Rhizofiltration of urban effluent : microbial ecology and conceptual treatment mechanisms

Postma, Ferdinand (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Polluted urban runoff is a challenge that is globally met by governing bodies employing best management practices (BMPs). One such BMP is rhizofiltration, a novel type of phytoremediation BMP designed to mimic riparian ecology, with the goal of rapidly filtering large volumes of urban runoff before it enters rivers. The physical, chemical and biological mechanisms behind pollutant removal within a rhizofiltration system however, are still largely unknown. The overall aim of this study was therefore to assess the ability of a pilot scale rhizofiltration system to reduce concentrations of the physico-chemical pollutants ammonium, chemical oxygen demand (COD), nitrate, phosphate, sulphate and suspended solids, as well as microbial indicators of faecal pollution, in simulated urban runoff. The faecal indicators included coliphages, faecal coliforms, potentially pathogenic yeasts (PPY) and Salmonella and/or Shigella. To achieve this study’s aim a conceptual model was first constructed to identify potential bacterial mechanisms of pollution removal and to estimate the effect of physico-chemical conditions on microbial communities within the rhizofilter medium. Then, the overall performance of the filter was measured with regard to its bioregeneration and sorption capacity for the abovementioned pollutants. Sorption equilibrium, for most of the pollutants in the simulated runoff percolating through the filter, was reached within 45 minutes. Partial bioregeneration of the filter medium occurred within a week for ammonium, COD, phosphate and sulphate, as well as for the microbial pollutants. Evidence was subsequently obtained supporting the hypothesis that this regeneration is brought about by microbial activity, since metagenomic (16S rDNA high throughput sequencing) and phospholipid fatty acid (PLFA) analyses revealed the presence of viable dynamic microbial populations within the rhizofilter medium. Significant correlations between relative quantities of microbial operational taxonomic units (OTUs) and nutrient concentrations were also uncovered. The rhizofilter plants selected for a microbial community distinct from an unplanted control, however, this did not relate to differences in filter performance. This phenomenon was ascribed to the rapid percolation rate and design of the rhizofilter which maximizes aeration of the filter medium. It was contended that these properties, combined with the composition of the simulated urban runoff, selected for functionally similar organisms. The Actinomycetales were the most abundant bacterial group in both the planted and unplanted filter media. However, the plants appeared to select for Mycobacteriaceae and nitrifiers identified as the Nitrospiraceae. Among the transient OTUs in the filter media were taxa associated with the human gut, including the Campylobacteraceae, Moraxellaceae, Porphyromonadaceae and Prevotellaceae, while the Enterobacteriaceae containing faecal coliforms were below the detection limit of the metagenomic analysis. Strains of four Candida species consistently occurred in the simulated urban runoff. The abundance of these PPY in the influent and effluent of the rhizofilter were affected by physico-chemical factors. Subsequent metagenomic analysis of the fungal community within the filter media revealed a low relative abundance of candidal PPY. In short, the rhizofilter design and wastewater composition selected for copiotrophic aerobic microorganisms capable of mineralizing potentially recalcitrant organic carbon and driving oxidative processes such as nitrification whilst removing human microbial commensialists and pathogens.

AFRIKAANSE OPSOMMING: Besoedelde stedelike afloop is ’n uitdaging wat wêreldwyd deur bestuursliggame aangespreek word deur beste bestuurspraktyke (BBP). Een so ’n BBP is risofiltrasie, ’n nuwe tipe fitoremediëring BBP wat ontwerp is om oewerekologie na te boots, met die doel om groot volumes stedelike afloopwater vinnig te filtreer voor dit riviere bereik. Die fisiese, chemiese en biologiese meganismes wat die grondslag van risofiltrasie vorm, is egter nog grootliks onbekend. Die oorhoofse doel van hierdie studie was daarom om die vermoë van ‘n proefskaal risofiltrasiesisteem te toets vir die vermindering van konsentrasies van die fisikochemiese besoedelstowwe insluitende ammonium, chemiese suurstofvraag (CSV), nitraat, fosfaat, sulfaat en gesuspendeerde vaste stowwe, asook mikrobiese indikators van fekale besoedeling, in gesimuleerde stedelike afloop. Die fekale indikators sluit in kolifage, fekale koliforme, potensiële patogeniese giste (PPG) en Salmonella en/of Shigella. Om hierdie studie se doelwit te bereik, is ‘n konseptuele model gemaak om potensiële bakteriese meganismes van besoedelingverwydering te identifiseer en om die effek van fisikochemiese kondisies op mikrobiese gemeenskappe in die risofiltermedium te beraam. Daarna is die algehele werkverrigting van die filter gemeet ten opsigte van sy bioregenerasie en sorpsiekapasiteit van die bogenoemde besoedelstowwe. Sorpsie-ekwilibrium vir die meeste van die besoedelstowwe in die gesimuleerde afloop wat deur die filter geperkuleer het, is binne 45 minute bereik. Gedeeltelike bioregenerasie van die filtermedium het binne ‘n week plaasgevind vir ammonium, CSV, fosfaat en sulfaat, asook vir die mikrobiese besoedelstowwe. Bewyse is gevolglik gevind wat die hipotese ondersteun dat hierdie regenerasie aangewakker is deur mikrobiese aktiwiteit, aangesien metagenomiese (16S rDNA hoë omset volgordebepaling) en fosfolipied-vetsuuranalises (FLVS) die teenwoordigheid van lewensvatbare dinamiese mikrobiese populasies in die risofiltermedium aan die lig gebring het. Beduidende korrelasies tussen relatiewe hoeveelhede van mikrobiese operasionele taksonomiese eenhede (MOTE) en nutriëntkonsentrasies is ook blootgelê. Die risofilter het vir ‘n mikrobiese gemeenskap geselekteer wat verskil van die ongeplante kontrole, hoewel dit nie aanleiding tot verskille in filterwerking gegee het nie. Hierdie verskynsel is toegeskryf aan die vinnige perkuleringstempo en ontwerp van die risofilter wat belugting van die filtermedium optimaliseer. Dit is geargumenteer dat hierdie eienskappe, saam met die samestelling van die gesimuleerde stedelike afloop, vir funksioneel eenderse organismes selekteer. Die Actinomycetales was die algemeenste bakteriese groep in beide die geplante en ongeplante filtermedia. Dit het egter voorgekom of die plante selekteer vir Mycobacteriaceae en nitrifiseerders wat as die Nitrospiraceae geïdentifiseer is. Onder die kortstondige MOTE in die filtermedia was taksa wat geassosieer word met die menslike dermkanaal, soos die Campylobacteraceae, Moraxellaceae, Porphyromonadaceae en Prevotellaceae, terwyl die Enterobacteriaceae-bevattende fekale koliforme laer as die waarnemingsvlak van die metagenomiese analise was. Stamme van vier Candida spesies het gereeld in die gesimuleerde stedelike afloop voorgekom. Die talrykheid van hierdie PPG in die invloei en uitvloei van die risofilter is deur fisikochemiese faktore beïnvloed. Daaropvolgende metagenomiese analise van die fungusgemeenskap in die filtermedia het daarop gedui dat Candida spesies 'n lae relatiewe voorkoms gehad het. Kortom, die risofilter en afvalwatersamestelling selekteer vir kopiotrofiese aerobe mikroörganismes wat in staat is om potensieel moeilik afbreekbare organiese koolstof te mineraliseer en oksidatiewe prosesse soos nitrifikasie te dryf, terwyl dit menslike kommensialiste en patogene verwyder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98274
This item appears in the following collections: