Aerobic Biological Treatment Processes Research Articles

Study on the degradability of plastics with prodegradant additives during anaerobic and aerobic biological waste treatment processes

The degradability of conventional plastic packaging specimens made from PP and PET, that were produced with novel prodegradant additives, was investigated during biological waste treatment processes. The additives were merchandised to foster the degradation of commodity plastics by enzymatic or by abiotic processes. Four different plastic packaging specimens and two different additives were evaluated for their biodegradability during anaerobic and aerobic waste treatment conditions. Aerobic treatment was investigated in laboratory rotting tests, simulating conditions during composting in a plant according to the Austrian state-of-the-art, while anaerobic treatment was investigated in laboratory digestion reactors. The study shows that only the PET specimens showed a loss of mass of ca. 6.5%, during 50 days of digestion at 52 °C. None of the specimens degraded during the aerobic rotting process. None of the materials fragmented into microplastic particles of sizes > 1 mm under the investigated conditions. However, FTIR analysis revealed the oxidation in the case of PP specimens, which indicated a mediated oxidation process during composting, independent of the merchandised mechanism of predegradation. Under anaerobic conditions, the plastic specimens containing reactors produced more biogas within the first 20 days of digestion, that did not originate from an observable degradation of the plastics.

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.

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.

Simultaneous biodegradation of phenolics and petroleum hydrocarbons from semi-coking wastewater: Construction of bacterial consortium and their metabolic division of labor

Phenols and petroleum hydrocarbons were the main contributors to COD in semi-coking wastewater, and their removal was urgent and worthwhile. The microbial strains were selected to construct microbial community for the wastewater treatment. The concentration of phenols was decreased from 2450 ± 1.2 mg/L to 200 ± 0.9 mg/L, and the removal rate of petroleum hydrocarbons was up to 97.08 ± 0.09 % by microorganisms. After phenolic compounds with high toxicity were removed by bioaugmentation, the treated semi-coking wastewater was more biodegradable, and its water quality has been significantly improved. Through GC–MS and high-through sequencing technology, the metabolic division of labor in degradation of phenols, ring-cleavage of aromatic compounds, mineralization of metabolites was further revealed. The microbial community consisting of Pseudomonas stutzeri N2 and Rhodococcus qingshengii FF could effectively and simultaneously remove phenols and petroleum hydrocarbons, and these two strains possess great potential of being applied in aerobic biological treatment process of large-scale semi-coking wastewater.

Long-term performance and metagenomic analysis of full-scale anaerobic granular sludge bioreactors for low aerobically-biodegradable synthetic fiber manufacturing wastewater treatment

The synthetic fiber manufacturing wastewater (FMW) contained large amounts of tetrahydrofuran (THF), 3-buten-1-ol (BDO) and 1,4-butanediol (BTO) and showed a high chemical oxygen demand (COD) of 7,992 ± 2,252 mg L−1. Ratio of the biological oxygen demand (BOD5) and COD of the FMW stream was analyzed as only 0.094, which reflected the low aerobically biodegradable property. For complementing existed aerobic biological treatment process, an external circulation sludge bed (ECSB) system consisting of two full-scale anaerobic granular sludge (AnGS) bioreactors was constructed and continuous operation for more than 25 months. Even though feed fluctuations occurred, robust performance of the system was exhibited with consistent high removals of COD (85.5 ± 4.4%), THF (79.8 ± 8.6%), BDO and BTO (both 100%). Fractionation analyses of AnGS at nine heights of the two bioreactors showed that the bigger size (>0.5 mm) dominated at the bottom (>92.1%). Morphology and elemental analyses of AnGS were helpful to see surface depositions in line with water analyses. Anaerobic biodegradations were also highlighted in a comprehensive analysis of carbon and nitrogen fractions, phosphates, sulfates and other minerals. Moreover, metagenomic analyses revealed Methanomicrobia and Methanosaeta in archaea and Exilispira in bacteria were the dominant genera in microbial community structure, which given more insights of anaerobic biodegradation in the two full-scale bioreactors.

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.

Formation of oxygenated polycyclic aromatic hydrocarbons from polycyclic aromatic hydrocarbons during aerobic activated sludge treatment and their removal process

Though previous studies have focused on the removal of polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) in wastewater treatment plants, there is a lack of information on the transformation from PAHs to OPAHs during the activated sludge treatment. In this study, a batch experiment was carried out to simulate the aerobic biological treatment process, and the fungi species was detected by high-throughput sequencing. In the result, the transformation from PAHs (anthracene) to OPAHs (anthraquinone) was confirmed. A higher temperature (25°C/35°C) and higher initial concentration (5.0μg/L) of anthracene promoted the formation of anthraquinone, compared with a lower temperature (10°C) and lower initial concentration (0.5μg/L). The relevant functional fungi for the transformation were detectable in the activated sludge (Candida_parapsilosis, Candida_tropicalis and Bjerkandera-sp), confirming the biotransformation. After 168h, anthraquinone was totally biodegraded, indicating that activated sludge treatment was satisfactory for PAHs removal from the aspect of the biodegradation of the intermediate OPAHs. Furthermore, the possible factors influencing the biodegradation of both PAHs and OPAHs were also determined. The lower molecular weight compounds were more easily biodegraded than the higher ones. The temperature around 25°C was more appropriate for compounds removal than 35°C or 10°C, because the microbial species were more plentiful in activated sludge at 25°C. Different initial concentrations (0.5μg/L, 5.0μg/L) did not significantly influence the removal efficiency. However, the compounds we added to the samples could be more easily removed than those inherent in the samples, probably resulting from the stronger combination of the inherent compounds with the dissolved organic matters. The results from the batch experiment could be valid indicators for the effect of real wastewater treatment process.

Assessing the influence of oil and grease and salt content on fish canning wastewater biodegradation through respirometric tests

Fish canning industry wastewaters have high organic matter, oil and grease and salt (NaCl) content, which make difficult a proper treatment before discharge. In this work, their treatment was evaluated via activated sludge aerobic biological process through respirometric tests. Inhibition was found to be significant for NaCl concentrations higher than 17.5 g/L. On the other hand, the oil and grease content affects the wastewater biodegradability in the same way that the organic matter content expressed as chemical oxygen demand: the lower oil and grease and organic matter concentrations, the lower the percentage of wastewater biodegradability. As a final conclusion, the aerobic biological treatment process by activated sludge proved to be appropriate to treat fish canning industrial wastewaters, leading to high organic matter degradation rates (average value of 4900 mgO2/gCOD.d). Additionally, the experimental results achieved with the respirometric tests may be useful for the design of activated sludge plants to treat this type of wastewaters.

Enhancing Biodegradability of Refractory Aromatics in Wastewater: Pretreatment with Elemental Iron

Chlorinated aromatics, nitroaromatics, and azoaromatics are widely used in industry. As a result, these compounds are commonly present in industrial wastewater. Aerobic biological treatment processes are often inefficient for wastewaters containing these organic pollutants because most of these aromatic compounds are resistant to aerobic degradation. The goal of this research is to investigate the feasibility of elemental iron to pretreat wastewater through reduction of the azo and nitro functions, thus making these compounds more biodegradable prior to entering biological treatment processes, such as activated sludge. The experimental approach involved a series of batch reduction experiments to test the treatability, via chemical reduction, of a suite of compounds (nitrobenzene, 2,4-dinitrotoluene, orange G, orange II, orange IV, orange I, 1,2,4-trichlorobenzene, and pentachlorophenol) as well as the effects that various synthetic wastewater components would have on reduction rates. Once reduction products were identified in the batch reduction experiments, they were tested for their aerobic biodegradability through batch biodegradation and respirometric studies. A set of column experiments to examine iron life span were the final precursor to design and operation of a bench-scale integrated iron column-activated sludge treatment system for azo dyes. Results from batch reduction experiments indicate that azo dyes and nitroaromatics are rapidly transformed to their reduced counterparts. In all cases, the pretreatment of recalcitrant compounds via reduction with elemental iron enhanced their aerobic biodegradability This title belongs to WERF Research Report Series ISBN: 9781843396765 (eBook)

Performance of municipal waste stabilization ponds in the Canadian Arctic

Abstract The majority of small remote communities in the Canadian arctic territory of Nunavut utilize waste stabilization ponds (WSPs) for municipal wastewater treatment because of their relatively low capital and operational costs, and minimal complexity. New national effluent quality regulations have been implemented in Canada, but not yet applied to Canada's Arctic due to uncertainty related to the performance of current wastewater treatment systems. Waste stabilization pond (WSP) treatment performance is impacted by community water use, pond design, and climate. The greatest challenge arctic communities experience when using passive wastewater treatment technologies is the constraints imposed by the extreme climate, which is characterized as having long cold winters with short cool summers that can be solar intense. The removal of carbonaceous biochemical oxygen demand (CBOD 5 ), total suspended solids (TSS), and ammonia-nitrogen were measured during the summer treatment period (late June until early September) from 2011 to 2014 in the WSP systems of four Nunavut communities; Pond Inlet, Clyde River, Grise Fiord and Kugaaruk. Monitoring results showed that WSPs in their current single cell design can achieve greater than 80% removal of CBOD 5 and TSS but were challenged to produce effluent quality that meets secondary wastewater treatment standards ( 5 and TSS). This study points to the need for revisions of design guidelines for facultative WSPs in the Arctic, as current systems are anaerobic and do not contain sufficient dissolved oxygen required to consistently support aerobic biological treatment processes.

A combined evaluation of the characteristics and acute toxicity of antibiotic wastewater

The conventional parameters and acute toxicities of antibiotic wastewater collected from each treatment unit of an antibiotic wastewater treatment plant have been investigated. The investigation of the conventional parameters indicated that the antibiotic wastewater treatment plant performed well under the significant fluctuation in influent water quality. The results of acute toxicity indicated that the toxicity of antibiotic wastewater could be reduced by 94.3 percent on average after treatment. However, treated antibiotic effluents were still toxic to Vibrio fischeri. The toxicity of antibiotic production wastewater could be attributed to the joint effects of toxic compound mixtures in wastewater. Moreover, aerobic biological treatment processes, including sequencing batch reactor (SBR) and aerobic biofilm reactor, played the most important role in reducing toxicity by 92.4 percent. Pearson׳s correlation coefficients revealed that toxicity had a strong and positive linear correlation with organic substances, nitrogenous compounds, S2−, volatile phenol, cyanide, As, Zn, Cd, Ni and Fe. Ammonia nitrogen (NH4+) was the greatest contributor to toxicity according to the stepwise regression method. The multiple regression model was a good fit for [TU50-15min] as a function of [NH4+] with the determination coefficient of 0.981.

Fates of chlorinated volatile organic compounds in aerobic biological treatment processes: The effects of aeration and sludge addition

The emission of volatile organic compounds (VOCs) from wastewater treatment plants (WWTPs) is becoming an environmental issue of increasing concern. As biological treatment has been considered as one important approach for VOC removal, lab-scale batch experiments were conducted in this study to investigate the fates of four chlorinated hydrocarbons, including chloroform, carbon tetrachloride, trichloroethylene (TCE), and tetrachloroethylene (PERC), in the biological treatment processes with respect to the effects of aeration and sludge addition. The VOC concentrations in the phases of air, water, and sludge under four simulated treatment stages (the first sedimentation, the forepart and rear part of aerobic biological treatment, and the second sedimentation) were analyzed. The results were used to understand the three-phase partitioning of these compounds and to estimate their potentials for volatilization and biological sorption and degradation in these technologies with the concept of fugacity. It was observed that the VOCs were mainly present in the water phase through the experiments. The effects of aeration or sludge addition on the fates of these VOCs occurred but appeared to be relatively limited. The concentration distributions of the VOCs were well below the reported partitioning coefficients. It was suggested that these compounds were unsaturated in the air and sludge phases, enhancing their potentials for volatilization and biological sorption/degradation through the processes. However, the properties of these chlorinated VOCs such as the volatility, polarity, or even biodegradability caused by their structural characteristics (e.g., the number of chlorine, saturated or unsaturated) may represent more significant factors for their fates in the aerobic biological treatment processes. These findings prove the complication behind the current knowledge of VOC pollutions in WWTPs and are of help to manage the adverse impacts on the environment and public health by the VOCs from these particular sources.

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.

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.

Degradation of pulp and paper-mill effluent by thermophilic micro-organisms using batch systems

Paper manufacturers produce large quantities of wastewater, which can have deleterious effects on the receiving waters; therefore there is a need to find a treatment process which can minimize these effects considerably. A suitable aerobic biological treatment process that can be used with great success involves the use of thermophilic micro-organisms. This technology has many advantages, which include rapid biodegradation rates, low sludge yields, and excellent process stability. Batch studies were conducted on two types of activated sludge (pulp-mill sludge and sewage sludge) at 40 ° C, 50 ° C and 60 ° C to determine the feasibility of thermophilic degradation of bleach pulp-mill effluent in terms of increasing aeration, biomass concentration and nutrient addition. Preliminary batch studies had confirmed the feasibility of thermophilic degradation, as COD removal achieved with the pulp-mill sludge was 55.2%, 37.6% and 31.4% at 40 ° C, 50 ° C and 60 ° C after 5d, respectively while the COD removal with sewage sludge was 50.2%, 37.3% and 27% under the same conditions. Degradation was further improved, using the same inocula in subsequent experiments and this confirmed that an acclimatization period is required, prior to degrading the bleach pulp-mill effluent. Thermophilic degradation of pulp-mill effluent occurs at temperatures of up to 60°C; however, once final degradation is obtained, it decreases significantly as temperature increases. Keywords : thermophilic micro-organisms, pulp and paper mill effluent, degradation, batch systems Water SA Vol. 31(4) 2005: 575-580

High rate aerobic treatment of synthetic wastewater using enhanced coagulation high-performance compact reactor (EC-HCR)

The high-performance compact reactor (HCR) is a type of JLR system for wastewater aerobic biological treatment processes. HCR has demonstrated outstanding performance with respect to space–time yield in more than 20 industrial applications, whereas, it has the disadvantage of cloudy effluent because of the disappearance of filamentous organisms in the HCR reactor. This study examined the potential of a new enhanced coagulation HCR (EC-HCR) system to improve the effluent quality of HCR. Results showed that, when 20–25 mg/L FeCl 3 was added as coagulant into the coagulation tank, the effluent turbidity of EC-HCR system was lower. EC-HCR system could be operated at high organic loading and had high COD removal efficiency under short hydraulic retention time. When influent COD varied at 300–450 and 500–650 mg/L, there was no obvious difference on effluent COD compared with and without coagulant added. When influent with high COD concentration of 1000–1600 mg/L was treated, the COD removal efficiency could be improved obviously when 20 mg/L coagulant was added. There was no obvious difference between the nitrogen concentration in the effluent with and without coagulant, whereas, the phosphorus removal efficiency improved markedly when 20 mg/L coagulant was added into coagulation tank.

Treatment of High-Strength Pharmaceutical Wastewater and Removal of Antibiotics in Anaerobic and Aerobic Biological Treatment Processes

Anaerobic and aerobic treatment of high-strength pharmaceutical wastewater was evaluated in this study. A batch test was performed to study the biodegradability of the wastewater, and the result indicated that a combination anaerobic-aerobic treatment system was effective in removing organic matter from the high-strength pharmaceutical wastewater. Based on the batch test, a pilot-scale system composed of an anaerobic baffled reactor followed by a biofilm airlift suspension reactor was designed. At a stable operational period, effluent chemical oxygen demand (COD) from the anaerobic baffled reactor ranged from 1,432 to 2,397mg∕L at a hydraulic retention time (HRT) of 1.25 day, and 979 to 1,749mg∕L at an HRT of 2.5 day, respectively, when influent COD ranged from 9,736 to 19,862mg∕L. As a result, effluent COD of the biofilm airlift suspension reactor varied between 256 and 355mg∕L at HRTs of from 5.0 to 12.5 h. The antibiotics ampicillin and aureomycin, with influent concentrations of 3.2 and 1.0mg∕L, respectively, could be partially degraded in the anaerobic baffled reactor: ampicillin and aureomycin removal efficiencies were 16.4 and 25.9% with an HRT of 1.25 day, and 42.1 and 31.3% with HRT of 2.5 day, respectively. Although effective in COD removal, the biofilm airlift suspension reactor did not display significant antibiotic removal, and the removal efficiencies of the two antibiotics were less than 10%.

Enhanced Biodegradation of Azo Dyes Using an Integrated Elemental Iron‐Activated Sludge System: I. Evaluation of System Performance

The objective of this research is to evaluate an integrated system coupling zero-valent iron (Fe(0)) and aerobic biological oxidation for the treatment of azo dye wastewater. Zero-valent (elemental) iron can reduce the azo bond, cleaving dye molecules into products that are more amenable to aerobic biological treatment processes. Azo dye reduction products, including aniline and sulfanilic acid, were shown to be readily biodegradable at concentrations up to approximately 25 mg/L. Batch reduction and biodegradation data support the proposed integrated iron pretreatment and activated sludge process for the degradation of the azo dyes orange G and orange I. The integrated system was able to decolorize dye solutions and yield effluents with lower total organic carbon concentrations than control systems without iron pretreatment. The success of the bench-scale integrated system suggests that iron pretreatment may be a feasible approach to treat azo dye containing wastewaters.

Comparative Performance of RBC Operated under Pressure and Open to the Atmosphere at High Loading Conditions

The aim of this research was to investigate the effects of pressure on aerobic biological wastewater treatment processes. For the purpose of the investigation two specially designed, identical, laboratory-scale rotating biological contactor (RBC) units were constructed. One of these was held in a steel pressure vessel while the other, as reference unit, was operated open to the atmosphere. The treatment capabilities of the pressurized unit, compared to those of the reference unit, were determined for a variety of organic loading rates at a 5-bar pressure. The unit under pressure was able to produce a much better effluent, in comparison with the reference unit when operating at higher loading conditions. The filtered BOD5 in the effluent from the unit under pressure was always less than 10 mgL−1, whereas the sludge yield coefficient was as low as 0.21 kg dry solids/kg BOD5 removed, even with the unit loaded even at an organic loading rate of 27.0 g BOD5/m2 · day. However, the development of the nitrification decreased sharply as the organic loading increased. The indication is that the unit under pressure is able to operate over a wide range of loading with a small variation in the effluent quality. The principal benefits of increasing pressure were recorded to be significantly improved nitrification and a decrease in the sludge yield coefficient.