RESUMEN
Regarding curtailing carbon emissions in wastewater treatment, the high-rate contact stabilization (HiCS) process outperforms others in removing dissolved organic matter (DOM) but struggles with poor settling performance. To boost operation performance and clarify the correlation between process parameters, DOM variations, effluent quality, and microbial metabolism within the HiCS system, the impacts of sludge properties on sludge settlement and organic matter (OM) capture efficiency were explored, and soluble fluorescent components in the DOM and extracellular polymeric substances (EPS) were identified and scrutinized. Results unveil that the feast/famine (F/F) regime in the HiCS process predominantly governs sludge activation in the stabilization phase, influencing sludge properties such as morphology characteristics, biological activity, and EPS secretion. At the same hydraulic retention time, reducing the sludge retention time (SRT) led to looser and smaller activated sludge flocs, increased microbial activity, and higher EPS production, particularly protein content in loosely bound EPS (LB-PN), which adversely impacted settling performance. High-throughput sequencing revealed that richness and diversity of the microbial community decreased with SRT. Acidobacteriota and Patescibacteria, associated with nitrifying and denitrifying bacteria, significantly decreased. EPS-producing Firmicutes increased, enhancing EPS secretion, while filamentous Chloroflexi decreased, aligning with a reduced organic mineralization rate. Settlement and biological activity emerged as key factors affecting OM recovery, peaking at 43.97% with a 4-day SRT. The ratio of the sum of tryptophan-like and tyrosine-like components to fulvic-like components ((C1+C2)/C3) was proposed as a fluorescence indicator, serving as a hub to connect operational parameters, F/F regime, sludge status and process performance. When this ratio falls within the range of 1.04-1.36 during the stabilization phase, HiCS sludge achieves optimal status for OM capture with low aeration energy consumption.
RESUMEN
Capturing the abundant organic matter residing in wastewater can not only reduce the emission of CO2 from the source, but the enriched organics can also be used for anaerobic fermentation to generate and offset energy consumption in wastewater treatment processes. The key is to find or develop low-cost materials that can capture organic matter. Herein, sewage sludge-derived cationic aggregates (SBC-g-DMC) were successfully prepared via a hydrothermal carbonization process coupled with a graft copolymerization reaction for recovering organic matter from wastewater. Based upon preliminary screening of synthesized SBC-g-DMC aggregates regarding grafting rate, cationic degree, and flocculation performance, SBC-g-DMC2.5 aggregate prepared with 60 mg of initiator, DMC-to-SBC mass ratio of 2.5:1, 70 °C, and 2 h of reaction time was selected for further characterization and evaluation. Results showed that SBC-g-DMC2.5 aggregate has a positively-charged surface over a wide pH range of 3-11 and a hierarchical micro-/nano-structure, endowing it with an excellent organic matter capture efficiency (97.2% of pCOD, 68.8% of cCOD, and 71.2% of tCOD). Meanwhile, SBC-g-DMC2.5 exhibits inappreciable trapping ability for the dissolved COD, NH3-N, and PO43-, guaranteeing the regular running of subsequent biological treatment units. Electronic neutralization, adsorption bridging, and sweep coagulation between cationic aggregates surface and organic matter were identified as the primary mechanisms for SBC-g-DMC2.5 to capture organics. This development is expected to provide a theoretical reference for sewage sludge disposal, carbon reduction, and energy recovery during municipal wastewater treatment.