Anaerobic Digestion of Sugarcane Vinasse Through a Methanogenic UASB Reactor Followed by a Packed Bed Reactor

Critical State of the Art of Sugarcane Industry Wastewater Treatment Technologies and Perspectives for Sustainability

The worldwide pressure on water resources is aggravated by rapid industrialization, with the food industry, particularly sugar factories, being the foremost contributor. Sugarcane, a primary source of sugar production, requires vast amounts of water, over half of which is discharged as wastewater, often mixed with several byproducts. The discharge of untreated wastewater can have detrimental effects on the environment, making the treatment and reuse of effluents crucial. However, conventional treatment systems may not be adequate for sugarcane industry effluent treatment due to the high organic load and variable chemical and mineral pollution. It is essential to explore pollution-remediating technologies that can achieve a nexus (water, energy, and food) approach and contribute to sustainable development. Based on the extensive literature, membrane technologies such as the membrane bioreactor have shown promising results in treating sugarcane industry wastewater, producing treated water of higher quality, and the possibility of biogas recovery. The byproducts generated from this treatment can also be recovered and used in agriculture for food security. To date, membrane technologies have demonstrated successful results in treating industrial wastewater. This critical review aims to evaluate the performance of traditional and conventional processes in order to propose sustainable perspectives. It also serves to emphasize the need for further research on operating conditions related to membrane bioreactors for valuing sugarcane effluent, to establish it as a sustainable treatment system.

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.

High-retention membrane bioreactors for sugarcane vinasse treatment: Opportunities for environmental impact reduction and wastewater valorization

Ethanol production has increased over the years, and Brazil ranking second in the world using sugarcane as the main raw material. However, 10-15 L of vinasse are generated per liter of ethanol produced. Besides large volumes, this wastewater has high polluting potential due to its low pH and high concentrations of organic matter and nutrients. Given the high biodegradability of the organic matter, the treatment of this effluent by anaerobic digestion and membrane separation processes results in the generation of high value-added byproducts such as volatile fatty acids (VFAs), biohydrogen and biogas. Membrane bioreactors have been widely evaluated due to the high efficiency achieved in vinasse treatment. In recent years, high retention membrane bioreactors, in which high retention membranes (nanofiltration, reverse osmosis, forward osmosis and membrane distillation) are combined with biological processes, have gained increasing attention. This paper presents a critical review focused on high retention membrane bioreactors and the challenges associated with the proposed configurations. For nanofiltration membrane bioreactor (NF-MBR), the main drawback is the higher fouling propensity due to the hydraulic driving force. Nonetheless, the development of membranes with high permeability and anti-fouling properties is uprising. Regarding osmotic membrane bioreactor (OMBR), special attention is needed for the selection of a proper draw solution, which desirably should be low cost, have high osmolality, reduce reverse salt flux, and can be easily reconcentrated. Membrane distillation bioreactor (MDBR) also exhibit some shortcomings, with emphasis on energy demand, that can be solved with the use of low-grade and residual heat, or renewable energies. Among the configurations, MDBR seems to be more advantageous for sugarcane vinasse treatment due to the lower energy consumption provided by the use of waste heat from the effluent, and due to the VFAs recovery, which has high added value.

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.

Anaerobic digestion of vinasse and water treatment plant sludge increases methane production and stability of UASB reactors

Studies are still needed to increase the stability and efficiency of methane production from vinasse. Therefore, operations strategies, such as the anaerobic digestion with one or more wastes and adding micronutrients, especially iron, become attractive. The performance of two treatment systems, each one composed of two UASB reactors in series, operated under mesophilic (R1_M and R2_M) and thermophilic (R1_T and R2_T) temperature conditions, was evaluated in the anaerobic digestion of vinasse (ADV). First, the reactors were operated with the effluent recirculation and increasing organic loading rate (OLR) up to 20 g COD_total L^-1d^-1 in the R1_M and R1_T. Then, the anaerobic digestion of vinasse and water treatment plant (WTP) sludge (ADVS) was performed in the proportions of 25:75 to 50:50 (% v/v) in both systems. In the ADV, applying the highest OLR, the mesophilic and thermophilic reactors instabilities happened. The ADVS of over 35% of WTP sludge promoted the recovery of the mesophilic and thermophilic UASB reactors with significantly reduced total volatile acids and increased alkalinity and biogas production. The higher average values of the volumetric methane production (VMP) occurred in the ADVS at 50% of WTP; in the R1_M and R1_T, they were 3.23 and 3.00 L CH₄ L^-1d^-1, respectively. In the ADV, the thermophilic system presented higher VMP concerning the mesophilic for OLR up to 15 g COD_total L^-1d^-1. For higher OLR, the mesophilic system showed better carrying capacity and stability. The ADVS with above 35% of WTP sludge promoted similar benefits in the two systems, with no significant differences in COD_total removal and VMP. Therefore, adding iron by WTP sludge in ADVS improves methane production and increases the stability of UASB reactors under mesophilic and thermophilic conditions.

Biogas production by anaerobic co-digestion of sugarcane biorefinery byproducts: Comparative analyses of performance and microbial community in novel single-and two-stage systems

Anaerobic co-digestion (AcD) of sugarcane biorefinery byproducts (hemicelluloses hydrolysate (HH), vinasse, yeast extract and sugarcane bagasse fly ashes was evaluated using new anaerobic reactors fed with organic loading rates (OLR) from 0.9 to 10.8 gCODL^-1d^-1. The best results were obtained in a two-stage system when the OLR was 5.65 gCODL^-1d^-1, leading to a total chemical oxygen demand (COD) removal of 87.6 % and methane yield of 243NmLCH₄gCODr^-1. Microbial community analyses of sludge from both systems (one and two-stages) revealed structural changes and relationship among the main genus found (Clostridium (62.8%), Bacteroides(11.3 %), Desulfovibrio (19.1 %), Lactobacillus(67.7 %), Lactococcus (22.5%), Longilinea (78%), Methanosaeta (19.2 %) and Syntrophus (18.9 %)) with processes performance, kinetic and hydrodynamic parameters. Moreover, biomass granulation was observed in the novel structured anaerobic reactor operated at single stage due to sugarcane bagasse fly ash addition.

Economic and environmental sustainability for anaerobic biological treatment of wastewater from paper and cardboard manufacturing industry

The sustainable application of an up-flow anaerobic baffled reactor (UABR) to treat real paper and cardboard industrial effluent (PCIE) containing bronopol (2-bromo-2-nitropropan-1, 3-diol) was investigated. At a hydraulic retention time (HRT) of 11.7 h and a bronopol concentration of 7.0 mg L^-1, the removal efficiencies of total chemical oxygen demand (COD_total), COD_soluble, COD_particulate, total suspended solids (TSS), volatile suspended solids (VSS), carbohydrates, and proteins were 55.3 ± 5.2%, 26.8 ± 2.3%, 94.4 ± 4.6%, 89.4 ± 2.6%, 84.5 ± 3.2%, 72.1 ± 1.8%, and 22.4 ± 1.8%, respectively. The conversion of complex organics (e.g., carbohydrates and proteins) into bio-methane (CH₄) was assisted via enzyme activities of, in U (100 mL)^-1, α-amylase (224-270), α-xylanase (171-188), carboxymethyl cellulase (CM-cellulase) (146-187), polygalacturonase (56-126), and protease (67,000-75300). The acidogenic condition was dominant at a short HRT of 2.9 h, where methane yield dropped by 32.5%. Under this condition, the growth of methanogenic bacteria could be inhibited by volatile fatty acids (VFA) accumulation. The analysis of Fourier-transform infrared (FTIR) spectra detected peaks relevant to methylene and nitro groups in the sludge samples, suggesting that entrapment/adsorption by the sludge bed could be a major mechanism for removing bronopol. The economic feasibility of UABR, as proposed to receive 100 m³ d^-1 of PCIE, showed a payback period (profits from environmental benefits, biogas recovery, and carbon credit) of 7.6 yr. The study outcomes showed a high connection to the environmental-, economic-, and social-related sustainable development goals (SDGs).

Valorization of Distillery Stillage for Bioenergy Production: A Review

In alcohol distilleries, the amount of distillery stillage generated can be up to 15 times larger than the amount of alcohol produced. The stillage has high concentrations of organics and nitrogen, a low pH, and a dark brown color. Currently, stillage is mainly used for soil fertilization. For this purpose, it requires thickening and is used seasonally, which creates storage problems and transport costs. To reduce environmental pollution, physicochemical and biological processes have been employed for the treatment of distillery stillage. However, according to bioeconomy principles, the stillage should be transformed into value-added products. Therefore, this review paper focuses on methods of stillage processing that enable energy recovery. Due to its high content of organic compounds, stillage is often used as a raw material for biogas production. Accordingly, anaerobic digestion of stillage is discussed, including an overview of the bioreactors used and the effects of operational parameters on organics removal and biogas production. The necessity of integrating anaerobic stillage treatment with other treatment processes is presented. As complex compounds that are present in the stillage (mainly polyphenols and melanoidin) are difficult to biodegrade and have antibacterial activities, the effect of their recovery on biogas production is described. Next, the possibility of converting distillery stillage to bioethanol and biohydrogen is presented. In addition, bioelectrochemical treatment of distillery stillage using microbial fuel cells is discussed. For all these treatment methods, current challenges and opportunities are given.

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.

Microbiota profile in mesophilic biodigestion of sugarcane vinasse in batch reactors

The vinasse is a residue of ethanol production with the potential for methane production, requiring an allochthonous inoculum. Several microorganisms act in the different phases of anaerobic digestion, and the identification of these microbial communities is essential to optimize the process. The characterization of the microbiota involved in the biodigestion of vinasse was observed in the initial stage (IS), at the peak of methane production (MS) and the end of the process (FS) of the best performance assay by high-throughput sequencing. The highest methane production was 0.78 mmolCH₄.gVS.h^-1 at 243.7 h in the substrate/inoculum ratio of 1.7, with consumption partial of acetic, propionic and isobutyric acids and an 82% reduction of chemical oxygen demand. High microbial diversity was found. The genera Clostridium, Acinetobacter, Candidatus Cloacamonas, Bacteroides, Syntrophomonas, Kosmotoga, the family Porphyromonadaceae and the class Bacteroidia were the most abundant in the maximum methane production. Methane production was driven by Methanobacterium and Methanosaeta, suggesting the metabolic pathways used were hydrogenotrophic and acetoclastic.