The impact of soluble microbial products on trace organic contaminant degradation
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With the increasing popularity of biological filtration for drinking water treatment, a better understanding is needed of the biological removal mechanisms of trace organic contaminants (TrOC). Microorganisms in drinking-water biofilters excrete soluble microbial products (SMP), which provide an additional carbon source to the heterotrophic microbial community. The primary objective of this research was to investigate if heterotrophic microorganisms that are acclimated to complex SMP produced by nitrifying microorganisms will transform TrOC at an increased rate as compared to heterotrophic microorganisms that are acclimated to simple carbon sources. Batch experiments were conducted with a mixed heterotrophic culture and a pure culture, Pseudomonas aeruginosa, fed either a simple organic (acetate) or SMP. After the cultures were acclimated to these carbon sources, they were spiked with two TrOC, 2- methylisoborneol (2-MIB) and geosmin. In addition, two controls were run: an azide control to account for sorption to biomass and a no-biomass control to account for sorption to glassware and volatilization. The removal of 2-MIB and geosmin in the cultures was monitored over time. These batch experiments demonstrated no substantial advantage in 2-MIB or geosmin biodegradation due to heterotrophic acclimation to this particular SMP as compared to acclimation to acetate. This result might have been influenced by the low specific ultraviolet absorbance (SUVA) of the SMP in this study (0.083 L/mg-min), which suggests a low degree of aromaticity in the mixture. However, the data suggest that these particular SMP instigate co-metabolic geosmin removal. To better understand the effect of nitrifier SMP on TrOC removal in drinking-water biofilters, future experiments should be conducted with several well-characterized, complex organic mixtures that have higher SUVA values than that of the SMP in this study; these mixtures could include natural organic matter isolated from surface water and SMP produced by a nitrifying biofilm.