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<p>The high-rate activated sludge (HRAS) process is an advanced biological wastewater treatment approach designed with short hydraulic retention time (HRT) and sludge retention time (SRT) to enhance rapid organic carbon uptake in sludge and enable energy recovery via anaerobic digestion. This review comprehensively examines the historical development, system configurations, and key operational parameters of HRAS—including HRT, SRT, dissolved oxygen (DO), and food-to-mass ratio (F/M)—and their effects on carbon capture, sludge production, and methane generation. The critical roles of dominant microbial community, particularly <i>Proteobacteria</i> and <i>Bacteroidetes</i>, in bioflocculation, organic matter stabilization, and nutrient transformation are highlighted. Mechanistic models (ASM1–ASM3) adapted for short-SRT HRAS systems are evaluated for their ability to predict carbon and nutrient flows and improve simulation accuracy. Operational challenges such as nutrient removal limitations, sludge settling, and emerging contaminants are critically discussed, along with potential strategies for performance enhancement. Furthermore, the review assesses the energy recovery potential and electricity savings achievable through HRAS implementation. These insights provide a foundation for optimizing HRAS performance and advancing sustainable wastewater treatment strategies worldwide.</p> Graphical Abstract <p></p>

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A Critical Review of Economic, Microbial, and Design Aspects of High-rate Activated Sludge Process: Is HRAS the Future of Sustainable Wastewater Treatment?

  • 期刊论文

  • 发表日期：

    2026年4月17日

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  • Ghazale Faridizad,
  • Mohammad Reza Mehrnia,
  • Elham Abdollahzadeh Sharghi

摘要

The high-rate activated sludge (HRAS) process is an advanced biological wastewater treatment approach designed with short hydraulic retention time (HRT) and sludge retention time (SRT) to enhance rapid organic carbon uptake in sludge and enable energy recovery via anaerobic digestion. This review comprehensively examines the historical development, system configurations, and key operational parameters of HRAS—including HRT, SRT, dissolved oxygen (DO), and food-to-mass ratio (F/M)—and their effects on carbon capture, sludge production, and methane generation. The critical roles of dominant microbial community, particularly Proteobacteria and Bacteroidetes, in bioflocculation, organic matter stabilization, and nutrient transformation are highlighted. Mechanistic models (ASM1–ASM3) adapted for short-SRT HRAS systems are evaluated for their ability to predict carbon and nutrient flows and improve simulation accuracy. Operational challenges such as nutrient removal limitations, sludge settling, and emerging contaminants are critically discussed, along with potential strategies for performance enhancement. Furthermore, the review assesses the energy recovery potential and electricity savings achievable through HRAS implementation. These insights provide a foundation for optimizing HRAS performance and advancing sustainable wastewater treatment strategies worldwide.

Graphical Abstract