Aeration Power Research Articles

Advancing precision fermentation: Minimizing power demand of industrial scale bioreactors through mechanistic modelling

Minimizing power consumption in large-scale aerobic fermentation is essential for cost-effective operations. A mechanistic model of aerobic precision fermentation was developed integrating microbial growth parameters, thermodynamic data, and bioreactor properties. Results showed that agitation power dominated energy consumption at low oxygen transfer rates (OTR), shifting to aeration power (70 % of total) at high cell growth rates. In high OTRs, mixing time reduced to 60 s from an initial value of 211 s. Scale-up from 5 m³ to 100 m³ decreased total specific power by 88 %. Operating at elevated headspace pressure lowered agitation speed, reducing total power consumption at high OTR. Impeller to bioreactor diameter ratio impacted the required agitation speed without significantly altering total power demand. Experimental data in a 100 L case study indicated a 0.43 kW.m⁻³ average power requirement across a 96-hour fermentation period. Our model demonstrates effective strategies for minimization of power consumption in industrial-scale aerobic fermentations.

Aeration rate and power requirements for CO2-replete cultivation of the red seaweed Devaleraea mollis (Pacific dulse) in a tumble tank

The red seaweed Devaleraea mollis, commonly known as Pacific dulse, is a sustainable source of healthy food, food ingredients, and plant-based proteins. Land-based aquaculture of red seaweed typically employ tumble culture systems, where compressed air is delivered to the bottom of the tank to provide gas exchange and promote mixing. However, aeration is a potentially costly process because compressed air must be bubbled into the liquid, and power is required to drive the air compressor. In this study, fundamental relationships between aeration rate, biomass productivity, and aeration power consumption were developed for tumble tank cultivation of the red seaweed Pacific dulse under CO2-replete growth conditions. The biomass productivity (g biomass L−1 d−1) of D. mollis in tumble culture was measured over seven weekly harvest cycles over a range of aeration rates (0.086–0.684 L air L−1 liquid min−1) for fine-bubble (1–5 mm) and coarse-bubble (2–3 cm) aerators, and then correlated to the CO2 transfer rate (CO2-TR, mmol CO2 L−1 h−1). The CO2-TR consolidated aeration rate, CO2 partial pressure, boundary layer diffusion, and gas sparger characteristics (bubble size, interfacial area) into a single parameter. This analysis required measurements of the gas-to-liquid mass transfer coefficient (kLa) for estimation of CO2-TR, and pressure drop across the gas diffuser for aeration power consumption. CO2-replete biomass productivity required a CO2-TR that was three times the CO2 demand. For fine-bubble aeration, both CO2-TR and aeration power consumption were higher than for coarse-bubble aeration over the range of aeration rates tested. However, when the aeration rate needed to achieve CO2-replete biomass productivity was approached, fine-bubble aeration required less energy consumption due to lower aeration requirement. The optimum was achieved at an aeration rate of 0.26 L air L−1 culture min−1 using fine-bubble aeration, which provided an areal biomass productivity of 490 g FW m−2 d−1 (fresh mass) or 32 g AFDW m−2 d−1 (ash-free dry mass), at an aeration energy power requirement of 1.5 kWh/kg FW (22 kWh/kg AFDW). Overall, this study showed that aeration systems can easily limit biomass productivity and result in high aeration energy consumption per kg of biomass produced if the aeration processes are not thoughtfully considered. The key tradeoff was that aeration energy consumption increased significantly as CO2-replete biomass productivity was approached. Therefore, optimization would require the use of an aerator system that provides the best possible kLa and lowest pressure drop at the lowest possible aeration rate.

Machine learning methods for anomaly classification in wastewater treatment plants

Modern wastewater treatment plants base their biological processes on advanced control systems which ensure compliance with discharge limits and minimize energy consumption responding to information from on-line probes. The correct readings of probes are particularly crucial for intermittent aeration controllers, which rely on real-time measurements of ammonia and oxygen in biological tanks. These data are also an important resource for developing artificial intelligence algorithms that can identify process or sensor anomalies, thus guiding the choices of plant operators and automatic process controllers. However, using anomaly detection and classification algorithms in real-time wastewater treatment is challenging because of the noisy nature of sensor measurements, the difficulty of obtaining labeled real-plant data, and the complex and interdependent mechanisms that govern biological processes. This work aims at thoroughly exploring the performance of machine learning methods in detecting and classifying the main anomalies in plants operating with intermittent aeration. Using oxygen, ammonia and aeration power measurements from a set of plants in Italy, we perform both binary and multiclass classification, and we compare them through a rigorous validation procedure that includes a test on an unknown dataset, proposing a new evaluation protocol. The classification methods explored are support vector machine, multilayer perceptron, random forest, and two gradient boosting methods (LightGBM and XGBoost). The best performance was achieved using the gradient boosting ensemble algorithms, with up to 96% of anomalies detected and up to 84% and 62% of anomalies classified correctly on the first and second datasets respectively.

Delivering sustainable water infrastructure to regional NSW communities

ABSTRACT Water utilities with a population base of greater than 50,000 people can have several economically viable options for ensuring their services provide climate resilience and carbon neutrality through optimisation of their two largest operational expenses (OPEX): power for STP aeration and power for water supply pumping. Energy optimisation can be approached from a number of perspectives, including design, equipment selection, instrumentation and control, energy recovery from the sewage, pumping off-peak, reuse of sewage and water treatment residuals, etc. Smaller water utilities with less than 50,000 people have less latitude for applying these approaches due the lack of economic viability for smaller facilities, lack of staff or other. Smaller water utilities must still strive towards reducing their carbon footprints but maintain affordability to rate payers. Public Works Advisory (PWA) provides technical, advisory and design services to Government Agency clients, including Local Government Areas or LGAs. The PWA partnership with LGAs assists at the local level to deliver on the commitments of NSW and Australia to reducing greenhouse gas (GHG) emissions by 2030. Directly reducing the take and use of grid power supplied by coal fired power stations can have favourable outcomes, both for reducing GHGs and OPEX. The use of solar photovoltaic (PV) systems in Australia is particularly attractive due to the continent having the highest direct normal irradiation or DNI. Current literature gives few examples of real operating data from PV systems in duty on water infrastructure, particularly for smaller installations. PWA target the highest OPEX areas for management of water and sewage and demonstrate with actual operating data from three full-scale case studies. PV panels can be economically employed by smaller water utilities for acceptable Internal Rate of Returns (IRRs), with or without batteries, to help reduce their overall carbon footprints.

Performance evaluation of first full-scale primary filtration using a fine pore cloth media disk filter.

Over the past 20years, various new filter technologies have been developed that can be used to (a) enhance the performance of or (b) replace conventional primary treatment facilities. To enhance the performance of a primary sedimentation facility, primary effluent is filtered to further reduce the constituent concentrations discharged to the secondary treatment facilities. This form of primary enhancement is known as primary effluent filtration (PEF). In the second case, where some type of filter technology is used to replace primary sedimentation, the process application is known as primary filtration (PF). The principal focus of this paper is on the performance of the first full-scale PF project using a fine pore cloth media disk filter to maximize the diversion of carbon for the production of energy and to reduce energy usage. Performance data from related pilot-scale cloth disk primary filter (CDPF) systems are included for process verification. The removal performance for total suspended solids (TSS) from the three CDPF installations varied from 83% to 85%, as compared to 55%-60% typically achieved with primary sedimentation. The total overall TSS removal performance achieved with PF is essentially the same as that achieved with PEF, without the need for a primary sedimentation tank. The removal performance for five-day biochemical oxygen demand (BOD5 ) from the three CDPF installations varied from 46% to 58%, as compared to 32%-38% BOD removal typically achieved with primary sedimentation. The full-scale CDPF results reported in this paper are from an on-going research and demonstration project, conducted for the California Energy Commission (CEC), to demonstrate the potential energy savings that can be achieved through the implementation of PF. PRACTITIONER POINTS: The performance of the first full-scale primary filtration system using a fine pore cloth disc filter is evaluated in this project. Design and operational criteria of the primary filtration technology were established in this project to implement in full scale installations. Primary filtration was demonstrated to increase the diversion of carbon for the production of energy and to reduce energy usage. Significant decrease in aeration power requirement and increase in digester gas production are possible with primary filtration. Footprint reduction (both for primary and secondary treatment) are other important attributes of primary filtration.

Toward Sustainability in Rural Areas: Composting Palm Tree Residues in Rotating Bioreactors

Huge quantities of palm tree residues are available annually in Saudi Arabia; they are often disposed of by burning, leading to large environmental pollution and health problems. Enclosed composting may be a successful method for utilizing these residues. Effective composting in a rotary bioreactor depends on the composting materials and the frequencies of the rotation–aeration process. Here, we attempted to determine the optimal method for composting these residues in a bioreactor. Four identical pilot-scale bioreactors (D1–D4) were used. The respective aeration–rotation frequencies were continuous (D1), and 20 min per 1 h (D2), 2 h (D3), and 3 h (D4); the rotation speed of the bioreactors was 3 rpm. Three periods were analyzed; their names and their respective lengths for D1, D2, D3, and D4 were as follows: the lag period was 10 h for each, the mesophilic periods were 13, 14, 89, and 231 h, and the thermophilic periods were 0, 55, 71, and 17 h. The peak compost temperatures (Tc, max) for D1, D2, and D3 were 65.2, 57.2, and 46.9 °C, and were achieved at 36, 71, and 108 h of operation, respectively. In D1, Tc quickly declined after reaching Tc, max due to limited microbial activity at Tc > 60 °C. In D2, a Tc of 50–57.2 °C was maintained for 61 h, and the highest organic matter degradation (OMD) of 0.30 was achieved. During the composting period, the carbon to nitrogen (C/N) ratio and moisture contents (MC) remained in the optimal ranges for microorganisms and did not affect the composting process. The results indicated that combined aeration–rotation for 20 min every hour (D2) gave the best results for composting palm tree residues, it ensured the hygiene safety of the end product, and it also consumed less power for aeration and rotation than D1.

A comparative study of impeller aerators configurations

This paper presents a comparative experimental study of different configurations of mechanical surface aerators used in wastewater treatment plants. A laboratory scale tank equipped with different configurations for aeration process was installed to compare the standard aeration efficiency and power consumption of curved blade impellers with 3, 6, 9, and 12 blades. Different parameters thought to have significant effects on standard aeration efficiency (SAE) and power consumption, such as submergence depth and rotating speed were studied. Results show that an optimum configuration (9 blades) has the highest aeration efficiency (2.60 Kg. O2/KW.hr) at 500 rpm. Also, a submersion depth ratio of 0.35 was optimum, giving the highest standard aeration efficiency, as increasing submergence depth ratio above this value causes drop in standard aeration efficiency as a result of inevitable increase in input power consumption in this case.

Multilevel Adaptive Control of Alternating Aeration Cycles in Wastewater Treatment to Improve Nitrogen and Phosphorous Removal and to Obtain Energy Saving

This work presents an adaptive control of the process of alternating aeration/non-aeration cycles for wastewater treatment. It is aimed at improving nitrogen and phosphorous removal efficiency and reducing energy consumption. It comprises two control levels. The first decides when to switch on and off aeration by comparing the Dissolved Oxygen (DO) and the Oxidation Reduction Potential (ORP) with two activation thresholds. The second, a supervisory control, continuously adapt their values by analyzing the working conditions of the reactor (organic matter and ammonium loads). These working conditions are described by four parameters obtained from the DO and ORP curves: Oxygen Uptake Rate (OUR), Oxygen Rise Average Slope (ORAS), ORParrow and Nitrate and Oxygen Uptake Rate (NOUR). It also adjusts the aeration system power to adapt it to those conditions. This adaptive control has been implemented in a laboratory scale prototype and its performance compared with that provided by another control with fixed thresholds and aeration power implemented in a similar prototype. The adaptive control clearly outperforms that without adaptation in nitrogen and phosphorous removal efficiency and requires lower energy consumption. Similar efficiencies were obtained for organic matter removal (higher than 90% in both cases).

Diurnal stratification of oxygen in shallow aquaculture ponds in central Europe and recommendations for optimal aeration

The common carp (Cyprinus carpio) is an important livestock in regions of Central Europe, where it is bred in shallow, turbid ponds (mean depth 1 m). A frequent problem observed in this form of aquaculture is hypoxia, which confines the fish close to the surface, preventing them from optimally feeding at the bottom. According to information propagated in textbooks and good practice guidebooks and internet documents, the best solution to that is aeration in the early morning hours, when oxygen concentration is supposed to be minimal. While we wanted to test the feasibility of photovoltaic power for aeration of ponds, we detected that on days with bright sunshine the lowest oxygen concentration occurs in the afternoon at the bottom layer of a shallow pond, and that oxygen distribution is highly influenced by thermal stratification. This formation of layers of different temperatures within the water body inhibits the diffusion of oxygen. A breaking of the stratification effectively increases the oxygen concentration, elevating the overall amount of oxygen in the pond. Consequently, the drop in oxygen concentration at night is less dramatic, and critically low levels of oxygen in deeper zones of the pond are avoided. A comparison between the oxygen distribution and daytime or nighttime aeration showed that on days with bright sunshine it is more effective to force mixing of the entire water column during the day, making the use of a photovoltaic power system feasible. This offers a simple and elegant solution for ponds which are not connected to the power grid.

Enhancement of methane production by Methanosarcina barkeri using Fe3O4 nanoparticles as iron sustained release agent

Anaerobic digestion has attracted attention because it does not require power for aeration, it reduces excess sludge and it generates methane gas. However, the growth rate of anaerobic microorganisms is slow, resulting in low treatment efficiency. In this study, the impact of Fe3O4 nanoparticles (NPs) on the growth of methanogens, which is the rate-determining step in anaerobic digestion, was investigated using a pure culture of Methanosarcina barkeri as the model methanogen. M. barkeri were cultivated in iron free medium, as well as in media amended with various concentrations of Fe3O4 NPs with a mean diameter of 8.1 ± 2.4 nm. The production of methane gas was greatly increased when organisms were cultured in media containing NPs. After the methane production was saturated, methanol was newly added to the culture, which resulted in additional methane generation at a higher production rate than occurred during the initial round of cultivation in media containing 20 ppm Fe3O4 NPs. In addition, no evidence of negative impacts of Fe3O4 NPs on the growth of M. barkeri was observed. Taken together, these results strongly suggest that adding Fe3O4 NPs into the fermenter as an agent of sustained iron release can enable sustainable methane fermentation.

CFD simulation of fluid dynamic and biokinetic processes within activated sludge reactors under intermittent aeration regime

Due to the aeration system, biological reactors are the most energy-consuming facilities of convectional WWTPs. Many biological reactors work under intermittent aeration regime; the optimization of the aeration process (air diffuser layout, air flow rate per diffuser, aeration length …) is necessary to ensure an efficient performance; satisfying the effluent requirements with the minimum energy consumption.This work develops a CFD modelling of an activated sludge reactor (ASR) which works under intermittent aeration regime. The model considers the fluid dynamic and biological processes within the ASR. The biological simulation, which is transient, takes into account the intermittent aeration regime. The CFD modelling is employed for the selection of the aeration system of an ASR. Two different aeration configurations are simulated. The model evaluates the aeration power consumption necessary to satisfy the effluent requirements. An improvement of 2.8% in terms of energy consumption is achieved by modifying the air diffuser layout. An analysis of the influence of the air flow rate per diffuser on the ASR performance is carried out. The results show a reduction of 14.5% in the energy consumption of the aeration system when the air flow rate per diffuser is reduced. The model provides an insight into the aeration inefficiencies produced within ASRs.

Aeration costs in stirred-tank and bubble column bioreactors

To overcome knowledge gaps in the economics of large-scale aeration for production of commodity products, Aspen Plus is used to simulate steady-state oxygen delivery in both stirred-tank and bubble column bioreactors, using published engineering correlations for oxygen mass transfer as a function of aeration rate and power input, coupled with new equipment cost estimates developed in Aspen Capital Cost Estimator and validated against vendor quotations. These simulations describe the cost efficiency of oxygen delivery as a function of oxygen uptake rate and vessel size, and show that capital and operating costs for oxygen delivery drop considerably moving from standard-size (200m3) to world-class size (500m3) reactors, but only marginally in further scaling up to hypothetically large (1000m3) reactors. This analysis suggests bubble-column reactor systems can reduce overall costs for oxygen delivery by 10–20% relative to stirred tanks at low to moderate oxygen transfer rates up to 150mmol/L-h.

Comparative evaluation of wastewater-treatment microbial fuel cells in terms of organics removal, waste-sludge production, and electricity generation

Microbial fuel cells (MFCs) are devices that exploit living microbes for electricity generation coupled to organics degradation. MFCs are expected to be applied to energy-saving wastewater treatment (WWT) as alternatives to activated-sludge reactors (ASRs). Although extensive laboratory studies have been performed to develop technologies for WWT-MFCs, limited information is available for comparative evaluation of MFCs and ASRs in terms of organics removal and waste-sludge production. In the present study, laboratory WWT experiments were performed using cassette-electrode MFCs and ASRs that were continuously supplied either with artificial domestic wastewater (ADW) containing starch and peptone or with artificial industrial wastewater (AIW) containing methanol as the major organic matter. We found that these two types of WWT reactors achieved similar organics-removal efficiencies, namely, over 93% based on chemical oxygen demands for the ADW treatment and over 97% for the AIW treatment. Sludge was routinely removed from these reactors and quantified, showing that amounts of waste sludge produced in MFCs were approximately one-third or less compared to those in ASRs. During WWT, MFCs continuously generated electricity with Coulombic efficiencies of 20% or more. In reference to ASRs, MFCs are demonstrated to be attractive WWT facilities in terms of stable organics removal and low waste-sludge production. Along with the unnecessity of electric power for aeration and the generation of power during WWT, the results obtained in the present study suggest that MFCs enable substantial energy saving during WWT.

Application of the activated sludge model to aerated lagoons

The different kinds of aerated lagoons, which exclude anaerobic pre-treatment ponds, are described and the design approach for aerated lagoons is explained. This hinges around ensuring that the 1st lagoon is suspension mixed and the second and any additional are facultative. Selection of the retention time for the 1st lagoon is important to ensure complete utilization of the influent biodegradable organics. Minimum retention times to achieve this at 14 degreesC and 22 degreesC were determined with the general activated sludge kinetic simulation model for (i) readily biodegradable soluble organics (BSO) only, (ii) slowly biodegradable particulate organics (BPO) only, (iii) real municipal wastewater (20% BSO and 80% BPO) and (iv) real municipal wastewater with 5% OHO active VSS mass seed. The minimum hydraulic retention times for these four cases are: at 14 degreesC 1.3, 3.0, 2.0 and 1.5 d, respectively, and at 22 degreesC 0.3, 2.0, 1.2 and 1.0 d, respectively. From a comparison of the simulation results with the steady-state model calculations, washout of OHOs takes place at about 75% of these retention times. Approximate equations to estimate the power requirements for aeration by mechanical surface aerators and mixing are given. These equations are combined with those of the steady-state activated sludge lagoon model for calculating the oxygen requirements and the aeration power density (W/m3) in each lagoon. With these equations, it is shown that influent COD concentration needs to be between an upper and lower limit band to ensure that the 1st lagoon is suspension mixed and the second lagoon is facultative. This COD concentration band decreases as the influent flow increases. The important conclusion arising from this is that if the aerated lagoon system is applied for small rural communities, where land for these large systems is likely to be available, then additional mixing energy above that for aeration will need to be provided to ensure that the 1st lagoon is suspension mixed - this additional aeration cost makes it unlikely that aerated lagoons will be applied for municipal wastewater treatment. Matching mixing and aeration power requirements for industrial organic wastewaters is easier because these usually are significantly stronger than municipal wastewaters.

Influence of temperature and COD loading on biological nitrification–denitrification process using a trickling filter: an empirical modeling approach

To cut down aeration power for nitrification, we constructed a biological nitrification–denitrification process with a trickling filter for nitrification and an anaerobic biological filter for denitrification. The influences of temperature and chemical oxygen demand (COD) loading on the nitrification and denitrification performance of the process are discussed in this paper through experimental and empirical modeling approaches. The model constants were determined by the experimental data of the process using municipal wastewater in Ryukoku University. Then, the influences of temperature and COD loading were estimated by the model. The COD levels required for NO3–N removal depended on both, the temperature and influent COD/NO3–N ratio. A lower temperature and higher influent COD/NO3–N ratio increased the COD requirement, because of the different responses between denitrifying bacteria and heterotrophic bacteria against temperature, COD, and NO3–N concentrations. In addition, our experimental system could satisfy the Japanese effluent standard at temperatures higher than 12 °C. The dissolved nitrogen (DN) concentration in the final effluent was more strongly affected by the NH4–N discharged from the trickling filter than it was by the residual NO3–N in the effluent from the denitrification tank. Therefore, the enhancement of the nitrification efficiency in the trickling filter was inferred to enhance the nitrogen removal efficiency. To prevent a low nitrogen removal efficiency at temperatures lower than 15 °C, it was necessary to set the low hydraulic loading.

Aeration energy requirements for lipid production by Scenedesmus sp. in airlift bioreactors

Microalgae have potential to yield various bioenergy products, including algal biodiesel. For algal energy production, the process energy input must be substantially lower than the product energy. Airlift photobioreactors provide controlled environments with good mixing and mass transfer; however, previous work reports a net energy ratio (NER; energy produced divided by energy consumed) less than 1. Here, the energy consumption in these reactors was improved by combined optimisation of superficial gas velocity and its CO2 concentration. Increasing CO2 concentration resulted in increased tolerance to lower superficial gas velocities, down to a critical minimum value. A 75% reduction in aeration power input was obtained by reducing superficial gas velocity from 0.0210 to 0.0052ms−1 at 5 400ppm CO2, without substantial reduction in biomass concentration (2.27 to 1.93gL−1, respectively) or productivity (0.189 to 0.173gL−1d−1, respectively). The NER under these conditions was 5.47 for biomass plus lipid and 1.01 for lipid only. The CO2 supply rate, product of superficial gas velocity and CO2 concentration, correlated with the CO2 transfer rate which influenced algal productivity. The range of NERs measured across the superficial gas velocities studied indicates the ability to optimise algal cultivation in photobioreactors for the improved feasibility of algal bioenergy.

Nitrogen and phosphorus removal in an airlift intermittent circulation membrane bioreactor

A new airlift intermittent circulation integrated bioreactor was developed for simultaneous nitrogen and phosphorus removal of wastewater, in which, circulation of mixed liquid between mixing zone and aeration zone was realized by aeration power, alternately anaerobic/anoxic bio-environment in mixing zone was realized by intermittent circulation and simultaneous nitrogen and phosphorus removal was obtained through strengthened denitrifying phosphorus removal process. Removal performance of the reactor was investigated and pollutant removal and transfer mechanism in one operation circle was analyzed. The experiment results indicated that under the influent condition of chemical oxygen demand (COD) concentration of 642.1 mg/L, total nitrogen (TN) of 87.4 mg/L and PO43−-P of 12.1 mg/L, average removal efficiencies of COD, TN and PO43−-P reached 96.4%, 83.2% and 90.5%, respectively, with the hydraulic residence time of 22 hr and operation circle time of 185 min. Track studies indicated that the separation of aeration and mixing zones and intermittent circulation of mixed liquid between the two zones provided distinct biological environments spatially and temporally, which ensured the occurrence of multifunctional microbial reactions.

Aerated lagooning of agro-industrial wastewater: depuration performance and energy requirements

Intensive depuration plants have often shown low reliability and economic sustainability, when utilised for agro-industrial wastewater treatment, due to the particular wastewater properties: high organic load and essential oil concentrations, acidity, nutrient scarcity and qualitative-quantitative variability of effluents. Aerated lagooning systems represent a suitable alternative, because they are able to assure good reliability and low energy requirements, avoiding the drawbacks shown by the intensive depuration plants. In order to optimize performance of the lagooning systems, particularly in terms of energy requirements, depuration processes of aerobic-anaerobic aerated lagoons were investigated, both at full- and laboratory-scale. Citrus processing wastewater were subject to bubble aeration with low flow rates and limited time; the removal rate of organic load was evaluated and energy requirements of different depuration schemes were compared. The experimental investigations in full-scale aerated lagoons showed a low energy supply (0.21-0.59 kWh per kg of COD (Chemical Oxygen Demand) removed with an average value of 0.45 kWh kgCOD –1), an adequate equalisation capability and constantly good depurative performance also with high concentrations of essential oil (500-1000 ppm). The experimental investigations in lab-scale aerated tanks under controlled conditions indicated the possibility of decreasing energy requirements (down to 0.16 kWh kgCOD –1) by reducing aeration power (down to 0.6 W m–3) and limiting aeration time to night 12 hours only, when energy price is lower. In spite of the low aeration, the COD removal rates were on the average six-fold higher compared to the anaerobic tank. Other outcomes indicated an ability of the spontaneous microflora to adapt to high concentrations of essential oils, which however did not provide an increase of the removal rate of the organic load in the experimented scheme.

Removal Characteristics of Pollutants in Airlift Intermittent Circulation Membrane Bioreactor

An airlift intermittent circulation mebrane bioreactor was developed for simultaneous nitrogen and phosphorus removal of wastewater, in which, circulation of mixed liquid between anaerobic zone and oxic zone was realized by aeration power, intermittent anaerobic/anoxic bio-environment in anaerobic zone was realized by intermittent circulation and simultaneous nitrogen and phosphorus removal was obtained through strengthened denitrifying phosphorus removal process. Pollutant removal and transfer mechanism in one operation circle was analyzed. The experiment results indicated that the separation of distinct biological environments specially and temporally, which ensured the requirement of different microorganisms and the occurrence of bio reaction. Nitrogen and phosphorus removal was realized through the processes of convention nitrification-denitrification, SND, anaerobic phosphorus release and oxic-absorption and denitrifying phosphorus removal.

Upgrade of a large scale oxidation ditch plant

A large-scale oxidation ditch (OD) plant had been upgraded by modifying the aeration and stirring technique of the ditches. Through upgrade, surface turbine aerators have been installed together with the existing aeration rotors. A turbulent stirring was created by the addition of the new turbine aerators, while the recirculation motion achieved by the original rotors. The two aeration techniques (turbulent stirring and recirculation motion) were operated at different ratios ranging from 0.0–1.0. As a result, by operating the turbulent stirring and gradual dispensing with recirculation motion, the system version gradually converted from an OD to a conventional activated sludge. Firstly, the gradual conversion from recirculation motion to turbulent stirring was performed under constant oxygenation level (DO) approximately 1.0 mg/L. Secondly; the turbulent stirring was increased with constant running of recirculation motion associated with gradual increase of DO level up to 2.5 mg/L. The effect of aeration and stirring on removal efficiency, sludge production, and sludge settleability has been revealed. It was found that turbine aerators could be added successfully inside ODs to increase the whole system efficiency. Firstly, at constant DO level, under same aeration power, turbulent stirring increased the removal efficiency of COD from 65 to 74%. The observed sludge yield (Yobs) came down from 0.31 to 0.25 gm volatile suspended solids (VSS)/gm BOD. Furthermore, the sludge settleability was enhanced from SVI = 137 to 115. Secondly, increased DO level with the new turbulent stirring, increased removal efficiency of COD from 65 to 95%. Moreover, the system achieved a nitrification efficiency of 70%. Finally, the sludge settleability was improved from SVI = 164 to 92 with minimum sludge yield.