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Waste glycerol can be subjected to various processing operations, including purification and refining, to obtain glycerol of an appropriate purity. Alternative methods for utilising waste glycerol are also being sought, e.g., by converting it into other valuable chemical products or biofuels. Therefore, various technologies are being developed to ensure effective and sustainable utilisation of this type of waste. The production of value-added products from waste glycerol strongly determines the improvement of the economic viability of biofuel production and corresponds to the model of a waste-free and emission-free circular economy. This paper characterises the mechanisms and evaluates the efficiency of existing methods for microbiological utilisation of waste glycerol into liquid biofuels, including biodiesel, bioethanol and biobutanol, and identifies further production avenues of value-added products. In addition, it presents the results of a bibliographical analysis of publications related to the production of liquid fuels and economically valuable products from glycerol, assesses the progress of research and application work and, finally, identifies areas for future research. [ABSTRACT FROM AUTHOR]

Anaerobic wastewater treatment is, in many cases, a justified alternative to typical activated sludge processes, from a technological, economic, and ecological point of view. The optimisation of fermentation reactors is primarily concerned with increasing the biodegradation of organic compounds and biogas production, as well as improving efficiency in the removal of nitrogen and phosphorus compounds. The aim of the research was to determine the impact of using low-cost recycled filling on the efficiency of treating real confectionery wastewater in a vertical anaerobic labyrinth flow bioreactor. The experiments focused on selecting the organic loading rate that would allow for the effective biodegradation and removal of pollutants, as well as the efficient production of biomethane. It was found that the tested reactor can operate efficiently at a maximum organic loading rate (OLR) of 7.0–8.0 g of chemical oxygen demand (COD)/L·d. In this OLR range, high efficiency was guaranteed for both wastewater treatment and biogas production. However, increasing the OLR value to 8.0 g COD/L·d had a significant negative effect on the methane (CH4) content in the biogas. The most efficient variants achieved a biodegradation efficiency of around 90% of the organic compounds, a CH4 content of over 70% in the biogas, and a biogas yield of over 400 L/kg of COD removed. A significant influence of the applied OLR on the ratio of free organic acids (FOS) to total alkaline capacity (TAC) and pH was observed, as well as a strong correlation of these indicators with the specific biogas yield and CH4 content. The application of a solution based on the use of a hybrid system of anaerobic granulated sludge and an anaerobic filter resulted in an efficient treatment process and an almost complete elimination of suspensions from the wastewater. [ABSTRACT FROM AUTHOR]

There is a need to find methods to intensify the anaerobic digestion process. One possibility is the use of pretreatment techniques. Many laboratory tests confirm their effectiveness, but in most cases, there is no verification work carried out on industrial plants. A reliable and complete evaluation of new solutions can only be carried out in plants that reflect operating conditions at a higher readiness technological level. This has a direct impact on the scientific value and, above all, on the high application value of innovative technologies. The aim of our research carried out under laboratory conditions and on a large scale was to determine the technological and energy efficiency of the use of hydrodynamic cavitation in the pretreatment of a waste mixture from dairy farms. It has been shown that hydrodynamic cavitation significantly increases the concentration of organic compounds in the dissolved phase. In the most effective variants, the increase in the content of these indicators was over 90% for both COD and TOC. The degree of solubilisation achieved was 49 ± 2.6% for COD and almost 52 ± 4.4% for TOC. Under laboratory conditions, the highest effects of anaerobic digestion were achieved after 10 min of pretreatment. The amount of biogas was, on average, 367 ± 18 mL/gCOD, and the amount of methane was 233 ± 13 mL/gCOD. Further large-scale optimisation trials showed that after 8 min of hydrodynamic cavitation, the biogas yield was 327 ± 8 L/kgCOD with a CH4 content of 62.9 ± 1.9%. With this variant, the net energy yield was 66.4 ± 2.6 kWh/day, a value that was 13.9% higher than the original variant with 10 min of disintegration and 3.1% higher than the variant without pretreatment. [ABSTRACT FROM AUTHOR]

The supply of waste glycerol is rising steadily, partially due to the increased global production of biodiesel. Global biodiesel production totals about 47.1 billion liters and is a process that involves the co-production of waste glycerol, which accounts for over 12% of total esters produced. Waste glycerol is also generated during bioethanol production and is estimated to account for 10% of the total sugar consumed on average. Therefore, there is a real need to seek new technologies for reusing and neutralizing glycerol waste, as well as refining the existing ones. Biotechnological means of valorizing waste glycerol include converting it into gas biofuels via anaerobic fermentation processes. Glycerol-to-bioenergy conversion can be improved through the implementation of new technologies, the use of carefully selected or genetically modified microbial strains, the improvement of their metabolic efficiency, and the synthesis of new enzymes. The present study aimed to describe the mechanisms of microbial and anaerobic glycerol-to-biogas valorization processes (including methane, hydrogen, and biohythane) and assess their efficiency, as well as examine the progress of research and implementation work on the subject and present future avenues of research. [ABSTRACT FROM AUTHOR]

The characteristics of excess aerobic granular sludge, related to its structure and chemical composition, limit the efficiency of anaerobic digestion. For this reason, pre-treatment methods and compositions with other organic substrates are used. In earlier work, no attempt was made to intensify the methane fermentation of the excess aerobic granular sludge by adding fatty waste materials. The aim of the research was to determine the effects of co-digestion of pre-hydrodynamically cavitated aerobic granular sludge with waste fats on the efficiency of methane fermentation under mesophilic and thermophilic conditions. The addition of waste fats improved the C/N ratio and increased its value to 19. Under mesophilic conditions, the highest effects were observed when the proportion of volatile solids from waste fats was 25%. The amount of biogas produced increased by 17.85% and CH4 by 19.85% compared to the control. The greatest effects were observed in thermophilic anaerobic digestion at 55 °C, where a 15% waste fat content in volatile solids was ensured. This resulted in the production of 1278.2 ± 40.2 mL/gVS biogas and 889.4 ± 29.7 mL/gVS CH4. The CH4 content of the biogas was 69.6 ± 1.3%. The increase in biogas and CH4 yield compared to pure aerobic granular sludge anaerobic digestion was 34.4% and 40.1%, respectively. An increase in the proportion of waste fats in the substrate had no significant effect on the efficiency of methane fermentation. Strong positive correlations (R2 > 0.9) were observed between biogas and CH4 production and the C/N ratio and VS concentration. [ABSTRACT FROM AUTHOR]

The use of aerobic granular sludge is a promising and future-proof solution for wastewater treatment. The implementation of this technology requires the development of efficient and cost-effective methods for the management of excess sludge. The aim of the research was to evaluate the effects of hydrodynamic cavitation on the efficiency of aerobic granular sludge digestion. Respirometric measurements were performed at a temperature of 38 °C and an initial organic load of 5.0 gVS/L. The changes in the properties of the pretreated biomass, the kinetics of methane fermentation, the amount and composition of the biogas produced, and an energetic evaluation of the process were carried out. A significant influence of hydrodynamic cavitation on the transfer of organic compounds into the dissolved phase was demonstrated. The degree of solubilisation was 37% for COD and 42% and for TOC. The efficiency of CH4 production from the pretreated sludge reached a value of 496 ± 12 mL/gVS, which corresponds to an increase of 19.6% compared to the raw biomass. The influence of cavitation on the CH4 content of the biogas was not observed. Strong correlations were found between the efficiency of anaerobic digestion and the concentration of dissolved organic compounds and the hydrodynamic cavitation time used. The gross energy yield was closely correlated with the amount of CH4. The highest comparable values of 3.12 Wh/gTS to 3.18 Wh/gTS were found in the variants in which the hydrodynamic cavitation (HC) time was between 15 min and 50 min. The highest net energy production of 2890 kWh/MgTS was achieved after 15 min of pretreatment. [ABSTRACT FROM AUTHOR]