PhD. (Department of Biotechnology, Faculty of Applied and Computer Sciences), Vaal University of Technology. / South Africa utilises more antiretroviral (ARV) compounds per capita than any other nation in the fight against Human Immune Deficiency Virus (HIV) or acquired immunodeficiency syndrome (AIDS). Considering the main entrance pathways of antiviral drugs into the urban water cycle, excretions via urine or faeces from treated individuals play a dominant role. Due to the limited efficiency of conventional biological treatment (activated sludge), ARVs were detected in South African wastewater treatment plant effluents and surface waters. This poses a threat to aquatic environments due to the toxicity of ARVs and can be a potential contributor to ARV resistance due to persistent low level ARV exposure in the general population. This study investigated the efficacy of a moving bed biofilm reactor (MBBR) for ctybtri8nthe elimination of five ARV compounds i.e., tenofovir, emtricitabine, nevirapine, ritonavir and efavirenz from synthetic wastewater. Furthermore, the study also looked at the shift in microbial community compositions of biofilms in the MBBR due to exposure to the ARV compounds. Lastly, the ecotoxicity of the MBBR’s influent and effluent along with the actual ARV compounds were examined. The capacity of ARV degradation by the MBBR was investigated by spiking synthetic wastewater influent with 10 μg/L of five ARV compounds. Actual removal during treatment was assessed by sampling the inlets and outlets of the reactor. A targeted solid phase extraction method with Ultra High Pressure Liquid Chromatography coupled to quadrupole time of flight mass spectrometry (LC-MS/MS) was used to quantify the five ARV compounds. Microbial diversity (alpha-diversity) of seeded sludge from a full-scale municipal WWTP and biofilm samples from a laboratory scale MBBR system during pre- and post-introduction of ARV compounds was investigated by Illumina sequencing of the 16S rRNA gene. Ecological toxicity of the MBBR’s influent and effluent along with the five ARV compounds was determined using the Vibrio fischeri, Daphnia magna and Selenastrum capricornutum toxicity test kits and measured as EC50. After MBBR treatment; Nevirapine, Tenofovir, Efavirenz, Ritonavir and Emtricitabine all showed marked reduction in concentration between the influent and effluent of the MBBR. On average, the percentage removed for Nevirapine, Tenofovir, Efavirenz, Ritonavir and Emtricitabine was 62.31%, 74.18%, 93.62%, 94.18% and 94.87% respectively. Microbial diversity results demonstrated that the introduction of antiretroviral drugs affects the bacterial community composition and diversity considerably. For instance, Nitrosomonas, Nitrospira and Alicycliphilus were found to be higher in post introduction of ARV compounds biofilm samples than in biofilm samples before the introduction of ARV compounds. The EC50 for Tenofovir, Emtricitabine, Nevirapine, Ritonavir and Efavirenz were 82.5, 41.7, 39.3, 60.3 and 0.21 mg/L respectively for S. capricornutum; 81.3, 50.7, 49, 87.1 and 0.43 mg/L respectively for D. magna; and 73.5, 55.1, 41.3, 83.6 and 0.55 mg/L respectively for V. fischeri. The EC50 of the influent and effluent were found to be above 100% concentration, therefore they could not be specifically determined. The ecotoxicity results show that ARV compounds are potentially toxic to the environment, with efavirenz being more toxic than the other four ARV compounds tested. Since there were no toxic effects observed from the effluent, it can be assumed that mineralisation has occurred, or the transformation products are of less or equal toxicity to the influent (because the influent did not show any toxic effects to the model organisms tested).

Η δέσμευση του P με την μορφή του στρουβίτη θεωρείται από τις εναλλακτικές μεθόδους ανάκτησης του P από τα υγρά απόβλητα. Ο στρουβίτης χρησιμοποιείται ως αργά αποδεσμευόμενο λίπασμα, ως υλικό για την σταθεροποίηση αμμωδών εδαφών και συμβάλλει στην αειφόρο ανάπτυξη. Η καταβύθιση του στρουβίτη σε υπέρκορα διαλύματά του υπό σταθερή θερμοκρασία εξαρτάται από τον υπερκορεσμό και από την παρουσία ξένων ιόντων ή ουσιών. Στόχος της παρούσας διατριβής, ήταν η μελέτη της κινητικής της καταβύθισης του στρουβίτη σε συνθήκες σύστασης αντίστοιχες των αστικών αποβλήτων. Η θερμοδυναμική ανάλυση γίνεται με μοντελοποίηση του ειδομορφισμού της υδατικής φάσης ενώ η μελέτη της κινητικής με την μέθοδο του σταθερού υπερκορεσμού η οποία επιτρέπει την διερεύνηση του ρόλου των ιόντων Ca, των βαρέων μετάλλων και οργανικών υδατοδιαλυτών ενώσεων με μεγάλη ακρίβεια και επαναληψιμότητα. Επίσης, διερευνήθηκε ο ετερογενής σχηματισμός του στρουβίτη με την χρήση κρυσταλλικών φύτρων στρουβίτη, SiO2, CaCO3 και πυριτικής άμμου για την μελέτη της πρόσφυσης του καταβυθιζόμενου στερεού στα υποστρώματα αυτά. Προσδιορίστηκε επίσης το γινόμενο διαλυτότητας του στρουβίτη προσεγγίζοντας την ισορροπία από υπέρκορα και ακόρεστα διαλύματα σε διαφορετικές τιμές ιονικής ισχύος. Με την ενζυμική υδρόλυση πολυφωσφορικών οξέων από ειδικά ένζυμα, τις φωσφατάσες, και την σταδιακή απελευθέρωση φωσφορικών ιόντων επετεύχθη ελεγχόμενη καταβύθιση του στρουβίτη σε υψηλούς υπερκορεσμούς. Τέλος, μελετήθηκε η κινητική της διάλυσης του στρουβίτη σε ακόρεστα διαλύματα συνθετικού αποβλήτου και σε διαφορετικές τιμές pH. Από τα κινητικά αποτελέσματα, με βάση την κλασσική θεωρία τη πυρηνογένεσης, προέκυψαν στενά όρια μεταστάθειας του συστήματος και η επιφανειακή διάχυση των δομικών μονάδων ότι είναι το βραδύ στάδιο, το οποίο ελέγχει την καταβύθιση. Το ποσοστό απομάκρυνσης φωσφόρου ήταν 60-65% και από τις δοκιμές συσσωμάτωσης, προέκυψαν ελαφρά σταθεροποιημένα δοκίμια κατάλληλα για εφαρμογές σε καλλιεργήσιμα εδάφη. / Phosphorus precipitated in the form of struvite is a new prospective alternative in phosphorus recovery from wastewaters. Struvite may be used as a slow-released fertilizer, as fitment for stabilization of sandy soil areas and contributing towards sustainable development. Struvite precipitation in supersaturate solution at constant temperature depends on the supersaturation and the presence of foreign ions or substrates. The aim of this thesis was the investigation of struvite precipitation kinetics at conditions similar to municipal wastewaters. The thermodynamic analysis had been done by suitable speciation of aqueous medium while the kinetics of precipitation was investigated with constant solution supersaturation method. This method provides reliable and highly reproducible kinetics results of the effect of calcium ions, heavy metals and organic soluble compounds on the spontaneous precipitation of struvite. The heterogeneous formation of struvite was also investigated in order to examine struvite precipitated adhesion at different substrates. Struvite crystals, SiO2, CaCO3, and silicate sand were used to inoculate the supersaturated solutions. The thermodynamic solubility product of struvite was determined once equilibrium had been attained, when undersaturated and supersaturated solutions were allowed to reach equilibrium, at different ionic strengths values. Controlled struvite precipitation in solutions highly supersaturated was also achieved by the slow evolution of the supersaturation when sufficient phosphate was released from the enzymic action through the phosphatase mediated decomposition of polyphosphates. Finally, the kinetics of struvite dissolution was examined in undersaturate synthetic wastewater solutions at different pH values. The kinetics results, according to the classical nucleation theory, showed that the system stability range was very narrow and a surface diffusion controlled mechanism. A phosphorus recovery corresponding to 60-65% of the initially present phosphorus is feasible. Laboratory experiments using loose sand packs showed mildly consolidated agglomerates that can be used properly for cultivable land.