Integrated Fixed-film Activated Sludge Reactor Research Articles

Comparing methanol and glycerol as carbon sources for mainstream partial denitrification/anammox in an IFAS process.

This study explored the implementation of mainstream partial denitrification with anammox (PdNA) in the second anoxic zone of a wastewater treatment process in an integrated fixed film activated sludge (IFAS) configuration. A pilot study was conducted to compare the use of methanol and glycerol as external carbon sources for an IFAS PdNA startup, with a goal to optimize nitrogen removal while minimizing carbon usage. The study also investigated the establishment of anammox bacteria on virgin carriers in IFAS reactors without the use of seeding, and it is the first IFAS PdNA startup to use methanol as an external carbon source. The establishment of anammox bacteria was confirmed in both reactors 102 days after startup. Although the glycerol-fed reactor achieved a higher steady-state maximum ammonia removal rate because of anammox bacteria (1.6 ±0.3g/m2/day) in comparison with the methanol-fed reactor (1.2±0.2g/m2/day), both the glycerol- and methanol-fed reactors achieved similar average in situ ammonia removal rates of 0.39 ±0.2g/m2/day and 0.40 ±0.2g/m2/day, respectively. Additionally, when the upstream ammonia versus NOx (AvN) control system maintained an ideal ratio of 0.40-0.50 g/g, the methanol-fed reactor attained a lower average effluent TIN concentration (3.50 ±1.2mg/L) than the glycerol-fed reactor (4.43 ±1.6mg/L), which was prone to elevated nitrite concentrations in the effluent. Overall, this research highlights the potential for PdNA in IFAS configurations as an efficient and cost-saving method for wastewater treatment, with methanol as a viable carbon source for the establishment of anammox bacteria. PRACTITIONER POINTS: Methanol is an effective external carbon source for an anammox startup that avoids the need for costly alternative carbon sources. The methanol-fed reactor demonstrated higher TIN removal compared with the glycerol-fed reactor because of less overproduction of nitrite. Anammox bacteria was established in an IFAS reactor without seeding and used internally stored carbon to reduce external carbon addition. Controlling the influent ammonia versus NOx (AvN) ratio between 0.40 and 0.50 g/g allowed for low and stable TIN effluent conditions.

Stimulating extracellular polymeric substances production in integrated fixed-film activated sludge reactor for advanced nitrogen removal from mature landfill leachate via one-stage double anammox

Introducing carbon sources to achieve nitrogen removal from mature landfill leachate not only increases the costs and carbon emissions but also inhibits the activity of autotrophic bacteria. Thus, this study constructed a double anammox system that combines partial nitrification-anammox (PNA) and endogenous partial denitrification-anammox (EPDA) within an integrated fixed-film activated sludge (IFAS) reactor. In this system, PNA primarily contributes to nitrogen removal pathways, achieving a nitrite accumulation rate of 98.23%. The production of extracellular polymer substances (EPS) in the IFAS reactor is stimulated by introducing co-fermentation liquid. Through the utilization of EPS, the system effectively achieves EPDA with the nitrite transformation rate of 97.20%. Under the intermittent aeration operation strategy, EPDA combined with PNA and anammox in the oxic and anoxic stages enhanced the nitrogen removal efficiency of the system to 99.70 ± 0.12%. The functional genus Candidatus kuenenia became enriched in biofilm sludge, while Thauera and Nitrosomonas predominated in floc sludge.

Biomass types of nitrate-reducing denitrifiers to differentiate the hybrid community allocation of partial denitrification (PD) and anammox: IFAS vs MBBR

Partial denitrification (PD) and anaerobic ammonia oxidation (anammox) are modern treatment processes that can be combined to provide energy- and resource-efficient nitrogen removal methods; however, these processes are challenging to implement as a one-stage hybrid system. The coupling forms to achieve steady long-term PD/anammox operation need to be investigated. In this study, two reactors were operated for 300 days at 25 ± 1℃, in which one was inoculated with PD biofilms and anammox biofilms in a moving bed biofilm reactor (MBBR), and the other was inoculated with PD flocs and anammox biofilms in an integrated fixed-film activated sludge (IFAS) reactor. The results showed that the IFAS reactor had suprerior nitrogen removal performance, with the effluent total nitrogen (TN) concentration in the MBBR and IFAS of 5.17 ± 0.94 mg∙L−1 and 1.52 ± 0.75 mg∙L−1, respectively. Illumina MiSeq sequencing showed that Thauera and OLB8 were the dominant nitrate-reducing denitrifiers in PD biofilms in MBBR and flocs in IFAS, respectively. Since Thauera tended to selectively immigrate to the anammox biofilms, nitrate-reducing denitrifiers and anammox bacteria (AnAOB) coexisted in the anammox biofilms in MBBR. This decreased the PD activity (486.14 ± 23.04 mg∙(L∙d)−1 to 249.66 ± 26.90 mg∙(L∙d)−1) in the PD biofilms. On the contrary, nitrate-reducing denitrifiers and AnAOB were separately allocated in flocs and anammox biofilms in the IFAS reactor. The retention of PD biomass and superior mass transfer performance of the activated sludge flocs maintained a higher PD activity (2193.20 ± 26.62 mg∙(L∙d)−1), which provided sufficient NO2−-N for AnAOB and was beneficial to the growth of AnAOB. Hence, IFAS may be a potentially superior coupling mode for the PD/anammox process for engineering applications.

Environmental sustainability assessment of a fixed media based and package type integrated fixed-film activated sludge reactor in India: A damage-oriented approach

The sustainability of new and emerging wastewater treatment technologies/systems is a matter of vital significance. In this regard, the life cycle assessment (LCA) of a package type integrated fixed-film activated sludge (IFAS) reactor, treating municipal wastewater, was carried out using SimaPro software (8.0.5 faculty version) and IMPACT 2002 + methodology. The analysis of environmental impacts, associated with the construction phase, and investigated operational scenarios (steady-state, dissolved oxygen variation, and intermittent aeration) of studied IFAS reactor, is presented in this study. The LCA analysis results revealed that the main negative impacts i.e. eutrophication and eco-toxicity of the IFAS reactor were associated with the usage of stainless steel in construction of reactor. It was observed that considering damage indicators, intermittent aeration phase III causes minimum impact (∼43% on human health, ∼2% on ecosystem quality, ∼44% on climate change, and ∼45% on resources), as compared to dissolved oxygen phase III. The study showed that among all the operational scenarios, IA phase III exert ∼2–45% less burden on the environment in most of the midpoint impact categories, except for aquatic eutrophication impact. DO phase III contributed minimum impact on aquatic eutrophication category, mainly due to best effluent characteristics. Overall, the investigations of the present study revealed that among various input resources, energy utilization is the most significant contributor to the environmental impacts associated with the investigated IFAS reactor, and presented the highest importance among four damage categories.

Redworm elimination in an integrated fixed-film activated sludge reactor

Two pilot-scale biological nutrient removal bioreactors were operated side by side under selected flow rate conditions. One reactor was operated under an integrated fixed-film activated sludge (IFAS) reactor configuration, and the second reactor was operated under a conventional activated sludge reactor configuration. The relatively high dissolved oxygen (DO) and low food-to-microorganism ratio created a favourable environment for the proliferation of redworm identified as Aeolosoma hemprichi in the IFAS reactor from day 116, which led to significant deterioration on ammonia removal in the IFAS reactor. The removal efficiencies of chemical oxygen demand (COD) and phosphorus were not significantly affected by the redworm bloom. Several strategies were applied to eliminate the redworms from the IFAS reactor. The most effective strategy was shutting off the DO supply in the aerobic zone and stopping the influent feed for 48 h. Finally, it took about 1·5 months for the IFAS reactor to recover from performing the worm elimination strategy.

Evaluation of the Efficiency of Integrated Fixed-Film Activated Sludge reactor for Treatment of Wastewater from Vegetable Oil Industries

Evaluation of the Efficiency of Integrated Fixed-Film Activated Sludge reactor for Treatment of Wastewater from Vegetable Oil Industries

Biodegradation and nutrients removal from greywater by an integrated fixed-film activated sludge (IFAS) in different organic loadings rates

In this study, the efficiency of Integrated Fixed-film Activated Sludge (IFAS) system in synthetic greywater treatment and nutrients removal was studied in duration of 105 days according to different Organic Loadings Rates (OLRs). The study was operated in pilot-scale and OLRs of 0.11–1.3 gCOD/L.d. Scanning Electron Microscope (SEM) image showed that the biofilm with a proper thickness was formed on IFAS reactor’s media. The results indicated that the best removal efficiency of BOD5, COD, and TSS were 85.24, 92.52 and 90.21%, respectively, in an organic loading of 0.44 gCOD/L.d. Then, with the OLR increased, the removal efficiencies of BOD5, COD, and TSS increased as long as the organic loading reached 0.44 gCOD/L.d. But with the OLR increased more, the removal efficiency of these parameters decreased. The ANOVA statistical test results showed that the mean difference of removal efficiency in organic loadings for BOD5 (p ≤ 0.001) and COD (p = 0.003) was significant, while it was insignificant for TSS (p = 0.23). The best removal efficiencies of Total Nitrogen (TN) and Total Phosphorus (TP) were 89.60 and 86.67%, respectively, which were obtained at an OLR of 0.44 gCOD/L.d. By increasing OLR up to 0.44 gCOD/L.d, removal efficiencies of TN and TP increased, while the removal efficiency decreased with the OLR increased more, and this difference was statistically significant (p = 0.021). Finally, the results showed that the IFAS system provided a proper efficiency in treatment of the synthetic greywater and it could be used in a full scale.

Dynamic modeling of nitrogen removal for a three-stage integrated fixed-film activated sludge process treating municipal wastewater.

The integrated fixed-film activated sludge (IFAS) process is being increasingly used to enhance nitrogen removal for former activated sludge systems. The aim of this work is to evaluate a numerical model of a new nitrifying/denitrifying IFAS configuration. It consists of two carrier-free reactors (anoxic and aerobic) and one IFAS reactor with a filling ratio of 43% of carriers, followed by a clarifier. Simulations were carried out with GPS-X involving the nitrification reaction combined with a 1D heterogeneous biofilm model, including attachment/detachment processes. An original iterative calibration protocol was created comprising four steps and nine actions. Experimental campaigns were carried out to collect data on the pilot in operation, specifically for modelling purpose. The model used was able to predict properly the variations of the activated sludge (bulk) and the biofilm masses, the nitrification rates of both the activated sludge and the biofilm, and the nitrogen concentration in the effluent for short (4-10 days) and long (300 days) simulation runs. A calibrated parameter set is proposed (biokinetics, detachment, diffusion) related to the activated sludge, the biofilm and the effluent variables to enhance the model prediction on hourly and daily data sets.

Linking nitrification characteristic and microbial community structures in integrated fixed film activated sludge reactor by high-throughput sequencing.

The primary goal of this study is to investigate ammonia removal, abundance of nitrifying bacteria and microbial community structures in a laboratory-scale integrated fixed film activated sludge (IFAS) reactor. The results of Illumina MiSeq sequencing based on 16S rRNA genes showed Proteobacteria and Bacteroidetes were the dominant phyla in both biofilm and suspended sludge samples in the IFAS reactor. The dominant ammonia-oxidizing bacteria (AOB) species was Nitrosomonas and the dominant nitrite-oxidizing bacteria species was Nitrospira. The contribution of biofilm to ammonia removal increased from 4.0 ± 0.9% to 37.0 ± 2% when the temperature decreased from 25 °C to 10 °C. The real-time polymerase chain reaction (PCR) result showed the abundance of AOB in suspended sludge was higher than that in biofilm at the same time. However, nitrification is more dependent on attached growth than on suspended growth in the IFAS reactor at 15 °C and 10 °C and the abundance of AOB in biofilm was also higher than that in suspended sludge. The more robust ammonia removal rate at low temperatures by biofilm contributed to the relatively stable ammonia removal, and biofilm attached on carriers in the IFAS reactor is advantageous for nitrification in low-temperature environment.

Free nitrous acid inhibition of biological phosphorus removal in integrated fixed-film activated sludge (IFAS) system

Free nitrous acid (FNA) inhibition of anoxic and aerobic phosphorous removal in an integrated fixed-film activated sludge (IFAS) system with different FNA adaptation was investigated. A bench scale sequencing batch reactor (SBR) with plastic media was operated in an anaerobic/anoxic/aerobic sequence. During the anoxic period, nitrite was fed into the reactor at different concentrations to select for biomass adapted to 0.06 and 0.4μg HNO2-NL−1 of FNA during anoxic stage in Phase I and II, respectively. Long term anoxic/aerobic phosphorus removal was achieved in the IFAS reactor in both phases. In Phase I, aerobic phosphorous uptake was inhibited at higher level compared with anoxic phosphorus uptake. In Phase II, DPAO in both suspended and attached forms could adapt and were not inhibited at FNA level four times higher than the adapted concentration. The PAO’s aerobic activity in Phase II, did not show significant adaptation and was inhibited at slightly lower level compared with that in Phase I. The FNA inhibition of aerobic phosphorous uptake rate in attached biomass was 20% of that in suspended forms. In batch testes with the FNA level was raised to three times the adapted concentration, the contribution of attached biomass to overall anoxic and aerobic phosphorus uptake increased by 20% and 39%, respectively. The attached biomass could allow an IFAS system to be less inhibited and better maintain phosphorous removal at sudden FNA inhibition events.

Application of a Novel Functional Gene Microarray to Probe the Functional Ecology of Ammonia Oxidation in Nitrifying Activated Sludge

We report on the first study trialling a newly-developed, functional gene microarray (FGA) for characterising bacterial and archaeal ammonia oxidisers in activated sludge. Mixed liquor (ML) and media biofilm samples from a full-scale integrated fixed-film activated sludge (IFAS) plant were analysed with the FGA to profile the diversity and relative abundance of ammonia-oxidising archaea and bacteria (AOA and AOB respectively). FGA analyses of AOA and AOB communities revealed ubiquitous distribution of AOA across all samples – an important finding for these newly-discovered and poorly characterised organisms. Results also revealed striking differences in the functional ecology of attached versus suspended communities within the IFAS reactor. Quantitative assessment of AOB and AOA functional gene abundance revealed a dominance of AOB in the ML and approximately equal distribution of AOA and AOB in the media-attached biofilm. Subsequent correlations of functional gene abundance data with key water quality parameters suggested an important functional role for media-attached AOB in particular for IFAS reactor nitrification performance and indicate possible functional redundancy in some IFAS ammonia oxidiser communities. Results from this investigation demonstrate the capacity of the FGA to resolve subtle ecological shifts in key microbial communities in nitrifying activated sludge and indicate its value as a tool for better understanding the linkages between the ecology and performance of these engineered systems.

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.

Oxygen transfer and uptake, nutrient removal, and energy footprint of parallel full-scale IFAS and activated sludge processes

Integrated fixed-film activated sludge (IFAS) processes are becoming more popular for both secondary and sidestream treatment in wastewater facilities. These processes are a combination of biofilm reactors and activated sludge processes, achieved by introducing and retaining biofilm carrier media in activated sludge reactors. A full-scale train of three IFAS reactors equipped with AnoxKaldnes media and coarse-bubble aeration was tested using off-gas analysis. This was operated independently in parallel to an existing full-scale activated sludge process. Both processes achieved the same percent removal of COD and ammonia, despite the double oxygen demand on the IFAS reactors. In order to prevent kinetic limitations associated with DO diffusional gradients through the IFAS biofilm, this systems was operated at an elevated dissolved oxygen concentration, in line with the manufacturer’s recommendation. Also, to avoid media coalescence on the reactor surface and promote biofilm contact with the substrate, high mixing requirements are specified. Therefore, the air flux in the IFAS reactors was much higher than that of the parallel activated sludge reactors. However, the standardized oxygen transfer efficiency in process water was almost same for both processes. In theory, when the oxygen transfer efficiency is the same, the air used per unit load removed should be the same. However, due to the high DO and mixing requirements, the IFAS reactors were characterized by elevated air flux and air use per unit load treated. This directly reflected in the relative energy footprint for aeration, which in this case was much higher for the IFAS system than activated sludge.

Diagnosis and Quantification of Glycerol Assimilating Denitrifying Bacteria in an Integrated Fixed-Film Activated Sludge Reactor via13C DNA Stable-Isotope Probing

Glycerol, a byproduct of biodiesel and oleo-chemical manufacturing operations, represents an attractive alternate to methanol as a carbon and electron donor for enhanced denitrification. However, unlike methanol, little is known about the diversity and activity of glycerol assimilating bacteria in activated sludge. In this study, the microbial ecology of glycerol assimilating denitrifying bacteria in a sequencing batch integrated fixed film activated sludge (SB-IFAS) reactor was investigated using (13)C-DNA stable isotope probing (SIP). During steady state SB-IFAS reactor operation, near complete nitrate removal (92.7 ± 5.8%) was achieved. Based on (13)C DNA clone libraries obtained after 360 days of SB-IFAS reactor operation, bacteria related to Comamonas spp. and Diaphorobacter spp. dominated in the suspended phase communities. (13)C assimilating members in the biofilm community were phylogenetically more diverse and were related to Comamonas spp., Bradyrhizobium spp., and Tessaracoccus spp. Possibly owing to greater substrate availability in the suspended phase, the glycerol-assimilating denitrifying populations (quantified by real-time PCR) were more abundant therein than in the biofilm phase. The biomass in the suspended phase also had a higher specific denitrification rate than the biofilm phase (p = 4.33e-4), and contributed to 69.7 ± 4.5% of the overall N-removal on a mass basis. The kinetics of glycerol based denitrification by suspended phase biomass were approximately 3 times higher than with methanol. Previously identified methanol assimilating denitrifying bacteria were not associated with glycerol assimilation, thereby suggesting limited cross-utilization of these two substrates for denitrification in the system tested.