Biologically Active Filters: A Sustainable Treatment Process for Emerging Contaminants

With widespread occurrence and increasing concern of emerging contaminants in source water, the hypothesis that existing filters and adsorbents in water treatment plants can be converted to biologically active filters (BAFs) to treat these compounds was tested. The media included granular activated carbon (GAC) and anthracite/sand dual media, which were collected from two treatment plants. In a bench-scale study with duplicate columns, BAF performance was monitored studying DOC removal, UV₂₅₄ reduction, and adenosine triphosphate (ATP) concentration as function of depth. For GAC BAFs, greater oxygen consumption, increased pH drop, and greater DOC removal normalized to ATP were observed suggesting increased microbial activity as compared to dual-media BAFs. Sixteen emerging contaminants were spiked in the source water. At an 18 min EBCT, GAC BAFs were highly effective with overall removals greater than 80% without pre-ozonation; exceptions included tri(2-chloroethyl) phosphate (TCEP) and iopromide. With a 10 min EBCT, the degree of removal reduced with less than half removed at greater than 80%. The dual-media BAFs showed limited removals with only four compounds removed greater than 80% (acetaminophen, ibuprofen, trimethoprim, and 17β-estradiol), and 10 compounds reduced by less than 50% with either EBCT. Pre-ozonation (3 mg/L) improved the removal of PPCPs in GAC and to a greater extent in dual media at both EBCTs. The microbial community on BAF media is believed to play a crucial role in removal of natural organic matter and emerging contamiants. Next generation sequencing (Illumina MiSeq) was used to characterize the microbial communities in the influent, effluent, and media. Proteobacteria was observed to be most dominant bacteria in BAF influents and BAF media serving as a source for the latter. Planctomycetes phyla were dominant as well in both GAC and dual-media BAF. Based on a factorial analysis, media type was the most significant factor affecting the abundance of five bacterial phyla and 10 bacterial classes. EBCT impacted the abundance of the dominant bacteria phylum Proteobacteria at the phyla level, while the effect of pre-ozonation was observed to be significant at the class level for the two dominant bacteria, Proteobacteria and Planctomycetes.