Enhancement of iron-based nitrogen removal with an electric-magnetic field in an upflow microaerobic sludge reactor (UMSR)

Role of diffusible signal factor in regulating aerobic granular sludge formation under temperature shocks

Signal-molecule-mediated strategies are proposed for aerobic granular sludge (AGS), but the regulatory mechanisms behind AGS formation are largely unexplored. In this study, two sequence batch reactors (SBRs) were operated to investigate the regulation of diffusible signal factor (DSF) in AGS formation. DSF secretion in Reactor 2 (R2: 10 °C→25 °C) decreased by 15 % compared to Reactor 1 (R1: 25 °C→10 °C), correlating with a 26 % increase in extracellular polymeric substance (EPS) concentration, resulting in a 63 % acceleration of the granulation process. After temperature shocks in R2, DSF concentration increased by 70 %, while EPS concentration decreased by 47 %. Batch tests confirmed that DSF inhibited EPS secretion. Combined 16S rRNA analysis and machine learning identified key bacteria responsible for secreting EPS and signal molecule. The decrease in the abundances of these bacteria reduced EPS production. These findings on DSF regulation of EPS secretion provide an in-depth understanding of enhanced AGS granulation.

Effect of thermal hydrolysis pretreatment on the stabilization of sludge with different solid contents during autothermal thermophilic aerobic digestion

Sludge stabilization was affected by solid content during autothermal thermophilic aerobic digestion (ATAD). Thermal hydrolysis pretreatment (THP) could alleviate the issues of high viscosity, slow solubilization and low ATAD efficiency caused by increased solid content. The influence of THP on the stabilization of sludge with different solid contents (5.24%-17.14%) during ATAD was investigated in this study. The results demonstrated that stabilization was achieved with volatile solid (VS) removal of 39.0%-40.4% after 7-9 days of ATAD for sludge with solid content of 5.24%-17.14%. The solubilization of sludge with different solid contents reached 40.1%-45.0% after THP. The rheological analysis indicated that the apparent viscosity of sludge was obviously reduced after THP at different solid contents. The increase in fluorescence intensity of fulvic acid-like organics, soluble microbial by-products and humic acid-like organics in the supernatant after THP and the decrease in fluorescence intensity of soluble microbial by-products after ATAD were detected by excitation emission matrix (EEM). The molecular weight (MW) distribution in the supernatant elucidated that the proportion of 50 kDa < MW < 100 kDa increased to 16%-34% after THP and the proportion of 10 kDa < MW < 50 kDa decreased to 8%-24% after ATAD. High throughput sequencing showed that the dominant bacterial genera shifted from Acinetobacter, Defluviicoccus and Norank_f__norank_o__PeM15 to Sphaerobacter and Bacillus during ATAD. This work revealed that solid content of 13%-17% was appropriate for efficient ATAD and rapid stabilization under THP.