{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,27]],"date-time":"2026-10-27T00:35:48Z","timestamp":1793061348834,"version":"4.5.0"},"reference-count":29,"publisher":"Springer Science and Business Media LLC","issue":"36","license":[{"start":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T00:00:00Z","timestamp":1791849600000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"},{"start":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T00:00:00Z","timestamp":1791849600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"}],"content-domain":{"domain":["link.springer.com"],"crossmark-restriction":false},"short-container-title":["Environ Sci Pollut Res"],"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>\n                    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\u2009\u2192\u2009DHS\u2009\u2192\u2009moving 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 (COD\n                    <jats:sub>Cr<\/jats:sub>\n                    ), biochemical oxygen demand (BOD), total suspended solids (TSS), NH\u2084\u207a\u2013N, NO\u2083\u207b\u2013N, total nitrogen, and\n                    <jats:italic>Escherichia coli<\/jats:italic>\n                    were analyzed weekly and monthly to evaluate organic removal, nitrification, and microbial reduction. DHS effluent (77\u201385% COD\n                    <jats:sub>Cr<\/jats:sub>\n                    , BOD removal, and a 1.5 log\u2081\u2080 reduction in\n                    <jats:italic>E. coli<\/jats:italic>\n                    ) consistently met Japanese discharge standards. Downsizing to nine units, that is, reducing the hydraulic retention time, maintained effluent quality, confirming the system\u2019s flexibility under declining inflows. Statistical comparison among operational periods showed no significant difference in NH\u2084\u207a\u2013N loading rate, whereas NH\u2084\u207a\u2013N removal efficiency was significantly higher after sponge sheet installation. The sponge sheet enhanced hydraulic dispersion and nitrification, reducing NH\u2084\u207a\u2013N from 16\u201319 to 9\u00a0mg N\u00b7L\u207b\n                    <jats:sup>1<\/jats:sup>\n                    and promoting NO\u2083\u207b\u2013N 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.\n                  <\/jats:p>","DOI":"10.1007\/s11356-026-38300-y","type":"journal-article","created":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T05:35:22Z","timestamp":1791869722000},"page":"17285-17299","update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Long-term monitoring of a full-scale parallel-unit downflow hanging sponge system with adaptive capacity for fluctuating wastewater flows in Japan"],"prefix":"10.1007","volume":"33","author":[{"given":"Yasuyuki","family":"Takemura","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shinichi","family":"Yamazaki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takashi","family":"Matsueda","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Satoshi","family":"Ohmori","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akihiro","family":"Nagano","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Motofumi","family":"Taniwaki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Noriko","family":"Tomioka","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Masataka","family":"Aoki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4181-2171","authenticated-orcid":false,"given":"Kazuaki","family":"Syutsubo","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,10,13]]},"reference":[{"key":"38300_CR1","doi-asserted-by":"publisher","DOI":"10.1016\/j.heliyon.2021.e06375","volume":"7","author":"D Bernal","year":"2021","unstructured":"Bernal D, Restrepo I, Grueso-Casquete S (2021) Key criteria for considering decentralization in municipal wastewater management. 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Sanki Engineering Co., Ltd. contributed technical advice on the reactor configuration but had no role in data analysis, interpretation, or the decision to submit the manuscript for publication. All other authors declare no competing interests.","order":4,"name":"Ethics","label":"Competing interests","group":{"name":"EthicsHeading","label":"Declarations"}}]}}