Investigating the removal of Candida and other potential pathogens from wastewater via an experimental rhizofiltration system

Belford, Ian (2013-03)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Water is a requirement of life and its quality, as well as quantity, is very important for sustaining the world‟s economy and human population. However, microbial and chemical pollution of water systems is on the increase, and can mainly be attributed to urban runoff, domestic and industrial discharges, inadequate sanitation, as well as ageing water treatment facilities. Practical solutions for the treatment of runoff are necessary to ensure water systems remain clean and safe for both human use and crop irrigation. Consequently, the ability of a rhizofiltration system to remove chemical and microbial contaminants from urban runoff was evaluated. A rhizofiltration system was constructed at the Stellenbosch Sewage Works, into which settled sewage could be distributed to determine if the presence of reeds improved the removal of chemicals, indicator organisms, pathogens, and potentially pathogenic yeasts. Indications were obtained that settled sewage from the Stellenbosch Sewage Works was microbiologically and chemically comparable to samples collected from the polluted Plankenburg River after a four day settling period in the storage tank constructed for the rhizofiltration system. This showed that the influent of the rhizofiltration system could be considered as urban runoff after four days of settling in the tank. The planted (experimental) and unplanted (control) side of the rhizofiltration system showed similar removal rates with regard to suspended solids, ammonium, Chemical Oxygen Demand, phosphates and sulphates in the influent, which percolated through the system within 45 min. Microbiologically, the experimental side was more effective than the control side in terms of faecal coliform, yeast and Salmonella removal but no difference was found between the two sides with regard to coliphage removal. The majority of yeasts that were isolated belonged to the genus Candida, and the experimental side was more effective than the control side in removing these opportunistic pathogens from wastewater. During the same experiments a number of antibiotic resistant bacteria were isolated which seemed to proliferate within the filter, the majority of which formed part of the Burkholderia cepacia complex. Additionally, the experimental side of the filter was significantly more effective at removing faecal coliforms, potentially pathogenic yeasts and Salmonella trapped within the sand, compared to the control side, six days after the wastewater percolated through the filter. In vitro sand filter experiments revealed that the presence of B. cepacia in the sand may be responsible for trapping some of the Candida species present in wastewater as it percolates through the sand, and thus may prolong the period in which these yeasts are subjected to the antagonistic effect of root exudates or other microbes.

AFRIKAANSE OPSOMMING: Water is 'n voorvereiste vir lewe, en die kwantiteit en kwaliteit daarvan is vir die instandhouding van die wêreldekonomie en die menslike bevolking noodsaaklik. Mikrobiese en chemiese besoedeling is egter aan die toeneem en kan hoofsaaklik aan stedelike afloop, huishoudelike en industriële afval, onvoldoende sanitasie en verouderende fasiliteite vir die behandeling van water toegeskryf word. Praktiese oplossings vir die behandeling van afloop is noodsaaklik om te verseker dat die waterstelsels skoon en veilig sal bly vir beide menslike gebruik en die besproeiing van gewasse, en daarom is die vermoë van „n rhizofiltreerstelsel om chemiese en mikrobiese kontaminante uit stedelike afloop te verwyder, geëvalueer. 'n Rhizofiltreerstelsel is by Stellenbosch se rioolwerke gebou, waarin besinkte riool gepomp kon word om te bepaal of riete die verwydering van chemikalieë, indikatororganismes, patogene en potensiële patogeniese giste kon verbeter. Aanduidings is gevind dat besinkte riool van die Stellenboschse rioolwerke mikrobiologies en chemies vergelykbaar is met monsters wat vanuit die besoedelde Plankenburgrivier verkry is. Hierdie resultaat is verkry na vier dae besinking in die opgaartenk wat vir die rhizofiltreerstelsel gebou is. Dit dui aan dat die invloei van die rhizofiltreerstelsel as stedelike afloop beskou kan word na vier dae besinking in die tenk. Die beplante (eksperimentele) en onbeplante (kontrole) kante van die rhizofiltreerstelsel het vergelykbare verwyderingskoerse getoon ten opsigte van gesuspendeerde vastestowwe, ammoniak, “Chemical Oxygen Demand”, fosfate en sulfate in die invloei, wat binne 45 min deur die sisteem geperkoleer het. Mikrobiologies was die eksperimentele kant meer suksesvol as die kontrole kant in terme van die verwydering van fekale coliforme, giste en Salmonella, maar daar was geen verskil ten opsigte van die twee kante se verwydering van colifage gevind nie. Die meerderheid giste wat verwyder is, behoort aan die genus Candida, en die eksperimentele kant het dié oppertunistiese patogene meer suksesvol uit afvalwater verwyder. Gedurende dieselfde eksperimente is 'n aantal antibiotikumbestande bakterieë ook geïsoleer, wat blykbaar binne die filter vermeerder en waarvan die meerderheid deel gevorm het van die Burkholderia cepacia kompleks. Daarby was die eksperimentele kant van die filter beduidend meer effektief vir die verwydering van fekale kolivorme, potensieel patogeniese giste en Salmonella wat binne die sand vasgevang was, vergeleke met die kontrole kant, ses dae nadat die afval water deur die filter geperkoleer het. In vitro sand filter eksperimente het getoon dat die teenwoordigheid van B. cepacia in die sand verantwoordelik mag wees om van die Candida spesies teenwoordig in die afvalwater vas te vang soos dit deur die sand perkoleer, en daardeur die tydperk te verleng waarin die giste aan die antagonisitese effek van die wortelafskeidings of ander mikrobes blootgestel is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/79806
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