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Biofilm and granular sludge processes depend on diffusion of substrates. Despite their importance for the kinetic description of biofilm reactors, biofilm diffusion coefficients reported in literature vary greatly. The aim of this simulation study was to determine to what extent the methods that are used to measure diffusion coefficients contribute to the reported variability. Granular sludge was used as a case study. Six common methods were selected, based on mass balances and microelectrodes. A Monte Carlo simulation was carried out to determine the theoretical precision of each method, considering the uncertainty of various experimental parameters. A model-based simulation of a diffusion experiment was used to determine the theoretical accuracy as a result of six sources of error: solute sorption, biomass deactivation, mass transfer boundary layer, granule roughness, granule shape, and granule size distribution. Based on the Monte Carlo analysis, the relative standard deviation of the different methods ranged from 5% to 61%. In a theoretical experiment, the six error sources led to an 37% underestimation of the diffusion coefficient. This highlights that diffusion coefficients cannot be determined accurately with existing experimental methods. At the same time, the need for measuring precise diffusion coefficients as input value for biofilm modeling can be questioned, since the output of biofilm models has a limited sensitivity toward the diffusion coefficient.
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Fenômenos Fisiológicos Bacterianos , Biofilmes/crescimento & desenvolvimento , Simulação por Computador , Modelos Biológicos , Esgotos/microbiologiaRESUMO
Complex substrates, like proteins, carbohydrates, and lipids, are major components of domestic wastewater, and yet their degradation in biofilm-based wastewater treatment technologies, such as aerobic granular sludge (AGS), is not well understood. Hydrolysis is considered the rate-limiting step in the bioconversion of complex substrates, and as such, it will impact the utilization of a large wastewater COD (chemical oxygen demand) fraction by the biofilms or granules. To study the hydrolysis of complex substrates within these types of biomass, this paper investigates the anaerobic activity of major hydrolytic enzymes in the different sludge fractions of a full-scale AGS reactor. Chromogenic substrates were used under fully mixed anaerobic conditions to determine lipase, protease, α-glucosidase, and ß-glucosidase activities in large granules (>1 mm in diameter), small granules (0.2-1 mm), flocculent sludge (0.045-0.2 mm), and bulk liquid. Furthermore, composition and hydrolytic activity of influent wastewater samples were determined. Our results showed an overcapacity of the sludge to hydrolyze wastewater soluble and colloidal polymeric substrates. The highest specific hydrolytic activity was associated with the flocculent sludge fraction (1.5-7.5 times that of large and smaller granules), in agreement with its large available surface area. However, the biomass in the full-scale reactor consisted of 84% large granules, making the large granules account for 55-68% of the total hydrolytic activity potential in the reactor. These observations shine a new light on the contribution of large granules to the conversion of polymeric COD and suggest that large granules can hydrolyze a significant amount of this influent fraction. The anaerobic removal of polymeric soluble and colloidal substrates could clarify the stable granule formation that is observed in full-scale installations, even when those are fed with complex wastewaters. KEY POINTS: ⢠Large and small granules contain >70% of the hydrolysis potential in an AGS reactor. ⢠Flocculent sludge has high hydrolytic activity but constitutes <10% VS in AGS. ⢠AGS has an overcapacity to hydrolyze complex substrates in domestic wastewater.
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Esgotos , Eliminação de Resíduos Líquidos , Anaerobiose , Reatores Biológicos , HidróliseRESUMO
The highly variable characteristics of waste activated sludge (WAS) hinder the comparison of experimental results on WAS bioconversion between the different studies that use excess sludge from different origin. Sludge grown under laboratory conditions with synthetic wastewater as feed showed high resistance to commonly applied pre-treatment techniques, such as thermal pre-treatment. However, a distinctly higher bioconversion of this sludge was recorded compared to WAS from a full-scale wastewater treatment plant (WWTP). The observed results casted concern on the suitability of the experimental laboratory-based data for practice. The physicochemical and biochemical characteristics of both WAS and lab-grown sludge are dependent on the wastewater characteristics or growth media on which the sludges were grown. The objective of this study was to formulate a growth medium that results into a lab-grown sludge which shows high similarity to the WAS coming from a specific full-scale WWTP in response to a pre-treatment technique. More specifically, in this study we targeted the formation of slowly-biodegradable lab-grown sludge that is similarly responsive to mild thermal pre-treatment with H2O2 addition. By comparing real and synthetic wastewaters, we discussed the various wastewater constituents that may lead to a higher degree of recalcitrance of the produced sludge. We then formulated a growth medium, which was fed to a lab-scale activated sludge reactor and evaluated the nutrient removal capacity, as well as the characteristics of the cultivated sludge before and after pre-treatment. Finally, the growth medium was modified to provoke a change in both the bioconversion and in the response to mild thermal pre-treatment. The growth medium proposed in this study resulted in a slowly-biodegradable sludge (195 ± 3.7 NLCH4/kgVSadded) that after thermal pre-treatment resulted in an increase in methane production of 9 %, which was similar to the WAS coming from the full-scale WWTP. It was concluded that not only the bioconversion but also the response to mild thermal pre-treatment of lab-grown sludge was determined by the composition of the growth media.
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Esgotos , Eliminação de Resíduos Líquidos , Anaerobiose , Reatores Biológicos , Peróxido de Hidrogênio , Metano , Águas ResiduáriasRESUMO
The presence of toxic compounds in wastewater can cause problems for organic matter and nutrient removal. In this study, the long-term effect of a model xenobiotic, 2-fluorophenol (2-FP), on ammonia-oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and phosphate accumulating organisms (PAO) in aerobic granular sludge was investigated. Phosphate (P) and ammonium (N) removal efficiencies were high (>93%) and, after bioaugmentation with 2-FP degrading strain FP1, 2-FP was completely degraded. Neither N nor P removal were affected by 50 mg L-1 of 2-FP in the feed stream. Changes in the aerobic granule bacterial communities were followed. Numerical analysis of the denaturing gradient gel electrophoresis (DGGE) profiles showed low diversity for the ammonia monooxygenase (amoA) gene with an even distribution of species. PAOs, including denitrifying PAO (dPAO), and AOB were present in the 2-FP degrading granules, although dPAO population decreased throughout the 444 days reactor operation. The results demonstrated that the aerobic granules bioaugmented with FP1 strain successfully removed N, P and 2-FP simultaneously.
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Reatores Biológicos , Nitrificação , Nitrogênio , Fosfatos , Esgotos , Águas ResiduáriasRESUMO
Aerobic granular sludge (AGS) technology allows simultaneous nitrogen, phosphorus, and carbon removal in compact wastewater treatment processes. To operate, design, and model AGS reactors, it is essential to properly understand the diffusive transport within the granules. In this study, diffusive mass transfer within full-scale and lab-scale AGS was characterized with nuclear magnetic resonance (NMR) methods. Self-diffusion coefficients of water inside the granules were determined with pulsed-field gradient NMR, while the granule structure was visualized with NMR imaging. A reaction-diffusion granule-scale model was set up to evaluate the impact of heterogeneous diffusion on granule performance. The self-diffusion coefficient of water in AGS was â¼70% of the self-diffusion coefficient of free water. There was no significant difference between self-diffusion in AGS from full-scale treatment plants and from lab-scale reactors. The results of the model showed that diffusional heterogeneity did not lead to a major change of flux into the granule (<1%). This study shows that differences between granular sludges and heterogeneity within granules have little impact on the kinetic properties of AGS. Thus, a relatively simple approach is sufficient to describe mass transport by diffusion into the granules.
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Esgotos/microbiologia , Eliminação de Resíduos Líquidos , Purificação da Água , AerobioseRESUMO
Despite aerobic granular sludge wastewater treatment plants operating around the world, our understanding of internal granule structure and its relation to treatment efficiency remains limited. This can be attributed in part to the drawbacks of time-consuming, labor-intensive, and invasive microscopy protocols which effectively restrict samples sizes and may introduce artefacts. Time-domain nuclear magnetic resonance (NMR) allows non-invasive measurements which describe internal structural features of opaque, complex materials like biofilms. NMR was used to image aerobic granules collected from five full-scale wastewater treatment plants in the Netherlands and United States, as well as laboratory granules and control beads. T1 and T2 relaxation-weighted images reveal heterogeneous structures that include high- and low-density biofilm regions, water-like voids, and solid-like inclusions. Channels larger than approximately 50 µm and connected to the bulk fluid were not visible. Both cluster and ring-like structures were observed with each granule source having a characteristic structural type. These structures, and their NMR relaxation behavior, were stable over several months of storage. These observations reveal the complex structures within aerobic granules from a range of sources and highlight the need for non-invasive characterization methods like NMR to be applied in the ongoing effort to correlate structure and function.
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Esgotos , Eliminação de Resíduos Líquidos , Aerobiose , Reatores Biológicos , Espectroscopia de Ressonância Magnética , Países BaixosRESUMO
Bathers release bacteria in swimming pool water, but little is known about the fate of these bacteria and potential risks they might cause. Therefore, shower water was characterized and subjected to chlorination to identify the more chlorine-resistant bacteria that might survive in a chlorinated swimming pool and therefore could form a potential health risk. The total community before and after chlorination (1 mg Cl2 L-1 for 30 s) was characterized. More than 99% of the bacteria in the shower water were Gram-negative. The dominant bacterial families with a relative abundance of ≥10% of the total (non-chlorinated and chlorinated) communities were Flavobacteriaceae (24-21%), Xanthomonadaceae (23-24%), Moraxellaceae (12-11%) and Pseudomonadaceae (10-22%). The relative abundance of Pseudomonadaceae increased after chlorination and increased even more with longer contact times at 1 mg Cl2L-1. Therefore, Pseudomonadaceae were suggested to be relatively more chlorine resistant than the other identified bacteria. To determine which bacteria could survive chlorination causing a potential health risk, the relative abundance of the intact cell community was characterized before and after chlorination. The dominant bacterial families in the intact community (non-chlorinated and chlorinated) were Xanthomonadaceae (21-17%) and Moraxellaceae (48-57%). Moraxellaceae were therefore more chlorine resistant than the other identified intact bacteria present.
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Bactérias/crescimento & desenvolvimento , Halogenação , Microbiologia da Água , Purificação da Água , Cloro , ÁguaRESUMO
Full-scale thermal hydrolysis processes (THP) showed an increase in nutrients release and formation of melanoidins, which are considered to negatively impact methanogenesis during mesophilic anaerobic digestion (AD). In this research, fractionation of THP-sludge was performed to elucidate the distribution of nutrients and the formed melanoidins over the liquid and solid sludge matrix. Degradation of the different fractions in subsequent AD was assessed, and the results were compared with non-pre-treated waste activated sludge (WAS). Results showed that the THP-formed soluble melanoidins were partially biodegradable under AD, especially the fraction with molecular weight under 1.1 kDa, which was related to protein-like substances. The use of THP in WAS increased the non-biodegradable soluble chemical oxygen demand (sCOD) after AD, from 1.1% to 4.9% of the total COD. The total ammoniacal nitrogen (TAN) concentration only slightly increased during THP without AD. However, after AD, TAN released was 34% higher in the THP-treated WAS compared to non-treated WAS, i.e., 36.7 ± 0.7 compared to 27.4 ± 0.4 mgTANreleased/gCODsubstrate, respectively. Results from modified specific methanogenic activities (mSMAs) tests showed that the organics solubilised during THP, were not inhibitory for acetotrophic methanogens. However, after AD of THP-treated sludge and WAS, the mSMA showed that all analysed samples presented strong inhibition on methanogenesis due to the presence of TAN and associated free ammonia nitrogen (FAN). In specific methanogenic activities (SMAs) tests with incremental concentration of TAN/FAN and melanoidins, TAN/FAN induced strong inhibition on methanogens, halving the SMA at around 2.5 gTAN/L and 100 mgFAN/L. Conversely, melanoidins did not show inhibition on the methanogens. Our present results revealed that when applying THP-AD in full-scale, the increase in TAN/FAN remarkably had a greater impact on AD than the formation of melanoidins.
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Esgotos , Eliminação de Resíduos Líquidos , Esgotos/química , Anaerobiose , Eliminação de Resíduos Líquidos/métodos , Amônia , Hidrólise , Nitrogênio , Metano , Reatores BiológicosRESUMO
Granular sludge processes are frequently used in domestic and industrial wastewater treatment. The granule buoyant density and biomass density are important parameters for the design and operation of granular sludge reactors. Different methods to measure the granule density include the pycnometer method, the Percoll density gradient method, the dextran blue method, and the settling velocity method. In this study, a comparison was made between these four methods to measure granule density for granules from a full-scale granular sludge plant treating domestic sewage. The effect of salinity on granule density was assessed as well. Three out of the four evaluated methods yielded comparable results, with granule buoyant densities between 1025.7 and 1028.1 kg/m3 and granule biomass densities between 71.1 and 71.5 g/L (based on volatile suspended solids (VSS)). The settling velocity method clearly underestimated the granule density, due to the complex relation between granule properties and settling velocity. The pycnometer method was the most precise method, but it was also quite susceptible to bias. The granule buoyant density increased proportionally with salinity, to 1049.2 kg/m3 at 36 g/L salinity. However, the granule biomass density, based on VSS, remained constant. This showed that the granule volume was not affected by salinity and that the buoyant density increase was the result of diffusion of salts into the granule pores. Overall, the granule density can be measured reliably with most methods, as long as the effect of salinity is considered. The results are discussed in light of operational aspects for full-scale granular sludge plants.
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Esgotos , Purificação da Água , Reatores Biológicos , Eliminação de Resíduos Líquidos/métodos , SaisRESUMO
This study reports the effects of microaeration on a laboratory-scale AnMBR (MA-AnMBR) fed with synthetic concentrated domestic sewage. The imposed oxygen load mimics the oxygen load coming from a dissolved air flotation (DAF) unit, establishing an anaerobic digester-DAF (AD-DAF) combination with sludge recycling. Results showed a reduced COD concentration in the MA-AnMBR permeate compared with the AnMBR permeate, from 90 to 74 mgCOD L-1, and a concomitant 27% decrease in biogas production. The MA-AnMBR permeate ammonium (NH4+) concentration increased by 35%, to 740 mgNH4+-N L-1, indicating a rise in the hydrolytic capacity. Furthermore, the MA-AnMBR biomass seemingly adapted to an increased oxygen load, which corresponded to 1% of the influent COD load (approximately 55 mLO2 d-1). Concomitantly, an increase in the superoxide dismutase activity (SOD) of biomass was detected. Meanwhile, negligible changes were observed in the specific methanogenic activity (SMA) of the microaerated biomass that was subjected to an oxygen load equivalent to 3% of the influent COD load in batch tests. The obtained results showed that an AD-DAF system could be a promising technology for treating concentrated domestic wastewater, improving sewage sludge hydrolysis, and overall organic matter removal when compared to an AnMBR.
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The pre-treatment of waste activated sludge (WAS) has become more common since it often results in improved bioconversion to methane, in both rate and extent. However, thorough insights on the possible effects and mechanisms of mild pre-treatment techniques, such as temperatures <100 °C combined with the addition of H2O2, are still limited. This study reports the effects of the addition of 5-30 mgH2O2/g TS and its interaction with thermal pre-treatment at 70 °C on methane production, using WAS as the substrate. It was found that the addition of H2O2 increased the methane production rate, coinciding with a decrease in apparent viscosity of WAS, which probably improved mass transfer under non-ideal mixing conditions. While H2O2 solubilized proteins and carbohydrates and mineralized a small fraction of the humic substances in WAS, these biochemical transformations did not suffice to explain the observed extent and rate of methane production. A decreased particle size, the presence of Fenton's reagent, and the presence of cationic polymers in the WAS were discarded as the reasons for the observed decrease in apparent viscosity. It was concluded that the pre-treatment conditions applied in the present study might be a strategy to enhance mixing conditions in full-scale anaerobic digesters.
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In aerobic granular sludge (AGS) reactors, granules of different sizes coexist in a single reactor. Their differences in settling behaviour cause stratification in the settled granule bed. In combination with substrate concentration gradients over the reactor height during the anaerobic plug-flow feeding regime, this can result in functional differences between granule sizes. In this study, we compared the hydrolytic activity in granules of 4 size ranges (between 0.5 and 4.8 mm diameter) collected from a full-scale AGS installation. Protease and amylase activities were quantified through fluorescent activity assays. To visualise where the hydrolytic active zones were located within the granules, the hydrolysis sites were visualized microscopically after incubating intact and sliced granules with fluorescent casein and starch. The microbial community was studied using fluorescent in situ hybridization (FISH) and sequencing. The results of these assays indicated that hydrolytic capacity was present throughout the granules, but the hydrolysis of bulk substrates was restricted to the outer 100 µm, approximately. Many of the microorganisms studied by FISH, such as polyphosphate and glycogen accumulating organisms (PAO and GAO), were abundant in the vicinity of the hydrolytically active sites. The biomass-specific hydrolysis rate depended mainly on the available granule surface area, suggesting that different sized granules are not differentiated in terms of hydrolytic capacity. Thus, the substrate concentration gradients that are present during the anaerobic feeding in AGS reactors do not seem to affect hydrolytic activity at the granule surfaces. In this paper, we discuss the possible reasons for this and reflect about the implications for AGS technology.
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Aerobic granular sludge (AGS) is an advanced biofilm-based technology for wastewater treatment. Diffusion of substrates into the granules is a key aspect of this technology. Domestic wastewater contains soluble organic substrates of different sizes that could potentially diffuse into the granules. In this study, the relation between the molecular weight of a substrate and its diffusion coefficient within the granule was studied with model substrates (polyethylene glycols (PEGs) with a molecular weight between 62 and 10 000 Da). The diffusion coefficients of the model substrates within granules from a full-scale installation were measured with the 'transient uptake of a non-reactive solute' method. The diffusion coefficients in the granules were not significantly different from the diffusion coefficients in water, at least up to 4000 Da molecular weight. This indicates that these PEGs were not obstructed by the granule matrix. The 10 kDa PEG behaved differently from the lighter PEGs, as it could not penetrate the entire granule. Furthermore, the granule structure was characterized with Environmental Scanning Electron Microscopy (ESEM). The granules displayed an open structure with large macropores and semi-solid regions, which contained microbial cells. The diffusion results suggest that most diffusing molecules were unobstructed in the macropores and barely obstructed in the semi-solid regions. Only the diffusion of the 10 kDa PEG seemed to be hindered by the semi-solid regions, but not by the macropores. Lastly, the apparent molecular weight distribution of domestic wastewater soluble COD was determined with ultrafiltration membranes of 100, 10, and 1 kDa molecular weight cut-off. The influent fractionation revealed that a large part (61-69%) of the influent soluble COD was lighter than 1 kDa. As molecules lighter than 1 kDa diffuse easily, the majority of the influent soluble COD can be considered as diffusible COD. These findings provide new insight into the availability of influent COD for granular sludge.
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Sludge predation by aquatic worms results in an increased sludge reduction rate, which is mainly due to the specific removal of a protein fraction from the sludge. As microorganisms play an essential role in sludge hydrolysis a better understanding of the microbial community involved in the worm predation process will provide more insight into the relations between the aquatic worms, their associated microbiome and the efficient sludge reduction. In this study, the microbial community associated with predation by the Tubifex tubifex was investigated. The microbial diversity in the samples of the worm faeces (WF), predated activated sludge and protein-rich substrates were compared. The results indicated that predation on sludge resulted in a microbial change from Actinobacteria (44%) in the sludge, to Proteobacteria (64%) and Bacteriodites (36%) in the WF. Interestingly, the faecal microbial community was more related to the community in (predated) protein-rich substrates than to the community in predated or endogenously respirated activated sludge samples. This similar microbial community could be due to microbial utilisation of protein hydrolysis products. Alternatively, conditions in the worm gut could facilitate a protein hydrolysing community which assists in protein hydrolysis. The genera Burkholderiales, Chryseobacterium and Flavobacterium were found to be associated with predation by T. tubifex.
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Microbiota , Oligoquetos , Animais , Reatores Biológicos , Esgotos , Eliminação de Resíduos LíquidosRESUMO
Worm predation (WP) by Tubifex tubifex was investigated using waste activated sludge (WAS) as the substrate. In order to better understand the sludge degradation mechanisms during WP, the activity of five common hydrolytic enzymes was determined and compared among the initial feed activated sludge, endogenous respirated sludge and worm predated sludge. The results showed that the enzymatic activity decreased upon aerobic (worm) treatment of WAS and that this activity was predominantly associated with the removed solids fraction of the sludge. Interestingly, the protease activity showed a smaller decrease in activity when the worms were present. Flow cell cytometry revealed the release of intestinal bacteria from the worms, which are presumed to be largely responsible for the observed protease activity. Additionally, experiments in which T. tubifex were treated with antibiotics showed that the worms are responsible for a maximum of 73% of the observed proteolytic activity. The remaining 27% is attributed to the intestinal bacteria that exhibit a synergistic relationship with T. tubifex towards protein hydrolysis.
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Comportamento Alimentar , Oligoquetos/fisiologia , Eliminação de Resíduos Líquidos/métodos , Animais , Biodegradação Ambiental , Proteínas , Esgotos/microbiologiaRESUMO
Worm predation (WP) on activated sludge leads to increased sludge degradation rates, irrespective of the type of worm used or reactor conditions employed. However, the cause of the increased sludge degradation rates remains unknown. This paper presents a comparative analysis of the physical and biochemical aspects of predated sludge, providing insight into the hydrolytic mechanisms underlying WP. To this end, the sessile worm Tubifex tubifex was used as a model oligochaete and was batch cultivated in an 18-L airlift reactor. Predation on activated sludge showed an average reduction rate of 12 ± 3.8%/d versus 2 ± 1.3%/d for endogenous respirated sludge. Sludge predation resulted in an increased release of inorganic nitrogen, phosphate and soluble chemical oxygen demand (sCOD). The sCOD consisted mainly of polysaccharides; however, fluorescence excitation emission matrix spectroscopy analysis also revealed the presence of Tryptophan-protein-like substances. Results suggest that the released polysaccharides contain a protein-like element. Additionally, soluble iron increased slightly in concentration after WP. The extent of hydrolysis seemed to reach an average plateau of about 40% volatile solids (VS) reduction after 4 days, which is substantially higher than the 29% VS reduction for endogenous decay of activated sludge after 30 days. Furthermore, T. tubifex predominantly consumed the protein fraction of the extracellular polymeric substances. Results suggest that that the worms specifically target a fraction of the sludge that is predominantly biodegradable under aerobic conditions, albeit at significantly higher degradation rates when compared to the endogenous decay of waste activated sludge.
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Oligoquetos/metabolismo , Eliminação de Resíduos Líquidos/métodos , Animais , Reatores Biológicos , EsgotosRESUMO
In this study, N2O formation and emissions from a full-scale partial nitritation (SHARON) reactor were identified through a three-weeks monitoring campaign during which the off-gas was analysed for N2O, O2, CO2 and NO. The overall N2O emission was 3.7% of the incoming ammonium load. By fitting the N2O emission to a theoretical gas stripping profile, the N2O emissions could be assigned to aerobically formed N2O and N2O formed under anoxic conditions. This was further substantiated by liquid N2O measurements. Under standard operation, 70% of the N2O emission was attributed to anoxic N2O formation. Dedicated experiments revealed that low dissolved oxygen concentrations (<1.0 gO2·m(-3)) and longer anoxic periods resulted in an increased N2O emission. Minimising or avoiding anoxic conditions has the highest effect in lowering the N2O emissions. As an additional result, the use of the off-gas N2O concentration measurements to monitor the gas-liquid mass transfer rate coefficient (kLa) during dynamic reactor operation was demonstrated.
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Poluentes Atmosféricos/análise , Reatores Biológicos , Nitrificação , Óxido Nitroso/metabolismo , Eliminação de Resíduos Líquidos/métodos , Compostos de Amônio/análise , Eliminação de Resíduos Líquidos/instrumentaçãoRESUMO
Aerobic granular sludge is extremely promising for the treatment of effluents containing toxic compounds, and it can economically compete with conventional activated sludge systems. A laboratory scale granular sequencing batch reactor (SBR) was established and operated during 444 days for the treatment of an aqueous stream containing a toxic compound, 2-fluorophenol (2-FP), in successive phases. Initially during ca. 3 months, the SBR was intermittently fed with 0.22 mM of 2-FP added to an acetate containing medium. No biodegradation of the target compound was observed. Bioaugmentation with a specialized bacterial strain able to degrade 2-FP was subsequently performed. The reactor was thereafter continuously fed with 0.22 and 0.44 mM of 2-FP and with 5.9 mM of acetate (used as co-substrate), for 15 months. Full degradation of the compound was reached with a stoichiometric fluoride release. The 2-FP degrading strain was successfully retained by aerobic granules, as shown through the recovering of the strain from the granular sludge at the end of the experiment. Overall, the granular SBR has shown to be robust, exhibiting a high performance after bioaugmentation with the 2-FP degrading strain. This study corroborates the fact that bioaugmentation is often needed in cases where biodegradation of highly recalcitrant compounds is targeted.
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Técnicas de Cultura Celular por Lotes/instrumentação , Reatores Biológicos/microbiologia , Fenóis/isolamento & purificação , Rhodococcus/metabolismo , Esgotos/microbiologia , Aerobiose , Biodegradação AmbientalRESUMO
Aerobic granular sludge is a novel compact biological wastewater treatment technology for integrated removal of COD (chemical oxygen demand), nitrogen, and phosphate charges. We present here a multiscale model of aerobic granular sludge sequencing batch reactors (GSBR) describing the complex dynamics of populations and nutrient removal. The macro scale describes bulk concentrations and effluent composition in six solutes (oxygen, acetate, ammonium, nitrite, nitrate, and phosphate). A finer scale, the scale of one granule (1.1 mm of diameter), describes the two-dimensional spatial arrangement of four bacterial groups--heterotrophs, ammonium oxidizers, nitrite oxidizers, and phosphate accumulating organisms (PAO)--using individual based modeling (IbM) with species-specific kinetic models. The model for PAO includes three internal storage compounds: polyhydroxyalkanoates (PHA), poly phosphate, and glycogen. Simulations of long-term reactor operation show how the microbial population and activity depends on the operating conditions. Short-term dynamics of solute bulk concentrations are also generated with results comparable to experimental data from lab scale reactors. Our results suggest that N-removal in GSBR occurs mostly via alternating nitrification/denitrification rather than simultaneous nitrification/denitrification, supporting an alternative strategy to improve N-removal in this promising wastewater treatment process.