Global municipal solid waste (MSW) generation will increase to 2.2 billion tons per year by 2025 as per the World Bank projection. Improper waste management often leads to environmental degradation (i.e. water, air and soil pollution), transmission of diseases, and the release of greenhouse gases emissions, which contributes to climate change. To combat these problems, several countries are following the waste to energy (WtE) approach, which significantly reduces the volume of waste and generates renewable energy. Thus, the present study focuses on the municipal solid waste generation, composition, and waste to energy conversion technologies. Thermal conversion processes including incineration, pyrolysis, and gasification for heat, bio-oil, and syngas generation are already well established and are being employed in several countries. Currently, researchers are trying to improve the efficiency of biochemical methods such as anaerobic digestion, microbial fermentation, and microbial fuel cells for biogas, biohydrogen, and bioelectricity generation from MSW. This review explains the recent focus on microbial fermentation and microbial fuel cells for biofuels and bioelectricity production. Development of these technologies can lead to suitable eco-friendly approaches for the future. WtE technologies are important components of circular economy that will assist to achieve the demand of clean energy in future.

Aspergillus nidulans is a filamentous fungus that is a potential resource for industrial enzymes. It is a versatile fungal cell factory that can synthesize various industrial enzymes such as cellulases, β-glucosidases, hemicellulases, laccases, lipases, proteases, β-galactosidases, tannases, keratinase, cutinases, and aryl alcohol oxidase. A. nidulans has shown the potential to utilize low-cost substrates such as wheat bran, rice straw, sugarcane bagasse, rice bran, coir pith, black gram residue, and chicken feathers to produce enzymes cost-effectively. A. nidulans has also been known as a model organism for the production of heterologous enzymes. Several studies reported genetically engineered strains of A. nidulans for the production of different enzymes. Native as well as heterologous enzymes of A. nidulans have been employed for various industrial processes.

The production of crop residues in India is estimated to be about 500-550 million tons annually. It is estimated that about 93 million tons of crop residues is burnt annually which is not only wastage of valuable biomass resources but pollution of the environment with the production of green house gases also. Among different low cost crop residues, black gram residue as the substrate produced maximal endoglucanase, FPase, and β-glucosidase activities from Aspergillus nidulans AKB-25 under solid-state fermentation. During optimisation of cultural parameters A. nidulans AKB-25 produced maximal endoglucanase (152.14 IU/gds), FPase (3.42 FPU/gds) and xylanase (2441.03 IU/gds) activities. The crude enzyme was found effective for the saccharification of pearl millet stover and bio-deinking of mixed office waste paper. The crude enzyme from A. nidulans AKB-25 produced maximum fermentable sugars of 546.91 mg/g from alkali-pretreated pearl millet stover by saccharification process at a dose of 15 FPU/g of substrate. Pulp brightness and deinking efficiency of mixed office waste paper improved by 4.6% and 25.01% respectively and mitigated dirt counts by 74.70% after bio-deinking. Physical strength properties like burst index, tensile index and double fold number were also improved during bio-deinking of mixed office waste paper.

Rice straw is valuable resource that has been used as substrate for cost effective production of xylanase under solid-state fermentation by a newly isolated white rot fungi, S. commune ARC-11. Out of eleven carbon sources tested, rice straw was found most effective for the induction of xylanase that produced 4288.3 IU/gds of xylanase by S. commune ARC-11. Maximum xylanase production (6721.9 IU/gds) was observed on 8^th day of incubation at temperature (30 °C), initial pH (7.0) and initial moisture content (70.0%). The supplementation of ammonium sulphate (0.08% N, as available nitrogen) enhanced the xylanase production up to 8591.4 IU/gds. The xylanase production by S. commune ARC-11 was further improved by the addition of 0.10%, (w/v) of Tween-20 as surfactant. The maximum xylanase activities were found at pH 5.0 and temperature 55 °C with a longer stability (180 min) at temperature 45, 50 and 55 °C. This xylanase preparation was also evaluated for the pre-bleaching of ethanol-soda pulp from Eulaliopsis binata. An enzyme dosage of 10 IU/g of xylanase resulted maximum decrease in kappa number (14.51%) with a maximum improvement 2.9% in ISO brightness compared to control.

Schizophyllum commune is a basidiomycete that is capable of producing different valuable metabolites such as schizophyllan-a polysaccharide, ethanol, and lignocellulolytic enzymes. Schizophyllan finds application in the food industry, pharmacy, and oil recovery. It acts as a non-specific stimulator of immune system. It shows bioactivities such as antineoplastic, antibacterial, anti-cancer, anti-inflammatory, and antiparasitic properties. S. commune is capable of producing bioethanol directly in a single step using lignocellulosic biomass. Lignocellulolytic enzymes including cellulase, xylanase, pectinase, laccase, lignin peroxidase, and manganese peroxidase, are also synthesized efficiently by different strains of S. commune. Being a good producer of ligninolytic enzymes, S. commune has been shown to be effective for the degradation of various synthetic dyes. This article reviews the production of schizophyllan, ethanol, and enzymes and the utilization of S. commune for lignocellulose degradation and decolorization of synthetic dyes.