Дисертації з теми "Aeration efficiency"

Aeration is the process of increasing the dissolved oxygen content of water, which is an important water quality parameter for the survival of flora and fauna on this planet. The dissolved oxygen level can be increased using hydraulic structures or by installing mechanical aerators. Hydraulic structures proved to be an economical and efficient way of enhancing the aeration process, thereby increasing the dissolved oxygen in the water stream. It develops large amounts of air bubbles; as a result, contact surface area increases, and hence the water-air -mass transfer accelerates. Weirs are having the highest aeration efficiency among all hydraulic structures. Various researchers study the aeration process involved in weirs and various experiments have been done to study the parameters involved. As literature said that the aeration efficiency of the different hydraulic structures depends on their geometry. According to past studies, the researchers have stated that the hydraulic structures help enhance the dissolved oxygen of the water body. Rivers clean themselves naturally after movement over a certain distance by the process of aeration. It is also known as the self-cleaning nature of rivers. Weirs also follow the same process for cleaning as well as maintaining the various water quality parameters. They function in the same manner as rivers naturally perform the self-cleansing process for its purification. In the self-cleansing process, the river clears itself and maintains various water quality parameters. In order to enhance the DO content of the water body (river, dams, and reservoirs), an experimental study was conducted in Fluid Mechanics and Hydraulic Laboratory at the Delhi Technological University. The primary goal of this research was to increase the DO content of the water body through aeration. The author conducted an experimental study over three different types (Type-A, Type-B, and Type-C) of Piano Key Wier models and compared them to achieve this goal. The present study's findings conclude that the aeration of the free-flowing water can be enhanced by constructing hydraulic structures across the stream or river.

Achieving energy neutrality has shifted focus towards aeration systems optimization, due to the high energy consumption of aeration processes in modern advanced wastewater treatment plants. The activated sludge wastewater treatment process is dependent on aeration efficiency which supplies the oxygen needed in the treatment process. The process is a complex heterogeneous mixture of microorganisms, bacteria, particles, colloids, natural organic matter, polymers and cations with varying densities, shapes and sizes. These activated sludge parameters have different impacts on aeration efficiency defined by the OTE, % and alpha. Oxygen transfer efficiency (OTE) is the mass of oxygen transferred into the liquid from the mass of air or oxygen supplied, and is expressed as a percentage (%). OTE is the actual operating efficiency of an aeration system. The alpha Factor (α) is the ratio of standard oxygen transfer efficiency at process conditions (αSOTE) to standard oxygen transfer efficiency of clean water (SOTE). It is also referred to as the ratio of process water volumetric mass transfer coefficient to clean water volumetric mass transfer coefficient. The alpha factor accounts for wastewater contaminants (i.e. soap and detergent) which have an adverse effect on oxygen transfer efficiency. Understanding their different impacts and how different treatment technologies affect aeration efficiency will help to optimize and improve aeration efficiency so as to reduce plant operating costs. A pilot scale study of fine pore diffuser fouling and mitigation, quantified by dynamic wet pressure (DWP), oxygen transfer efficiency and alpha measurement were performed at Blue Plains, Washington DC. In the study a mechanical cleaning method, reverse flexing (RF), was used to treat two diffusers (RF1, RF2) to mitigate fouling, while two diffusers were kept as a control with no reverse flexing. A 45 % increase in DWP of the control diffuser after 17 month of operation was observed, an indication of fouling. RF treated diffusers (RF1 and RF2) did not show any significant increase in DWP, and in comparison to the control diffuser prevented a 35 % increase in DWP. Hence, the RF fouling mitigation technique potentially saved blower energy consumption by reducing the pressure burden on the air blower and the blower energy requirement. However, no significant impact of the RF fouling mitigation treatment technique in preventing a decrease in alpha-fouling (𝝰F) of the fine pore diffusers over time of operation was observed. This was because either the RF treatment method maintained wide pore openings after cleaning over time, or a dominant effect of other wastewater characteristics such as the surfactant concentration or particulate COD could have interfered with OTE. Further studies on the impact of wastewater characteristics (i.e., surfactants and particulate COD) and operating conditions on OTE and alpha were carried out in another series of pilot and batch scale tests. In this study, the influence of different wastewater matrices (treatment phases) on oxygen transfer efficiency (OTE) and alpha using full-scale studies at the Blue Plains Treatment Plant was investigated. A strong relationship between the wastewater matrices with oxygen transfer characteristics was established, and as expected increased alphas were observed for the cleanest wastewater matrices (i.e., with highest effluent quality). There was a 46 % increase in alpha as the total COD and surfactant concentrations decreased from 303 to 24 mgCOD/L and 12 to 0.3 mg/L measured as sodium dodecyl sulphate (SDS) in the nitrification/denitrification effluent with respect to the raw influent. The alpha improvement with respect to the decrease in COD and surfactant concentration suggested the impact of one or more of the wastewater characteristics on OTE and alpha. Batch testing conducted to characterize the mechanistic impact of the wastewater contaminants present in the different wastewater matrices found that the major contaminants influencing OTE and alpha were surfactants and particulate/colloidal material. The volumetric mass transfer coefficient (kLa) measurements from the test also identified surfactant and colloidal COD as the major wastewater contaminants present in the influent and chemically enhanced primary treatment (CEPT) effluent wastewaters impacting OTE and alpha. Soluble COD was observed to potentially improve OTE and alpha due to its contribution in enhancing the oxygen uptake rate (OUR). Although the indirect positive impact of OUR on alpha observed in this study contradicts some other studies, it shows the need for further investigation of OUR impacts on oxygen transfer. Importantly, the mechanistic characterization and quantitative correlation between wastewater contaminants and aeration efficiency found in this study will help to minimize overdesign with respect to aeration system specification, energy wastage, and hence the cost of operation. This study therefore shows new tools as well as the identification of critical factors impacting OTE and alpha in addition to diffuser fouling. Gas transfer depression caused by surfactants when they accumulate at the gas-liquid interface during the activated sludge wastewater treatment process reduces oxygen mass transfer rates, OTE and alpha which increases energy cost. In order to address the adverse effect of surfactants on OTE and alpha, another study was designed to evaluate 4 different wastewater secondary treatment strategies/technologies that enhances surfactant removal through enhanced biosorption and biodegradation, and to also determine their effect on oxygen transfer and alpha. A series of pilot and batch scale tests were conducted to compare and correlate surfactant removal efficiency and alpha for a) conventional high-rate activated sludge (HRAS), b) optimized HRAS with contactor-stabilization technology (HRAS-CS), c) optimized HRAS bioaugmented (Bioaug) with nitrification sludge (Nit S) and d) optimized bioaugmented HRAS with an anaerobic selector phase technology (An-S) reactor system configuration. The treatment technologies showed surfactant percentage removals of 37, 45, 61 and 87 %, and alphas of 0.37 ±0.01, 0.42 ±0.02, 0.44 ±0.01 and 0.60 ±0.02 for conventional HRAS, HRAS-CS, Bioaug and the An-S reactor system configuration, respectively. The optimized bioaugmented anaerobic selector phase technology showed the highest increased surfactant removal (135 %) through enhanced surfactant biosorption and biodegradation under anaerobic conditions, which also complemented the highest increased alpha (62 %) achieved when compared to the conventional HRAS. This study showed that the optimized bioaugmented anaerobic selector phase reactor system configuration is a promising technology or strategy to minimize the surfactant effects on alpha during the secondary aeration treatment stage
Ph. D.

Nitrogen, when present in excess, can cause eutrophication in waterways, which may result in hypoxia and the desertion or death of aquatic life. As nitrogen continues to pollute our water, wastewater discharge limits are becoming more stringent with effluent limits based on preserving receiving waters. This project took place at the Hampton Roads Sanitation District's, Chesapeake-Elizabeth Wastewater Treatment Plant; a High-Rate Activated Sludge (HRAS) plant with no primary clarifiers operating at an SRT of 1.5" 2 days without biological nitrogen removal (BNR). BNR is considered more cost-effective than comparable chemical and physical processes, but it requires considerable resources to meet increasingly strict discharge limits. As these limits decrease, the resource requirement increases, making them no longer cost-effective. By 2021 HRSD anticipates the plant will be included in a bubble permit, resulting in a total nitrogen (TN) effluent target of approximately 5-8 mg/L. Conventional BNR plants remove carbon and nitrogen simultaneously, which requires both increased volume (capital costs) and aeration energy demand (operating costs). As an alternative, HRSD is pilot testing an A/B process; a two-sludge system comprised of a carbon removal stage followed by a nitrogen removal stage. The very high rate, low dissolved oxygen (DO) A-stage could reduce the organic load, allowing the B-stage to perform BNR within the existing reactor volume and eliminating the need for primary clarifiers. However, improper control of the carbon removal system can lead to carbon and alkalinity deficiencies, which results in poor nitrogen removal. This is mediated by employing a short-cut nitrogen removal technology. A novel aeration strategy based on set-points for reactor ammonia, nitrite and nitrate concentrations with the aim of maintaining equal effluent ammonia and nitrate + nitrite (NOx) concentrations was successfully employed. The goal was to inhibit nitrite-oxidizing bacteria (NOB) so the nitrification process stopped at nitrite. This helps promote an effluent with equal parts ammonia and nitrite, which is amenable to anammox polishing to achieve low effluent nitrogen concentrations. NOB suppression has been successfully applied in sidestream anaerobic digestion waste streams because NOB out-selection is favored in warm, nitrogen-rich conditions. However, the cold, dilute conditions of continuous mainstream processes are not favorable to NOB out-selection. The mechanisms employed to achieve sidestream NOB out-selection are not reasonable for mainstream applications. This study employed operational and process control strategies to aggressively out-select NOB based on optimizing the chemical oxygen demand (COD) input, imposing transient anoxia, aggressive solids retention time (SRT) operation approaching ammonia oxidizing bacteria (AOB) washout, and a dissolved oxygen concentration (DO) of 1.5 mg O2/L during aeration. This pilot-scale study demonstrated that when run aggressively, the proposed online aeration control is able to out-select NOB in mainstream conditions and provide relatively high nitrogen removal without supplemental carbon and alkalinity at a low hydraulic retention time (HRT). Successful full-scale implementation would promote improved water quality that is economically sustainable. The ability of two different process configurations (full intermittent aeration and Modified Ludzak-Ettinger [MLE]) to achieve high nitrite accumulation and nitrogen removal efficiencies in four equal volume tanks in series followed by a cone-bottom clarifier in a pilot scale biological nitrogen removal (BNR) process (V=0.61 m3) was evaluated. All four biological reactors were equipped with a variable speed mixer, a 17.7 cm membrane disc diffuser, and a Hach LDO probe. Aeration capacity in all four tanks allowed the system to be operated with or without a defined anoxic zone. Both processes utilized a novel aeration strategy based on set-points for reactor ammonia, nitrite and nitrate concentrations with the aim of maintaining equal effluent ammonia and NOx concentrations. The B-stage had a variable HRT (2-7 hours) and a variable influent flow rate. When operating in the MLE configuration, an internal mixed liquor recycle (IMLR) line returned nitrified mixed liquor from the last aerobic reactor to the anoxic reactor using a peristaltic pump at a rate between 200-450% of the influent flow. When IMLR was used the first tank was not aerated. RAS from the clarifier was returned to the anoxic zone at 100% of the influent flow. SRT was controlled by wasting solids from the last aerobic tank. The wasting was automated to maintain desired SRT. The nitrite accumulation ratio (NAR), NO2- -N/(NO2- -N+ NO3- -N), was best under full intermittent aeration, achieving 0.43+0.10 at a 3 hour HRT and influent carbon to ammonia ratio (COD/NH4+-N) of 7.9+1.4. As an MLE, the NAR decreased with increasing internal mixed liquor return (IMLR); at IMLR of 200%, 325% and 450%, the NAR was 0.20+0.04, 0.17+0 and 0.14+0.03, respectively. The MLE did, however, improve the overall TIN removal efficiency compared to operation where all reactors were intermittently aerated. The TIN removal efficiency was best under MLE operation, increasing as the IMLR and influent COD/NH4+-N increased. When the IMLR was 200%, 325% and 450%, the TIN removal efficiencies were 76.4+4.0%, 80.2+0% and 86.3+5.0%, respectively, which corresponded to an influent COD/NH4+-N and HRT of 9.2+0.8 and 4 hr, 9.8+0.4 and 6 hr, and 10.3+1.2 and 6 hr, respectively. In addition to process operation, key issues of filamentous bulking were assessed. Concrete solutions to this continual issue are not available as the unique features of each plants influent and process dynamics prohibit the formulation of a universal solution. Filaments observed throughout this study included Type 0041, Type 0675, Type 0803, Nocardia, Thiothrix I and Thiothrix II. Type 0041 and Type 067 were observed throughout the study and are typical of BNR systems; they arguably do not contribute to settling issues. Type 0803 filaments are linked to low F/M, high SRT systems. It was present at the start of the experiment and then no longer detected. Nocardia made a brief appearance on day 72 causing temporary foaming issues. This was fixed by vacuuming the surface of the clarifier daily and may be attributed to the high surface area to volume ratio present in pilot-scale systems. Thiothrix I and Thiothrix II were observed after day 93, however, never as the dominant species. Thiothrix related bulking was observed in the A-stage (Miller et al, 2012), which was attributed to high sulfide and organic acids in the influent raw wastewater during high temperature periods and carryover of sulfide and Thiothrix from the over-sized A-stage clarifier. The goals of this evaluation were to identify favorable parameters of common filaments and establish their impacts on the system. Typically an SVI of 150 mL/g indicates good settling. Overall the study experienced good settling (128.3+36.3 mL/g), indicating that operating under different influent substrate concentrations and process configurations did not result in poor settling.
Master of Science

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%.

Baigiamajame magistro darbe nagrinėjamos pneumatinių bei mechaninių aeravimo sistemų problemos, jų konstrukcijos. Taip pat išnagrinėti veiksniai įtakojantys aeratorių efektyvumą. Išnagrinėjus konstrukcijas pasirinkti 3 aeratoriai su kuriais atlikti eksperimentai bei įvertintas jų efektyvumas. Darbą sudaro 8 dalys: įvadas, tyrimo objektas ir problemos aprašymas, tiriamųjų aeravimo sistemų apžvalga bei konstrukcijų analizė, mechaninių ir pneumatinių aeravimo sistemų efektyvumo analizė, tyrimo metodika bei eksperimentinis stendas, tyrimo rezultatai, išvados, literatūros sąrašas.
The following masters work consists of the analyse of the pneumatic and mechanical aeration systems, these problems and construction. Also explored factors who does influence for the efficiency of the aerators. When the constructions were explored, 3 aerators were selected, the experiments was made and valuated the efficiency. There are 8 chapters: introduction, the object of the analys and description of the problem, review of the explored aeration systems and analys of the constructions, efficiency analysis of mechanical and pneumatic aeration systems, methodology of the analysis and case of the experiment, results of the analysis, conclusions and suggestions, the list of the literature.

The study is about Nitrogen removal from the low concentrated mainstream wastewater after Upflow Anaerobic Sludge Blanket reactor process (UASB) by single-stage Partial Nitritation/Anammox process in a pilot scale reactor at Hammarby Sjöstad in Stockholm. A mixture of various concentrations of dissolved oxygen and different aeration methods have been tested in the pilot scale reactor in five months divided into five periods where the temperature was set at 15° C throughout the study. The best result was in period 4, the average nitrogen removal efficiency was 52% varying between 40 and 60 % with aeration method of the ratio R = 1/3 (R = 20 minutes with aeration to 40 minutes without aeration) and a dissolved oxygen concentration of 1.3 mg/L. Partial nitritation/Anammox is considered more environmentally friendly due to reduced energy requirements for aeration, no need for an external carbon source. The process also allows for a more cost-effective nitrogen removal from wastewater.
Vatten är nödvändigt för existensen av allt liv på jorden och spelar en avgörande roll i alla mänskliga aktiviteter. Antropogena aktiviteter förorenar denna viktiga resurs och medför stor risk för människors och djurs hälsa samt växter. Kvävebelastning från jordbruket och avloppsvatten i mark- eller vattenmiljön har resulterat till övergödning, vilket är ett miljö- och ekonomiskt problem på grund av en obalans mellan ekosystemtillförseln och den naturliga näringsförbrukningen. I denna studie behandlades avloppsvatten i en pilotskala reaktor med en integrerad fastfilm aktiverat slam (IFAS) som drivs med ett enstegs partial nitritation/Anammox-process. Kväverening från den lågkoncentrerade huvudström avloppsvatten efter Uppflöde Anaerob Slam Blankett reaktor process (UASB) undersöktes. En blandning av olika koncentrationer av upplöst syre och olika luftningsmetoder har testats i pilotskala reaktorn i fem månader uppdelad i fem perioder där temperaturen sattes vid 15° C under hela studien. De bästa resultaten i kväve reningseffektivitet var 52 % i genomsnitt i period 4 varierande mellan 40 och 60 %, luftningsmetod med ett förhållande av R = 1/3 (R = 20 minuter med luftning till 40 minuter utan luftning) och ett upplöst syre Koncentration av 1,3 mg/l. Jämförelsen tog hänsyn till alla former av utsläpp av kväve- och energikostnader för luftning. Under de senaste decennierna har vattenbehandlingsprocesserna haft många positiva utvecklingar, vilket har lett till en kvalitetsförbättring av vatten samtidigt som kostnaden för kväveavlägsnande från avloppsvatten har minskat. För närvarande flyttar kvävereningsteknik från konventionell nitrifikations/denitrifikationsprocessen till partiell nitritation/Anammox (PN/A) -processen kallad deammonification. Det verkar som om den största svårigheten är att upprätthålla en stabil ackumulation av nitrit medan man försöker delvis med nitritation av ammonium. Partiell nitritation/Anammox (PN/A) anses vara mer kostnadseffektivt avlägsnande av kväve från avloppsvatten, mer miljövänligt än konventionella nitrifikations-denitrifikationsprocesser på grund av minskat energibehov för luftning och inget behov av en yttre källa av kol.

Mestrado em Tecnologias do Ambiente - Tecnologias Ambientais - Instituto Superior de Agronomia
The energy consumption of wastewater treatment processes had become an important tool parameter for designers and engineers in the wastewater treatment industry, and efforts to improve the energy efficiency of the equipments represent a great challenge. The present study proposes the use of the Air Micro-Bubble Bioreactor (AMBB), with a working volume of 14 dm3 and a hydraulic retention time of 14 days, operating in continuous mode to treat winery wastewater from second racking period, for seven different runs, during 167 days. The organic loads fluctuations, usual in the winemaking industry, and the aeration time rate (ATR), both related to energy costs, were the studied variables. The chemical oxygen demand (COD) was selected as a key parameter to monitor the AMBB performance. The total polyphenol compounds were also followed. The effect of the organic loading rate OLR was assessed by adjusting feed substrate concentration between 0.16-0.44 kg COD m-3 d-1. The ATR varied between 1, 5 and 15 min h-1. Each run was operated until steady state was reached with respect to COD concentration. All runs showed a positive answer for COD removal, having a minimum efficiency of 70%. Also the COD removal efficiency showed to be not dependent on the applied OLR and the decrease in the ATR to 5 min h-1 was accompanied by a nearly three-fold reduction in energy consumption without relevant changing on the final COD removal efficiency (93-96%). However, the total polyphenol compounds removal was highly affected by decreasing the ATR from 15 to 1 min h-1, leading to a decrease in the total polyphenols removal efficiency from 94% to 4%. In the present study, we report for the first time the impact of oxygen-limited conditions in the AMBB performance with emphasis on the efficiency energy use. The polyphenols as a performance indicator, the energy costs of treated wastewater and COD removal efficiency achieved in pilot scale show the technical feasibility of the process, giving a sustainable solution for this important sector of activity.

In the production of pulp, paper and cardboard, a large amount of water is used daily. The water has to be purified in the internal purifying plant before it reaches the receiving body of water. In the biological purifying stage at the Stora Enso Skoghall mill, an aerated basin is used where the microorganisms, using oxygen, oxidize the organic material to carbon dioxide. The air is pumped from the bottom of the basin and the oxygen can then be transported from the air bubbles to the water through diffusion. The problem with aeration of waste water from the forest industry is that wood residues, such as fatty acids, are making the transport of oxygen in water more difficult. Previous studies show that adding salt improves aeration and the use of energy during the aeration process decreases. In many of the Swedish forest industries the electric power required for the aeration process is responsible for more than 50% of the total use of energy. The aim of this report is to study the aeration of waste water from a forest industry in order to make the aeration in the biological purification stage more energy efficient. The experimental part includes aeration experiments and measurement of surface tension when adding salt in clean and untreated process water. All experiments have been carried out in lab-scale at Karlstad University. The salts used during the study were sodium chloride, lime sludge and also precipitator dust, of which the two latter are by-products of pulping. The project has reached its goal, to compare and measure the speed of aeration when adding different salts to waste water from the forest industry in order to make the purification process more efficient.  This study shows that adding by-products may increase the speed of the aeration of waste water from the forest industry and decrease the use of energy during the aerobic treatment process. Adding precipitator dust to the fabrication water increases the speed of the aeration by 60%. The standard oxygen transfer rate (SOTR) decreased from 314tonnes O2/d to 118tonnes O2/d. The energy demand during the aeration process decreased by 100 MWh per day.
Vid framställning av massa, papper och kartong används dagligen stora mängder vatten som måste renas vid det interna reningsverket innan det når recipienten. En av industrierna är Stora Enso, Skogshalls bruk. I det biologiska reningessteget vid Skoghalls bruk används en luftad damm där mikroorganismer med hjälp av syre oxiderar det organiska materialet till koldioxid. Luft pumpas in från botten av dammen och syret kan transporteras från luftbubblorna till vattnet genom diffusion. Problemet vid syresättning av skogsindustriellt avloppsvattnet är att vedrester som exempelvis fettsyror följer med avloppsvattnet och försvårar syretransporten. Tidigare studier visar att vid tillsats av salt förbättras syresättningen och att energianvändningen vid luftningsprocessen minskar. De salter som valts i den här undersökningen är natriumklorid samt mesa och elfilteraska. Varav det två sista är biprodukter från massaframställningen. I många av Sveriges skogsindustrier står elen till luftningsprocessen för mer än 50 % av den totala energianvändningen. Det här arbetet syftar till att undersöka syresättningen av ett skogsindustriellt avloppsvatten med avsikt att energieffektivisera luftningen i det biologiska reningssteget. Den experimentella delen omfattar syresättningsförsök samt mätning av ytspänning vid tillsats av salt i både rent vatten och obehandlat processvatten. Samtliga försök har utförts i labbskala vid Karlstads universitet. Det här arbetet har uppnått sitt mål med att jämföra och mäta hastigheten av syresättning vid tillsats av olika salter i skogsindustriellt avloppsvatten med avsikt att energieffektivisera reningsprocessen. Resultatet tyder på att tillsats av biprodukter kan öka hastigheten vid syresättning av skogsindustriellt avloppsvatten och därmed minska energianvändningen vid den aeroba reningsprocessen. Vid tillsats av elfilteraska i processvattnet ökar hastigheten av syresättningen med 60 %. Det verkliga syrebehovet i dammen, SOTR sjönk från 314 ton O2/dygn till 118 ton O2/dygn. Energibehovet vid luftningsprocessen minskade med 100 MWh/dygn.

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
In wastewater treatment, activated sludge systems have been a technology widely applied as secondary treatment. During this step, which has a strong biological aspect, it is necessary to introduce oxygen supply for the maintenance of metabolic activity of the bacteria through the aerators. Aeration devices are responsible for most of the energy consumption in this stage. In this background, the influence of three aeration intensities (atmospheric air flow 3.5, 7.0 and 10.5 L.min-1) and the concentration of dissolved oxygen (DO) on the dimension of activated sludge flocs as well as on the efficiency of organic matter removal were assessed using a traditional activated sludge system which was fed with synthetic domestic wastewater. Samples were taken weekly from the three units that make up the system feed, aeration and storage tank in order to verify the Chemical Oxygen Demand (COD). It was established the process efficiency through a comparison between the initial and final COD. Besides the parameters already mentioned, this monitoring work on activated sludge batch system was also observed by Mixed Liquor Suspend Solids (MLSS), Volatile Suspend Solids (VSS), pH and temperature measures. The results have showed a maximum removal efficiency around 75% in the first aeration sequence and approximately 85% for the second and third one. For the first aeration, the DO concentration remained higher than 3.0 mg.L-1 and a diameter range from 10 to 60 μm was observed. In the second e third sequence, the DO concentration remained higher than 4.0 mg.L-1 with a diameter range of 10 until 200 μm. Although the sequence 1 and 2 have presented similar performances for organic matter removal, the sequence 2 promoted a regular floc size distribution and with lower values of Sludge Volumetric Index (SVI) meaning a better flocculating ability. In addition, the results reaffirmed what the literature has reported: higher DO concentrations produce flocs with greater dimensions
No tratamento de ?guas residu?rias, os sistemas de lodos ativados t?m sido uma tecnologia largamente aplicada como tratamento secund?rio. Durante essa etapa, a qual possui uma caracter?stica fortemente biol?gica, ? necess?rio o fornecimento de oxig?nio para a manuten??o da atividade metab?lica das bact?rias atrav?s de aeradores. Os dispositivos de aera??o s?o respons?veis pela maior parte do consumo de energia ao longo dessa fase. Nesse contexto, a influ?ncia de tr?s intensidades de aera??o (vaz?o de ar atmosf?rico de 3,5, 7,0 e 10, 5 L.min-1) e a concentra??o de oxig?nio dissolvido (OD) sobre a dimens?o de flocos de lodo ativado, e bem como sobre a efici?ncia de remo??o foram avaliadas utilizando um sistema tradicional de lodos ativados alimentado com efluente dom?stico sint?tico. Amostras foram retiradas semanalmente das tr?s unidades que compunham o sistema tanque de alimenta??o, de aera??o e de armazenamento para verificar a Demanda Qu?mica de Oxig?nio (DQO). A efici?ncia do processo foi estabelecida atrav?s da compara??o entre a DQO inicial e final. Al?m dos par?metros j? mencionados, este trabalho de monitoramento do sistema de lodos ativados de bancada foi observado tamb?m por meio de medi??es de S?lidos em Suspens?o Totais (SST) e Vol?teis (SSV), pH e temperatura. Os resultados mostraram uma efici?ncia m?xima de remo??o de quase 75% na primeira sequ?ncia de aera??o e aproximadamente 85% para a segunda e terceira sequ?ncias. Para a primeira aera??o, a concentra??o de OD manteve-se maior que 3,0 mg.L-1 e uma faixa de di?metro de 10 a 60 μm foi observada, enquanto que na segunda e terceira sequ?ncia, a concentra??o de OD permaneceu superior a 4,0 mg.L-1 com uma faixa de di?metro de 10 a 200 μm. Embora a sequ?ncia 2 e 3 tenham apresentado, ambas, desempenhos similares para remo??o de mat?ria org?nica, a sequ?ncia 3 promoveu uma distribui??o de tamanho de flocos mais regular e com baixos valores de ?ndices Volum?tricos do Lodo (IVL), configurando em uma melhor habilidade de sedimenta??o. Em adi??o, os resultados reafirmam o que literatura tem relatado, maiores concentra??es de OD produzem flocos com maiores dimens?es

Pharmaceutical compounds comprise a wide range of substances that are consumed in large quantities by modern societies and are generally released into local sewer networks through excretion. This research aimed to identify the factors affecting the removal efficiencies of these compounds in biological wastewater treatment plants (WWTPs) under different environmental conditions. Of the pharmaceutical compounds selected for this study, the highest influent concentrations measured in municipal wastewater treatment plants (MWWTPs) were for paracetamol, naproxen and bezafibrate (> 1 μg/L), followed by carbamazepine, atenolol, lidocaine, sulfamethoxazole and NACS (<1 μg/L). In hospital wastewater treatment plants (HWWTPs), the highest concentrations measured were for paracetamol and caffeine (> 10 μg/L), followed by ciprofloxacin and NACS (1–6 μg/L), and finally bezafibrate, carbamazepine, atenolol, lidocaine, clarithromycin and sulfamethoxazole (< 1μg/L). Antibiotic drugs were detected in HWWTPs, but rarely detected in MWWTPs. In general, the hospital wastewaters contained relatively higher levels of pharmaceuticals than municipal wastewaters. The removal efficiencies of the pharmaceutical compounds ranged widely. This was found to be related to characteristics and operational parameters of the individual WWTPs. The MWWTPs that utilized long aeration and biomass retention times (HRT,SRT), as evidenced by the occurrence of complete nitrification, were more efficient at removing paracetamol, naproxen, bezafibrate and atenolol, than the non-nitrifying plants with relatively shorter HRT and SRT. HWWTPs that operated under elevated ambient temperatures (> 26°C) achieved higher removal efficiencies (90%) for several compounds, including paracetamol, caffeine, sulfamethoxazole, ciprofloxacin, clarithromycin, NACS, atenolol, carbamazepine and lidocaine. In addition to the elevated ambient temperatures, elevated HRT and SRT and less dilution can lead to increased active biomass and can result in higher removal rates for the pharmaceutical compounds. Overall, the removal efficiencies of pharmaceuticals in WWTPs have been correlated to the type of treatment plant, the plants’ operational parameters (HRT, SRT), the climatic conditions (temperature and dilution effect of rainfall) and characteristics of the micropollutants (type and concentration). Aerobic and anaerobic batch biodegradation experiments were conducted to observe the removal of paracetamol, naproxen, ibuprofen and sulfamethoxazole at various SRTs. The biodegradation rates varied widely ranging from poor, to moderate, to high, depending on the SRT. Paracetamol was highly biodegradable under both aerobic and anaerobic conditions. Sulfamethoxazole was poorly biodegradable under aerobic conditions but highly biodegradable under anaerobic conditions. Relatively slow biodegradation rates were observed for ibuprofen and naproxen under both conditions; longer microbial adaptation periods for these two compounds were probably required. The most important factor affecting the removal of the compounds was the SRT. Therefore, the conclusion was drawn that combining anaerobic and aerobic systems with longer SRT and HRT could bring about significant reductions in the emissions of these contaminants into the environment via WWTPs; this is also a cost-effective option.

碩士
國立雲林科技大學
環境與安全工程系碩士班
95
This study was focus at the efficiency of petrochemical wastewater treatment by deep aeration system The treating process was carried out from August, 2004 to September, 2006. There are 7 parameters including pH, COD, BOD loading, MLSS, SV30, SS was monitored. From the result of experiment, control at pH = 7∼8, MLSS = 1000∼2000 mg/l, SV30 = 100ml/l, DO = 4∼6 mg/l, retention time = 30∼35 hrs, SVI = 80~200, BOD loading = 0.25∼0.35 kg COD/kg MLSS-day. The removal efficiency of COD is 94％ and the effluent of COD is 59.5 mg/l. This effluent can meet the effluent standard.

碩士
國立高雄第一科技大學
環境與安全衛生工程所
91
The oxygen transferring efficiencies for deep-shaft aeration processes was investigated in this study to develop energy-saving aerator systems. Both diffusers and jet aerators were tested in the study and their oxygen transferring efficiencies were compared, too. Several research objectives including to conduct aerator tests in a full-scale pilot aeration tank, to measure aeration efficiencies of both diffuser and jet aeration systems, to adopt computational fluid dynamics (CFD) software to simulate both fluid and oxygen concentration fields in the reaction tank and to elucidate their relationships, and, finally, to develop a energy-saving aerator system for deep-shaft aeration processes were interested in this study. Series of purging experiments were conducted in a deep-shaft aeration tank by using ambient air as an oxygen source. At least two water depths of 9 m and 11 m, respectively, were tested in this study. Before aeration testes, proper amount of Na2SO3 and CoCl2 was added to the tank to consume the residual D.O. in water and more than 4 D.O. meters with data logs were assembled in the deep-shaft aeration tank to measure dissolved oxygen concentrations during the experiments. Both oxygen transfer coefficients (KLa) and oxygen transfer rates (OTR) for the aeration systems were calculated for the tests. The experimental results showed the KLa value for traditional diffuser was 2.035 hr-1 and 1.870 hr-1 for the water depth of 9 m and 11m, respectively. But they were lower than those in the jet aeration system. 2.937 hr-1 and 2.537 hr-1 of KLa for water depth of 9 m and 11m, respectively, could be achieved in jet abreaction systems. The oxygen transfer rates for the jet aeration system were 0.378 kg-O2/KW-hr of water depth of 9 m and 0.429 kg-O2/KW-hr of water depth 11 m, respectively, and both of them were higher than diffuser aerator system. The jet aeration system can save 7.24-31.93 % energy consumption than the diffuser. There are several reasons that may cause jet aeration system achieving higher oxygen transfer efficiencies. The jet aeration system produces higher mixing conditions, which can enhance oxygen transfer rates, is one reason and less power consumption in the Ventric pipe also cause it save more energy. This research also indicates that the highest aeration efficiencies can be achieved as the flowrate ratio of the aeration air to circle water equal to 0.8.

碩士
國立中興大學
農業機械工程學系
87
The aeration cone is the main equipment of pure oxygen absorption system for the recently domestic used water recirculating culture system. The operational control of the aeration cone which controls the Dissolved Oxygen (DO) value of water outlet and the oxygen transfer rate, is mainly by changing the inlet water flowrate and the regulatory valve setting pressure of pure oxygen. In this study, the temperature of water was maintained at about 30℃. When the inlet water flowrate of the aeration cone was controlled between 270-330L/min, the DO value of water outlet would demonstrate a decreasing tendency with the increasing of the inlet water flowrate. When the regulatory valve setting pressure was controlled between 0.35-0.40kg/cm2 (cm square), both of the DO value of water outlet and the oxygen transfer rate would increase as the regulatory valve setting pressure raised. The experimental results showed that the oxygen transfer rate was between 1.137-1.647g/min, the oxygen absorption efficiency was maintained between 72.4-81.5%, the oxygen transfer efficiency was between 0.0681-0.0941kg/kW-hr, the aeration effectiveness was 60.67-70.87%, and the utilization efficiency was maintained between 44.2-58.7%. Furthermore, the relative height between positions of the culture tank and the aeration cone can be designed and planned using Bernoulli's equation. The water lever inside the aeration cone would drop as the regulatory valve setting pressure increased and raise as the inlet water flowrate increased. The water level inside the aeration cone must be kept at least over 60 cm to avoid the water level being too low as the undissolved oxygen inside the aeration cone smuggled with the water flow to the culture tank resulting a waste of oxygen leaking to the atmosphere.

碩士
嘉南藥理大學
環境資源管理系
105
This study aimed to improve the pollution removal efficiency of subsurface flow constructed wetlands by partial circulation and aeration. The experiment had been divided into two systems: the experimental system (HSSF-A) where partial circulation and aeration have been installed and the control system (HSSF-B) which was only a traditional a traditional subsurface flow constructed wetlands. Both models have the same design and operating conditions treating campus wastewater. Based on the experimental results, there is an increase from 43.7% on HSSF-B to 63.4% on HSSF-A under the condition of low concentration of biochemical oxygen demand (12.16mg / L). Moreover, the data have shown that the experimental system (HSSF-A) outperformed the control system (HSSF-B) with a recorded removal of ammoniacal nitrogen of 98% and 12%, respectively. Hence, there was no observed NO2- - N accumulation in both systems giving low effluent concentrations of 0.02 and 0.01 mg/L, respectively, as well as with the nitrate concentration. These results proved that aeration and partial circulation can effectively improve the organic pollution and nitrogen removal efficiency of the system.

Due to the growing awareness of climate change, there is a need to quantify GHGs from different sources. The water industry, which provides the water supply, wastewater collection, and treatment and discharge, contributes significantly to total energy consumption and consequently to GHG emissions in developed countries. In WRRFs, large amounts of organic and inorganic matter are transformed and transferred from the water phase to the atmosphere, lithosphere, and/or biosphere through emissions from process tanks, and treated effluents and biosolids that are disposed in the environment. All three main GHGs (i.e. CO2, CH4, and N2O) are emitted from WRRFs. N2O is currently the GHG of major concern with regards to direct emissions from WRRFs. N2O has a GWP 265–298 times that of CO2 for a 100-year timescale which makes this the single most important ozone depleting compound of our century. Anthropogenic activity is responsible for about 40% of the global N2O production and a 15% concentration increase has been observed since 1750. To date 3% of the anthropogenic N2O production is recognized to be generated by wastewater treatment. WRRFs designed for nutrients removal have been observed to emit up to 7% of the influent nitrogen load as gaseous N2O. In a WRRFs the bioreactor is currently recognized as the most emitting treatment step in these terms. In addition to this, the aerated compartment of bioreactors is generally recognized to cause between 45 to 75 % of the plant’s energy expenditure. Considering both the contribution of N2O emissions and energy expenditure, the biological step of a WRRF represents the large majority of the CFP of a WRRF. Measuring and accounting for N2O emissions and aeration efficiency requires standard methods allowing to obtain comparable measurements among different WRRFs and reproducible within the same facility in order to derive solid classifications. However, especially for N2O, there is the need of a unified protocol with general standardized guidelines for a sound assessment at different WRRFs. Both N2O and aeration efficiency measurements protocols present major lacks and assumptions. This thesis puts in evidence major weaknesses of protocols for N2O emission and aeration efficiency measurements proposing possible improvements in terms of sampling strategy, calculation methods and equipment. As measurements of N2O emissions and aeration efficiency are used to understand process dynamics and design new CFP minimization scenarios, also modelling WRRFs is very important in this view, given the system complexity. Modelling tools allow to design new plant operation and control strategies (aimed at minimizing these emissions) and evaluate their long term effect on the WRRF limiting trials (and risks). Current N2O kinetic models are highly developed in describing the biochemical processes, however, as they are developed in lab-controlled conditions, they are yet troublesome when it comes to full-scale applications. This is most probably due to a poor representation of local concentrations by the plant’s model layout and often to an over-parametrization of the biokinetic model. The modelled description of the plant’s layout is nowadays often erroneously underestimated, but its design should be one of the most important steps in the definition of a plant’s model as it has important effects on the calculation effort, the calibration of the kinetic model, and nonetheless, on its predictive power. This thesis considers one of the most advanced kinetic models available in the literature and shows how, using a better representation of hydrodynamics, this can improve its performances. As effective applications, and applicability, of kinetic models for N2O prediction in full scale are still limited, possible modelling alternatives are evaluated in this work. The application of a qualitative, knowledge-based risk assessment model (N2O risk model) to a full-scale datasets is provided to prove the concept of its use. The N2O risk model shows to be effective in helping to unravel the dynamics behind N2O production and to be able to give valuable insight in the mechanisms of N2O production. In addition to this, seen the crescent quantity of data that current WRRFs have available, and the fact that the amount of information is too often unused wasting part of the value of sensors and SCADA systems. A data mining approach is also presented. In this regard, this thesis gives a practical application of a data mining technique to derive potential relations with respect to N2O emission among variables that are routinely measured at WRRFs. The testing of different clustering algorithms and their critical evaluation is shown in view of an online application. This is furnishing a possible new root to the use of SCADA data for understanding and mitigating N2O emissions by translating hidden information into clear operational instructions. In summary, this thesis raises the main concerns about N2O and aeration efficiency assessment analyzing major weaknesses and suggesting possible solutions for developing more robust standardized methods. It further provides an overview of different N2O modelling approaches proposing possible developments to enhance capabilities to recognize sources of emission and provide clues for developing CFP reduction strategies.

碩士
國立宜蘭大學
環境工程學系碩士班
99
Recently, not only economic is growing fast, but water pollution is getting serious day after day. Many countries develop constructed wetland as a new technique for water pollution treatment, due to the lower cost of operation and easier maintenance. In this study, experiments were carried out in a laboratory scale three-zone free water surface constructed wetlands (FWS) which is divided into three units including full vegetabled zone 1, open water area and full vegetabled zone 2. The experiments are designed to test aeration and no aeration environment to provide varied microbes and plants proceeding purification. Because the nitrification of the open water area is not obvious in three-zone free water surface constructed wetland, the overall nitrogen removal rate doesn’t reach high value as expected. Consequently, artificial aeration on open water area will promote both nitrification and nitrogen removal. The objective of this study is to investigate the nitrogen removal efficiency of different pollution loading in three-zone free water surface constructed system. The air-water ratio and aeration position were used as parameters. The experiments were conducted the nitrogen form change and the effect to water quality in three units. The study involved low and high nitrogen pollution loading which include two and five tests, respectively. Experiments of two pollution loading tests contained both no aeration and aeration. In addition, we also investigate the high pollution loading test efficiency in different air-water ratio (6:1 and 12:1) at bottom and middle layer. The experimental result showed that NH3-N removal of no aeration and aeration in low pollution loading test were 94.9 % and 97.7 %, respectively. TN (total nitrogen) removal were 77.3 % and 85.3 %, BOD removal were 93.8 % and 95.4 %, respectively. Additionally, NH3-N removal of air-water ratio (12:1) at middle layer in high pollution loading test was 89.7 %. However, NH3-N removal of no aeration in high pollution loading test, which was the lowest removal efficiency, declined to 29.3 %, and the others were between 51.9 % and 54.3 %. TN removal ranged from 48.5 % to 60.0 %. BOD had higher removal efficiency, the removal ranged between 89.4 % and 97.5 %. In summary, aerating in low pollution loading will improve the removal of NH3-N, TN and BOD. It illustrated that aerating in bottom layer could increase nitrogen removal. In contract, aerating for high pollution loading, despite the significant increasing removal of NH3-N and BOD, the removal of TN decrease. It showed that aeration can enhance nitrification availably, and let NH3-N transform into NOx-N. Futhermore, artificial aeration in air-water 12:1 at middle layer is the most effective. Consequently, if aerating appropriately in the open water area in three-zone free surface water constructed wetland, dissolved oxygen will increase. As a result, promote nitrification can improve the nitrogen transformation and removal efficiency for the constructed wetlands.

碩士
嘉南藥理大學
環境資源管理系
106
To improve the low efficiencies of pollutant degradation induced by lacking of sufficient oxygen transportation, there were two modifications of the artificial aeration and nitrate-dependent anaerobic ferrous oxidation (NAFO) was installed in a horizontal subsurface flow (HSSF) constructed wetland (CW). In the campus of Chia-Nan University of pharmacy and science, there were 2 systems established in this study which included an experimental system and a control one with identical dimension. The former (HSSF-H) installed those modifications while the other (HSSF-F) was regarded as a control system which only possessed a gravel bed and the aquatic plant (Hydrocotyle verticillata Thunb.). In the stage I of the experimental program, there only installed an artificial aeration in HSSF-G and the NAFO device added to HSSF-G in the stage II. The water quality parameters; biochemical oxygen demand (BOD), ammonia-nitrogen (ammonia-nitrogen; NH3-N), nitrate-nitrogen, nitrite- nitrogen, total Kjeldahl nitrogen (TKN), total nitrogen (TN), total Phosphorus (TP), ferrous iron (Fe2+), and total iron (TFe) were used to evaluate the removal efficiencies of HSSF-H and HSSF-F. The conclusions obtained in this study was described in the following. According the experimental results, there was significant differences between the BOD removal ratios of HSSF-G and HSSF-F. In the stage I, the removal ratios of HSSF-G and HSSF-F were 91.3 % and 71.5 %, respectively. When the NAFO device activated in the stage II, the removal ratios of HSSF-G maintained at 93.6 % and that of HSSF-F was 63.7 %. It implied that the aeration could effectively improve the BOD removal performance and the NAFO device played no negative role in the BOD removal process. It also found a similarity between the removal tendencies of NH3-N and TKN in HSSF-F and HSSF-G. In the stage I, the removal ratio of NH3-N in HSSF-G, 77.7%, was not significantly different from that in HSSF-F, 86.1%. As for the stage II, the removal ratios of NH3-N were 87.1 % and 86.6 %, respectively. No significant difference existed between these removal ratios of NH3-N. Similar tendency also occurred in the removal of TKN. In the stage I, a lower removal ratio of TKN in HSSF-G, 72.1 %, still observed and a higher one, 83.1 %, without significant difference from that of HSSF-G resulted in in HSSF-F. When coming to stage II, the removal ratios of TKN in HSSF-G and HSSF-F, 81.0% and 80.6%, were quit close to each other. As for the removal of TN in the stage I, they were 63.7 % and 82.8 % for HSSF-G and HSSF-F, respectively. In the stage II, those removal ratios became 69.5 % and 78.2 %, respectively. A lower removal ratio of HSSF-G mainly resulted from the lower removal ratio of TKN and NO3─-N which might be induced by the competition of organic carbon source. There observed a significant difference between the TP removals of HSSF-G and HSSF-F. No effective improvement of TP removal was activated by NAFO process. It was because that the suitable pH for the sedimentation of ferric phosphate was about 8 while the pH in HSSF-G ranges from 6.58 to 7.06. It was not a proper pH for the sedimentation of ferric phosphate.

碩士
國立中央大學
環境工程研究所碩士在職專班
99
Aeration is a key control activated sludge processes, which can be achieved by various methods. The performance of membrane fine bubble diffuser was studied here. A model system similar to real aeration tank, that is, depth of 3~4 m, was used to eliminate the size effects in studies of small scale. The effects of temperature, water depth, aeration velocity, and salt concentration on the overall oxygen transfer coefficient (KLa20) were examined. The temperature correction factor was confirmed to be similar to that suggested by ASCE. The KLa20 was also found to be decreased than increased before 200 mg/L of sodium chloride and remained similar after that. It was similar to the effects of suspended solids, for which the reason is still not clear. The oxygen transfer coefficient and correction factors of two different municipal wastewaters and a organic pigment wastewater were examined. It was found that although the municipal wastewater came from different places and the compositions of them were slightly different, the values of the correction factors are similar, which is 0.67 ~ 0.69. However, for the organic pigment wastewater, the correction factors varied significantly from batch to batch. The result suggested that due to the variation in wastewater quality, the aeration efficiency might be affected correspondingly and, therefore, the performance of activated sludge system was not stable.

碩士
嘉南藥理大學
環境資源管理系
106
In order to enhance the removal efficiency of constructed wetland (CW) under high load conditions, this study set up three sets of small modular systems for surface flow constructed wetlands which includes FWS-A operated in a continuous aeration mode with a shorter bio-gravel wall, FWS-B operated in an intermittent aeration with a longer bio-gravel wall, and a control one (FWS-C). By these FWS CWs, this study investigated the effects of the bio-gravel wall length and aeration mode on the of pollutants removal efficiency. During the experimental period, it included 5 stages with different hydraulic retention times (HRT) and aeration modes.The performance of FWS CWs was evaluated by the water quality parameters which included biochemical oxygen demand (BOD), total ammonia-nitrogen (TAN), nitrite-nitrogen (NO2－-N), nitrate-nitrogen (NO3－-N), total Kjeldahl nitrogen (TKN), total nitrogen (TN), and total phosphorous (TP).. During the experimental period at Stage-III, FWS-A operated under a continuous aeration without control dissolved oxygen (DO). FWS-B aerated on an aeration ratio (AR=8 : 16； 8 hours aeration ： 16 hours non-aeration). The HRT of FWS-A, FWS-B, and FWS-C were 3.24. d, 3.27 d, and 2.28 d, respectively. From the experimental results, the removal rates of BOD were 70.3 %, 64.2 %, and 9.2 %, respectively. The TAN removal rates were: 99.6 %, 95.9%, and 81.5 %, respectively. The TKN removal rates were 97.9 %, 97 %, and 77.7 % and TN removal rates were 81.5 %, 89.8 %, and 76.4 %, respectively. By an optimizing process of Stage-IV, FWS-A operated under a continuous aeration but controlled the DO, while FWS-B intermittently aerated for AR=6 : 6. The HRT of FWS-A, FWS-B, and FWS-C system were: 1.52 d, 1.54 d, and 1.48 d, respectively and the responding removal ratios of BOD were 76.9%, 67.2%, and 37.6%, respectively. The TAN removal rates were 93.7%, 95.0%, and 73.1%, respectively. The TKN removal rates were 79.5 %. 84%, and 61.4% and TN removal rates were 76.3 %, 83.9%, and 61.5%, respectively. These results showed that the longer the HRT in CW operation was, the better the removal efficiency would be, but the experimental group can also be used under the finer operation strategy. A half-time reduction in HRT created a quite good removal performance. According to the results of the experiments in Stage-I~V, the artificial aeration was quite helpful for the removal of nitrogenous pollutants and organic pollutants by CW and the bio-gravel wall in this research system could also improve the artificial aeration of FWS CW. The bio-gravel wall also improved the accumulation of NO3－-N caused by the continuous aeration in FWS CW. For the removal of TP, the removal rate was not affected by the aeration mode and bio-gravel wall.

碩士
國立臺灣大學
生物環境系統工程學研究所
96
The dissolved oxygen（DO）is nearly none at the bottom of water at the midstream of Tanshui river. Therefore, this study is applying an air-lift column to deal with low DO condition of water and investigating hydraulic characteristic of Dadaocheng Basin as air-lift column design reference resources. In this study, the air-lift column is a low energy costing and intermittently operating device which can mix different water layers. Field experiments in summer and winter are operated to measure the oxygen consumption rate of the sediment. And the air-lift column efficiency of the increased oxygen rate、the water mixing ability and the oxygen spread of ability are fast. Standard experiment of air-lift column is carried out in static state water. And compare the efficiency of the two types of column design. In addition, this study measures the increased oxygen efficiency and diffusive ability of the aeration boat to build up the database for river renovation. Results show DO below 3ppm and without-delaminating during the period of flood tide and only about 1ppm in the ebb tide in the Dadaocheng watershed. The oxygen consumption rate of the sediment are 9±6 mg/m2/min in summer (water temp. 26℃) and 5±5 mg/m2/min in winter (water temp. 19℃). The standard aeration efficiency (SAE) of air-lift column is 1.50 kgO2/kw/hr, up-welled water volume is 621~629 ml. when it is applied to the low speed flow watershed, the agitated range is about 3 m、the increased oxygen rate at the outlet is 0.86mg/l and the electric cost is 0.38 NT dollar/mgO2/l/hour. The increased oxygen rate of the aeration boat in Kaohsiung is 1.8mg/l and electric cost is 6.99 NT dollar/mgO2/lhour. Comparing water quality improvement ability and the oxygen spread of ability between indirect oxygen increasing air-lift column and continuous aeration boat, indirect oxygen increasing method has better performance than continuous oxygen increasing method. To sum up, the air-lift column can be one of the physics methods to effect oxygen increasing.

碩士
國立成功大學
機械工程學系
107
The high-efficiency aerator is a pump with upper and lower blades. The upper layer is a air pump and lower layer is a water pump. The air and water pushed out by the blade and mixed at a pipe. It can increase the amount of dissolved oxygen. The power used in this design is a 750W (1HP) DC brushless motor that produces micron-sized bubbles and a jet of water up to 13 meters. In addition, the pump can be rotated 360 degrees. After the experimental measurement, it is proved that the aeration effect caused by it is more than 100 times that of the traditional waterwheel. Overall, this design has the effect of saving electricity and super high oxygen. It will greatly improve the breeding environment, reduce subsidence of the formation, and improve sewage treatment efficiency. Rate and improve the problem of water eutrophication. This design follows the guidance of Dr. Sen-Yung Lee and Dr. Shueei-Muh Lin and refer to the design derivation of Xu Shuzheng's master thesis of Kunshan University of Science and Technology. Then, We modified the size of the pump and designed a highly efficient aerator that met the requirements.