Computer Program Development for the Design of Integrated Fixed Film Activated Sludge Wastewater Treatment Processes

The Integrated Fixed Film Activated Sludge (IFAS) wastewater treatment systems are activated sludge biological nutrient removal processes that have been enhanced by the addition of biofilm support media into the aerobic zone of the system to obtain year round nitrification in activated sludge systems that otherwise could not support it. The objective of this study was to develop a computer package called “IFAS” that allows steady-state simulation of IFAS wastewater treatment processes based on the International Association Water Quality general model for activated sludge and empirical equations for chemical oxygen demand (COD) uptake and nitrification on integrated fixed film developed at Virginia Tech. The current version of the IFAS program supports only sponge-type media; however, the model could be modified for other media if the appropriate equations and required parameters values are known. Data obtained from IFAS sponge media pilot scale plants treating a weak municipal wastewater supplemented by sodium acetate, urea, sodium bicarbonate, and potassium phosphates and operated at different aerobic mean cells residence times were used to evaluate the model with parameter values for nitrification and COD uptake rates developed in batch studies. The model-generated ammonia and soluble COD profiles were insignificantly different statistically from the experimental data. The IFAS model satisfactorily predicts carbonaceous removal and nitrification, and has the potential to be a useful tool for scientists and engineers seeking to design and optimize either IFAS or conventional biological nutrient removal activated sludge systems.     

Activated Sludge Process Modification for Sludge Yield Reduction Using Pulp and Paper Wastewater

Implications of conventional activated sludge (CAS) process modification to a low sludge production (LSP) process have been studied for treating pulp and paper wastewaters. The activated sludge process is modified to a two-stage design to establish a microbial food chain that would result in reduced sludge production. The return activated sludge in the LSP process bypasses the first (dispersed growth) stage to be received only by the second (predatory) stage. The resulting once-through operation of the dispersed growth (DG) stage makes it potentially susceptible to bacterial washout under hydraulic shock conditions. A sensitivity analysis of the DG stage operation was performed by varying its hydraulic residence time. The experimental data revealed that the optimal DG stage hydraulic residence is between 3 and 5?h, with bacterial washout likely to be initiated within 2?h. Based on laboratory results, it appears that a well-designed LSP system is likely to be able to handle day-to-day variations in hydraulic and organic loading rates. The LSP process produced 36% less sludge than the CAS process while consuming approximately 25% more oxygen. The treatment performance of the two systems was comparable except that the LSP sludge had much better settling and dewatering properties.     

Utilization of an Activated Sludge for the Improvement of an Existing Thermophilic Wastewater Treatment System

A pilot-scale activated sludge system was started to determine its effectiveness in treating the thermophilic biological effluent from an existing organic chemical industrial wastewater treatment system. Preliminary results demonstrated that an additional 95% biological oxygen demand and 65% dissolved organic carbon removal was achieved. In addition, significant biodegradation of the volatile organic compounds and organic nitrogen was observed.     

Comparison of Bacterial Bioluminescence with Activated Sludge Oxygen Uptake Rates during Zinc Toxic Shock Loads in a Wastewater Treatment System

The use of a bioengineered bioluminescent bacterium (Shk1) for monitoring zinc toxicity was evaluated with samples from a municipal activated sludge wastewater treatment plant and in a bench-scale activated sludge system. Bioluminescent measurements were compared with oxygen uptake rates of activated sludge samples. In batch experiments with activated sludge, the Zn EC50 for Shk1 bioluminescence was 16 mg/L, while the Zn EC50 for activated sludge OURs was approximately 58 mg/L. In the bench-scale system, the influent Zn concentrations tested were 50 and 200 mg/L in toxic shock loads of about 4 h duration. Soluble Zn transport through the influent, aeration basin, and clarifier was able to be monitored by the decrease in Shk1 bioluminescence. However, bioluminescence in samples from the aeration basin decreased faster than activated sludge specific oxygen uptake rates. Differences in responses of Shk1 and the activated sludge community may be due to differences in the assay conditions, the growth forms, physiology of the organisms, or previous cultivation conditions.     

Statistical Comparison of Bioassays for Assessment of Toxicity of Organic Components of Wastewater to Activated Sludge

In aquatic toxicity testing, no single test species responds appropriately to all toxicants. Therefore test batteries consisting of several individual assays are becoming more common. The species comprising a test battery should be representative of the entire system of interest. Each assay should be complementary to other components in the test battery and the test battery should not include redundant tests. We studied the selection of test battery components for the assessment of the toxicity of organic chemicals to activated sludge. The assays considered were the continuous Shk1, Microtox, Polytox, activated sludge respiration inhibition, Nitrosomonas, and Tetrahymena assays. The correlations between the toxicity data obtained from these assays were analyzed by examining the correlation matrix and by principal component analysis. These statistical methods showed that the Nitrosomonas assay should be included in test batteries plus one of the remaining five assays for assessing toxicity of organic compounds to activated sludge.     

Modeling and Control of Oxygen Transfer in High Purity Oxygen Activated Sludge Process

A dynamic mathematical model for the high purity oxygen activated sludge process, which incorporates structured biomass, gas–liquid interactions and control systems, was developed. The model was calibrated using pilot plant data associated with the development of the West Point Treatment Plant near Seattle, Wash. The calibrated model was used to simulate oxygen transfer rates for various operating conditions. Simulations showed that an optimal control system can reduce aerator power by 33% as compared to a conventional design, and reduce average oxygen feed gas by as much as 18%. Vent gas purity control dramatically reduced the peak aerator horsepower required to maintain set point dissolved oxygen concentration during high loadings. Step feed operation reduced the stag-to-stage variation in aerator horsepower and also reduced the required peak power. Predicted power savings for a 605,000?m3/day plant were $500,000 per year at current power costs.     

Replacing Outliers and Missing Values from Activated Sludge Data Using Kohonen Self-Organizing Map

Modeling the activated sludge wastewater treatment plant plays an important role in improving its performance. However, there are many limitations of the available data for model identification, calibration, and verification, such as the presence of missing values and outliers. Because available data are generally short, these gaps and outliers in data cannot be discarded but must be replaced by more reasonable estimates. The aim of this study is to use the Kohonen self-organizing map (KSOM), unsupervised neural networks, to predict the missing values and replace outliers in time series data for an activated sludge wastewater treatment plant in Edinburgh, U.K. The method is simple, computationally efficient and highly accurate. The results demonstrated that the KSOM is an excellent tool for replacing outliers and missing values from a high-dimensional data set. A comparison of the KSOM with multiple regression analysis and back-propagation artificial neural networks showed that the KSOM is superior in performance to either of the two latter approaches.     

Biological Kinetic Data Evaluation of an Activated Sludge System Coupled with an Ultrafiltration Membrane

A membrane bioreactor (MBR) system treating wastewater containing high molecular weight compounds was operated at solids retention times (SRTs) ranging from 30 to 2 days. Chemical oxygen demand removal efficiencies exceeded 99% and effective nitrification was obtained at SRTs between 30 and 5 days. A significant shift in the biological population structure was observed at the 2 days SRT as the content of gram-negative microorganisms increased and nitrifying bacteria were washed out. At this low SRT, limitations in the biological reaction kinetics resulted in incomplete degradation of the feed protein increasing the presence of soluble organic matter in the effluent. Furthermore, the diluted mixed liquor prevented the formation of a filtration cake on the membrane surface, further deteriorating effluent quality. Biological kinetic data parameters were analyzed using three different representations for biomass: volatile suspended solids, lipid phosphates, and total enzymatic activity. All three indicators exhibited similar trends resulting in very comparable estimates for endogenous decay coefficients, thus demonstrating the reliability of volatile suspended solids as a measure for biological activity in activated sludge. Lower than typical endogenous decay rates in the MBR suggested favorable environmental conditions for respiration and a lower potential for self oxidation and predation. The true yield coefficient was in the range of conventional activated sludge systems, refuting previous suggestions of lower yields in MBRs.     

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 2,397?mg/L at a hydraulic retention time (HRT) of 1.25 day, and 979 to 1,749?mg/L at an HRT of 2.5 day, respectively, when influent COD ranged from 9,736 to 19,862?mg/L. As a result, effluent COD of the biofilm airlift suspension reactor varied between 256 and 355?mg/L at HRTs of from 5.0 to 12.5 h. The antibiotics ampicillin and aureomycin, with influent concentrations of 3.2 and 1.0?mg/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%.     

Evidence and Long-Term Feasibility of Enhanced Biological Phosphorus Removal in Oxidation-Ditch Type of Aerated-Anoxic Activated Sludge Systems

This study investigated the potential of four full-scale oxidation ditches to accomplish enhanced biological phosphorus removal (EBPR). Despite the fact that none of the tested oxidation ditches were designed to perform EBPR, mixed liquors from all four ditches showed good specific phosphorus release and uptake rates, a typical characteristic of a typical EBPR biomass. The specific phosphorus release rates ranged from 0.042- to 0.254-mg P/mg VSS-d and the specific phosphorus uptake rates ranged from 0.023- to 0.125-mg P/mg VSS-d for the tested full-scale plants. The EBPR potential of one of the full-scale plants (Central Davis Sewer District) was further studied by changing the aeration patterns in the ditch. The mixed liquor in this full-scale plant exhibited good phosphorus release and uptake trends and dissolved phosphorus, as low as 1.26 mg/L, could be accomplished in the final effluent of this plant as a result of this optimization. The long-term feasibility of the EBPR in this full-scale was tested by running a bench-scale EBPR reactor, in which the anaerobic phase was replaced with aerated-anaerobic phase to simulate the mixed liquor environment that exists in Central Davis mixed liquor and, in general, in all oxidation-ditch-type activated sludge configurations. The bench-scale reactor showed consistent EBPR activity in the absence of an anaerobic environment and more than 85% phosphorus removal could be maintained in the reactor for more than 400 days. The intrafloc microanaerobic/anoxic zones, which may be present in the mixed liquor, did not seem to add to the EBPR efficiency under aerated-anaerobic conditions. Cloning and sequencing using Rhodocyclus specific forward primer RHC439 showed the abundance of organisms most closely falling in Rhodocyclaceae family but not related to Candidatus Accumulibacter phosphatis. Simultaneous 4′-6–Diamidino-2–phenylindole (DAPI) staining and fluorescent in situ hybridization (FISH) using RHC439 probe clearly demonstrated the participation of polyphosphate accumulating organism (PAOs) targeted by RHC439 (i.e., in Rhodocyclaceae family). Microautoradiography assisted FISH using RHC439 further confirmed the participation of PAOs in Rhodocyclaceae family.     

Integration of Processes to Treat Wastewater and Source-Separated Urine

Human urine contributes 80% of the total nitrogen and 40–50% of the total phosphate load to municipal wastewater. This study examines the impact of separate urine collection and treatment on wastewater treatment. An integrated wastewater and urine treatment process was defined, in which single high-rate ammonium removal over nitrite and anaerobic ammonium oxidation processes and struvite recovery are at the heart of the nutrient management. The model study demonstrated that if 50% or more of urine were collected and treated separately, integrated wastewater treatment with more compact and energy-efficient processes would be possible. The integrated wastewater and urine treatment is compared to an existing state-of-the-art treatment process. The main advantage of urine separation is not only a better effluent quality. Existing processes including tertiary treatment can already produce very good effluent quality with total effluent nitrogen and phosphate concentrations of 2.5 and 0.5?g/m3, respectively. The main advantage of urine separation is the production of this same good effluent quality with a remarkable saving in resources. With sufficient urine separation, generation of net primary energy is possible.     

Contribution of the Estrogen-Degrading Bacterium Novosphingobium sp. Strain JEM-1 to Estrogen Removal in Wastewater Treatment

This study aimed to investigate the contribution to estrogen removal from the activated sludge of an estrogen-degrading bacterium, Novosphingobium sp. Strain JEM-1, isolated by the writers from the activated sludge. The cell numbers of the Strain JEM-1 were investigated in two full-scale wastewater-treatment plants using real-time PCR. Strain JEM-1 appears to be commonly distributed in the activated sludge. The cell numbers of Strain JEM-1 in the oxidation ditch process were higher than those in the conventional activated sludge (CAS) process, and the effluent concentrations of E1 in the CAS process tended to decrease with increased cell numbers of Strain JEM-1. In a bench-scale experiment to investigate bioaugmentation with Strain JEM-1, there was a significant difference in the effluent concentrations of estrogens between the experimental series and the control series. Linear relationships were observed between cell numbers of Strain JEM-1 and the efficiency of removal of estrogens. These results suggest that Strain JEM-1 contributes to the estrogen removal in the activated sludge.     

Influence of COD/N Ratios on Simultaneous Removal of C and N Compounds in Biological Wastewater Treatment in Sequencing Fed-Batch Reactor and Kinetic Analysis

The impact of chemical oxygen demand/nitrogen (COD/N) values of feed wastewater on COD and nitrogen removal and biomass growth in a sequencing fed-batch reactor (SFBR) operation was investigated. The multiple microbial reactions involved in the simultaneous removal process of carbonaceous and nitrogenous components in the SFBR system were analyzed using a set of kinetics mathematical model. The results indicate that COD/N ratios strongly influence COD and total nitrogen removal efficiency. The COD removal efficiency per gram microorganism changed from 64.3 to 78.1% at COD/N = 11.9–2.5. The total nitrogen removal efficiency changed from 10.3 to 34.2% at COD/N = 2.5–11.9. However, variable COD/N ratios of feed wastewater are not marked for biomass growth rate.     

Kinetics of Phosphorus Release and Uptake in a Membrane-Assisted Biological Phosphorus Removal Process

A long-term comparative study on the kinetics of enhanced biological phosphorus removal (EBPR) was carried out in pilot scale membrane-assisted and conventional biological phosphorus removal processes, by monitoring system performance, phosphorus mass balances, and maximum specific rates in off-line batch tests. The two systems exhibited similar performance in the removal of soluble phosphorus (P) from the influent wastewater, in the specific P release observed in the anaerobic zone, and in the maximum specific P release and volatile fatty acid (VFA) uptake rates. However, when the VFA in the influent was limiting, the conventional EBPR (CEBPR) process performed significantly better than the membrane (MEBPR) counterpart, and this behavior was also reflected in the kinetics of P release. Denitrifying dephosphatation was observed to be significant in both processes during periods of satisfactory P removal. When the aerobic recycle ratio was reduced to a minimum level, the anoxic P uptake activity in the CEBPR sludge was lower than that of the MEBPR sludge. Finally, the biomass decay rates of the two sludge types were estimated to be comparable, with significant reduction of the decay under unaerated conditions.     

Evaluation of Mixing and Performance of Lab-Scale Upflow Anaerobic Sludge Blanket Reactors Treating Domestic Wastewater

The effects of varying hydraulic retention time (HRT) and associated upflow velocity on mixing and reactor performance were evaluated in five lab-scale upflow anaerobic sludge blanket (UASB) reactors treating real domestic wastewater. The mixing and transport studies were carried out with the help of tracer experiments at various HRTs using a pulse tracer input. A number of existing models were assessed for the analysis of the time series of observed tracer concentrations. The plug-flow reactor (PFR) model with two-zone dispersion better simulated the time series of tracer concentrations at all HRTs than other models, such as single compartment dispersion, completely mixed flow reactors (CMFRs) in series, and a combination of CMFR and PFR. The dispersion coefficients obtained from the two-zone dispersion model correlated well with the dispersion analysis expression for flow in a circular cylinder, and the correlation can be used for the prediction of dispersion in a UASB reactor. The analysis of reactor performance data indicated that reduction of dispersion owing to decrease in the upflow velocity resulted in increased sulfidogenic activity in the reactor. This was attributed to the inability of the sulfate reducers to colonize in the reactor at high upflow velocity and mixing condition.     

Treatment of Chlorophenols by UV-Based Processes: Correlation of Oxidation By-Products, Wastewater Parameters, and Toxicity

The aim of the study was to evaluate the toxicity and biodegradability of para-chlorophenol (p-CP) model wastewater when treated by UV and UV/H2O2 processes. We investigated the correlations between the toxicity and the concentration of p-CP and its oxidation by-products, as well as other parameters—summarizing characteristics which potentially indicate hazardous water components, e.g., AOX (adsorbable organic halides), TOC (total organic carbon), and COD and BOD5 (chemical and biochemical oxygen demand). Biodegradability is estimated by the BOD5/COD ratio. The toxic effects were investigated on luminescent bacteria Vibrio fischeri, determining the EC50 value. The correlation between each data pair was estimated using a statistical approach calculating the Spearman rank coefficients. The biodegradability of the p-CP model wastewater was improved by the UV/H2O2 process; the BOD5/COD ratio increased from 0.37 to 0.73 after a 1-h treatment (F = 1243??mJ?cm-2). According to the calculated Spearman rank coefficient, the highest correlation with toxicity data among all monitored parameters was obtained for hydroquinone and benzoquinone, as by-products of p-CP degradation, as well as for the BOD5/COD ratio.