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

• Published in: Journal of water process engineering Vol. 60; p. 105101
• Main Authors: Trikannad, Shreya Ajith, Attiani, Valentina, van der Wielen, Paul W.J.J., Smidt, Hauke, van der Hoek, Jan Peter, van Halem, Doris
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2024
• Subjects: Ammonium; Dissolved organic carbon; Ripening period; Schmutzdecke; Scraping; Slow sand filters; Slow sand filters; Dissolved organic carbon; Schmutzdecke; Ripening period; Ammonium; Scraping
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.105101

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. [Display omitted] •The main prokaryotic taxa in mature SSF bed remain unchanged after scraping.•Scraping temporarily affects the functionality of the top layers.•The dominant taxa reside beyond the Schmutzdecke.•Deeper layers of mature SSFs offset any scraping effect on microbial biomass in the effluent, and DOC and NH4+ removal.•cATP and ICC are key indicators to assess SSF re-stabilisation when monitored over the entire filter height.