Exploring organic micropollutant biodegradation under dynamic substrate loading in rapid sand filters

Area of Science:

• Environmental microbiology
• Water treatment technologies
• Environmental chemistry

Background:

• Microbial removal of trace organic micropollutants (OMPs) in drinking water is challenging.
• Nitrifying and heterotrophic bacteria in rapid sand filters (RSFs) can biodegrade OMPs using ammonia and dissolved organic matter (DOM).
• Substrate loading patterns significantly influence microbial activity and OMP biodegradation, but data at environmentally relevant concentrations are scarce.

Purpose of the Study:

• To investigate the biodegradation rates of 16 OMPs in RSFs under varying substrate loading rates and empty bed contact times (EBCT).
• To elucidate the impact of dissolved organic matter (DOM) and ammonia loading on OMP biodegradation mechanisms.
• To determine optimal operational strategies for enhancing microbial OMP removal in drinking water treatment.

Main Methods:

• Experimental investigation of 16 OMPs biodegradation rates in rapid sand filters (RSFs).
• Manipulation of substrate loading rates (ammonia and DOM) and empty bed contact times (EBCT).
• Analysis of OMP removal efficiencies and microbial activity under different operational conditions.

Main Results:

• Dissolved organic matter (DOM) enhanced paracetamol biodegradation but hindered 2,4-D, mecoprop, and benzotriazole removal via substrate competition.
• Lower DOM/benzotriazole ratios and higher ammonia loading improved benzotriazole biodegradation.
• Nitrification stimulation enhanced benzotriazole removal but inhibited heterotrophic OMP biodegradation; longer EBCT favored metformin but suppressed paracetamol and benzotriazole removal.

Conclusions:

• Optimal substrate loading for OMP biodegradation in RSFs is OMP-specific.
• Understanding substrate competition and co-metabolism is crucial for designing effective OMP removal strategies.
• Tailoring RSF operation based on priority OMPs can enhance microbial removal of micropollutants in drinking water treatment.