Integrated Fixed-film Activated Sludge Systems Research Articles

The Nitrogen Removal Performance and Microbial Community of Integrated Fixed-Film Activated Sludge Systems with Carriers

The Nitrogen Removal Performance and Microbial Community of Integrated Fixed-Film Activated Sludge Systems with Carriers

Fate of pharmaceutically active compounds in a pilot-scale A2O integrated fixed-film activated sludge (IFAS) process treating municipal wastewater

The goal of this research was to study the operation of an integrated fixed-film activated sludge system (IFAS), in anaerobic/anoxic/aerobic (A2O) configuration for the elimination of emerging pollutants, in particular of 27 pharmaceutical active compounds (PhACs) (eight anti-inflammatory and/or analgesic pharmaceuticals (AIAPs), six antibiotics, four b-blockers, two antihypertensives/diuretics, three lipid regulators-bezafibrate and four psychiatric medications). Different operational conditions were analyzed in the biological reactor, controlling at all times both the amount of suspended and fixed biomass present. The A2O-IFAS system has obtained similar or higher removal efficiency (RE) in the elimination of organic matter, and especially of nutrients, nitrogen (N) and phosphorous (P), with respect to the conventional A2O system, working however with very low values of the sludge retention time (SRT) (4.0 days) and mix liquid suspended solid (MLSS) in the reactor (1822 mg L-1). In general, conventional activated sludge (CAS) and IFAS processes show the importance of operating at high SRT and MLSS concentration, that give low food/microorganisms (F/M) ratio, to increase the RE of several PhACs. However, the A2O-IFAS system, operating with low mixed liquor SRT and MLSS has achieved similar or better RE of PhACs, obtaining the highest average REs values (>80%) for fenofibrate, acetaminophen, ibuprofen, naproxen, clarithromycin and atenolol. According to the results obtained, due to the affordable cost and well-demonstrated performance, IFAS systems become one of the most promising technology for conventional wastewater treatment plants (WWTP) upgrading.

Effect of Carrier Filling Ratios on Dissolved Organic Nitrogen Removal in Integrated Fixed-Film Activated Sludge Systems Treating Municipal Wastewater

Previous research has focused on the removal characteristics of inorganic nitrogen in the integrated fixed-film activated sludge (IFAS) process. However, information on dissolved organic nitrogen (...

The role of the external mass transfer resistance in nitrite oxidizing bacteria repression in biofilm-based partial nitritation/anammox reactors

A model-based study was developed to analyse the behaviour of Moving Bed Biofilm Reactor (MBBR) and Integrated Fixed-Film Activated Sludge (IFAS) reactor configurations for the removal of nitrogen in the main water line of municipal wastewater treatment plants via partial nitritation/anammox (PN/AMX). The basic principles and underlying mechanisms linking operating conditions to process performance were investigated, with particular focus on nitrite oxidizing bacteria (NOB) repression and resulting volumetric conversion rates. The external mass transfer resistance is a major factor differentiating granular sludge PN/AMX processes from MBBR or IFAS systems. The external mass transfer resistance was found to promote the metabolic coupling between anammox (AMX) and ammonia oxidizing bacteria (AOB), crucial for NOB repression in the biofilm. Operation at low bulk DO prevents NOB proliferation in the flocs of IFAS systems as AMX activity limits nitrite availability (the so-called AMX nitrite sink). Importantly, the effectiveness of the AMX nitrite sink strongly depends on the AMX sensitivity to oxygen. Also, over a broad range of operational conditions, the seeding of AOB from the biofilm played a crucial role in maintaining their activity in the flocs. From a practical perspective, while low DO promotes NOB repression, lower nitrogen loads have to be applied to maintain the same effluent quality. Thus, a trade-off between NOB repression and volumetric conversion capacity needs to be defined. To this end, IFAS allow for higher volumetric rates, but the window of operating conditions with effective NOB repression is smaller than that for MBBR. Ultimately, this study identified the principles controlling NOB in MBBR and IFAS systems and the key differences with granular reactors, allowing for the interpretation of (seemingly contradictory) published experimental results.

Characterization of microbial communities during start-up of integrated fixed-film activated sludge (IFAS) systems for the treatment of oil sands process-affected water (OSPW)

In this study, integrated fixed-film activated sludge (IFAS) microbial development and degradation efficiency were investigated for oil sands process-affected water (OSPW) remediation. IFAS microbial community was characterized using 454 high-throughput 16S rRNA gene pyrosequencing that revealed that the IFAS seed sludge (activated sludge [AS] from the Gold Bar Wastewater Treatment Plant [GBWTP]) showed the greatest richness and evenness of bacterial community, as compare to other biomass samples. The Chao 1 value and the Shannon diversity index showed that the bacterial richness and microbial diversity in biofilms were significantly higher than those in flocs in both IFAS systems. Proteobacteria, Nitrospirae, Acidobacteria, and Bacteroidetes were dominant phyla in both flocs and biofilms in IFAS reactors. It is also noted that the phyla and class distributions of flocs and biofilms were significantly different. Principal coordinate analysis (PCoA) indicated that there were substantial differences between OSPW indigenous microbes and flocs and biofilm microbes in IFAS. Overall, a relatively low ozone dose (30mg/L utilized) combined with IFAS reactor treatment significantly increased the organic contaminants removal. The combined ozonation and IFAS system showed the promise for OSPW treatment.

Optimization of ozonation combined with integrated fixed-film activated sludge (IFAS) in the treatment of oil sands process-affected water (OSPW)

Effects of hydraulic retention time (HRT) and the chemical oxygen demand/nitrogen (COD/N) ratio on the microbial community composition of integrated fixed-film activated sludge (IFAS) and its ability to treat raw and ozonated oil sands process-affected water (OSPW) were evaluated. After 11 months of HRT and ammonium optimization, 54.56% of the COD and 30.20% of the acid extractable fraction (AEF) were removed in raw OSPW IFAS, and 56.83% of the COD and 51.51% of the AEF were removed in ozonated OSPW IFAS. Extension of the HRT in the IFAS had no significant effect on the removal of COD and nitrogen, whereas a lower COD/N ratio increased the removal of organics and total nitrogen. The quantitative polymerase chain reaction (q-PCR) indicated that the abundance of nitrifier and denitrifier genes decreased during HRT optimization, and increased significantly after ammonium optimization. Proteobacteria, Nitrospirae, Acidobacteria, and Bacteroidetes were the dominant phyla in IFAS flocs and biofilms according to 454 sequencing. Proteobacteria showed significant decreases in flocs and biofilms after HRT and ammonium IFAS optimization. Nitrospirae and Acidobacteria showed significant upward trends in all biomass forms in optimized IFAS systems compared to unoptimized IFAS systems.

Practical experience with full-scale structured sheet media (SSM) integrated fixed-film activated sludge (IFAS) systems for nitrification.

Many wastewater treatment plants in the USA, which were originally designed as secondary treatment systems with no or partial nitrification requirements, are facing increased flows, loads, and more stringent ammonia discharge limits. Plant expansion is often not cost-effective due to either high construction costs or lack of land. Under these circumstances, integrated fixed-film activated sludge (IFAS) systems using both suspended growth and biofilms that grow attached to a fixed plastic structured sheet media are found to be a viable solution for solving the challenges. Multiple plants have been retrofitted with such IFAS systems in the past few years. The system has proven to be efficient and reliable in achieving not only consistent nitrification, but also enhanced bio-chemical oxygen demand removal and sludge settling characteristics. This paper presents long-term practical experiences with the IFAS system design, operation and maintenance, and performance for three full-scale plants with distinct processes; that is, a trickling filter/solids contact process, a conventional plug flow activated sludge process and an extended aeration process.

Application of cigarette filter rods as biofilm carrier in an integrated fixed-film activated sludge reactor

Bio-carriers are an important component of integrated fixed-film activated sludge (IFAS) processes. In this study, the capability of cigarette filter rods (CFRs) as a bio-carrier in IFAS processes was evaluated. Two similar laboratory-scale IFAS systems were operated over a 4-month period using Kaldnes-K3 and CFRs as IFAS media. The process performance was studied by using chemical oxygen demand (COD). The organic loading rate was in the range 0.5-2.8 kgCOD/(m(3)·d). The COD average removal efficiencies were 89.3 and 93.9% for Kaldnes-K3 (reactor A) and cigarette filters (reactor B), respectively. The results demonstrate that the performance of the IFAS reactor containing CFRs was comparable to the reactor using Kaldnes. The CFRs, which have a high porous surface area and entrapment ability for microbial cells, could be successfully used in biofilm reactors as a bio-carrier.

Comparison of Conventional and Integrated Fixed‐Film Activated Sludge Systems: Attached‐ and Suspended‐Growth Functions and Quantitative Polymerase Chain Reaction Measurements

Pilot-scale integrated fixed-film activated sludge (IFAS) and non-IFAS control systems were compared, with respect to overall performance and functional behaviors and microbial population composition in the attached and suspended phases. The suspended phases of the control and IFAS systems exhibited similar rates of ammonia consumption; the attached phase in the second aerobic IFAS reactor had significantly higher rates of ammonia consumption and nitrate production than any other biomass source, and the attached biomass from the first aerobic reactor had the lowest ammonia consumption rates. Quantitative polymerase chain reaction (qPCR) indicated the presence of the ammonia-oxidizing bacteria Nitrosomonas oligotropha and the nitrite-oxidizing bacteria Nitrospira spp. and Nitrobacter spp. Mathematical modeling and qPCR both indicated greater concentrations of nitrifiers in the attached phases of a downstream aerobic reactor relative to the upstream reactor, possibly because of increased competition from heterotrophs for space in the attached phase of the upstream aerobic reactor.

Exploring the relationship between viscous bulking and ammonia-oxidiser abundance in activated sludge: A comparison of conventional and IFAS systems

This study investigated the nature of viscous sludge bulking within a molasses-fed integrated fixed-film activated sludge (IFAS) and conventional activated sludge (AS) plant by routinely measuring the total carbohydrate and protein fractions of the mixed liquor (ML). The impacts of sludge settleability and plant performance on the relative abundance of ammonia-oxidising bacteria (AOB) ( Nitrosomonas oligotropha-cluster) were also investigated using quantitative polymerase chain reaction (qPCR). Results showed that sludge volume index (SVI) correlated positively with the amount of ML total carbohydrate in both the IFAS and traditional AS plants, highlighting the influential role that ML polysaccharide concentration plays on sludge settleability in these reactors. Results also revealed a negative relationship between the AOB/total Bacteria ratio and SVI, demonstrating that a poor settling sludge generally coincided with periods of relatively low AOB abundance. The existence of these relationships suggests that readily available organic carbon (molasses) was likely to have been present in excess in these systems. Our qPCR results also showed that concentrations of both AOB and total Bacteria genomic copies detected within the ML of the IFAS and conventional AS plants were remarkably similar. For the IFAS system, results showed that the ML supported an equivalent number of AOB (per gram of biomass) to that detected on the plastic IFAS media carriers, suggesting that the suspended biomass fraction plays an equally important role in the overall nitrification performance of these systems. Interestingly, large observed variations in AOB and AOB/total Bacteria ratio measured within both the ML and IFAS media carriers had no measurable impact on the apparent nitrification performance of these systems; indicating the presence of some excess or ‘reserve’ nitrifying capacity above that which is required for effective plant performance. Results presented here also constitute the first known side-by-side comparison of the distribution of AOB in IFAS and conventional racetrack-like AS plants at the full-scale level.

Interactions Between Suspended Biomass and Biofilm in Integrated Fixed-Film Activated Sludge (IFAS) Bioreactors: Process Design Implications for IFAS Systems

Interactions Between Suspended Biomass and Biofilm in Integrated Fixed-Film Activated Sludge (IFAS) Bioreactors: Process Design Implications for IFAS Systems

How Does IFAS Affect Distributions of AOB and NOB Communities? Population Measurements and Modeling of Pilot Scale Systems

Integrated fixed film activated sludge (IFAS) affects on performance and microbial populations of nitrifying bacteria were investigated in pilot scale systems with a non-IFAS control. Biomass from the suspended phase in the control system, the suspended phase in the IFAS system, and the attached phases from two aerobic reactors in series were analyzed through batch testing to determine rates of nitrification and populations structures in using quantitative PCR (qPCR). Suspended phases from IFAS and non-IFAS systems yielded similar rates of ammonia removal, which were higher than the attached biomass rates in the first aerobic reactor, while the second aerobic reactor attached growth provided the highest rates of nitrification. Nitrifier populations monitored by qPCR demonstrated the presence of the AOB Nitrosomonas oligotropha and the NOBs Nitrospira and Nitrobacter. Results from mathematical modeling calibrated to process performance was in agreement with qPCR measurements in terms of the relative quantities of AOBs and NOBs in the different phases.

IFAS Pilot Study for Cold Weather Nitrogen Reduction

Facing a new effluent total nitrogen discharge limit, the Town of Stafford Springs Connecticut chose to upgrade their Water Pollution Control Facility using a fixed media Integrated FixedFilm/ Activated Sludge (IFAS) system. The IFAS media would allow a retrofit of the existing aeration basins for biological nutrient removal without having to add basin volume. The raw influent wastewater was a mixture of municipal and industrial wastes that included at high concentration of fibrous suspended solids from a local textile manufacturer. Because of the unusual nature of the wastewater, a pilot study was commissioned to confirm the design basis for the IFAS system. After good initial results, the pilot study was cut short due to operational difficulties associated with the fibrous influent. Other fixed media IFAS systems were studied to help confirm the design rate, and the Town decided to proceed with construction of the IFAS system in April of 2009.

Stability and capacity enhancements of activated sludge process by IFAS technology

This research was conducted to evaluate the capacity and stability of the Activated Sludge (AS) process retrofitted to the Integrated Fixed Film Activated Sludge (IFAS) process. Hydraulic retention time (HRT) and solids retention time (SRT) were used as independent variables in this investigation. The IFAS and AS processes were operated in parallel for carbon removal and nitrification at 6, 8, and 10 hours HRTs at which 4, 6, and 8 days SRTs were maintained. The AS system failed to attain steady state conditions at 10 hours HRT with 4 days SRT, 8 hours HRT with 4 and 6 days SRTs, and 6 hours HRT with 4, 6, and 8 days SRTs, whereas the IFAS system was stabilized until the SRT and HRT were at 4 days and 6 hours, respectively. Excessive filamentous microorganisms were observed in the IFAS and AS systems as the results of completely-mixed condition and high readily biodegradable organic content in the wastewater. The filamentous bulking was apparently the cause of system failure and the reduction of nitrification in the AS system. As the HRTs and SRTs were decreased or the system loadings increased, it was clearly demonstrated that the IFAS system was higher in capacity and stability than the AS system. The attached biomass in the IFAS system suppressed the growth of filamentous microorganisms by reducing the amount of substrates in contact with the filamentous microorganisms providing the system stability. Nitrification was completed in the IFAS system and could be independent of the suspended SRT. Both AS and IFAS systems could provide the same performance for COD removal at the experimental conditions.

Effects of dissolved oxygen on biological nitrogen removal in integrated fixed film activated sludge (IFAS) wastewater treatment process

The objective of this research was to determine the effects of dissolved oxygen on the biological nitrogen removal in the Integrated Fixed Film Activated Sludge (IFAS) and Modified Ludzack-Ettinger (MLE) systems. The carbonaceous and nitrogen removals were investigated at the COD/Nitrogen (C/N) ratios of 4, 6, and 10, and the dissolved oxygen (DO) concentrations of 2, 4, and 6 mg/L. The experimental results indicate that the C/N ratios of 4, 6, and 10 and the DO concentrations of 2, 4, and 6 affected insignificantly on the chemical oxygen demand (COD) removal, but significantly on the nitrogen removal as the consequences of different nitrification and denitrifcation rates in both systems. The COD removal was nearly completed throughout this study because glucose was used as a primary carbon source in the wastewater and both systems were operated at high SRT relative to the minimum SRT requirement for COD removal. The experimental conditions used in this study apparently led to nitrite accumulation in both IFAS and MLE systems. It is suggested that there is no benefit of installing media in the IFAS system at the C/N ratio of 10 because the system was underloaded with the nitrogen. The lower DO concentration, the greater denitrification in the anoxic zone was achieved because nitrite nitrogen was used as an electron acceptor. At the C/N ratios of 4 and 6, the IFAS system was higher in capacity for nitrification as a result of attached biomass on the support media in the aerobic zone. The DO concentration of 6 mg/L is required to maximize the nitrification rates in the systems under these experimental conditions resulting in greater oxidized nitrogen for denitrification in the anoxic zones. The denitrification in the aerobic zone of the IFAS system is not evaluated due to unavailability of nitrite information. The optimal DO concentrations for biological nitrogen removal in the IFAS system at the C/N ratios of 4, 6, and 10 in this study were 6, 6, and 2 mg/L, respectively.

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.

Performance of IFAS wastewater treatment processes for biological phosphorus removal

Integrated fixed film activated sludge (IFAS) is a promising process for the enhancement of nitrification and denitrification in conventional activated sludge systems that need to be upgraded for biological nutrient removal (BNR), particularly when they have space limitations or need modifications that will require large monetary expenses. Several studies have reported successful implementations of IFAS at temperate zone wastewater treatment facilities, typically by placement of fixed film media into aerobic zones. However, nearly all of the implementations have not included enhanced biological phosphorus removal (EBPR) in the upgraded systems. This is possibly because the treatment plants have been operated at low mixed liquor mean cell residence times (MCRTs), and EBPR would wash out of the systems at the low temperatures encountered, making it difficult to maintain EBPR. The primary objective of this study was to investigate the incorporation of EBPR into IFAS systems, and study the interactions between the fixed biomass and the mixed liquor suspended solids with respect to substrate competition and nutrient removal efficiencies. Three pilot-scale UCT/VIP configuration systems were used, one as a control and the other two with Bioweb ® media integrated into some of the anoxic and aerobic reactors. The systems were operated at different MCRTs, and influent COD/TP ratios, and with split influent flows. The experimental results confirmed that EBPR could be incorporated successfully into IFAS systems, but the redistribution of biomass resulting from the integration of fixed film media, and the competition of organic substrate between EBPR and denitrification would affect performances. Also, the integration of fixed film media into the anoxic reactors affected performances differently from media in aerobic reactors.

ACHIEVING ADVANCED WASTEWATER TREATMENT STANDARDS WITH IFAS

Integrated Fixed-film Activated Sludge (IFAS) systems is a hybrid system consisting of both suspended and fixed biomass growth, and it is achieved by incorporating a media that support biofilms in existing aeration basin. By promoting the growth of both carbonaceous-removing and nitrifying bacteria, an integrated fixed-film activated sludge (IFAS) process can improve effluent quality without expanding the plant significantly. The fixed biomass, which grows on the captive support media, provides a higher biomass inventory without significantly increasing the suspended solids inventory. This significantly increases the biological capacity of the system without increasing the physical aeration basin size. The demonstration of the IFAS technology has shown that the installation of fixed film media within an existing aeration basin can provide substantial improvements in effluent quality and process operations. This paper discusses several popular IFAS systems and presents case studies to illustrate the application of the technology.