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.

Increased solid waste pollution and the negative effect of fossil fuel consumption on the environment are issues that would require more scientific attention and application to deal effectively with these phenomena. Wastepaper, a major component of solid waste, is classified as organic waste due to the presence of cellulose, a glucose-based biopolymer that is part of its structural composition. The saccharification of cellulose into glucose, a fermentable sugar, can be achieved with a hydrolytic enzyme known as cellulase. Although cellulase from fungal species such as Trichoderma, Aspergillus, and Penicillium are well described, knowledge about cellulase isolated from the brown garden snail is limited as it has not been the subject of many research endeavors. The waste paper has been described as a suitable resource for bio-energy development due to cellulose, a structural component of this bio-material that can be degraded into glucose, a fermentable sugar. Although paper materials such as newspaper, office paper, filter paper, Woolworths and Pick and Pay (retailers) advertising paper, as well as foolscap paper, were saccharified by different cellulases, the degradation of these paper materials by garden snail cellulase is a novel investigation from our laboratory. With the effects of temperature and incubation time on this cellulase action when degraded paper materials have already been investigated and reported, this study dealt with the garden snail cellulase action when degraded paper materials at different pH values. Most of the paper materials were degraded optimally at a pH value of 6.0, while optimum saccharification was observed at pH 4.5 when newspaper and brown envelope paper were degraded, with office paper showing maximum bioconversion at pH 7.0. The difference in the structural composition of the paper materials also affects the degree of saccharification, as the amount of sugar released from the various paper materials at optimum pH values is not similar. Together with other catalytic parameters, the pH value of this enzymatic catalysis is also to be considered when designing the development of waste paper as a bio-product resource, with limiting environmental pollution as an additional advantage of this process.

It is well established that pretreatment of lignocellulosic biomass is required to achieve an effective enzymatic saccharification process. At the present time, most of the touted pre-treatment technologies would cause environmental pollution and unsustainable water use for the pretreated material prior to enzymatic saccharification. To address these shortcomings, the pretreatment technology which combines the supercritical CO₂, SC-CO₂ (a green solvent), acetic acid, and steam explosion was used to assess the pretreatment of wheat straw for enzymatic saccharification. The effects of solvent concentration, impregnation temperature and time, pre-treatment time, and temperature, as well as SC-CO₂ pressure, contact time, and temperature, were evaluated. The results identified that at the optimum SC-CO₂ pressure of 18 MPa, the highest amount of reducing sugars (RS) was produced from the cellulosic pulp using Acetic acid/Steam/SC-CO₂ at 200 °C for 30 min, a value 20% more than the pulp produced with the Water/Steam/SC-CO₂. The effectiveness of the pretreatment process was attributed not only to delignification and defibrillation but also to the exposure of the cellulose structure evidenced from the proportion of the β-glycosidic linkages as shown by FTIR. Passing SC-CO₂ after the pretreatment reduces the amounts of fermentation inhibitors and eliminates the use of wash water.

Lignocellulosic biomass is considered as a recalcitrant substrate for anaerobic digestion due to its complex nature that limits its biological degradation. Therefore, suitable preprocessing for the improvement of the performance of conventional anaerobic digestion remains a challenge in the development of anaerobic digestion technology. The physical and chemical characteristics of wheat straw (WS), as a representative lignocellulosic biomass, have a significant impact on the anaerobic digestion process in terms of quantity and quality of the produced biogas. This study aimed at investigating the enzymatic saccharification and detoxification of straw prior to anaerobic digestion with the final objective of enhancing the performance of conventional anaerobic systems of recalcitrant fractions of agricultural waste. The experimental activity was performed in lab and pilot scale treating WS. Alkaline delignification of straw using sodium hydroxide (NaOH) was studied prior to enzymatic hydrolysis for the production of easily biodegradable sugars. After defining the optimum conditions for the pretreatment scheme, the anaerobic digestability of the effluents produced was measured. Finally, the final liquid effluents were fed to a pilot scale anaerobic digester of 0.5 m³ volume, applying an increasing organic loading rate (OLR) regime (in terms of chemical oxygen demand (COD) from 0.2 to 15 kg COD/m³/day). The optimum conditions for the delignification and enzymatic hydrolysis of WS were defined as 0.5 M NaOH at 50 °C for 3–5 h and 15 μL Cellic CTec2/g pretreated straw at 50 °C. It was proven that the resulting liquid effluents could be fed to an anaerobic digester in the ratio that they are produced with satisfactory COD removal efficiencies (over 70%) for OLRs up to 10 kg COD/m³/day. This value is correspondent to a hydraulic retention time of around 7.5 days, much lower than the respective one for untreated straw (over 12 days).

The present study investigated the effect of thermo-chemical pretreatment on the enhancement of enzymatic digestibility of olive mill stones (OMS), as well as its possible valorisation via bioconversion of the generated free sugars to alcohols. Specifically, the influence of parameters such as reaction time, temperature, type and concentration of dilute acids and/or bases, was assessed during the thermo-chemical pretreatment. The hydrolysates and the solids remaining after pretreatment, as well as the whole pretreated slurries, were further evaluated as potential substrates for the simultaneous production of ethanol and xylitol via fermentation with the yeast Pachysolen tannophilus. The digestibility and overall saccharification of OMS were considerably enhanced in all cases, with the maximum enzymatic digestibility observed for dilute sodium hydroxide (almost 4-fold) which also yielded the highest total saccharification yield (91% of the total OMS carbohydrates). Ethanol and xylitol yields from the untreated OMS were 28 g/kg OMS and 25 g/kg OMS, respectively, and were both significantly enhanced by pretreatment. The highest ethanol yield was 79 g/kg OMS and was achieved by the alkali pretreatment and separate fermentation of hydrolysates and solids, whereas the highest xylitol yield was 49 g/kg OMS and was obtained by pretreatment with sulphuric acid and separate fermentation of hydrolysates and solids.

Sawdust, a major waste product of the forestry industry, is accumulating along the Lagos Lagoon in Lagos, Nigeria, without it being effectively managed. Besides its use in The saccharification of sawdust could contribute to the development of renewable energy sources and feedstock for bioproduct development. The process is, however, not that straightforward as variables such as the type of cellulase enzyme, pretreatment of the cellulose substrate, and optimizing of cellulase to cellulose ratio are a few that need to be optimized for the process to be effective in terms of glucose production.manufacturing sound-absorbing boards to reinforce concrete beams and for energy purposes, its potential as a renewable energy source and feedstock for bio-product development has not yet been realized. Cellulose, a glucose biopolymer and structural component of cellulose can be hydrolyzed by a hydrolytic enzyme known as cellulase. During the process, the enzyme breaks the B-1,4-glucosidic bond, which keeps the glucose units together, and by acting on this bond, numerous glucose units are released. As part of sawdust, the cellulose molecule is not freely available for the degradation action of the cellulase enzyme as it is strongly associated with lignin, which acts as bio-glue, keeping cellulose and hemicellulose together. Delignification is an effective technique that was used to make the sawdust from ten different trees along the Lagos Lagoon in Nigeria more susceptible to saccharification by cellulase isolated from the fungus Aspergillus niger. Delignified and non-delignified sawdust masses between 2 mg and 10 mg were incubated with the A. niger cellulase solution (2 mg.mL-1), whereafter, the amount of sugar produced by the cellulase action was determined. The percentage saccharification of each sawdust material was also linked with the amount of sugar produced during cellulase action. From these investigations was concluded that delignification increased sugar production when almost all the masses of different sawdust materials were degraded. It was also observed that the ratio of sawdust mass to enzyme concentration is an important variable that influences the effectiveness of the saccharification process. The percentage saccharification of the various sawdust materials was also determined, and it indicated that the highest percentage of saccharification was not obtained when the highest amount of sawdust was degraded, producing the highest amount of sugar.

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.

The uncontrolled production of waste is a daily phenomenon that is experienced by most global communities, and the situation worsens due to the lack of effective waste management procedures. Solid waste such as sawdust is primarily produced by the forestry industry and although it is utilized by certain countries as briquettes to make fire or as an absorbent to clean fluid spillage as well as a component of ceilings, most of the sawdust along the Lagos Lagoon in Nigeria is left unattended as waste, contributing to environmental pollution. Cellulose, composed of glucose units is a structural component of sawdust and when saccharified the resulting glucose can be fermented into renewable substances such as bio-ethanol. The cellulose degradation process can be performed with a cellulase enzyme such as available in the fungus Aspergillus niger and during the current investigation, this enzyme system was used to bio-convert the cellulose component of sawdust from ten different trees along the Lagoon into glucose. To increase the cellulase action all sawdust materials were delignified before cellulase action with the main aim of determining the optimum pH value for maximum degradation of the various sawdust materials. The pH-related saccharification profile of each type of sawdust was constructed as well as the relative percentage of saccharification and it was concluded that all the materials were optimum degraded at acidic pH-values which varied between pH 5.0 and pH 6.0 that are like optimum pH-values reported for the other types of cellulose materials.

The present study evaluated the sequential biodiesel-bioethanol production from seaweeds. A total of 22 macroalgal species were collected at different seasons and screened based on lipid and carbohydrate contents as well as biomass production. The promising species was selected, based on the relative increase in energy compounds (REEC, %), for further energy conversion. Seasonal and annual biomass yields of the studied species showed significant variations. The rhodophyte Amphiroa compressa and the chlorophyte Ulva intestinalis showed the highest annual biomass yield of 75.2 and 61.5 g m⁻² year⁻¹, respectively. However, the highest annual carbohydrate productivity (ACP) and annual lipid productivity (ALP) were recorded for Ulva fasciata and Ulva intestinalis (17.0 and 3.0 g m⁻² year⁻¹, respectively). The later was selected for further studies because it showed 14.8% higher REEC value than Ulva fasciata. Saturated fatty acids (SAFs) showed 73.4%, with palmitic acid as a dominant fatty acid (43.8%). Therefore, biodiesel showed high saturation degree, with average degree of unsaturation (ADU) of 0.508. All the measured biodiesel characteristics complied the international standards. The first route of biodiesel production (R1) from Ulva intestinalis showed biodiesel recovery of 32.3 mg g⁻¹ dw. The hydrolysate obtained after saccharification of the whole biomass (R2) and lipid-free biomass (R3) contained 1.22 and 1.15 g L⁻¹, respectively, reducing sugars. However, bioethanol yield from R3 was 0.081 g g⁻¹ dw, which represented 14.1% higher than that of R2. Therefore, application of sequential biofuel production using R3 resulted in gross energy output of 3.44 GJ ton⁻¹ dw, which was 170.9% and 82.0% higher than R1 and R2, respectively. The present study recommended the naturally-grown Ulva intestinalis as a potential feedstock for enhanced energy recovery through sequential biodiesel-bioethanol production.

Agro-industrial waste can be used to replace traditional carbohydrates, such as sucrose, starch, and glucose in many industrial fermentation processes. This study investigated the conversion of pre-treated waste sweetpotato vines (SV) into lipid by Trichosporon fermentans under the separate hydrolysis and fermentation (SHF) and the simultaneous saccharification and fermentation (SSF) processes. The results showed that SV autoclaving significantly increased the lipid accumulation of T. fermentans compared with acid or alkaline hydrolysis. The effects of different pre-treatments on SV were also studied by scanning electron microscopy and Fourier transform infrared spectroscopy, which showed the partial removal of the aliphatic fractions, hemicelluloses, and lignin during pre-treatment. Moreover, the lipid yield of T. fermentans in SSF was 6.98 g L⁻¹, which was threefold higher than that (2.79 g L⁻¹) in SHF, and the lipid contents of yeast in SSF and SHF were 36 and 25%, respectively. Overall, this study indicated that SSF using autoclaved SV could increase the growth and lipid production of T. fermentans and provided an efficient way to realize the resource utilization of waste SV.