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Pilot-scale ambient and low temperature research into the enhancement of aerobic digestion of waste activated sludge, through control of mixed liquor pH (MLpH), was performed using an extended aeration and a high rate waste sludge. To offset MLpH decreases encountered during nitrification, Ca(OH)₂ and NaHCO₃ were used to control MLpH in the series pH 6, 7 and 8. The performance and behaviour of the digesters, under both controlled and uncontrolled MLpH conditions, were monitored through parameters related to volatile mass reduction, sludge mass metabolism, quality of digested end-product and soluble characteristics of the digester effluent. Volatile mass reduction was significantly affected by MLpH control, under certain conditions. Improvements in reduction performance of >100% over the uncontrolled condition were noted, depending on sludge origin; however, it was concluded that only certain temperature ranges should be targeted for the most effective use of MLpH control, since use of MLpH control in ranges wherein little improvement would be realized was felt to be uneconomical. Analysis of volatile mass reduction rates, based on a series of 1 day batch conditions (necessitated by the reactor flow scheme and the variability of the digestion process), demonstrated that reactor performance oscillated around a mean performance value; MLpH control acted to reduce these oscillations, such that the digesters performed closer to the mean value more of the time. Temperature sensitivity coefficients were quite variable, and a single value did not describe all situations. It was proposed that θ was influenced by digestion system, operating temperature, sludge type and MLpH level. The use of this coefficient for determining the operating ranges most suitable for MLpH control was advanced. The fate of the nutrients nitrogen and phosphorus were greatly influenced by MLpH control. The use of Ca(OH)₂ resulted in less release of phosphorus from the solid phase, with subsequently low effluent PO₄-P concentrations in the neutral MLpH range. The drawback of this reaction was found to be the production of inert inorganic sludge solids, thereby illustrating the need for a trade-off between the various benefits and drawbacks of the enhanced digestion process. Nitrification proceeded at all temperatures, and in conditions previously thought to be inhibitory to the chemolithotrophic organisms. Digester effluent quality was improved through MLpH control, but substantial concentrations of NOx-N were observed under some conditions. Based on direct comparisons with previous lab-scale research, it was concluded that the enhancement process had very good potential for implementation at the full-scale level, either for the improvement of existing underdesigned processes, or for the initial design of more efficient aerobic digestion facilities. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Nearly 700,000 Virginians depend on septic tanks and other wastewater treatment systems for treatment of household wastes. The Joint Subcommittee Report HJR 7 1987 reported that sixty percent of Virginia's residential septic “systems and drainfields are operating improperly. With the demand for rural and suburban development increasing, a viable alternative to septic systems and drainfields is needed. One proposed alternative is single family package treatment systems. One vital concern is that a majority of these systems discharge directly into surface waters. Thus, the objective of this study was to evaluate the performance of aerated package treatment systems (APTS). Five APTS located in southwest Virginia were chosen. Each site was visited three times during 1990 and 1991, and various parameters were monitored from the primary settling chamber, aeration chamber, and effluent. Systems were sampled in the morning, afternoon, and night. Also, two dye studies were conducted to evaluate hydraulic displacement. The results indicated that overall field performance was poor due to unreliable maintenance by homeowners, an ineffective chlorinator/dechlorinator system, inadequate biological treatment, and mechanical malfunctions. Eighty-one percent and 62% of the effluent samples were found to have five day Biochemical Oxygen Demand (BOD,) and total suspended solid (SS) concentrations exceeding 30 mg/L, respectively. Effluent dissolved oxygen values were less than 5 mg/L, the state's standard for small package treatment systems. Sixty-four percent of the effluent samples were found to contain more than 200 fecal coliforms/100 mL. In five instances where disinfection was evident, chlorine residuals were detected in the effluent, which also violates state standards. / Master of Science

An Entrapped-Mixed-Microbial-Cell (EMMC) process was investigated for its simultaneous removal of carbon and nitrogen in a single bioreactor with the influent COD/N ratio varying from 4 to 15 and influent alkalinity of 140 mg CaCO3/L and 230 mg CaCO3/L. The reactor was operated with alternate schedules of intermittent aeration. Two different sizes of carriers (10 * 10 * 10 mm3 and 20 * 20 * 20 mm3) were studied. The medium carrier (10 * 10 * 10 mm3) system presents higher nitrogen removal and COD removal compared to the large carrier system. The nitrogen removal efficiency is related to the ratio of COD/N in the influent. With the increase of the COD/N ration in the influent, the nitrogen removal efficiency is increased. The average reductions of nitrogen were over 92% and the average reductions of SCOD and BOD5 are over 95% and 97%, respectively, in the medium carrier system. This is operated at the HRT of 12 hours and 0.5 hour aeration and 2 hours of non-aeration, and the COD/N ratio of 15 in the influent. Changing alkalinity from 140 to 230 mg CaCO3/L has no effect in both large and medium carriers for the nitrogen removal efficiency. The pH, oxidation – reduction potential (ORP) and dissolved oxygen (DO) were used to monitor the biological nitrogen removal. It was found that the ORP (range from -100 to 300 mV) can be used to provide better effluent quality measured as total-nitrogen of less than 10 mg/L. Also, the impact of influent COD/N ratio on the effluent quality (measured as Inorg.-nitrogen) for the EMMC process is very important. Compared to other two compact biological wastewater treatment processes, membrane bioreactor (MBR) and moving bed biofilm reactor (MBBR), the EMMC process with the intermittent aeration has higher removal efficiencies of carbon and nitrogen, easier operation, lower O&M cost, lower energy requirement, and more compact. The total cost requirement is less than $3.27 per 1000 gallons (3.785 m 3) of treated settled domestic sewage per day. It is apparent that the EMMC process is technically feasible for the simultaneous removal of carbon and nitrogen under the operation on a schedule of intermittent aeration and suitable to be used for replacement or upgrading of existing treatment plant at land limited area.

This study focused on three potential problems with the operation of aerobic package treatment systems: hydraulic retention time, laundry detergents, and hydraulic surges. To determine the effect of hydraulic retention time on system performance, six bench scale activated sludge systems were constructed. Wastewater from an actual residence was collected twice per week and fed to the small activated sludge systems. Two of the systems had a hydraulic retention time of 2 days, two had a hydraulic retention time of 1 day and two had a hydraulic retention time of 0.5 days. Effluent quality was stable and good with regard to chemical oxygen demand (COD) and ammonia (NH)-N) and seemed to be independent of hydraulic retention time. All of the systems performed well, despite considerable variability in influent strength. To study the effect of high concentrations of laundry detergents on the operation of package treatment systems, three of the six laboratory systems were fed high concentrations of detergent. Other than some residual COD from the detergent, no effect on system performance was observed. The final component of the study was the modification of an existing package treatment system to equalize flows from an automatic washing machine. After a month of operation the modified system produced a more constant effluent quality, than did the unmodified system. The field system, with and without modification, had a low mixed liquor suspended solids (MLSS) concentration (35 mg/L). This was probably the result of the long hydraulic retention time. As a result of the low MLSS the system, with and without modification, did not meet Virginia effluent requirements for BODs, TSS or D.O. or generally accepted levels of NH₃-N. / Master of Science

This study evaluated physical and biological treatments of bio-oil process water to decrease organic contaminants. A three-sequential-column filtration system compared four treatments: three columns filled with kenaf only; three columns filled with wood shavings only; first column filled with wood shavings and two with kenaf; and first column filled with kenaf and two with wood shavings. The kenaf and wood shavings were composted after filtration. The filtrate water underwent further bio-treatment by adding aeration and selected bacteria. After filtration and bio-treatment, oil and grease concentrations were reduced over 80 percent and toxicity reduced over 90 percent. There were no significant differences among filtration treatments. Most of the oil and grease was removed by the first column. Aeration significantly decreased the concentration of oil and grease and toxicity in the filtrate water. Composting of the bioiltration matrices significantly reduced the oil and grease concentrations at day 45 by 80 percent.

Thesis (M.Tech.: Chemical Engineering)-Dept. of Chemical Engineering, Durban University of Technology, 2005 1 v. (various pagings) / In bubble-less aeration oxygen diffuses through the membrane in a molecular form and dissolves in the liquid. Oxygen is fed through the lumen side of silicone rubber tube. On the outer surface of the membrane there is a boundary layer that is created by oxygen. This then gets transported to the bulk liquid by convective transport created by water circulation through the pump. The driving force of the convective transport is due to concentration difference between the dissolved oxygen in water and oxygen saturation concentration in water at a particular temperature and pressure. The design of a membrane aerated bioreactor needs an understanding of the factors that govern oxygen mass transfer. It is necessary to know the effects of operating conditions and design configurations. Although various methods of bubble-less aeration have been reported, there still exists a lack of knowledge on the immersed membrane systems. This study is aiming at contributing to the development of an immersed membrane bioreactor using silicone rubber tubular membrane as means of providing oxygen. The secondary objective was to investigate the influence that the operating conditions and module configuration have on the system behaviour. From the experimental study, the characteristic dissolved oxygen -time curve show that there is a saturation limit equivalent to the equilibrium dissolved oxygen concentration, after which there is no increase in dissolved oxygen with time. At ambient conditions the equilibrium dissolved oxygen is approximately 8 mg/L. This is when water is in contact with air at one atmospheric pressure. At the same conditions the equilibrium dissolved oxygen concentration when water is in contact with pure oxygen is approximately 40 mg/L. This is why all the experiments were conducted from 2mg/L dissolved oxygen concentration in water, to enable enough time to reach equilibrium so as to determine mass transfer coefficient. The most important parameters that were investigated to characterise the reactor were, oxygen supply pressure, crossflow velocity, temperature and module orientation. Observations from the experimental study indicated that when the system is controlled by pressure, crossflow does not have a significant effect on mass transfer. When the system is controlled by the convective transport from the membrane surface to the bulk liquid, pressure does not have a significant effect on mass transfer. All four effects that were investigated in the study are discussed.

Water is a fundamental need for existence of mankind. Only 0.01 % of total global water is readily available for human consumption as fresh water. The rapid increase in human population and consequent rise in urbanization and industrialization is producing a stress on this meager water resource. Water at the same time is a renewable resource, ie with suitable treatment it can be made re-useable. Aeration is one of the important processes employed in activated sludge process of the biological treatment units of wastewater. In this process the level of dissolved oxygen in the effluent is raised to the required amounts to decompose organic matters present in the effluent and thereby to reduce the BOD (biochemical oxygen demand) of the effluent by a physical means called “aeration process”. The aeration process consumes as much as 60-80% of total power requirements of wastewater treatment plants. Therefore, the efficiency in design of aeration process is required so that treatment and its power consumption can be economized. With the objective of optimizing the aeration process the present work in this thesis endeavors to develop an aeration which is efficient as well as economical. The various geometric parameters that affect the aeration process in mechanical surface aerators have been optimized. In the present work circular surface aeration tanks have been used. There are two types of circular tanks: Baffled and unbaffled. Separate optimal geometric parameters have been obtained for baffled and unbaffled circular tanks. With optimal geometric similitude scale up studies were done. Reynolds number and Froude number criteria has been found unsuitable for scaling oxygen transfer rates. Theoretical power per unit volume parameter is the most suitable scaling parameter for oxygen transfer rates in both baffled and unbaffled circular tanks. Baffled circular tanks are found to give better performance in terms of oxygen transfer rates as compared to unbaffled tanks. In contrast unbaffled tanks give better performance in terms of power consumption as compared to baffled circular tanks. General correlations have been developed for oxygen transfer rates for both baffled and unbaffled circular surface aerations tanks which incorporate all the geometric and dynamic parameters. These correlations help in the design of new treatment facilities as well as evaluating and up gradation of existing facilities. Power consumption studies have also been conducted on circular surface aeration tanks. Geometric parameters affect the power consumption significantly. Using the optimal geometric similarity conditions obtained for oxygen transfer rates the scale up studies for power consumption has also been done. Reynolds and Froude criteria are found to be giving scale effects for non dimensional power consumption parameter, power number. Theoretical power per unit volume parameter is found to be the scaling parameters for power number and a suitable correlation equation has been developed for baffled circular surface aeration tanks. General correlations have been developed for power number in baffled and unbaffled circular tanks. A novel type of self aspirating tube sparger system has been developed. It is like a bubble aerator with a rotor. The various geometric parameters that affect oxygen transfer rates have been optimized in baffled circular surface aeration tank. The optimal geometrically similar tanks have been used for scale up studies. Theoretical power per unit volume parameter is found to be the scaling parameter for oxygen transfer rates in circular surface aeration tanks with self aspirating sparger systems. Circular baffled tanks with a special sparger system gives very much higher oxygen transfer rates (as much as 5.7 times) as compared to circular tanks. The oxygen transfer rates data from literature also show lower values as compared to the system developed in this thesis. Geometrically similar unbaffled tanks have also been used with self aspirating sparger system. For same power consumption oxygen transfer rate in circular surface aeration tanks with self aspirating sparger system is higher as compared to circular tanks without self aspirating system. Mixing mechanisms in surface aeration tanks depend upon two different extreme length scales of time, namely macromixing and micromixing. Small scale mixing close to the molecular level is referred to as micromixing; whereas macromixing refers to the mixing on a large scale. The effect of geometrical parameters on macromixing time has been studied. The scaling parameters for macromixing and micromixing have been developed and simulation equations governing these time scales are also presented.

Thesis (M.Tech.: Chemical Engineering)-Dept. of Chemical Engineering, Durban University of Technology, 2005 1 v. (various pagings) / In bubble-less aeration oxygen diffuses through the membrane in a molecular form and dissolves in the liquid. Oxygen is fed through the lumen side of silicone rubber tube. On the outer surface of the membrane there is a boundary layer that is created by oxygen. This then gets transported to the bulk liquid by convective transport created by water circulation through the pump. The driving force of the convective transport is due to concentration difference between the dissolved oxygen in water and oxygen saturation concentration in water at a particular temperature and pressure. The design of a membrane aerated bioreactor needs an understanding of the factors that govern oxygen mass transfer. It is necessary to know the effects of operating conditions and design configurations. Although various methods of bubble-less aeration have been reported, there still exists a lack of knowledge on the immersed membrane systems. This study is aiming at contributing to the development of an immersed membrane bioreactor using silicone rubber tubular membrane as means of providing oxygen. The secondary objective was to investigate the influence that the operating conditions and module configuration have on the system behaviour. From the experimental study, the characteristic dissolved oxygen -time curve show that there is a saturation limit equivalent to the equilibrium dissolved oxygen concentration, after which there is no increase in dissolved oxygen with time. At ambient conditions the equilibrium dissolved oxygen is approximately 8 mg/L. This is when water is in contact with air at one atmospheric pressure. At the same conditions the equilibrium dissolved oxygen concentration when water is in contact with pure oxygen is approximately 40 mg/L. This is why all the experiments were conducted from 2mg/L dissolved oxygen concentration in water, to enable enough time to reach equilibrium so as to determine mass transfer coefficient. The most important parameters that were investigated to characterise the reactor were, oxygen supply pressure, crossflow velocity, temperature and module orientation. Observations from the experimental study indicated that when the system is controlled by pressure, crossflow does not have a significant effect on mass transfer. When the system is controlled by the convective transport from the membrane surface to the bulk liquid, pressure does not have a significant effect on mass transfer. All four effects that were investigated in the study are discussed.