Recovery of microbial biomass and purification performance after scraping of full-scale slow sand filters

Shreya Ajith Trikannad*, Valentina Attiani, Paul W.J.J. van der Wielen, Hauke Smidt, Jan Peter van der Hoek, Doris van Halem

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Slow sand filters (SSFs) are widely used in drinking water production to improve microbial safety and biological stability of water. Full-scale SSFs are maintained by scraping the biomass-rich top layers of sand. The period of downtime required for filter recovery after scraping is a major challenge due to limited knowledge of the re-stabilisation of purification processes. This study examined the recovery of microbial biomass, and removal of dissolved organic carbon (DOC) and ammonium (NH4+) in water phase and/or on sand along the depth of a scraped full-scale SSF. Scraping reduced microbial biomass on sand in the top layers, while the main prokaryotic taxa remained unaltered. Cellular ATP (cATP) and intact cell counts (ICC) in water sampled from the top layers increased, indicating a temporary disruption in functionality for 37 days. However, stable concentrations of cATP and ICC and similar microbial community composition in the effluent after scraping revealed that deeper layer biofilms offset any scraping effect. Consistent DOC and NH4+ removal after scraping showed that deeper layers effectively performed the role of the top layer. These findings highlight the resilience and robustness of microbial communities in mature full-scale SSFs and their contribution to water treatment efficiency after disturbances caused by scraping.
Original languageEnglish
Article number105101
Number of pages12
JournalJournal of Water Process Engineering
Publication statusPublished - 2024


  • Slow sand filters
  • Schmutzdecke
  • Scraping
  • Ripening period
  • Dissolved organic carbon
  • Ammonium


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