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This research involves design and implementation of computer program for simulation of a wastewater treatment plant. The program has the capability to be interfaced with an existing analog wastewater plant process flow training board which is equipped with meter readouts of key process variables and adjustable control valves. It is planned that the total system simulator could be used to train wastewater treatment plant operators to afford them hands-on dynamic experience in plant operations. The wastewater treatment process modeled is the activated sludge process. Beginning with the known plant design stead-state equations for this particular process an algorithm was developed to simulate the treatment process through probable system dynamics. All assumptions are presented in a logical manner and used to develop the necessary transient equations. The success of this project demonstrates that a simulation program which emulates a waste treatment process is possible; however, it is suggested that further research is needed to provide deeper insight into variable changes during system transients.

Yes / For the first time, an Euler-Lagrange model for Computational Fluid Dynamics (CFD) is used to model a full-scale gas-mixed anaerobic digester. The design and operation parameters of a digester from a wastewater treatment works are modelled, and mixing is assessed through a novel, multi-facetted approach consisting of the simultaneous analysis of (i) velocity, shear rate and viscosity flow patterns, (ii) domain characterization following the average shear rate value, and (iii) concentration of a non-diffusive scalar tracer. The influence of sludge’s non-Newtonian behaviour on flow patterns and its consequential impact on mixing quality were discussed for the first time. Recommendations to enhance mixing effectiveness are given: (i) a lower gas mixing input power can be used in the digester modelled within this work without a significant change in mixing quality, and (ii) biogas injection should be periodically switched between different nozzle series placed at different distances from the centre. / The first author is funded via a University of Birmingham Postgraduate Teaching Assistantship award.

<p>Validerat; 20111223 (anonymous)</p>

The presence of biologically-active estrogenic endocrine disrupting compounds (EDCs) in treated effluents from biological wastewater treatment facilities has prompted wide-spread interest in the behavior of these contaminants during the activated sludge process. The yeast-estrogen screen (YES) was used to quantify the estrogenic activity of samples taken from different areas of three wastewater treatment facilities. An estrogenic mass-balance around these facilities revealed that the majority of influent estrogenic activity was removed in the activated sludge process, but the main route for EDC discharge to the natural environment was via the treated effluent. The estrogenic activity in the effluent from a membrane bioreactor (MBR) was lower compared to a fully aerobic activated sludge process using secondary clarification, suggesting that enhanced removal of particulate and colloidal material may improve EDC removal efficiency. Colloidal material was obtained from settled mixed liquor suspended solids (MLSS) collected from a pilot MBR and a full-scale activated sludge process that included anoxic and aerobic zones. The MLSS was sized fractionated by filtration, and used to quantify the sorption coefficients for pyrene, 17&#946;-estradiol (E2), and 17α-ethinylestradiol (EE2) by fluorescence quenching. The MLSS-derived colloidal organic carbon (COC) sorption coefficient (Kcoc) for pyrene ranged from (< 1 to 80) L/kgcoc, indicating a similar affinity for pyrene compared to natural organic matter. Kcoc coefficients for E2 ranged between (< 1 to 158) L/kgcoc for E2 and (< 1 to 228) L/kgcoc for EE2, and are the highest E2 and EE2 sorption coefficients reported in the literature to date. There was a strong correlation between the Kcoc coefficients and molar extinction coefficient at 280 nm (e280) for pyrene and E2, suggesting that the interaction of the π;-electrons is an important factor in determining overall sorption behavior. There was no such correlation for EE2. Based on the Kcoc coefficients and COC concentrations of the samples, between 1 and 50% of the aqueous E2 and EE2 concentrations were associated with colloidal material. In a novel application of the YES bioassay, the bioavailability of colloid-associated E2 was quantified by comparing the EC50 values of the dose-response curves generated in the presence and absence of size fractionated COC. An increase in EC50 values as a function of COC concentration was attributed to a reduction in bioavailability of E2, suggesting that MLSS-derived COC can reduce, but not eliminate, the biological impact of EDCs. However, there was a high degree of variability in the EC50 values, and estimates of the colloid-associated E2 fraction based on the Kcoc-e280 correlation were unsuccessful in accurately predicting increases in EC50 values. Nevertheless, the YES bioassay may represent a powerful tool in determining the bioavailability of EDCs in complex environmental samples. Results from this research effort suggest that the colloidal phase derived from activated sludge systems represents an important transport vehicle whereby EDCs and other trace organic compounds can enter into the natural environment. Consequently, wastewater treatment plants discharging to sensitive ecosystems or involved with direct water reuse programs should optimize the treatment process to remove colloidal material. / Ph. D.

Utilization of the activated sludge process is widespread although many of the mechanisms that make it work are still relatively misunderstood. Recent studies have indicated that dual substrate limitations may occur in the process. Several misconceptions in the basic fundamentals regarding the rates and mechanisms involved in oxygen transfer to wastewater systems also exist. This research investigation examined the effects of the mean cell residence time and wastewater stoichiometry on the operation of the completely mixed activated sludge process under a dual substrate limitation. At low mean cell residence times (θ_c) the system was growth C limited with respect to carbon and at high mean cell residence times the system was oxygen limited. Oxygen transfer studies were conducted to ascertain the relationship between the steady state oxygen transfer coefficient (K_La) and the oxygen uptake rate of the mixed liquor (R). The objectives of this research were accomplished by operating two continuous flow bench scale activated sludge units at COD:TKN ratios of 6.07:1 and 0.65:1. Reactor-1 was operated at a COD:TKN = 6.07:1 and was always growth limited with respect to organic carbon while Reactor-2 was operated at a COD:TKN = 0.65:1 and was carbon limited at low mean cell residence times and oxygen limited at high θ_c values. Mean cell residence time served as the primary control parameter during the laboratory studies and was varied form approximately 2.5 to 21.0 days. Theoretical studies were also conducted in which biokinetic and stoichiometric equations were used to develop a model to simulate the process operating under carbon and oxygen limitations. The model was found to yield results that were similar to the actual experimental data collected. Further refinement of the model by including inhibition functions would result in a model with better predictability. Examination of the experimental data collected during the laboratory study revealed several interesting conclusions. Operation of the activated sludge process at a low COD:TKN ratio (0.65:1) and under an oxygen limitation at high mean cell residence times can result in high levels of free ammonia and nitrite that will lead to a deterioration in effluent quality. Increased removal efficiencies for COD, TKN and NH₃-N can be achieved by operating the process at a high COD:TKN ratio (6.07:1). Steady state oxygen transfer coefficients determined in the mixed liquor of the reactors indicated there was a direct relationship to the oxygen uptake rate of the activated sludge (R). This observation is quite significant since standard aeration theory states that K_La is constant for a given aeration device. Nonsteady state K_La values determined on the effluent from each reactor indicated that K_La was a constant. Alpha and beta coefficients determined from nonsteady state tests on wastewater effluent from each reactor showed no trend with the mean cell residence time. / Ph. D.