Microbial ecology of E.coli removal mechanisms and drinking water production in slow sand filters exposed to emerging contaminants
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Slow sand filters (SSFs) are a water treatment technology which can produce high quality water through a combination of physical and the activity of their microbial community. SSFs are easy to operate and have and low energy demand, therefore they suppose an alternative to produce in an affordable and non-contaminant fashion. However, relatively little is known about the microbial ecology underpinning contaminants removal. This thesis explores the microbial ecology of E. coli removal mechanisms during drinking water production with SSFs exposed to the fourth types of estrogen (estrone, estradiol, estriol and ethynyl-estradiol) and five pharmaceuticals (atenolol, hydrochlorothiazide, salbutamol, valsartan and carbamazepine) In the first experimental chapter, impact of a commensal and an environmental E. coli strain on the SSFs microbial community structure was investigated, showing that the microbial ecosystem resisted the introduction of E. coli without changes in their structure. It was also proven that the environmental strain did not become naturalized in the filters biofilm. In the second experimental chapter impact of two emerging contaminants (estrogen and pharmaceuticals) on E. coli removal efficiency and SSFs microbial community structure was investigated. ECs did not decrease E. coli removal efficiency, however, SSFs exposed to the ECs had a differentiated prokaryotic community. Finally in the third experiment chapter, a DNA-SIP combined with amplicon sequencing approach with isotopically labelled E. coli was used to investigate the biological E. coli removal mechanisms and impact of ECs in those mechanisms. Results showed that the main predators in the filters were protozoa Vorticella, Arcella and Strobilidium, and also micro-crustacean Eudiaptomus and the nematode Tobrilus. similarities and differences in the eukaryotic groups (mainly protozoa) responsible of E. coli removal. Understanding the microbial ecology associated a key process such bacteria elimination is necessary to achieve better SSFs design and for predicting the filtration process performance based on their microbial ecology structure. It will also contribute to understand the protozoa grazing phenomenon as a driving factor on the microbial structure dynamics in both natural and engineered microbial communities.
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