The effects of temperature and mean cell residence time (MCRT) on processes involved in biological nitrogen and phosphorus removal were investigated by operating pilot-scale continuous-flow reactors over a range of temperatures and MCRITs. Two systems were operated as high-rate University of Cape Town (UCT) biological nutrient removal (BNR) processes. A third system was operated as a conventional, fully aerobic activated sludge system for comparison. Less aerobic volume was needed to achieve complete nitrification in the BNR system than in the conventional system when temperature and MCRT conditions were suitable for complete nitrification. This occurred at 15 d MCRT and temperatures from 10 to 20 °C., and at 5 d MCRT and 20 °C. However, the BNR system was more susceptible to nitrifier washout at 5 d MCRT and temperatures of 10 and 15 °C. Although less volume was needed for complete nitrification in the BNR system, specific nitrification rates and the degree of nitrification were equal in the two systems when compared on the basis of aerobic MCRT. This phenomenon occurred because the MLVSS concentrations were higher in the aerobic zone of the BNR system than in the conventional system for the same organic loading and total MCRT. Nitrification and denitrification rates were a function of MCRT and temperature, with temperature having a greater effect at lower MCRTs. Batch experiments showed that anoxic uptake of phosphorus occurred, although at a much lower rate than aerobic uptake. Biological phosphorus removal was adversely affected by colder temperatures. Operation of the BNR process at the lowest MCRT which provided complete nitrification prevented washout of phosphorus removal organisms, and provided the best combined nitrogen and phosphorus removal when phosphorus removal was COD-limited. Higher MCRIs were optimal under P-limiting conditions. Anaerobic stabilization ranging from 8% to 27% was measured in the BNR system, and was a function of temperature at a 15 d MCRI. A mechanism for anaerobic stabilization was proposed. Yield coefficients for the BNR and the conventional system were equal and were 0.41 mgVSS/mgCOD. The decay rate in the BNR system, 0.063 d⁻¹, was lower than the decay rate in the conventional system, 0.110 d⁻¹. This resulted in higher MLVSS concentrations in the BNR system. / Ph. D.

Colloidal gas aphrons (CGAs) are typically a 55 to 70% dispersion of 50 +/- 40 micron-sized air bubbles in water. Generation of CGAs has proceeded to allow continuous production of up to 80 liters per minute. Previous laboratory testing has demonstrated the effectiveness of CGA flotation for removing fine particulates, such as coal fines, food wastes, phosphate slimes, algae, as well as oils from contaminated solutions. This study involved comparing CGA flotation versus dissolved air flotation (DAF) in a wastewater treatment sludge media. Initially, laboratory tests were conducted to see if field testing was warranted, and to screen possible surfactant chemicals to be used in any such field testing. Three surfactants were tested individually; sodium dodecylbenzene sulfonate (NaDBS), alkyl dimethyl benzyl ammonium chloride (BTC-824), and cetyl pyridinium chloride (CPC). From the laboratory results and observations, it appeared that the CGA flotation tests using both NaDBS and CPC were more effective than DAF. Tests using BTC-824 were inconsistent due to bubble instability. Overall, the laboratory results and observations seemed encouraging, and field testing was initiated. Next, four field tests were conducted at Pepper's Ferry Regional Wastewater Treatment Authority (PFRWTA) in which CGA flotation was used to try and enhance the performance of a DAF system. Tests were conducted by adding CGAs directly into the sludge influent line of PFRWTA's DAF system. Although CPC gave the best laboratory results, NaDBS was used in the field testing due to its availability and cost. Results from all four field tests showed that a more concentrated effluent sludge was obtained when CGA flotation was used to enhance DAF. The field test results for the raffinates were inconclusive. Overall, the results from the field testing seem promising. From these tests, CGA flotation appears to be an improvement over DAF in producing more concentrated effluent sludges when tested in a wastewater treatment sludge media. CGA flotation could enhance and/or possibly replace DAF in certain industrial applications. / Master of Science

Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Can salts present in an aqueous industrial effluent be retained by the [me ash that is produced as a by-product of gasification or by power stations utilising coal as the raw material? In order to answer this question, the actual chemistry that occurs during the mixing and settling process, needs to be understood. At the Sasol Secunda petrochemical plants in South Africa, ash is produced as a byproduct from the gasification of coal, and by the coal-fired power stations (steam plants). The [me portion of the ash (± 50J.lm in diameter) is disposed of through the use of a closed loop wet ash disposal system. The ash is transported as a slurry to the disposal sites (ash darns). The industrial effluent used to transport the ash consists mainly of the recycled ash effluent, known as clear ash effluent (CAE), as well as a variety of process waste streams containing high concentrations of salts. This mixture of ash and water is pumped to ash dams, where the ash is allowed to settle and is therefore separated from the effluent. From the ash darns the effluent flows into evaporation dams, and finally into CAE dams before being returned to the ash plant in Sasol 2 and 3 to be mixed once again with the ash. During this contact time of the ash with the water certain chemical reactions may occur. If one understands what chemical reactions occur during this process, and under what conditions they occur, then it will be possible to utilise the ash disposal system to its full potential, possibly enhancing the salt retention ability. An investigation was thus conducted into what processes actually occurs during the entire ash water contact period. The overall aim of the project was to obtain an understanding of the functioning of the [me ash disposal system so that its efficiency can be improved upon, and furthermore, so that the ash darns can be utilised more effectively in retaining salts. This investigation focussed on the chemical reactions that occur when an industrial effluent is mixed with fine ash, and consisted of four main aspects: • A literature survey on related issues. • An analysis and evaluation of the changes that occur in the actual disposal system. • Laboratory column experiments to investigate, in more detail, the different chemical reactions, which occur during the different stages of the disposal process. • The drilling of boreholes into the ash dams to obtain core material at a variety of depths and locations for analysis purposes. From this investigation it was concluded that salts are retained in the ash dams; based on the results obtained from the laboratory column experiments and the production rate of the fine ash from Sasol 2 and Sasol 3, the potential amount of salts that can be removed from the system (either due to precipitation or water retention in the ash dams) is approximately 95 tons/day. The salts that were found to be most pertinent to the wet ash disposal system utilised at Sasol, Secunda, are Ca, S04, Na, and Cl. Of these, Ca, S04 and Na were identified in literature to be the components most commonly associated with fly ash leachate. The Ca chemistry, which occurs in the ash disposal system, was explored extensively. Is was found that Ca, which is initially present in the fresh fine ash as lime, is leached from the ash into the effluent, where it reacts with carbon dioxide in the atmosphere, and is therefore removed from the system due to the precipitation of calcite. Sodium, S04, and Cl were all found to be retained in the ash; the S04 appears to be retained in a stable form within the ash, not merely due to hydraulic retention, which suggests that the ash system has the potential to act as a salt sink for S04 ions. The mechanism of salt retention in the ash darns was found to be predominantly by means of hydraulic retention, and therefore the salts have the potential to be flushed out of the ash dams into the underlying soil material. However, results from the core drilling exercise revealed that there doesn't appear to be a significant seepage of elements from the ash fill material into the underlying vertisol material. Some components (AI, Fe, Na, K, Mg, Cr, P, Ti and V) from the older, and inactive ash dam, do appear to have percolated into the underlying material. However, a significant amount of water, and therefore salts, are still retained in the ash dam. In terms of the mineralogical composition of the ash dams, a significant difference was observed between the mineral phases present in the ash fill material of an active and an inactive ash dam. Ettringite was detected throughout the borehole drilled into the inactive ash darn, and was not evident at all in the core material from the two boreholes drilled into the active dam, which suggests that this mineral is formed in the ash darns over a long time period. The minerals quartz and mullite were found in the fresh [me ash as well as in most of the core material obtained from the drilling exercise. The mineralogical composition of the ash fill samples, from the boreholes drilled into the centre of the active and inactive ash darns, was found to be very consistent with depth. This finding, combined with the fact that the chemical composition of the core samples varied more significantly in the borehole located near the edge of the active fine ash darn, indicated that the lateral position of the ash in the ash dam influences the chemical reactions that occur. Overall, from this investigation it was concluded that although the chemistry, involved in the mixing of an industrial effluent with fine ash, is extremely complex and site-specific, it is possible to determine the most significant changes which occur within a wet ash disposal system. Besides providing one with a better understanding of the working of the Secunda ash disposal system, the results of this investigation have also provided the framework for future research on this topic and related issues, i.e. the construction of a pilot scale ash darn set-up; further column experiments to investigate the extent to which S04 ions can be removed from the system; the influence of the addition of CO2 to the system; and more extensive core drilling in the vicinity of the ash darns. / AFRIKAANSE OPSOMMING: Kan soute teenwoordig in 'n industriële uitvloeisel teruggehou word in fynas geproduseer as neweproduk van steenkoolkragsentrales? Om 'n antwoord op hierdie vraag te kry, moet die chemiese reaksies wat gebeur tydens die meng en wegdoening van die as en aswater verstaan word. By die Sasol petrochemiese aanlegte in Secunda, Suid Afrika, word fynas geproduseer as 'n neweproduk in die vergassing en die stoomopwekkingprosesse. Die fynas (50)lm diameter) word weggedoen deur 'n geslote nat asstelsel. Die industriële uitvloeisel wat gebruik word vir die vervoer van die as bestaan hoofsaaklik uit hergebruikte aswater (genoem CAE - clear ash effluent), asook 'n verskeidenheid ander prosesafvalstrome wat hoë konsentrasies soute bevat. Die mengsel van as en aswater word in 'n asflodder gepomp na die asdamme, waar die as besink en sodoende geskei word van die waterfase (aswater). Vanaf die asdamme vloei die aswater na verdampingsdamme, en daarna na die CAE damme, vanwaar die CAE weer na die Sasol aanleg teruggepomp word om weer met as gemeng te word. Gedurende die kontak tussen die CAE en as gebeur sekere chemiese reaksies. Indien hierdie reaksies verstaan word, en onder watter toestande dit plaasvind, kan die asdamstelsel tot volle kapasiteit benut word deur moontlik die soutretensie binne die asdam te verhoog. 'n Ondersoek is gedoen om te bepaal watter prosesse plaasvind gedurende kontak tussen die as en water. Die doel van die ondersoek was om 'n beter begrip te kry oor die funksionering van die fynas-wegdoeningstelsel en om te bepaal of die asdamme meer effektiefbedryfkan word om moontlik meer soute te akkommodeer. Die ondersoek het uit vier hoofaspekte bestaan: • Literatuuroorsig, • 'n Analise en evaluering van die veranderinge wat plaasvind oor die asdamstelsel, • Laboratoriumskaal kolomeksperimente om in meer besonderhede die chemiese reaksies wat 'n rol in die aswaterstelsel speel, te bepaal, en • Die boor van toetsgate op die bestaande asdamme om boorkerne te ontleed by bepaalde dieptes en liggings. Uit die ondersoek is bevind dat soute wel in die asdamme behou word. As die kolomtoetse as basis gebruik word, en die produksietempo van fynas vanaf Sasol 2 en 3, dan kan daar 'n potensiële 95 ton soute per dag deur die asstelsel verwyder word (deur hoofsaaklik waterretensie en presipitasie van soute). Die mees prominente soute wat in die Sasol asstelsel voorkom is Ca, S04, Na, en Cl. Vanhierdie soute, is Ca, S04, en Na deur die literatuur geïdentifiseer as komponente wat met vliegas loog geassosieer word. Die Ca chemie, wat in die asstelsel plaasvind, is in besonderhede ontleed. Dit is bevind dat Ca, teenwoordig in die vars fynas as kalk, vanuit die as in die aswater geloog word, waar dit dan met atmosferiese CO2 reageer en dan vanuit die stelselverwyder word deur die presipitasie van kalsiet. Natrium, S04 en Cl word in die as teruggehou. Dit wil voorkom asof die S04 in 'n stabiele vorm in die as teruugehou word, nie net deur die hidrouliese retensie nie en dat die asstelsel dalk as 'n potensiële sink vir S04 kan optree. Die meganisme van soutretensie in die asdamme is hoofsaaklik deur hidrouliese retensie, met die gevolg dat die soute potensieel in die onderliggende grond uitgewas kan word. Die resultate van die boorkernondersoek wys egter dat daar nie beduidende uitwassing van hierdie soute in die grond is nie. Dit wil voorkom of sekere komponente (Al, Fe, Na, K, Mg, Cr, P, Ti en V) van die ou en onaktiewe asdam in die grond geloog is. 'n Beduidende verskil was gevind tussen die minerale fases in die asmateriaal van die aktiewe en onaktiewe asdamme. Ettringiet was teenwoordig deur die hele diepte van die boorkern van die onaktiewe dam, maar was nie teenwoordig in beide boorkerns van die gate op die aktiewe asdam nie. Dit impliseer dat hierdie mineraaloor 'n langer tyd gevorm word. Kwarts en mulliet was deurentyd in al die boorkerne teenwoordig. Die mineralogie van die boorkern van die middel van die aktiewe asdam was baie konstant met diepte (in teenstelling met dié van die boorkern op die kant van die asdam) wat daarop dui dat die laterale posisie van die as in die asdam die chemiese reaksies wat mag plaasvind kan beïnvloed. Die ondersoek bevestig dat alhoewel die chemiese reaksies betrokke in die aswaterstelsel baie kompleks en liggingspesifiek is, die mees beduidende veranderinge wat in die asstelsel plaasvind, wel bepaal kan word. Die ondersoek het benewens 'n beter begrip van hoe die asdamme reageer, ook 'n raamwerk gegee vir verdere navorsing in hierdie veld, bv. die bou van 'n loodsskaal-asdam, verdere kolomtoetse om die vermoë van die asstelsel om S04 ione te verwyder te bepaal en die invloed van gemanipuleerde kalsiet presipitasie deur die byvoeging van CO2.

Emerging contaminants (EC) are unregulated substances that have entered the environment for as long as they have been produced through human activities. Within the ECs family, pharmaceuticals and personal-care products (PPCPs) is a class of the most common pollutants employed in everyday urban activities. Current regulatory approaches are inadequate to address these contaminants and the presence of such chemicals in the aquatic environment and their potential deleterious effects has received an increasing attention from the public and scientific community. Influent and effluent wastewater from Daspoort Waste Water Treatment Works (WWTW), which treats wastewater from the central Pretoria area, were sampled and analysed from January to December 2015 for pharmaceuticals and personal care products by gas chromatography time of flight mass spectrometry (GC/TOF-MS). Thirteen pharmaceuticals were selected for focused study in wastewater which include; (acetaminophen, bisphenol A, carbamazepine, diclofenac, 17α-estradiol, 17β-estradiol, estriol, famciclovir, fenoprofen, ibuprofen, primidone, progesterone and testosterone) based on the criteria of their prescription volumes in both private and public health sector in South Africa. The development of a sensitive and reliable analytical method for the simultaneous determination of PPCPs in aquatic samples was carried out; using a combined solid-phase extraction (SPE) isolation and clean-up, followed by derivatization prior to GC/TOFMS determination. A seven points concentration levels linear calibration curve with correlation coefficient (R2) ranged from 0.9988 to 0.9999 was obtained. The limits of detection (LOD) and the limit of quantification (LOQ) ranged from 0.01-0.27 μg L-1 and 0.03-0.91 μg L-1 respectively for target PPCPs. Repeatability studies gave % RSD within 3.41 – 11.72 % for peak area. The % RSD values for reproducibility studies were 2.88 – 9.91% for peak area over the three concentrations (ibuprofen: 0.4, 2 and 8 μg L-1) evaluated during 5 days. These results indicated that the proposed method has excellent precision as evidenced by very stable peak area for the analytes. The recovery testing carried out, exhibited recoveries ranging from at least 82-115% and 81-115 % in tap water and Milli-Q water respectively, with % RSD less than 12%, showing that the overall PPCPs determination method including the extraction procedure was a repeatable method.. The method was applied to target PPCPs from Daspoort influent and effluent wastewater in Pretoria (South Africa). Natural hormones and antiviral drug were not detected in all the samples analysed by this method. Bisphenol A, acetaminophen, carbamazepine, ibuprofen and diclofenac were detected at low concentrations, ranging from 0.052-135.42 μg L-1 in wastewater. The level of bisphenol A, primidone, carbamazepine, ibuprofen and diclofenac in effluent wastewater were found to be lower in comparison to the influent. Several other non-target compounds, such as benzophenone, caffeine, methocarbamol, efavirenz, atrazine, dioxaphetyl butyrate, nevirapine, androsta-1,4-diene-3,17-dione, cis-tramadol, batyl alcohol, paredrine, 7-acetyl-6-ethyl-1,1,4,4-tetramethyltetralin, propylparaben, eugenol, cholesterol, stigmasterol, guaifenesin, benzyl benzoate, 4-tert-octylphenol, diethyltoluamide, dicyclomine, terbuthylazine, spiroxamine, bis(2-ethylhexyl) phthalate, bumetrizole , were also detected in the wastewater sample using the developed method. / Chemistry / M. Sc. (Chemistry)