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

Journal article (2024)

Authors

S.A. Trikannad Sanitary Engineering - CEG
Valentina Attiani Wageningen University & Research
P.W.J.J. van der Wielen Wageningen University & Research, KWR Water Research Institute
Hauke Smidt Wageningen University & Research
J.P. van der Hoek Waternet, Sanitary Engineering - CEG
D. van Halem Sanitary Engineering - CEG
Research Group
Sanitary Engineering (CEG) (TU Delft)
Copyright: © 2024 S.A. Trikannad, Valentina Attiani, Paul W.J.J. van der Wielen, Hauke Smidt, J.P. van der Hoek, D. van Halem
DOI
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https://doi.org/10.1016/j.jwpe.2024.105101
Schmutzdecke Ammonium Slow sand filters Scraping Ripening period Dissolved organic carbon
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Published Date

2024

Language

English

Faculty

Civil Engineering & Geosciences

Department

Water Management

Research Group

Sanitary Engineering

Abstract

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.