Impacts of Biological Filtration on Disinfection Byproduct Control during Drinking Water Purification: A Critical Review

Biofiltration, particularly biological activated carbon and sand filtration, is widely implemented as a low-chemical, energy-efficient barrier to attenuate disinfection byproduct (DBP) precursors. However, biofilters are living, time-evolving ecosystems that can transition from a net “sink” to a net “source” of reactive precursors. This review synthesized evidence that biofiltration exhibits selective removal: hydrophobic and high-molecular-weight C-DBP precursors are preferentially removed, whereas hydrophilic N-DBP (e.g., HANs, NDMA) precursors readily break through and may be newly produced. The authors clarified the mechanistic basis of precursor generation, highlighting (i) biofilm turnover that releases intracellular organic matter enriched in amines and nucleic acids, (ii) continuous production and sloughing of soluble microbial products and extracellular polymeric substances that elevate protein-like DON, and (iii) media aging and stratification that diminish removal efficacy. Regression analysis estimated sink–source transition for N-DBP precursor removal at approximately log10(bed volumes) = 5.38 (∼240,000 bed volumes), a practical reference in drinking water treatment plants. Furthermore, the authors identified critical operational tipping points, including oxidant pre-exposure, temperature fluctuations, and nutrient stoichiometry, that can trigger this functional inversion. Finally, a risk-oriented framework is proposed, advocating for precursor-specific monitoring (e.g., fluorescence signatures) and intelligent process control to stabilize biofilter performance against emerging genotoxic risks.