Aerobic Wastewater Treatment Processes Research Articles

Fouling and structural changes of Shirasu porous glass (SPG) membrane used in aerobic wastewater treatment process for microbubble aeration

In the present study a hydrophilic SPG membrane was used for microbubble generation to aerate a pilot-scale biofilm reactor treating synthetic municipal wastewater. The external fouling of SPG membrane was observed and identified during continuous operation of the bioreactor. Then the SPG membrane was cleaned offline by ultrasonic, thermal and acid treatment to remove fouling layer, organic and inorganic foulants on the membrane surface. The structural changes of SPG membrane were investigated after fouling and offline cleaning, using scanning electron microscopy (SEM), mercury and gas adsorption porosimetry, X-ray Diffraction (XRD), and Infrared (IR) absorption. SEM tests clearly demonstrated that these offline cleaning methods were effective to clear membrane external fouling. There was no obvious change in membrane pore size distribution after SPG membrane fouling and offline cleaning, but the membrane porosity and pore surface area increased slightly. XRD and IR analysis also showed that rare inorganic or organic foulants deposited on the pore surface inside the membrane. Therefore, the external fouling was identified as the main mechanism of SPG membrane fouling used in aerobic wastewater treatment process. The microbubble generation and oxygen mass transfer deteriorated due to external fouling of SPG membrane, which recovered after membrane offline cleaning.

MLVSS에 따른 Jet Loop Reactor (JLR)에서 동력량과 공기량이 산소전달률에 미치는 영향

Abstract : Oxygen transfer rate generally determines the performance of an aerobic wastewater treatment process that treats high strength wastewater such as food wastewater, animal wastewater and landfill leachate. In this paper, OUR and K L ･a were evaluated by using Jet Loop Reactor (JLR) according to the concentration of a mixed liquor volatile suspended solid (MLVSS), oxygen (air) flow rate and energy input as the variable of the operating conditions. Also, a nonlinear regression model was proposed by the statistical methods with the calculated K L ･a. As a results, in case of applying the high strength wastewater which has to maintain high MLVSS, the energy input and the air flow rate are major parameters oxygen transfer rate in JLR. Finally, the final nonlinear regression model had been developed as a function of E/V, Q g , and µ c . Key Words : Jet Loop Reactor (JLR), Oxygen Transfer Rate, Volumetric Mass Transfer Coefficient (K L ･ a) 요약: 산소전달률은 음폐수, 축산폐수 그리고 매립지 침출수와 같은 고농도 폐수처리를 호기성 공정으로 처리할 시 그 성과를 결정하는 아주 중요한 요소이다. 본 논문에서는, Jet Loop Reactor (JLR)를 이용하여 공기유량과 동력량을 운전조건의 변수로 두고 미생물의 농도에 따른 산소소비율(Oxygen uptake rate, OUR)과 물질전달계수(Volumetric mass transfer coefficient, K

Aerobic Wastewater Treatment Processes History and Development

Aerobic Wastewater Treatment Processes: History and Development discusses the widely differing influences on the development of aerobic treatment such as water supply, toxic trade effluents, microscopy and population growth in urban areas. It covers the historical development of sewage treatment and the emergence of aerobic biological treatment from the early nineteenth century to the present day. The importance of water supply is examined and the influence this had on the water-carriage system, and the consequent discharge of sewage into rivers. The factors which govern process selection and process development are discussed. There is a continued impetus to reduce land area, capital costs, running costs, and to optimise performance and process control. The discovery of the activated sludge process is detailed including the development, in the early 1900s, of many forms of this process. Industrial wastes were discharged to biological treatment systems and the impact of such pollutants is reviewed. The work of Royal Commissions, River Boards and the National Rivers Authority is summarised, and the advances in chemical analysis and “on-line” measurement of chemical quality characteristics. Later developments such as reed beds and the use of hybrid treatment systems are covered. Examples are included such as the “fixed film” activated sludge process which has found application for small communities in package form, and also for large-scale municipal treatment plants. Aerobic Wastewater Treatment Processes: History and Development is valuable reading for students of the following courses on CIWEM Dip examination, WITA and B Tech and Environmental Science and Civil Engineering. ISBN: 9781843395423 (Print) ISBN: 9781780400952 (eBook)

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.

Metabolic models to investigate energy limited anaerobic ecosystems

Anaerobic wastewater treatment is shifting from a philosophy of solely pollutants removal to a philosophy of combined resource recovery and waste treatment. Simultaneous wastewater treatment with energy recovery in the form of energy rich products, brings renewed interest to non-methanogenic anaerobic bioprocesses such as the anaerobic production of hydrogen, ethanol, solvents, VFAs, bioplastics and even electricity from microbial fuel cells. The existing kinetic-based modelling approaches, widely used in aerobic and methanogenic wastewater treatment processes, do not seem adequate in investigating such energy limited microbial ecosystems. The great diversity of similar microbial species, which share many of the fermentative reaction pathways, makes quantify microbial groups very difficult and causes identifiability problems. A modelling approach based on the consideration of metabolic reaction networks instead of on separated microbial groups is suggested as an alternative to describe anaerobic microbial ecosystems and in particular for the prediction of product formation as a function of environmental conditions imposed. The limited number of existing relevant fermentative pathways in conjunction with the fact that anaerobic reactions proceed very close to thermodynamic equilibrium reduces the complexity of such approach and the degrees of freedom in terms of product formation fluxes. In addition, energy limitation in these anaerobic microbial ecosystems makes plausible that selective forces associated with energy further define the system activity by favouring those conversions/microorganisms which provide the most energy for growth under the conditions imposed.

Comparative performance evaluation of full-scale anaerobic and aerobic wastewater treatment processes in Brazil

This article evaluates and compares the actual behavior of 166 full-scale anaerobic and aerobic wastewater treatment plants in operation in Brazil, providing information on the performance of the processes in terms of the quality of the generated effluent and the removal efficiency achieved. The observed results of effluent concentrations and removal efficiencies of the constituents BOD, COD, TSS (total suspended solids), TN (total nitrogen), TP (total phosphorus) and FC (faecal or thermotolerant coliforms) have been compared with the typical expected performance reported in the literature. The treatment technologies selected for study were: (a) predominantly anaerobic: (i) septic tank + anaerobic filter (ST + AF), (ii) UASB reactor without post-treatment (UASB) and (iii) UASB reactor followed by several post-treatment processes (UASB + POST); (b) predominantly aerobic: (iv) facultative pond (FP), (v) anaerobic pond followed by facultative pond (AP + FP) and (vi) activated sludge (AS). The results, confirmed by statistical tests, showed that, in general, the best performance was achieved by AS, but closely followed by UASB reactor, when operating with any kind of post-treatment. The effluent quality of the anaerobic processes ST + AF and UASB reactor without post-treatment was very similar to the one presented by facultative pond, a simpler aerobic process, regarding organic matter.

Fault diagnosticability for an aerobic batch wastewater treatment process

This work is concerned with the evaluation of detectability and isolability for analytical- and signal-based fault detection and isolation (FDI). Based on a case study, an aerobic sequencing batch reactor (SBR) for wastewater treatment (WWT), and its known analytical process model, it is first shown that analytical FDI approaches are not feasible through application of structural analysis. An FDI approach based on the respiration signal is then demonstrated to be viable, using information from a novel application of sensitivity theory. These findings are validated with an FDI procedure that uses extracted signal characteristics and classification to successfully diagnose deviations of some model parameters.

Microstructure of copolymers of polyhydroxyalkanoates produced by glycogen accumulating organisms with acetate as the sole carbon source

The so-called glycogen accumulating organisms (GAOs), found in mixed culture anaerobic–aerobic wastewater treatment processes, are used to produce polyhydroxyalkanoates (PHAs) copolymers from a single, simple carbon source—acetate. These polymers consist of 3-hydroxybutyrate (HB), 3-hydroxyvalerate (HV), 3-hydroxy-2-methylvalerate (HmV) and 3-hydroxy-2-methylbutyrate (HmB) with a non-HB fraction of up to 37%. A detailed characterisation using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy demonstrates that these products are true copolymers if produced under anaerobic conditions. The HmV and HmB monomers are identified and their incorporation in the polymer verified via two-dimensional (2D) NMR spectroscopy. The monomer sequence distribution analysis using a known polymer characterisation model suggests that these polyesters are mixtures of random copolymers and thus likely possess desirable properties for practical use. This assessment is supported by the polymers’ physical characteristics. It was further revealed from the study that the inclusion of aerobic periods into the process could improve the overall polymer yields but resulted in production of HB monomers only, likely in the form of separate homopolymer blocks. The study for the first time investigated the microstructure of GAO-produced biopolymers and shows that GAOs have a potential for producing high-quality polymers from a simple carbon source.

Diagnosis of abnormal conditions of an aerobic SBR process

Process fault diagnosis (PFD) allows a control system to maintain the operation of a process under the presence of faults. This is a critical feature for a discontinuous activated sludge waste water treatment (WWT) process in a sequencing batch reactor (SBR), treating waste water contaminated with organic toxic compounds. Here, a methodology for diagnosis based on the extraction of characteristics from the respiration signal, a known indicator for biological activity in aerobic WWT processes, and their classification is proposed. The usefulness of the signal for the detection and classification of a set of defined abnormal conditions was verified through sensitivity analysis. The analysis not only shows the effects of parameter deviations but also indicates the characteristics to be extracted from the respiration signal for a successful classification. Results obtained by simulation indicate that the signal based PFD can successfully cope with uncertainties common in this type of bioprocesses, which prevent the straightforward application of analytical PFD approaches.

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.

ONLINE MONITORING OF AN AEROBIC SBR PROCESS BASED ON DISSOLVED OXYGEN MEASUREMENT

This paper presents results that enable monitoring of an aerobic sequencing batch wastewater treatment (WWT) process based on online dissolved oxygen (DO) concentration measurement. It introduces the sequential process and the DO dynamics, presents a formal discrete event system (DES) model for the traditional SBR process and a modification that enables online monitoring of the respiration rate during the reaction phase and of the oxygen transfer parameter KLa over process cycles. Finally a test method for verifying the presence of substrate in the reactor is introduced. Parts of the results have been validated with experimental data from the EOLI project.

Water reuse for irrigation from waste water treatment plants with seasonal varied operation modes

Irrigation periods are usually limited to vegetation periods. The quality requirements for treated wastewater for disposal and for reuse are different. The reuse of water for irrigation allows partly the reuse of the wastewater's nutrients (N and P). Outside the irrigation period the water must be treated for disposal, thus nutrient removal is often required in order to avoid detrimental effects on the receiving surface water body. Only wastewater treatment plants with different operation modes for different seasons can realise these requirements. The nitrification is the most sensitive biological process in the aerobic wastewater treatment process. At low water temperatures the nitrifying bacteria need several weeks to re-start full nitrification after periods without NH4-removal. Therefore it is necessary to develop options for waste water treatment plants which allow a fast re-start of the nitrification process. Based on theoretical considerations and computer simulations of the activated sludge treatment process, one possibility for implementing a wastewater treatment plant with different seasonal operation modes is evaluated.

Automation of an anaerobic~aerobic wastewater treatment process

In this paper, the treatment capacity and effluent quality of an anaerobic-aerobic sewage treatment system composed of a upflow anaerobic sludge blanket unit in series with a sequencing batch reactor (SBR) is evaluated. The aerobic part of the system (the SBR) is automated and the concentration of dissolved oxygen is used as a control parameter for the aeration period.

Fate of methanol in an anaerobic digester

This paper mill was concerned with the anaerobic biodegradability of methanol, its by-products and the potential for gas stripping the system. A series of laboratory-scale experiments were conducted to evaluate the fate of methanol during anaerobic treatment. According to our research result, more than 99% of methanol contained in the condensate was biodegraded during anaerobic digestion. From an anaerobic digester batch test, the second order bio- degradation rate constant, k b2, was estimated to range from 3.97◊10 -3 m 3 /g·day (when only condensate was fed) to 4.06◊10 -2 m 3 /g·day (when condensate was fed at a proposed rate). The by-products from methanol degradation such as acetaldehyde, and methyl ethyl ketone, were degraded completely in 32 hours. Since the anaerobic treatment process has a retention time of 5 days, condensate by-products are believed to be completely biodegraded. The introduction of condensate into the existing anaerobic pretreatment process appears to improve the treatment efficiency, leading to a more stable anaerobic treatment as well as a reduced sludge generation in the aerobic wastewater treatment process due to the reduced organic loading.

Thermophilic Aerobic Wastewater Treatment in Continuous-Flow Bioreactors

Thermophilic aerobic biological wastewater treatment was investigated at 55°C in continuous-flow bioreactors using a synthetic wastewater containing gelatin and α-lactose as principal organic constituents. By operating multiple continuous-flow bioreactors at different hydraulic residence times (HRTs), the maintenance constant (kd) was calculated to be 0.046 day−1, a value approximately 10-fold lower than that previously reported for thermophilic processes but similar to that for mesophilic treatment. Investigation into the bacterial community structure by denaturing gradient gel electrophoresis of polymerase chain reaction-amplified 16S ribosomal RNA genes revealed that the dominant phylotypes in the bioreactors changed as a function of HRT. Cell reactivity, measured as the specific content of protein and RNA, declined as HRT increased. Catabolic enzyme activities specific to the principal organics in the synthetic wastewater, however, increased at higher HRTs. In conclusion, the performance of thermophilic aerobic biological wastewater treatment processes was similar to that of conventional mesophilic processes with respect to maintenance requirements (i.e., cell yields) as well as bacterial community shifts, cell reactivity, and cell activity.

Microbiology and chemistry for environmental scientists and engineers

Introduction to Microbiology. Bacteria. The Eucaryotic Protists. Viruses and Metazoa. Laboratory Techniques introduction to Chemistry. Organic Chemistry. Biological Molecules. Microbial Metabolism. Microbial Growth. Water Quality Chemistry. Environmental Water Chemisty. Water Pollution. Aerobic Wastewater Treatment Processes. Anaerobic Wastewater Treatment. Composting. Industrial Wastewater Treatment. Environmental Microbiology. Pathogens. Water Treatment.

Factors Affecting Oxygen Transfer in Lab-Scale Activated Sludge Reactors Treating Bleached Kraft Mill Effluent

Abstract In aerobic biological wastewater treatment processes, oxygen must be transferred from the gas phase to the liquid phase to support oxidation of dissolved organics and endogenous metabolism by the bacteria. Power required to supply this oxygen in suspended growth systems can represent a significant fraction of the operating costs of such processes. In this study, the interfacial mass transfer coefficient KLa for water was found to be reduced by up to 28% (average 13%) by the addition of antifoaming agent. KLa values were reduced by up to 43% (average 26%) by the dissolved organics in primary treated bleached kraft mill effluent. There was no significant difference between the KLa for water and biologically treated bleached kraft mill effluent.

Application of multi-wavelength fluorometry for monitoring wastewater treatment process dynamics

Much of the methodology employed for characterizing wastewater and in modeling wastewater treatment processes employs off-line analysis. Off-line analysis is time consuming and not ideally suited to developing process control strategies. Clearly a rapid, inexpensive and reliable method suitable for following organic consumption and biomass production on-line would be very useful. In this study multiple excitation—multiple emission fluorometry was examined as a method for monitoring wastewater treatment processes. Results were first obtained for defined protein solutions and activated sludge to identify characteristic excitation and emission wavelength pairs. These results were then used to develop a rapid off-line assay for measurement of synthetic feeds consisting of protein substrates for batch aerobic and anoxic wastewater treatment processes and for on-line monitoring of cellular metabolic states in an anoxic process. Step-wise multiple regression and principal component analysis were employed for data analysis. The former was used to determine the most informative excitation and emission wavelength pairs while the latter was applied to reduce fluorescent spectra dimensions. Analysis of the batch kinetics suggests that this approach is valid and revealed some dynamic features of protein utilization and biomass accumulation under aerobic and anoxic conditions. A correlation was developed between COD-removal rates and the fluorescence signals in the two processes using fluorescent emission spectra rather than single signals. The data suggests that this multiple excitation—multiple emission fluorometry may be a suitable method for following wastewater and activated sludge dynamics and could be used as the basis for the development of expert system based biosensors.

An investigation of the model of aerobic waste water treatment processes

The aim of the paper is to derive and investigate the sensitivity model of the aerobic batch waste water treatment processes, described by Monod equations, in order to correct the a-priory information about the model parameters to match the current experimental data. The sensitivity analysis enables to determine the effective parameters and their initial values in an estimation procedure by considering their influence on the substrate and microorganisms concentration. This contributes to the solution of some problems concerning the uniqueness and convergence of the parameter estimation.

Microstructure of Copoly(3-hydroxyalkanoates) Produced in the Anaerobic-Aerobic Activated Sludge Process

The sequence structures of bacterially synthesized copoly(3-hydroxyalkanoates), isolated from the sludge developed in the anaerobic–aerobic waste-water treatment process containing propionate as a carbon source, were analysed by 13C NMR spectroscopy. These copolyesters were composed of four different monomer units, 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxy-2-methylbutyrate and 3-hydroxy-2-methylvalerate. By using water/acetone mixed solvent, one of the copolyester samples was fractionated into fractions by differences in average molecular weights as well as in monomer compositions. The carbonyl carbon resonances, split due to differences in diad sequences, were analysed on the basis of Bernoullian statistics. It is suggested that these copolyesters were mixtures of random copolymers with different monomer compositions.