Impact of wet aerobic pretreatments on cellulose accessibility and bacterial communities in rape straw

Enhancing Lignocellulose Degradation and Mycotoxin Reduction in Co-Composting with Bacterial Inoculation

The burgeoning global silage industry has precipitated challenges related to the sustainable utilization of mycotoxin-contaminated silage. To understand the effect of bio-enhancement on lignocellulose degradation and mycotoxin reduction, mycotoxin-contaminated silage and rape straw were co-composted without (CK) or with different bacterial agents and their combinations. Compared to CK, the inoculation of Weissella paramesenteroides and Bacillus subtilis could increase the degradation rate of cellulose by 39.24% and lignin by 22.31% after composting. Inoculation of W. paramesenteroides and Paenibacillus sp. significantly enhanced cellulose and lignin degradation rates by 26.75% and 15.48%, respectively. Furthermore, this treatment significantly reduced mycotoxin levels (p < 0.05), including Aflatoxin B1 (AFB1, 64.48% reduction), T-2 toxin (65.02%), Ochratoxin A (OTA, 61.30%), Zearalenone (ZEN, 67.67%), and Vomitoxin (DON, 48.33%). Inoculation with Paenibacillus sp. and other bacteria increased total nitrogen by 48.34-65.52% through enhancing microbiological activity. Therefore, Paenibacillus sp. in combination with other bacteria could increase compost efficiency and reduce mycotoxin presence for better and safer utilization of agricultural waste by-products, enabling faster conversion of contaminated silage into safe soil amendments, which could reduce agricultural waste management costs.

Employing deep eutectic solvent synthesized by cetyltrimethylammonium bromide and ethylene glycol to advance enzymatic hydrolysis efficiency of rape straw

An efficient deep eutectic solvent (DES) was synthesized by cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG) and employed to treat rape straw (RS) for advancing enzymatic saccharification in this work. By optimizing the pretreatment parameters, the results displayed that the novel DES was strongly selective towards removing lignin and xylan while preserving cellulose. Under optimum conditions with 1:6 of CTAB: EG in DES, 180 °C and 80 min, the enzymatic hydrolysis efficiency of RS was enhanced by 46.0% due to the 62.2% of delignification and 53.2% of xylan removal during CTAB: EG pretreatment. In terms of the recalcitrant structure of RS, DES pretreatment caused the increment of cellulosic accessibility, reduction of hydrophobicity and surface area of lignin, and migration of cellulosic crystalline structure, which was associated with its enzymatic hydrolysis efficiency. Overall, this study presented an emerging method for the effective fractionation and valorization of lignocellulosic biomass within biorefinery technology.

Strategies of pretreatment of feedstocks for optimized bioethanol production: distinct and integrated approaches

Bioethanol is recognized as a valuable substitute for renewable energy sources to meet the fuel and energy demand of the nation, considered an environmentally friendly resource obtained from agricultural residues such as sugarcane bagasse, rice straw, husk, wheat straw and corn stover. The energy demand is sustained using lignocellulosic biomass to produce bioethanol. Lignocellulosic biomass (LCBs) is the point of attention in replacing the dependence on fossil fuels. The recalcitrant structure of the lignocellulosic biomass is disrupted using effective pretreatment techniques that separate complex interlinked structures among cellulose, hemicellulose, and lignin. Pretreatment of biomass involves various physical, chemical, biological, and physiochemical protocols which are of importance, dependent upon their individual or combined dissolution effect. Physical pretreatment involves a reduction in the size of the biomass using mechanical, extrusion, irradiation, and sonification methods while chemical pretreatment involves the breaking of various bonds present in the LCB structure. This can be obtained by using an acidic, alkaline, ionic liquid, and organosolvent methods. Biological pretreatment is considered an environment-friendly and safe process involving various bacterial and fungal microorganisms. Distinct pretreatment methods, when combined and utilized in synchronization lead to more effective disruption of LCB, making biomass more accessible for further processing. These could be utilized in terms of their effectiveness for a particular type of cellulosic fiber and are namely steam explosion, liquid hot water, ammonia fibre explosion, CO2 explosion, and wet air oxidation methods. The present review encircles various distinct and integrated pretreatment processes developed till now and their advancement according to the current trend and future aspects to make lignocellulosic biomass available for further hydrolysis and fermentation.

Temporal heterogeneity of bacterial communities and their responses to Raphidiopsis raciborskii blooms

To elucidate the interspecies connectivity between cyanobacteria and other bacteria (noncyanobacteria), microbial diversity and composition were investigated through high-throughput sequencing (HTS) in a drinking water reservoir in Chongqing city, Southwest China, during Raphidiopsis raciborskii blooms. Significant temporal changes were observed in microbial community composition during the sampling period, primarily reflected by variations in relative bacterial abundance. The modularity analysis of the network demonstrated that the bacterial community forms co-occurrence/exclusion patterns in response to variations in environmental factors. Moreover, five modules involved in the dynamic phases of the R. raciborskii bloom were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups. The reservoir was eutrophic (i.e., the average concentrations of total nitrogen (TN) and total phosphorus (TP) were 2.32 and 0.07 mg L^-1, respectively) during the investigation; however, Pearson's correlation coefficient showed that R. raciborskii was not significantly correlated with nitrogen and phosphorus. However, other environmental factors, such as water temperature, pH, and the permanganate index, were positively correlated with R. raciborskii. Importantly, Proteobacteria (α-, γ-Proteobacteria), Acidobacteria, Chloroflexi, and Firmicutes were preferentially associated with increased R. raciborskii blooms. These results suggested that the transition of R. raciborskii bloom-related microbial modules and their keystone species could be crucial in the development and collapse of R. raciborskii blooms and could provide a fundamental basis for understanding the linkage between the structure and function of the microbial community during bloom dynamics.

Study of soil microorganisms modified wheat straw and biochar for reducing cadmium leaching potential and bioavailability

The application of crops straw and biochar in trace metals remediation from the contaminated environment attracted more and more attention during the past decade. Although there has been some review work on the mechanism of trace metals stabilization by crops straw, the effects and mechanisms of interaction among soil indigenous-microbes and crops-straw for trace metal adsorption and stabilization is still unclear. In this study, the dynamic effects along with potential mechanisms of wheat-straw (WS), wheat-straw biochar (WBC) and biologically modified wheat-straw (BMWS) were conducted to investigate the adsorption, leaching behaviour, chemical fractions and bioavailability of cadmium (Cd). The results showed that the biosorption capacity (q_e) was most elevated in the BMWS treatment (14.42 mg g^-1) as compared to WBC (6.28 mg g^-1) and WS (4.20 mg g^-1). The application of BMWS, WBC and WS at the rate of 3% significantly reduced Cd concentration in leachate to 53, 45 and 21% respectively, as compared to control. The addition of BMWS reduced the exchangeable Cd fraction resulted an increase in organic matter and carbonate bound Cd fraction in the soil. The DTPA extractable Cd was significantly decreased by 31.2 and 28.6% with the application of BMWS and WBC at 3% w/w respectively as compared to control. The research results may provide a novel perceptive for the development of functional materials and strategies for eco-friendly and sustainable trace metal remediation in contaminated soil and water by combination of straw and soil-indigenous microorganisms.

Bio-pretreatment promote hydrolysis and acidification of oilseed rape straw: Roles of fermentation broth and micro-oxygen

Oilseed rape straw (ORS) is capable of producing renewable energy. However, cellulose, hemicellulose and lignin are intertwined together in ORS, which makes it difficult for anaerobic digestion (AD). Hence, pretreatment is the key factor in reducing the rate-limiting step of AD. This study reports that the pretreatment combined fermentation broth and micro-oxygen could enhance the degradation of ORS. The maximum biodegradation ratios of cellulose, hemicellulose, and lignin (CHL) were 20.6%, 18.1%, and 24.7%, respectively, at 120 mL/gVS/d oxygen load. The maximum volatile fatty acids and soluble chemical oxygen demand of hydrolysis and acidification of the pretreated groups were significantly higher than that of the control groups. Microorganisms in the fermentation broth at micro-aerobic conditions led to the reduction of CHL content, and altered the structure of ORS. The fermentation broth bio-pretreatment could effectively decrease the functional groups related to lignin.

Biomethane recovery from olive mill residues through anaerobic digestion: A review of the state of the art technology

Residues from production of olive oil are generated yearly in great amounts, both in liquid and solid forms. Different waste treatment systems were proposed in literature, to minimize environmental pollution while raising the energy recovery. Anaerobic digestion is one of the available routes to recover energy from waste via production of biogas while reducing organic load and pollutants to the environment. The use of farming and agro industrial wastes as co-substrate in anaerobic digestion can induce benefits related to the simultaneous treatment of different wastes. In particular, co-digestion can significantly enhance the process stability as well as the bio-methane generation. This work aims at reviewing the latest achievements in anaerobic digestion of olive mill residues, focusing on the aspects that can mostly favor the process, principally from a technical but also from an economical point of view. For the mono-digestion processes, methane yields up to 419 L_CH4 kg_VS^-1 were reported for olive mill wastewaters (Calabrò et al. 2018), while a production of 740 L_CH4 kg_VS^-1 was achieved when digesting olive mill solid waste together with olive mill wastewater and milk whey (Battista et al. 2015). An increase up to 143% in the methane yield was also reported when the feedstock was subjected to a 5 days aeration before digesting it in a semi-continuous stirred tank reactor (González-González and Cuadros 2015).

Enzymatic decolorization of melanoidins from molasses wastewater by immobilized keratinase

The aim of this work was to study the ability of commercial immobilized hydrolases in the decolorization of molasses wastewater. Commercial immobilized keratinase obtained the highest decolorization yield (86.6-91.1%) among all of commercial immobilized enzymes tested. Immobilized keratinase had the potential to replace immobilized oxidoreductase to decolorize molasses wastewater. Keratinase from Meiothermus taiwanensis WR-220 (KMT) immobilized on modified bagasse cellulose obtained a decolorization yield of 84.7-90.2%. It removed 60.2-65.6% of colorants and 61.4-69.8% of chemical oxygen demand (COD) for 5 days continuously. Notably, the treatment cost was less than 0.15 dollar per ton. Immobilized KMT-wt had similar performance with commercial immobilized keratinase in bleaching molasses wastewater. Importantly, it was more economic. Finally, the results confirmed that additional reaction catalyzing the unsaturated bonds to destroy the conjugated system by keratinase, weakening the chromogenic group of melanoidins. Accordingly, this work is meaningful to the industrial decolorization of molasses wastewater.

Potentials of using mixed culture bacteria incorporated with sodium bicarbonate for hydrogen production from water hyacinth

The aim of this study is to assess the potentials of using mixed culture bacteria incorporated with different concentrations of NaHCO₃ for hydrogen production from water hyacinth (WH). The lowest hydrogen yield (HY) of 30.4 ± 1.9 mL/g_TVS, H₂ content (HC) of 19.5 ± 1.5% and hydrogenase enzyme (HE) activity of 0.06 ± 0.01 mgM.B_reduced/min were registered for the cultures without supplementation of NaHCO₃. The HY, HC, and HE activity were maximized at levels of 69.2 ± 4.3 mL/g_TVS, 58.4 ± 3.6% and 0.18 ± 0.01 mgM.B_reduced/min. respectively for the anaerobes supplied with 3.0 g NaHCO₃/L. Furthermore, cellulose, hemicellulose, and lignin destruction efficiencies were 37.2 ± 2.3, 30.0 ± 1.9 and 20.9 ± 1.3% respectively due to the increase of cellulase and xylanase activities up to 2.73 ± 0.17 and 1.87 ± 0.12 U/mL, respectively. Moreover, the abundance of Firmicutes was substantially increased and accounted for 71% of the total OTU's. Microbes belonging to the order Clostridiales and OPB54 were particularly enriched in the medium supplemented with NaHCO₃.

Effect of particle size reduction and ensiling fermentation on biogas formation and silage quality of wheat straw

The effect of ensiling fermentation and mechanical pretreatment on the methane yield of lignocellulosic biomass was investigated in order to determine the optimum pretreatment conditions for biogas production. Wheat straw was treated using the following techniques: mechanical disintegration by chopping and extruder-grinding to particle sizes of 2.0 and 0.2cm, respectively, and ensiling by 30% and 45% total solids with addition of enzymatic, chemical and biological silage additives individually and in combination. The total and volatile solid content, biochemical methane potential and products of silage fermentation of 32 variants were tested. The results indicate that the methane potential increased by 26% (from 179 to 244mLCH₄g^-1VS) by reducing particle size. The maximum methane potential of 275mLCH₄g^-1VS was obtained from silage with 30% total solids and extruder grinding. However, the effect of the addition of silage additives on the methane potential was limited.