Aerobic Wastewater Treatment Processes Research Articles

Modeling Method for Aerobic Zone of A2O Based on KPCA-PSO-SCN

Sewage treatment plants face significant problems as a result of the annual growth in urban sewage discharge. Substandard sewage discharge can also be caused by rising sewage treatment expenses and unpredictable procedures. The most widely used sewage treatment process in urban areas is the Anaerobic–Anoxic–Oxic (A2O) sewage treatment process. Therefore, modeling the sewage treatment process and predicting the effluent quality are of great significance. A process modeling method based on Kernel Principal Component Analysis–Particle Swarm Optimization–Stochastic Configuration Network (KPCA-PSO-SCN) is proposed for the A2O aerobic wastewater treatment process. Firstly, eight auxiliary variables were determined through mechanism analysis, including Chemical Oxygen Demand (COD) and ammonia nitrogen (NH4+) and nitrate nitrogen (NO3−) of influent water, pH, temperature (T), Mixed Liquor Suspended Solid (MLSS), Dissolved Oxygen (DO) and hydraulic residence time (HRT) in the aerobic zone. Dimensionality reduction was carried out using the kernel principal component analysis method based on the Gaussian function, and the eight-dimensional data were changed to five-dimensional data, which improved the running speed and efficiency of subsequent models. Then, according to the advantages of the particle swarm optimization algorithm, such as low calculation cost and fast convergence, combined with the advantages of stochastic configuration network general approximation performance, the PSO-SCN model was established to predict the three water quality indexes of effluent COD, NH4+, and NO3− for the aerobic zone. The experimental results proved the effectiveness of the model. Compared with classic water quality prediction algorithm models such as SCN, PSO-BP, RBF, PSO-RBF, etc., the superiority of the PSO-SCN algorithm model was demonstrated.

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.

Biosorption and biotransformation behaviours of veterinary antibiotics under aerobic livestock wastewater treatment processes

To study the fate of veterinary antibiotics released from swine wastewater treatment plants (SWTP), 10 antibiotics were investigated in each unit of a local SWTP periodically. Over a 14-month period of field investigation into target antibiotics, it was confirmed that tetracycline, chlortetracycline, sulfathiazole, and lincomycin were used in this SWTP, with their presence observed in raw manure. Most of these antibiotics could be effectively treated by aerobic activated sludge, except for lincomycin, which was still detected in the effluent, with a maximum concentration of 1506 μg/L. In addition, the potential for removing antibiotics was evaluated using lab-scale aerobic sequencing batch reactors (SBRs) that were dosed with high concentrations of antibiotics. The SBR results, however, showed that both sulfonamides and macrolides, as well as lincomycin, can achieve 100% removal in lab-scale aerobic SBRs within 7 days. This reveals that the potential removal of those antibiotics in field aeration tanks can be facilitated by providing suitable conditions, such as adequate dissolved oxygen, pH, and retention time. Furthermore, the biosorption of target antibiotics was also confirmed in the abiotic sorption batch tests. Biotransformation and hydrolysis were identified as the dominant mechanism for removing negatively charged sulfonamides and positively charged antibiotics (macrolides and lincomycin) in SBRs. This is due to their relatively low sorption affinity (resulting in negligible to 20% removal) onto activated sludge in abiotic sorption tests. On the other hand, tetracyclines exhibited significant sorption behavior both onto activated sludge and onto soluble organic matters in swine wastewater supernatant, accounting for 70%–91% and 21%–94% of removal within 24 h, respectively. S-shape sorption isotherms with saturation were observed when high amounts of tetracyclines were spiked into sludge, with equilibrium concentrations ranging from 0.4 to 65 mg/L. Therefore, the sorption of tetracyclines onto activated sludge was governed by electrostatic interaction rather than hydrophobic partition. This resulted in a saturated sorption capacity (Qmax) of 17,263 mg/g, 1637 mg/g, and 641.7 mg/g for OTC, TC, and CTC, respectively.

Design of a High-Rate Wastewater Treatment Process for Energy and Water Recovery at Biorefineries

Industrial wastewaters rich in organic carbon have potential for value generation, but conventional, low-rate, anaerobic–aerobic wastewater treatment (WWT) processes often incur significant capital expenses and energy consumption. In this study, we leveraged experimental data for biorefinery-derived wastewaters to characterize the implications of transitioning from a conventional, low-rate process to a high-rate, multistage anaerobic process. We designed and simulated these WWT processes across seven first- and second-generation (1G/2G) biorefineries and evaluated the implications for biorefinery sustainability through techno-economic analysis (TEA) and life cycle assessment (LCA). Compared to the conventional design, the new process can substantially reduce capital costs and electricity usage. These improvements were particularly evident for 2G biorefineries, translating to 5%–13% lower minimum product selling prices (MPSPs) and 7%–135% lower 100-year global warming potentials (GWPs; the 135% reduction is due to the transition of one biorefinery from net emission [0.87 kg of CO2e·gal–1] to net sequestration [−0.31 kg of CO2e·gal–1]). Biorefineries could further reduce the MPSP through the renewable identification number (RIN) credits by upgrading and selling the biogas as renewable natural gas, but at the expense of increasing GWP. When normalized, the COD management cost ranged from $–56 to $465 per tonne of COD, indicating that wastewater could be a net source of revenue for some biorefineries.

고효율 생물반응기에 의한 과일 가공 음료 폐수처리

It is well-known that fruit processing beverage wastewater is one of the severely contaminated industrial wastewaters containing high BOD concentration. This makes it difficult to maintain the proper DO concentration needed in conventional aerobic wastewater treatment process unless the high BOD concentration is properly reduced by pretreatment processes such as anaerobic digestion. In this study, a full-scale high-efficiency bioreactor was applied to cope with the high BOD loading in fruit processing beverage wastewater as a pretreatment of the activated sludge process. The high-efficiency bioreactor, which has multiple draft-tubes for both internal circulation of mixed liquors and aeration, has a merit of requiring small land area for installation. The results of the full-scale high-efficiency bioreactor for fruit processing beverage wastewater treatment were compared with those of anaerobic filter. It was found that the high-efficiency bioreactor was greatly effective in aeration, maintaining a DO level of 2.47 mg/L on average. Substantial removal of pollutants were achieved in the high-efficiency bioreactor, which were 89.9% for BOD, 86.2% for CODMn, 57% for SS,78.9% for T-N, and 80.3% for T-P, while those of an aerobic filter were 45.5% for BOD, 43.1% for CODMn, 50.8% for SS, 55.3% for T-N, and 59.6% for T-P. Thus, it has been demonstrated that the high-efficiency bioreactor had good stability and suitability for the treatment of fruit processing beverage wastewater, as a pretreatment of conventional aerobic wastewater treatment.

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.

Microalgae cultivation in wastewater effluent from tilapia culture pond for enhanced bioethanol production.

The large number of wastewaters are generated because of the various production processes. Vegetable and fish processing can be considered an important industry for wastewater generation. The essential method for completing this waste is to digest the organic matter using anaerobic digestion followed by aerobic wastewater treatment processes; however, wastewater from tilapia culture pond retains considerable quantities of inorganic substances, particularly nutrients like nitrogen and phosphorus. The optimal conditions for cultivating Chlorella vulgaris from wastewater treatment effluent from tilapia culture pond were investigated in this study. The appropriate conditions were found to be 10% initial stock suspension, 20 cm depth, and 12 days of culture conditions. C. vulgaris had an optical density of 0.649, a cell density of 17.68 × 105 cells/mL, and biomass of 0.376 ± 94.21 mg/L after cultivation. Discharged wastewater from the fishpond was utilized for the improved growth of microalgae and obtained biomass was used for bioethanol production. This study verified that fishpond wastewater is the best source of nutrients for algal mass production and biofuel applications.

Long-term effect of graphene oxide on the aerobic granular sludge wastewater treatment process

This study investigated the bioreactor performance, production of extracellular polymeric substance (EPS), and microbial activity of a granulated sequencing batch reactor (SBR) by increasing the graphene oxide nanoparticle (GO NP) concentration stepwise. The GO NPs reduced the removal of chemical oxygen demand (COD), ammonia, and phosphorus, whereas the nitrite and nitrate contents of the effluent were kept stable during the experiment. The ammonia-nitrogen (NH4-N) and COD removal rates were deceased considerably from 99% and 95–96.2% and 78.6% at 55 mg/L GO NPs; furthermore, at 115 mg/L GO NPs, the NH4-N and COD removal rates further decreased to 88.5% and 59.3%. The removal of phosphorus decreased even at small concentrations of graphene oxide (GO), and the inhibitory effect enhanced with an increase in the GO NP content. The increased amounts of nanoparticles significantly influenced the microbial activity of aerobic granular sludge (AGS). The specific oxygen uptake rate (SOUR) decreased from 42.04 to 33.14 mg O2/g MLVSS*h, specific ammonia oxidation rate (SAOR) declined from 4.84 to 4.12 mg N/g MLVSS*h, specific phosphorus uptake rate (SPUR), and specific phosphorus release rate (SPRR) significantly decreased from 13.1 and 10.05–8.2 and 8.7 mg P/g MLVSS*h after 98 days. However, the specific nitrite and nitrate reduction rate (SNIRR and SNRR), and the specific nitrite oxidation rate (SNOR) remained relatively stable. The EPS content of sludge was initially 5.95 mg/g MLVSS, but the presence of GO up a concentration of 55 mg/L promoted the secretion of EPS and increased to 11.86 mg/g MLVSS. At higher GO concentrations, the secretion of EPS was inhibited. After 14 days, when the influent synthetic wastewater (SWW) did not contain GO NP, the AGS SBR performance showed a remarkable recovery capability.

Performance evaluation of down-flow hanging sponge reactor for direct treatment of actual textile wastewater; Effect of effluent recirculation to performance and microbial community

The textile industry discharges large amounts of polluted wastewater containing synthetic dyes. A down-flow hanging sponge (DHS) reactor is a novel aerobic wastewater treatment process that utilizes a sponge as a biomass-retaining carrier. This sponge carrier has both aerobic and anaerobic zones owing to different dissolved oxygen concentrations. In this study, the process performance of a DHS reactor treating actual textile wastewater obtained from a factory in Japan was evaluated. The effects of hydraulic retention time (HRT) and effluent recirculation (recirculation ratio = 1) on the DHS process performance were investigated. The DHS reactor showed good organic (up to 93 ± 13% of BOD) and nitrogen removal (56 ± 14% of TN) abilities during the entire experimental period. The color removal efficiencies of the DHS reactor were 55 ± 15%, 53 ± 26%, 72 ± 34%, and 35 ± 22% with HRTs of 4 h, 4 h + effluent recirculation (R = 1), 8 h + effluent recirculation (R = 1), and 8 h, respectively. Microbial community structure analysis of the DHS retained sludge showed that genus Acinetobacter was detected predominantly and reported as an azo dye-degrading bacterium. Effluent recirculation was also observed to increase the presence of aromatic-degrading bacteria and protists in the DHS reactor. These results suggest that the DHS reactor is suitable for textile wastewater treatment. Furthermore, the effluent recirculation is effective for enhancing decolorization performance.

A high-throughput assay to quantify protein hydrolysis in aerobic and anaerobic wastewater treatment processes.

Proteins, an important fraction of the organic matter in wastewater, typically enter a treatment facility as high molecular weight components. These components are degraded by extracellular protein hydrolytic enzymes, denoted as proteases. Adequate protein hydrolysis monitoring is crucial, since protein hydrolysis is often a rate-limiting step in wastewater treatment. However, current monitoring tools lack a high sample throughput and reliable quantification. Here, we present an improved assay for high-throughput protein hydrolysis rate measurements in wastewater treatment applications. A BODIPY FL casein model substrate was implemented in a microplate format for continuous fluorescent quantification. Case studies on a conventional and a high-rate aerobic municipal wastewater treatment plant and a lab-scale, two-stage, anaerobic reactor provided proof-of-concept. The assay presented in this study can help to obtain monitoring-based process insights, which will in turn allow improving biological performance of wastewater treatment installations in the future. KEY POINTS: • Protein hydrolysis is a crucial step in biological wastewater treatment. • Quantification of the protein hydrolysis rate enables in-depth process knowledge. • BODIPY FL casein is a suitable model substrate for a protein hydrolysis assay. • High sample throughput was obtained with fluorescent hydrolysis quantification. Graphical abstract.

A Comparative Study of Conventional Aerator and Microbubble Generator in Aerobic Reactors for Wastewater Treatment

Aeration in aerobic reactor for wastewater treatment has an important role in determining its performance. In this case, sufficient oxygen supply with good mixing is necessary to guarantee a good pollutant biodegradation. However, biodegradation is not the only parameter to consider when designing an aerator, energy consumption and cost also have important roles. In this study, a conventional air diffuser (CAD) and a low-cost microbubble generator (MBG) were compared in a 400-L reactor for two aerobic wastewater treatment process configurations, i.e. suspended culture and attached culture (with pumice stones). Dissolved oxygen (DO) concentration throughout the reactor was initially investigated with tap water. Results indicated that the maximum DO which could be obtained for the two type of aerators were almost similar, in the range of 7.7 to 7.9 mg/L. But the lowest values are different, i.e. 5.6 mg/L for CAD and 6.8 mg/L for MBG, showing that homogeneity was better for MBG. This might be due to smaller bubble sizes produced by MBG which were able to stay inside the liquid for a longer time. Afterward, comparison of the two aerators were performed for aerating activated aerobic sludge. Without pumice stones, DO concentration for MBG and CAD was almost similar, but for MBG, lower values were found in the bottom of the tank indicating the higher activated sludge concentration. When using pumice stones, MBG again shows its superiority indicated by a higher DO values reaching 6.4 mg/L, compared to 5.6 mg/L for the CAD. These results revealed the promising potential of MBG as a low-cost aerator to be used in aerobic reactor for wastewater treatment with attached culture.

Sulfate reducing bacteria-based wastewater treatment system integrated with sulfide fuel cell for simultaneous wastewater treatment and electricity generation

This study aimed to design a sulfate-reducing bacteria (SRB)-based wastewater treatment system (SWTS) integrated with a sulfide fuel cell (SFC) as an alternative to the energy-intensive aerobic wastewater treatment process. The result showed that the COD/sulfate ratio and hydraulic retention time (HRT) were two important parameters in a SWTS. The highest COD and sulfate removal efficiency rates were at a HRT of 4 h at a COD/sulfate ratio of 0.67, reaching 83 ± 0.2% and 84 ± 0.4% with sulfate removal rates of 4.087 ± 32 mg SO42−/d, respectively. A microbial analysis revealed that the dominance of nine OTUs belonging to SRB closely affected the high sulfate removal efficiency in the SWTS. At the HRT of 8 h, voltage of 0.02 V and a power density level of 130 mW/m2 were obtained with sulfide removal efficiency of 99 ± 0.5%. These results overall demonstrate that SRB can serve as a green and effective route for wastewater treatment.

Why Novel Sanitary Systems are Hardly Introduced?

Innovations are required in urban infrastructures due to the pressing needs for mitigating climate change and prevent resource depletion. In order to address the slow pace of innovation in urban systems, this paper analyses factors involved in attempts to introduce novel sanitary systems. Today new requirements are important: sanitary systems should have an optimal energy/climate performance, with recovery of resources, and with fewer emissions. Anaerobic digestion has been suggested as an alternative to current aerobic waste water treatment processes. This paper presents an overview of attempts to introduce novel anaerobic sanitation systems for domestic sanitation. The paper identifies main factors that contributed to a premature termination of such attempts. Especially smaller scale anaerobic sanitation systems will probably not be able to compete economically with traditional sewage treatment. However, anaerobic treatment has various advantages for mitigating climate change, removing persistent chemicals, and for the transition to a circular economy. The paper concludes that loss avoidance, both in the sewage system and in the waste water treatment plants, should play a key role in determining experiments that could lead to a transition in sanitation.

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.

Phylogenetic diversity and in situ detection of eukaryotes in anaerobic sludge digesters.

Eukaryotic communities in aerobic wastewater treatment processes are well characterized, but little is known about them in anaerobic processes. In this study, abundance, diversity and morphology of eukaryotes in anaerobic sludge digesters were investigated by quantitative real-time PCR (qPCR), 18S rRNA gene clone library construction and catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Samples were taken from four different anaerobic sludge digesters in Japan. Results of qPCR of rRNA genes revealed that Eukarya accounted from 0.1% to 1.4% of the total number of microbial rRNA gene copy numbers. The phylogenetic affiliations of a total of 251 clones were Fungi, Alveolata, Viridiplantae, Amoebozoa, Rhizaria, Stramenopiles and Metazoa. Eighty-five percent of the clones showed less than 97.0% sequence identity to described eukaryotes, indicating most of the eukaryotes in anaerobic sludge digesters are largely unknown. Clones belonging to the uncultured lineage LKM11 in Cryptomycota of Fungi were most abundant in anaerobic sludge, which accounted for 50% of the total clones. The most dominant OTU in each library belonged to either the LKM11 lineage or the uncultured lineage A31 in Alveolata. Principal coordinate analysis indicated that the eukaryotic and prokaryotic community structures were related. The detection of anaerobic eukaryotes, including the members of the LKM11 and A31 lineages in anaerobic sludge digesters, by CARD-FISH revealed their sizes in the range of 2–8 μm. The diverse and uncultured eukaryotes in the LKM11 and the A31 lineages are common and ecologically relevant members in anaerobic sludge digester.

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.

Inhibitory effects of sulfide on nitrifying biomass in the anaerobic–anoxic–aerobic wastewater treatment process

AbstractBACKGROUNDLong pipeline transportation of wastewater usually generates high concentration of sulfide; however, information on nitrification inhibition by sulfide in the anaerobic–anoxic–aerobic (AAO) process is still scarce. This study focused on how sulfide could inhibit nitrification activity in the AAO process, and the inhibitory effect of initial sulfide concentration and anaerobic exposure time on the behavior of nitrifying biomass.RESULTSThe net maximum specific growth rate (μAUT‐bAUT) was, respectively, 0.06 ± 0.01 and 0.31 ± 0.03 d−1 at 15 and 20°C in a full‐scale AAO wastewater treatment plant for long‐pipeline transported wastewater. The μAUT‐bAUT was not affected by 6.2 mg L−1 sulfide under aerated condition, but reduced by 75.9% after unaerated exposure for 0.5 h. The first‐order kinetic constant of sulfide inhibition under anaerobic conditions was 0.658 h−1, and half maximal inhibition concentration of sulfide on nitrification was 36.0 and 10.0 mg L−1 after 1.0 h and 1.5 h anaerobic exposure, respectively.CONCLUSIONNitrifying biomass was sensitive to the presence of sulfide under anaerobic conditions. The inhibitory reaction of sulfide on nitrifying biomass under anaerobic conditions conformed to the first‐order kinetic reaction, while the effect of initial sulfide concentration on nitrification inhibition matched the modified Monod model. © 2013 Society of Chemical Industry

Removal of aromatic hydrocarbons (BTX) in anoxic and anaerobic wastewater treatment processes

Benzene, toluene and xylenes (BTX) are a group of toxic and volatile aromatic compounds prevalent in many industrial wastewaters and they are often determined in municipal wastewater. Usually, BTX-containing wastewater is treated by conventional aerobic wastewater treatment process. However, the removal mechanisms are controversial since these compounds tend to be readily stripped from the aqueous phase to the atmosphere. On the other hand, their efficient removal is essential to reduce the subsequent disposal of such substances into the waters of the receiver. Batch tests with activated sludge process under anoxic and anaerobic conditions have been performed for assessment of the removal of specific organic contaminations BTX (benzene, toluene, and o- and p-xylene). The investigations were carried out in the laboratory anoxic reactors of 5 L volume. The content of activated sludge (TSS) was 5 g/L and concentrations of BTX in treated wastewater were in the range 0.25–2.37 mg/L of each of the compounds. The batch tests have showed enhanced BTX removal abilities under anoxic wastewater treatment. The rates of BTX removal in average: 0.214 mg/L d for benzene, 0.251 for toluene, 0.131 for o-xylene and 0.133 for p-xylene have been estimated. For anaerobic investigations the reactors of 2.5 L volume were used. The BTX removal under wastewater anaerobic digestion ranged from 28 to 63%.

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.