Wastes are unceasingly generated in the world, and most of them can be recycled, reused, or recovered to promote a circular economy. Among waste treatment approaches, the anaerobic digestion (AD) process has been considered as an ideal process due to its ecological benefits (reduction of unpleasant odor, pathogens accumulation, or greenhouse gas emission), social and economic advantages, and energy saving. In addition to biogas production, this process can be used to produce various bioproducts, such as biopolymers, bioplastics, biomass, biofertilizers, and biolipids. Interestingly, the AD process residue or digestate is a nutrient-rich by-product that can be used as a biofertilizer for agronomical purposes to balance N-P cycle in the soils. Despite of numerous benefits of AD, less than 1 % of waste is treated by this process. This process has the potential to be integrated with other waste treatment approaches to increase waste treatment efficiency. Therefore, it is essential to focus on each advantage and clarify ambiguity in order to satisfy more countries for employing AD for waste treatment. In this review, various benefits of AD are evaluated; and its potential impacts on particularly agriculture are examined in detail. Additionally, potential biomass and wastes that can be used for anaerobic digestion worldwide are deliberated. Besides, a critical perspective has been developed on the economic, environmental, and social evaluation of the benefits of AD and, as a final point, focused on an integrated circular cascading approach. 

This work innovatively merges engineered food structures with additive manufacturing technology to tailor food for different dysphagia levels using filamentous Fungus Aspergillus oryzae biomass through a co-axial 3D food printing process. In order to 3D print samples with different textures, calcium chloride (CaCl2) and calcium gluconolactate (Gluco) were tested at different concentrations alongside three alginate concentrations. The structural and morphological analysis of the printed samples was conducted before cooking, followed by texture analysis and the measurement of cutting strength on cooked samples. Dysphagia food level classification was measured following the International Dysphagia Diet Standardisation Initiative (IDDSI) guidelines. Results revealed that Gluco minimally altered texture but affected appearance, resulting in soft samples (hardness ≈ 1.3 N) with fibrous structures, while CaCl2 increased hardness (from ≈ 1 N to 4.68 N) through alginate-ion Ca2+ interaction. All samples passed the IDDSI test, confirming suitability for dysphagic individuals. This successfully engineered personalised food with tailored texture meeting nutritional requirements. 

While olive oil is an important food product in the Mediterranean Sea Basin, olive oil mill wastewater (OOMW) and olive pomace, which are by-products of olive oil, are released in excessive quantities. OMWW is an important source of environmental pollutants due to its slightly acidic pH, high contents of phenol and chemical oxygen demand (COD). To overcome this problem, it was aimed to investigate the potential use of OOMW as an alternative substrate for biomass production by filamentous fungi in this study. For the cultivation, three edible fungi (Aspergillus oryzae CBS 819.72, Neurospora intermedia CBS 131.92, and Rhizopus delemar CBS 145940) were tested. Among them, A. oryzae was found to be a promising fungus in biomass production containing 14.9% protein. The protein content of the biomass was improved to 44.9% (w/w) by adding a nitrogen source (sodium nitrate) and removing the suspended solids. Concomitantly, 35-44% of COD reduction was also obtained after the fungal cultivation. Thus, the potential use of olive oil mill wastewater for the cultivation of fungal biomass was determined and at the same time, its pre-treatment was provided. However, the content of the obtained fungal biomass should be determined and its usability as feed should be investigated.

The scientific interest in volatile fatty acids (VFAs) as an energy source and chemical precursor in ruminant diets has been longstanding, as it has significant implications for animal physiology and well-being. The present study explores the substitution of volatile fatty acids (VFAs) derived from agro-food residues via acidogenic fermentation as an alternative energy source in ruminant feed. Utilizing the gas production method, rumen digestibility assays were conducted, wherein the recovered VFA effluent from the acidogenic fermentation of apple pomace and potato protein liquor was substituted for 10%, 20%, and 30% of the total mixed ration (TMR) energy. Various parameters such as gas, VFA yield and composition, VFA peak intervals, changes in pH, and ammonium nitrogen content were investigated. Based on the results obtained, provision of 20% and 30% of the energy with VFAs did not increase methane production or did not cause significant pH alternations. Nevertheless, such supplementation resulted in increased production and accumulation of VFAs in the rumen media. The bioconversion of agro-food side streams into VFAs opens a new path in sustainable nutrient recovery and feed production from low value agro-industrial residues.

Flue gases are the gases which are produced from industries related to chemical manufacturing, petrol refineries, power plants and ore processing plants. Along with other pollutants, sulfur present in the flue gas is detrimental to the environment. Therefore, environmentalists are concerned about its removal and recovery of resources from flue gases due to its activation ability in the atmosphere to transform into toxic substances. This review is aimed at a critical assessment of the techniques developed for resource recovery from flue gases. The manuscript discusses various bioreactors used in resource recovery such as hollow fibre membrane reactor, rotating biological contractor, sequential batch reactor, fluidized bed reactor, entrapped cell bioreactor and hybrid reactors. In conclusion, this manuscript provides a comprehensive analysis of the potential of thermotolerant and thermophilic microbes in sulfur removal. Additionally, it evaluates the efficacy of a multi-enzyme engineered bioreactor in this process. Furthermore, the study introduces a groundbreaking sustainable model for elemental sulfur recovery, offering promising prospects for environmentally-friendly and economically viable sulfur removal techniques in various industrial applications. 

The production of date syrup yields a substantial amount of date press cake (DPC), fibrous and moisturising material with great potential for generating value through bioprocessing. However, the recalcitrant structure of DPC affects the yield of products in bioprocesses. To boost the accessibility of the structure as well as increase the soluble fraction of carbohydrates and facilitate further enzymatic hydrolysis, hydrothermal and dilute acid (0.5% (v/v) sulfuric acid) pretreatments as cost-effective and feasible methods were applied on DPC at relatively low temperatures (80, 100, 120 and 140 degrees C) and reaction times (60 and 90 min). The success in pretreatment was then evaluated by a post-enzymatic treatment using an enzyme cocktail of cellulases and hemicelluloses. Based on total accessible sugar with minimum produced inhibitors, an optimal operating condition was considered acid pretreatment at 120 degrees C for 90 min with a 55.02% increase in total sugar yield. To explore the potential use of pretreated DPC, an anaerobic digestion was conducted on untreated and acid-pretreated DPC at 120 degrees C for 90 min. The results showed that pretreatment increased the total bioproduct yield, including hydrogen, ethanol, and volatile fatty acid yields, by 59.75%. This demonstrates the significant impact of pretreatment on product yields in a bioprocess. 

The growing demand for sustainable ruminant feed alternatives has motivated the application of bioconversion approaches for the valorization of agro-food byproducts (AFB) into feed additives and supplements. The present study thoroughly investigated substituting volatile fatty acids (VFAs) obtained from acidogenic fermentation (AF) of AFB as an energy source in ruminant feed. Rumen in vitro digestibility assays were conducted utilizing the gas production method, wherein the VFAs obtained from AF of apple pomace and potato protein liquor was substituted with partial silage and concentrate energy at levels of 10%, 20%, and 30%. The results indicate that substituting 20% of the concentrate’s energy with VFA mixture significantly reduced methane production and had no adverse effect on the production and accumulation of VFAs in the simulated rumen media. Conversely, replacing 10% of the silage energy with VFAs led to a decrease in methane production and further enhanced the production of VFAs. Readily digestible VFAs in ruminant feed have the potential to enhance energy availability and sustainability in ruminant farming practices, aligning with the principles of circular economy and waste valorization. 

Rhodosporidium toruloides, an oleaginous yeast, is a potential feedstock for biodiesel production due to its ability to utilize lignocellulosic biomass-derived hydrolysate with a considerably high lipid titer of 50–70 % w/w. Hence, for the first-time environmental assessment of large-scale R. toruloides-based biodiesel production from wood hydrolysate and crude glycerol was conducted. The global warming potential was observed to be 0.67 kg CO2 eq./MJ along with terrestrial ecotoxicity of 1.37 kg 1,4-DCB eq./MJ and fossil depletion of 0.13 kg oil eq./MJ. The highest impacts for global warming (∼45 %) and fossil depletion (∼37 %) are attributed to the use of chloroform for lipid extraction while fuel consumption for transportation contributed more than 50 % to terrestrial ecotoxicity. Further, sensitivity analysis revealed that maximizing biodiesel yield by increasing lipid yield and solid loading could contribute to reduced environmental impacts. In nutshell, this investigation reveals that environmental impact varies with the type of chemical utilized.

Synthesis gas (syngas) fermentation represents a promising biological method for converting industrial waste gases, particularly carbon monoxide (CO) and carbon dioxide (CO2) from industrial sources (e.g. steel production or municipal waste gasification), into high-value products such as biofuels, chemicals, and animal feed using acetogenic bacteria. This review identifies and addresses key challenges that hinder the large-scale adoption of this technology, including limitations in gas mass transfer, an incomplete understanding of microbial metabolic pathways, and suboptimal bioprocess conditions. Our findings emphasize the critical role of microbial strain selection and bioprocess optimization to enhance productivity and scalability, with a focus on utilizing diverse microbial consortia and efficient reactor systems. By examining recent advancements in microbial conditioning, operational parameters, and reactor design, this study provides actionable insights to improve syngas fermentation efficiency, suggesting pathways towards overcoming current technical barriers for its broader industrial application beyond the production of bulk chemicals.