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.     

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.     

Dynamic Growth Rates of Microbial Populations in Activated Sludge Systems

Results of mathematical modeling and whole cell 16S ribosomal RNA-targeted fluorescence in situ hybridizations challenge the widely held perception that microbial populations in “steady-state” activated sludge systems share a common net growth rate that is proportional to the inverse of the mean cell residence time. Our results are significant because they encourage bioprocess engineers to appreciate the differences in growth physiology among individual microbial populations in complex mixed microbial communities such as suspended growth activated sludge bioreactor systems.     

Simulating Activated Sludge System by Simple-to-Advanced Models

Models ranging through simple, intermediate, and International Water Association complex activated sludge models (ASMs) were evaluated to compare their ability to describe biomass growth and substrate removal in an activated sludge system. A membrane-activated sludge bench-scale system was used to treat a complex synthetic wastewater over a wide range of operating conditions, ranging from 1 to 15 days solids retention time and 4 to 12 h hydraulic retention time. Total suspended solids, volatile suspended solids (VSSs), and total and soluble chemical oxygen demands (CODs) were monitored in the influent, the reactor, and the effluent. A variety of substrate removal formulations were used with the simple and intermediate models. Although all models provide excellent prediction of biomass growth, the intermediate model was best. Prediction of substrate removal was good with models that incorporated a nonbiodegradable component in the influent. ASM3 was the best model for predicting effluent soluble COD, but overall, the intermediate model was judged best for prediction of mixed liquor VSS and effluent soluble COD.     

Nitrification in Pure Oxygen Activated Sludge Systems

Mixed liquor pH and temperature are two parameters that affect the growth rate of nitrifying bacteria and therefore the minimum solids retention time required to achieve nitrification. The objective of this study was to determine the consequence of low mixed liquor pH, and to determine if pH depression could be alleviated by recovering alkalinity through denitrification in a pure oxygen activated sludge system. The study was conducted at the University of Manitoba using laboratory scale, pure oxygen activated sludge reactors, fed with primary effluent. The results indicated that when denitrification was not included in the process, the concentration of CO2 in the headspace of the pure oxygen reactors increased to as high as 15% due to carbon oxidation and endogenous respiration. The high CO2 concentration in the headspace combined with low alkalinity caused by nitrification resulted in bulk mixed liquor pHs below 5.5. In order to maintain complete nitrification at a temperature of 24°C and a mixed liquor pH of 5.5, a solids retention time (SRT) of 12 days was required. In comparison, when denitrification was included in the process the pH of the mixed liquor was increased to 6.4 allowing for full nitrification at an SRT of 5.6 days at a temperature of 24°C. The increase in pH in the denitrification trains was attributed to three factors: recovery of alkalinity through the denitrification process, the conversion of influent carbon to CO2 in the anoxic reactor allowing the CO2 to escape to the atmosphere, and the recycle of mixed liquor super saturated with CO2 from the pure oxygen reactor to the anoxic reactor allowing the CO2 to escape to the open atmosphere. It was determined that the nitrifier growth rate at 12°C was approximately 50% of the rate measured at 24°C. At mixed liquor pHs between 6.0 and 6.3 at a temperature of 12°C, the specific nitrifier growth rate was between 0.12 and 0.15?d?1, while at 24°C, the specific nitrifier growth rate was between 0.25 and 0.30?d?1 at pHs ranging from 5.0 to 6.1     

Modeling a Combined Anaerobic/Anoxic Oxide and Rotating Biological Contactors Process under Dissolved Oxygen Variation by Using an Activated Sludge-Biofilm Hybrid Model

A hybrid model which incorporated a biofilm model into the general dynamic model was developed to predict the effluent quality of a combined activated sludge and biofilm process—Taiwan National Central University Process 1. The system was performed under three different dissolved oxygen (DO) conditions in the oxic tank, including 2.0, 1.0, and 0.5 mg/L. When the DO increased from 0.5 to 2.0 mg/L, the soluble biodegradable substrate (SS) and soluble phosphate (PO4) in the effluent were not significantly influenced. Their removal efficiencies were above 92 and 94%. Ammonia–nitrogen (NH3) removal efficiency increased from 36 to 83% and nitrate–nitrogen (NO3) increased from 1.7 to 2.9 mg/L. In biofilm, when the DO was 2.0 mg/L, the active autotrophic biomass (ZA) fraction was 15.7% (surface) to 12.9% (substratum). But when the DO was 0.5 mg/L, the ZA fraction became lower and the fraction was 6.2% (surface) to 3.5% (substratum). The fraction of active nonpoly-P heterotrophic biomass (ZH) in the biofilm did not vary significantly, the values were about 28–35%. ZI decreased as the DO increased. SS in the biofilm did not vary significantly and was maintained at about 2.0 mg/L. When DO increased, NO3 also increased, NH3 decreased from 13.1 to 1.8 mg/L in biofilm.     

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.     

2,4,6 Tri-Chlorophenol Containing Wastewater Treatment Using a Hybrid-Loop Bioreactor System

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and 30?days, while the feed COD (2600±100?mg?L?1), TCP (370±10?mg?L?1), and the hydraulic residence time (25?h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20?days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCP, COD, and toxicity removals. More than 95% of COD, TCP, and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120?mg?TCP?gX?1?day?1) at a sludge age of 20?days. TCP inhibition was eliminated by operation of the system at sludge age above 20?days to obtain nearly complete COD, TCP, and toxicity removal.     

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.     

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.     

Modeling VOC Emissions in the High-Purity Oxygen Activated Sludge Process

Mass balances for volatile organic compounds (VOCs) were added to a structured mathematical model of the high-purity oxygen activated sludge (HPO-AS) process. The model was sized to correspond to two large existing HPO-AS treatment plants. The stripping of ten different VOCs was modeled and compared to stripping from conventional air activated sludge process. The results show that the covered aeration tanks can reduce stripping by more than 90%, depending on the specific VOC. If biodegradation is considered, the HPO-AS process degrades more than the conventional process due to the higher liquid-phase concentrations that result because of reduced stripping. The increase in biodegradation depends on the VOCs degradability but should increase to nearly 100% for highly volatile but biodegradable VOCs.     

Activated Carbon Addition to an Activated Sludge Model Reactor for Color Removal from a Cotton Textile Processing Wastewater

Color removal from cotton textile processing wastewater by addition of powdered activated carbon (PAC) into a lab-scale activated sludge system was examined. The activated sludge system was continuously operated in different sludge ages (SRTs) and hydraulic retention times (HRTs). SRT = 30?d and HRT = 1.6?d operation resulted in up to 36% color removal and 94% COD removal. PAC was added 100, 200, and 400 mg/L into the activated sludge system under these operating conditions. The results indicated that 100 mg/L PAC was sufficient to remove the maximum color measured (up to 50 m?1) from the wastewater. The addition of PAC did not affect chemical oxygen demand (COD) removal significantly. Oxygen uptake rate (OUR) tests were also performed to investigate the microbial activities controlling the system performance. The average OUR was 74.1 mg/L/h without PAC addition while it was 70 mg/L/h with PAC addition. Adsorbable organic halogens of the effluent wastewater decreased from 400 to 50 μg/L with the addition of PAC. Toxicity dilution factor decreased from 2 to 1.5 with the PAC addition into the activated sludge system.     

Robust Optimal Design of Activated Sludge Bioreactors

This paper proposes an algorithm for a robust optimal design of the biological reactor and secondary settling facilities in suspended growth nitrogen and phosphorus removal systems. Robust optimization includes uncertainty in the decision-making procedure and seeks a solution that remains “close” to optimal for all potential operation scenarios. It thus differs fundamentally from the deterministic and stochastic approaches, where uncertainty is ignored or a solution based on either the most likely scenario or the average performance over all potential scenarios is produced. The robust optimization of a suspended growth system is a multiobjective optimization problem concerned with minimization of the global costs and variability of the system’s performance around the optimal. The proposed robust optimization approach uses the ASM3 model, making use of its performance prediction capabilities to produce a powerful tool for designing activated sludge systems. The algorithm was applied to the design of the biological reactor and secondary settling facilities for the Vila Real municipal wastewater treatment plant (Portugal).     

Evaluation of Integrated Fixed Film Activated Sludge Wastewater Treatment Processes at High Mean Cells Residence Time and Low Temperatures

Suspended solids mean cells residence time (MCRT) and temperature are two key parameters for designing Integrated Fixed Film Activated Sludge (IFAS) wastewater treatment processes, as an alternative for achieving year-round nitrification. It has been demonstrated from both full-scale and bench-scale studies that IFAS can accomplish year-round nitrogen removal and denitrification in aerobic zones in winter when operated with suspended growth MCRTs less than the critical MCRT for nitrifiers, thus avoiding increasing reactor or clarifier volumes. The objective of this study was to investigate the performances of IFAS systems that were operated at relative high MCRT compared to nitrifier washout MCRT and low temperature for biological nutrient removal. The comparison between two IFAS systems with Accuweb media in both the anoxic and aerobic zones, and a conventional three zone biological nutrient nemoval (BNR) system was conducted at 10°C with a 10 day MCRT using the UCT/VIP configuration for both systems and feeding with Blacksburg domestic wastewater. Influent flow was split 50% to the first anaerobic reactor and 50% to the first anoxic reactor to enhance denitrification in one of IFAS systems and the conventional BNR control system whereas 100% of the influent flow was fed to the first anaerobic reactor in the other IFAS system. The data from this investigation indicated that the performances of the control and IFAS systems were insignificantly different under the experimental operating conditions for both biological nitrogen and biological phosphorus removal except for IFAS with integrated fixed film media in the anoxic zone and when 50% of the influent was added directly to the first anoxic reactor.     

Thermal Treatment of Waste Activated Sludge Using Liquid Boiling

In this work we investigated the use of a short time, low superheat boiling process to treat biological sludge. The treated sludge would exhibit a deteriorated filterability, and a marked increase in soluble organics content. A large portion of extracellular polymers was released from the solid phase by boiling. The microbial density levels of the total coliform bacteria and the heterotrophic bacteria were reduced after treatment. Dilution in sludge concentration could allow more organic compounds to be hydrolyzed and a greater fraction of microbes to be disinfected when compared with the undiluted samples.     

Effect of Ozone on Filamentous Bulking in a Laboratory Scale Activated Sludge Reactor Using Respirometry and INT-Dehydrogenase Activity

Filamentous bulking can be controlled by the addition of oxidant chemical agents such as ozone. To evaluate the ozone effect on activated sludge from a laboratory scale reactor, different techniques were applied: Settleability test, respirometry (oxygen uptake rate), and the INT-dehydrogenase activity test carried out both by spectrophotometry (DHAa) and image analysis (DHAi). In activated sludge, the respirometric technique and the spectrophotometric DHAa quantified ozone action on the total respiratory activity of flocs; in contrast, the image DHAi test was applied to evaluate the specific action of ozone on filamentous microorganisms. The conditions for application of the INT-dehydrogenase activity test were standardized using pure cultures of a filamentous microorganism (Sphaerotilus natans) and a floc-forming bacterium (Acinetobacter anitratus). For activated sludge with filamentous bulking, ozone doses and treatment times necessary to improve settleability were established. Ozone dose levels and contact times influence the viability of bacteria in flocs and filaments and the finding of appropriate parameters to preserve floc viability and, at the same time, inhibiting filaments is essential to filament control by ozonation.     

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.     

Radiation-Assisted Process Enhancement in Wastewater Treatment

Laboratory and pilot tests were conducted to investigate the use of ionizing radiation at an activated sludge wastewater treatment facility with residuals processing. Operational enhancements were investigated with respect to bulking control, thickening enhancement, and anaerobic stabilization processes. Radiation caused permanent effects in measured sludge parameters including solids content, chemical oxygen demand, ammonia-nitrogen, zeta potential, specific surface area, resistance to filtration, sludge volume index, pH, organic acid production, and digester gas evolution. Analysis of beneficial effects from preliminary studies and pilot tests demonstrated that a dose of 2–3 kGy would be potentially successful for bulking control and to a lesser degree, enhanced thickening and radiation-assisted anaerobic digestion. A cost analysis based on preliminary tests determined that a centralized electron beam irradiator could be applied economically in an integrated approach at an estimated annual savings of $0.2–2.7 million depending upon the application. Considering that the annual cost of operating an accelerator unit was estimated at $2.4 million ($2.16/m3), this might translate into an important savings for a large-scale wastewater treatment facility.     

SSPRSD Using a Filamentous Fungal Strain Penicillium expansum BS30 Isolated from Wastewater Sludge

A filamentous fungal strain (Penicillium expansum BS30) isolated from a municipal wastewater treatment plant was used in this study to simultaneously reduce sludge solids, pathogens, and improve the sludge settling and dewaterability [simultaneous solids and pathogens reduction, settling and dewatering (SSPRSD)] in shake flask and 10-L bioreactor experiments. The fungal strain role in the SSPRSD process was evaluated at different temperatures and inoculum (spores) concentrations. The best performance of the process was achieved at incubation temperature of 25°C and inoculum concentration of 106?spores/mL. At these optimal conditions, suspended solids (SS) and volatile SS were degraded >50 and >53%, respectively. The capillary suction time value recorded (<13?s) was lower than that required for sludge dewaterability (<20?s). The populations of total coliforms and Salmonella (pathogen indicators) were reduced by two and four log cycles, respectively. A study on molecular screening of penicillin biosynthesis gene cluster and toxic organic compounds degrading machinery of the fungal strain was also conducted. It was found that the fungal strain possessed the penicillin-producing gene and toxic organic compounds degrading genes, and therefore may be helpful in degrading these compounds.     

Using the Kinetics of Biological Flocculation and the Limiting Flux Theory for the Preliminary Design of Activated Sludge Systems. I: Model Development

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume hydrolysis is the rate-limiting step, but none consider the role that the kinetics of biological flocculation and the sludge settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetic of biological flocculation, and have analyzed its role on the removal of particulate COD in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. This paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge settling properties with the aeration tank behavior, and is a reasonable first approximation that can be used for activated sludge system design and operation.