Biological Nutrient Removal Systems Research Articles

Advancing wastewater treatment technologies: The role of chemical engineering simulations in environmental sustainability

Wastewater treatment stands as a critical component in mitigating environmental pollution and safeguarding public health. This review delves into the pivotal role of chemical engineering simulations in advancing wastewater treatment technologies towards enhanced environmental sustainability. The modernization of wastewater treatment processes necessitates a comprehensive understanding of the complex physical, chemical, and biological interactions involved. Chemical engineering simulations offer a powerful toolset for modeling and optimizing these processes with a focus on efficiency, effectiveness, and sustainability. Firstly, simulations enable the prediction and analysis of pollutant removal mechanisms within treatment systems. By simulating various operating conditions and configurations, engineers can optimize treatment processes to achieve higher removal efficiencies while minimizing resource consumption and waste generation. Secondly, simulations aid in the design and development of innovative treatment technologies, such as membrane filtration, advanced oxidation processes, and biological nutrient removal systems. Through computational modeling, engineers can assess the performance and feasibility of these technologies under different scenarios, facilitating informed decision-making and accelerating their implementation. Furthermore, chemical engineering simulations play a crucial role in addressing emerging challenges in wastewater treatment, including the removal of emerging contaminants such as pharmaceuticals, microplastics, and endocrine-disrupting chemicals. By simulating the behavior of these contaminants within treatment systems, engineers can devise targeted strategies for their removal, thus mitigating their adverse environmental and public health impacts. Chemical engineering simulations serve as indispensable tools for advancing wastewater treatment technologies towards greater environmental sustainability. By facilitating the optimization, design, and innovation of treatment processes, simulations contribute to the development of more efficient, cost-effective, and environmentally friendly solutions for managing wastewater and protecting our ecosystems. Embracing these simulation-driven approaches is essential for achieving the ambitious goals of sustainable development and ensuring a cleaner, healthier future for generations to come.

Advancing wastewater treatment technologies: The role of chemical engineering simulations in environmental sustainability

Wastewater treatment stands as a critical component in mitigating environmental pollution and safeguarding public health. This review delves into the pivotal role of chemical engineering simulations in advancing wastewater treatment technologies towards enhanced environmental sustainability. The modernization of wastewater treatment processes necessitates a comprehensive understanding of the complex physical, chemical, and biological interactions involved. Chemical engineering simulations offer a powerful toolset for modeling and optimizing these processes with a focus on efficiency, effectiveness, and sustainability. Firstly, simulations enable the prediction and analysis of pollutant removal mechanisms within treatment systems. By simulating various operating conditions and configurations, engineers can optimize treatment processes to achieve higher removal efficiencies while minimizing resource consumption and waste generation. Secondly, simulations aid in the design and development of innovative treatment technologies, such as membrane filtration, advanced oxidation processes, and biological nutrient removal systems. Through computational modeling, engineers can assess the performance and feasibility of these technologies under different scenarios, facilitating informed decision-making and accelerating their implementation. Furthermore, chemical engineering simulations play a crucial role in addressing emerging challenges in wastewater treatment, including the removal of emerging contaminants such as pharmaceuticals, microplastics, and endocrine-disrupting chemicals. By simulating the behavior of these contaminants within treatment systems, engineers can devise targeted strategies for their removal, thus mitigating their adverse environmental and public health impacts. Chemical engineering simulations serve as indispensable tools for advancing wastewater treatment technologies towards greater environmental sustainability. By facilitating the optimization, design, and innovation of treatment processes, simulations contribute to the development of more efficient, cost-effective, and environmentally friendly solutions for managing wastewater and protecting our ecosystems. Embracing these simulation-driven approaches is essential for achieving the ambitious goals of sustainable development and ensuring a cleaner, healthier future for generations to come.

Refinement of the "Candidatus Accumulibacter" genus based on metagenomic analysis of biological nutrient removal (BNR) pilot-scale plants operated with reduced aeration.

Members of the "Candidatus Accumulibacter" genus are widely studied as key polyphosphate-accumulating organisms (PAOs) in biological nutrient removal (BNR) facilities performing enhanced biological phosphorus removal (EBPR). This diverse lineage includes 18 "Ca. Accumulibacter" species, which have been proposed based on the phylogenetic divergence of the polyphosphate kinase 1 (ppk1) gene and genome-scale comparisons of metagenome-assembled genomes (MAGs). Phylogenetic classification based on the 16S rRNA genetic marker has been difficult to attain because most "Ca. Accumulibacter" MAGs are incomplete and often do not include the rRNA operon. Here, we investigate the "Ca. Accumulibacter" diversity in pilot-scale treatment trains performing BNR under low dissolved oxygen (DO) conditions using genome-resolved metagenomics. Using long-read sequencing, we recovered medium- and high-quality MAGs for 5 of the 18 "Ca. Accumulibacter" species, all with rRNA operons assembled, which allowed a reassessment of the 16S rRNA-based phylogeny of this genus and an analysis of phylogeny based on the 23S rRNA gene. In addition, we recovered a cluster of MAGs that based on 16S rRNA, 23S rRNA, ppk1, and genome-scale phylogenetic analyses do not belong to any of the currently recognized "Ca. Accumulibacter" species for which we propose the new species designation "Ca. Accumulibacter jenkinsii" sp. nov. Relative abundance evaluations of the genus across all pilot plant operations revealed that regardless of the operational mode, "Ca. A. necessarius" and "Ca. A. propinquus" accounted for more than 40% of the "Ca. Accumulibacter" community, whereas the newly proposed "Ca. A. jenkinsii" accounted for about 5% of the "Ca. Accumulibacter" community.IMPORTANCEOne of the main drivers of energy use and operational costs in activated sludge processes is the amount of oxygen provided to enable biological phosphorus and nitrogen removal. Wastewater treatment facilities are increasingly considering reduced aeration to decrease energy consumption, and whereas successful BNR has been demonstrated in systems with minimal aeration, an adequate understanding of the microbial communities that facilitate nutrient removal under these conditions is still lacking. In this study, we used genome-resolved metagenomics to evaluate the diversity of the "Candidatus Accumulibacter" genus in pilot-scale plants operating with minimal aeration. We identified the "Ca. Accumulibacter" species enriched under these conditions, including one novel species for which we propose "Ca. Accumulibacter jenkinsii" sp. nov. as its designation. Furthermore, the MAGs obtained for five additional "Ca. Accumulibacter" species further refine the phylogeny of the "Ca. Accumulibacter" genus and provide new insight into its diversity within unconventional biological nutrient removal systems.

The ASM2d model with two-step nitrification can better simulate biological nutrient removal systems enriched with complete ammonia oxidizing bacteria (comammox Nitrospira)

The discovery of comammox Nitrospira, a complete ammonia-oxidizing microorganism belonging to the genus Nitrospira, has brought new insights into the nitrification process in wastewater treatment plants (WWTPs). The applicability of Activated Sludge Model No. 2 d with one-step nitrification (ASM2d-OSN) or two-step nitrification (ASM2d-TSN) for the simulation of the biological nutrient removal (BNR) processes of a full-scale WWTP in the presence of comammox Nitrospira was studied. Microbial analysis and kinetic parameter measurements showed comammox Nitrospira was enriched in the BNR system operated under low dissolved oxygen (DO) and long sludge retention time (SRT). The relative abundance of Nitrospira under the conditions of stage I (DO = 0.5 mg/L, SRT = 60 d) was about twice of that under stage II conditions (DO = 4.0 mg/L, SRT = 26 d), and the copy number of the comammox amoA gene for stage I was 33 times higher than that for stage II. Compared to the ASM2d-OSN model, the ASM2d-TSN model simulated the performance of the WWTP under stage I conditions better, and the Theil inequality coefficient values of all the tested water quality parameters were lower than using ASM2d-OSN. These results indicate that an ASM2d model with two-step nitrification is a better choice for the simulation of WWTPs with the presence of comammox.

Efficient organic carbon utilization for combined nutrient removal and biogas production in hybrid biofilm activated sludge system

Moving bed biofilm technology is a successful and promising biological treatment process considered for cost-effective management of wastewaters. In this study, a hybrid moving bed biofilm pilot plant was operated and obtained results were compared with simulation results of two biological processes: a conventional Biological Nutrient Removal (BNR) system and a novel hybrid activated sludge configuration implemented with Moving Bed Biofilm Reactor (MBBR) and a reactive primary clarifier (RPC). An efficient organic carbon entrapment (87%) was obtained in reactive primary clarifier where the major component (95%) of the total Chemical Oxygen Demand (COD) was determined as slowly hydrolysable (XS1), according to respirometric tests. Pilot plant and simulation studies exhibited that an improved nitrogen and phosphorus removal performance, as well as higher biogas production (47%) were obtained by organic carbon redirection in proposed hybrid configurations, securing a 40% less reactor volume. Investigation of the economic aspects indicated that hybrid system has a lower operating cost (i.e., 23% less air requirement, 40% less mixing energy requirement), does not require internal recirculation pumps, and produces more energy through anaerobic digestion compared to conventional BNR. Therefore, proposed novel hybrid configuration is more efficient for the treatment of municipal wastewater in terms of Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) within the energy self-sufficient treatment plant approach and sustainable treatment plant operation.

Long term operation of a phototrophic biological nutrient removal system: Impact of CO2 concentration and light exposure on process performance

The utilization of non-aerated microalgae-bacterial consortia for phototrophic biological nutrient removal (photo-BNR) has emerged as an alternative to conventional wastewater treatment. Photo-BNR systems are operated under transient illumination, with alternating dark-anaerobic, light-aerobic and dark-anoxic conditions. A deep understanding of the impact of operational parameters on the microbial consortium and respective nutrient removal efficiency in photo-BNR systems is required. The present study evaluates, for the first time, the long-term operation (260 days) of a photo-BNR system, fed with a COD:N:P mass ratio of 7.5:1:1, to understand its operational limitations. In particular, different CO2 concentrations in the feed (between 22 and 60 mg C/L of Na2CO3) and variations of light exposure (from 2.75 h to 5.25 h per 8 h cycle) were studied to determine their impact on key parameters, like oxygen production and availability of polyhydroxyalkanoates (PHA), on the performance of anoxic denitrification by polyphosphate accumulating organisms. Results indicate that oxygen production was more dependent on the light availability than on the CO2 concentration. Also, under operational conditions with a COD:Na2CO3 ratio of 8.3 mg COD/mg C and an average light availability of 5.4 ± 1.3 W h/g TSS, no internal PHA limitation was observed, and 95 ± 7%, 92 ± 5% and 86 ± 5% of removal efficiency could be achieved for phosphorus, ammonia and total nitrogen, respectively. 81 ± 1.7% of the ammonia was assimilated into the microbial biomass and 19 ± 1.7% was nitrified, showing that biomass assimilation was the main N removal mechanism taking place in the bioreactor. Overall, the photo-BNR system presented a good settling capacity (SVI ∼60 mL/g TSS) and was able to remove 38 ± 3.3 mg P/L and 33 ± 1.7 mg N/L, highlighting its potential for achieving wastewater treatment without the need of aeration.

Model-based fractionation of biomass in a biological nutrient removal system and its effect on the removal efficiencies.

Fractionation of active biomass in a five-stage Bardenpho process was accomplished using an MS Excel wastewater treatment plant modeling tool based on Activated Sludge Model No. 3 extended with a bio-P module. The biomass fractions within the treatment system were predicted as autotrophs, ordinary heterotrophs, and phosphorus accumulating organisms (PAOs). Several simulations were performed in a Bardenpho process using various C/N/P ratios in primary effluent. Biomass fractionation was obtained from steady-state simulation results. The results suggest that the mass percentage of autotrophs, heterotrophs, and PAOs in active biomass range from 1.7 to 7.8%, 5.7-69.0%, and 23.2-92.6%, respectively, depending on characteristics of primary effluent. Results of principal component analysis showed that TKN/COD ratio in primary effluent determines the population of autotrophs and ordinary heterotrophs whereas PAO population is mainly a function of TP/COD ratio.

High concentrations of dissolved organic nitrogen and N-nitrosodimethylamine precursors in effluent from biological nutrient removal process with low dissolved oxygen conditions

The presence of dissolved organic nitrogen (DON) in biological nutrient removal (BNR) effluent has led to increased concern about its adverse effects on wastewater discharge and reuse applications. Previous studies have demonstrated efficient biological inorganic nitrogen removal in BNR under low dissolved oxygen (DO) conditions; however, information on DON is scarce. This study investigated low-DO effects on DON and N-nitrosodimethylamine (NDMA) precursor concentrations in BNR effluents. Identical BNR reactors consisting of an external real-time DO intelligent control system were operated at three different DO concentrations (0.3, 1.0, and 4.0 mgO2/L). Surprisingly, significantly higher values of effluent DON (p<0.05, t-test) and NDMA precursors (p<0.01, t-test) were observed at lower DO levels. Ultrahigh-resolution mass spectrometry analysis showed that molecules produced by microbes at low-DO levels exhibited high proteins/amino sugars-like and low normal oxidation state of carbon characteristics, which possibly acted critical roles in NDMA formation. Furthermore, path analysis by partial least-squares path modeling suggested that NDMA formation potential had strong associations with microbe-DON network stability of microbe-DON co-occurrence interactions (r=0.979, p<0.01). These results highlight the necessity of reconsidering the feasibility of BNR systems operating at low-DO concentrations considering the adverse effects of DON on wastewater discharge and reuse applications.

Survival strategy of comammox bacteria in a wastewater nutrient removal system with sludge fermentation liquid as additional carbon source

Complete ammonia oxidizing (comammox) bacteria are frequently detected in wastewater biological nutrient removal (BNR) systems. This study identified “Candidatus Nitrospira nitrosa”-like comammox bacteria as the predominant ammonia oxidizers (97.5–99.4%) in a lab-scale BNR system with acetate and sludge fermentation liquid as external carbon sources. The total nitrogen and phosphorus removals of the system were 75.9% and 86.9% with minimal N2O emission (0.27%). Low ammonia concentration, mixotrophic growth potentials and metabolic interactions with diverse heterotrophs collectively contributed to the survival of comammox bacteria in the system. The recovered draft genomes of comammox bacteria indicated their potentials in using acetate and propionate but not butyrate. Acetate and propionate indeed stimulated the transcription of comammox amoA genes (up-regulated by 4.1 folds compared with no organic addition), which was positively correlated with the ammonia oxidation rate of the community (r = 0.75, p < 0.05). Comammox bacteria could provide vitamins/cofactors (e.g., cobalamin and biotin) to heterotrophs (e.g., Burkholderiaceae), and in return receive amino acids (e.g., phenylalanine and tyrosine) from heterotrophs, which they cannot synthesize. Compared with comammox bacteria, ammonia oxidizing bacteria (AOB) exhibited lower metabolic versatility, and lacked more pathways for the synthesis of amino acids and vitamin/cofactors, leading to their washout in the studied system. BNRs with comammox bacteria as the major nitrifiers hold great potentials in achieving superior performance at low aeration cost and low N2O emission and at full-scale plants.

Evaluation of PAO adaptability to oxygen concentration change: Development of stable EBPR under stepwise low-aeration adaptation

Recent research has shown the adaptability of Biological Nutrient Removal (BNR) systems to very low level dissolved oxygen (DO) concentration, mainly focusing in the nitrification ability that maintains the nitrogen oxidation process even at very low DO levels. Although step-wise aeration decrease on Enhanced Biological Phosphorus Removal (EBPR) is not fully comprehended. This study investigated the effect of reaching micro-aeration with adaptation strategies on EBPR performance. A step-wise oxygen concentration decrease, arriving at an average aeration level of 0.4 mgO2/L was evaluated, with an outcome of approximately 90 % phosphorus removal efficiency. Compared with different aeration modes, the highest phosphorus (P)-removal efficiency, P-release and lowest effluent phosphorus was achieved in gradual DO decrease strategy. On the other hand, an instant decrease in aeration from stable EBPR process from 2 mgO2/L to 0.4 mgO2/L adversely impacted P-removal by decreasing the efficiency to average 60 % and deteriorating the phosphorus removing microbial consortium. Comparison of results between instant and gradual DO-decrease, indicated the sensitivity of microorganisms to aeration. Microbial adaptation to decreased oxygen availability is crucial to reach high process performance. This study proposes, a potential aeration mode, which contributes in reduction of energy consumption in BNR systems through wastewater treatment.

Evaluating CO2 emissions from continuous flow and batch growth systems under autotrophic mode: Implications for GHG accounting of biological nutrient removal

The oxidation of ammonia by autotrophic bacteria is a central part of the nitrogen cycle and a fundamental aspect of biological nutrient removal (BNR) during wastewater treatment. Autotrophic ammonia oxidation produces protons and results in net-CO2 production due to the neutralizing effect of bicarbonate alkalinity. Attention must be paid to the propensity for this produced CO2 to be transferred to the atmosphere where it can act as a greenhouse gas (GHG). In the context of BNR systems, bicarbonate-derived CO2 emissions should be considered distinct from the biogenic CO2 that arises from cellular respiration, though this distinction is not made in current GHG accounting practices. The aim of this study was to evaluate the performance of two experimental systems operated under autotrophic mode and buffered with bicarbonate, to investigate the relationship between ammonia removal and gaseous CO2 emissions. The first system consisted of continuously aerated lab-scale batch reactors, which were effective in demonstrating the important link between ammonia oxidizer activity, pH, and gaseous CO2 production. Depletion of the buffer system always led to a rapid decline in system pH and cessation of CO2 emissions when the pH fell below 7.0. The second system was a tubular continuous-flow biofilm reactor which permitted comparison of ammonia removal and CO2 emission rates. A linear relationship between ammonia removal and CO2 emissions was demonstrated and the quantified CO2 production was relatively close to that which was predicted based on the stoichiometry of nitrification, with this CO2 being detected in the gas phase. It was apparent that this system offered minimal resistance to the mass transfer of CO2 from the liquid to gas, which is an important factor that determines how much of the bicarbonate-derived CO2 may contribute to greenhouse gas emissions in engineered systems such as those used for BNR.

BNR시스템에 있어서 하수중의 미세플라스틱 거동

BNR시스템에 있어서 하수중의 미세플라스틱 거동

Integrated life cycle assessment-analytic hierarchy process (LCA-AHP) with sensitivity analysis of phosphorus recovery from wastewater in Metro Manila

The adverse environmental impact caused by eutrophication has recently prompted the Philippine government to issue stringent regulatory standards for wastewater effluent quality. The involved stakeholders and industries are assessing the integration of biological nutrient removal (BNR) technologies in the current sewage treatment plant (STP) scenario. Moreover, efforts are being done to utilize wastewater as a resource such us recovery of nutrients as struvite fertilizer from the wastewater sludge. Since BNR and nutrient recovery systems are not yet integrated in STPs, the magnitude of the environmental impacts are yet to be evaluated in the Philippine setting. This study covers the holistic evaluation of the overall environmental performance scores of the following scenarios using a consequential Life Cycle Assessment (LCA) framework integrated with Analytic Hierarchy Process (AHP) in the context of Water-Energy-Food Nexus: 1) current STP scenario; 2) BNR technology; and 3) nutrient recovery system. The environmental impact assessment was done using IMPACT 2002+ methodology in terms of the following impact indicators: human health, ecosystem quality, climate change, resources, aquatic acidification, and aquatic eutrophication. Value judgments from relevant stakeholders were elicited to rank the relative importance of the impact indicators in the evaluation of the overall environmental performance score. The LCA-AHP results show that the integration of a nutrient recovery system is the most preferred scenario. Sensitivity analysis was also done to evaluate the effects of changes in diet and utilization of alternative energy.

Discharge or reuse? Comparative sustainability assessment of anaerobic and aerobic membrane bioreactors.

Water reuse is believed to be a sustainable solution to overcome the scarcity of freshwater. Aerobic and anaerobic membrane bioreactors are becoming an effective technology for wastewater treatment and reuse. Aerobic membrane bioreactors show good nutrient removal, whereas those that are anaerobic have nutrient-rich effluent, enabling the direct agricultural use of the effluent. As a result, the end use will dictate the potential environmental impacts of the bioreactor's application. Therefore, with the consideration of the end use (i.e., discharge or reuse) of the effluent, this study aimed to compare the environmental and economic impacts associated with full-scale aerobic and anaerobic membrane bioreactors for municipal wastewater treatment under different end use scenarios using life cycle assessment and cost analysis. The results of these analyses show that anaerobic bioreactors have greater environmental impacts and life cycle cost than aerobic bioreactors in the discharge scenario due to the incorporation of a biological nutrient removal system. In the reuse scenario, anaerobic membrane bioreactors have lower impacts that are attributable to the offset of the nutrients required for crops, and the potential benefits vary depending on the types of crops receiving the reclaimed water. Integrating anaerobic membrane bioreactors with agricultural fertigation resulted in effluent water nitrate concentrations (after crop uptake and soil treatment) of <2mg L-1 in most U.S. states. This indicated that the use of the anaerobic membrane bioreactors effluent for fertigation could be a win-win solution to both irrigation water shortage and high environmental impact associated with nutrient removal.

The occurrence and role of Nitrospira in nitrogen removal systems

Application of the modern microbial techniques changed the paradigm about the microorganisms performing nitrification. Numerous investigations recognized representatives of the genus Nitrospira as a key and predominant nitrite-oxidizing bacteria in biological nutrient removal systems, especially under low dissolved oxygen and substrate conditions. The recent discovery of Nitrospira capable of performing complete ammonia oxidation (comammox) raised a fundamental question about the actual role of Nitrospira in both nitrification steps. This review summarizes the current knowledge about morphological, physiological and genetic characteristics of the canonical and comammox Nitrospira. Potential implications of comammox for the functional aspects of nitrogen removal have been highlighted. The complex meta-analysis of literature data was applied to identify specific individual variables and their combined interactions on the Nitrospira abundance. In addition to dissolved oxygen and influent nitrogen concentrations, temperature and pH may play an important role in enhancing or suppressing the Nitrospira activity.

Removal of antibiotic resistance genes in various water resources recovery facilities.

Water resources recovery facilities (WWTPs) are hotspots for antibiotic resistance genes (ARGs) and pose a significant threat to environments. Therefore, ARG removal efficiencies of WWTPs are of great importance. In this study, conventional activated sludge (CAS), biological nutrient removal (BNR), sequencing batch reactor (SBR), membrane bioreactor (MBR), package MBR, and WWTP with coagulation-flocculation and UV disinfection units were investigated in terms of their removal efficiencies on overall bacterial genes with 16S rDNA and seven ARGs including the genes aadA, blaCTX-M , cmlA, ermB, sul1, tetA, and qnrS corresponding to commonly used antibiotics aminoglycosides, β-lactams, amphenicols, macrolides-lincosamides-streptogramins, sulfonamides-trimethoprim, tetracyclines, and quinolones, respectively. Seasonal abundance of overall genes and ARGs in influents and effluents of each WWTPs was determined by quantitative polymerase chain reaction. Membrane bioreactor and package MBR systems showed the highest removal efficiency up to 5-log reductions. Seasonal changes affected ARG removal efficiencies of BNR and CAS significantly (p<0.05). The lowest log reductions were determined in summer for BNR and in both autumn and winter for CAS. The abundance of the genes increased in sludge treatment of CAS. In all WWTPs tested, ARG removal rates were correlated with the 16S rDNA gene removal (p>0.05). The results elucidated that the removal mechanism was not ARG-specific. PRACTITIONER POINTS: Removal of genes in WWTPs was found to be not ARG-specific. MBR and package MBR systems had the highest gene removal efficiencies. Effluents of the MBR systems still retained up to 104 genecopynumber/ml. Removal of genes in CAS and BNR systems showed seasonal variations. The copy numbers of the genes increased in the sludge of CAS.

A novel metabolic-ASM model for full-scale biological nutrient removal systems

This study demonstrates that META-ASM, a new integrated metabolic activated sludge model, provides an overall platform to describe the activity of the key organisms and processes relevant to biological nutrient removal (BNR) systems with a robust single-set of default parameters. This model overcomes various shortcomings of existing enhanced biological phosphorous removal (EBPR) models studied over the last twenty years. The model has been tested against 34 data sets from enriched lab polyphosphate accumulating organism (PAO)-glycogen accumulating organism (GAO) cultures and experiments with full-scale sludge from five water resource recovery facilities (WRRFs) with two different process configurations: three stage Phoredox (A2/O) and adapted Biodenitro™ combined with a return sludge sidestream hydrolysis tank (RSS). Special attention is given to the operational conditions affecting the competition between PAOs and GAOs, capability of PAOs and GAOs to denitrify, metabolic shifts as a function of storage polymer concentrations, as well as the role of these polymers in endogenous processes and fermentation. The overall good correlations obtained between the predicted versus measured EBPR profiles from different data sets support that this new model, which is based on in-depth understanding of EBPR, reduces calibration efforts. On the other hand, the performance comparison between META-ASM and literature models demonstrates that existing literature models require extensive parameter changes and have limited predictive power, especially in the prediction of long-term EBPR performance. The development of such a model able to describe in detail the microbial and chemical transformations of BNR systems with minimal adjustment to parameters suggests that the META-ASM model is a powerful tool to predict and mitigate EBPR upsets, optimise EBPR performance and to evaluate new process designs.

Mass fluxes of nitrogen and phosphorus through water reclamation facilities: Case study of biological nutrient removal, aerobic sludge digestion, and sidestream recycle.

At water reclamation facilities, recycling of nutrients (nitrogen and phosphorus) from solids-handling processes to the mainstream treatment process can have detrimental effects on biological nutrient removal systems. In this study, mass fluxes of nitrogen and phosphorus were quantified through the treatment trains at the Northwest Regional Water Reclamation Facility (NWRWRF) and the adjoining Biosolids Management Facility (BMF), which receives sludge from several water reclamation facilities in Hillsborough County, Florida. The driving objectives were to determine (a) whether the return stream from BMF to NWRWRF (i.e., the "sidestream") represents a significant source of nitrogen and phosphorus to NWRWRF, and (b) whether the sidestream return from BMF is interfering with biological nutrient removal processes at NWRWRF. We determined that nearly half of the overall phosphorus flux into NWRWRF is recycled from the BMF sidestream. This leads to an increased cost of treatment, for example, for alum used in phosphorus removal at NWRWRF. In contrast to phosphorus, the flux of nitrogen from BMF to NWRWRF is small (~3%) compared with the flux of nitrogen entering NWRWRF in raw wastewater. However, nitrogen in the sidestream is mostly in the form of nitrate, which prevents anaerobic conditions from developing in the fermentation basin at NWRWRF, and thereby interferes with the enhanced biological phosphorus removal (EBPR) process. Some measurements suggest that fermentation and release of phosphorus may occur in the return activated sludge line (despite the relatively short residence time in that line), which supports EBPR and may partially compensate for anoxic (denitrifying) conditions in the fermentation basin. Therefore, overall, NWRWRF is able to meet its permit limits for phosphorus through a combination of EBPR and alum addition. Although the fluxes measured here are particular to the treatment systems under consideration, the general trends observed are likely to apply to many similar facilities that employ biological nutrient removal, aerobic digestion, and sidestream recycle, particularly those with regional biosolids management facilities. We recommend that such facilities consider (a) removal or recovery of phosphorus from their sidestreams and (b) returning sidestreams downstream of fermentation basins to avoid inhibition of EBPR processes. PRACTITIONER POINTS: Sidestreams from aerobic digestion can represent significant sources of phosphorus to mainstream wastewater treatment. Recycle of nitrate in aerobic digestion sidestreams can interfere with enhanced biological phosphorus removal (EBPR) during mainstream treatment. Fermentation of return activated sludge (RAS) can support EBPR, even under short average hydraulic residence times (minutes).

Determination of Microbial Community in a Pilot Scale Two-Stage Step-Feed Biological Nutrient Removal Process

&lt;p&gt;Microbial community was determined in a pilot-scale two-stage step-feed biological nutrient removal system treating municipal wastewater with 10 m3 d-1 capacity. Grit chamber effluent at Istanbul Ataköy Biological Wastewater Treatment Plant was used as influent wastewater. In the pilot plant, the influent wastewater was split into two fractions to anaerobic and anoxic2 tank. Nitrosomonas, Nitrosospira, Accumulibacter, and Dechloromonas along with some other uncultured microorganisms were determined in the aerobic, anoxic and anaerobic stages. COD, TN, NH4+-N, TP, PO43--P, SS, and VSS removal efficiencies were found to be 86.7%, 80.3%, 92.5%, 89.5%, 87.5%, 94.8%, and 95.0% in average, respectively, at 5000 mg MLSS L-1 and 15 days of SRT and 16 hours of HRT. The results indicated that microbial community in the process was quite similar with those in the nutrient removal processes with no step feeding. This process can be used cost-effectively to remove carbon and nutrients from medium-strength municipal wastewaters.&lt;/p&gt;&#x0D;

Insights gained into activated sludge nitrification through structural and functional profiling of microbial community response to starvation stress

An improved understanding of nitrifying microbial communities in wastewater treatment is imperative for proper design and operation of biological nutrient removal systems.