Start-up of an aerobic granular sludge system from stored granules: Evaluating the impact of storage period on biomass activity and stability and the effect of temperature on nitrification and phosphorus removal rates.

Aerobic granular sludge (AGS) has been considered a breakthrough within the wastewater treatment sector. However, the long reactor start-up for the formation of granules is challenging and may hinder the spread of this technology. To circumvent this obstacle, inoculation of the reactors with pre-formed granules from existing plants is an interesting approach. In this context, issues related to biomass storage becomes very relevant. In this study, reactivation of aerobic granular biomass after storage was evaluated in a sequencing batch reactor (SBR) designed for achieving simultaneous organic matter, nitrogen and phosphorus removal. Two different scenarios, short (40 days) and long (180 days) storage periods, were assessed, and their influence on the granules physical properties and bioactivity was addressed. The results revealed that the granules stored for a shorter period showed higher resistance to breakage and underwent smooth color changes. On the other hand, the biomass stored for a longer period acquired a dark color and was more susceptible to disruption during reactivation. The granules stored for 6 months become swollen and exhibited an irregular morphology and fluffy structure within the first days of reactivation. Consequently, their settling properties were adversely affected, and some parameters such as the food-to-microorganism ratio had to be adjusted to prevent granules disintegration. Regarding the bioactivity of important microbial functional groups, COD removal was rapidly restored within a few days of SBR operation with the biomass stored for a shorter period. However, it took longer for the biomass stored for 180 days to reach the same performance observed for the granules stored for 40 days. A similar trend is valid for nitrification. In the experiments with sludge stored for a longer time, it took almost twice as long to reach effluent ammonium concentrations lower than 1 mg NH4+-N L-1 compared to the test using biomass stored for 40 days. Phosphate removal was strongly affected by biomass storage, especially after 180 days of inactivity, a condition found to be detrimental for polyphosphate-accumulating organisms. Finally, cycle tests were also conducted to assess substrate conversion rates for comparison between different trials and evaluate the influence of temperature (10-35 °C) on nitrification and phosphate removal rates.

Identification and validation of the mode of action of the chalcone anti-mycobacterial compounds.

OBJECTIVES: The search for new TB drugs has become one of the great challenges for modern medicinal chemistry. An improvement in the outcomes of TB chemotherapy can be achieved by the development of new, shorter, cheap, safe and effective anti-TB regimens. METHODS: Chalcones (1a-1o) were synthesized and evaluated for their antimycobacterial activity against Mycobacterium bovis BCG using growth inhibition assays. Compound 1a was selected as a 'hit' compound. The mode of action of compound 1a, was identified by mycolic acid methyl esters (MAMEs) and fatty acid methyl esters (FAMEs) analysis using thin layer chromatography. Dose dependent experiments were conducted by over-expressing components of FAS-II in M. bovis BCG to confirm the target. Ligand binding using intrinsic tryptophan assay and molecular docking were used to further validate the target. RESULTS: MAMEs and FAMEs analysis showed dose-dependent reduction of MAMEs with the overall abundance of FAMEs suggesting that compound 1a targets mycolic acid biosynthesis. Direct binding of 1a to InhA was observed using an intrinsic tryptophan fluorescence binding assay, and a 2-fold IC50 shift was observed with an InhA overexpressing strain confirming InhA as the cellular target. CONCLUSION: The chalcone 1a exhibits potent antimycobacterial activity, displays a good safety profile and is a direct inhibitor of InhA, a key component in mycolic acid synthesis, validating this series for further anti-TB drug development.

Assessing the performance and microbial community of hybrid moving bed and conventional membrane bioreactors treating municipal wastewater.

A conventional (SB-CMBR) and a hybrid moving-bed (SB-HMBR) sequencing batch membrane bioreactor treating municipal wastewater were compared during their start-up in terms of organic matter and nutrient removal, membrane fouling characteristics and microbial community. Both systems exhibited similar COD, ammonium, total nitrogen (TN) and phosphorus removal efficiency, amounting up to 96%, 99%, 70% and 85%, respectively. Results from cycle tests revealed that the contribution of attached biomass to the overall ammonium removal in the hybrid reactor was marginal. Moreover, higher despite the similar phosphorus removal efficiency attained in both reactors, nitrate-dosing activity batch assays specifically revealed that the anoxic phosphate uptake rate (PUR) in the SB-HMBR was 1.71 times higher than in the SB-CMBR. Moreover, a higher frequency of Candidatus Accumulibacter-related polyphosphate-accumulating organisms was observed in the biofilm carriers of the hybrid reactor. These findings may explain why the overall PUR was almost 50% higher in the SB-HMBR. By operating the reactors in sequencing batch mode, adhesion of particles on the membrane surface was reduced while fouling was mitigated as compared to continuous MBR systems. Better filterability conditions with lower fouling rate were found in the SB-HMBR, important features of the hybrid reactor for reducing membrane cleaning-related energy demand.

Development of aerobic granular sludge under tropical climate conditions: The key role of inoculum adaptation under reduced sludge washout for stable granulation.

Aerobic granular sludge (AGS) is a promising technology for wastewater treatment. However, the success of the process depends on the formation of stable granular biomass, which is associated with the microbiological aspects of the sludge and reactor operating conditions. In this study, the development of AGS from a poor nitrifying flocculent sludge obtained in a sewage treatment plant designed only for organic matter removal was assessed in a sequencing batch reactor (SBR) under tropical climate conditions (temperatures of 28 ±â€¯4 °C). The results showed that, despite the alternating anaerobic-aerobic conditions during the granules selection phase under high sludge washout rates (low settling time), readily biodegradable organic matter was mainly removed aerobically. The formed granules were unstable, exhibiting a substantial amount of filaments and pasty consistency. The biomass characteristics (e.g., sludge volume index, density, diameter and settling velocity) were negatively impacted as complete granulation was reached, while biomass loss and degranulation became inevitable. Poor nitrification and no enhanced biological phosphate removal (EBPR) were observed. Implementation of a new operational strategy incorporating an adaptation of the seed sludge under reduced washout conditions (high settling time) prior to the granules selection stage enabled most of the influent organics to be removed anaerobically. Besides allowing a feast-famine regime to be established in the reactor, the sludge acclimation phase favoured the development of slow-growing organisms and suppressed the appearance of filamentous-like structures. Fast-settling granules with regular shape remained stable in the long-term, while high ammonium (>95%) and total nitrogen removal (>90%) was obtained. However, EBPR activity was very unstable, most likely due to the high temperatures. The findings of this study are important for the spreading of the AGS technology worldwide, especially in developing countries where the conditions are different in all aspects.

Interpreting the effect of increasing COD loading rates on the performance of a pre-anoxic MBBR system: implications on the attached and suspended biomass dynamics and nitrification-denitrification activity.

A pre-anoxic MBBR system was subjected to increasing organic loading rates up to 18 gCOD/(m(2) day). At 3 gCOD/(m(2) day), most of the incoming organic matter was removed via denitrification. However, at higher loads, anoxic COD removal became limited by the nitrite/nitrate supply from the aerobic reactor, which assumed an important role in this conversion. Despite the application of low dissolved oxygen (DO) levels (<2 mg/L) in this tank, nitrification was observed to be nearly complete until 8 gCOD/(m(2) day). As the organic input was increased, the maximum specific nitrifying activity gradually declined. Activity tests suggested that an oxygen-limited environment was established in the biofilm. At lower loads [3-8 gCOD/(m(2) day)], the nitrification product obtained was affected by the DO concentration, whereas from 16 to 21 gCOD/(m(2) day), nitrite/nitrate profiles were likely associated with microbial stratification in the biofilm. The results also indicated that the role of the suspended biomass in the overall nitrification and denitrification can be very significant in high loaded MBBRs and should not be neglected, even at low HRTs.

Integration of biofiltration and advanced oxidation processes for tertiary treatment of an oil refinery wastewater aiming at water reuse.

The combination of biological and chemical oxidation processes is an interesting approach to remove ready, poor, and non-biodegradable compounds from complex industrial wastewaters. In this study, biofiltration followed by H2O2/UV oxidation (or microfiltration) and final reverse osmosis (RO) step was employed for tertiary treatment of an oil refinery wastewater. Biofiltration alone allowed obtaining total organic carbon (TOC), chemical oxygen demand (COD), UV absorbance at 254 nm (UV254), ammonium, and turbidity removal of around 46, 46, 23, 50, and 61 %, respectively. After the combined biological-chemical oxidation treatment, TOC and UV254 removal amounted to 88 and 79 %, respectively. Whereas, the treatment performance achieved with different UV lamp powers (55 and 95 W) and therefore distinct irradiance levels (26.8 and 46.3 mW/cm(2), respectively) were very similar and TOC and UV254 removal rates were highly affected by the applied C/H2O2 ratio. Silt density index (SDI) was effectively reduced by H2O2/UV oxidation, favoring further RO application. C/H2O2 ratio of 1:4, 55 W UV lamp, and 20-min oxidation reaction corresponded to the experimental condition which provided the best cost/benefit ratio for TOC, UV254, and SDI reduction from the biofilter effluent. The array of treatment processes proposed in this study has shown to be adequate for tertiary treatment of the oil refinery wastewater, ensuring the mitigation of membrane fouling problems and producing a final effluent which is suitable for reuse applications.

Combined organic matter and nitrogen removal from a chemical industry wastewater in a two-stage MBBR system.

Pesticide-producing factories generate highly polluting wastewaters containing toxic and hazardous compounds which should be reduced to acceptable levels before discharge. In this study, a chemical industry wastewater was treated in a pre-denitrification moving-bed biofilm reactor system subjected to an increasing internal mixed liquor recycle ratio from 2 to 4. Although the influent wastewater characteristics substantially varied over time, the removal of chemical oxygen demand (COD) and dissolved organic carbon was quite stable and mostly higher than 90%. The highest fraction of the incoming organic matter was removed anoxically, favouring a low COD/N environment in the subsequent aerobic nitrifying tank and thus ensuring stable ammonium removal (90-95%). However, during pH and salt shock periods, nitrifiers were severely inhibited but gradually restored their full nitrifying capability as non-stressing conditions were reestablished. Besides promoting an increase in the maximum nitrification potential of the aerobic attached biomass from 0.34 to 0.63 mg [Formula: see text], the increase in the internal recycle ratio was accompanied by an increase in nitrogen removal (60-78%) and maximum specific denitrification rate (2.7-3.3 mg NOx(-)--N). Total polysaccharides (PS) and protein (PT) concentrations of attached biomass were observed to be directly influenced by the influent organic loading rate, while the PS/PT ratio mainly ranged from 0.3 to 0.5. Results of Microtox tests showed that no toxicity was found in the effluent of both the anoxic and aerobic reactors, indicating that the biological process was effective in removing residual substances which might adversely affect the receiving waters' ecosystem.

Tracking the dynamics of heterotrophs and nitrifiers in moving-bed biofilm reactors operated at different COD/N ratios.

In this study, the impact of COD/N ratio and feeding regime on the dynamics of heterotrophs and nitrifiers in moving-bed biofilm reactors was addressed. Based on DGGE analysis of 16S rRNA genes, the influent COD was found to be the main factor determining the overall bacterial diversity. The amoA-gene-based analysis suggested that the dynamic behavior of the substrate in continuous and pulse-feeding reactors influenced the selection of specific ammonium-oxidizing bacteria (AOB) strains. Furthermore, AOB diversity was directly related to the applied COD/N ratio and ammonium-nitrogen load. Maximum specific ammonium oxidation rates observed under non-substrate-limiting conditions were observed to be proportional to the fraction of nitrifiers within the bacterial community. FISH analysis revealed that Nitrosomonas genus dominated the AOB community in all reactors. Moreover, Nitrospira was found to be the only nitrite-oxidizing bacteria (NOB) in the fully autotrophic system, whereas Nitrobacter represented the dominant NOB genus in the organic carbon-fed reactors.

Enhancing clinically-relevant shoulder function assessment using only essential movements.

Kinematic functional evaluation with body-worn sensors provides discriminative and responsive scores after shoulder surgery, but the optimal movements' combination has not yet been scientifically investigated. The aim of this study was the development of a simplified shoulder function kinematic score including only essential movements. The P Score, a seven-movement kinematic score developed on 31 healthy participants and 35 patients before surgery and at 3, 6 and 12 months after shoulder surgery, served as a reference. Principal component analysis and multiple regression were used to create simplified scoring models. The candidate models were compared to the reference score. ROC curve for shoulder pathology detection and correlations with clinical questionnaires were calculated. The B-B Score (hand to the Back and hand upwards as to change a Bulb) showed no difference to the P Score in time*score interaction (P > .05) and its relation with the reference score was highly linear (R(2) > .97). Absolute value of correlations with clinical questionnaires ranged from 0.51 to 0.77. Sensitivity was 97% and specificity 94%. The B-B and reference scores are equivalent for the measurement of group responses. The validated simplified scoring model presents practical advantages that facilitate the objective evaluation of shoulder function in clinical practice.

Treatment of petroleum refinery wastewater containing heavily polluting substances in an aerobic submerged fixed-bed reactor.

Petroleum refineries produce large amount of wastewaters, which often contain a wide range of different compounds. Some of these constituents may be recalcitrant and therefore difficult to be treated biologically. This study evaluated the capability of an aerobic submerged fixed-bed reactor (ASFBR) containing a corrugated PVC support material for biofilm attachment to treat a complex and high-strength organic wastewater coming from a petroleum refinery. The reactor operation was divided into five experimental runs which lasted more than 250 days. During the reactor operation, the applied volumetric organic load was varied within the range of 0.5-2.4 kgCOD.m(-3).d(-1). Despite the inherent fluctuations on the characteristics of the complex wastewater and the slight decrease in the reactor performance when the influent organic load was increased, the ASFBR showed good stability and allowed to reach chemical oxygen demand, dissolved organic carbon and total suspended solids removals up to 91%, 90% and 92%, respectively. Appreciable ammonium removal was obtained (around 90%). Some challenging aspects of reactor operation such as biofilm quantification and important biofilm constituents (e.g. polysaccharides (PS) and proteins (PT)) were also addressed in this work. Average PS/volatile attached solids (VAS) and PT/VAS ratios were around 6% and 50%, respectively. The support material promoted biofilm attachment without appreciable loss of solids and allowed long-term operation without clogging. Microscopic observations of the microbial community revealed great diversity of higher organisms, such as protozoa and rotifers, suggesting that toxic compounds found in the wastewater were possibly removed in the biofilm.

Evaluating the main and side effects of high salinity on aerobic granular sludge.

Salinity can adversely affect the performance of most biological processes involved in wastewater treatment. The effect of salt on the main conversion processes in an aerobic granular sludge (AGS) process accomplishing simultaneous organic matter, nitrogen, and phosphate removal was evaluated in this work. Hereto, an AGS sequencing batch reactor was subjected to different salt concentrations (0.2 to 20 g Cl(-) l(-1)). Granular structure was stable throughout the whole experimental period, although granule size decreased and a significant effluent turbidity was observed at the highest salinity tested. A weaker gel structure at higher salt concentrations was hypothesised to be the cause of such turbidity. Ammonium oxidation was not affected at any of the salt concentrations applied. However, nitrite oxidation was severely affected, especially at 20 g Cl(-) l(-1), in which a complete inhibition was observed. Consequently, high nitrite accumulation occurred. Phosphate removal was also found to be inhibited at the highest salt concentration tested. Complementary experiments have shown that a cascade inhibition effect took place: first, the deterioration of nitrite oxidation resulted in high nitrite concentrations and this in turn resulted in a detrimental effect to polyphosphate-accumulating organisms. By preventing the occurrence of the nitrification process and therefore avoiding the nitrite accumulation, the effect of salt concentrations on the bio-P removal process was shown to be negligible up to 13 g Cl(-) l(-1). Salt concentrations equal to 20 g Cl(-) l(-1) or higher in absence of nitrite also significantly reduced phosphate removal efficiency in the system.

Temperature and salt effects on settling velocity in granular sludge technology.

Settling velocity is a crucial parameter in granular sludge technology. In this study the effects of temperature and salt concentrations on settling velocities of granular sludge particles were evaluated. A two-fold slower settling velocity for the same granules was observed when the temperature of water decreases from 40 °C to 5 °C. Settling velocities also decreased with increasing salt concentrations. Experiments showed that when granules were not pre-incubated in a solution with increased salt concentration, they initially floated. The time dependent increase in mass and hence in settling speed of a granule due to salt diffusion into the granule was dependent on the granule diameter. The time needed for full salt equilibrium with the bulk liquid took 1 min for small particles from the top of the sludge bed and up to 30 min for big granules from the bottom of the sludge bed. These results suggest that temperature and salt concentration are important parameters to consider in the design, start-up and operation of granular sludge reactors and monitoring of these parameters will aid in a better control of the sludge management in anaerobic and aerobic granular sludge technology. The observations also give an explanation for previous reports which were suggesting that a start-up of granular sludge reactors is more difficult at low temperatures.

Measuring biomass specific ammonium, nitrite and phosphate uptake rates in aerobic granular sludge.

Aerobic granular sludge (AGS) technology offers the possibility to remove organic carbon, nitrogen and phosphorus in a single reactor system. The granular structure is stratified in such a way that both aerobic and anaerobic/anoxic layers are present. Since most of the biological processes in AGS systems occur simultaneously, the measurement and estimation of the capacity of specific conversions is complicated compared to suspended biomass. The determination of the activities of different functional groups in aerobic granular sludge allows for identification of the potential metabolic capacity of the sludge and aids to analyze bioreactor performance. It allows for comparison of different sludges and enables improved understanding of the interaction and competition between different metabolic groups of microorganisms. The most appropriate experimental conditions and methods to determine specific ammonium, nitrite and phosphate uptake rates under normal operation of AGS reactors were evaluated and described in this study. Extra biomass characterization experiments determining the maximum uptake rate of these compounds on optimized conditions were performed as well to see how much spare capacity was available. The methodologies proposed may serve as an experimental frame of reference for investigating the metabolic capacities of microbial functional groups in biofilm processes.

Temperature and salt effects on settling velocity in granular sludge technology.

Settling velocity is a crucial parameter in granular sludge technology. In this study the effects of temperature and salt concentrations on settling velocities of granular sludge particles were evaluated. A two-fold slower settling velocity for the same granules where observed when the temperature of water decreases from 40 °C to 5 °C. Settling velocities also decreased with increasing salt concentrations. Experiments showed that when granules were not pre-incubated in a solution with increased salt concentration, they initially floated. The time dependent increase in mass and hence in settling speed of a granule due to salt diffusion into the granule was dependent on the granule diameter. The time needed for full salt equilibrium with the bulk liquid took 1 min for small particles from the top of the sludge bed and up to 30 min for big granules from the bottom of the sludge bed. These results suggest that temperature and salt concentration are important parameters to consider in the design, start-up and operation of granular sludge reactors and monitoring of these parameters will aid in a better control of the sludge management in anaerobic and aerobic granular sludge technology. The observations also give an explanation for previous reports which were suggesting that a start-up of granular sludge reactors is more difficult at low temperatures.

Simultaneous nitrogen and phosphate removal in aerobic granular sludge reactors operated at different temperatures.

The main biological conversions taking place in two lab-scale aerobic granular sludge sequencing batch reactors were evaluated. Reactors were operated at different temperatures (20 and 30 °C) and accomplished simultaneous COD, nitrogen and phosphate removal. Nitrogen and phosphate conversions were linked to the microbial community structure as assessed by fluorescent in situ hybridization (FISH) analysis. Anoxic tests were performed to evaluate the contribution of anoxic phosphate uptake to the overall phosphate removal and to clarify the denitrification pathway. Complete nitrification/denitrification and phosphate removal were achieved in both systems. A considerable fraction of the phosphate removal was coupled to denitrification (denitrifying dephosphatation). From the results obtained in anoxic batch experiments dosing either nitrite or nitrate, denitrification was proposed to proceed mainly via the nitrate pathway. Denitrifying glycogen-accumulating organisms (DGAOs) were observed to be the main organisms responsible for the reduction of nitrate to nitrite. A significant fraction of the nitrite was further reduced to nitrogen gas while being used as electron acceptor by denitrifying polyphosphate-accumulating organisms (PAO clade II) for anoxic phosphate uptake.

Improved phosphate removal by selective sludge discharge in aerobic granular sludge reactors.

Two lab-scale aerobic granular sludge sequencing batch reactors were operated at 20 and 30°C and compared for phosphorus (P) removal efficiency and microbial community composition. P-removal efficiency was higher at 20°C (>90%) than at 30°C (60%) when the sludge retention time (SRT) was controlled at 30 days by removing excess sludge equally throughout the sludge bed. Samples analyzed by fluorescent in situ hybridization (FISH) indicated a segregation of biomass over the sludge bed: in the upper part, Candidatus Competibacter phosphatis (glycogen-accumulating organisms--GAOs) were dominant while in the bottom, Candidatus Accumulibacter phosphatis (polyphosphate-accumulating organisms--PAOs) dominated. In order to favour PAOs over GAOs and hence improve P-removal at 30°C, the SRT was controlled by discharging biomass mainly from the top of the sludge bed (80% of the excess sludge), while bottom granules were removed in minor proportions (20% of the excess sludge). With the selective sludge removal proposed, 100% P-removal efficiency was obtained in the reactor operated at 30°C. In the meantime, the biomass in the 30°C reactor changed in color from brownish-black to white. Big white granules appeared in this system and were completely dominated by PAOs (more than 90% of the microbial population), showing relatively high ash content compared to other granules. In the reactor operated at 20°C, P-removal efficiency remained stable above 90% regardless of the sludge removal procedure for SRT control. The results obtained in this study stress the importance of sludge discharge mainly from the top as well as in minor proportions from the bottom of the sludge bed to control the SRT in order to prevent significant growth of GAOs and remove enough accumulated P from the system, particularly at high temperatures (e.g., 30°C).

Effect of different operational conditions on biofilm development, nitrification, and nitrifying microbial population in moving-bed biofilm reactors.

In this study, the effect of different operational conditions on biofilm development and nitrification in three moving-bed biofilm reactors (MBBRs) was investigated: two reactors were operated in a continuously fed regime and one in sequencing-batch mode. The presence of organic carbon reduced the time required to form stable nitrifying biofilms. Subsequent stepwise reduction of influent COD caused a decrease in total polysaccharide and protein content, which was accompanied by a fragmentation of the biofilm, as shown by scanning electron microscopy, and by an enrichment of the biofilm for nitrifiers, as observed by fluorescent in situ hybridization (FISH) analysis. Polysaccharide and protein concentrations proved to be good indicators of biomass development and detachment in MBBR systems. Ammonium- and nitrite-oxidizing bacteria activities were affected when a pulse feeding of 4 g of NH(4)-N/(m(2)·day) was applied. Free nitrous acid and free ammonia were likely the inhibitors for ammonium- and nitrite-oxidizing bacteria.

The contribution of exopolysaccharides induced struvites accumulation to ammonium adsorption in aerobic granular sludge.

Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH4+-N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides.

Effect of elevated salt concentrations on the aerobic granular sludge process: linking microbial activity with microbial community structure.

The long- and short-term effects of salt on biological nitrogen and phosphorus removal processes were studied in an aerobic granular sludge reactor. The microbial community structure was investigated by PCR-denaturing gradient gel electrophoresis (DGGE) on 16S rRNA and amoA genes. PCR products obtained from genomic DNA and from rRNA after reverse transcription were compared to determine the presence of bacteria as well as the metabolically active fraction of bacteria. Fluorescence in situ hybridization (FISH) was used to validate the PCR-based results and to quantify the dominant bacterial populations. The results demonstrated that ammonium removal efficiency was not affected by salt concentrations up to 33 g/liter NaCl. Conversely, a high accumulation of nitrite was observed above 22 g/liter NaCl, which coincided with the disappearance of Nitrospira sp. Phosphorus removal was severely affected by gradual salt increase. No P release or uptake was observed at steady-state operation at 33 g/liter NaCl, exactly when the polyphosphate-accumulating organisms (PAOs), "Candidatus Accumulibacter phosphatis" bacteria, were no longer detected by PCR-DGGE or FISH. Batch experiments confirmed that P removal still could occur at 30 g/liter NaCl, but the long exposure of the biomass to this salinity level was detrimental for PAOs, which were outcompeted by glycogen-accumulating organisms (GAOs) in the bioreactor. GAOs became the dominant microorganisms at increasing salt concentrations, especially at 33 g/liter NaCl. In the comparative analysis of the diversity (DNA-derived pattern) and the activity (cDNA-derived pattern) of the microbial population, the highly metabolically active microorganisms were observed to be those related to ammonia (Nitrosomonas sp.) and phosphate removal ("Candidatus Accumulibacter").

Ammonium adsorption in aerobic granular sludge, activated sludge and anammox granules.

The ammonium adsorption properties of aerobic granular sludge, activated sludge and anammox granules have been investigated. During operation of a pilot-scale aerobic granular sludge reactor, a positive relation between the influent ammonium concentration and the ammonium adsorbed was observed. Aerobic granular sludge exhibited much higher adsorption capacity compared to activated sludge and anammox granules. At an equilibrium ammonium concentration of 30 mg N/L, adsorption obtained with activated sludge and anammox granules was around 0.2 mg NH4-N/g VSS, while aerobic granular sludge from lab- and pilot-scale exhibited an adsorption of 1.7 and 0.9 mg NH4-N/g VSS, respectively. No difference in the ammonium adsorption was observed in lab-scale reactors operated at different temperatures (20 and 30 °C). In a lab-scale reactor fed with saline wastewater, we observed that the amount of ammonium adsorbed considerably decreased when the salt concentration increased. The results indicate that adsorption or better ion exchange of ammonium should be incorporated into models for nitrification/denitrification, certainly when aerobic granular sludge is used.