Slow sand filtration is a proven and sustainable technology for drinking water treatment in small communities. The process, however, is sensitive to lower water temperatures that can lead to decreased biological treatment, and high raw water turbidity levels that can lead to premature clogging of the filter and frequent cleaning requirements, resulting in increased risk of pathogen breakthrough. Multistage filtration, consisting of roughing filtration followed by slow sand filtration, can overcome these treatment limitations and provide a robust treatment alternative for surface water sources of variable water quality in northern climates, which typically experience water temperatures ranging down to 2&deg;C. Prior to this study, however, multistage filtration had yet to be systematically challenged in colder climates, including testing of its performance under increased hydraulic loadings and elevated influent turbidity together with cold water conditions. The primary goal of this research was to demonstrate the reliability of multistage filtration for small communities in northern climates with reference to the Ontario Safe Drinking Water Act. In this research, testing was conducted on two different pilot multistage filtration systems and fed with water from the Grand River, a municipally and agriculturally impacted river in Southern Ontario. One system featured pre-ozonation and post-granular activated carbon (GAC) stages, and shallower bed depths in the roughing filter and slow sand filter. The other system featured deeper bed depths in the roughing filter and slow sand filter, two parallel roughing filters of different design for comparison, and a second stage of slow sand filtration for increased robustness. Removal of turbidity, total coliforms, and fecal coliforms under a range of influent turbidities (1 to >100 NTU), water temperatures (~2 to 20&deg;C), and hydraulic loading rates (0. 2 to 0. 8 m/h) were investigated. In addition, the slow sand filters in each pilot system were challenged with high concentrations (~10⁶ oocyst/L) of inactivated <i>Cryptosporidium parvum</i> oocysts. The performance of both pilot multistage filtration systems was highly dependent on the biological maturity of the system and its hydraulic loading rate. In a less mature system operating in cold water conditions (<5&deg;C), effluent turbidity was mostly below 0. 5 NTU during periods of stable influent turbidity (no runoff events) and a hydraulic loading of 0. 4 m/h, however, runoff events of high influent turbidity (>50 NTU), increased hydraulic loadings (0. 6 m/h), and filter cleaning occasionally resulted in effluent turbidity above 1 NTU. Furthermore, in a less mature system operating during runoff events of high turbidity, reducing the hydraulic loading rate to 0. 2 m/h was important for achieving effluent turbidity below 1 NTU. However, in a more mature system operating in warm water conditions (19-22&deg;C), effluent turbidity was consistently below 0. 3 NTU at a hydraulic loading rate of 0. 4 m/h, and below 0. 5 NTU at 0. 8 m/h, despite numerous events of high influent turbidity (>25 NTU). It remains to be seen whether this performance could be sustained in colder water temperatures with a fully mature filter. Removal of coliform bacteria was occasionally incomplete in a less mature multistage system, whereas, in a more mature system operating in warm water conditions (>9&deg;C), removal was complete in all measurements. Furthermore, the average removal of <i>Cryptosporidium</i> was greater than 2. 5 logs in both systems (with hydraulic loading rates ranging from 0. 4 to 0. 8 m/h) and improved with increased filter maturity. Each individual stage of the multistage system was an important treatment barrier in the overall process of turbidity and pathogen removal. The roughing filter was not only important for protecting the slow sand filter from solids loading and increasing its run length, but was also a significant contributor to coliform removal when the system was less mature. Removal of turbidity was significantly improved when the roughing filter was more mature, suggesting that biological treatment was an important treatment mechanism in the roughing filter. Although pre-ozonation was used mainly for the removal of organic carbon and colour, it achieved complete removal of coliform bacteria and was also suspected to be important for enhanced removal of turbidity. The second slow sand filter in series provided additional robustness to the process by reducing effluent turbidity to below 1 NTU during cold water runoff events of high turbidity and increased hydraulic loadings (0. 6 m/h), while achieving effluent below 0. 3 NTU during normal periods of operation. It also provided additional removals of coliforms under challenging operating conditions, and contributed an additional average removal of <i>Cryptosporidium</i> of 0. 8 logs, which resulted in cumulative removal of 3. 7 logs, approximately 1 log greater than all the other challenge tests. Collectively, the entire multistage system performed well with water temperatures ranging down to 2&deg;C, limited filter maturity, elevated raw water turbidities, and increased hydraulic loading rates. Its ability to meet the current Ontario turbidity regulations and greater than 2 log removal of <i>Cryptosporidium</i> over a range of operating conditions, with little or no process adjustment, is a testament to the robustness and minimal maintenance requirements of the process, which are desirable attributes for small water systems that are often located in rural areas. While this research demonstrated the performance of multistage filtration using pilot scale testing, it is important to note that full-scale plants tend to produce significantly better results than pilot facilities, due to long term biological maturation of the system. Overall, multistage filtration is a sustainable and cost-effective technology that, through this research, appears to be a safe, reliable, and robust treatment alternative for small and non-municipal water systems in North America and the developing world. Further, based on its performance with challenging influent water quality and cold water conditions, multistage filtration holds particular promise for small communities in northern climates that are required to meet safe drinking water regulations, but are dependent on surface water sources of variable water quality and temperatures.

Submitted in fulfilment of the requirements for the Degree of Master of Engineering, Durban University of Technology, 2017. / In this research, the woven fibre microfiltration (WFMF) fabric which is produced locally in South Africa is used as a membrane material. It is cheaper in price in comparison with the current commercial membrane materials that are in use. The WFMF is also more robust when compared with the commercial membrane materials thus is able to withstand harsh working conditions. From previous studies on the WFMF, it has been shown that it can be used as a membrane material without any compromise to permeate quality. This research seeks to optimize the working conditions of this membrane material (WFMF) with an aim of achieving lower running costs and better anti fouling strategies in comparison to the commercial MBRs. The objectives and aims of this research was to come up with a MBR system whose running cost is lower than that for the commercial systems, which can be adapted for use in any environment, especially in the hardship regions where its robustness would be an added advantage. The performance of the WFMF submerged MBR was also optimised including antifouling operating regimes. This study was done in a pilot plant that was set up at Veolia wastewater treatment plant, Durban Metro Southern Works. The feed water for the pilot plant was pumped from the return activated sludge mixing chamber by means of a submersible pump. The MLSS concentration of the feed water was about 12 g/l. The various investigations that were conducted in the course of this research included the effect of spacing between membrane modules, relaxation steps and frequencies, evaluation of aeration rates and evaluation of coarse vs. fine bubbles which were all aimed at optimizing the performance of the immersed WFMF MBR. The permeate was checked for turbidity and COD levels to ensure that they were within the accepted water standards. From the experiments it is shown that the critical flux increased with an increase in aeration rate which is in concurrence with the literature and a starting flux of 30 LMH was chosen for the running of the pilot plant for the various experimental runs to be carried out. For the pipe diffuser height effect experimental run, the best results were achieved at a height of 5 cm below the membrane modules and the use of a pipe diffuser gave better results than the use of a disc diffuser. For the membrane module spacing effect the best results were obtained at the smallest possible width i.e. 3.5 mm. The best relaxation step sequence was found to be 9 mins on and 1 min off. COD, turbidity and DO was continuously determined during the course of the experimentation. Further studies should be done on use of the disc diffuser with increased surface area of aeration holes and also hole sizes of smaller diameters to check on its effectiveness as a means of reducing fouling on the membrane surface. / M

Das maximale Trubaufnahmevermögen eines Filterkuchens ist ein wichtiges Kriterium für die Vorhersagbarkeit der Standzeit des Filters. In Praxisfiltrationen in Brauereien konnte nachgewiesen werden, dass sich die Filtration mit Zellulose als Filterhilfsmittel grundsätzlich in zwei Bereiche unterteilen lässt. Zunächst verläuft der Anstieg der Druckdifferenz linear, geht dann aber zu jeweils versuchsspezifisch unterschiedlichen Zeitpunkten in den exponentiellen Verlauf über, was auf eine Kompaktierung der freien Durchgangskanäle des Filterkuchens zurückzuführen ist. Mehrmalige Regenerationen verbessern die Trübungsreduzierung der Filterhilfsmittelmischung, was durch verminderte Wasserwerte und Darcy-Werte im Labor nachgewiesen werden konnte. Wie bereits aus der Kieselgurfiltration bekannt, sind Standzeit und Trübungsreduzierung der Zellulosefiltration in entscheidendem Maß von der Filtrierbarkeit der Biere abhängig und mit den Werten eines Kieselgurfilters vergleichbar.

Thesis submitted in partial fulfillment for the Degree of Master of Technology: Chemical Engineering, Durban University of Technology, 2010. / THE OBJECTIVE of this study was to devise a purification process, using ultrafiltration membranes as the core technology, for the preparation of corn steep liquor (CSL) as a fermentation feedstock. This process inherently required the development of a pretreatment system for the ultrafiltration membranes for the removal of suspended solids and high fouling material from corn steep liquor. The ultrafiltration membrane system was required for the separation and removal of colloidal solids from corn steep liquor, and to fractionate and separate out unwanted proteins, to render the feedstock suitable for sterilisation and subsequent fermentation. THE CONCEPT of membrane technology was investigated in order to find a more practical alternative for what was deemed to be a difficult process problem. In particular, various pretreatment technologies were investigated to form a compact and robust process package. THE CORN STEEP LIQUOR, a by-product of the corn wet milling process, was obtained from African Products, Germiston, in the form of a concentrated slurry directly from an evaporator system. A diagnostic of the feedstock was carried out and from this information, it was decided that three pretreatment options would be investigated. The first option was the pH treatment of the corn liquor, by the addition of ammonia which induced the precipitation of solids. This was followed by liquid-solid separation, and the clarified liquor was fed to the membrane system. The second option looked at the separation of suspended solids from the liquor by the use of broth conditioning additives and separation of the solids by a decanter centrifuge. The third option investigated was the use of a gyratory screening system for the removal of all solids greater than 100 μ in size. IN THE pH TREATMENT of CSL, the process is effected by the addition of base to pH 7. The technology involves neutralisation of CSL in a mixing system, under predetermined conditions of temperature, agitation and rate of addition, followed by subsequent liquid-solid separation. Trials were conducted on a pilot plant to test the process. Initial trials, conducted on a small scale pilot filter press, proved to be successful for this application. A suspended solids removal of up to 98% was achieved. The average suspended solids in the filtrate was found to range between 0.1 to 0.25 %. Tests were also conducted on a hired “state of art” filtration plant under various conditions. A diaphragm membrane press was found to provide the best performance. Protein recoveries of above 95 % at fluxes of 35 L/m2h at temperatures above 50 °C, and an incremental application of feed pressure was most suited for the process. The removal of the colloidal solids by the above-mentioned process was found to improve the quality of sterilisation. A reduction of more than 90 % in coagulated solids was achieved. v i IT WAS OBSERVED that the separation of suspended solids from CSL is enhanced by the use of coagulation and flocculation. Although not commonly used for this purpose, it was felt that a decanter centrifuge was well suited for the subsequent separation of the flocs from the clarified liquor. This work describes the results of the trials with such a device and the impact of broth conditioning on the efficiency of the separation. Trials have been conducted using an Alfa-Laval Model NX210 decanter, which was not specifically built for the work and therefore imposed several limitations on its performance. Despite these shortcomings, preliminary trials proved to be successful in achieving the separation objective. Tests were conducted using five different batches of CSL. With a maximum suspended solids loading of 4.3 % and a feed rate of 700 L/h, a solids recovery of 90 % was achieved. The clarified liquor contained residual solids between 0.5 and 0.8 %. The sludge had a solids concentration that ranged between 43 % and 65 %. COAGULATION AND FLOCCULATION dosages were kept within the limits of the laboratory evaluations. Flocculant dosages were controlled between 100 and 200 ppm, with the coagulant operating at higher dosages of between 400 and 2000 ppm. The only controllable parameter on the machine itself was the scroll differential speed. The best performance in terms of the cake dryness and centrate clarity was obtained at the lowest scroll differential speed of 4 rpm. THE USE OF GYRATORY SCREENS entailed passing the raw liquor through a set of two screens. The technology involves the use of a gyratory mechanism, which aids in the cleaning of the screens during continuous operation. Trials have been conducted on a pilot plant to test the system. Since the unit used was designed specifically for quick on-site screening exercises, it did not possess the added flexibility and robustness of a properly designed full scale unit. This imposed some limitations on its performance. However, despite these shortcomings, the trials conducted on the pilot plant proved to be successful in meeting the outlined objectives. A NUMBER OF TRIALS were performed on various batches of CSL. There was considerable batch to batch variation in the suspended solids content of the CSL and this was found to ultimately affect the throughput of the screening process. The feed suspended solids varied between 10 and 18 %. The highest throughput achieved was 400 L/h at a feed suspended solids loading of 14.5 %. It was found that temperature made a significant impact on the separation. The loss of heat in the feed stream caused excessive coagulation to occur thus increasing the suspended solids loading and lowering the throughput. The total solids in the sludge stream varied between 45 and 77 %. Protein loss in the sludge stream was around 1 %. Careful attention had to be given to the handling of the sludge stream. This stream displayed rheological characteristics typical of a non-Newtonian thixotropic fluid. The 100 μm screen operated best vi i when prior separation was done using a 180 to 200 μm screen. This reduced the solids loading on the tighter screen and increased the throughput by 10 to 15 %. The self cleaning mechanism also performed more efficiently under these conditions. THE SELECTED OPTION was then based on the influence the operation had on the ultrafiltration membranes, sterilisation of the product prior to fermentation and ultimately the fermentation performance. Subsequent testing of the pretreatment options were performed on an ultrafiltration membrane test cell. The product from the gyratory screens were found to produce the best overall results, where the highest fluxes and least amount of fouling occurred on the membranes tested. ONCE THE PRETREATMENT OPTION was decided, the development of the membane ultrafiltration system was then pursued. Trials were conducted on a laboratory scale, in a membrane test cell, to determine the preliminary screening of the membrane type, fouling effects and fluxes. It was found that polyvinylidene and polyacrylonitrile membranes produced the best overall fluxes of 11.25 and 10.96 L/m2h respectively. These membranes produced permeate protein concentrations of 121 and 115 g/L respectively. Sterilisation tests conducted on the permeate streams produced also showed that these two membranes had the lowest suspended solids concentrations. FERMENTABILITY tests conducted, showed that the ultrafiltered CSL, from these two membranes, produced increased cell counts and protein utilisation along with an increased product yield. Approximately 42 g/L of biomass was generated with lysine yields of 46 g/L. Further testwork revealed the non-Newtonian nature of CSL and its inherent viscosity effects. BENCH-SCALE testwork was conducted for various membrane configurations. With tubular membranes and hollow fibre membranes, average fluxes of 6.23 and 4.5 L/m2h were achieved respectively. Spiral wound membranes were found to be more consistent in their performance, with average fluxes of around 6.25 L/m2h. For the spiral wound membranes, it was found that the Desal-2 mesh spacer with a 80 mil thickness was most appropriate for the duty. PILOT PLANT testwork was conducted to scale-up the membrane system and to eliminate possible risks associated with the technology. The pilot plant studies showed up a number of principle design variables which needed careful attention. The flaws in the piloting system were subsequently rectified and this helped to improve the overall performance of the system.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Arsenic is a highly toxic, easily transportable and widespread contaminant in groundwater throughout the world. Arsenic causes acute toxicity by disrupting biological functions. In groundwater arsenic concentrations can reach up to a few milligrams per liter. Current regulations on arsenic content in drinking water are becoming more stringent and require the standard to be reduced to a few parts per billion. Arsenic exists as oxyanions in aqueous solution in either trivalent or pentavalent oxidation states depending on the oxidation-reduction potential and pH of the medium. Several treatment methods are available for removing arsenic from water. However, cost, operational complexity of the technology, skill required to operate the technology and disposal of arsenic bearing residual are factors that should be considered before the selection of any treatment method. Most of these techniques are also effective only in removing As(V) and not As(III). N,N’-bis(2-mercaptoethyl)isophthalamide), abbreviated BDTH2, is known to effectively precipitate soft heavy metals from water. A solid-supported reagent with the metal capture ability of BDTH2 would be ideal to use as a filtration column packing material for removal of aqueous As(III). In order to attain this objective, a new dithiol compound, 2,2'-(isophthaloylbis(azanediyl))bis(3-mercaptopropanoic acid) (abbreviated ABDTH2) has been synthesized and immobilized on silica beads. Silica-supported reagent ABDTH2 (SiABDTH2) thus prepared, completely removed As(III) from water by forming As-S bonds. In batch study, SiABDTH2 reduced the concentration of As(III) in aqueous solutions from 200 ppb to below 5 ppb at pH 5, 7 and 9. XAFS study of ABDT-As(III) and SiABDT-As(III) indicated that arsenic was present in +3 oxidation state as well as As(III) was only bonded to sulfur atom of ABDT unit. When SiABDTH2 was used as filtration column material, only 3% of ABDTH2 was leached out from the column. However, 100% As(III) was removed from 20 L of 200 ppb As(III) aqueous solution at a flow rate of 20 mL/min.

The traditional filter paper assay for saccharifying cellulase originally described by M. Mandels et al (1976) has been modified to make possible low activity determinations of Trichoderma cellulases. The enzymatic activity appears to decline during a prolonged incubation period if no precautions have been taken. By means of adding bovine serum albumin and potassium chloride as protein stabilizers and sodium azide as an antimicrobial agent filter paper activities in the range from 0.02 to 0.37 (IUPAC assay, 1987) can be estimated by extending the incubation time up to 20 hours. Filter paper activity values obtained by this method may be compared to those obtained by the IUPAC assay by using a conversion factor from 1.4 to 1.7. Acid whey and sweet whey permeate have been investigated as media for growth and metabolite production by Trichoderma reesei QM 9414 using shake flask cultures and spore inocula. In the case of acid whey the mycelial growth after 2 weeks is 13 mg dry weight /ml substrate. The specific growth rate is 0.29/day. The fungus appears to metabolize the whey protein the first 2 weeks. The alkalinity of acid whey rises continuously over a three week period up to a pH of 8.5. In the case of whey permeate the maximal mycelial weight gain is 4.4 mg/ml which appears after 8 days. A rise in net soluble protein level comes after 3-5 days and reaches a maximum value of 0.23 mg/ml after 2 weeks. The pH of whey permeate rises continuously to 7.5 after 3 days and then slowly declines. The net production of cellulases is low on both media. Dilution 1:6 of the acid whey, supplementation with ammonium sulfate and pHadjustments did not enhance the production of cellulases. Acid whey supports a significant growth and sweet whey permeate shows potential for extracellular protein production. A literature review surveys the composition and uses of acid whey, environmental aspects of whey wastes, the fungus Trichoderma reesei, the mode of action of the Trichoderma reesei cellulase system and the structure of cellulose in cotton and wood. / Graduation date: 1994

Dissolved organics in wastewater samples were separated into three size fractions (0-1,000 amu, 1,000-10,000 amu, and 10,000 amu-0.22 m) using ultrafiltration (UF) membranes. The mass distribution within each fraction was adjusted by using a new permeation coefficient model to account for membrane rejection. Dissolved organic and soluble BOD (sBOD) removals in a trickling filter were studied for the different size fractions. The Logan trickling filter model was recalibrated and used to generate predicted removals by size fraction of sBOD, dissolved organic carbon (DOC), and biodegradable DOC (bDOC) for a given influent. Although there was moderate agreement between observed and predicted removals, more investigation is needed to explain shifts in material between different size fractions. Of the three parameters, bDOC may offer a better parameter for modelling trickling filter performance than sBOD.

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