Oxidation Ditch Process Research Articles

Design characteristics of Curved Blade Aerator w.r.t. aeration efficiency and overall oxygen transfer coefficient and comparison with CFD modeling

The main objective of this work is to design a high efficiency curved-blade-surface mechanical aerator for oxidation ditch, which is used to treat municipal and domestic sewage. Aeration experiments were conducted in oxidation ditch made up of mild steel sheets to study the design characteristics of curved blade surface mechanical aerator. The paper critically examines six different configurations of aerators, which were developed, fabricated and tested in the laboratory for its various dynamic parameters, such as diameter of aerators (D), speed (N) and immersion depth (h). Out of the different configurations tested, the curved blade rotor (CBR) emerged as a potential aerator with blade tip angle of 47°. The overall oxygen transfer co-efficient (KLa) was observed to be as high as 10.33 h-1 and the optimum aerator efficiency (AE) was found to be 2.269 kgO2/kWh. The standard aeration efficiency (SAE) of CBR was observed to be higher as compared to other aerators used for oxidation ditch process. Dimensional analysis was used to develop equations that describe the aerator’s behavior. Further, a CFD model is also developed for better understanding of the process that takes place inside the ditch. To prepare it 3D and steady flow, k-e turbulence model of flow was used and the simulation runs were carried out for one phase model to generate the data so as to compare it with experimentally observed values. Keywords: Oxidation ditch, dissolved oxygen, aerator, overall oxygen transfer coefficient, aeration efficiency, CFD

Monitoring and evaluation of removal of pathogens at municipal wastewater treatment plants

The concentrations and removal of Cryptosporidium, Giardia, and microbial indicators, including somatic coliphages and fecal coliforms were investigated through the wastewater treatment processes at three municipal wastewater treatment plants in Beijing, China. The experimental results showed that the concentrations of Cryptosporidium in untreated wastewater, primary treatment effluent, secondary treatment effluent, tertiary treatment effluent were 33-600, 67-333, 0-9 and 0-0.4 oocysts L(-1), and that of Giardia were 130-3,600, 533-2,033, 0-32 and 0-2.1 cysts L(-1), respectively. The reduction ratios of Cryptosporidium and Giardia by the primary treatment process were 0.12 log and 0.18 log, respectively. Oxidation ditch process had higher reduction efficiency to Cryptosporidium and Giardia than anaerobic-anoxic-oxic process and conventional activated sludge process, probably because of longer retention time and higher sludge concentration. Membrane ultrafiltration had a notably better efficiency to reduce microorganisms, especially Cryptosporidium and Giardia, than conventional flocculation sedimentation and sand filtration process, as the tertiary treatment. Comparing with total coliforms, fecal coliforms and heterotrophic bacteria, concentration of somatic coliphages was correlated better with that of Cryptosporidium and Giardia in untreated wastewater and secondary treatment effluent.

Contribution of the Estrogen-Degrading Bacterium Novosphingobium sp. Strain JEM-1 to Estrogen Removal in Wastewater Treatment

This study aimed to investigate the contribution to estrogen removal from the activated sludge of an estrogen-degrading bacterium, Novosphingobium sp. Strain JEM-1, isolated by the writers from the activated sludge. The cell numbers of the Strain JEM-1 were investigated in two full-scale wastewater-treatment plants using real-time PCR. Strain JEM-1 appears to be commonly distributed in the activated sludge. The cell numbers of Strain JEM-1 in the oxidation ditch process were higher than those in the conventional activated sludge (CAS) process, and the effluent concentrations of E1 in the CAS process tended to decrease with increased cell numbers of Strain JEM-1. In a bench-scale experiment to investigate bioaugmentation with Strain JEM-1, there was a significant difference in the effluent concentrations of estrogens between the experimental series and the control series. Linear relationships were observed between cell numbers of Strain JEM-1 and the efficiency of removal of estrogens. These results sugges...

Flow characteristic and wastewater treatment performance of a pilot-scale airlift oxidation ditch

A pilot-scale airlift oxidation ditch using bubble diffuser and baffle as aerator was operated in a wastewater treatment plant (WWTP) to investigate its flow characteristic and wastewater treatment performance. Compared with the conventional oxidation ditch process, effective depth and oxygen utilization efficiency of this new process was improved by underwater aeration. Furthermore, it had a reversed velocity distribution, which decreased from the bottom to the top on vertical section. Velocity measurement showed that a velocity over 0.2 m/s at the bottom was sufficient to prevent sludge settlement during long term operation. Application of these concepts would save land area and energy consumption by about 25%–50% and 55%, respectively. In this new system, organic biodegradation and nitrification could be well achieved. Denitrification could occur steadily in the straight part by adjusting the airflow rate. An average TN removal rate of 63% was achieved with dissolved oxygen (DO) concentrations between 0.6 mg/L and 1.5 mg/L. The main pollutants in the effluent could meet the strictest discharge standard (COD<50 mg/L, NH4 +−N < 5 mg/L, and TN < 15 mg/L) in China now.

Anoxic phosphorus removal in a pilot scale anaerobic-anoxic oxidation ditch process

The anaerobic-anoxic oxidation ditch (A2/O OD) process is popularly used to eliminate nutrients from domestic wastewater. In order to identify the existence of denitrifying phosphorus removing bacteria (DPB), evaluate the contribution of DPB to biological nutrient removal, and enhance the denitrifying phosphorus removal in the A2/O OD process, a pilot-scale A2/O OD plant (375 L) was conducted. At the same time batch tests using sequence batch reactors (12 L and 4 L) were operated to reveal the significance of anoxic phosphorus removal. The results indicated that: The average removal efficiency of COD, NH4+, PO43−, and TN were 88.2%, 92.6%, 87.8%, and 73.1%, respectively, when the steady state of the pilotscale A2/O OD plant was reached during 31–73 d, demonstrating a good denitrifying phosphorus removal performance. Phosphorus uptake took place in the anoxic zone by poly-phosphorus accumulating organisms NO2− could be used as electron receptors in denitrifying phosphorus removal, and the phosphorus uptake rate with NO2− as the electron receptor was higher than that with NO3− when the initial concentration of either NO2− or NO3− was 40 mg/L.

Oxidation ditch process using curved blade rotor as aerator

Oxidation ditch process is used to treat the municipal and domestic sewage. The untreated sewage generates fouling smell, harmful bacteria, etc. which is hazardous for public health and degrades the environment by librating noxious gases. This paper examines the use of curved blade aerator for oxidation ditch process. The rotor, which controls the aeration, is the main component of the aeration process. Therefore, the objective of this study is to find out the variations in overall oxygen transfer coefficient and aeration efficiency for different configurations of aerators by varying the parameters like speed of aerator, depth of immersion and blade tip angles so as to yield higher values of overall oxygen transfer coefficient and aeration efficiency. Four aerators of different configuration were developed and fabricated in the laboratory and were tested for above mentioned parameters. A mathematical model is developed for predicting the values of k L a and aeration efficiency which has R 2 values of 0.97 and 0.99 for experimentally determined and calculated values. In laboratory studies, the optimum value of overall oxygen transfer coefficient and aeration efficiency were observed to be 10.33/h and 2.269 kg O 2 /kWh for aerator speed of 48 rpm, 5.5 cm depth of immersion and 47 o blade tip angle for curved blade aerator.

Removal and degradation characteristics of natural and synthetic estrogens by activated sludge in batch experiments

The removal and degradation characteristics of natural and synthetic estrogens by activated sludge were investigated by a series of batch experiments using the activated sludge samples of four actual wastewater treatment plants and synthetic wastewater spiked with estrogen. The rapid removal and degradation of 17β-estradiol (E2) and estrone (E1) were observed by the activated sludge samples of the oxidation ditch process which operated at higher solids retention time (SRT). On the other hand, E1 tended to remain both in the water phase and the sludge phase in the activated sludge samples of the conventional activated sludge process which operated at lower SRT. The anoxic condition was considered to be not favorable to the effective removal of estrogens as compared with the aerobic condition. The removal and degradation of EE2 showed the lag phase, which neither E2 nor E1 showed, but EE2 was finally removed and degraded completely after 24 h. The removal of estrogens in the water phase did not follow the first-order-rate reaction because a large part of the spiked estrogen was immediately removed from the water phase to the sludge phase by adsorption.

Controlling sludge settleability in the oxidation ditch process

This paper describes an investigation aimed at developing an operating technique for controlling sludge settleability in the oxidation ditch form of the nitrification denitrification activated sludge process. It was hypothesized that specific sludge volume index (SSVI) is lowest at an optimum process anoxic fraction and increases at higher and lower fractions. Using effluent ammonia:nitrate ratio as a surrogate for anoxic fraction, it was found that a simple empirical model based on a three solids retention time moving average nitrogen ratio was able to replicate the long-term SSVI variations in two independent oxidation ditches at a full-scale plant. Operating data from a second oxidation ditch plant during periods when a prefermenter was on- or off-line showed that SSVI also varies with RBCOD, greater RBCOD giving lower SSVI. It was concluded that best settleability occurs at about the same anoxic fraction as lowest effluent total nitrogen concentration, with an ammonia:nitrate ratio of about 1. An operating rule of thumb is to use dissolved oxygen control to maintain effluent ammonia and nitrate nitrogen concentrations about equal. A third oxidation ditch plant deliberately operated in this manner achieved 15-month median operating values for SSVI of 60 mL/g and for effluent ammonia, nitrate and total N, respectively, of 0.2, 0.3 and 2.0 mg N/L.

Comparison of natural estrogen removal efficiency in the conventional activated sludge process and the oxidation ditch process

The presence of natural estrogens, 17 β-estradiol (E2), estrone (E1) and estriol (E3), as well as estrogenic activity in wastewater influents and secondary effluents were investigated in 20 full-scale wastewater treatment plants in Japan. In all of the influent samples, natural estrogens were detected at concentrations above the minimum limits of detection (0.5 ng/L). The concentrations of natural estrogens detected in the effluent of oxidation ditch plants were generally lower than previously reported values. On the other hand, in the conventional activated sludge plants, increments of E1 during biological treatment were frequently observed although E2 and E3 were removed effectively in the process. The removal rates of natural estrogens or estrogenic activity show no observed statistical relationship with the solids retention time (SRT) and the hydraulic retention time (HRT). However, the plants with high SRT or HRT generally showed high and stable removal of both natural estrogens and estrogenic activity.

Biological Nutrient Removal using an IACOD Process: determining the Combined Effects of Low Temperature and Long Solids Retention Time

This study was undertaken using an intermittently aerated cylindrical oxidation ditch (IACOD) process for biological nutrient removal. The kinetic aspects of nitrification, denitrification, and phosphorus release/uptake were investigated by conducting a pilot-scale operation under various contact times for the aerobic/anoxic reactor, SRTs, and HRTs. The effects of temperature were also evaluated. The results of the study revealed that a cycle time of 180 min. (i.e., the aerobic contact time of 60 min. followed by the anoxic contact time of 120 min.) enhanced the biological nutrient removal at an aerobic SRT of 8.3 days and an HRT of 24 hours in the aerobic/anoxic reactor. Even during the winter months with mixed liquor temperatures between 9.6 °C and 12 °C at an aerobic SRT of 10 days, the IACOD process was capable of almost completely nitrifying the influent NH4 +-N. The IACOD process was also capable of denitrifying the NO3 −-N in the aerobic/anoxic reactor, yielding effluent NO3 −-N concentrations of less than 2.0 mg l−1 N. Furthermore, the release and abundant uptake of phosphorus successfully occurred at this low temperature range. The enhanced biological phosphorus removal rates increased steadily as the temperature increased from 9.6 °C to 22 °C. However, an inhibition of phosphorus release was observed at a temperature range of 18 °C to 20 °C. This inhibition might have been caused by the sudden increase in the NO3 −-N concentration of the return sludge, which was induced by the rapid nitrification of the influent NH4 +-N at a relatively elevated temperature. The inhibition was not prolonged due to the subsequent increase in the denitrification rate as the temperature increased further to 20 °C and above.

Characteristics of the Treated Wastewater of Rural Sewerage by Oxidation Ditch Process for the Agricultural Use

Characteristics of the Treated Wastewater of Rural Sewerage by Oxidation Ditch Process for the Agricultural Use

An innovative integrated oxidation ditch with vertical circle for domestic wastewater treatment

A bench-scale experiment using an innovative integrated oxidation ditch process with vertical circle was carried out to remove carbonaceous substrates and ammonia nitrogen. The new process not only reduces land area of about 50% and energy consumption by 40% comparing with the conventional oxidation ditch with intrachannel clarifier, but also it has the characteristics of compact configuration, simple operation and easy maintenance. In this new system, the clarifier does not affect the hydrodynamic characteristics of the mixed liquid in the ditch, and the sludge can automatically return to the down ditch. The nitrification process and carbonaceous organic biodegradation could be performed well. At HRT of 12–20 h, and temperature of 10–30 °C, the average concentrations of COD, SS, and NH + 4–N in the effluent were 21, 15.2, and 1 mg/l, respectively, when the average concentrations of COD, SS, and NH + 4–N in the influent were averaged 420, 152, and 59.2 mg/l, respectively.

Oxygen Transfer Testing in an Oxidation Ditch Process

Oxygen Transfer Testing in an Oxidation Ditch Process

オキシデーションディッチにおける放線菌の増殖に関する調査研究

The OD (oxidation ditch) systems occasionally produce significant amounts of foam and scum.Then in this study, some OD plants were examined and the number of actinomycetes cells was assessed. The results obtained were as follows: Scumming was considered to be due to the growth of actinomycetes in the OD tank (aeration tank), which was largest in the OD process. In case of scumming, actinomycetes was found to be transferred from the MLSS to the scum and thickened. Then the multiple of thickening ranged from 1.5 to 5.8. The values of the specific growth rate calculated by the data of the three plants, were between 0.07 and 0.11 (1/day), which were about one half as large as that of the conventional activated sludge process. By comparison between the new scum and the old scum, actinomycetes was considered to increase not in the scum, but in the MLSS.

Oxidation-Ditch Process Using Small Wastewater Treatment Equipment and the Application of the Kinetic Model

Oxidation-Ditch Process Using Small Wastewater Treatment Equipment and the Application of the Kinetic Model

Evaluation of IAWQ Activated Sludge Model No. 2 using steady‐state data from four full‐scale wastewater treatment plants

Several new tools, including the Activated Sludge Model No.2 (ASM No. 2) developed by the International Association on Water Quality, are becoming available to analyze the nutrient removal capability of existing wastewater treatment plants (WWTPs). The ASM No. 2 is a potentially inexpensive and effective tool, but its use needs to be evaluated. To solve the differential equations in the model, the computer program Activated Sludge Simulation Program (ASIM 3.0) was used. The model was calibrated using data from the Mauldin Road WWTP, which is a nutrient removal plant. Only 6 of 71 stoichiometric and kinetic parameter values were changed from suggested default values. The stoichiometric and kinetic parameters determined for the Mauldin Road WWTP were then used to develop models for the Lower Reedy, Gilder Creek, and Durbin Creek WWTPs. The calibrated model was subsequently confirmed using separate data sets for each WWTP. The model was successfully calibrated and confirmed at the Lower Reedy WWTP. This plant uses high‐speed mechanical surface aerators, and it achieves significant phosphorus removal. It was modeled by specifically considering the flow pattern likely to be created by these aerators. Several options to improve the phosphorus removal capability of the Lower Reedy WWTP were evaluated. The simulation results suggested that phosphorus removal performance could be improved by repositioning the mechanical surface aerators to produce a defined anaerobic zone and by providing dissolved oxygen control. The performance of the Durbin Creek and Gilder Creek WWTPs, which use oxidation ditch processes, could not be fully simulated using the model. Potential reasons for this failure are discussed.

New operational support system for high nitrogen removal in oxidation ditch process

A new operational support system for the oxidation ditch process has been developed. It calculates the operational index from the concentration of the dissolved oxygen in the ditch and the operator decides the aeration conditions to keep the index within the target range. Simulation and experimental results have led to creation of an operational index with an optimum value for every type of aeration. For example, the ratio of aerobic to anaerobic zone length (LAER/LANA ratio) is for the 1-point continuous aeration process, the ratio of aerobic to anaerobic duration time (TAER/TANA ratio) is for the 2-point intermittent aeration process and so on. Their optimum values are all 1, suggesting that the ratio of denitrification to nitrification rates is around 1 under typical conditions of the general oxidation ditch process. These indexes are very practical because they can be obtained without complex calculation.

New operational support system for high nitrogen removal in oxidation ditch process

A new operational support system for the oxidation ditch process has been developed. It calculates the operational index from the concentration of the dissolved oxygen in the ditch and the operator decides the aeration conditions to keep the index within the target range. Simulation and experimental results have led to creation of an operational index with an optimum value for every type of aeration. For example, the ratio of aerobic to anaerobic zone length (LAER/LANA ratio) is for the I-point continuous aeration process, the ratio of aerobic to anaerobic duration time (TAER/TANA ratio) is for the 2-point intermittent aeration process and so on. Their optimum values are all 1, suggesting that the ratio of denitrification to nitrification rates is around 1 under typical conditions of the general oxidation ditch process. These indexes are very practical because they can be obtained without complex calculation.

An Improvement of an Oxidation Ditch Process for the Low Alkalinity Wastewater Treatment and Various Influent Conditions

The oxidation ditch process (OD) had been propagated for small scale domestic wastewater treatment through the 1960s in Holland, by the benefits of capital and maintenance cost and easy maintenance. But it was not suitable for large scale plants due to the wide area and maintenance problems at the beginning. After that, the process spread through European countries and all over the world in conjunction with improvements in the equipment and the system. In the early stage in Japan, OD plants frequently experienced pH decline problems from low loading and excess aeration, as the alkalinity of domestic waste water in Japan is less than that of western countries. In this paper, a one-point aeration ditch process, developed by using a down-pumping submerged-turbine aerator, is introduced. The formation of an aerobic zone and an anoxic zone in the ditch is confirmed, and it is reported that the pH decline problem is solved by the effective, concurrent nitrification and denitrification in the ditch, with an indication of the alkalinity balance. Furthermore, new preparations and improvements of the OD process suitable to the various influent conditions, such as a counterplan to alleviate excess low loading, a variant water depth operation, etc. are explained by the full-scale examples.

Oxidation-Ditch Process Using Falling Water as Aerator

This paper examines the use of falling water as an aerator for the oxidation-ditch process. The study was carried out in order to clarify the characteristics of this process and compare it with other oxidation-ditch processes. The method uses pumps that lift wastewater and cause it to develop a head, creating a cascade or waterfall. Application of this concept may reduce construction costs for wastewater treatment plants. Furthermore, nitrogen removal is made easier through simple control of pump speed, on-off functions, and change in the height of the waterfall. Aeration efficiency is similar to that of aerators used in other oxidation-ditch processes. The power input of this oxidation-ditch-aeration process was the lowest of all the oxidation-ditch processes. This oxidation-ditch process also provides various other advantages for waste-treatment plants.