Understanding of the contribution of the fungal treatment conditions in a wheat straw biorefinery that produces enzymes and biogas

Decisional tool development and application for techno-economic analysis of fungal laccase production

Textile and medical effluents causing bioaccumulation and biomagnification have been successfully biodegraded by fungal laccases. Here, a decision-making tool was developed and applied to evaluate 45 different laccase production strategies which determined the best potential source from a techno-economical perspective. Laccase production cost was calculated with a fixed output of 109 enzymatic units per batch (USD$per109U) and a sensitivity analysis was performed. Results indicate that optimization of enzymatic kinetics for each organism is essential to avoid exceeding the fermentation time point at which production titer reaches its peak and, therefore, higher production costs. Overall, the most cost-effective laccase-producing strategy was obtained when using Pseudolagarobasidium acaciicola with base production cost of USD $42.46 per 109 U. This works serves as platform for decision-making to find the optimal laccase production strategy based on techno-economic parameters.

Laccase production by Pleurotus ostreatus using cassava waste and its application in remediation of phenolic and polycyclic aromatic hydrocarbon-contaminated lignocellulosic biorefinery wastewater

The treatment of contaminants from lignocellulosic biorefinery effluent has recently been identified as a unique challenge. This study focuses on removing phenolic contaminants and polycyclic aromatic hydrocarbons (PAHs) from lignocellulosic biorefinery wastewater (BRW) applying a laccase-assisted approach. Cassava waste was used as a substrate to produce the maximum yield of laccase enzyme (3.9 U/g) from Pleurotus ostreatus. Among the different inducers supplemented, CuSO₄ (0.5 mM) showed an eight-fold increase in enzyme production (30.8 U/g) after 240 h of incubation. The catalytic efficiency of laccase was observed as 128.7 ± 8.47 S^-1mM^-1 for syringaldazine oxidation at optimum pH 4.0 and 40 °C. Laccase activity was completely inhibited by lead (II) ion, mercury (II) ion, sodium dodecyl sulphate, sodium azide and 1,4 dithiothretiol and induced significantly by manganese (II) ion and rhamnolipid. After treating BRW with laccase, the concentrations of PAHs and phenolic contaminants of 1144 μg/L and 46160 μg/L were reduced to 96 μg/L and 16100 μg/L, respectively. The ability of laccase to effectively degrade PAHs in the presence of different phenolic compounds implies that phenolic contaminants may play a role in PAHs degradation. After 240 h, organic contaminants were removed from BRW in the following order: phenol >2,4-dinitrophenol > 2-methyl-4,6-dinitrophenol > 2,3,4,6-tetrachlorophenol > acenaphthene > fluorine > phenanthrene > fluoranthene > pyrene > anthracene > chrysene > naphthalene > benzo(a)anthracene > benzo(a)pyrene > benzo(b)fluoranthene > pentachlorophenol > indeno(1,2,3-cd)pyrene > benzo(j) fluoranthene > benzo[k]fluoranthène. The multiple contaminant remediation from the BRW by enzymatic method, clearly suggests that the laccase can be used as a bioremediation tool for the treatment of wastewater from various industries.

Review on the preparation of fuels and chemicals based on lignin

Lignin is by far the most abundant natural renewable aromatic polymer in nature, and its reserves are second only to cellulose. In addition to the rich carbon content, the structure of lignin contains functional groups such as benzene rings, methoxyl groups, and phenolic hydroxyl groups. Lignin degradation has become one of the high value, high quality and high efficiency methods to convert lignin, which is of great significance to alleviating the current energy shortage and environmental crisis. This article introduces the hydrolysis methods of lignin in acidic, alkaline, ionic liquids and supercritical fluids, reviews the heating rate, the source of lignin species and the effects of heating rate on the pyrolysis of lignin, and briefly describes the metal catalysis, oxidation methods such as electrochemical degradation and photocatalytic oxidation, and degradation reduction methods using hydrogen and hydrogen supply reagents. The lignin degradation methods for the preparation of fuels and chemicals are systematically summarized. The advantages and disadvantages of different methods, the selectivity under different conditions and the degradation efficiency of different catalytic combination systems are compared. In this paper, a new approach to improve the degradation efficiency is envisioned in order to contribute to the efficient utilization and high value conversion of lignin.

Laccases—Versatile Enzymes Used to Reduce Environmental Pollution

The accumulation of waste and toxic compounds has become increasingly harmful to the environment and human health. In this context, the use of laccases has become a focus of interest, due to the properties of these versatile enzymes: low substrate specificity, and water formation as a non-toxic end product. Thus, we begin our study with a general overview of the importance of laccase for the environment and industry, starting with the sources of laccases (plant, bacterial and fungal laccases), the structure and mechanism of laccases, microbial biosynthesis, and the immobilization of laccases. Then, we continue with an overview of agro-waste treatment by laccases wherein we observe the importance of laccases for the biodisponibilization of substrates and the biodegradation of agro-industrial byproducts; we then show some aspects regarding the degradation of xenobiotic compounds, dyes, and pharmaceutical products. The objective of this research is to emphasize and fully investigate the effects of laccase action on the decomposition of lignocellulosic materials and on the removal of harmful compounds from soil and water, in order to provide a sustainable solution to reducing environmental pollution.

Fungal pretreatment parameters for improving methane generation from anaerobic digestion of corn silage

Corn silage was treated by white rot fungi (WRF) to investigate the effect of pretreatment on material's ability to produce methane in anaerobic digestion (AD). The selective fungi Pleurotus ostreatus and Dichomitus squalens promoted biogas generation, whereas the non-selective Trametes versicolor and Irpex lacteus had negative effect. Cumulative methane production after 10-day pretreatment with P. ostreatus at 28 °C rose 1.55-fold. The longer pretreatments of 30 and 60-days had smaller effect. When the pretreatment with P. ostreatus was carried out at 40 °C a high H₂S release affected the AD process. Effect of WRF action dependent on the type of corn silage. With typical corn silage, the lignin depolymerisation raised the methane generation from 0.301 to 0.465 m³kg_VS^-1. In contrast, extensive decomposition of hemicellulose in hybrid corn silage deteriorated the effect of pretreatment on methane production.

Fungal lignocellulolytic enzymes and lignocellulose: A critical review on their contribution to multiproduct biorefinery and global biofuel research

The continuous increase in the global energy demand has diminished fossil fuel reserves and elevated the risk of environmental deterioration and human health. Biorefinery processes involved in producing bio-based energy-enriched chemicals have paved way to meet the energy demands. Compared to the thermochemical processes, fungal system biorefinery processes seems to be a promising approach for lignocellulose conversion. It also offers an eco-friendly and energy-efficient route for biofuel generation. Essentially, ligninolytic white-rot fungi and their enzyme arsenals degrade the plant biomass into structural constituents with minimal by-products generation. Hemi- or cellulolytic enzymes from certain soft and brown-rot fungi are always favoured to hydrolyze complex polysaccharides into fermentable sugars and other value-added products. However, the cost of saccharifying enzymes remains the major limitation, which hinders their application in lignocellulosic biorefinery. In the past, research has been focused on the role of lignocellulolytic fungi in biofuel production; however, a cumulative study comprising the contribution of the lignocellulolytic enzymes in biorefinery technologies is still lagging. Therefore, the overarching goal of this review article is to discuss the major contribution of lignocellulolytic fungi and their enzyme arsenal in global biofuel research and multiproduct biorefinery.

Bio-Delignification of Green Waste (GW) in Co-Digestion with the Organic Fraction of Municipal Solid Waste (OFMSW) to Enhance Biogas Production

The organic fraction of municipal solid waste (OFMSW) is recognized as a suitable substrate for the anaerobic digestion (AD) process and is currently considered a mature technology. A promising strategy to enhance biogas yield and productivity is the co-digestion of OFMSW with other organic biomass, such as green waste (GW), a mixture of leaves, grass, and woody materials originated from private yards and public greenspace management. The main limitation to the use of GW for biogas production is the high percentage of the lignocellulosic fraction, which makes necessary a pretreatment of delignification to dissolve the recalcitrant structure. In this study, a new strategy of sustainable bio-delignification using the white-rot fungi Bjerkandera adusta (BA) in comparison with other chemical pretreatments were investigated. Untreated and treated GW were, respectively, submitted to anaerobic co-digestion with OFMSW. AD processes were carried out in a lab-scale plant for 30 days in thermophilic conditions (55 °C). Biogas cumulative production was increased by about 100% in the case of treated GW compared with that of just OFMSW, from 145 to 289 Nm3 CH4/ton SV, and productivity almost doubled from 145 to 283 Nm3/ton FM * day. The measured average methane content values in the cumulative biogas were 55% from OFMSW and 54% from GW. Moreover, over 95% of the biogas was produced in 20 days, showing the potential opportunity to reduce the AD time.

An overview of fungal pretreatment processes for anaerobic digestion: Applications, bottlenecks and future needs

Lignin modifying or extracellular enzymes secreted by the white rot fungi have the ability of degrading wide range of lignocellulosic substrates and organic pollutants. Lignocellulosic biomass, despite being a renewable source of energy, is difficult to hydrolyse (hydrolysis being rate-limiting stage in anaerobic digestion process). Various pre-treatment techniques like physical, chemical, thermo-chemical and biological to enhance the accessibility of microbes to carbohydrates have been studied. Recently, usage of white- rot fungi in a biological pre-treatment technique have received renewed interest due to its low cost and eco-friendly nature. This review deals with: a) lignocellulosic biomass recalcitrance, b) various pre-treatment techniques and its economic feasibility, c) delignification and hydrolysis mechanism using white-rot fungi, d) factors controlling white-rot fungi pre- treatment process, and e) improvement in methane production through solid-state anaerobic digestion of white-rot fungi pre-treated lignocellulosic biomass. Finally a future perspective is also included.

Two-stage banana leaves wastes utilization towards mushroom growth and biogas production

Banana leaves wastes (BL) were subjected to fungal treatment using Pleurotus ostreatus to produce edible mushrooms and biogas in the anaerobic digestion process. Effects of fungal treatment on mushrooms production, lignin degradation, trace elements compositions and biogas yield during the anaerobic digestion process were evaluated. Treatment with P.ostreatus for 36 d resulted in the production of 181 ± 19 g of edible mushrooms per 2 kg of BL with biological efficiency of 37 ± 4%. Lignin concentration in fungal treated BL decreased by 10% indicating an improvement on its digestibility. Important trace elements (Fe, Mn, Mo, Co and Ni) necessary for the improvement of the anaerobic digestion process were also significantly reduced (P < 0.05) during the fungal treatment process. The biogas yield for the fungal treated BL was 282 mL g^-1 VS^-1 of which this study suggests that could be improved through trace element supplementation during the anaerobic digestion process.

Laccases in Food Industry: Bioprocessing, Potential Industrial and Biotechnological Applications

Laccase is a multi-copper oxidase that catalyzes the oxidation of one electron of a wide range of phenolic compounds. The enzyme is considered eco-friendly because it requires molecular oxygen as co-substrate for the catalysis and it yields water as the sole by-product. Laccase is commonly produced by fungi but also by some bacteria, insects and plants. Due it is capable of using a wide variety of phenolic and non-phenolic substrates, laccase has potential applications in the food, pharmaceutical and environmental industries; in addition, it has been used since many years in the bleaching of paper pulp. Fungal laccases are mainly extracellular enzyme that can be recovered from the residual compost of industrial production of edible mushrooms as Agaricus bisporus and Pleurotus ostreatus. It has also been isolated from microorganisms present in wastewater. The great potential of laccase lies in its ability to oxidize lignin, one component of lignocellulosic materials, this feature can be widely exploited on the pretreatment for agro-food wastes valorization. Laccase is one of the enzymes that fits very well in the circular economy concept, this concept has more benefits over linear economy; based on "reduce-reuse-recycle" theory. Currently, biorefinery processes are booming due to the need to generate clean biofuels that do not come from oil. In that sense, laccase is capable of degrading lignocellulosic materials that serve as raw material in these processes, so the enzyme's potential is evident. This review will critically describe the production sources of laccase as by-product from food industry, bioprocessing of food industry by-products using laccase, and its application in food industry.

The Future Agricultural Biogas Plant in Germany: A Vision

After nearly two decades of subsidized and energy crop-oriented development, agricultural biogas production in Germany is standing at a crossroads. Fundamental challenges need to be met. In this article we sketch a vision of a future agricultural biogas plant that is an integral part of the circular bioeconomy and works mainly on the base of residues. It is flexible with regard to feedstocks, digester operation, microbial communities and biogas output. It is modular in design and its operation is knowledge-based, information-driven and largely automated. It will be competitive with fossil energies and other renewable energies, profitable for farmers and plant operators and favorable for the national economy. In this paper we discuss the required contribution of research to achieve these aims.