Long-term monitoring of a full-scale parallel-unit downflow hanging sponge system with adaptive capacity for fluctuating wastewater flows in Japan
5 affiliations
- 1Regional Environment Conservation Division, National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki 305-8506 Japan
- 2Department of Civil Engineering and Architecture, National Institute of Technology (KOSEN), Maizuru College, 234 Shiroya, Maizuru, Kyoto, 625-8511 Japan
- 3Sanki Engineering Co., Ltd., 7-10-1 Chuorinkan, P.C., Yamato, Kanagawa 242-0007 Japan
- 4Water and Sewerage Division, Susaki City Hall, 2-3-11 Nishimachi, Susaki, Kochi, 785-0009 Japan
- 5Research Center for Water Environment Technology, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo, 113-8656 Japan
Abstract
This study presents a 30-month full-scale evaluation of a parallel-unit downflow hanging sponge (DHS) system with adaptive downsizing capability at the Susaki Sewage Treatment Plant, Japan. The DHS reactor comprised ten identical units operated in parallel, allowing capacity adjustment by varying the number of active units. The system (primary sedimentation tank → DHS → moving bed biological filter) was monitored under normal, low-temperature (winter), partial downsizing, and sponge sheet installation (upper part of the sponge media-filled segment) conditions. Dichromate-based chemical oxygen demand (CODCr), biochemical oxygen demand (BOD), total suspended solids (TSS), NH₄⁺–N, NO₃⁻–N, total nitrogen, and Escherichia coli were analyzed weekly and monthly to evaluate organic removal, nitrification, and microbial reduction. DHS effluent (77–85% CODCr, BOD removal, and a 1.5 log₁₀ reduction in E. coli) consistently met Japanese discharge standards. Downsizing to nine units, that is, reducing the hydraulic retention time, maintained effluent quality, confirming the system’s flexibility under declining inflows. Statistical comparison among operational periods showed no significant difference in NH₄⁺–N loading rate, whereas NH₄⁺–N removal efficiency was significantly higher after sponge sheet installation. The sponge sheet enhanced hydraulic dispersion and nitrification, reducing NH₄⁺–N from 16–19 to 9 mg N·L⁻1 and promoting NO₃⁻–N accumulation. Compared to the conventional activated sludge process previously employed, DHS used 83% less power and reduced excess sludge generation, demonstrating its potential as a sustainable, energy-efficient alternative for small- to medium-scale sewage treatment facilities with aging infrastructure. These findings highlight DHS as a resilient and socially viable solution for regions with declining populations, ensuring reliable wastewater treatment despite demographic and economic challenges.
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BibTeX
@article{takemura2026longterm,
title = {{Long-term monitoring of a full-scale parallel-unit downflow hanging sponge system with adaptive capacity for fluctuating wastewater flows in Japan}},
author = {Yasuyuki Takemura and Shinichi Yamazaki and Takashi Matsueda and Satoshi Ohmori and Akihiro Nagano and Motofumi Taniwaki and Noriko Tomioka and Masataka Aoki and Kazuaki Syutsubo},
journal = {Environmental Science and Pollution Research International},
year = {2026},
month = oct,
doi = {10.1007/s11356-026-38300-y},
url = {https://doi.org/10.1007/s11356-026-38300-y},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Long-term monitoring of a full-scale parallel-unit downflow hanging sponge system with adaptive capacity for fluctuating wastewater flows in Japan
AU - Yasuyuki Takemura
AU - Shinichi Yamazaki
AU - Takashi Matsueda
AU - Satoshi Ohmori
AU - Akihiro Nagano
AU - Motofumi Taniwaki
AU - Noriko Tomioka
AU - Masataka Aoki
AU - Kazuaki Syutsubo
PY - 2026
DA - 2026/10/13
JO - Environmental Science and Pollution Research International
DO - 10.1007/s11356-026-38300-y
UR - https://doi.org/10.1007/s11356-026-38300-y
AB - This study presents a 30-month full-scale evaluation of a parallel-unit downflow hanging sponge (DHS) system with adaptive downsizing capability at the Susaki Sewage Treatment Plant, Japan. The DHS reactor comprised ten identical units operated in parallel, allowing capacity adjustment by varying the number of active units. The system (primary sedimentation tank → DHS → moving bed biological filter) was monitored under normal, low-temperature (winter), partial downsizing, and sponge sheet installation (upper part of the sponge media-filled segment) conditions. Dichromate-based chemical oxygen demand (CODCr), biochemical oxygen demand (BOD), total suspended solids (TSS), NH₄⁺–N, NO₃⁻–N, total nitrogen, and Escherichia coli were analyzed weekly and monthly to evaluate organic removal, nitrification, and microbial reduction. DHS effluent (77–85% CODCr, BOD removal, and a 1.5 log₁₀ reduction in E. coli) consistently met Japanese discharge standards. Downsizing to nine units, that is, reducing the hydraulic retention time, maintained effluent quality, confirming the system’s flexibility under declining inflows. Statistical comparison among operational periods showed no significant difference in NH₄⁺–N loading rate, whereas NH₄⁺–N removal efficiency was significantly higher after sponge sheet installation. The sponge sheet enhanced hydraulic dispersion and nitrification, reducing NH₄⁺–N from 16–19 to 9 mg N·L⁻1 and promoting NO₃⁻–N accumulation. Compared to the conventional activated sludge process previously employed, DHS used 83% less power and reduced excess sludge generation, demonstrating its potential as a sustainable, energy-efficient alternative for small- to medium-scale sewage treatment facilities with aging infrastructure. These findings highlight DHS as a resilient and socially viable solution for regions with declining populations, ensuring reliable wastewater treatment despite demographic and economic challenges.
SN - 0944-1344
SN - 1614-7499
ER -