Integrated Fixed-film Activated Sludge System Research Articles

Comprehensive comparison of integrated fixed-film activated sludge (IFAS) and AAO activated sludge methods: Influence of different operational parameters

Due to limited land availability in municipal wastewater treatment plants, integrated fixed-film activated sludge (IFAS) technology offers significant advantages in improving nitrogen removal performance and treatment capacity. In this study, two systems, IFAS and Anaerobic-Anoxic-Oxic Activated sludge process (AAO), were compared by adjusting parameters such as hydraulic retention time (HRT), nitrifying solution recycle ratio, sludge recycle ratio, and dissolved oxygen (DO). The objective was to investigate pollutant removal capacity and differences in microbial community composition between the two systems. The study showed that, at an HRT of 12 h, the IFAS system exhibited an average increase of 5.76%, 8.85%, and 12.79% in COD, NH4+-N, and TN removal efficiency respectively, compared to the AAO system at an HRT of 16 h. The TP concentration in the IFAS system reached 0.82 mg/L without the use of additives. The IFAS system demonstrated superior effluent results under lower operating conditions of HRT, nitrification solution recycle ratio, and DO. The 16S rDNA analysis revealed higher abundance of denitrification-related associated flora, including Proteobacteria, Bacteroidetes, and Planctomycetota, in the IFAS system compared to the AAO system. Similarities were observed between microorganisms attached to the media and activated sludge in the anaerobic, anoxic, and oxic tanks. q-PCR analysis indicated that the incorporation of filler material in the IFAS system resulted in similar abundance of nitrifying bacteria genes on the biofilm as in the oxic tank. Additionally, denitrifying genes showed higher levels due to aeration scouring and the presence of alternating aerobic-anaerobic environments on the biofilm surface, enhancing nitrogen removal efficiency.

Deciphering the role of hydraulic retention time (HRT) in integrated fixed-film activated sludge (IFAS) system under aniline stress: Effects on microbial succession and communication

Integrated fixed-film activated sludge (IFAS) system offered an energy-efficient option for nitrogen removal from aniline wastewater. The regulation of hydraulic retention time (HRT) has been reported to affect the fate of functional microbial communities with different generation cycles, but the role of HRT in IFAS under aniline stress has not been sufficiently revealed. Herein, it was observed that shortening the HRT altered the mechanisms underlying the adaptation of a continuous flow micro-aerated IFAS system to aniline stress, thereby negligibly impacting the removal of aniline. The total nitrogen removal rate in Y2 (HRT = 0.5 day) was 40.28 % higher than Y1 (1 day), and 23.7 % higher than Y3 (0.25 day). This could be attributed to Y2 having an ample supply of electron donors for denitrification compared to Y1, as well as showing weaker stress to inhibit nitrification compared to Y3. Furthermore, with the progressive intensification of stress induced by HRT reduction, microorganisms gradually enhanced their adaptation to aniline. This led to an increased migration of microorganisms towards the inner layers of the biofilm, resulting in enhanced functional complementarity between the sludge and biofilm in Y2. Also, there was a distinct development of autotrophic denitrification, with arenimonas predominant in Y1, and Thauera predominant in Y2 and Y3. Moreover, Y2 possessed a high abundance of functional genes related to the production and reception of quorum sensing signal molecules, which may enhance the electron transport-dependent nitrogen metabolism reaction.

Efficient nitrogen removal and substrate usage in integrated fixed-film activated sludge-anammox system under seasonal temperature variation

To elucidate how integrated fixed-film activated sludge (IFAS) system favors nitrogen removal performance under seasonal temperature variations, two push-flow reactors were operated with and without carriers under the same operating conditions. The results show that the IFAS system had significant advantages in shock response and low temperature adaptation, with a nitrogen removal rate of 0.37–0.53 kg-N(m3·d)-1 at the temperature of 8–12 °C. Anammox bacteria on carriers were almost unaffected by temperature variation, and its nitrogen removal contribution rate stabilized at 55 % in the IFAS system. The Haldane model reveals that the specific anammox activity in the IFAS system was 28 % to 49 % higher than that in the control system at 13 °C. Candidatus_Jettenia, with the highest abundance of 45 %, was the dominant species in the IFAS system and preferred to attach to the carriers. This study provides a feasible scheme for the application of anammox process.

Unveiling the roles of biofilm in reducing N2O emission in a nitrifying integrated fixed-film activated sludge (IFAS) system.

Biofilm process such as integrated fixed-film activated sludge (IFAS) system has been preliminarily found to produce less nitrous oxide (N2O) than suspended sludge system. However, the N2O emission behaviors and underlying N2O mitigation mechanism in such hybrid system remain unclear. This study therefore aims to fully unveil the roles of biofilm in reducing N2O emission in a nitrifying IFAS system with the aid of some advanced technologies such as N2O microsensor and site-preference analysis. It was found that ammonia oxidation occurred mostly in the sludge flocs (˃ 86%) and biofilm could reduce N2O emission by 43.77% in a typical operating cycle. Biofilm not only reduced nitrite accumulation in nitrification process, inhibiting N2O production via nitrifier denitrification pathway, but also served as a N2O sink, promoting the reduction of N2O via endogenous denitrification. As a result, N2O emissions from the IFAS system were 50%-83% lower than those from the solo sludge flocs. Further, more N2O emission was reduced in the presence of biofilm with decreasing the dissolved oxygen level in the range of 0.5-3.0 mg O2/L. Microbial community and key enzyme analyses revealed that biofilm had relatively high microbial diversity and unique enzyme composition, providing a reasonable explanation for the changed contributions of different N2O production pathways and reduced N2O emission.

Operational strategies enhancing sewage sludge minimization in a combined integrated fixed-film activated sludge – oxic settling anaerobic system

A lab-scale integrated fixed-film activated sludge (IFAS) reactor was mplemented with the oxic-settling anaerobic (OSA) cycle for reducing sewage sludge production through the addition of an anoxic/anaerobic sludge holding tank (SHT) along the sludge recycle line. The IFAS-OSA system was operated under the different hydraulic retention time (HRT) in the SHT (HRTSHT) of 12 h and 6 h, at an oxidation-reduction potential (ORP) < −91 mV and solid retention time (SRT) between 39 and 126 d. Furthermore, the effect of temperature increase in the SHT (TSHT) from ambient (19.8–25.6 °C) to mesophilic (35 °C) conditions was investigated. The system performances were monitored in terms of sludge minimization and dewaterability efficiencies as well as carbon and nutrients reduction. The observed sludge yield (Yobs) for the IFAS system was 0.37(±0.06) mg VSS/mg COD. After OSA implementation Yobs decreased by 32% and 46–65% at HRTSHT of 12 h and 6 h, respectively, indicating that prolonged exposure to anoxic/anaerobic conditions was not beneficial for sludge reduction. The lowest Yobs of 0.09(±0.05) mg VSS/mg COD (76% lower than that in the IFAS system) was obtained at an HRTSHT of 6 h and when TSHT was set at 35 °C. OSA implementation did not affect COD and NH4+ oxidation of the IFAS system (90–96% and 99%, respectively) and improved total nitrogen (TN) reduction (31–53%) due to improved denitrification in the SHT. On the contrary, sludge dewaterability worsened following OSA implementation, which was linked to the increased levels of exopolymeric substances in the suspended biomass.

Effect of dissolved oxygen concentration on performance and mechanism of simultaneous nitrification and denitrification in integrated fixed-film activated sludge sequencing batch reactors

Integrated fixed-film activated sludge (IFAS) is a superior system for achieving simultaneous nitrification and denitrification (SND), however, the impact of dissolved oxygen (DO) has not been fully elucidated. Therefore, this study investigated the effect of DO concentration on performance and mechanism of SND in IFAS system. Results showed that IFAS outperformed control systems and achieved optimal SND performance at a DO concentration of 0.5 mg/L, with an SND efficiency of 88.51% and total nitrogen removal efficiency of 82.78%. Typical cycles analysis demonstrated limited-DO promoted SND performance. Further analysis implied biofilms exhibited high biomass and denitrification activity with decreasing DO. Microbial community analysis revealed low DO concentrations were responsible for abundant functional groups and genes associated with SND and promoted unconventional nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated microbial interactions, responses to DO, and keystone genera. This study helps understanding the roles of DO for enhanced SND in IFAS.

A novel cross-flow honeycomb bionic carrier promotes simultaneous nitrification, denitrification and phosphorus removal in IFAS system: Performance, mechanism and keystone species

Simultaneously achieving efficient nitrogen (N) and phosphorus (P) removal without adding external carbon source is vital for carbon-neutral wastewater treatment. In this study, a novel cross-flow honeycomb bionic microbial carrier (CF) was developed to improve the efficiency of simultaneous nitrification, denitrification, and P removal (SNDPR) in an integrated fixed-film activated sludge (IFAS) system. A parallel laboratory-scale sequencing batch reactor with the commercialized microbial carriers (CM) (CM-IFAS) was performed as the comparative system for over 233 d The results demonstrated that CF-IFAS exhibited a more consistent N removal efficiency and better performance than CM-IFAS. In the CF-IFAS, the highest N and P removal efficiencies were 95.40% and 100%, respectively. Typical cycle analysis revealed that nitrate was primarily removed by the denitrifying glycogen-accumulating organisms in the CF-IFAS and by denitrifying phosphate-accumulating organisms in the CM-IFAS. The neutral community model showed that the microbial community assembly in both the reactors was driven by deterministic selection rather than stochastic factors. Compared to those in CM-IFAS, the microorganisms in CF-IFAS were more closely related to each other and had more keystone species: norank_f_norank_o_norank_c_OM190, SM1A02, Defluviicoccus, norank_f_ Saprospiraceae, and norank_f_Rhodocyclaceae. The absolute contents of the genes associated with N removal (bacterial amoA, archaeal amoA, NarG, NapA, NirS, and NirK) were higher in CF-IFAS than in CM-IFAS; the N cycle activity was also stronger in the CF-IFAS. Overall, the microecological environment differed between both systems. This study provides novel insights into the potential of bionic carriers to improve SNDPR performance by shaping microbial communities, thereby providing scientific guidance for practical engineering.

Morphological and Spatial Heterogeneity of Microbial Communities in Pilot-Scale Autotrophic Integrated Fixed-Film Activated Sludge System Treating Coal to Ethylene Glycol Wastewater.

The understanding of microbial compositions in different dimensions is essential to achieve the successful design and operation of the partial nitritation/anammox (PN/A) process. This study investigated the microbial communities of different sludge morphologies and spatial distribution in the one-stage PN/A process of treating real coal to ethylene glycol (CtEG) wastewater at a pilot-scale integrated fixed-film activated sludge (IFAS) reactor. The results showed that ammonia-oxidizing bacteria (AOB) was mainly distributed in flocs (13.56 ± 3.16%), whereas anammox bacteria (AnAOB) was dominated in the biofilms (17.88 ± 8.05%). Furthermore, the dominant AnAOB genus in biofilms among the first three chambers was Candidatus Brocadia (6.46 ± 2.14% to 11.82 ± 6.33%), whereas it was unexpectedly transformed to Candidatus Kuenenia (9.47 ± 1.70%) and Candidatus Anammoxoglobus (8.56 ± 4.69%) in the last chamber. This demonstrated that the niche differentiation resulting from morphological (dissolved oxygen) and spatial heterogeneity (gradient distribution of nutrients and toxins) was the main reason for dominant bacterial distribution. Overall, this study presents more comprehensive information on the heterogeneous distribution and transformation of communities in PN/A processes, providing a theoretical basis for targeted culture and selection of microbial communities in practical engineering.

Analyzing the roles of cyclic dimeric guanosine monophosphate (c-di-GMP) on the formation of autotrophic granules and autotrophic biofilm in integrated fixed-film activated sludge (IFAS) reactor

This study is the first to reveal the important roles of c-di-GMP on the formation of autotrophic granular sludge (AUGS) and autotrophic biofilm (AUB) in integrated fixed-film activated sludge (IFAS) system. The results revealed that the partial nitrification/anammox (PN/A) performance was successfully developed in the IFAS system and high nitrogen removal efficiency was obtained. Notably, it was clearly indicated that the intracellular c-di-GMP content was highly linearly correlated with the concentration of protein (PN) in tightly bound extracellular polymeric substances (TB-EPS) during AUGS formation. It was also found that the c-di-GMP content was highly linearly correlated with the PN concentration during AUB formation, and also had a good linear correlation with the polysaccharide (PS) content in TB-EPS. This proves that intracellular c-di-GMP played a vital role in regulating the TB-EPS secretion, thereby further affecting the aggregation ability of AUGS and AUB. In addition, when the c-di-GMP regulates the content of PN in TB-EPS, the secondary structure of the PN also changes significantly correspondingly, affecting the hydrophobicity of AUGS and AUB. In long-term operation, Candidatus_Kuenenia, Nitrosomonas and Flavobacterium gradually became dominant species, which were considered to favor the formation of AUGS and AUB by promoting the production of c-di-GMP and TB-EPS.

Partial denitrification-anammox (PdNA) application in mainstream IFAS configuration using raw fermentate as carbon source.

This research examined the feasibility of raw fermentate for mainstream partial denitrification-anammox (PdNA) in a pre-anoxic integrated fixed-film activated sludge (IFAS) process. Fermentate quality sampled from a full-scale facility was highly dynamic, with 360-940 mg VFA-COD/L and VFA/soluble COD ratios ranging from 24% to 48%. This study showed that PdNA selection could be achieved even when using low quality fermentate. Nitrate residual was identified as the main factor driving the PdN efficiency, while management of nitrate conversion rates was required to maximize overall PdNA rates. AnAOB limitation was never observed in the IFAS system. Overall, this study showed PdN efficiencies up to 38% and PdNA rates up to 1.2 ± 0.7g TIN/m2 /d with further potential for improvements. As a result of both PdNA and full denitrification, this concept showed the potential to save 48-89% methanol and decrease the carbon footprint of water resource recovery facilities (WRRF) by 9-15%. PRACTITIONER POINTS: Application of PdNA with variable quality fermentate is feasible when the nitrate residual concentration is increased to enhance PdN selection. To maximize nitrogen removed through PdNA, nitrate conversion rates need enhancement through optimization of upstream aeration and PdN control setpoints. The IFAS PdNA process was never anammox limited; success depended on the degree of PdN achieved to make nitrite available. Application of PdNA with fermentate can yield 48-89% savings in methanol or other carbon compared with conventional nitrification and denitrification. Integrating PdNA upstream from polishing aeration and anoxic zones guarantees that stringent limits can be met (<5mg N/L).

COD/TN ratios shift the microbial community assembly of a pilot-scale shortcut nitrification-denitrification process for biogas slurry treatment.

In this study, effects of carbon to nitrogen (COD/TN) ratios of biogas slurry on shortcut nitrification-denitrification in a pilot-scale integrated fixed film activated sludge (IFAS) system were investigated. Lowering the COD/TN ratio from 11.7 to 6.2 exerted a negative impact on shortcut nitrification-denitrification performance. Accordingly, the NH3-N and TN removal rates decreased from 94.4 to 91.2% and 92.3 to 85.9%, respectively. The dynamics of microbial assembly was analyzed by MiSeq sequencing, and the denitrifying functional genes were quantified by qPCR. The results showed that ammonia oxidizing bacteria and amoA gene were more abundant on the biofilm of oxic tank, indicating they play a key role in NH3-N removal. Autotrophic, endogenous, and fast heterotrophic kinetics denitrifiers were coexisted and enriched in the IFAS system with a decreasing of COD/TN ratio. TN removal was mainly affected by denitrifiers (including Arenimonas, Acidovorax, and Thaurea) harboring narG and nirS genes. Canonical correspondence analysis proved that COD/TN ratio was the most critical factor driving the succession of microbial community. Dissolved oxygen (DO) and pH were found positively correlated with denitrifiers at low COD/TN ratio conditions. As a result, NH3-N and TN removal were effectively enhanced when the DO level in the oxic tank of IFAS system was increased to 1.0-3.0 mg/L.

Fate of sloughed biomass in integrated fixed-film systems.

Fate of biofilm sloughing was assessed in a laboratory-scale (LS) integrated fixed-film sequencing batch reactor (IF-SBR) treating synthetic wastewater and in a full-scale (FS) integrated fixed-film activated sludge (IFAS) system treating municipal wastewater. It was observed that the properties of biofilms and flocs, including sludge volume index (SVI), mixed liquor suspended solids (MLSS), effluent suspended solids (ESS), relative hydrophobicity, and composition of extracellular polymeric substance (EPS) were associated with biofilm sloughing and formation of large granular flocs in the LS IF–SBR. In the FS IFAS system, the changes were studied at the molecular level. For example, the extracted EPS content results (the protein to polysaccharide ratio decreased in the flocs and increased in the biofilms, with biofilm sloughing) were complemented with the confocal laser scanning microscopy (CLSM) coupled with molecular specific staining. CLSM analyses revealed that micro-colonies rich in polysaccharides readily sloughed from the carriers. Live-dead staining revealed areas of the biofilm where the viability of biomass was a contributing factor associated with areas of the biofilm susceptible to sloughing. 16S rRNA gene sequencing (Illumina) of FS IFAS samples revealed greater diversity (α-diversity) in biofilms compared to flocs. Biofilm sloughing resulted in a decrease in diversity in biofilms and a corresponding increase in the flocs during sloughing. Microbial population dynamics revealed that bacteria known for denitrification (for example, Comamonadaceae) detached from the biofilms during sloughing, readily associated with the suspended biomass, and were retained in the bioreactors.

Optimization nutrient removal at different volume ratio of anoxic-to-aerobic zone in integrated fixed-film activated sludge (IFAS) system

This study evaluated the influence of different volume ratios of the anoxic-to-aerobic zone (Vano/Vaer) on the enhancement of nitrogen and phosphorus removal in an integrated fixed-film activated sludge (IFAS) system. As the Vano/Vaer increased from 1:2 to 2:1, the removal of organic carbon, nitrogen and phosphorus nutrients of the IFAS system was improved. At Vano/Vaer = 1:1, the removal effect of nitrogen and phosphorus nutrients was optimal, and the average removal rates of COD, NH4+-N, TN, and TP of the system reached 90 ± 3.2%, 98.2 ± 1.4%, 88.9 ± 2.2%, and 89.1 ± 2.7%, respectively. As the volume of the anoxic zone continued to increase, the denitrifying phosphate-accumulating capacity of the system was enhanced, and the highest ratio of specific anoxic and aerobic phosphorus uptake rate could reach 65.3%. Analysis of the molecular evaluation showed that, the proportion of nitrifying bacteria in the biofilm gradually increased as Vano increased. Moreover, denitrifying phosphate-accumulating organisms (DNPAOs), ammonia-oxidizing archaea (AOA), and anaerobic ammonium oxidizing (Anammox) bacteria were all enriched all showed enrichment in the biofilm of fiber carriers, which further strengthened the system's synergistic removal of nitrogen and phosphorus.

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.

Experimental investigation of petrochemical industrial wastewater treatment by a combination of integrated fixed-film activated sludge (IFAS) and electro-Fenton methods

The toxic and dangerous wastewater from the petrochemical industry should be effectively treated before it is discharged into the environment. In this study, the electro-Fenton (EF) process was performed as a pre-treatment for petrochemical wastewater that resulted from olefin, methanol, aromatic, ammonia, and urea units. The effects of the solution pH, electric current, hydrogen peroxide (H2O2) concentration, and reaction time on chemical oxygen demand (COD) removal and sludge volume index (SVI) values were investigated. The treated wastewater of an EF process was used as feed for an integrated fixed-film activated sludge (IFAS) process. The effect of the ratio of the inlet wastewater volume to the activated sludge in the aeration tank and the influence of the fixed media and retention time on the IFAS system capacity were evaluated. The results showed that an increase in the electric current and H2O2 concentration led to an improvement in the COD removal while increasing the pH had a negative effect on the wastewater treatment. Furthermore, the initial pH of 3, electric current of 160 mA, H2O2 concentration of 65 mM, and reaction time of 30 min were introduced as optimum conditions for the subsequent stage of the treatment. Finally, the IFAS system demonstrated better performance than the conventional activated sludge (AS) method.

Adaptability of Nitrifying Biofilm Systems to Low Temperature: MBBR and IFAS

The long-term effects of a decreasing temperature on the nitrification performance, biofilm characteristics, and nitrifier community in a moving-bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS) system were investigated at various temperatures (20, 15, and 10℃) to explore the adaptability of nitrifying biofilm systems to low temperatures. During the experiment, the extracellular polymeric substances (EPS) in the biofilms increased with decreasing temperature, which resulted in an increased biofilm mass and thickness. As there was only a biofilm phase in the MBBR to remove ammonia, the part of the carriers in the MBBR at 10℃ became plugged, which partially led to a deterioration in the effluent water quality. This indicated that the IFAS system was more adaptable to low temperatures than was the MBBR. Meanwhile, the results for the nitrifier activities showed that, although the nitrification contribution rate of the suspended phase in the IFAS system always dominated during the experiment, that of the fixed phase with regards to the ammonia uptake rate (AUR) gradually increased from 30.72% at 20℃ to 39.85% at 10℃. This indicated that the biofilm played an enhanced role in nitrification in the IFAS system. Moreover, the qPCR results revealed that the nitrifier copies of the number of biofilms increased slightly with decreased temperature, and coincided with an increase in biomass, which partially compensated for the decreased nitrification activity. These findings provide a theoretical basis for the application of the biofilm systems to wastewater treatment.

Contrasting distribution of antibiotic resistance genes and microbial communities in suspended activated sludge versus attached biofilms in an integrated fixed film activated sludge (IFAS) system

Suspended activated sludge (AS) and carrier-attached biofilms simultaneously exist in an integrated fixed film activated sludge (IFAS) system. However, the differentiation of antibiotic resistance genes (ARGs) and microbial communities in different types of biofilms is rarely reported. In this study, successions of ARGs and microbial communities of AS and two types of suspended carrier-attached biofilms over seasons were investigated in the IFAS system of one municipal wastewater treatment plant. Results showed that substantial differences were found in the distribution pattern of ARGs, bacterial communities, and predicted microbial function between AS and attached biofilms. The relative abundances of all detected ARGs in AS were significantly higher than those in attached biofilms. ARGs with higher relative abundances generally existed in K3 carrier (surface area ≥ 800 m2/m3) attached biofilms than those in K1 carrier (surface area ≥ 450 m2/m3) biofilms. The relative abundances of ARGs were negatively correlated with temperature and biochemical oxygen demand (BOD5) and positively correlated with ammonium nitrogen contents for AS but not for attached biofilms. No significant relationship was found between the extracellular polymeric substance (EPS) content and ARG abundance for all samples. Temperature, BOD5, and ammonium nitrogen contents were closely connected to microbial communities. The Bray–Curtis distance of bacterial communities between two adjacent sampling seasons for AS was larger than those of two attached biofilms. Network analysis indicated that the AS network had more positive links and intense connections than the attached biofilm networks, potentially facilitating the dissemination of ARGs. The differential distribution of ARGs among the three types of samples was significantly correlated with the microbial co-occurrence network topological properties. Bray–Curtis distance and network analysis suggest that microbial community is more robust in attached biofilms than in suspended AS. This work provides a more in-depth understanding of ARGs and microbial community distributions in wastewater biofilms.

Loofah Sponges as Bio-Carriers in a Pilot-Scale Integrated Fixed-Film Activated Sludge System for Municipal Wastewater Treatment

Fixed-film biofilm reactors are considered one of the most effective wastewater treatment processes, however, the cost of their plastic bio-carriers makes them less attractive for application in developing countries. This study evaluated loofah sponges, an eco-friendly renewable agricultural product, as bio-carriers in a pilot-scale integrated fixed-film activated sludge (IFAS) system for the treatment of municipal wastewater. Tests showed that pristine loofah sponges disintegrated within two weeks resulting in a decrease in the treatment efficiencies. Accordingly, loofah sponges were modified by coating them with CaCO3 and polymer. IFAS pilot tests using the modified loofah sponges achieved 83% organic removal and 71% total nitrogen removal and met Vietnam’s wastewater effluent discharge standards. The system achieved considerably high levels of nitrification and it was not limited by the loading rate or dissolved oxygen levels. Cell concentrations in the carriers were twenty to forty times higher than those within the aeration tank. Through 16S-rRNA sequencing, the major micro-organism types identified were Kluyvera cryocrescens, Exiguobacterium indicum, Bacillus tropicus, Aeromonas hydrophila, Enterobacter cloacae, and Pseudomonas turukhanskensis. This study demonstrated that although modified loofah sponges are effective renewable bio-carriers for municipal wastewater treatment, longer-term testing is recommended.

Biodegradation of high acrylamide concentrations in integrated fixed film activated sludge (IFAS) wastewater treatment system

The study was to evaluate the capacity of IFAS technology to enhance the acrylamide (AM) biodegradation in the biological wastewater treatment systems at high concentrations of 200, 300, 400, and 800 mg AM/L. Two sequencing batch reactor (SBR) systems operating as the IFAS and conventional activated sludge (AS) were operated at the solids retention time (SRT) of 9.0 days and hydraulic retention time (HRT) of 24 h at the operating temperature of about 28 °C. The experimental results revealed that the mixed culture bacteria in the IFAS system biodegraded acrylamide at the removal efficiencies of 64.9, 82.4, 99.5, and 86.3% while the AS system removed 36.4, 75.1, 71.8 and 55.9% at the acrylamide concentrations of 200, 300, 400, and 800 mg AM/L, respectively. As acrylamide concentrations increased in the wastewater, the sludge productions decreased due to the acrylamide toxicity, but the biodegradation rates increased resulting from less complexity of mixed substrates. Ammonia was stripped out due to relative high temperature and pH; therefore, the ammonia inhibition effects on the acrylamide biodegradation were not found. Due to the media clogging, the diffusion of substrates was limited; therefore, biodegradation rates in the IFAS system were remarkably less than the AS system. It can be concluded that the IFAS was superior to the AS system because of additional fixed film biomass.

Simultaneous nitrogen and dissolved methane removal from an upflow anaerobic sludge blanket reactor effluent using an integrated fixed-film activated sludge system

One of the main drawbacks of upflow anaerobic sludge blanket (UASB) reactors that treat low-strength sewage at room temperature is related to the low quality of their effluents in terms of dissolved methane, organic matter, and nitrogen content. The present study aims to evaluate the feasibility of using an integrated fixed-film activated sludge (IFAS) system as an alternative post-treatment technology to mitigate the environmental impact of such effluents. For this purpose, a pilot plant composed of a UASB (120 L) followed by an IFAS (66 L) system was operated for 407 days. Special attention was paid to the suspended biomass retention capacity and the dissolved methane and nitrogen removal potential of the IFAS post-treatment system. Furthermore, the role of carriers on denitrification and nitrification processes and the microbial communities present in the biofilm were also analyzed. Average total chemical oxygen demand (CODT) and ammonium removal efficiencies of 92 ± 3% and around 57 ± 16% were attained throughout the entire operation, respectively. During a first period in which biomass was maintained in both biofilms and suspension, and nitrite was the main electron acceptor, maximum nitrogen removal and methane removal efficiencies of 32.5 mg TN L-1 and 93% were observed in the IFAS system, respectively. However, throughout the second period, in which suspended biomass was completely washed out from the IFAS system, and nitrate became the main electron acceptor, these values decreased to 18 ± 4 mg TN Lfeed-1 and 77 ± 12%, respectively. Surprisingly, throughout the entire operation, it was observed that around 50 and 41% of the total nitrogen and methane removals observed in the IFAS system, respectively, were carried out in the aerobic compartment. Aerobic methane oxidizers and anammox were detected with significant relative abundances in the biofilm carriers used in the anoxic and aerobic compartments using 16S rRNA gene amplicon sequencing analysis. Therefore, the use of an IFAS system could be suited to diminish greenhouse gas emissions and nutrients concentration for those sewage treatment plants that used UASB systems, especially in countries with temperate and warm climates.