Evaluating the Mechanisms and Efficiency of Johkasou Systems for Decentralized Domestic Effluent Treatment: A Review

Johkasou systems have emerged as quintessential examples of decentralized wastewater treatment technologies due to their compact design, easy operation, and robust resistance to mechanical impact attributes that are particularly effective in mitigating and treating rural domestic wastewater. Although the efficiency of the Johkasou process in removing nitrogen and phosphorus has been well-documented, a comprehensive synthesis of the underlying mechanisms and influencing factors is still elusive. This review seeks to elucidate these aspects by detailing the biogeochemical pathways involved in nitrogen and phosphorus removal, characterizing the key microbial consortia, and addressing the potential accumulation of nitrous oxide (N2O). Furthermore, the review critically examines the impact of various media used in Johkasou systems on nutrient removal efficacy, with a particular emphasis on nitrogen. It also proposes a range of practical adjustments to design parameters, including dissolved oxygen (DO), pH, temperature, and hydraulic retention time (HRT), to enhance process performance. Finally, the practical implementation of Johkasou systems and their integration with ancillary processes in actual domestic sewage treatment scenarios are synthesized, providing a theoretical foundation for advancing Johkasou methodologies in rural areas.