Electrochemical pretreatment of yard waste to improve biogas production: Understanding the mechanism of delignification, and energy balance

Enhancement of hydrogen production in dark fermentation of corn stover hydrolysates through composite electric field pretreatment: Improving enzymatic efficiency and regulating microbial metabolic balance

This study investigates the effects of composite electric field pretreatment (CEP) on hydrogen production from corn stover enzymatic hydrolysates in dark fermentation. The findings reveal that under optimal conditions, the CEP group achieved a cumulative hydrogen yield of 77.3  ±  2.6 mL/g TS, marking a 55.3 % increase compared to the control group without the electric field. CEP significantly enhances the fermentation capacity of enzymatic hydrolysates during the acid-stage of dark fermentation by disrupting the lignin structure and optimizing cellulase hydrolysis efficiency. Additionally, pH self-regulation is facilitated through the interaction between volatile fatty acids (VFAs) and ammonia nitrogen. Microbial community analysis revealed that CEP shifts the metabolic balance between Clostridium_sensu_stricto_1 and Lactococcus, leading to increased hydrogen yield and concentration during acid fermentation. Notably, Terrisporobacter exhibited a superior acid-producing capability compared to Bacteroides during the dark fermentation of enzymatic hydrolysates. This study provides a new perspective for the practical application of corn stover.

Development of lignocellulosic biorefineries for the sustainable production of biofuels: Towards circular bioeconomy

The idea of environment friendly and affordable renewable energy resources has prompted the industry to focus on the set up of biorefineries for sustainable bioeconomy. Lignocellulosic biomass (LCB) is considered as an abundantly available renewable feedstock for the production of biofuels which can potentially reduce the dependence on petrochemical refineries. By utilizing various conversion technologies, an integrated biorefinery platform of LCB can be created, embracing the idea of the 'circular bioeconomy'. The development of effective pretreatment methods and biocatalytic systems by various bioengineering and machine learning approaches could reduce the bioprocessing costs, thereby making biomass-based biorefinery more sustainable. This review summarizes the development and advances in the lignocellulosic biorefineries from the LCB to the final product stage using various different state-of-the-art approaches for the progress of circular bioeconomy. The life cycle assessment which generates knowledge on the environmental impacts related to biofuel production chains is also summarized.

Br-/BrO--mediated highly efficient photoelectrochemical epoxidation of alkenes on α-Fe2O3

Epoxides are significant intermediates for the manufacture of pharmaceuticals and epoxy resins. In this study, we develop a Br^-/BrO^- mediated photoelectrochemical epoxidation system on α-Fe₂O₃. High selectivity (up to >99%) and faradaic efficiency (up to 82 ± 4%) for the epoxidation of a wide range of alkenes are achieved, with water as oxygen source, which are far beyond the most reported electrochemical and photoelectrochemical epoxidation performances. Further, we can verify that the epoxidation reaction is mediated by Br^-/BrO^- route, in which Br^- is oxidized non-radically to BrO^- by an oxygen atom transfer pathway on α-Fe₂O₃, and the formed BrO^- in turn transfers its oxygen atom to the alkenes. The non-radical mediated characteristic and the favorable thermodynamics of the oxygen atom transfer process make the epoxidation reactions very efficient. We believe that this photoelectrochemical Br^-/BrO^--mediated epoxidation provides a promising strategy for value-added production of epoxides and hydrogen.

Evaluation of electro-oxidation and Fenton pretreatments on industrial fruit waste and municipal sewage sludge to enhance biogas production by anaerobic co-digestion

This study presents the effect of electro-oxidation and Fenton pre-treatment on anaerobic co-digestion (AnCoD) of fruit-juice industrial waste (FJW) and municipal sewage sludge (MSS). Biogas production increased from 767 mL to 857 mL and 918 mL after EO and Fenton pretreatment, respectively. The methane amount increased by 28% and 39% for EO and Fenton processes. The removal efficiencies of soluble COD, carbohydrate, and protein for the conditions with the highest biogas production as a result of the pretreatment process were 48%, 65%, 61% for the Fenton pre-treatment, and 37%, 52%, and 39% for the EO pre-treatment, respectively. Cumulative biogas production efficiency for all pre-treated mixtures was estimated with kinetic models. In addition, an evaluation has been made regarding cost, economic gain, and energy consumption of the pre-treatment processes.

Thermo-chemo-sonic pretreatment of lignocellulosic waste: Evaluating anaerobic biodegradability and environmental impacts

In the present study, yard waste was pretreated by thermo-chemo-sonic pretreatment prior to anaerobic digestion to improve its anaerobic biodegradability. First, the pretreatment conditions were optimized using Box-Behnken design based response surface methodology for the maximum organic matter solubilisation. Then, the possible mechanism of delignification by thermo-chemo-sonic pretreatment was discussed. Moreover, the anaerobic digestion performance of untreated yard waste (UYW) and pretreated yard waste (PYW) was compared. The optimum pretreatment condition based on the increase in soluble COD and volatile solids (VS) was: 2997 kJ/kgTS ultrasonic energy, 74 °C, and 10.1 pH. The highest methane yield of 374 ± 28 mL/gVS_added for the PYW at the optimum condition was achieved, which was 37.5 % higher than the UYW (272 ± 16 mL/gVS_added). Finally, the environmental impacts associated with anaerobic digestion of both UYW and PYW were compared. The life cycle assessment confirmed a positive environmental impact of pretreatment.

Hydrothermal carbonization of garden waste by pretreatment with anaerobic digestion to improve hydrohcar performance and energy recovery

Sustainable and resourceful utilization of garden waste with high lignocellulosic content remains a huge challenge, anaerobic digestion (AD) and hydrothermal treatment provide prospective technologies with achieving environmental and economic benefits. In this study, a 7-28 d AD was provided as a biomass pretreatment means and combined with hydrothermal carbonization (HTC) to treat three typical garden wastes (leaves, branches, grass). The results showed that AD pretreatment could effectively change the surface composition and structure properties of the feedstocks and thus modulating the properties of the hydrochar downstream. Compared to the unpretreatment samples, the specific surface area (SSA), higher heating value (HHV), energy density and nutrient elements (P and K) of hydrochar obtained by AD pretreatment were significantly improved and enriched, respectively. Specifically, the highest HHV of hydrochar obtained from leaves, branches, and grass were 25.71, 25.63, and 23.81 MJ/kg, which obtained with 21, 14, and 7 d of AD pretreatment respectively. The P contents of hydrochar of leaves and grass pretreated with AD for 14 and 7 d were 205% and 15% higher than those without AD pretreatment, respectively. Additionally, in this coupled system, the biomass energy recovery of 90.2% (78.2% biochar and 12.0% CH₄) was achieved on leaves pretreated with AD for 21 d. Energy recovery of 81.2% (66.8% biochar, 14.4% CH₄) and 71.3% (39.7% biochar, 31.6% CH₄) was obtained by 14 d of AD pretreatment on branches and grass, respectively. Thus, this study enhances energy utilization efficiency and reduces secondary waste generation, providing valuable new insights into AD coupled with HTC technology.

Alkaline electro-hydrolysis pretreatment of rice straw for enhanced biogas production under ambient temperature

Biogas production can supplement the renewable energy target of the world. For this abundantly available agricultural waste like wheat and rice straw can be used. Biogas generation using this waste will curb the stubble burning incidences, reduce greenhouse gases, enhance farmer’s income, and strengthen the energy security of many countries. The recalcitrant nature of rice straw is a barrier to its hydrolysis, which is a prerequisite of the anaerobic digestion (AD) process. Alkaline, electro-hydrolysis, and a combination of both pretreatment (alkaline electrohydrolysis) methods are undertaken in the present study. Batch reactors at ambient temperature were used for AD of rice straw at different inoculums to substrate ratios (ISR) of 0.5, 0.75, and 1.0 to observe the effect on biogas/methane yield. Among these, a higher amount of biogas was obtained for ISR of 0.5 in all sets of experiments. The combined pretreatment method yielded biogas of 315.9 mL/gVS (equivalent to methane of 167.4 mL/gVS). For pretreat-ed rice straw by electro-hydrolysis, alkaline, and combined (alkaline and electro-hydrolysis) respectively, the methane yields were 7.03, 18.13, and 49.82% higher than untreated rice straw. The biogas had approximately 53% of methane content. The use of rice straw for biogas production may prove a viable alternative for clean and sustainable energy. In the studies, a first-order kinetic model is found to fit better the experimental results.

Sequential and consolidated bioprocessing of biogenic municipal solid waste: A strategic pairing of thermophilic anaerobe and mesophilic microaerobe for ethanol production

Feedstock availability and its pretreatment, high process economics and insufficient ethanol (H_Et) titres necessitated the bioprocesses that are sustainable. The advanced consolidated bioprocessing (CBP_Seq) strategy presently considered for improved H_Et production involves, sequential coupling of CBP thermophile, Clostridium thermocellum ATCC-27405 with mesophilic microaerobe, Pichia stipitis NCIM-3498. Biogenic municipal solid waste (BMSW) pretreated with 0.5% NaOH (CS_PBMSW) served as the sole carbon source. CBP_Seq (23.99 g/L) fared better than CBP standalone (18.10 g/L) wherein 1.32-folds improvement in H_Et titre was recorded. Considering insufficient xylanase titre in cellulosome complex of C. thermocellum, CBP_Seq was performed employing exogenous xylanases (CBP_SeqE) to improve xylan digestibility and H_Et yield. CBP_SeqE-II biosystem at pH 5 showed maximum H_Et titre of 36.90 g/L which corresponds to yield of 0.26 g H_Et/ g CS_PBMSW. This study substantiates efficacy of CBP_SeqE-II biosystem in sustainable bioethanol production from BMSW in a single reactor without laborious steps.

Anaerobic digestion of hazelnut (Corylus colurna) husks after alkaline pretreatment and determination of new important points in Logistic model curves

In this study, anaerobic digestion (AD) of hazelnut (Corylus colurna) husks (HH) was investigated by NaOH pretreatment at 1-6% w/w concentrations. The highest methane yield was 278.45 ± 7.85 mL/g volatile solid (VS), and this was obtained in a 4% NaOH pretreated reactor. In this reactor, the methane yield increased by 162.2% compared to that in the control. The concentrations of volatile fatty acids (VFAs) varied during the digestion process according to the different NaOH pretreatment results. The highest lignosellulosic solubilizations were obtained in a 6% NaOH pretreated reactor. Furthermore, in the second part of kinetic studies, it was defined critical points for cumulative methane yield (CMY) in the Logistic model (LM). These points were the absolute acceleration point (PAA), maximum acceleration point (PAM), inflection point (PI), maximum deceleration point (PDM), and asymptotic deceleration point (PDA). Using these points on the CMY curves, the AD process of HH was mathematically interpreted and explained.