Global increase in demand for food supply has resulted in surplus generation of wastes. What was once considered wastes, has now become a resource. Studies were carried out on the conversion of biowastes into wealth using methods such as extraction, incineration and microbial intervention. Agro-industry biowastes are promising sources of carbon for microbial fermentation to be transformed into value-added products. In the era of circular economy, the goal is to establish an economic system which aims to eliminate waste and ensure continual use of resources in a close-loop cycle. Biowaste collection is technically and economically practicable, hence it serves as a renewable carbon feedstock. Biowastes are commonly biotransformed into value-added materials such as bioethanol, bioplastics, biofuels, biohydrogen, biobutanol and biogas. This review reveals the recent developments on microbial transformation of biowastes into biotechnologically important products. This approach addresses measures taken globally to valorize waste to achieve low carbon economy. The sustainable use of these renewable resources is a positive approach towards waste management and promoting circular economy.

This research aims to study the wet torrefaction (WT) and saccharification of sorghum distillery residue (SDR) towards hydrochar and bioethanol production. The experiments are designed by Box-Behnken design from response surface methodology where the operating conditions include sulfuric acid concentration (0, 0.01, and 0.02 M), amyloglucosidase concentration (36, 51, and 66 IU), and saccharification time (120, 180, and 240 min). Compared to conventional dry torrefaction, the hydrochar yield is between 13.24 and 14.73%, which is much lower than dry torrefaction biochar (yield >50%). The calorific value of the raw SDR is 17.15 MJ/kg, which is significantly enhanced to 22.36–23.37 MJ/kg after WT. When the sulfuric acid concentration increases from 0 to 0.02 M, the glucose concentration in the product increases from 5.59 g/L to 13.05 g/L. The prediction of analysis of variance suggests that the best combination to maximum glucose production is 0.02 M H₂SO₄, 66 IU enzyme concentration, and 120 min saccharification time, and the glucose concentration is 30.85 g/L. The maximum bioethanol concentration of 19.21 g/L is obtained, which is higher than those from wheat straw (18.1 g/L) and sweet sorghum residue (16.2 g/L). A large amount of SDR is generated in the kaoliang liquor production process, which may cause environmental problems if it is not appropriately treated. This study fulfills SDR valorization for hydrochar and bioenergy to lower environmental pollution and even achieve a circular economy.

In this work, valorisation pathways of brewers’ spent grains (BSG) towards biofuels production under the biorefinery concept were studied utilizing experimental data that provide a common base for straightforward comparison. The dehydration and the recovery of used oil, bioethanol and biogas from BSG were studied. The process units involved were thoroughly investigated and optimized. The oil extraction efficiency reached up to 70% using solid-liquid extraction process with hexane as solvent. The optimal ethanol yield achieved was 45% after the application of acid pretreatment, enzymatic hydrolysis with CellicCTec2 and fermentation with S. Cerevisiae. As far as biogas potential is concerned, the raw BSG, defatted BSG and stillage presented values equal to 379 ± 19, 235 ± 21 and 168 ± 39 mL biogas/g for respectively. Through the combination of the proposed schemes, three biorefinery scenarios were set up able to produce biodiesel, bioethanol and/or biogas. Material flow diagrams were set up in order to assess these schemes. Given that BSG could ensure ‘green’ energy production in the range of 4.5–7.0 million MJ/y if the European BSG potential is fully valorised, BSG could substantially contribute to the biofuel energy strategy.

At present, coal is considered one of the main components for the production of cheap, high-energy and environmentally attractive slurry fuels. The latter can be produced on the basis of low-grade coal dust or coal processing wastes. Thus, coal-water slurries and coal-water slurries containing petrochemicals are produced. The involvement of coal and oil processing wastes expands the scope of raw materials, reduces the fuel costs from traditional energy sources and modifies the main economic characteristics of power plant performance. However, it also increases the impact of coal-fired thermal power stations on the environment. In the last 30–50 years, many efforts have been made to decrease the negative impact of human industrial activity on climate. Involving plant-based components in the process of energy generation to save energy and material resources looks very promising nowadays. This research studies the influence of adding typical bioliquids (bioethanol, turpentine, glycerol) on the concentration of anthropogenic emissions from coal-water slurry combustion. Relative mass concentrations of bioliquids varied in a small range below 20%. We focused on the concentration of the most hazardous sulfur and nitrogen oxides from the combustion of typical filter cakes, as well as plant-containing slurries. It was established that the concentration of sulfur oxides can be decreased (as compared to coal) by 75%, whereas that of nitrogen oxides by almost 30%. Using a generalizing criteria expression, we illustrated the main benefits of adding bioliquids to slurry fuels in comparison with coal. Adding 20% of glycerol was found to provide maximum advantages.

PURPOSE OF REVIEW: The depletion of fossil reserves and environmental challenges associated with fossil fuels are major drivers of the search for sustainable renewable energy sources. Bioethanol production from macroalgae is one of the promising alternatives to reduce use of fossil fuels and achieve energy security and ecological sustainability. The purpose of this review is to critically discuss the options to optimize the process parameters for steady production of bioethanol from macroalgae. RECENT FINDINGS: A comprehensive literature review reveals that bioethanol production from macroalgae not only depends on the macroalgae type but also on the selection of pretreatment, hydrolysis, and fermentation options. Unlike the first- and second-generation feedstocks, macroalgae contains low concentrations of glucans. Thus high bioethanol concentration cannot be achieved by converting only glucans. Therefore, it is important to produce bioethanol from other carbohydrate components of macroalgae, such as alginate, sulphated polysaccharides, carrageenan, mannitol, and agar. The selection of the right hydrolysing agents (e.g., enzyme and/or acid) and steps to minimize formation of inhibitors during the process were found to be important factors affecting the efficiency of hydrolysis process. The hydrolysis enzymes currently used were developed for lignocellulosic and starch-based biomass, not for macroalgae, which is different in polysaccharide structure and composition. Also, the lack of appropriate fermenting microorganisms capable of converting heterogeneous monomeric sugars in macroalgae is a major factor limiting bioethanol yield during the fermentation process. This review systematically discusses the implications of selecting different macroalgae types. The optimization of process parameters of different bioethanol production steps such as pretreatments, hydrolysis, and fermentation is discussed. It can be concluded that high bioethanol yield can be achieved by considering macroalgae type and composition, selecting appropriate pretreatment, hydrolysis, and fermenting microbes, and with effective bioethanol purification.

This article reports the deliverables of the experimental study on the production of a completely renewable biofuel from Manilkara zapota fruit and seed oil. It was attempted to synthesis ethyl ester from Manilkara zapota seed oil using bioethanol synthesized from decayed Manilkara zapota fruit. Bioethanol was produced through fermentation of decayed Manilkara zapota fruit, waste skin, and pulp with Saccharomyces cerevisiae and then distilled at 72°C. The bioethanol yield was noted as 10.45% (v/w). The 95.09% pure bioethanol and 4.9% water molecules were present in the distilled sample. Mechanically extracted raw Manilkara zapota seed oil was used for ethyl ester conversion. The molar ratio of bioethanol to oil, the quantity of KOH, and process temperature were investigated for the maximum yield of Manilkara zapota ethyl ester. A 9:1 molar ratio of bioethanol to oil, 1.5% (w/w) KOH, and 70°C process temperature were identified as enhanced ethanolysis process parameters. The maximum yield of ethyl ester was identified as 93.1%. Physicochemical characteristics of Manilkara zapota oil, bioethanol, and ethyl ester were measured as per the corresponding ASTM standards. It was found that both Manilkara Zapota ethyl ester and bioethanol synthesized from decayed Manilkara zapota fruit could be promising substitutes for fossil diesel and gasoline.

In this study, the feasibility of banana straw (BS) hydrolysate as carbon source and reutilizing the pretreated liquor (PL) of BS in the Rhodosporidium toruloides fermentation was explored for the first time. When BS hydrolysate was used as the carbon source, total biomass concentration, lipid concentration, and lipid content under optimal conditions reached 15.52 g/L, 5.83 g/L, and 37.56% (w/w), respectively, which was similar to the results of pure sugar control. After detoxification, 50% PL can be returned to enzymatic hydrolysis and fermentation, and total biomass concentration, lipid concentration, and lipid content can reach 15.14 g/L, 5.59 g/L, and 36.91% (w/w). Then, ethanol stillage (ES) was used as the nitrogen source. The NaCl and glycerol of ES could promote lipid accumulation, reaching 7.52 g/L under optimized conditions. Finally, microbial lipid production from BS hydrolysate and ES without any additional nutrients was investigated, and the maximum total biomass concentration, lipid concentration, and lipid content were 13.55 g/L, 4.88 g/L, and 36.01% (w/w), respectively. Besides, the main compositions of microbial lipid produced were C16 and C18, and the biodiesel production from the microbial lipid could meet Chinese and US standard through theoretical numerical calculation.

Black liquor is generated from the pretreatment process of biomass-based bioethanol production and due its environmental impact, should be treated effectively before discharged to the water body. Chemical treatment using coagulation-flocculation method was commonly used for wastewater treatment. In the case of black liquor, chemical treatment is often insufficient and further treatment was needed to degrade lignin in order to reduce its black coloration. This present study investigated the two-step treatment to decolorize black liquor using chemical coagulation-flocculation and biological treatment using white-rot fungus Trametes versicolor INACC F200. The biological treatment was optimized by applying a response surface methodology (RSM) of the utilization of CuSO₄ concentration, Tween 80 concentration, and agitation. Furthermore, lignin degradation was also confirmed using FTIR and LC-MS. Initial chemical treatment using ferrous sulfate and polyacrylamide as coagulant-flocculant with a ratio of 3:3, resulted in black liquor decolorization at 80.9% and reduced the COD up to 90.77%. A full quadratic stepwise model was utilized with CuSO₄ inducer, Tween 80 mediator, and agitation speed as the independent variables. Optimum decolorization of 96.188% was predicted when using 2 mM CuSO₄, 2% Tween 80, and an agitation speed of 150 rpm. The highest enzyme activity during the decolorization process was lignin peroxidase (LiP). FT-IR and LC-MS profile showed that lignin-associated bond was eliminated and the molecular weight of lignin was decreased after the treatment. This study concludes the effective decolorization and delignification of black liquor by the two-step chemical and biological treatment.

Biofuels are the cheapest source of energy, and the continuous decline of traditional sources of energy with the increasing population leads to looking for alternatives to reduce the consumption of traditional sources of energy. Bioethanol production from lignocellulosic wastes and cellulosic wastes is not a new approach for fuel production but a cheap and accessible way for the production of fuel. Bacillus is one of the major species that can act as a source of diversified enzymes. In this study, it was emphasized on screening and isolation of a novel, characterization, and best catalytic action on both celluloses and proteins in the presence of different carbon and nitrogen sources. It was observed the effective catalytic breakdown of cellulose with the crude enzyme to glucose allowed fur for fermentation with Saccharomyces, ultimately leading to the generation of alcohol. The study aims to isolate the microbes that can produce cellulases and enzymes and could be used for biodegradation to produce ethanol in the reaction. The maximum enzyme activity was achieved at 3.112 UI with optimized pH and temperature, and the maximum conversion of sugars into alcohol was about 70% in the newspaper, cartons, colored paper, and disposable paper cups. An essential observation was the decolorization of the origami craft paper within 24 hours. The study was involved in enhancing the maximum Enzyme activity of cellulases from different cellulosic raw materials. Hence, it was achieved by JCB strain, optimization of pH, temperature, and acids for the biodegradation. The presence of peaks at 3200 and 2900 was a confirmation of ethanol bonds in the biodegradation reaction mixtures.

Agricultural and agro-industrial wastes (e.g., potato peel waste) are causing severe environmental problems. The processes of pretreatment, saccharification, and fermentation are the major obstacles in bioethanol production from wastes and must be overcome by efficient novel techniques. The effect of exposing the fungi (yeast) Saccharomyces cerevisiae to laser source with the addition of graphitic carbon nitride nanosheets (g-C₃N₄) with different concentrations on bioethanol production was investigated through the implementation of a batch anaerobic system and using potato peel waste (PPW). Dichromate test was implemented as quantitative analysis for quantification of the bioethanol yield. The benefits of this test were the appearance of green color indicating the identification of ethanol (C₂H₅OH) by bare eye and the ease to calculate the bioethanol yield through UV–visible spectrophotometry. The control sample (0.0 ppm of g-C₃N₄) showed only a 4% yield of bioethanol; however, by adding 150 ppm to PPW medium, 22.61% of ethanol was produced. Besides, laser irradiations (blue and red) as influencing parameters were studied with and without the addition of g-C₃N₄ nanomaterials aiming to increase the bioethanol. It was determined that the laser irradiation can trigger the bioethanol production (in case of red: 13.13% and in case of blue: 16.14% yields, respectively) compared to the control sample (in absence of g-C₃N₄). However, by adding different concentrations of g-C₃N₄ nanomaterials from 5 to 150 ppm, the bioethanol yield was increased as follows: in case of red: 56.11% and, in case of blue: 56.77%, respectively. It was found that using fungi and exposing it to the blue laser diode source having a wavelength of 450 nm and a power of 250 mW for a duration of 30 min with the addition of 150 mg L⁻¹ of g-C₃N₄ nanomaterials delivered the highest bioethanol yield from PPW.