Process optimization by decoupled control of key microbial populations: distribution of activity and abundance of polyphosphate-accumulating organisms and nitrifying populations in a full-scale IFAS-EBPR plant

Effects of a novel sawdust-modified carrier on performance, bioaccumulation and microbial community of sequencing batch reactor

The impact of a novel sawdust-modified carrier on the performance of aerobic sequencing batch reactor (SBR) was examined. Compared with the conventional polyethylene (PE) carrier, the sawdust-modified carrier had coarse surface and porous side wall, which was beneficial for the rapid formation of biofilm. The biomass of sawdust-modified carrier was 3.4 ± 0.7 times more than those of PE carrier at the end of this study. The biofilm gotten from suspended carrier had higher extracellular polymeric substances (EPS) concentrations than activated sludge (AS). The EPS from biofilm contained higher proportions of polysaccharides compared to those from AS. The SBR with addition of sawdust-modified carrier exhibited higher ammonia nitrogen removal efficiency (84.8%) than the one with addition of conventional PE carrier (73.1%) in a typical cycle at 12 h. The volumetric nitrification rates of modified carrier were higher than those of conventional PE carrier. High throughput sequencing revealed that sawdust-modified carriers exhibited greater microbial richness and diversity compared with traditional PE carriers. Saccharimonadales was the most predominant genus that removed organic matter under aerobic condition, whereas Nitrospira was the dominant nitrifying genus. The present study verifies the advantage of sawdust-modified carrier, which has the potential for the full-scale application in the future.

Research on carbon and nitrogen removal of tetramethylammonium hydroxide containing wastewater by combined anaerobic/integrated fixed film activated sludge process

Tetramethylammonium hydroxide (TMAH) is widely used as a developer and etchant in the thin-film transistor liquid crystal display industry, which is the main component of developer wastewater with low C/N ratio. This study investigated TMAH degradation by combined anaerobic/integrated fixed film activated sludge (A/IFAS) process, especially for nitrogen removal. Effects of process condition on the TMAH degradation were studied, including dissolved oxygen concentration in IFAS reactor and the temperature of anaerobic reactor. Especially, the nitrogen removal was studied through the monitoring of intermediate products during TMAH biodegradation. The results indicated that lower the anaerobic treatment temperature can provide more available organic matters to enhance the denitrification in the subsequent IFAS reactor. Less oxygen supply in the IFAS reactor contributed to simultaneous nitrification and denitrification. Removal efficiency of total organic carbon and total nitrogen was up to 95.8% and 80.7%, when the temperature of anaerobic treatment was controlled at 30 °C with the DO kept at 0.7 mg/L. It indicated that A/IFAS process was efficient in carbon and nitrogen removal for TMAH degradation. The results also confirmed intermediate products of TMAH biodegradation can be used as the electron donor during denitrification, including trimethylamine, dimethylamine and methylamine. Illumina MiSeq sequencing showed that Proteobacteria was the dominant phylum contribute to nitrogen removal. Compared to sludge flocs in IFAS reactor, richer community and higher microbial diversity were observed in the biofilm.

Research progress of anaerobic ammonium oxidation (Anammox) process based on integrated fixed-film activated sludge (IFAS)

The integrated fixed-film activated sludge (IFAS) process is considered one of the cutting-edge solutions to the traditional wastewater treatment challenges, allowing suspended sludge and attached biofilm to grow in the same system. In addition, the coupling of IFAS with anaerobic ammonium oxidation (Anammox) can further improve the efficiency of biological denitrification. This paper summarises the research progress of IFAS coupled with the anammox process, including partial nitrification anammox, simultaneous partial nitrification anammox and denitrification, and partial denitrification anammox technologies, and describes the factors that limit the development of related processes. The effects of dissolved oxygen, influent carbon source, sludge retention time, temperature, microbial community, and nitrite-oxidising bacteria inhibition methods on the anammox of IFAS are presented. At the same time, this paper gives an outlook on future research focus and engineering practice direction of the process.

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.

Ecological mechanisms of biofilm development in the hybrid sludge-biofilm process: Implications for process start-up and optimization

The hybrid sludge-biofilm processes have been widely applied for the construction or upgradation of biological wastewater treatment process. Ecological mechanisms of biofilm development remain unclear in the hybrid ecosystem, because of the intricate interactive effects between sludge and biofilms. Herein, the establishment principles of biofilms with distinct coexisting sludge amounts were uncovered by varying sludge retention times (SRTs) from 5 to 40 days in the hybrid process. With the increasing of SRTs, biofilm biomass decreased with the increase of suspended sludge, resulting in lower biofilm proportion. As estimated by the Gompertz growth model, the increased sludge amounts (i.e., higher SRTs of 20 and 40 days) prolonged the initial colonization stage and decreased the specific development rate of biofilms when compared to lower sludge amounts with the shorter SRTs (i.e., 5 and 10 days). Null model analysis demonstrated that deterministic homogenous selection could facilitate the colonization and accumulation of biofilms with less coexisting sludge (SRT of 10 days). However, stochastic ecological drift and homogenizing dispersal dominated the colonization and accumulation stages of biofilms with more coexisting sludge (SRT of 20 days), respectively. The ecological networks reflected that positively-related taxa presented taxonomic relatedness, whereas high inconsistency of taxonomic relatedness was observed among aggregate forms or development stages as affected by varied SRTs. The high incidence of intra-taxa co-occurrence patterns suggested that taxa with similar ecological niches could be specifically selected in biofilms when being exposed with less coexisting sludge. This study uncovered ecological mechanisms of biofilm development driven by varying the SRTs of suspended sludge, which would help to propose appropriate strategies for the efficient start-up and optimization of the hybrid sludge-biofilm system.

Effect of return activated sludge diversion ratio on phosphorus removal performance in side-stream enhanced biological phosphorus removal (S2EBPR) process

In this study, a lab-scale continuous flow side-stream enhanced biological phosphorus (P) removal (S2EBPR) reactor was operated for 247 days treating synthetic wastewater with influent carbon to phosphorus (C/P) ratio of 25.0 g COD/g P and influent PO43--P of 7.4 ± 0.3 mg P/L. The effect of the return activated sludge (RAS) diversion ratio on S2EBPR reactor was investigated by comparing P removal performance, microbial activity, and community structure. The results showed that the RAS diversion ratio of 8.0%, by yielding a side-stream sludge retention time (SRTSS) of ∼60 h, resulted in the lowest effluent PO43--P concentration of 0.5 ± 0.3 mg P/L. The results of in situ process profiles and ex situ P release and uptake batch tests under different RAS diversion conditions showed that the more anaerobic P release was obtained in the side-stream reactor, the higher the P removal efficiency and EBPR activity were achieved. The stoichiometric ratios observed in EBPR activity tests indicated a polyphosphate accumulating organisms (PAOs) metabolism mainly dependent on the glycolysis pathway. The results of microbial ecology analysis revealed that the optimized SRTSS would give a competitive advantage to PAOs in the S2EBPR process. By obtaining statistically reliable results, this study would provide guidance for wastewater treatment plants to achieve optimal P removal performance in S2EBPR configuration.

Toward Integrating EBPR and the Short-Cut Nitrogen Removal Process in a One-Stage System for Treating High-Strength Wastewater

Enhanced biological phosphorus removal (EBPR) is an economical and sustainable process for phosphorus removal from wastewater. Despite the widespread application of EBPR for low-strength domestic wastewater treatment, limited investigations have been conducted to apply EBPR to the high-strength wastewaters, particularly, the integration of EBPR and the short-cut nitrogen removal process in the one-stage system remains challenging. Herein, we reported a novel proof-of-concept demonstration of integrating EBPR and nitritation (oxidation of ammonium to nitrite) in a one-stage sequencing batch reactor to achieve simultaneous high-strength phosphorus and short-cut nitrogen removal. Excellent EBPR performance of effluent 0.8 ± 1.0 mg P/L and >99% removal efficiency was achieved fed with synthetic high-strength phosphorus wastewater. Long-term sludge acclimation proved that the dominant polyphosphate accumulating organisms (PAOs), Candidatus Accumulibacter, could evolve to a specific subtype that can tolerate the nitrite inhibition as revealed by operational taxonomic unit (OTU)-based oligotyping analysis. The EBPR kinetic and stoichiometric evaluations combined with the amplicon sequencing proved that the Candidatus Competibacter, as the dominant glycogen accumulating organisms (GAOs), could well coexist with PAOs (15.3-24.9% and 14.2-33.1%, respectively) and did not deteriorate the EBPR performance. The nitrification activity assessment, amplicon sequencing, and functional-based gene marker quantification verified that the unexpected nitrite accumulation (10.7-21.0 mg N/L) in the high-strength EBPR system was likely caused by the nitritation process, in which the nitrite-oxidizing bacteria (NOB) were successfully out-selected (<0.1% relative abundance). We hypothesized that the introduction of the anaerobic phase with high VFA concentrations could be the potential selection force for achieving nitritation based on the literature review and our preliminary batch tests. This study sheds light on developing a new feasible technical route for integrating EBPR with short-cut nitrogen removal for efficient high-strength wastewater treatment.

Effect of Operating Parameters on the Performance of Integrated Fixed-Film Activated Sludge for Wastewater Treatment

Integrated fixed-film activated sludge (IFAS) is a hybrid wastewater treatment process that combines suspended and attached growth. The current review provides an overview of the effect of operating parameters on the performance of IFAS and their implications for wastewater treatment. The operating parameters examined include hydraulic retention time (HRT), solids retention time (SRT), dissolved oxygen (DO) levels, temperature, nutrient loading rates, and aeration. Proper control and optimization of these parameters significantly enhance the treatment efficiency and pollutant removal. Longer HRT and appropriate SRT contribute to improved organic matter and nutrient removal. DO levels promote the growth of aerobic microorganisms, leading to enhanced organic matter degradation. Temperature influences microbial activity and enzymatic reactions, impacting treatment efficiency. Nutrient loading rates must be carefully managed to avoid system overload or inhibition. Effective aeration ensures uniform distribution of wastewater and biofilm carriers, optimizing contact between microorganisms and pollutants. IFAS has been used in water reuse applications, providing a sustainable and reliable water source for non-potable uses. Overall, IFAS has proven to be an effective and efficient treatment process that can provide high-quality effluent suitable for discharge or reuse. Understanding the effects of these operating parameters helps to optimize the design and operation for efficient wastewater treatment. Further research is needed to explore the interactions between different parameters, evaluate their impact under varying wastewater characteristics, and develop advanced control strategies for improved performance and sustainability.

Microbial indicators of efficient performance in an anaerobic/anoxic/aerobic integrated fixed-film activated sludge (A2O-IFAS) and a two-stage mesophilic anaerobic digestion process

An analysis of the community structure, diversity and population dynamics of Bacteria and Archaea in the suspended and attached biomass fractions of a pilot-scale anaerobic/anoxic/aerobic integrated fixed-film activated sludge (A²O-IFAS) was executed. Along with this, the effluents of the acidogenic (AcD) and methanogenic (MD) digesters of a two-stage mesophilic anaerobic (MAD) system treating the primary sludge (PS) and waste activated sludge (WAS) generated by the A²O-IFAS were also analyzed. Non-metric multidimensional scaling (MDS) and Biota-environment (BIO-ENV) multivariate analyses were performed to link population dynamics of Bacteria and Archaea to operating parameters and removal efficiencies of organic matter and nutrients, in search of microbial indicators associated with optimal performance. In all samples analyzed, Proteobacteria, Bacteroidetes and Chloroflexi were the most abundant phyla, while the hydrogenotrophic methanogens Methanolinea, Methanocorpusculum and Methanobacterium were the predominant archaeal genera. BIO-ENV analysis disclosed strong correlations between the population shifts observed in the suspended and attached bacterial communities of the A²O-IFAS and the removal rates of organic matter, N and P. It is noteworthy that the incorporation of carriers combined with a short sludge retention time (SRT = 4.0 ± 1.0 days) enhanced N removal performance of the A²O by favoring the enrichment of bacterial genera able to denitrify (Bosea, Dechloromonas, Devosia, Hyphomicrobium, Rhodobacter, Rhodoplanes, Rubrivivax, and Sulfuritalea) in the attached biomass fraction. In addition, operation at short SRT enabled the generation of a highly biodegradable WAS, which enhanced the biogas and methane yields in the two-stage MAD. An increase in the relative abundance of Acetobacteroides (uncultured Blvii28 wastewater-sludge group of Rikenellaceae family) correlated positively with the volatile solids removal rate (%VSR), CH₄ recovery rate and %CH₄ in the biogas (r > 0.8), supporting their relevance for an efficient methanogenesis in two-stage systems.

Deciphering community assembly and succession in sequencing batch moving bed biofilm reactor: Differentiation between attached and suspended communities

Elucidating community assembly and succession is crucial to understanding the ecosystem functioning. Herein, the ecological processes underpinning community assembly and succession were studied to uncover the respective ecological functions of attached biofilms and suspended biomass in a sequencing batch moving bed biofilm reactor. Compared with suspended biomass, attached biofilms presented higher relative abundances of Nitrospira (2.94 %) and Nitrosomonas (1.25 %), and contributed to 66.89 ± 11.37 % and 68.11 ± 12.72 % of nitrification and denitrification activities, respectively. The microbial source tracking result demonstrated that early formation of suspended biomass was dominated by the seeding effect of detached biofilms in the start-up period (days 0-30), while self-growth of previous suspended biomass was eventually outcompeted the seeding effect when the reactor stabilized (days 31-120). Null model and ecological network analysis further suggested distinctive ecological processes underpinning the differentiation between attached and suspended communities in the same reactor. Specifically, in the start-up period, positive interactions facilitated early formation of attached (73.84 %) and suspended communities (59.41 %), while homogenous selection (88.89 %) and homogenizing dispersal (65.71 %) governed assembly of attached and suspended communities, respectively. When the reactor stabilized, attached and suspended communities showed low composition turnover as reflected by dominant homogenizing dispersal, while they presented distinctive trends of interspecies interactions. This study sheds light on discrepant ecological processes governing community differentiation of attached biofilms and suspended biomass, which would provide ecological insights into the regulation of hybrid ecosystems.

Impact of operational strategies on a sidestream enhanced biological phosphorus removal (S2EBPR) reactor in a carbon limited wastewater plant

Water resource recovery facilities are faced with stringent effluent phosphorus limits to reduce nutrient pollution. Enhanced biological phosphorus removal (EBPR) is the most common biological route to remove phosphorus; however, many facilities struggle to achieve consistent performance due to limited carbon availability in the influent wastewater. A promising process to improve carbon availability is through return activated sludge (RAS) fermentation via sidestream EBPR (S2EBPR). In this study, a full-scale S2EBPR pilot was operated with a sidestream plus carbon configuration (SSRC) at a carbon-limited facility. A model based on the pilot test was developed and calibrated in the SUMO platform and used to explore routes for improving orthophosphate (OP) effluent compliance. Modeling results showed that RAS diversion by itself was not sufficient to drive OP removal to permit limits of 1 mg L^-1, therefore, other strategies were evaluated. Supplemental carbon addition of MicroC® at 1.90 L min^-1 and controlling the phosphorus concentration below 3.5 mgP L^-1 in the primary effluent (PE) proved to be valid supplemental strategies to achieve OP removal below 1 mg L^-1 most of the time. In particular, the proposed supplemental carbon flow rate would result in an improvement of the rbCOD:P ratio from 17:1 to 26:1. The synergistic approach of RAS diversion and supplemental carbon addition increased the polyphosphate accumulating organisms (PAO) population while minimizing the supplemental carbon needed to achieve consistent phosphorus removal. Overall, this pilot and modeling study shows that joint strategies, including RAS diversion, carbon addition and PE control, can be effective to achieve optimal control of OP effluent.

Enhanced biological phosphorus and nitrogen removal by high-concentration powder carriers: extracellular polymeric substance, microbial communities, and metabolic pathways

In this study, diatomite, activated carbon, and iron-carbon (Fe-C) were used as biological carriers for the integrated fixed-film activated sludge process. Biomass, pollutant removal efficiency, and extracellular polymer were tested, and the effect of nitrogen and phosphorus removal, enzyme activity, and microbial diversity were studied after the sludge retention time was changed. The mechanism of carrier enriching microorganism and promoting pollutant degradation was studied. The results showed that the addition of these three carriers contributed to the enrichment of nitrifying bacteria in the system, and the NH₄⁺-N removal efficiency was above 98%. Diatomite and Fe-C could improve pollutant removal by increasing the activity of the electron transfer system. The abundance of denitrogenation-related reductases and the enzymes synthesizing poly-β-hydroxybutyrate was increased in activated carbon. The addition of Fe-C increased the abundance of denitrifying phosphate-accumulating organisms by approximately 25% and the removal efficiency of total phosphorus by 12.61-14.88% at the end of the long-term operation.

Nitrification kinetics, N2O emission, and energy use in intermittently aerated hybrid reactor under different organic loading rates

This study investigated the impact of intermittent aeration strategies and reduction in the reactor's organic and nitrogen loading rates on the course of particular stages of the nitrification process, as well as energy consumption and N2O emissions in a hybrid reactor with nitrification/denitrification. Each of the analysed series revealed the greatest ammonia oxidation activity in activated sludge flocs. The highest activity of nitrite nitrogen oxidation was demonstrated in the case of biofilm. A reduction in the reactor's organic and nitrogen loading rate value had a greater effect on changes in the activity of ammonia-oxidizing bacteria than nitrite-oxidizing bacteria. In a system where the operation of air pumps was controlled through switching them and off according to the adopted ratio between non-aerated and aerated sub-phase times and the assumed oxygen concentration, a reduction in the duration of aerated sub-phases caused no decrease in energy use for aeration. Lower N2O emission was recorded when the reactor operated with a longer duration of aerated sub-phases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13762-022-04715-6.

Metagenomics reveals a full-scale modified integrated fixed-film activated sludge process: Enhanced nitrogen removal and reduced sludge production

This study provides a side-by-side comparative investigation between the full-scale conventional activated sludge (CAS) and the high-concentration powder carrier bio-fluidized bed (HPB) processes. The results showed that the HPB total nitrogen removal efficiency increased by 10.86 % more than CAS. The anammox pathway increased by 6.92 %, while the simultaneous nitrification-denitrification pathway increased by 4.27 %. Also, the effluent's total nitrogen of the HPB process was stabilized below 10 mg/L, which can withstand the impact of industrial wastewater better. More energy and substance (protein) were consumed to attach to the carriers and resist external selective pressure to produce extracellular polymeric substance rather than sludge production in the HPB process. For a 10,000 m³/d HPB wastewater treatment plant, lowering the total nitrogen and sludge production saved $110,369.64 in annual operating costs.

Microbial composition and nitrogen removal pathways in a novel sequencing batch reactor integrated with semi-fixed biofilm carrier: evidence from a pilot study for low- and high-strength sewage treatment

The sequencing batch reactor (SBR) activated sludge process is a well-established technology for sewage treatment. One of the drawbacks of SBRs, however, total nitrogen (TN) removals is insufficient. By means of introducing four improvements, including semi-fixed biofilm carrier, sludge elevation mixing and change for the mode of influent and effluent, compliant standard for TN discharge was obtained in this novel SBR configuration during low- and high-strength sewage load. To illustrate the microbial compositions and functions of the attached biofilm on semi-fixed carrier and the suspended aggregates, as well as the nitrogen removal pathway, high throughput 16S rRNA gene amplicon sequencing, PICRUSt2 algorithm, and KEGG database were applied. The results revealed that (i) the microbial communities from suspended aggregates and biofilm samples were significantly different from each other; (ii) during low-strength sewage loads, TN removal was mainly by nitrification-denitrification. The suspended aggregates was responsible for denitrification, while the biofilm was focused on ammonium oxidation; (iii) during high-strength sewage loads, function of nitrate reductase from suspended aggregates was faded, and anammox and N assimilation by biofilm became dominant. Meanwhile, TN removal referring to the formation of L-glutamine via assimilation was the main pathway.

Phosphorous removal and recovery from urban wastewater: Current practices and new directions

Phosphate rocks are an irreplaceable resource to produce fertilizers, but their availability will not be enough to meet the increasing demands of agriculture for food production. At the same time, the accumulation of phosphorous discharged by municipal wastewater treatment plants (WWTPs) is one of the main causes of eutrophication. In a perspective of circular economy, WWTPs play a key role in phosphorous management. Indeed, phosphorus removal and recovery from WWTPs can both reduce the occurrence of eutrophication and contribute to meeting the demand for phosphorus-based fertilizers. Phosphorous removal and recovery are interconnected phases in WWTP with the former generally involved in the mainstream treatment, while the latter on the side streams. Indeed, by reducing phosphorus concentration in the WWTP side streams, a further improvement of the overall phosphorus removal from the WWTP influent can be obtained. Many studies and patents have been recently focused on treatments and processes aimed at the removal and recovery of phosphorous from wastewater and sewage sludge. Notably, new advances on biological and material sciences are constantly put at the service of conventional or unconventional wastewater treatments to increase the phosphorous removal efficiency and/or reduce the treatment costs. Similarly, many studies have been devoted to the development of processes aimed at the recovery of phosphorus from wastewaters and sludge to produce fertilizers, and a wide range of recovery percentages is reported as a function of the different technologies applied (from 10-25% up to 70-90% of the phosphorous in the WWTP influent). In view of forthcoming and inevitable regulations on phosphorous removal and recovery from WWTP streams, this review summarizes the main recent advances in this field to provide the scientific and technical community with an updated and useful tool for choosing the best strategy to adopt during the design or upgrading of WWTPs.

Modeling, simulation and control of biological and chemical P-removal processes for membrane bioreactors (MBRs) from lab to full-scale applications: State of the art

Phosphorus (P) removal from the domestic wastewater is required to counter the eutrophication in receiving water bodies and is mandated by the regulatory frameworks in several countries with discharge limits within 1-2mgPL-1. Operating at higher sludge retention time (SRT) and higher biomass concentration than the conventional activated sludge process (CASP), membrane bioreactors (MBRs) are able to remove 70-98% phosphorus without addition of coagulant. In full-scale facilities, enhanced biological phosphorus removal (EBPR) is assisted by the addition of metal coagulant to ensure >95% P-removal. MBRs are successfully used for super-large-scale wastewater treatment facilities (capacity >100,000 m3d-1). This paper documents the knowledge of P-removal modeling from lab to full-scale submerged MBRs and assesses the existing mathematical models for P-removal from domestic wastewater. There are still limited studies involving integrated modeling of the MBRs (full/super large-scale), considering the complex interactions among biology, chemical addition, filtration, and fouling. This paper analyses the design configurations and the parameters affecting the biological and chemical P-removal in MBRs to understand the P-removal process sensitivity and their implications for the modeling studies. Furthermore, it thoroughly reviews the applications of bio-kinetic and chemical precipitation models to MBRs for assessing their effectiveness with default stoichiometric and kinetic parameters and the extent to which these parameters have been calibrated/adjusted to simulate the P-removal successfully. It also presents a brief overview and comparison of seven (7) chemical precipitation models, along with a quick comparison of commercially available simulators. In addition to advantages associated with chemical precipitation for P-removal, its role in changing the relative abundance of the microbial community responsible for P-removal and denitrification and the controversial role in fouling mitigation/increase are discussed. Lastly, it encompasses several coagulant dosing control systems and their applications in the pilot to full-scale facilities to save coagulants and optimize the P-removal performance.

Analysis of the Status and Improvement of Microalgal Phosphorus Removal from Municipal Wastewater

Phosphorus, as one of the main pollutants in municipal sewage, has received increasing attention recently. Phosphorus recovery also increases the sustainable development of municipal wastewater. Since algae have the ability to effectively redirect nutrients, including phosphorus, from municipal sewage to algae biomass, municipal sewage treatments involving microalgae have piqued the interest of many researchers. The phosphorus removal depends on the potential of the microalgae to absorb, preserve, or degrade phosphorus in municipal wastewater. It is, therefore, of great interest to study the mechanisms underlying the absorption, storage, and degradation of phosphorus by microalgae to ensure the viability of this phosphorus removal process in wastewater. The objectives of this review were to summarize phosphorus metabolism in microalgae, examine key external and internal factors impacting phosphorous removal by microalgae from wastewater, and examine the status of phosphorous-metabolism-related research to improve our understanding of microalgae-based municipal wastewater treatments. In addition, the methods of recovery of microalgae after phosphorous removal were summarized to ensure the sustainability of municipal wastewater treatment. Finally, a potential approach using nanomaterials was proposed to enhance the overall phosphorous removal performance in municipal wastewater through the addition of nanoparticles such as magnesium and iron.

Characterization of domestic wastewater released from 'green' households and field study of the performance of onsite septic tanks retrofitted into aerobic bioreactors in cold climate

This study aimed to investigate the efficacy of private septic systems retrofitted into aerobic bioreactors with 'SludgeHammer' technology. In addition, the study attempted to characterize the strength of domestic wastewater released from 'green' households practicing water conservation strategies. Ten retrofitted onsite septic systems were studied in the Edmonton area, Alberta (AB) Canada during winter. These systems could remove BOD₅ and TSS by 92 ± 5 and 92 ± 6% respectively which, according to Albertan regulatory standards, were characteristic removal efficiencies of the secondary treatment in the subsequent drain field. These removal efficiencies were remarkable given the strength of the influent wastewater. The raw wastewater carried significantly high pollutant concentrations (1160 ± 350 mg BOD₅/L, 1653 ± 1174 mg TSS/L, 99 ± 19 mg NH₄⁺-N/L, 100 ± 56 mg TN/L, and 39 ± 28 mg PO₄^3--P/L), characterizing it as high-strength domestic wastewater. Mixing provided by the aerator could only suspend 1/34^th (3% m/m) of the solids in the bioreactor and consequently released significantly low solid concentrations (195 ± 206 mg TSS/L) into the final treatment component. As such, this technology did not impair the natural function of septic tanks or did not create any unintended excessive solid loading on drain field as a consequence of the added mixing energies provided by the active aeration. Nitrogen balance suggested the possibility of simultaneous nitrification and denitrification (SND) in the aerobic bioreactors. In some cases, PO₄^3--P removal efficiency was as high as that in enhanced biological phosphate removal (EBPR) process (81-97%). Phosphorus balance estimated that non-assimilative pathways (i.e., EBPR + biologically induced phosphate precipitation (BIPP)) contributed 50-99% to overall phosphorus removal in the system. Long HRTs, high influent BOD₅ and anaerobic/aerobic zoning in the bioreactor most likely provided favorable conditions for SND and high phosphorus removal efficiencies in the retrofitted onsite wastewater treatment systems (OWTS).

Recent progress in integrated fixed-film activated sludge process for wastewater treatment: A review

Integrated fixed-film activated sludge (IFAS) process is considered as one of the leading-edge processes that provides a sustainable solution for wastewater treatment. IFAS was introduced as an advancement of the moving bed biofilm reactor by integrating the attached and the suspended growth systems. IFAS offers advantages over the conventional activated sludge process such as reduced footprint, enhanced nutrient removal, complete nitrification, longer solids retention time and better removal of anthropogenic composites. IFAS has been recognized as an attractive option as stated from the results of many pilot and full scales studies. Generally, IFAS achieves >90% removals for combined chemical oxygen demand and ammonia, improves sludge settling properties and enhances operational stability. Recently developed IFAS reactors incorporate frameworks for either methane production, energy generation through algae, or microbial fuel cells. This review details the recent development in IFAS with the focus on the pilot and full-scale applications. The microbial community analyses of IFAS biofilm and floc are underlined along with the special emphasis on organics and nitrogen removals, as well as the future research perspectives.

Survey of full-scale sidestream enhanced biological phosphorus removal (S2EBPR) systems and comparison with conventional EBPRs in North America: Process stability, kinetics, and microbial populations

Sidestream EBPR (S2EBPR) is an emerging alternative process to address common challenges in EBPR related to weak wastewater influent and may improve EBPR process stability. A systematic evaluation and comparison of the process performance and microbial community structure was conducted between conventional and S2EBPR facilities in North America. The statistical analysis suggested higher performance stability in S2EBPR than conventional EBPR, although possible bias associated with other plant-specific factors might have affected the comparison. Variations in stoichiometric values related to EBPR activity and discrepancies between the observed values and current model predictions suggested a varying degree of metabolic versatility of PAOs in S2EBPR systems that warrant further investigation. Microbial community analysis using various techniques suggested comparable known candidate PAO relative abundances in S2EBPR and conventional EBPR systems, whereas the relative abundance of known candidate GAOs seemed to be consistently lower in S2EBPR facilities than conventional EBPR facilities. 16S rRNA gene sequencing analysis revealed differences in the community phylogenetic fingerprints between S2EBPR and conventional facilities and indicated statistically higher microbial diversity index values in S2EBPR facilities than those in conventional EBPRs. PRACTITIONER POINTS: Sidestream EBPR (S2EBPR) can be implemented with varying and flexible configurations, and they offer advantages over conventional configurations for addressing the common challenges in EBPR related to weak wastewater influent and may improve EBPR process stability. Survey of S2EBPR plants in North America suggested statistically more stable phosphorus removal performance in S2EBPR plants than conventional EBPRs, although possible bias might affect the comparison due to other plant-specific factors. The EBPR kinetics and stoichiometry of the S2EBPR facilities seemed to vary and are associated with metabolic versatility of PAOs in S2EBPR systems that warrant further investigation. The abundance of known candidate PAOs in S2EBPR plants was similar to those in conventional EBPRs, and the abundance of known candidate GAOs was generally lower in S2EBPR than conventional EBPR facilities. Further finer-resolution analysis of PAOs and GAOs, as well as identification of other unknown PAOs and GAOs, is needed. Microbial diversity is higher in S2EBPR facilities compared with conventional ones, implying that S2EBPR microbial communities could show better resilience to perturbations due to potential functional redundancy.

Impact of solid residence time (SRT) on functionally relevant microbial populations and performance in full-scale enhanced biological phosphorus removal (EBPR) systems

Investigations of the impact of solid residence time (SRT) on microbial ecology and performance of enhanced biological phosphorus removal (EBPR) process in full-scale systems have been scarce due to the challenges in isolating and examining the SRT from other complex plant-specific factors. This study performed a comprehensive evaluation of the influence of SRT on polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) dynamics and on P removal performance at Clark County Water Reclamation District Facility in Las Vegas, USA. Five parallel treatment trains with separated clarifiers were operated with five different SRTs ranging from 6 to 40 days. Microbial community analysis using multiple molecular and Raman techniques suggested that the relative abundances and diversity of PAOs and GAOs in EBPR systems are highly affected by the SRT. The resultant EBPR system stability and performance can be potentially controlled and optimized by manipulating the system SRT, and shorter SRT (<10 days) seems to be preferred. PRACTITIONER POINTS: Phosphorus removal performance and kinetics are highly affected by the operational solid residence time (SRT), with lower and more stable effluent P level achieved at SRT < 10 days. Excessive long SRTs above that needed for nitrification may harm EBPR performance; additionally, excessive long SRT may favor GAOs to dominate over PAOs and thus further reducing efficient use of rbCOD for EBPR. Microbial population abundance and diversity, especially those functionally relevant PAOs and GAOs, can impact the P removal performances, and they are highly dependent on the operational solid residence time. EBPR performance can be potentially controlled and optimized by manipulating the system SRT, and shorter SRT (≤10 days) seems to be preferred at the influent rbCOD/P ratio and environmental conditions as in the plant studied.

An improved ASM-GDA approach to evaluate the production kinetics of loosely bound and tightly bound extracellular polymeric substances in biological phosphorus removal process

This study established an extended activated sludge model no. 2 (ASM2) for providing a new recognition of the contributions of both loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) into phosphorus (P) removal by incorporating their formation and degradation processes during the anaerobic-aerobic cycle. For determining the best-fit values for the new model parameters (k _h,TB-EPS, k _h,LB-EPS, f _PP,TB-EPS, and f _PP,LB-EPS) in this extended ASM2, a novel and convenient gradient descent algorithm (GDA) based ASM (ASM-GDA) method was developed. Sensitivity analysis of f _PP,TB-EPS, f _PP,LB-EPS, k _h,TB-EPS, and k _h,LB-EPS on the model target outputs of S _PO4 , X _TB-EPS, X _LB-EPS, and X _PP proved the accuracy of the chosen parameters. Eight batch experiments conducted under different influential chemical oxygen demand (COD) and P conditions were quantitatively and qualitatively analyzed. Respectively, 9.37-9.64% and 4.17-4.29% of P removal by TB-EPS and LB-EPS were achieved. Self-Organizing Map (SOM) has shown its high performance for visualization and abstraction for exhibiting the high correlations of the influential COD/P concentrations and the P% removal by TB-EPS (and LB-EPS). Comprehensive analyses of the influences of influential COD and P concentration on the biological phosphorus removal process help us in successfully establishing the mechanism kinetics of production and degradation of P in a dynamic P biological-treatment model.

Optimization of nutrient removal of novel electrochemically active carriers by response surface methodology

In order to improve the nutrient removal capacity of the carriers in the integrated fixed-film activated sludge (IFAS) system, a novel electrochemically active carrier was developed in this study. The nutrient removal performance of the carrier under different operating conditions was deeply investigated based on response surface methodology. The higher concentration of mixed liquor suspended solid (MLSS) and lower dissolved oxygen (DO) value inhibited ammonium (NH₄⁺-N) removal performance of the carrier, while promoted total nitrogen (TN) depletion. Lower influent C/N ratio favored denitrification of the carrier. In addition, it was found that the enhanced removal of NH₄⁺-N and TN in IFAS depended not only on the increase of carrier biomass, but also on the electrochemical activity of the novel carrier. Under the most effective conditions, the novel carrier could improve the TN removal efficiency by 19.7% compared with the activated sludge process.

Moving bed biofilm reactor technology in municipal wastewater treatment: A review

The review encompasses the development of municipal wastewater treatment process using MBBR from early stages, established application, and recent advancements. An overview of main drivers leading to the MBBR technology development over its early stage is discussed. Biocarriers types and features together with biofilm development and role of extracellular polymeric substances (EPS) are presented, ultimately, addressing the challenge in decreasing startup time required for full operation. Furthermore, the review investigates the state of the art of MBBR technology for nutrient removal (i.e., COD and BOD, nitrogen and phosphorus) through process functionality and configuration of established (e.g., IFAS) and under development (e.g. PN/A) applications. Reactor operational characteristics such as filling fractions, mixing properties, dissolved oxygen requirements, and loading rates are presented and related to full scale examples. Current literature discussing the most recent studies on MBBR capability in reduction and removal of chemicals of emerging concern (CEC) released is presented. Ultimately, high rate carbon and nitrogen removal through A/B stage process are examined in its main operational parameters and its application towards energy neutrality suggesting novel MBBR application to further reduce energy requirements and plant footprint.

Quantify the contribution of anammox for enhanced nitrogen removal through metagenomic analysis and mass balance in an anoxic moving bed biofilm reactor

In this study, enhanced nitrogen removal through in situ enrichment of anammox bacteria was successfully obtained in a full-scale municipal wastewater treatment plant (WWTP). The WWTP was an anaerobic-anoxic-oxic (AAO) process and upgraded by adding moving carriers into the anoxic zone. Enhanced nitrogen removal was obtained during almost two years of operation. The significant nitrogen removal might be associated with the in situ enrichment of anammox bacteria on the adding carriers, as revealed by the comprehensive results of molecular analysis and ¹⁵N-stable isotope tracing tests. Quantitative PCR results indicated that anammox bacteria in the anoxic-carrier biofilms presented a higher abundance than flocculent sludge (16S rRNA: P < 0.005; HzsB: P < 0.042). The 16S rRNA amplicon sequencing showed significant differences in the phylum Planctomycetes (P < 0.001) between anoxic-carrier biofilms and flocculent sludge. And metagenomic sequencing analysis further revealed the anammox relative abundance in the anoxic-carrier biofilms was significantly higher than the reported level in the flocculent sludge of conventional WWTPs. In addition, ¹⁵N-stable isotope tracing tests showed that anammox could be combined with nitrate reduction by the anoxic-carrier biofilms. Thus, enriched anammox bacteria might contribute to nitrogen loss and lead to improvements in the nitrogen removal, which was also supported by the mass balance analysis of organic carbon, nitrogen, and phosphorus of the WWTP. Overall, this study suggests that anoxic-carrier biofilms might be a candidate to enhance nitrogen removal through partial anammox in municipal WWTPs.

Model-based evaluation of a trickling filter facility upgrade to biological nutrient removal

This article presents the feasibility evaluation and preliminary design of a wastewater treatment plant upgrade supported by simulation. The existing facility was based on trickling filters, and the objective of the upgrade was to achieve nutrients removal. The proposed solution modifies the existing primary clarifier to host an anaerobic-anoxic suspended growth reactor, which is an alternative that, to our knowledge, has not been proposed or explored so far. The trickling filters would remain as aerobic reactors. In this study, the novel treatment scheme has been assessed for the first time, through model simulations. The modified treatment train was simulated, showing that the anoxic zone is able to denitrify satisfactorily achieving the required effluent nitrogen concentration. However, to promote biological phosphorus removal, an additional aerobic zone combined with a bypass of activated sludge from the anoxic zone to the first trickling filter is needed, in order to provide aerobic conditions to the phosphate accumulating organisms. Several combinations of additional aerobic volume and sludge bypass flowrate were found to successfully achieve both nitrogen and phosphorus removal, using the existing facilities without the need for new reactors neither implementing modifications that could put the trickling filters' physical integrity at risk. The novel treatment scheme could be applied in other cases with similar flowsheet in the same context.

Trace organic contaminant removal in six full-scale integrated fixed-film activated sludge (IFAS) systems treating municipal wastewater

Trace organic contaminants (TrOCs) often pass through conventional activated sludge wastewater treatment plants (CAS-WWTPs) and are discharged into surface waters, where they can threaten aquatic ecosystems and human health, largely due to the hormone disrupting effects of certain TrOCs. The integrated fixed-film activated sludge (IFAS) process is a cost-effective means of upgrading CAS-WWTPs by adding free-floating carrier media, which promotes biofilm formation in the well-mixed suspended growth reactors, providing a potential niche for slow-growing microorganisms. Although IFAS upgrades are typically aimed at enhancing nutrient removal, limited bench- and pilot-scale data indicate that TrOC removal may also be improved. However, only limited reports which focus on a small number of compounds in individual full-scale IFAS-WWTPs have been published to date, and no data is available regarding the removal of estrogenic activity in full-scale IFAS-WWTPs. In this study, six full-scale IFAS-WWTPs were surveyed to quantify TrOC and estrogenic activity removal. Twenty-four hour composite samples of secondary influent and effluent (pre-disinfection) were analyzed for total suspended solids (TSS), chemical oxygen demand (COD), ammonia, total nitrogen (TN), total phosphorus (TP), estrogenic activity, and 98 TrOCs. The biomass distribution between the suspended growth phase (i.e. mixed liquor) and IFAS media was also assessed. All IFAS-WWTPs performed well in terms of TSS, COD, and ammonia removal. TN removal varied in accordance with nitrate removal. Total solids per liter of wetted reactor volume ranged from 2.5 to 7.6 g, with 40-60% attached to media. TrOCs with no detection (17) and those with high median removal (23, ≥90% average removal) were observed. Other TrOCs had lower and more variable removal efficiencies. Qualitative comparison with CAS literature shows potentially higher IFAS removal efficiencies for a number of compounds including several which have been previously indicated in bench- or pilot-scale studies (atenolol, diclofenac, gemfibrozil, DEET, 4-nonylphenol, and 4-tert-octylphenol), as well as the chlorinated flame retardants TCIPP and TDCIPP. Effluent estrogenic activity was found to be similar to that reported for full-scale CAS-WWTPs. These results provide the first survey of multiple full-scale IFAS-WWTPs employing mobile plastic carrier media in terms of basic chemical endpoints (removal of ammonia, TN, TP, and COD), the distribution of solids within the systems, and the removal of TrOCs and estrogenic activity.

Overview of strategies for enhanced treatment of municipal/domestic wastewater at low temperature

Biological wastewater treatment has been widely applied to municipal/domestic wastewater treatment systems. However, low temperature significantly decreases process performance. Furthermore, increasingly stringent effluent discharge standards are causing wastewater treatment facilities to have to improve and maintain contaminants removal under low temperature. Hence, this review aims to summarize strategies for enhanced treatment of municipal/domestic wastewater at low temperature. First, mechanisms of the effects of low temperature on wastewater treatment, including physiological characteristics, microbial growth rate, microbial activity, microbial community structure and sludge settleability, are analyzed. Strategies for performance intensifications at low temperature, mainly operational parameters regulation, bioaugmentation, biofilm technology, chemical phosphorus precipitation and application of novel process technologies, are then reviewed. Finally, future directions to address low temperature wastewater are highlighted. A special emphasis is given to the application of novel process/technology configurations to enhance process performance at low temperature in practical engineering.

Multiscale investigation of a symbiotic microalgal-integrated fixed film activated sludge (MAIFAS) process for nutrient removal and photo-oxygenation

The Integrated Fixed-Film Activated Sludge (IFAS) process is an advanced biological wastewater treatment process that integrates biofilm carriers within conventional activated sludge to uncouple the sludge retention time for nitrifiers and heterotrophic bacteria. In this study, we incorporated microalgae into the IFAS configuration for photo-oxygenation and evaluated the symbiotic reaction between microalgae and bacteria for both suspended solids and IFAS biofilm media. In a sequencing batch mode, the microalgae-IFAS system removed more than 99% ammonia and 51% phosphorous without the need for mechanical aeration. Biofilm microprofiles revealed localized photo-oxygenation by the algal biofilm and nitrification by nitrifiers on the IFAS media. Genetic sequencing showed that the addition of microalgae to the IFAS system promoted significant changes in the bacterial community structure and altered metabolic activity of several bacterial groups. Overall, this research represents a novel strategy for reducing energy consumption while meeting stringent effluent standards using a hybrid symbiotic microalgae-IFAS technology.

Cell membrane characteristics and microbial population distribution of MBBR and IFAS with different dissolved oxygen concentration

This paper investigated the influences of different dissolved oxygen (DO) concentration (0.71-1.32, 2.13-3.02 and 4.31-5.16 mg/L) on cell membrane characteristics and microbial population distribution of moving biofilm reactors. Two representative reactors, i.e., moving bed biofilm reactors and integrated fixed-film activated sludge were operated. Results indicated that both DO concentration of 0.71-1.32 mg/L and 4.31-5.16 mg/L could increase membrane lipid mobile fraction (49.4%-67.4%) of the microbes, however, through prompting the synthesis of branched fatty acids and unsaturated fatty acids, respectively. For the biofilms, the abundance of Bacteroidetes decreased and Actinobacteria increased with the increase of DO levels. The lowest EfOM content and the highest microbial diversities (1.14-1.52) was observed at DO of 2.13-3.02 mg/L. Redundancy analysis showed that changes of DO levels could alter cell membrane properties and bacterial community structures, and subsequently significantly influenced effluent organic matter composition of moving biofilm reactors.

Cost effectiveness of phosphorus removal processes in municipal wastewater treatment

Meeting stringent phosphorus (P) discharge standards remains one of the major challenges for wastewater utilities due to increased economic burdens associated with advanced (i.e., secondary, tertiary) treatment processes. In a trade-off between higher treatment cost and enhanced P removal, it is critical for the treatment plants to be able to select the most appropriate technology. To this end, established/emerging high performing P removal/recovery technologies (e.g., Modified University of Cape Towne process, Bardenpho process, membrane bioreactors, IFAS-EBPR, struvite recovery, tertiary reactive media filtration) were identified and full-scale treatment plant designs were developed. Using advanced mathematical modeling techniques, six different treatment configurations were evaluated in terms of performance and cost effectiveness ($/lb of P removed). Results show that the unit cost for P removal in different treatment alternatives range from $42.22 to $60.88 per lb of P removed. The MUCT BNR + tertiary reactive media filtration proved to be one of the most cost effective configurations ($44.04/lb P removed) delivering an effluent with total P (TP) concentration of only 0.05 mg/L. Although struvite recovery resulted in significant reduction in biosolids P, the decrease in effluent TP was not sufficient to meet very stringent discharge standards.

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.

A review: Driving factors and regulation strategies of microbial community structure and dynamics in wastewater treatment systems

The performance and stabilization of biological wastewater treatment systems ¹are closely related to the microbial community structure and dynamics. In this paper, the effects and mechanisms of influent composition, process configuration, operating parameters (dissolved oxygen [DO], pH, hydraulic retention time [HRT] and sludge retention time [SRT]) and environmental condition (temperature) to the change of microbial community structure and process performance (nitrification, denitrification, biological phosphorus removal, organics mineralization and utilization, etc.) are critically reviewed. Furthermore, some strategies for microbial community structure regulation, mainly bioaugmentation, process adjustment and operating parameters optimization, applied in the current wastewater treatment systems are also discussed. Although the recent studies have strengthened our understanding on the relationship between microbial community structure and wastewater treatment process performance, how to fully tap the microbial information, optimize the microbial community structure and maintain the process performance in wastewater treatment systems are still full of challenges.

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.

Performance evaluation of a novel anaerobic-anoxic sludge blanket reactor for biological nutrient removal treating municipal wastewater

A novel anaerobic-anoxic sludge blanket reactor, AnoxAn, unifies the non-aerated zones of the biological nutrient removal treatment train in a single upflow reactor, aimed at achieving high compactness and efficiency. The environmental conditions are vertically divided up inside the reactor with the anaerobic zone at the bottom and the anoxic zone above. This contribution presents the performance evaluation of the novel reactor in the removal of organic matter and nutrients from municipal wastewater, coupled with an aerobic hybrid MBR. The overall system achieved total nitrogen and phosphorus removal with average efficiencies of 75% and 89%, respectively. Separate anoxic and anaerobic conditions were maintained in AnoxAn, allowing anaerobic phosphate release and nearly complete anoxic denitrification in the single reactor operating with an HRT of 4.2h. Biomass was retained in the reactor achieving TSS concentration up to 10gL(-1) and partial hydrolysis of influent particulate organic matter.

Nutrient removal performance and microbial characteristics of a full-scale IFAS-EBPR process treating municipal wastewater

This work describes the nutrient removal performance and microbial characteristics of a full-scale integrated fixed-film activated sludge-enhanced biological phosphorus removal (IFAS-EBPR) process for municipal wastewater treatment. The polymerase chain reaction-denaturing gradient gel electrophoresis results showed that the presence of bacteria in this process, including Nitrosomonas sp., Nitrospira sp., Nitrobacter sp., Pseudomonas sp. and Acinetobacter sp., clusters. The fluorescence in situ hybridization results implied that there were more nitrifiers and denitrifiers on the biofilm carriers than in the suspended sludge, whereas more phosphorus-accumulating organisms (PAOs) resided in the suspended sludge. With the cooperation of these functional microbial populations both on the biofilm carriers and in the suspended sludge, the chemical oxygen demand (COD), NH4(+)-N, total nitrogen (TN) and total phosphorus (TP) removal efficiencies were maintained at 84, 97, 70 and 81%, and the effluent concentrations of them averaged 30, 1.0, 11.5 and 0.6 mg/L, which all satisfy the Chinese discharge standard (COD <50 mg/L, NH4(+)-N <5 mg/L, TN <15 mg/L and TP <1 mg/L), respectively. Therefore, the IFAS-EBPR process is a reliable and effective process for nutrient removal.

Interaction between phosphorus removal and hybrid granular sludge formation under low hydraulic selection pressure at alternating anaerobic/aerobic conditions

The hybrid granular sludge (HGS) formation and its performances on phosphorus removal were investigated in a sequencing batch airlift reactor. Under conditions of low superficial air velocity (SAV = 0.68 cm s(-1)) and relatively long settling time (15-30 min), aerobic granules appeared and coexisted with bio-flocs after 120 days operation. At the stable phase, 54% of total suspended solid (m/m) was granular sludge with the two typical sizes (D(mean) = 1.77 ± 0.33 and 0.89 ± 0.11 mm) in the reactor, where the settling velocity was 98.7 ± 12.4 and 37.8 ± 0.9 m h(-1) for the big and small granules. With progressive extension of anaerobic time from 15 to 60 min before aerobic condition per cycle during the whole experiment, the HGS system can be maintained at a high total phosphorus removal efficiency (ca. 99%) since Day-270. The phosphorus content (wt %) in biomass was respectively 9.54 ± 0.29, 7.60 ± 0.48 and 6.15 ± 0.59 for the big granules, small granules and flocs.

Understanding the contribution of biofilm in an integrated fixed-film-activated sludge system (IFAS) designed for nitrogen removal

The objective of this study is to improve knowledge on the integrated fixed-film-activated sludge (IFAS) system designed for nitrogen removal. Biofilm growth and its contribution to nitrification were monitored under various operating conditions in a semi-industrial pilot-scale plant. Nitrification rates were observed in biofilms developed on free-floating media and in activated sludge operated under a low sludge retention time (4 days) and at an ammonia loading rate of 45-70 gNH4-N/kgMLVSS/d. Operational conditions, i.e. oxygen concentration, redox potential, suspended solids concentration, ammonium and nitrates, were monitored continuously in the reactors. High removal efficiencies were observed for carbon and ammonium at high-loading rate. The contribution of biofilm to nitrification was determined as 40-70% of total NOx-N production under the operating conditions tested. Optimal conditions to optimize process compacity were determined. The tested configuration responds especially well to winter and summer nitrification conditions. These results help provide a deeper understanding of how autotrophic biomass evolves through environmental and operational conditions in 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.

Selection of denitrifying phosphorous accumulating organisms in IFAS systems: comparison of nitrite with nitrate as an electron acceptor

Nitrite and nitrate were compared as electron acceptors to select for denitrifying phosphorous accumulating organisms (DPAO) in two integrated fixed film activated sludge (IFAS 1 and IFAS 2) systems operated as sequencing batch reactors. The bench-scale experiment lasted one year and synthetic wastewater was used as feed. During anoxic conditions 20mgNO3(-)-NL(-1) were dosed into IFAS-1 and 20mgNO2(-)-NL(-1) were dosed into IFAS-2. Long term phosphorous and ammonia removal via nitritation were achieved in both systems and both attached and suspended biomass contributed to phosphorous and ammonia removal. DPAO showed no specific adaptation to the electron acceptor as evidenced by short term switch of feeding with nitrate or nitrite. Anoxic phosphorus uptake rate was significantly higher with nitrite than with nitrate. Results showed that DPAO activity with nitrite could be integrated into attached and suspended biomass of IFAS systems in long term operation.

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.

Micropollutant removal by attached and suspended growth in a hybrid biofilm-activated sludge process

Removal of organic micropollutants in a hybrid biofilm-activated sludge process was investigated through batch experiments, modeling, and full-scale measurements. Batch experiments with carriers and activated sludge from the same full-scale reactor were performed to assess the micropollutant removal rates of the carrier biofilm under oxic conditions and the sludge under oxic and anoxic conditions. Clear differences in the micropollutant removal kinetics of the attached and suspended growth were demonstrated, often with considerably higher removal rates for the biofilm compared to the sludge. For several micropollutants, the removal rates were also affected by the redox conditions, i.e. oxic and anoxic. Removal rates obtained from the batch experiments were used to model the micropollutant removal in the full-scale process. The results from the model and plant measurements showed that the removal efficiency of the process can be predicted with acceptable accuracy (± 25%) for most of the modeled micropollutants. Furthermore, the model estimations indicate that the attached growth in hybrid biofilm-activated sludge processes can contribute significantly to the removal of individual compounds, such as diclofenac.

Attachment surface energy effects on nitrification and estrogen removal rates by biofilms for improved wastewater treatment

Submerged biofilm systems, such as integrated fixed-film activated sludge (IFAS) and moving bed bioreactors (MBBRs), are increasingly being used for domestic wastewater treatment, often to improve nitrification. Little is known about whether and how biofilm attachment surface chemical properties affect treatment performance, although surface chemistry is known to affect attachment in other systems, and work with pure strains has suggested that attachment of nitrifying bacteria may be enhanced on high surface energy surfaces. The objective of this research was to systematically evaluate the effects of surface chemistry on biofilm quantity and rates of nitrification and estrogen removal. Biofilms were grown on four plastic attachment surfaces with a range of hydrophobicity and surface energy values (nylon, melamine, high-density-polyethylene [HDPE], and acetal polymeric plastic) by immersing them in a full scale nitrifying activated sludge wastewater treatment system, followed by batch test experiments. The attachment surface water contact angles ranged from 53° to 98° and surface energies ranged from 48.9 to 20.9 mJ/m(2). Attachment surface hydrophilicity and surface energy were positively correlated with total biomass attachment, with more than twice as much biomass on the highest surface energy, most hydrophilic surface (nylon) than on the lowest surface energy, least hydrophilic surface (acetal plastic). Absolute and specific nitrification rates were also correlated with hydrophilicity and surface energy (varying by factors of 5 and 2, respectively), as were absolute and specific removal first order rate constants of the hormones estrone (E1), β-estradiol (E2) and 17α-ethynylestradiol (EE2). These results suggested that attachment surface chemistry may be a useful design parameter for improving biofilm performance for removal of ammonia and endocrine disrupting hormones from wastewater. Further research is required to verify these results at longer time scales and with typical media geometries.

Nitrogen removal assessment through nitrification rates and media biofilm accumulation in an IFAS process demonstration study

An IFAS demonstration study was conducted at the 76,000 m(3)/day (20MGD) James River Wastewater Treatment Plant (JRTP) located in Newport News, Virginia by converting one fully-aerobic conventional aeration basin with dedicated secondary clarification to a 7041 m(3)/day (8404 m(3)/day max month) IFAS train in a modified Ludzack-Ettinger (MLE) configuration. During the study, biomass concentrations on the biofilm carriers were monitored (weekly) as well as nitrogen species concentrations in the IFAS reactor to quantify the nitrogen transformations occurring within the demonstration tank. In a related effort, nitrification kinetics for ammonia and nitrite oxidizing bacteria were monitored on a weekly basis for IFAS media alone, IFAS process mixed liquor without media, and IFAS mixed liquor and media together in an effort to identify the location of nitrification activity (i.e. on the media or in the suspended culture) in the IFAS process. Biomass quantity on the media was generally observed to be inversely related to temperature except during a period when an auxiliary carbon source contaminated with fungi was introduced. Both ammonia oxidizing and nitrite oxidizing bacterial activity were elevated on the carriers compared to the suspended culture (AOB(media): 4.97 mgNOx/gMLSS/hr; AOB(suspended): 1.72 mgNOx/gMLSS/hr; NOB(media): 7.55 mgNOx/gMLSS/hr; NOB(suspended): 0.82 mgNOx/gMLSS/hr) during all periods of the study. In-basin nitrification rates calculated based on nitrogen profiling efforts averaged 0.90 mgNOx/m(2)/day which was in good agreement with the average of 0.89 mgNOx/m(2)/day for IFAS mixed liquor and media from batch testing.