Microbial Adaptability to Organic Loading Changes in an Enhanced Biological Phosphorus Removal Process

The enhanced biological phosphorus removal (EBPR) performances of phosphate-accumulating organisms (PAOs) under organic loading fluctuations were investigated using a sequencing batch reactor (SBR) with anaerobic/oxic stages. The adaptability of PAOs was evaluated after establishing a normal steady-state condition [chemical oxygen demand (CODin)=150 mg/L]. During SBR operation, the initial COD was changed gradually or abruptly. When the initial COD increased gradually from the steady state to 300 mg/L, the biomass increased steadily and the system showed stable EBPR. However, when the initial COD oscillated from 150 to 300 or 50 mg/L abruptly, PAOs could not adapt themselves to these sudden changes, resulting in unstable EBPR. When the organic loading returned to a normal condition, the system was recovered to stable EBPR in 2 days after the high organic loading fluctuation, while it was not after the low organic loading fluctuation. Using fluorescent in situ hybridization technique, Rhodocyclus-related PAO population changes were monitored. It was demonstrated that PAOs would wash out faster under the low organic loading fluctuation than the high organic loading fluctuation.     

Comparison of Oxygen Transfer Parameters Determined from the Steady State Oxygen Uptake Rate and the Non-Steady-State Changing Power Level Methods

In this study, a laboratory scale Univ. of Cape Town enhanced biological phosphorus removal process was operated under controlled conditions at a solids retention time of 15 days. Results are presented for the process performance and oxygen transfer parameters determined by applying the steady state oxygen uptake rate (OUR) and the changing power level (CPL) techniques, as per ASCE standard guidelines. The testing periods were temporally separated to eliminate interference of the tests. During the application of the CPL method, the sludge volume index gradually increased and higher values of the oxygen transfer rate and alpha were measured, in comparison to the data from the steady state OUR method, under similar process performance. Furthermore, the mass transfer rate decreased as the CPL method of testing continued. In contrast, the oxygen transfer parameters remained uniform during the time when the OUR method was applied. The data indicated that the CPL method resulted in higher and variable oxygen transfer parameters, even though the process performance remained unchanged. Therefore, a more rigorous evaluation of the CPL method is recommended to clarify the validity of the test.     

Enhanced Biological Phosphorus Removal Performance and Microbial Population Changes at High Organic Loading Rates

A laboratory-scale sequencing batch reactor was operated and the dynamics of Rhodocyclus-related phosphorus-accumulating organisms (PAOs) population was monitored. After the system reached a steady state and showed a stable enhanced biological phosphorus removal status, the organic loading rate was increased from 160 to 1,020?g?COD?m?3?cycle?1 in five steps. When the P storage capacity reached maximum at 330?g?COD?m?3?cycle?1, the system lost the stability and the effluent phosphorus concentration fluctuated. As the organic loading rate increased from 160 to 1,020?g?COD?m?3?cycle?1, the PAO population decreased from 83.8±4.9 to 32.2±16.2% and internal polyphosphate content decreased from 0.20 to 0.03?mg?P?mg?VSS?1. Phosphate-accumulating metabolism was weakened as the organic loading rate increased and PAO population decreased concomitantly, whereas glycogen-accumulating metabolism increased at high organic loading rates as supported by the increased intracellular glycogen content and production of a higher fraction of intracellular poly-β-hydroxyl valerate.     

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.     

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.     

Simultaneous Nitrogen and Phosphorus Removal in a Continuously Fed and Aerated Membrane Bioreactor

This research demonstrated the feasibility of simultaneous biological nitrogen and phosphorous removal in a single tank membrane bioreactor without cycling of air and/or feed through operation at a low dissolved oxygen (DO) and a high biomass concentration. Chemical oxygen demand removal efficiency was more than 98% and total nitrogen removal efficiency was 55%. Seventy-five percent of the total nitrogen removal was through simultaneous nitrification–denitrification (SND) and 25% through assimilation into the biomass. Interestingly, more than 98% phosphorous was removed and microbiological analysis showed the presence of polyphosphate-accumulating organisms in the activated sludge. The operating mixed-liquor suspended solids was between 16 and 23?g/L. The optimum DO was found to be 0.7–0.8?mg/L.     

Evolutionary Multivariate Dynamic Process Model Induction for a Biological Nutrient Removal Process

This paper proposes an automatic process model induction system using an evolutionary computational intelligence, called grammar-based genetic programming, that is specially designed to automatically discover multivariate dynamic process models that best fit observed process data. This automatic process model induction system combines an evolutionary self-organizing system of genetic programming paradigm with various mathematical functions for a multivariate nonlinear model evolution using a grammar system via the mechanism of genetics and natural selection. The results demonstrate how the automatic process model induction system based on grammar-based genetic programming can be used to develop accurate and relatively cost-effective multivariate dynamic process models for the full-scale biological nutrient removal process. Multivariate dynamic process models are derived automatically in the form of understandable mathematical formulas that enable engineers to extract important knowledge hidden in the data and develop better operation and control strategies.     

Effect of Carbon Source on Biological Nitrogen and Phosphorus Removal in an Anaerobic-Anoxic-Oxic (A2O) Process

The effects of acetate and propionate on biological nitrogen and phosphorus removal in a plug-flow A2O process were evaluated in this study. The wastewater quality indexes and operation parameters were the same when different carbon sources were used. However, we observed no obvious effect of carbon source on nitrogen removal. Denitrifying phosphorus removal was found to play an important role in simultaneous nitrogen and phosphorus removal in anoxic reactors because almost the entire carbon source was used for polyhydroxyalkanoate (PHA) synthesis in anaerobic reactors, and there was no external carbon source left for heterotrophic denitrification. Propionate was found to be a more effective and energy-saving carbon source for biological nitrogen and phosphorus removal. In addition, the variations in the metabolic chemicals, such as phosphorus, PHA, glycogen, and oxygen, were lower when propionate was used than when acetate was used.     

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.     

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:P Ratio on Nitrogen and Phosphorus Removal in Fixed-Bed Filter

This study examined the effects of COD:N:P ratio on nitrogen and phosphorus removal in a single upflow fixed-bed filter provided with anaerobic, anoxic, and aerobic conditions through effluent and sludge recirculation and diffused air aeration. A high-strength wastewater mainly made of peptone, ammonium chloride, monopotassium phosphate, and sodium bicarbonate with varying COD, N, and P concentrations (COD: 2,500–6,000, N: 25–100, and P: 20–50 mg/L) was used as a substrate feed. Sodium acetate provided about 1,500 mg/L of the wastewater COD while the remainder was provided by glucose and peptone. A series of orthogonal tests using three factors, namely, COD, N, and P concentrations, at three different concentration levels were carried out. The experimental results obtained revealed that phosphorus removal efficiency was affected more by its own concentration than that of COD and N concentrations; while nitrogen removal efficiency was unaffected by different phosphorus concentrations. At a COD:N:P ratio of 300:5:1, both nitrogen and phosphorus were effectively removed using the filter, with removal efficiencies at 87 and 76%, respectively, under volumetric loadings of 0.1?kg?N/m3?d and 0.02?kg?P/m3?d.     

Effect of Cd(II) on Different Bacterial Species Present in a Single Sludge Activated Sludge Process for Carbon and Nutrient Removal

Heavy metal cadmium(II) was added stepwise into an A2O pilot plant to investigate the toxic effects of Cd(II) on the removal efficiencies, kinetic parameters (yield coefficients and maximum specific growth rates) and reaction rates of carbon, nitrogen and phosphate for the acclimatized heterotrophic and autotrophic bacteria. Results showed that 2?mg/L Cd(II) initially affected the biological reaction of phosphate removal. At Cd(II) 5?mg/L, the efficiencies of total nitrogen removal and nitrification were substantially dropped. At the same time, the yield coefficient and maximum specific growth rate of heterotrophs were significantly decreased from 0.8?g?COD/g?COD and 6.44?day?1 to 0.54?g?COD/g?COD and 4.67?day?1, respectively. And, the denitrification rate was inhibited by about 61%. The inhibition percentages of anaerobic release, anoxic and aerobic uptake rates of phosphate were about 76, 64, and 90%, respectively. When Cd(II) concentration was continually increased up to 35?mg/L, removal efficiency of chemical oxygen demand (COD) was significantly dropped. However, there was no obvious inhibition on the biological reactions of anaerobic ammonification.     

Removal of a Volatile Organic Compound in a Hybrid Rotating Drum Biofilter

A hybrid bioreactor, combining an activated sludge process (ASP) and a rotating drum biofilter (RDB), was developed and evaluated for the treatment of volatile organic compounds (VOCs) in waste gas streams. The effects of the influent VOC concentration and the organic loading rate on the VOC removal efficiency and on the pattern of biomass accumulation were investigated. Toluene was used as the model VOC, the flow rate of the waste gas stream was 0.59 L/s, and the empty-bed retention time (EBRT) in the ASP portion was 46 s with an actual retention time of about 2 s. The EBRT in the RDB portion was 38 s based on the drum volume. When the VOC feed concentration increased from 221 to 884 mg toluene/m3 (from 57.2 to 229 ppm), correspondingly the organic loading rate of the hybrid bioreactor increased from 1.58 to 6.32 kg chemical oxygen demand/m3/day (from 0.505 to 2.02kg?toluene/m3/day) based on the drum volume, both the ASP and RDB decreased, and the overall toluene removal efficiency declined from 99.8 to 74.1%. Biomass accumulation at different medium depths became more even when the organic loading rate was increased. Part of the applied VOC was biodegraded by the ASP, which suggests that this hybrid bioreactor could achieve longer runs between medium cleanings and higher VOC removal efficiencies than a single RDB bioreactor without an ASP portion at the same organic loading rate.     

Role of Bioflocculation on Chemical Oxygen Demand Removal in Solids Contact Chamber of Trickling Filter/Solids Contact Process

The trickling filter/solids contact (TF/SC) process was developed in the late 1970s to improve the quality of the final effluent from existing trickling filter plants, to be able to meet stricter Environmental Protection Agency effluent requirements. Although this process has successfully achieved this objective, it is still not completely understood, there is limited information regarding the flocculation phenomena occurring in the solids contact chamber (SCC), and no information could be found on the relationship between flocculation and organic matter removal kinetics. To better understand the kinetics of biological flocculation in a continuous flow SCC, a long-term experimental program was conducted using a TF/SC pilot plant constructed at the Marrero, La., wastewater treatment plant. This program started in January 1998 and has continued through date. The present article will focus on two major areas: (1) the kinetics of bioflocculation in the SCC; and (2) effect of bioflocculation on chemical oxygen demand (COD) removal. Analysis of the wastewater composition revealed that, on the average, only 18.7% of the total COD in the SCC influent is truly dissolved. Therefore, most of the total COD removal observed in the SCC must be due to a physical process, such as flocculation. The experimental data confirmed that flocculation of the particulate COD contained in the trickling filter effluent explains the high total COD removal observed at the SCC. Both total and colloidal COD removals are well explained by the first-order flocculation model.     

Removal of Nonbiodegradable Chemicals from Mixtures during Granular Activated Carbon Bioregeneration

The purpose of this research was to better understand the interactions between biodegradable and nonbiodegradable synthetic organic chemicals (SOCs) during bioregeneration of biologically active granular activated carbon (GAC) columns. Continuous-flow GAC bioregeneration experiments were conducted at different empty-bed contact times (EBCTs) using mixtures of a biodegradable (benzene or toluene) and a nonbiodegradable (perchloroethylene or carbon tetrachloride) SOC. The GAC was pre-equilibrated with respect to each combination of SOCs to facilitate the study of bioregeneration. If no dissolved oxygen limitations occurred in the bioregeneration experiments, the effluent biodegradable SOC concentration decreased over time and then remained low, after which the effluent nonbiodegradable SOC concentration also decreased because of the increased availability of adsorption sites on the GAC. Pre- and postexperimental GAC loadings show a marked decrease in the biodegradable SOC loading as well as an increase in the nonbiodegradable SOC loading. Greater degrees of bioregeneration were found for higher SOC equilibrium concentrations and longer EBCTs. Bioregeneration ranged from 28.8 to 45.5% of the initial biodegradable SOC loading after 13–17?days. These results illustrate an increase in GAC adsorption capacity for nonbiodegradable SOCs through bioregeneration of GAC containing biodegradable SOCs.     

Role of Mass Transfer Resistance in Overall Substrate Removal Rate in Upflow Anaerobic Sludge Bed Reactors

A kinetic model (incorporating intrinsic Haldane kinetics) and an empirical model (incorporating apparent Haldane kinetics) for phenol degradation in upflow anaerobic sludge bed (UASB) reactors were used. UASB-reactor performance data were also generated for model verification. From the independent batch study together with statistical analyses, the apparent Haldane kinetic constants k′ and Ki′ did not differ from the intrinsic k and Ki, but the apparent Ks′ was significantly larger than the intrinsic Ks (i.e., greater internal mass transfer resistance). From the calculated results (of overall effectiveness factor, Thiele modulus, and Biot number) together with parametric sensitivity analyses, the internal mass transfer resistance would play a more influential role than the external mass transfer resistance on the overall substrate removal rate in UASB reactors. The simulated residual phenol concentrations using the empirical model were in good agreement with the experimental data; the simulated results using the empirical model were also close to those using the kinetic model. Accordingly, the empirical model that can properly describe the overall substrate removal rate should be acceptable for process design of UASB reactors.     

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.     

Sulfur Impregnation on Activated Carbon Fibers through H2S Oxidation for Vapor Phase Mercury Removal

Sulfur was impregnated onto activated carbon fibers (ACFs) through H2S oxidation catalyzed by the sorbent surface in a fixed-bed reactor. By changing the temperature and duration of the sulfur impregnation process, ACFs with different sulfur contents were developed. Characterization of ACFs before and after sulfur impregnation was conducted by surface area analysis, energy dispersive X-ray analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy, and temperature programmed desorption. Vapor phase mercury adsorption experiments were carried out in a fixed-bed reactor. Sulfur was impregnated mainly as elemental sulfur and the amount of sulfur deposited on the ACF increased with an increase in impregnation temperature. Higher temperature leads to more uniform sulfur distribution inside the sorbent pores. The impregnation process can be explained by a combination of pore filling and monolayer adsorption, with the former mechanism predominating at low temperatures. In the absence of sulfur, the mercury adsorption capacity can be correlated with surface area and pore volume.     

In Situ Microscale Analyses of Activated Sludge Flocs in the Enhanced Biological Phosphate Removal Process by the Use of Microelectrodes and Fluorescent In Situ Hybridization

Phosphate concentration microprofiles were measured within activated sludge flocs in the enhanced biological phosphate removal (EBPR) process, and a fluorescent in situ hybridization and clone library analysis were conducted to indentify polyphosphate accumulating organisms (PAOs). The center of the flocs had the highest phosphate concentrations, and the stratification of the flocs found by microprofiling indicated that the PAOs were probably distributed evenly throughout the flocs. Under the assumption that the phosphate, which was generated because of phosphate release by microbial activity, was not consumed by microbes and was only transferred from the flocs to the bulk by diffusion during anaerobic conditions, the effective diffusion coefficient (Df) for phosphate release within the flocs was calculated to be 3.33×10?7?cm2/s at the end of the anaerobic phase of the EBPR process. These results provide a better understanding of the phosphate removal mechanism, and this understanding of the internal function of flocs can lead to improvement in the modeling, design, and operation of the biological phosphorus removal process.     

Effect of Dynamic Loading on Biological Nutrient Removal in a Pilot-Scale Liquid-Solid Circulating Fluidized Bed Bioreactor

A pilot-scale liquid-solid circulating fluidized bed (LSCFB) bioreactor was employed for biological nutrient removal from municipal wastewater at the Adelaide Pollution Control Plant, London, Ontario, Canada. Lava rock particles of 600?μm were used as a biomass carrier media. The system generated effluent characterized by <1.0?mg NH4–N/L, <6.0?mg NO3–N/L, <1.0?mg PO4–P/L, <10?mg TN/L, and <10?mg SBOD/L at an influent flow of 5?m3/d, without adding any chemicals for phosphorus removal and secondary clarification for suspended solids removal. The impact of the dynamic loading on the LSCFB effluent quality and its nutrient removal efficiencies were monitored by simulating wet weather condition at a maximum peaking factor of 3 for 4 h. The achievability of effluent characteristics of 1.1 mg NH4–N/L, 4.6 mg NO3–N/L, 37 mg COD/L, and 0.5 mg PO4–P/L after 24 h of the dynamic loading emphasize the favorable response of the LSCFB to the dynamic loadings and the sustainability of performance without loss of nutrient removal capacity.