Fungal biodegradation and multi-level toxicity assessment of vinasse from distillation of winemaking by-products

Isolation of functional ligninolytic Bacillus aryabhattai from paper mill sludge and its lignin degradation potential

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Isolation of a functional lignin-degrading Bacillus aryabhattai.

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Production of growth-associated LiP and MnP enzymes.

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Almost 84% KL degradation at 500 mg L⁻¹ KL concentration.

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KL biodegradation process was revealed by chemical analysis.

Kraft lignin (KL), is the major pollutant in pulp and paper effluent and due to its heterogeneous structure, it is resistant to the depolymerization process. It has drawn much attention from the researcher due to its challenging degradation process. In this study, a KL-degrading bacterium was isolated and screened from paper mill sludge. This bacterium was identified as ligninolytic Bacillus aryabhattai using biochemical and 16SrRNA gene analysis. B. aryabhattai showed maximum activities of lignin peroxidase-LiP (0.74 IU mL⁻¹) and manganese peroxidase-MnP (9.2 IU mL⁻¹) on the 4th day, and 5th day, respectively. A total 84% of KL (500 mg L⁻¹) reduction was observed after 14 days. The KL bio-degradation was confirmed based on changes in chemical stracture of KL and new metabolites identification using FTIR and GC–MS, respectively. The study concluded that B. aryabhattai maybe becomes a potential biological agent in KL biodegradation and treatment of other lignin-containing industrial effluents.

Vinasse odyssey: sugarcane vinasse remediation and laccase production by Trametes sp. immobilized in polyurethane foam

Vinasse is a high pollutant liquid residue from bioethanol production. Due to its toxicity, most vinasse is used not disposed of in water bodies but employed for the fertigation of sugarcane crops, potentially leading to soil salinization or heavy metal deposition. The anaerobic digestion of vinasse for energy production is the main alternative to fertigation, but the process cannot eliminate colored compounds such as melanoidins, caramels, or phenolic compounds. The treatment of raw vinasse with white-rot fungi could remove colored and persistent toxic compounds, but is generally considered cost-ineffective. We report the treatment of vinasse by an autochthonous Trametes sp. strain immobilized in polyurethane foam and the concomitant production of high titers of laccase, a high value-added product that could improve the viability of the process. The reuse of the immobilized biomass and the discoloration of raw vinasse, the concentration of phenolic compounds, BOD and COD, and the phytotoxicity of the treated vinasse were measured to assess the viability of the process and the potential use of treated vinasse in fertigation or as a complementary treatment to anaerobic digestion. Under optimal conditions (vinasse 0.25X, 30 °C, 21 days incubation, 2% glucose added in the implantation stage), immobilized Trametes sp. causes a decrease of 75% in vinasse color and total phenolic compounds, reaching 1082 U L^-1 of laccase. The fungi could be used to treat 0.50X vinasse (BOD 44,400 mg O₂ L^-1), causing a 26% decolorization and a 30% removal of phenolic compounds after 21 days of treatment with maximum laccase titers of 112 U L^-1, while reducing COD and BOD from 103,290 to 42,500 mg O₂ L^-1 (59%) and from 44,440 to 21,230 mg O₂ L^-1 (52%), respectively. The re-utilization of immobilized biomass to treat 0.50X vinasse proved to be successful, leading to the production of 361 U L^-1 of laccase with 77% decolorization, 61% degradation of phenolic compounds, and the reduction of COD and BOD by 75% and 80%, respectively. Trametes sp. also reduced vinasse phytotoxicity to Lactuca sativa seedlings. The obtained results show that the aerobic treatment of vinasse by immobilized Trametes sp. is an interesting technology that could be employed as a sole treatment for the bioremediation of vinasse, with the concomitant the production of laccase. Alternatively, the methodology could be used in combination with anaerobic digestion to achieve greater decolorization and reduction of phenolic compounds, melanoidins, and organic load.

Current trends for distillery wastewater management and its emerging applications for sustainable environment

Ethanol distillation generates a huge volume of unwanted chemical liquid known as distillery wastewater. Distillery wastewater is acidic, dark brown having high biological oxygen demand, chemical oxygen demand, contains various salt contents, and heavy metals. Inadequate and indiscriminate disposal of distillery wastewater deteriorates the quality of the soil, water, and ultimately groundwater. Its direct exposure via food web shows toxic, carcinogenic, and mutagenic effects on aquatic-terrestrial organisms including humans. So, there is an urgent need for its proper management. For this purpose, a group of researchers applied distillery wastewater for fertigation while others focused on its physico-chemical, biological treatment approaches. But until now no cutting-edge technology has been proposed for its effective management. So, it becomes imperative to comprehend its toxicity, treatment methods, and implication for environmental sustainability. This paper reviews the last decade's research data on advanced physico-chemical, biological, and combined (physico-chemical and biological) methods to treat distillery wastewater and its reuse aspects. Finally, it revealed that the combined methods along with the production of value-added products are one of the best options for distillery wastewater management.

A novel thermostable cellulase-producing Bacillus licheniformis A5 acts synergistically with Bacillus subtilis B2 to improve degradation of Chinese distillers' grains

Lack of effective degradation approaches of Chinese distillers' grains (CDGs) produced by Chinese liquor industry results in environmental pollution and economic waste. Cellulase activity was characterized at different temperatures to find thermostable cellulase-producing bacteria, and microbial co-culture method was used to improve the degradation of CDGs. Incubation of endoglucanase produced by Bacillus licheniformis A5 at 80 °C for 120 min showed 82% residual enzyme activity. Notably, enzyme activity increased by 30%-70% after co-culturing Bacillus licheniformis A5 and Bacillus subtilis B2. The two strains increased degradation rate of CDGs by 70% compared with optimized results of Bacillus subtilis B2 culture alone, and increased the reducing sugar content to 16.6 mg/mL. In addition, 2% ethanol increased degradation rate of CDGs by 15% in co-culture. The findings of this study imply that Bacillus licheniformis A5 acts synergistically with Bacillus subtilis B2 to improve degradation of CDGs.

Removal pattern of vinasse phenolics by Phlebia rufa, characterization of an induced laccase and inhibition kinetics modeling

Vinasse from the distillation of winemaking residues is a wastewater characterized by high levels of aromatic compounds. Batch cultures of Phlebia rufa showed a significant (p < 0.05) correlation between laccase activity and initial vinasse concentration. The pattern of biodegradation of hydroxybenzoic acids, hydroxycinnamic acids and flavonoids, assessed by HPLC-DAD, revealed that p-hydroxybenzoic acid is the most recalcitrant compound. Vinasse-induced laccase showed electrophoretic homogeneity and molecular weight of 62 kDa after being purified 21-fold. Optimum pH for oxidation of 2,6-dimethoxyphenol (2,6-DMP) was 3.5 and optimum temperature was 50 °C, with an activation energy of 42.8 kJ mol^-1. Catalytic efficiency of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) oxidation is about two orders of magnitude higher than 2,6-DMP oxidation, being their K_m values 36.2 ± 2.6 μM and 303.0 ± 44.7 μM, respectively and k_cat values 486.1 s^-1 and 179.6 s^-1, respectively. Akaike information criterion and Akaike weights were used to discriminate inhibition models that best fitted 2,6-DMP oxidation in the presence of inhibitors. Inhibition constants of mixed-type inhibitors azide and fluoride, and competitive-type inhibitor chloride, showed the following inhibitors potency: azide > fluoride > chloride. Taken together, this study is consistent with the assumption that P. rufa could be a useful tool for aerobic degradation of phenolic-rich wastewaters.

Pretreatment of Grape Stalks by Fungi: Effect on Bioactive Compounds, Fiber Composition, Saccharification Kinetics and Monosaccharides Ratio

Grape stalks, an inedible lignocellulosic residue from winemaking and agro-industrial grape juice production, can be valorized as a source of bioactive compounds and as feedstock for the saccharification and bioconversion of soluble sugars. Solid-state fermentation (SSF) by six white-rot fungi was applied as pretreatment. Fiber composition, free radical scavenging activity, four ligninolytic, and three hydrolytic enzyme activities were determined. Saccharification kinetics, yield, and productivity were evaluated and complemented with scanning electron microscopy (SEM), high performance liquid chromatography (HPLC) quantification of monosaccharides, and principal component analysis (PCA). After SSF, the biomass exhibited a drastic free radical scavenging activity decrease and the main enzymes produced were manganese-dependent peroxidase and xylanase. Scanning electron microscopy revealed the erosion of cell walls, and PCA exhibited a negative correlation between saccharification, and neutral detergent fiber and acid detergent lignin. Phlebia rufa pretreated biomass gave the highest sugars yield and productivity, representing a nearly three-fold increase compared to untreated samples. Also, monosaccharides quantification revealed that the 1:1 ratio of glucose to the sum of xylose plus galactose changes to the value of 2:1 after pretreatment. In this work, and for the first time, P. rufa proved to be an effective pretreatment of grape stalks for the saccharification and further bioconversion into value-added chemicals. In addition, lignocellulolytic enzymes were also produced through SSF.