Power Automation Equipment•2026•DOI: 10.16081/j.epae.202606001
The increasing penetration of renewable energy sources has introduced novel instability phenomena in power grids, such as sustained and repeated low-voltage ride-through events, which existing models fail to analyze or explain. This paper addresses the typical continuous-discrete hybrid characteristics of renewable energy generation systems at both the unit and station levels. It discusses the interwoven discrete multi-mode switching and continuous state evolution during faults, emphasizing the necessity of hybrid models. Four classes of hybrid models are compared, including hybrid automata, hybrid Petri nets, switching models, and piecewise affine models, with their applicable scenarios. For switching models and piecewise affine models, parameter identification methods are proposed, and their applicable scenarios are discussed. To tackle the challenge of aggregating dispersed renewable units with diverse discrete event states, a mechanism-data fusion hybrid model aggregation method is proposed. Future research directions for hybrid characteristic modeling of renewable energy generation systems are outlined. The review highlights that current hybrid models remain in an early stage, and mechanism-data fusion modeling is a promising supplement. Key challenges include balancing model complexity and accuracy, and addressing the contradiction between diverse transient behaviors and model universality.
Chinese Journal of Environmental Engineering•2026•DOI: 10.12030/j.cjee.202509020
The AAOA-MBR (anaerobic-anoxic-oxic-anoxic membrane bioreactor) process is widely used in municipal wastewater treatment, but its multi-stage internal recirculation complicates sludge retention time (SRT) and carbon source distribution. This study systematically regulated three reflux ratios (R1: membrane tank to oxic tank; R2: oxic tank to anoxic I tank; R3: anoxic II tank to anaerobic tank) in a pilot-scale system (0.24 m3·d−1) to reveal their effects on nutrient removal and membrane fouling. When R1:R2:R3 = 300%:200%:100%, effluent COD, TN, TP, and NH3-N met discharge standards. Reducing R1 and R2, thereby decreasing total reflux ratio from R=6 to R=3, shortened SRT, which suppressed nitrifier accumulation and increased effluent COD and TN, but decreased TP. High-throughput sequencing of anoxic I and oxic tanks showed that denitrifying bacteria (Thauera and Ottowia) relative abundances decreased from 0.68% to 0.42% and 0.51% to 0.24%, respectively, while the phosphorus-accumulating organism Candidatus_Accumulibacter increased from 0.78% to 1.12%, enhancing phosphorus removal. Additionally, lowering R1 to 200% caused sludge accumulation in the membrane tank, exacerbating membrane fouling. Thus, internal recirculation ratios must be adjusted based on influent characteristics to balance nutrient removal and membrane performance.
Chinese Journal of Environmental Engineering•2026•DOI: 10.12030/j.cjee.202509095
Biotrickling filtration (BTF) is a promising technology for treating volatile organic compounds (VOCs), but its application to hydrophobic alkanes like isohexane is hindered by mass transfer limitations, low degradation efficiency, and high operational costs. To address these bottlenecks, this study developed composite fillers by incorporating biochars derived from coffee grounds (CG), coconut shells (CS), corn cobs (CC), and activated carbon (AC) into a polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel matrix. The fillers were systematically characterized for water retention, pore structure, surface functional groups, crystalline phase, and acid-base resistance. Adsorption capacity, biofilm formation, and isohexane degradation were evaluated using the strain Rhodococcus ruber ZYH-ZY. Among the composites, CG@PVA-SA exhibited superior performance: water retention of 358 mg·g−1 (vs. 280 mg·g−1 for control), enhanced mesoporosity (specific surface area 4.77 m2·g−1, pore volume 11.46 cm3·kg−1, 10–30% higher than control), and robust acid-base stability (mass loss 21.37% at pH 2 and 31.98% at pH 10). Its saturated adsorption capacity reached 201.02 mg·kg−1 (vs. 114.24 mg·kg−1 for control), and it promoted bacterial colonization with a survival rate of 79.0% (vs. 37.2% for control). Static degradation tests showed 96.59% removal of 10 μL isohexane within 24 h. The abundant polar functional groups and suitable mesoporous structure of coffee ground biochar synergized with the PVA-SA matrix, enhancing water retention, mass transfer, and microbial colonization, thereby significantly improving isohexane purification. CG@PVA-SA is an ideal filler for BTF treatment of alkane VOCs, offering a cost-effective and efficient solution for industrial VOC control.