M.Ing. / The Rietvlei Water Treatment Plant was extended with a granular activated carbon (GAC) filtration system after an exhaustive series of tests, which were started in 1994. Upon commissioning towards the middle of 1999, a year of close monitoring followed to measure the GAC performance at full-scale. After verification that the GAC does indeed ensure a high quality product under all conditions, the emphasis shifted to the optimisation of the GAC handling and regeneration system. Frequently moving the entire GAC inventory from the filters to an off-site regeneration plant and back requires significant operational effort and contributes a major part of the total cost of the GAC system. A number of systematic investigations were carried out in response to a number of practical questions that arose at Rietvlei. The first part of the study was directed towards tracking and quantifying the GAC on and off site. The main findings were that 10.0% of the GAC is lost from the filter during backwashing (0.3%) and removal of GAC from the filter for regeneration (9.7%). The sump traps not all this GAC and 2.3% of the total inventory is lost to the river. Inserting a sieve at the outlet of the sump can eliminate this loss. A further 80.3% of the GAC in a filter is removed for regeneration, of which 18.7% is lost during the regeneration process. The minimising off this loss can only be achieved through the optimisation of the regeneration process, which falls within the domain of the regeneration contractor. The second part of the study was directed at the behaviour of the GAC whilst within the filter bed. The porosity and sphericity was determined by laboratory tests and calculations. The porosity was found to be 0.69 for the 12 x 40 size carbon and 0.66 for the 8 x 30 size carbon and the sphericity was found to be 0.67 for the 12 x 40 size carbon and 0.66 for the 8 x 30 size carbon. By using a calibrated bed expansion model, the bed expansion could be calculated at 9°C and 23°C for the two carbons gradings; the maximum temperature range experienced at Rietvlei. The main finding of this part of the study was that the average available freeboard is 650 mm for the 12 x 40 grading and 430 mm for the 8 x 30 grading, and therefore no GAC should wash over the weir at all during backwashing. The third part of the study measured the physical changes of the GAC found at different points in the GAC cycle. The main findings were that the small fraction of GAC washed out of the bed during backwashing and removal has a finer grading, higher apparent density and lower adsorption capacity than the GAC in the filter bed. There seems to be no marked attrition of the carbon or generation of fines during the removal and transport of the GAC to the regeneration plant. After regeneration, there was a 7% decrease in apparent density and a 30% increase in adsorption capacity. The final part of the study correlated the adsorption capacity of the GAC with its time in use as well as UV254 removal. After regeneration, UV254 removal begins at approximately 20% and declines to 14% after 400 days of operation, and to 10% after 600 days. After regeneration, the iodine number begins at approximately 800, declines to 600 after 400 days of operation, and to 500 after 600 days.

An evaluation of BioSand Filters, a method of Household Water Treatment, was conducted in Posoltega, Nicaragua, with objectives of determining the long-term filtration efficiency and the rate of sustained use. Field methods included microbial and turbidity water quality testing and interviews with filter users regarding the operation, maintenance and perceptions towards the filters. Of the 234 BioSand Filters installed in 1999 and 2004, only 24 were found to still be in operation. The average filtration efficiency was found to be 98% for total coliforms, 96% for E. coli and 88% for turbidity. Statistically significant effects on filtration efficiency were detected for the source contamination, the inverse of the flow rate, and the standing depth of water over the sand. A follow-up laboratory QA/QC procedure was undertaken to validate the field methods, which consisted of membrane filtration (MF) with m coliBlue24 growth media, and SolarCult dipslides. It was found that MF with m coliBlue24 produced useful reproducible results, and is an appropriate method for conducting field water quality testing. The dipslides were found to be an appropriate tool for testing source water quality and assessing the applicability of BioSand Filters, and may be an appropriate tool for local health representatives to promote safe water practices within the community. However, the dipslides should not be used as a presence / absence test for drinking water due to the high limit of detection. The low rate of sustained use (10%) is mostly a result of the structural failure of the concrete walls of the filter, in particular for those filters from 2004. Anecdotal evidence suggests insufficient quality control during the construction. The filtered water and the stored post-filtered water did not meet the WHO guidelines for safe drinking water on account of the presence of E. coli. Also identified were improper maintenance practices and unsafe storage of post-filtered water. These problems could have been addressed through the development of a holistic water system approach, such as the World Health Organization Water Safety Plan. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Photocatalysis is a series of advanced light-induced redox reaction processes resulting in the degradation and mineralization of organic pollutants in the presence of oxygen and water. Due to their capability to destroy contaminants under mild conditions, photocatalytic processes have attracted considerable attention in the field of waste-water treatment. However, photocatalytic reactions using the traditional TiO2 photocatalyst suffer from low energy efficiencies under solar irradiation. This low efficiency in the utilization of solar energy lies in its incapability in absorbing visible lights and also the high recombination rate of photo-excited species in photocatalysts. In addition, difficulties in the separation of fluids from micro- or nano-scale catalysts in large scale systems substantially impact cost efficiency in practice. In this thesis, strategies are explored which address these issues in order to improve the feasibility of solar photocatalysis. Two branches of photocatalytic transition metal-oxide semiconductor materials are investigated, namely bismuth-based and silver-based multi-phase heterogeneous photocatalysts. This research is focused on the design of visible-light-active metal-oxide photocatalysts to increase the absorption of visible light and to decrease the rates of electron-hole recombination, resulting in a high photocatalytic efficiency in regards to the degradation of organic pollutants. BiVO4 powder, synthesized from freshly made potassium metavanadate was prepared via hydrothermal treatment, characterized and experimentally investigated for the degradation of rhodamine B under visible light irradiation. The crystal structures and the specific surface areas of the composites, based on BiVO4 single phase crystal structures, are discussed. A multi-phase silver species (Ag2O/Ag3VO4/Ag4V2O7) photocatalyst was synthesized by adjusting the molar ratio of silver to vanadium (Ag to V) via hydrothermal method. The stabilities of as-prepared silver species composites regarding crystal structural changes due to photocatalytic reactions are investigated. Multi-phase silver species composites assisted with graphene oxide (GO-Ag2O/Ag3VO4/AgVO3) were synthesized at room temperature, and exhibited high visible-light photocatalytic activities regarding the degradation of model organic pollutants. The effect of graphene oxide addition on the photoactivity and on the photocorrosion of silver species composites under VLI is explored. The synergistic roles of each individual phase incorporated into the multi-phase composites are discussed regarding the photocatalytic performance.

Orientador: Ricardo de Lima Isaac / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-26T15:48:00Z (GMT). No. of bitstreams: 1 Reis_Gabrielados_M.pdf: 4501335 bytes, checksum: f41add1d19b9cc7987740fb6604a17ed (MD5) Previous issue date: 2014 / Resumo: Dentre as etapas do tratamento de água para abastecimento público a filtração é essencial para remoção de partículas e microorganismos nocivos à saúde humana. Devido ao reduzido tamanho e resistência à cloração, os oocistos de Cryptosporidium tornam-se um problema nas estações de tratamento de água. Neste estudo foi investigada a eficiência da filtração em meio granular constituído de areia recoberta com nanopartículas de prata na remoção de microesferas de poliestireno, que simulam oocistos de Cryptosporidium spp.. A presença das nanopartículas de prata pode ser uma barreira adicional no tratamento de água, proporcionando ao grão de areia uma camada positiva, auxiliando na remoção de oocistos. O sistema de filtração em escala de laboratório foi composto de microcolunas de vidro borossilicato (diâmetro interno 1 cm) preenchidas com areia previamente impregnadas por imersão em solução de nanopartículas de prata (concentração 0,1 g/L). Os filtros foram alimentados por uma suspensão de água deionizada contendo microesferas de poliestireno (diâmetro médio 2 ?m). A influência na qualidade da água na filtração foi avaliada quanto aos parâmetros: concentração de ácido húmico (2,5, 5,0 e 10,0 mg.L-1), pH (6, 7 e 8), força iônica (24, 48 e 105 mM) e concentração inicial de microesferas (1,3 x 105, 2,4 x 106 e 1,4 x 107 partículas/mL). O efeito do parâmetro taxa de filtração foi avaliado sob a condição operacional de 2,4, 4,8 e 48 m3/m2.dia. A remoção de partículas do filtro proposto foi da ordem de 99,0 % contra 92,0 % do filtro controle. Os filtros teste constituídos de camada de areia recoberta com prata tiveram desempenho superior, na remoção da turbidez, aos filtros controle, com eficiência de remoção da ordem de 81,1 %, ao se filtrar até 10 VP (volume de poros). Contudo, a turbidez não se mostrou um bom indicativo da remoção de microesferas. A impregnação por nanopartículas de prata tornou os filtros mais eficientes na remoção de microesferas de poliestireno que simulam oocistos de Cryptosporidium / Abstract: Among the steps in treating water for public supply filtration is essential for removal of particles and microorganisms harmful to human health. Due to the small size and resistance to chlorination, Cryptosporidium oocysts become a problem in water treatment stations. This study investigated the efficiency of the filtration medium consisting of granular sand coated with silver nanoparticles in the removal of polystyrene microspheres that simulate Cryptosporidium spp.. Presence of silver nanoparticles can be an additional barrier for water treatment, providing a positive layer, aiding in the removal of oocysts. The filtration laboratory scale system was composed of borosilicate glass micro columns (inner diameter 1 cm) filled with sand previously impregnated by immersion in a solution of silver nanoparticles (concentration 0.1 g/L). The filters were fed with a suspension of deionized water containing polystyrene microspheres (mean diameter 2 ?m). The influence on water quality in filtration was evaluated for the following parameters: concentration of humic acid (2.5, 5.0 and 10.0 mg.L-1), pH (6, 7 and 8), ionic strength (24, 48 and 105 mM) and initial concentration of microspheres 1.3 x 105, 2.4 x 106 and 1.4 x 107 particles/ml). The effect of the filtration rate parameter was evaluated under operating conditions of 2.4, 4.8 and 48 m3/m2.day. The removal of particles of test filter was approximately 99.0 % compared with 92.0 % of the control filter. The test filters consisting of silver coated sand layer exhibited superior performance in the removal of turbidity, the control filters, with removal efficiency of about 81.1 % when filtering up to 10 filter PV (pore volume). However, turbidity was not a good indicator of removal of microspheres. The impregnation with silver nanoparticles made filters more effective on the removal of polystyrene microspheres that simulate Cryptosporidium oocysts / Mestrado / Saneamento e Ambiente / Mestra em Engenharia Civil

>Magister Scientiae - MSc / In South Africa, water pollution problems have continued to increase due to increasing anthropogenic activities. The increasing number of organic contaminants in various water sources can be attributed to industrial development, population growth and agricultural run- off. These activities have impacted negatively on the availability and accessibility to sustainable clean water resources, exposing citizens to water borne diseases such as cholera, diarrhoea and typhoid fever; commonly reported among children. Advanced oxidation technologies such as dielectric barrier electrohydraulic discharge (EHD), also referred to as dielectric barrier discharge (DBD), have the ability to decompose persistent organics and eliminate microbes. DBD offers advantages such as efficiency, energy saving, rapid processing, use of few or no chemicals, and non-destructive impact on the ecosystem. The system is also capable of generating ozone, hydrogen peroxide, singlet oxygen, superoxide radicals, hydroxyl radicals and other active species. The combination of these reactive species has been reported to degrade biological and chemical pollutants rapidly and efficiently. In this study, the DBD system was optimized by investigating the effect of physico-chemical, electrical parameters and reactor configurations on Methylene Blue (MB) decolouration efficiency. The physico-chemical parameters included MB concentration, solution pH and conductivity, solution volume, NaCl electrolyte concentration in the electrode compartment and air flow rate. As for electrical parameters, the effects of voltage, electrode type and size on MB decolouration efficiency were studied. The effect of the aforementioned parameters on MB decolouration efficiency was assessed by varying one parameter at a time. The following physico-chemical parameters: time (from 0 - 60 minutes), pH (2.5 - 10.5), solution conductivity (5 - 20 mS/cm), MB concentration (0.5 – 10 mg/L), solution volume (500 – 2000 mL), NaCl electrode electrolyte concentration (10 – 50 g/L) and air flow rate (2– 4 L/min) were varied in their respective ranges under the applied experimental conditions: reactor air gap 2 mm, solution volume 1500 mL, NaCl electrolyte concentration of 50 g/L in the electrode compartment, voltage 25 V (7.8 kV), airflow rate 3 L/min, 0.5 mm silver electrode and a running time of 60 minutes. As for electrical parameters, voltage (from 20 - 25 V), electrode type (copper, silver and stainless steel) and electrode diameter (0.5 – 1.5 mm) were also altered individually at the applied experimental conditions. The reactor air gap was varied from 2 to 6 mm. At the same experimental conditions, the free reactive species generated mainly H2O2 and O3, were detected and quantified using the Eisenberg and indigo methods, respectively. The optimum physico-chemical parameters were found to be MB concentration 5 mg/L, concentration of NaCl electrolyte used in the central compartment of the DBD reactor 50 g/L, solution pH 2.5, solution conductivity 10 mS/cm, air flow rate 3 L/min, solution volume 1500 mL and an optimum contact time of 30 minutes. The optimum electrical parameters were found to be: applied voltage 25 and 1.5 mm silver electrode. The following parameters MB concentration, solution conductivity and pH, applied voltage and reactor configuration significantly affected MB decolouration efficiency compared to parameters such as solution volume, the inlet air flow rate, electrode type and size and NaCl electrolyte concentration in the electrode compartment, which were less effective in enhancing MB decolouration. Moreover, for all DBD experiments performed at the applied experimental conditions, complete decolouration of MB was achieved in the first 30 minutes. However, trends between the optimized parameters and MB decolouration efficiency were mostly observed after 10 minutes. The optimized DBD system reduced the treatment time from 30 to 20 minutes without any chemical additives. Moreover, at 5 mg/L MB under the applied optimum conditions, it was proved that besides 99% of MB decolouration reached after 60 minutes, 53% of total organic carbon (TOC) removal was also achieved. The chemical oxygen demand (COD) characterizing MB toxicity was less than 5 mg/L before as well as after the DBD experiment. After 10 minutes of experiment under the following conditions: Applied voltage 25 V, MB concentration 5 mg/L, solution pH (in between 6.04 and 6.64), solution volume 1500 mL, air flow rate 3 L/min, 0.5 mm silver electrode and a contact time of 60 minutes, about 3.73 x 10-5 mol/L H2O2 was produced which decreased to 2.93 x 10-5 mol/L 10 minutes later, while O3 concentration was initially very low and could not be detected. However, 0.5 mol/L of O3 was detected after 20 minutes of operating time, thereafter, H2O2 concentration decreased continuously with time while that of O3 fluctuated as the treatment time increased. Likewise, the energy density for the production of free reactive species reached 0.87 g/ kWh in the first 10 minutes due to the presence of chromophoric functional groups such as =N+(CH3)2 in MB structure that had to be destroyed. Thereafter, the energy consumption decreased progressively to zero with an increase in treatment time due to the destruction of =N+(CH3)2 groups in MB structure with time. The correlation between the rise in the of H2O2 concentration and energy density after 10 minutes was probably due to dissociation of OH- OH bonds in H2O2 by UV light to yield OH radicals which unselectively may have attacked MB dye. Thus, MB decomposition in the current DBD reactor was mostly initiated by H2O2 and O3. The irradiation of H2O2 by UV light generated in the DBD system was found to accelerate dye decomposition in the first 30 minutes of the experiment. The UV-vis analysis of treated MB samples confirmed that the complete decolouration of MB achieved in the first 30 minutes was due to the destruction of the chromophoric [=N+(CH3)2] group in Methylene blue structure, while the FT-IR confirmed the presence of traces of various functional groups such as C=C, C=O, C=N, NH, NH3, NO2, etc. characteristics of carboxylic acids, amines, amides, nitrogen based compounds (salts), aliphatic and unsaturated by-products remaining in the bulk solution after treatment. The salts analysis after treatment showed that 16 mg/L of nitrates and nitrites and 1.1mg/L of sulphates mainly originating from air and MB decomposition were present in the treated samples. The EHD/DBD system used in this study offers an approach to partially treat water/wastewaters and its optimization was able to significantly enhance the decomposition of the target MB dye as indicated by the reduction of total organic carbon (TOC) from 8.3 mg/L to 3.9 mg/L. Compared to previous research, this study successfully optimised a complete double cylindrical dielectric barrier discharge (DBD) reactor at ambient condition without any chemical additives.

>Magister Scientiae - MSc / Water is a strategic resource critical for basic human needs and for sustaining key economic sectors, including various emerging small businesses. The significance of water to everyday life become apparent mainly during periods of acute water shortages because of increasing population, industrial developments, droughts, and natural disasters that threatens the assurance of water supply. With the growing complexity of water supply challenges faced by the Phalaborwa WTW, there is a need to deploy technology and other means available to improve the provision of water and sanitation services. The aim of the study was to evaluate the telemetry system for managing the Phalaborwa WTW water supply process. / 2022

Reverse osmosis (RO) and nanofiltration (NF) membrane systems are high-pressure membrane filtration processes that can produce high quality drinking water. Biofouling, biofilm formation that exceeds a certain threshold, is a major problem in spiral wound RO and NF membrane systems resulting in a decline in membrane performance, produced water quality, and quantity. In practice, detection of biofouling is typically done indirectly through measurements of performance decline. Existing direct biofouling detection methods are mainly destructive, such as membrane autopsies, where biofilm samples can be contaminated, damaged and resulting in biofilm structural changes. The objective of this study was to test whether transparent luminescent planar oxygen sensing optodes, in combination with a simple imaging system, can be used for in-situ, non-destructive biofouling characterization. Aspects of the study were early detection of biofouling, biofilm spatial patterning in spacer filled channels, and the effect of feed cross-flow velocity, and feed flow temperature. Oxygen sensing optode imaging was found suitable for studying biofilm processes and gave detailed spatial and quantitative biofilm development information enabling better understanding of the biofouling development process. The outcome of this study attests the importance of in-situ, non-destructive imaging in acquiring detailed knowledge on biofilm development in membrane systems contributing to the development of effective biofouling control strategies.

In the theoretical part of diploma thesis is elaboreted literary search relating to problems with using of various modifications of coagulation tests. The experimental part of diploma thesis is focused on comparison of three types of coagulation tests during treatment of model water with increased content of humic matter. Concretly was compared classic jar test, modified jar test and centrifugation test. As a coagulant was used ferric sulphate. The efficiency of treatment was tested under various conditions (temperature, time of fast mixing and intensity of slow mixing). Information capability of results was evalueted on the basis of absorbance by 254 nm and 387 nm, residual concentration of iron and dichromate value. Obtained results were numerically processed and they are presented in the form of tables and graphs.

Att lufta biologiska bassänger vid ett avloppsreningsverk är en mycket energikrävande process. Genom att reglera lufttillförseln kan processen optimeras så att den blir så energisnål som möjligt men samtidigt bidrar till en god kvalitet på utgående vatten. Regleringen bör då ske vid flera punkter längs med en bassäng. I detta projekt har regleringen av syrehalten i aktivslamanläggningen vid Himmerfjärdsverket utvärderats och ett försök till förbättring av processen har genomförts. Verket har efterdenitrifikation varför aktivslamanläggningen enbart består av en luftad del där nitrifikation och oxidation av organiskt material sker. Styrsättet i verket är sådant att syrehalten regleras i början av varje luftningsbassäng. En syrehaltsgivare sitter ca 20 meter in i varje linje och en luftflödesgivare satt på vardera linjes huvudledning med luft. Kaskadreglering reglerar luftflödet. Den överordnade syrehaltsregulatorn beräknar börvärdet till luftflödesregulatorn. Börvärdet på syrehalten är normaltsatt till 2 mg/L. Detta reglersystem har lett till att då belastningen är låg ökade syrehalten kraftigt i slutet av varje linje medan höga belastningar gör att syrehalten sjunker för mycket mot slutet av bassängen så att reningsresultaten för ammonium blir sämre än önskvärt. Syre- och ammoniumprofiler, det vill säga syre- och ammoniumhalterna i vardera av linjernas sex zoner plottade mot zonerna, studerades på två av verkets linjer. Dessa gjordes under perioder med relativt låg belastning av ammonium. Då framkom att oavsett flöde skedde den mesta av reduktionen i linjernas två mittersta zoner. Målet blev då att försöka förskjuta reningen så att hela bassängen utnyttjades. Detta måste dock ske utan att reningen under perioder med högre belastning försämras. Det som också framkom var att det förekommer både belastningsvariationer och flödesvariationer till de olika linjerna. För att förbättra regleringen installerades en syrehaltsgivare, en luftflödesgivare och en reglerventil till varje zon i en av verkets linjer. Ett kaskadreglersystem installerades och trimmades in i varje zon. En börvärdesundersökning gjordes för att hitta den kombination av börvärden i de olika zonerna som gav ett gott reningsresultat och samtidigt minimerade energikonsumtionen. De kombinationer som testades var 1,5/1,5/2/2/1,5/1,5 och 1,5/2,5/2,5/2,5/2,5/2,5. Dessa kombinationer förväntades förskjuta reningen så att hela bassängen utnyttjades och pressa ner de syrehaltstoppar som stundtals uppstod i slutet av bassängen. Syrehaltstopparna försvann men en acceptabel reningsgrad erhölls ej med avseende på utgående ammoniumhalt från försökslinjen. Reningen i försökslinjen var försämrad jämfört med innan byte av syrehaltsreglering. Här skall dock noteras att vattentemperaturen hade sjunkit i förhållande till perioden med ursprunglig reglering vilket kan ha påverkat nitrifikationshastigheten negativt. Temperaturen var lägst under den sistnämnda kombinationen. Under den sistnämnda börvärdeskombinationen hade försökslinjen stundtals bättre rening än övriga linjer så denna börvärdeskombination ger en förhållandevis god reningskvalitet. För att jämföra energikonsumtionen togs ett samband fram mellan luftflöde och blåsmaskinernas effekt. Sambandet användes för att beräkna skillnaden i effektförbrukningen mellan de bägge reglersystemen. Denna räknades om till motsvarande årsenergiförbrukning för samtliga linjer. Resultatet blev att energikonsumtionen skulle kunna sänkas med 10 % för luftningssteget. / To aerate the biological basins at a wastewater treatment plant is a very energy intensive process. To make the process as energy efficient as possible the air supply should be controlled. This may also contribute to a better purification quality. To fulfill this, the control of air supply should occur at several points along a basin. In this project, control of the dissolved oxygen in the activated sludge basins at Himmerfjärden wastewater treatment plant is evaluated and improved. The plant has postdenitrification, why the activated sludge plant solely consists of an aerated part where nitrification and oxidation of organic matter occurs. The oxygen level in the aeration basins is controlled at the beginning of each aeration basin. An oxygen sensor is placed 20 meters from the inlet and an air flow meter is placed on the main inlet tube for air at each line. Cascade control is used to control the airflow rate. The primary dissolved oxygen controller calculates the set-point to the secondary air flow controller. The set-point of the oxygen level is normally set at 2 mg/L. During periods with low loads of ammonia, this control leads to an increased oxygen level at the end of each basin while the high loads causes the oxygen level to drop towards the end of the basin so that the treatment results for ammonium were less than desirable. Oxygen and ammonium profiles, i.e. oxygen and ammonia concentrations in each of the lines’ six zones were measured and plotted against the zones, were studied at two of the plant lines. These were made during periods of relatively low load of ammonium. It was found that regardless of flow, most of the reduction occurred in the two middle zones in each line. The goal then became to try to shift the treatment so that the entire basin was used. This must be done without lowering the treatment quality during periods of higher loadings. What also emerged was that there are variations between the lines both in load and in flow. To improve the control system, an oxygen sensor, an airflow meter and a control valve were installed in each zone in one of the plant lines. A cascade control system with two PI-controllers was installed and tuned in each zone. Different combinations of set points were analyzed to find the one that gave a good cleaning performance while minimizing energy consumption. The combinations tested were 1.5/ 1.5/2 /2 /1.5/1.5 and 1.5 / 2.5 / 2.5 / 2.5 / 2.5 / 2.5. These combinations were expected to push the treatment forward so that the entire basin was used. It should also and lower the oxygen peaks that sometimes occurred at the end of the basin. The oxygen peaks disappeared but an acceptable degree of purification of ammonium was not obtained. The purification in the experimental line was lower than before the change of aeration control. It should be noted that water temperature had decreased compared to before the change of control system which may have affected the rate of nitrification negatively. This may be a reason for the higher ammonium concentrations. The lowest temperature was measured during the last set- point combination. During that period the experimental line had a better purification compared to the other lines in the plant. To compare the energy consumption for the two control systems a relationship was calculated between the air flow rate and the power consumption of the blowers. This relationship was used to calculate the difference in power consumption between the two control strategies. This consumption was translated to the corresponding annual energy usage of all the lines. The result was that the energy consumption could be reduced by 10% for the aeration step.

Three membrane bioreactors, a low flux filter (LFF), a diafilter (DF), and an ion-exchange (IE) membrane bioreactor were used to treat water polluted with 50 ppm-N nitrate. The three systems were compared in terms of removal efficiency of nitrate, operational complexity, and overall quality of the treated water. In the low flux filter (LFF) membrane bioreactor an hemo-dialysis hollow fiber module was used and operated continuously for 29 days with a constant flux of permeate. The performance of the system was constant during the span of the experiment, which demonstrated that when the module was operated under constant low flux of permeate, the membrane filtration process was not affected by fouling. The removal rate of the LFF was 100% since the treated effluent did not contain nitrate or nitrite. The volumetric denitrification rate was 240 g-N day-1 m-3, which is within the range of denitrification rates obtained in tubular membrane modules. The treated effluent contained acetate, the carbon source of the biological process, and other inorganic nutrients, which showed that operating this ultrafiltration module at controlled flux did not improve the retention of these substances in the bioreactor. The same hemo-dialysis hollow fiber module employed in the LFF system was used in the diafilter (DF) membrane bioreactor. In the DF system, however, the membrane module was used as a contactor that separated the treated water and the bioreactor system, which allowed the transfer of solutes through the membrane porous structure and supported the growth of a biofilm on the membrane surface. The nitrate removal rate of the DF system increased from 76% to 91% during the 17 days assay. Unfortunately, this improvement could be attributed to microbial contamination of the water circuit because significant concentrations of the carbon source, acetate, nutrients, and nitrate were found in the treated effluent. The volumetric denitrification rate of the system was 200 g-N day-1 m-3, and the surface denitrification rate was lower than values previously reported for contactor membrane bioreactors. The results hereby presented do not evidence any advantage of operating the Filtral 20 ® membrane module as a contactor instead of as a filter such as in the LFF system. On the other hand, the third system herein presented, the IE membrane bioreactor, demonstrated several advantages of a contactor configuration but with a non-porous ion exchange membrane module in place of the Filtral 20 ®. As in a contactor system, the anion membrane provided a surface for biofilm growth, facilitated the transport of nitrate, and prevented mixing of treated water and bioreactor medium. Compared to the two previous systems, the most remarkable result of the IE was the reduction of secondary pollution in the treated water. The concentrations of phosphate and ethanol were zero and less than 1% of the concentration in the bioreactor, respectively. In addition, the IE system was less complex than the two other systems because the ion exchange membrane is non-porous. Therefore, unlike with porous contactors, it was not necessary to control the flux of treated water that could be lost through the bioreactor. The average surface denitrification rate of the IE system was 7.0 g-N day-1 m-2, which is higher than what had been reported for other contactor denitrification systems. However, because of the low surface to volume ratio of the membrane module that was used, the volumetric denitrification rate of the IE system was low, equivalent to 65 g-N day-1 m-3. / Master of Science