Effective control of nitrification processes employed at municipal wastewater treatment plants is essential for maintaining process reliability and minimizing environmental impacts and operating costs. While a range of process control strategies are available, they share a dependence on invasive liquid phase monitoring and are based on a periphery understanding of the metabolic status of the processes being controlled. Utilization of off-gas nitrous oxide (N2O) monitoring as a real-time indicator of the process metabolic status is a novel process control concept with the potential to address these concerns. This thesis details the development and evaluation of an off-gas N2O stress response based control technique. Examination of the stress response relationship demonstrated that it met the majority of the criteria of interest for process control. A simple feedback aeration control strategy was developed and evaluated through process simulation to determine the feasibility of implementation, cost effectiveness and associated environmental benefits. The off-gas N2O based control strategy provided better matching between aeration supply and metabolic demand, allowing the process to be maintained at the desired operating setpoints and avert nitrification failure. Performance was demonstrated to be similar to dissolved oxygen based feedback aeration control, although slightly more efficient at reduced dissolved oxygen concentrations. A technical, economic and environmental evaluation indicated that aeration control based on non-invasive off-gas N2O monitoring is technically feasible and has the potential to offer significant environmental and economic benefits including reductions in operating costs and process capital investment, as well as improved effluent compliance and reductions in emissions of gaseous pollutants including greenhouse gases. Overall, while off-gas N2O monitoring based aeration control techniques have the potential to provide significant economic and environmental benefits, a number of research questions remain to be answered. Future work in the form of long-term field trials is required to address these issues and allow quantification of economic and environmental benefits.

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 52-62).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Sept. 18, 2008). PDF text: ix, 228 p. : ill. (some col.) , maps (some col.) ; 4 Mb. UMI publication number: AAT 3297902. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (D.Eng.)--University of Delaware, 2008. / Principal faculty advisor: Paul T. Imhoff, Dept. of Civil and Environmental Engineering. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xi, 65 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-65).

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2007. / Includes bibliographical references (p. 45-47).

The objective of this research was to characterize the performance of a downflow bubblecontact (DBCA) hypolimnetic aerator — Speece Cone-. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of measure was examined: (a) the Oxygen Transfer Coefficient, KLa, corrected to 20°C, KLa₂₀ (hr­-¹), (b) the Standard Oxygen Transfer Rate, SOTR (g0₂.hr­-¹) (c) the Standard Aeration Efficiency, SAE (gO₂kWhr­-¹), and (d) the Standard Oxygen Transfer Efficiency, SOTE (%). Two sources of oxygen, Pressure Swing Adsorption (PSA) oxygen (87% purity) and air, were compared. KLa₂₀, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SAE deceased. An increase in inlet water velocity resulted in a decrease in KLa, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Treatments on air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on KLa₂₀, SOTE, SAE, and SOTE, when compared to treatments on PSA oxygen. The best performance was achieved with an inlet water velocity of 6.9-7.6 ms­-¹ and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66-72%. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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

No description available.

Within this study it was investigated how much energy and money that could be saved by implementing new aeration equipment and aeration control in Sternö wastewater treatment plant (WWTP). Sternö WWTP is a full-scale plant built in 1997 and dimensioned for 26 000 population equivalents. The plant has two parallel biological treatment lines with pre-denitrification. During the study, one of the treatment lines was used as a test line, where new aeration equipment and control was implemented. The other line was used as a reference line, where the aeration equipment and control was maintained as before. The new aeration equipment that was implemented to support the test line was an AtlasCopco screw blower, fine bubble Sanitaire low pressure diffusers and measurement equipment. Two control strategies were tested: oxygen control and ammonium control. The results show that 35 percentage points of the test line energy consumption was reduced with the new screw blower. The diffusers saved another 21 percentage points and by fine tuning the controllers, the oxygen concentrations and the air pressure a further 9 percentage points could be saved. The ammonium control gave no energy savings, since the lowest allowed DO set-point (0.7 mg L-1) kept effluent ammonium below the ammonium set-point of 1 mg L-1.  The final energy savings of the test line was 65 ± 2 %. Each aeration equipment upgrade increased the energy savings with: •    Blower 35 %. •    Diffusers 32 %. •    Oxygen control with decreased DO concentrations and air pressure 21 %. The final savings correspond to 13 % of the total energy consumption of Sternö WWTP. These savings are equivalent to annual savings of 178 MWh, which decreases the energy costs by 200 000 SEK per year. The payback period of the implemented aeration equipment and control was 3.7 years. / I denna studie har det undersökts hur mycket energi och pengar som kan sparas genom att installera ny luftningsutrusning och luftningsreglering i Sternö avloppsreningsverk. Reningsverket är beläget i Karlshamn och dimensionerat för 26 000 personekvivalenter. Den biologiska reningen är uppdelad på två parallella reningslinjer, där den ena användes till försök och den andra som referenslinje i denna studie. Den biologiska reningen utgörs av en konventionell aktivslamprocess med fördenitrifikation. Studien innefattade en simulering där två olika reglerstrategier för luftningen jämfördes. Simuleringen gjordes i programmet Benchmark Simulation Model no 1 och modellen anpassades för att efterlikna Sternö reningsverk på bästa sätt. De två reglerstrategierna för luftningen utgjordes av luftstyrning baserad på syrekoncentration i bioreaktorerna och luftstyrning baserad på utgående ammoniumkoncentration från bioreaktorerna. Simuleringen visade att energibesparingen från ammoniumreglering jämfört med en syrereglering är liten. Fördelen med ammoniumreglering är istället att den önskade reningsgraden lättare kan uppfyllas över året, trots varierande temperatur. Vid fullskaleförsök vid försökslinjen installerades ny luftningsutrustning (AtlasCopco blåsmaskin med skruvteknologi, Sanitaire småbubbliga diffusorer, samt mätnings-utrustning) och ny luftstyrning. Två luftstyrningsstrategier testades: syrereglering och ammoniumreglering. Resultaten visade att blåsmaskinen gav en energibesparing på 35 procentenheter, att diffusorerna gav en energibesparing på 21 procentenheter och att fininställd syrereglering tillsammans med sänkta syre- och lufttrycksnivåer gav en sänkning på 9 procentenheter. Ammoniumregleringen gav ingen energibesparing eftersom den lägst tillåtna syrekoncentrationen (0,7 mg L-1) höll ammonium-koncentrationen under sitt börvärde på 1 mg L-1. Den slutliga energibesparingen för testlinjen var 65 ± 2 %. Varje luftningsutrustning bidrog med följande energibesparing: •    Blåsmaskin 35 %. •    Diffusorer 32 %. •    Ny syrereglering med sänkta syre- och lufttrycksnivåer 21 %. Den slutliga energibesparingen i testlinjen motsvarar 13 % av Sternö reningsverks totala energiförbrukning, vilket gör att 178 MWh kan sparas per år. Den minskade energi-förbrukningen sänker energikostnaden för reningsverket med 200 000 SEK per år. Återbetalningstiden på den till försökslinjen installerade utrustningen var 3,7 år.