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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]

It has been proven that the biocenosis of microalgae and bacteria improves the chemical properties of biomass for its use in anaerobic digestion. However, this anaerobic digestion can be limited by the strong, compact, and complex structure of granulated biomass. Therefore, there is a need to search for an effective method for microalgal–bacterial granular sludge pretreatment, which has not been undertaken in previous scientific works. In this study, ultrasonic pretreatment was used to determine the effects of sonication on anaerobic digestion efficiency. Anaerobic digestion was performed in batch respirometric reactors. It was found that the ultrasonic pretreatment enhanced the biomass solubility; thus, the organic matter concentration increased more than six times compared to the variant without pretreatment. The study showed a positive effect of sonication on the kinetics of the anaerobic process and methane production. The highest methane yield was found in the variants in which the ultrasonication lasted from 150 s to 200 s, and this yield was from 534 ± 16 mL CH4/g VS to 561 ± 17 mL CH4/g VS. The data analysis confirmed strong correlations between the pretreatment time, the amount of biogas and methane production, and the gross energy gain. The highest net energy output and net energy gain were obtained for 150 s of sonication, and, respectively, were 4.21 ± 0.17 Wh/g VS and 1.19 ± 0.18 Wh/g VS. [ABSTRACT FROM AUTHOR]

Regulations in force urge for thermal pre-treatment of post-slaughter waste prior to its anaerobic digestion. Increased interest in biomethane as a fuel in gas networks or vehicles of road transport forces the need to look for heating methods that are alternative to heat recovery from cogeneration. The goal of this study was to determine the synergistic effect of simultaneous ultrasound heating and disintegration on the technological efficiency and energetic balance of the anaerobic digestion of high-load slaughter poultry wastewater. The highest efficiency of anaerobic digestion was obtained for the ultrasound thermal pre-treatment (60 min, 90 °C, OLR = 2.0 gCOD/dm3). In this experimental variant, the biogas production rate reached 9.0 ± 0.2 cm3/gCOD·h, biogas yield was 492 ± 10 cm3/gCOD, and the biogas produced contained 69.8 ± 1.4% CH4. Given the incurred energy outputs, the highest net energetic efficiencies, i.e., 5.92 ± 0.43 Wh and 5.80 ± 0.42 Wh, were obtained in the variants with the conventional thermal pre-treatment (60 min, 70 °C, OLR = 6.0 gCOD/dm3) and ultrasound thermal pre-treatment (60 min, 70 °C, OLR = 6.0 gCOD/dm3), respectively. [ABSTRACT FROM AUTHOR]

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO2 for dewatering, sanitization, and digestion improvement. Solidified CO2 is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO2 is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO2 in the pretreatment and management of sewage sludge. Using solidified CO2 for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO2 can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO2 cycle of biogas production–biogas upgrading–solidified CO2 production–sludge disintegration–digestion–biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO2 emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO2 generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process. [ABSTRACT FROM AUTHOR]

Production and consumption of confectionery products have increased worldwide, thus, effective management of wastewater produced is now an important issue. The confectionery high-load sewage was explored for biogas production in an innovative-design anaerobic reactor with labyrinth flow. The experimental studies were focused on determining the best technological parameters of anaerobic digestion for the effective removal of pollutants and obtaining high CH4 production efficiency. It was found that organic loading rate (OLR) of 5.0–6.0 g COD/L·d contributed to the highest CH4 generation of 94.7 ± 6.1 to 97.1 ± 5.1 L CH4/d, which corresponded to a high COD removal of 75.4 ± 1.5 to 75.0 ± 0.6%. Under such conditions the FOS/TAC ratio was below 0.4, indicating reactor stability, and pH was on the level of 7.15 ± 0.04 at OLR 5.0 g COD/L·d and 7.04 ± 0.07 at OLR 6.0 g COD/L·d. [ABSTRACT FROM AUTHOR]