Bioaugmented Sand Filter Columns Provide Stable Removal of Pesticide Residue From Membrane Retentate

Abstract

Drinking water resources, such as groundwater, are threatened by pollution. The pesticide metabolite 2,6-dichlorobenzamide (BAM) is one of the compounds frequently found in groundwater. Studies have attempted to add specific BAM-degrading bacteria to sand filters at drinking water treatment facilities. This biotechnology has shown great potential in removing BAM from contaminated water. However, the degradation potential was formerly lost after ~2–3 weeks due to a decrease of the degrader population over time. The aim of the present study was to overcome the constraints leading to loss of degraders from inoculated filters. Our approach was threefold: (1) Development of a novel inoculation strategy, (2) lowering the flowrate to reduce washout of cells, and (3) increasing the concentration of nutrients hereunder the pollutant in a smaller inlet water stream. The two latter were achieved via modifications of the inlet water by applying membrane treatment which, besides producing an ultra-pure water fraction, produced a residual water stream with nutrients including BAM concentrated in ~ten-fold reduced volume. This was done to alleviate starvation of degrader bacteria in the otherwise oligotrophic sand filters and to enable a decreased flowrate. By this approach, we achieved 100% BAM removal over a period of 40 days in sand filter columns inoculated with the BAM-degrader Aminobacter sp. MSH1. Molecular targeting of the degrader strain showed that the population of degrader bacteria persisted at high numbers throughout the sand filter columns and over the entire timespan of the experiment. 16S rRNA gene amplicon sequencing confirmed that MSH1 dominated the bacterial communities of the inoculated sand filter columns at experimental termination. The community composition of the indigenous prokaryotes, based on beta diversity, in the sand filter columns was governed by the feed water type i.e., membrane retentate or untreated water.

Toward Improved Bioremediation Strategies: Response of BAM-Degradation Activity to Concentration and Flow Changes in an Inoculated Bench-Scale Sediment Tank

“…If a particularly concentrated retentate solution is used to periodically regenerate the sand filter system through backwashing, this could potentially provide for such a regular disturbance/priming and further stimulate the bacterial degradation capacity in the inoculated sand filter system such that it would show activity beyond regulation “at the brink of substrate supply”. In fact, our results are in line with recent work by Ellegaard-Jensen et al, who observed excellent biodegradation performance in their inoculated sand filter for up to 60 days, and a decline in the BAM removal rate to 60% after 150 days, suggesting that also therein restimulation may have been needed.…”

The complete genome of 2,6-dichlorobenzamide (BAM) degrader Aminobacter sp. MSH1 suggests a polyploid chromosome, phylogenetic reassignment, and functions of plasmids

“…MSH1 was previously shown to grow on several carbohydrates with slower growth on succinate and acetic acid as carbon sources compared to glucose, fructose, and glycerol 44 . These properties might be important when accommodating MSH1 with an auxiliary C-source for improved maintenance in the oligotrophic waters where it finds its main application 13 , 15 . On the other hand, MSH1 does not possess genes involved in carbon fixation which rules out autotrophic growth using CO 2 .…”

“…On the other hand, long-term population persistence and catabolic activity in the sand filters were impeded, likely due to a combination of predation and wash out 13 , 14 , as well as to physiological and genetic changes. Reducing flow rate and improving inoculation strategy have demonstrated prolonged persistence and activity of MSH1 in bioaugmented sand filters 15 . However, other studies indicate that MSH1 shows a starvation survival response, in the nutrient (especially carbon) limiting environment of DWTPs, leading to reduced specific BAM degrading activity 16 .…”

Potential and limitations for monitoring of pesticide biodegradation at trace concentrations in water and soil

“…Identification and isolation of one catabolic gene required the use of several tools such as next generation sequencing (NGS), qPCR as well as the use of tandem mass spectrometry (MS–MS) for a full proteomic and metabolomic analysis. The use of molecular tools was key to monitor BAM biodegradation in sand filter columns similar to the ones from drinking water facilities (Ellegaard-Jensen et al 2020 ). This study is only one example on how monitoring molecular tools can facilitate the use of pesticides bioremediation technologies and contribute to water protection.…”