologies can reduce the size (from 23 × 3785-m³ to 3 × 3027-m³ fermentation tanks) and the wastewater footprint (from 50 to 10 m³/m³ IBE) of the IBE plant. Furthermore, given that the production of either fuel results in a similar increase in the value created by the sugarcane biorefinery and its energy efficiency, the alcohol mixture produced by clostridia is a promising alternative to the less energy-dense ethanol fuel.

Dynamics and resilience of soil mycobiome under multiple organic and inorganic pulse disturbances

Disturbances in soil can cause short-term soil changes, consequently changes in microbial community what may result in long-lasting ecological effects. Here, we evaluate how multiple pulse disturbances effect the dynamics and resilience of fungal community, and the co-occurrence of fungal and bacterial communities in a 389 days field experiment. We used soil under sugarcane cultivation as soil ecosystem model, and organic residue (vinasse - by-product of sugarcane ethanol production) combined or not with inorganic (organic residue applied 30 days before or together with mineral N fertilizer) amendments as disturbances. Application of organic residue alone as a single disturbance or 30 days prior to a second disturbance with mineral N resulted in similar changes in the fungal community. The simultaneous application of organic and mineral N as a single pulse disturbance had the greatest impact on the fungal community. Organic amendment increased the abundance of saprotrophs, fungal species capable of denitrification, and fungi described to have copiotrophic and oligotrophic lifestyles. Furthermore, the changes in the fungal community were not correlated with the changes in the bacterial community. The fungal community was neither resistant nor resilient to organic and inorganic disturbances over the one-year sampling period. Our findings provide insights on the immediate and delayed responses of the fungal community over one year to disturbance by organic and inorganic amendments.

Influence of COD/SO42- ratio on vinasse treatment performance by two-stage anaerobic membrane bioreactor

Vinasse is sulfate-rich wastewater due to sulfuric acid dosage in some ethanol production steps. The vinasse sulfate concentration is subject to seasonal variations. A two-stage anaerobic membrane bioreactor (2S-AnMBR) was operated to evaluate the influence of COD/SO₄^2- ratio on vinasse treatment performance by using a real vinasse sample under natural seasonal COD/SO₄^2- variation. This ratio directly affects the sulfidogenesis efficiency, which is responsible for different forms of inhibition in the anaerobic treatment of sulfate-rich wastewater. The bioreactor presented a stable performance at the highest COD/SO₄^2- ratios (50-94), with high removal of chemical oxygen demand (COD) (97.5 ± 0.4%) and volatile fatty acids (VFA) (98.0 ± 0.6%), but low removal of sulfate (69.9 ± 9.5%), indicating lower sulfate reducing bacteria (SRB) activity. In the lowest COD/SO₄^2- ratios (9-20), a deterioration in the removal of organic matter (87.0 ± 1.3%) and VFA (69.8 ± 15.5%) was observed, accompanied by sulfate removal increase (92.9 ± 2.6%). A significant correlation between COD fractions removed via methanogenesis and sulfidogenesis and the COD/SO₄^2- ratio was found, indicating that the increase of this ratio is beneficial to the methanogenic archaea activity. The occurrence of sulfidogenesis, favored by the lower COD/SO₄^2- ratios, induced the microbial soluble products (SMP) and extracellular polymeric substances (EPS) release and protein/carbohydrate ratio increase in the mixed liquor, contributing to the filtration resistance increase.

Biomethane production by thermophilic co-digestion of sugarcane vinasse and whey in an AnSBBR: Effects of composition, organic load, feed strategy and temperature

This work investigated the application of a thermophilic (55 °C) anaerobic reactor with immobilized biomass, mechanically stirred and operated in sequential batch and fed batch (AnSBBR) for environmental compliance and methane production by co-digesting cheese whey (W) and sugarcane vinasse (V). The assays were performed in four steps. In the first step the composition of 75%W:25%V (on a COD basis) was determined to be the most adequate for the anaerobic process. In the second step the applied volumetric organic load (AVOL) was increased and in the third step the feed strategy was modified achieving best results at AVOL of 25 gCOD.m^-3.d^-1, in which the removed organic matter efficiency was 72%, the molar productivity was 278 molCH₄.m^-3.d^-1 and methane yield was 15.3 mmolCH₄.gCOD^-1. In the fourth step the temperature was modified to 50 °C and 45 °C, achieving worse results. From the kinetic model adjusted to experimental data it was identified that the acetoclastic route was predominant in methane generation. The estimated energy recovered by co-digesting cheese whey and sugarcane vinasse using industrial information was 2.2 × 10⁴ MW h per month, equivalent (in Brazil) to the electricity consumption of about 135 × 10³ inhabitants or monthly savings of US$ 1,653,000 replacing the diesel oil consumed in the industry.

Microalgal biorefineries: Integrated use of liquid and gaseous effluents from bioethanol industry for efficient biomass production

A new method for CO₂ recovery was proposed for cultivation of different microalgae. First, a chemical fixation, where CO₂ was injected in alkalinized vinasse to form (bi)carbonate salts, was performed. In addition, biological fixation with CO₂-enriched air injection was also accomplished for evaluation of the most promising results. Two bioreactor systems, a stirred-tank reactor and a bubble column reactor, were employed. A higher carbon transfer rate (43.35 g.L^-1.h^-1) was achieved in the bubble column reactor using NaOH-alkalinized vinasse, along with reductions of the chemical oxygen demand (COD), biological oxygen demand (BOD) and turbidity (TD). This allowed the cultivation of microalgae and cyanobacteria at vinasse concentrations between 70 and 100%, reaching a biomass production of 2.25 g.L^-1 in 15 days of culture. The viability of chemical CO₂ fixation together with the use of 100% treated vinasse from a bioethanol production unit for microalgae cultivation has been demonstrated in a successfully integrated biorefinery approach.

Seasonal variation of the organic and inorganic composition of sugarcane vinasse: main implications for its environmental uses

Sugarcane vinasse is the main waste stream of the Brazilian agroindustry. The typical composition of sugarcane vinasse gives it a high polluting potential that implies the necessity to define sustainable strategies for managing this waste. Knowledge of the inorganic and organic composition of vinasse and its seasonal variation is extremely important to conduct scientific research to define alternative managements for vinasse disposal other than fertigation. This study evaluated the variability of vinasse composition throughout the same harvesting season and among three harvesting seasons of one Brazilian annexed biorefinery (2015-2017). The contents of chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), total solids (TS), suspended solids (SS), salinity (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-, F^-), nutrients (N, P, S), trace metals (Al³⁺, As²⁺, Ba²⁺, Cd²⁺, Cr³⁺, Co²⁺, Cu²⁺, Fe²⁺, Pb²⁺, Mn²⁺, Hg²⁺, Mo²⁺, Ni²⁺, Se²⁺, Zn²⁺), and specific soluble organic compounds (sugars, alcohols, and organic acids), as well as pH and conductivity, were monitored in 13 samples. The results indicated that sugarcane vinasse is a suitable feedstock for biological treatments, such as anaerobic digestion processes for energy recovery, as well as substrate for biomass (e.g., microalgae, energy crops, lignocellulosic biomass) growth. The application of a previous treatment makes vinasse a more environmentally friendly natural fertilizer for land fertigation.

Use of anaerobic co-digestion as an alternative to add value to sugarcane biorefinery wastes

In this study the anaerobic co-digestion (AcD) of sugarcane biorefinery by-products, i.e. hemicelluloses hydrolysate (HH) (obtained by hydrothermal pretreatment of sugarcane bagasse), vinasse, yeast extract (YE) and sugarcane bagasse fly ashes (SBFA), was optimized by means of biochemical methane potential experiments. The best experimental conditions of AcD (25-75% HH-to-vinasse mixture ratio; 1.0 g L^-1 YE; 15 g L^-1 SBFA and 100-0% HH-to-Vinasse; 1.5 g L^-1 YE; 45 g L^-1 SBFA) led to the production of 0.279 and 0.267 Nm³ of CH₄ per kg of chemical oxygen demand (COD) with an energy surplus of 0.43 and 0.34 MJ kg SB^-1, respectively. Adsorption experiments using SBFA were carried out and showed this residue could adsorb up to 61.71 and 17.32 mg g^-1 of 5-hydroxymethyl-2-furfuraldehyde and 2-furfuraldehyde, thereby reducing toxicity and improving biogas production.

Novel insights on the versatility of biohydrogen production from sugarcane vinasse via thermophilic dark fermentation: Impacts of pH-driven operating strategies on acidogenesis metabolite profiles

An innovative application of the anaerobic structured-bed reactor (AnSTBR) in thermophilic dark fermentation of sugarcane vinasse targeting biohydrogen (bioH₂) production was assessed. A detailed metabolite monitoring program identified the major substrates and primary metabolic pathways within the system. Increasing the applied organic loading rate positively affected bioH₂ production, reaching 2074 N mL-H₂ L^-1 d^-1 and indicating an optimal load of approximately 70 kg-COD m^-3 d^-1. Controlling the fermentation pH (5.0-5.5) was the primary strategy to maintain bioH₂-producing conditions, offsetting negative impacts associated with the compositional variability of vinasse. Metabolic correlations pointed out lactate as the primary substrate for bioH₂ production, indicating its accumulation as evidence of impaired reactors. The versatility of the acidogenic system was confirmed by identifying three major metabolic pathways according to the pH, i.e., lactate-producing (pH <5.0), bioH₂-/butyrate-producing (pH = 5.0-5.5) and bioH₂-producing/sulfate-reducing (pH >6.0) systems, which enables managing the operation of the reactors for diversified purposes in practical aspects.

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

This study investigated methane production in an anaerobic sequencing batch biofilm reactor (AnSBBR) by co-digesting sugarcane vinasse and cheese whey. The assessment was based on the influence of feed strategy, interaction between cycle time and influent concentration, applied volumetric organic load (OLR_A), and temperature over system stability and performance. The system showed flexibility with regard to the feed strategy, but the reduction of cycle time and influent concentration, at the same OLR_A, resulted in lower methane productivity. Increasing organic load, up to the value of 15.27 gCOD L^-1 day^-1, favored the process, increasing methane yield and productivity. Temperature reduction from 30 to 25 °C resulted in worse performance, although increasing it to 35 °C provided similar results to 30 °C. The best results were achieved at an OLR_A of 15.27 gCOD L^-1 day^-1, cycle time of 8 h, fed-batch operation, and temperature of 30 °C. The system achieved soluble COD removal efficiency of 89%, methane productivity of 208.5 molCH₄ m^-3 day^-1 and yield of 15.76 mmolCH₄ gCOD^-1. The kinetic model fit indicated methanogenesis preference for the hydrogenotrophic route. At the industrial scale estimative, considering a scenario with a sugarcane ethanol plant with ethanol production of 150,896 m³ year^-1, it was estimated energy production of 25,544 MWh month^-1.

Effect of process parameters on enhanced biohydrogen production from tequila vinasse via the lactate-acetate pathway

In this study, a lactate-type fermentation entailing the consumption of lactate and acetate (lactate-acetate pathway) is proposed to deal with lactic acid bacteria (LAB) inhibition during the production of biohydrogen (bioH₂) from tequila vinasse. The effects of total solids content, substrate concentration, nutrient formulation and inoculum addition on bioH₂ production performance were investigated. Batch experiments were performed in a 3-L completely mixed reactor at 35 °C and pH 6.5-5.8. The lactate-acetate pathway mediated consistent bioH₂ production which was influenced by inoculum addition followed by substrate concentration, nutrient formulation and solids content. Maximum bioH₂ production rate (225 NmL/L-h) and yield (124 NmL/g VS_added) were achieved by removing suspended solids and enhancing nutrient content, respectively. Illumina sequencing-based analysis revealed a dominance of Clostridium in the inoculum, which together with LAB and acetic acid bacteria shaped a keystone cluster for avoiding LAB inhibition while ensuring consistent bioH₂ production performance.

Performance improvement of a thermophilic sulfate-reducing bioreactor under acidogenic conditions: Effects of diversified operating strategies

The establishment of a sulfidogenic environment under thermophilic (55 °C) acidogenic conditions was assessed in an innovative structured-bed bioreactor to enhance sulfate removal and acetate production prior to methanogenesis. Diversified operating strategies, i.e., variations in the hydraulic retention time (HRT; 6-12 h), sulfate loading rate (SLR; 8-16 kg SO₄^2- m^-3 day^-1) and liquid phase recirculation ratio (0.0-57.0) were assessed to both enable the establishment of sulfate-reducing conditions and remove H₂S from the liquid phase. Ethanol was used as the only carbon source. Applying a low HRT (6 h) as the initial operating strategy severely hindered the establishment of sulfate-reducing bacteria (SRB) populations within the system (sulfate removal < 27.5%). In turn, applying effluent recirculation had a positive impact on the system (sulfate removal ∼ 60%) by providing an adequate buffer control along the entire height of the system, as well by displacing over 70% of the H₂S to the gaseous phase. The maintenance of pH values above 6.1 proved to be adequate for the sulfidogenic activity, whereas enhanced acidic conditions (pH < 6.0) at the basal portion of the reactor comprised a determining factor to hinder sulfate reduction. SRB were able to handle H₂S and acetate concentrations as high as 232 mg L^-1 and 3111 mg L^-1, respectively, after establishing an effective acidogenic/sulfidogenic environment, indicating that the proposed system has the potential to be used as the first stage in the anaerobic processing of sulfate-rich wastewater streams.