Aerobic Biological Wastewater Treatment Research Articles

Granular stability, nitrogen and phosphorus removal pathways of aerobic granular sludge treating real municipal wastewater at different temperatures

Variations in temperature (T) can affect the activity of microorganisms in aerobic granular sludge (AGS) and biological wastewater treatment. Seasonal or diurnal fluctuations specifically low T can affect the overall wastewater treatment performance. Here, the short-term response of AGS to variation in T was investigated in terms of granular stability, sewage treatment and biological nutrient removal (BNR) pathways. AGS cultivated under tropical climate at T ≥ 30 ℃ was incubated at 15–25 ℃ by decreasing either in 10–15 °C steps or in 5 °C steps. Ammonium (74 % at 15 ℃; 94 % at 20 ℃), total inorganic nitrogen (46 % at 15 ℃; 50 % at 20 ℃), and phosphorus (38 % at 15 ℃; 51 % at 20 ℃) removals were significantly lower at 15 ℃ and 20 ℃ than at 30 ℃ (ammonium: >99 %; total inorganic nitrogen: 99 %; phosphorus: 76 %). The effect of lower temperature on BNR was less prominent when T was gradually decreased in 5 ℃ steps from 30 to 15 ℃. Moreover, the impact of lower temperature was quickly recovered upon reverting to 30 ℃. Ammonium was removed by partial nitrification and denitritation pathway. While, phosphorus was removed through enhanced biological phosphorus removal (EBPR) via polyphosphate accumulating organisms (PAOs). About 2–4-fold difference in the gene copies of ammonium oxidizing bacteria (AOB), denitrifying bacteria, and PAOs between 5 ℃ and 10 ℃−15 ℃ changes, respectively, explained operation of partial nitrification-denitritation and EBPR mechanisms. This study shows that a gradual decrease in T from 30° to 15°C in 5 ℃ steps can avoid inhibition of BNR pathways in AGS reactors. The granules were found to be stable with excellent settling properties. However, the sludge was dominated by smaller granules at lower temperatures of 15 ℃ and 20 ℃ as compared to 30 ℃ warranting long-term studies for evaluating the potential impact of T on AGS process.

Innovations for the Treatment of Effluents in the Food Industry

During the processing phases of the food business, a large amount of water is used, resulting in a large volume of effluents. Raw materials, sanitary water for food processing, transportation, cooking, dissolving, auxiliary water, cooling, cleaning, and so on are all utilized extensively in the business. Traditional anaerobic or aerobic biological wastewater treatment processes can be employed to handle organic compounds found in food sector effluent. However, some hazardous chemicals to a microbial population may be present in the effluent due to varied consumption. The effluent may contain significant levels of suspended particles, nitrogen in various chemical forms, lipids, oils, phosphorus, chlorides, and high organic content. There are traditional and well-established methods for treating effluents in the food industry, such as the coagulation-flocculation process, electrochemical processes, and biological processes, which have proven to be quite effective when used as treatment methods in a variety of industries; however, such methods have limitations. Innovative techniques, such as microbial fuel cells (MFCs), microalgae, water ultrafiltration, nanofiltration, and membrane technologies, can replace or complement traditional methods in the future. The treatment method chosen will be determined by the industry's and its wastewater's characteristics.

Dynamic alpha factor prediction with operating data - a machine learning approach to model oxygen transfer dynamics in activated sludge

Aeration is an energy-intensive process of aerobic biological wastewater treatment. An accurate model of oxygen transfer dynamics in activated sludge tanks would improve design and operation of aeration systems. Such a model should consider spatial and diurnal variation of α-factor as well as site-specific conditions that impact oxygen transfer. For this dynamic prediction a machine learning approach was used for the first time. The data-driven method was based on long-term ex-situ off-gas measurements with pilot-scale reactors (5.8 m height, 8.3 m3 vol) coupled to full-scale activated sludge tanks on the sites of two conventional and a two-stage activated sludge treatment plant. The ex-situ off-gas method allowed to quantify theoretical off-gas parameters in non-aerated zones and thus consider the whole activated sludge tank. We introduced the α0-factor to compare aerated and non-aerated zones under nonsteady-state conditions. Like the established α-factor for steady-state conditions, the α0-factor describes oxygen transfer inhibiting effects in activated sludge. α0-factor was lowest in upstream denitrification zones. This indicates an anoxic elimination of oxygen transfer inhibiting wastewater contaminants which improved oxygen transfer in subsequent aerobic zones. Random Forest models predicted α0-factor reliably in all examined activated sludge tanks even for stormwater events and seasonal variation. Model development only required online sensor data already available to operators. Our results suggest that machine learning models can dynamically predict α-factors in a variety of activated sludge processes, thus considering site-specific conditions in model training without manual calibration.

Impact of saline valorization in contaminated municipal wastewater on the treatment performance and bacterial community dynamics of a membrane bioreactor

AbstractBackgroundDue to salt intrusion and the improper use of seawater for cleaning and flushing in food shops along coastal regions, the aerobic biological wastewater treatment process may have an adverse effect on treatment performance. This study demonstrates membrane bioreactor (MBR) performance for treating saline‐contaminated municipal wastewater. The aim of this study is to determine how much salt affects the efficiency of the process and how the functional bacterial community evolves in an MBR for treating actual municipal wastewater.ResultsAn MBR was applied for actual municipal wastewater treatment by increasing the NaCl concentration from 0 to 20 g L−1 with a hydraulic retention time of 12 h and complete sludge retention. High removal efficiencies of chemical oxygen demand (COD) (ranging from 80.3 to 82.8 mgL−1) and ammonium‐N (ranging from 40.8 to 44.4 mgL−1) were found at salinity concentrations of up to 7.8 ± 0.8 g L−1. However, the removal efficiency of COD was below 50% at high salinity concentrations of 17.9 ± 1.3 g L−1, whereas the removal rate of ammonium‐N had slightly changed with the value of 90%. In terms of bacterial composition, the largest dominant bacterial communities were Proteobacteria and Planctomycetota, both of which may be the predominant halotolerant/halophilic bacteria group. Additionally, Rhizobiales, Planctomycetales, Pirellulales, and Gemmatales (all of which are members of these phyla) were increased, suggesting that they played an important role in the biodegradation process.ConclusionThe MBR operation showed a good performance for treating municipal wastewater with high salinity concentrations, with a salt tolerance threshold of 7.8 g L−1. The experimental results indicate that the MBR system can be applied for treating municipal wastewater that is occasionally contaminated with seawater. © 2022 Society of Chemical Industry (SCI).

Shifts of microbial community structure along substrate concentration gradients in immobilized biomass for nitrogen removal

Immobilized biomass technology has been regarded as an effective strategy to enhance simultaneous nitrification and denitrification (SND) in existing aerobic biological wastewater treatment processes. Nevertheless, the mechanisms of SND in an aerobic immobilized biomass need to be proven. In this study, waste sludge from municipal wastewater treatment plants was immobilized by cellulose triacetate as bioplates, and an immobilized bioplate reactor (IBPR) was successfully established for nitrogen removal tests. The SND efficiency of the IBPR was increased 18% under the intermittent aeration (IA) mode compared with that under the continuous aeration (CA) mode. During IA operation, the IBPR achieved 96% COD removal and 76% NH4+-N removal, with 71% SND. The results of microbial community analysis by high-throughput sequencing showed that nitrogen-related functional bacteria were more abundant in the bioplates than in the attached biofilms. The colocalization of nitrifiers and denitrifiers in the bioplates was observed, and the microbial community of nitrogen-related functional bacteria clearly shifted with the substrate concentration gradients.

Imprints of Lockdown and Treatment Processes on the Wastewater Surveillance of SARS-CoV-2: A Curious Case of Fourteen Plants in Northern India

The present study investigated the detection of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) genomes at each treatment stage of 14 aerobic wastewater treatment plants (WWTPs) serving the major municipalities in two states of Rajasthan and Uttarakhand in Northern India. The untreated, primary, secondary and tertiary treated wastewater samples were collected over a time frame ranging from under-lockdown to post-lockdown conditions. The results showed that SARS-CoV-2 RNA was detected in 13 out of 40 wastewater samples in Jaipur district, Rajasthan and in 5 out of 14 wastewater samples in the Haridwar District, Uttarakhand with the E gene predominantly observed as compared to the N and RdRp target genes in later time-points of sampling. The Ct values of genes present in wastewater samples were correlated with the incidence of patient and community cases of COVID-19. This study further indicates that the viral RNA could be detected after the primary treatment but was not present in secondary or tertiary treated samples. This study implies that aerobic biological wastewater treatment systems such as moving bed biofilm reactor (MBBR) technology and sequencing batch reactor (SBR) are effective in virus removal from the wastewater. This work might present a new indication that there is little to no risk in relation to SARS-CoV-2 while reusing the treated wastewater for non-potable applications. In contrast, untreated wastewater might present a potential route of viral transmission through WWTPs to sanitation workers and the public. However, there is a need to investigate the survival and infection rates of SARS-CoV-2 in wastewater.

Detection of N-nitrosodimethylamine (NDMA) and its formation potential in hospital wastewater.

Hospital wastewaters contain high concentrations of pharmaceutical residues and other chemicals, and may present an important source for NDMA (N-nitrosodimethylamine) and its precursors in the aquatic environment. The present study evaluates the contribution of hospital wastewater to NDMA environmental load and identifies important sources within the hospital itself. For this purpose, wastewaters from five large hospitals in Israel were analyzed, and concentrations of NDMA were found in the range of 20.7-56.7 ng/L, which are similar to NDMA concentrations typically detected in domestic wastewater. The relative contribution of day surgery, oncology, laboratories, and central kitchen (in Sheba hospital) to the daily load of NDMA was calculated as 20.2%, 8.2%, 10%, and 43.2%, respectively. In addition, NDMA concentration in Sheba's mixed wastewater stream, measured throughout a complete working day, was highest at 14:00. This suggests the possible impact of lunchtime on NDMA concentration, and emphasizes the dominant contribution of central kitchen waste. Finally, formation potential of NDMA in the mixed stream was 7300 ng/L, in the upper range of domestic wastewater, but could be decreased by 70% during subsequent aerobic biological wastewater treatment.

When and why do gradients of the gas phase composition and pressure affect liquid-gas transfer?

Gas bubbles are introduced in water to absorb or strip volatile substances in a variety of unit operations, for example during (waste)water treatment. To calculate the transfer rate of substances between the liquid phase and the gas phase, different assumptions have been made in literature regarding the gas phase composition and hydraulic pressure, which both vary along the reactor height. In this study, analytical expressions were derived for the total (macroscopic) liquid-gas transfer rate, using either the complete gradients of the mole fraction and pressure (comprehensive approach) or a uniform value, for one or both of them. Simulations with the comprehensive model were performed to understand the effect of the type of volatile substance and of the reactor design and operating conditions on the total liquid-gas transfer rate. These effects were found to be highly interactive and often non-linear. Next, the simulation results of the comprehensive model were compared with those from models that assume either a uniform mole fraction or a uniform pressure in the complete reactor volume. This illustrated that for soluble substances, the mole fraction gradient strongly affects the total liquid-gas transfer rate, while the pressure gradient became only important under operating conditions that promote stripping (i.e., for a high concentration in the liquid phase and low concentration in the inlet gas). For very poorly soluble substances, the pressure became more important under conditions that promote absorption. These results on the importance of the mole fraction and pressure gradients remained equally valid when explicitly considering a typical variation of the volumetric overall transfer coefficient (KLa) along the reactor height. Finally, a simple and fast procedure was made available through a spreadsheet to select appropriate simplifying assumptions in reactor or plant-wide models. By applying the procedure to oxygen (O2), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and nitrogen gas (N2) in an aerobic biological wastewater treatment reactor, it was demonstrated that some common simplifications can lead to significant errors, for which corrections were proposed.

Biotreatment of high-salinity wastewater: current methods and future directions.

Saline wastewaters are usually generated by various industries, including the chemical, pharmaceutical, agricultural, and aquacultural industries. The discharge of untreated high-salinity wastewater may cause serious environmental pollution and damage the aquatic, terrestrial, and wetland ecosystems. For many countries, the treatment of saline wastewater has become an important task. Generally, saline wastewaters are treated through physical and chemical methods. However, these traditional techniques are associated with higher treatment costs and the generation of byproducts. In contrast, biotreatment techniques are environmentally friendly and inexpensive. This review highlights the sources and environmental concerns of high-salinity wastewater and illustrates the latest problems and solutions to the use of biological approaches for treating saline wastewater. Although high salinity may inhibit the effectiveness of aerobic and anaerobic biological wastewater treatment methods, such strategies as selecting salt-adapted microorganisms capable of degrading pollutants with tolerance to high salinity and optimizing operating conditions can be effective. This mini-review may serve as a reference for future efforts to treat high-salinity wastewater.

Performance Evaluation of Phosphorous Removal by Coagulation using Natural Coagulants

Phosphorous is one of the major nutrients contributing the increased eutrophication of lakes and natural waters. The concentration of phosphorus in domestic sewage is generally adequate to support aerobic biological wastewater treatment. Coagulation and flocculation processes can also to remove phosphorous from industrial wastewater.In this experimental study, an attempt is made to feasibility of natural coagulants like Cassia Alata, Calotropis Procera, Hyacinth bean, Banana leaves, Carcia Papaya, Acacia mearnsii, Jatropha Curcas, Cactus and Tamarind seeds on the decrease of Phosphorous from Industrial wastewater. The batch coagulation test was done to optimum graph was plotted between the removal efficiency all the chose coagulated. From the optimum trails, that the rate of phosphorous removal is more for hyacinth bean with a level of 75, trailed by casuarinas leaves with 74% and Banana leaves with 73%. Tamarind seed demonstrates the least Phosphorous expulsion from the wastewater with 56%. From the optimum trails, the Hyacinth bean can be utilized as a successful coagulant for the expulsion of phosphorus from the wastewater. In the optimum trails coagulation studies were carried out to investigate the factor like optimum dosage, pH, initial concentration of Phosphorous, Mixing time and the settling time which influences the removal of phosphorous by coagulation process. From the study, it might be inferred that the maximum percentage removal of phosphorous was acquired for the coagulant measurement of, pH of 8, the initial phosphorous concentration of, mixing time of and settling time of 45 minutes. It might be presumed that the Phosphorous removal from the industrial wastewater of 95% was conceivable when we kept up the optimum condition by the coagulation procedure..

Maximisation of the organic load rate and minimisation of oxygen consumption in aerobic biological wastewater treatment processes by manipulation of the hydraulic and solids residence time

A systematic experimental study of the effect of hydraulic residence time (HRT) and solids residence time (SRT) on conventional suspended-growth biological wastewater treatment processes was carried out. The aim of this study was to identify the conditions that minimise the reactor volume, i.e. maximise the organic load rate (OLR), and minimise the oxygen consumption. Lab-scale sequencing batch reactors (SBRs) were operated with glucose or ethanol as only carbon sources, with HRT in the range 0.25–4 day and SRT in the range 1–71 day. The highest OLR values which gave satisfactory performance were 4.28 and 4.14 gCOD/l.day for glucose and ethanol, respectively, which are among the highest reported for conventional aerobic suspended-growth processes. The highest OLR values were obtained with HRT = 0.25 day, SRT = 3.1 day for glucose and HRT = 0.5 day, SRT = 4.9 day for ethanol. The minimum oxygen consumption was 0.36 and 0.69 kg O2/kg COD removed for glucose and ethanol, respectively. In disagreement with conventional theories, it was found that biomass production also depended on the OLR as well as on the SRT, higher OLRs giving lower biomass production for the same SRT. From the kinetic analysis of the experimental data, this behaviour, which has important consequences for the design of biological wastewater treatment processes, was explained with a higher rate of endogenous metabolism at higher OLRs.

Artificial intelligence models for predicting the performance of biological wastewater treatment plant in the removal of Kjeldahl Nitrogen from wastewater

The current work demonstrates the support vector machine (SVM) and adaptive neuro-fuzzy inference system (ANFIS) modeling to assess the removal efficiency of Kjeldahl Nitrogen of a full-scale aerobic biological wastewater treatment plant. The influent variables such as pH, chemical oxygen demand, total solids (TS), free ammonia, ammonia nitrogen and Kjeldahl Nitrogen are used as input variables during modeling. Model development focused on postulating an adaptive, functional, real-time and alternative approach for modeling the removal efficiency of Kjeldahl Nitrogen. The input variables used for modeling were daily time series data recorded at wastewater treatment plant (WWTP) located in Mangalore during the period June 2014–September 2014. The performance of ANFIS model developed using Gbell and trapezoidal membership functions (MFs) and SVM are assessed using different statistical indices like root mean square error, correlation coefficients (CC) and Nash Sutcliff error (NSE). The errors related to the prediction of effluent Kjeldahl Nitrogen concentration by the SVM modeling appeared to be reasonable when compared to that of ANFIS models with Gbell and trapezoidal MF. From the performance evaluation of the developed SVM model, it is observed that the approach is capable to define the inter-relationship between various wastewater quality variables and thus SVM can be potentially applied for evaluating the efficiency of aerobic biological processes in WWTP.

Towards advanced aeration modelling: from blower to bubbles to bulk.

Aeration is an essential component of aerobic biological wastewater treatment and is the largest energy consumer at most water resource recovery facilities. Most modelling studies neglect the inherent complexity of the aeration systems used. Typically, the blowers, air piping, and diffusers are not modelled in detail, completely mixed reactors in a series are used to represent plug-flow reactors, and empirical correlations are used to describe the impact of operating conditions on bubble formation and transport, and oxygen transfer from the bubbles to the bulk liquid. However, the mechanisms involved are very complex in nature and require significant research efforts. This contribution highlights why and where there is a need for more detail in the different aspects of the aeration system and compiles recent efforts to develop physical models of the entire aeration system (blower, valves, air piping and diffusers), as well as adding rigour to the oxygen transfer efficiency modelling (impact of viscosity, bubble size distribution, shear and hydrodynamics). As a result of these model extensions, more realistic predictions of dissolved oxygen profiles and energy consumption have been achieved. Finally, the current needs for further model development are highlighted.

Research on Control Strategy of Dissolved Oxygen in Aerobic Wastewater Treatment Process

Aerobic biological wastewater treatment processes are difficult to be controlled because of their complex and nonlinear behavior, however, the control of the dissolved oxygen (DO) level in the reactors plays an important role in the operation of the facility, which affects the activity of activated sludge. A mathematical model of aeration system is established with the actual pulp and paper wastewater aerobic biological treatment process in Shandong as the background. Three control strategies for DO are designed. MATLAB simulation was carried out to compare the PID control, fuzzy control and fuzzy PID control of the step response. The robustness analysis of the three control systems is also researched. Conclusion is that the performance of Fuzzy PID control is the best.

Successful application of Shirasu porous glass (SPG) membrane system for microbubble aeration in a biofilm reactor treating synthetic wastewater

Microbubble aeration is supposed to be able to provide potential advantage for aerobic biological wastewater treatment due to enhancement of oxygen mass transfer. Then SPG membrane microbubble generation system was used to aerate a biofilm reactor treating a synthetic wastewater. Successfully long-term operation of the experimental system demonstrated the application feasibility of microbubble aeration in aerobic biological wastewater treatment. The air permeation of SPG membrane depended on its surface property and pore size, rather than membrane fouling which influenced microbubble generation and subsequent oxygen transfer. Stable and efficient COD removal was achieved but the ammonia removal became inefficient at high organic loading rate due to DO limitation. The suitable SPG membrane area-based COD removal capacity should be controlled around 6.69kgCOD/(m2d), considering the stable DO concentration and efficient contaminant removal. Microbubble floatation also provided contribution to suspending and colloidal contaminant removal. The oxygen utilization was estimated as high as almost close to 100% under certain conditions based on contaminant removal, but the energy consumption of this microbubble aeration system was also very high. To use hydrophobic SPG membranes and increase their air supply capacity could contribute to energy-saving.

Effect of microbubble and its generation process on mixed liquor properties of activated sludge using Shirasu porous glass (SPG) membrane system

Microbubble aeration is supposed to be able to provide potential advantage for aerobic biological wastewater treatment due to enhancement of oxygen mass transfer. On the other hand, microbubble and its generation methods might affect mixed liquor properties of activated sludge. Then SPG membrane microbubble generation system was used to investigate variation of mixed liquor properties of activated sludge in microbubble aeration. The results indicated that sludge floatation happened in microbubble aeration due to attachment of microbubbles to sludge flocs, resulting in a decrease in mixed liquor suspended solid (MLSS) concentration and poor sludge settleability. The strong shear stress caused by liquid circulation pump during microbubble generation led to sludge broken, resulting in decreased sludge floc size and sludge organics release, such as extracellular polymers (EPS). The organics release from broken sludge flocs was the main reason for increased both supernatant organic content (especially organic colloids) and consequent supernatant turbidity. The re-flocculation ability of broken sludge flocs also depended on sludge EPS release. In addition, the viscosity of mixed liquor increased along with sludge broken and increased supernatant organic content but the surface tension of mixed liquor remained constant. These results displayed the possible problems to apply microbubble aeration in aerobic wastewater treatment processes based on activated sludge.

Biodegradation of Coir Geotextiles Attached Media in Aerobic Biological Wastewater Treatment

Coir is a hard and tough organic fibre, rich in cellulose and lignin, and possesses high specific area and wetting ability - factors which are important for bacterial adhesion in fixed film processes. Few studies have been reported on the durability of coir geotextiles, when used in Civil Engineering applications such as slope protection works. However, its durability when used as the media in biofilters, for wastewater treatment extensively has not been studied yet. Durability of coir geotextiles has been assessed by keeping it in wet condition and measuring the tensile strength of the fibres, at different times. In the present study, coir geotextiles that were used as the attachment media in a biofilter, for treatment of organic rich wastewater was tested for durability. The units were operated as aerobic, gravity flow filters. Different wastewater parameters were employed in each of these runs. Tensile strength of the fibres was determined after each run. Results show that loss of tensile strength (or degradation) is influenced by the characteristics of the effluent wastewater to the filter, due to the growth of microorganisms which depends upon the concentration of substrates in the wastewater. Permeability studies shows reduction in permeability, is influenced by the organic loading rate on the filters and the duration of filter operation. SEM studies and E-DAX analysis shows the biodegradation of the fibres constituents, influenced by the substrate concentration.

Reduction of N2O and NO Generation in Anaerobic−Aerobic (Low Dissolved Oxygen) Biological Wastewater Treatment Process by Using Sludge Alkaline Fermentation Liquid

This paper reported an efficient method to significantly reduce nitrous oxide (N(2)O) and nitric oxide (NO) generation in anaerobic-aerobic (low dissolved oxygen) processes. It was found that by the use of waste-activated sludge alkaline fermentation liquid as the synthetic wastewater-carbon source, compared with the commonly used carbon source in the literature (e.g., acetic acid), the generation of N(2)O and NO was reduced by 68.7% and 50.0%, respectively, but the removal efficiencies of total phosphorus (TP) and total nitrogen (TN) were improved. Both N(2)O and NO were produced in the low dissolved oxygen (DO) stage, and the use of sludge fermentation liquid greatly reduced their generation from the denitrification. The presences of Cu(2+) and propionic acid in fermentation liquid were observed to play an important role in the reduction of N(2)O and NO generation. The analysis of the activities of denitrifying enzymes suggested that sludge fermentation liquid caused the significant decrease of both nitrite reductase activity to NO reductase activity ratio and NO reductase activity to N(2)O reductase activity ratio, which resulted in the lower generation of NO and N(2)O. Fluorescence in situ hybridization analysis indicated that the number of glycogen accumulating bacteria, which was reported to be relevant to nitrous oxide generation, in sludge fermentation liquid reactor was much lower than that in acetic acid reactor. The quantitative detection of the nosZ gene, encoding nitrous oxide reductase, showed that the use of fermentation liquid increased the number of bacteria capable of reducing N(2)O to N(2). The feasibility of using sludge fermentation liquid to reduce NO and N(2)O generation in an anaerobic-low DO process was finally confirmed for a municipal wastewater.

Effect of sonication assisted by titanium dioxide and ferrous ions on polyaromatic hydrocarbons (PAHs) and toxicity removals from a petrochemical industry wastewater in Turkey

AbstractBACKGROUND: In Izmir (Turkey) polyaromatic hydracarbon (PAH) removal efficiencies are low in petrochemical industry aerobic biological wastewater treatment plants because bacteria are not able to overcome the inhibition of these toxic and refractory organics. In order to increase PAHs removal, sonication process was chosen among other advanced treatment processes include sonication processes. The effects of ambient conditions, increasing sonication time, sonication temperature, TiO2 and Fe+2 concentrations on sonication at a petrochemical industry wastewater treatment plant in Izmir (Turkey) was investigated in a 650 W sonicator, at a frequency of 35 kHz and a 500 mL glass reactor.RESULTS: Increasing the temperature improved PAH removal after 150 min sonication at 30 °C and 60 °C. The maximum total PAH removal efficiencies were the same in a reactor containing 20 mg L−1 TiO2 and in a TiO2‐free reactor at 30 °C and 60 °C after 150 min sonication. Maximum 91% and 97% total PAH removals were obtained in a control reactor and a reactor containing 20 mg L−1 Fe+2 at 30 °C and 60 °C, respectively, after 150 min sonication. The PAH concentration was toxic to Daphnia magna, so that the EC50 value decreased significantly from 342.56 ng mL−1 to EC50 = 9.88 ng mL−1 and to EC50 = 3.35 ng mL−1, at the lowest TiO2 (0.1 mg L−1) and Fe+2 (2 mg L−1) concentrations, respectively, after 150 min sonication at 30 °C.CONCLUSION: PAHs and the acute toxicity in a petrochemical industry wastewater were removed efficiently through sonication. Copyright © 2010 Society of Chemical Industry

Mixing characterisation of full-scale membrane bioreactors: CFD modelling with experimental validation

Membrane Bioreactors (MBRs) have been successfully used in aerobic biological wastewater treatment to solve the perennial problem of effective solids–liquid separation. The optimisation of MBRs requires knowledge of the membrane fouling, biokinetics and mixing. However, research has mainly concentrated on the fouling and biokinetics ( Ng and Kim, 2007). Current methods of design for a desired flow regime within MBRs are largely based on assumptions (e.g. complete mixing of tanks) and empirical techniques (e.g. specific mixing energy). However, it is difficult to predict how sludge rheology and vessel design in full-scale installations affects hydrodynamics, hence overall performance. Computational Fluid Dynamics (CFD) provides a method for prediction of how vessel features and mixing energy usage affect the hydrodynamics. In this study, a CFD model was developed which accounts for aeration, sludge rheology and geometry (i.e. bioreactor and membrane module). This MBR CFD model was then applied to two full-scale MBRs and was successfully validated against experimental results. The effect of sludge settling and rheology was found to have a minimal impact on the bulk mixing (i.e. the residence time distribution).