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In this study, the pyrolysis of sewage sludge was explored through microwave-assisted pyrolysis. Three kinds of sludge (primary sludge, waste-activated sludge, and digested sludge) from a sewage treatment process were used. All three kinds of sewage sludge had a low microwave absorption capacity; therefore, an absorber was added to enable microwave-assisted pyrolysis. By using silicon carbide as the heating element, it was possible to increase the temperature within a short time by applying microwaves. During the microwave-assisted pyrolysis of sewage sludges, the amount of gas generated and the H2 and CO fraction of the produced gas increased as temperature increased. The pyrolysis of waste-activated sludge produced the greatest quantity of gas. However, the primary sludge produced the highest amount of syngas in terms of H2 and CO, which indicate the high-quality of the syngas.

Aerobic granular sludge (AGS) represents an aggregate of sludge formed through the self-immobilization of microorganisms under aerobic conditions. It is currently under scrutiny for its potential as a technology to reduce carbon emissions and promote sustainability. The practicality of AGS stems from its ability to encourage granule formation and enhance structural stability. In this study, a total of five cations (K+, Ca2+, Mg2+, Al3+, Fe3+) were introduced to facilitate stable structuring and the formation of granules for treating high-strength wastewater, such as side-stream treatment. As a result of the experiment, the loosely bound extracellular polymeric substances (LB-EPS) content in the cation-enhanced sludge witnessed a significant increase, leading to elevated total EPS content under all experimental conditions. Furthermore, the protein (PN)/polysaccharide (PS) ratio, a pivotal component of EPS influencing AGS's hydrophobicity and structural stability, exhibited a collective increase, with Mg2+ reaching the highest value of 1.7. The relationship between relative hydrophobicity and the PN/PS ratio was found to strongly impact sludge adhesion, with noteworthy results observed particularly for Mg2+, Al3+, and Fe3+. The viability of attached cells reached 96.8 %, the highest recorded in the case of Mg2+. In the context of treating high-strength wastewater, Mg2+ emerged as the optimal cation for accelerating AGS formation and enhancing structural stability.

Despite its numerous advantages, the aerobic granular sludge (AGS) process faces several challenges that hinder its widespread implementation. One such challenge is the requirement for high organic load ratios (OLR), which significantly impacts AGS formation and stability, posing a barrier to commercialization. In response to these challenges, this study investigates the granulation and treatment efficacy of the AGS process for treating high-concentration wastewater under various OLR and settling time. Three sequential batch reactors (R1, R2, R3) were operated at OLRs of 0.167, 0.33, and 1 kg COD/m3·day. The study focuses on analyzing key parameters including sludge characteristics, extracellular polymeric substances (EPS) content, PN/PS ratio, and microbial clusters. Results demonstrate that reducing settling time from 90 to 30 min enhances sludge settleability, resulting in a maximum 50.8 % decrease in SVI30 (from 98.1 to 122.8 mL/g to 51.9–81.3 mL/g), thereby facilitating the selection of beneficial microorganisms during granulation. Particularly, at R2, the PN/PS ratio was 4.3, and EPS content increased by 1.52-fold, leading to a 1.41-fold increase in sludge attachment. This observation suggests a progressive maturation of AGS. Additionally, analysis of microbial diversity and cluster composition highlights the influence of OLR variations on the ratios of Proteobacteria and Bacteroidetes. These findings emphasize the significant impact of SBR operational strategies on AGS process performance and biological stability, offering valuable insights for the efficient operation of future high-concentration wastewater treatment processes.

This study focused on characterizing sewage sludge, food waste, and livestock manure, representative of continuously generated organic wastes, along with their anaerobic digestion residues. Microwave assisted pyrolysis was employed to investigate the relationship between the properties of the raw organic wastes and the resulting pyrolysis products, utilizing the R-program for analysis. Evaluation of the pyrolysis products of these six organic wastes revealed that char yield was primarily influenced by ash and fixed carbon contents, with higher yields observed in residues from anaerobic digestion compared to the original organic waste. Liquid and gaseous product quantities were found to increase with volatile content, while high-fat content within the volatile fraction notably enhanced liquid product yields, impacting syngas production. Analysis of syngas composition indicated a negative correlation between high nitrogen content in the feedstock and H2 generation. Furthermore, examining the correlation between chemical properties of organic waste and pyrolysis products revealed a proportional increase in protein components with nitrogen content, suggesting potential improvements in pyrolysis efficiency through raw material pretreatment enhancements by the R program.