Laboratory Sequencing Batch Reactor Research Articles

Native microorganisms for sustainable dye biodegradation in wastewaters from jeans finishing.

The textile mill is one of the most water-consuming industries. Wastewater production is very high, and among the main generated pollutants are dyes. In particular, jeans finishing, which is performed all over the world, generates wastewater with indigo dye that has to be eliminated before discharge. This work studies the biological treatment of this type of wastewater using native microorganisms, i.e., without the need for external seed sludge to start-up the process. Two strategies for starting up the biological treatment using laboratory sequencing batch reactors have been compared: the addition of seed sludge from a biological reactor of a wastewater treatment plant and the non-addition of seed sludge, which means that native microorganisms (those in wastewater coming from the industry facilities) are responsible for COD and color degradation. Special attention is paid to biomass shift in both reactors, analyzing both bacterial and fungal populations. Results yielded more than 90% of COD and color removal after 25days in both reactors. MLSS increased in both reactors during the operation, reaching very similar values (around 1840mg/L). Rozellomycota was the predominant phylum in the reactors. Concerning bacteria, Planctomycetota abundance increased considerably in both reactors, which shows the important role of these bacteria in the treatment. It can be concluded that the lower bacterial diversity in the native population in comparison with the seeded sludge was shifting to a higher microbial diversity during the process, achieving a similar microbial population in reactors. It implies that it is not necessary to either work with isolated cultures or seeded sludge, which leads to a simpler and more sustainable solution for textile wastewater treatment in areas all over the world.

New insight into the granule formation in the reactor for enhanced biological phosphorus removal.

While granulated activated sludge exhibits high productivity, the processes of granule formation are incompletely studied. The processes of granule formation and succession of communities were investigated in a laboratory sequencing batch reactor (SBR) under conditions for enhanced biological phosphorus removal (EBPR) using microbiological and molecular techniques. Active consumption of acetate, primarily by the phosphate-accumulating organisms (PAO), commenced at day 150 of cultivation. This was indicated by the high ratio of molar P-released/acetate uptake (0.73-0.77 P-mol/C-mol), characteristic of PAO. During this period, two types of granule-like aggregates formed spontaneously out of the activated sludge flocs. The aggregates differed in morphology and microbial taxonomic composition. While both aggregate types contained phosphorus-enriched bacterial cells, PAO prevailed in those of morphotype I, and glycogen-accumulating organisms (GAOs) were predominant in the aggregates of morphotype II. After 250 days, the elimination of the morphotype II aggregates from the reactor was observed. The subsequent selection of the community was associated with the development of the morphotype I aggregates, in which the relative abundance of PAO increased significantly, resulting in higher efficiency of phosphorus removal. Metagenomic analysis revealed a predominance of the organisms closely related to Candidatus Accumulibacter IС and IIС and of Ca. Accumulibacter IIB among the PAO. Based on the content of the genes of the key metabolic pathways, the genomes of potential PAO belonging to the genera Amaricoccus, Azonexus, Thauera, Zoogloea, Pinisolibacter, and Siculibacillus were selected. The patterns of physicochemical processes and the microbiome structure associated with granule formation and succession of the microbial communities were revealed.

Effect of 4-nonylphenol on the performance and microbial community of a sequencing batch reactor

4-nonylphenol (4-NP) is one of the most relevant endocrine-disrupting compounds that can be found in wastewaters. In this work, the effect of dosing 1 mg·L−1 of 4-NP to simulated wastewater on the activated sludge process was assessed. For it, two laboratory sequencing batch reactors (SBR) were operated for 94 days, adding 1 mg·L−1 of 4-NP to the wastewater entering one of them (SBR-NP), while the other one (SBR-B) worked as a control reactor. Holistic study of 4-NP influence on activated sludge treatment was carried out, which included both the evolution of the biomass characteristics and the effect of this substance on reactor performance. Although the COD removal efficiency in SBR-NP was lower than in the reactor without 4-NP addition (SBR-B), COD removal efficiency of SBR-NP was always higher than 90%. From day 50, nitrification bacteria were inhibited in SBR-NP and cellular viability decreased from 85.7 ± 11.0% in the first 50 days to 63.0 ± 10.2% in the last 44 days. Concerning the microbial community analysis, both Nitrosomonas and Nitrospira abundances decreased in SBR-NP (from 0.62% to 0.45%, and from 2.39% to 1.01%, respectively). Proteobacteria abundance was considerably higher in SBR-NP at the end of the experiment (44.28% in SBR-NP and 25.88% in SBR-B), which was due to increase of Aquabacterium genus (13.00% and 0.00% in SBR-NP and SBR-B, respectively), playing an important role in 4-NP degradation. Thus, 4-NP presence, in the concentrations studied, affected heterotrophic and autotrophic bacteria differently, having a negative effect in the second group.

Assessment of laboratory scale cylindrical sequencing batch reactor for the treatment of abattoir effluent

Meat factory effluent contains fat, protein, diluted blood, and suspended solids. As a result, nutrient and organic concentrations in this effluent are incredibly high, and residues are slightly solubilized, likely to impact environmental pollution on streams, rivers, and other watercourses if discharged untreated. The biodegradation of abattoir waste was studied using a laboratory-scale cylindrical sequencing batch reactor (SBR) in aerobic mode. The aerobic sludge was collected from the aeration compartment of a paper and pulp effluent treatment facility and cultivated in a 2.83-L Perspex-based laboratory SBR. The raw wastewater comprised 6494 ± 2144 mg/l chemical oxygen demand (COD), 1946 ± 607 mg/l biochemical oxygen demand (BOD), 1722 ± 159 mg/l total suspended solids (TSS), 3062 ± 592 mg/l CaCO3 alkalinity, 7.00 ± 0.27 pH. The duration of a complete cycle was 24 h and comprised four phases: fill (5 min), react (23 h 10 min), settle (40 min) and draw (5 min). The whole experiment was divided into four phases and the dilution was done with the help of domestic sewage. In the first stage, the reactor was fed four times diluted slaughterhouse effluent on a 24-h cyclic operation for two weeks. After achieving a significant reduction in COD, the organic content of the input was raised by lowering the dilution factor. In the second and third phases, the reactor was fed three times and twice diluted samples for two weeks each operating at the same cyclic interval. In the final stage, raw effluent was fed to the reactor for two more weeks. The average COD value of diluted wastewater in the first, second, third and fourth phase was 1040 mg/l, 3168 mg/l, 4800 mg/l, and 5200 mg/l, respectively. The COD removal efficiency at the end of the first, second, third and fourth phase was 83%, 93%, 85% and 97%, respectively. The average BOD value of diluted wastewater at the end of the first, second, third and fourth phase was 1120 mg/l, 610 mg/l, 1502 mg/l, and 1350 mg/l, respectively. The BOD removal efficiency at the end of the first, second, third and fourth phase was 84%, 88%, 85% and 98%, respectively. After 8 weeks, at an organic loading rate of 3.06 kg/m3/d, the final phase has achieved BOD and COD removal efficiency of 98% and 97%, respectively. The pH and alkalinity levels were within acceptable ranges. After two months, the sludge's settling characteristics have improved, and the nitrification efficiency of the reactor was roughly 60% at the time of deactivation of the reactor.

Incorporation of the complete ammonia oxidation (comammox) process for modeling nitrification in suspended growth wastewater treatment systems

The newly discovered process complete ammonia oxidation (comammox) has changed the traditional understanding of nitrification. In this study, three possible concepts of comammox were developed and incorporated as part of an extended two-step nitrification model. For model calibration and validation, two series of long-term biomass washout experiments were carried out at 12 °C and 20 °C in a laboratory sequencing batch reactor. The inoculum biomass was withdrawn from a large biological nutrient removal wastewater treatment plant. The efficiency of the examined models was compared based on the behaviors of ammonia, nitrite, and nitrate in the studied reactor. Predictions of the conventional approach to comammox, assuming the direct oxidation of ammonia to nitrate, were slightly better than the two other approaches. Simulation results revealed that comammox could be responsible for the conversion of >20% of the influent ammonia load. Therefore, the role of commamox in the nitrogen mass balance in activated sludge systems should not be neglected and requires further investigation. Furthermore, sensitivity and correlation analysis revealed that the maximum growth rates (μ), oxygen half-saturation (KO), and decay rates (b) of the canonical nitrifiers and comammox were the most sensitive factors, and the highest correlation was found between μ and b among all considered kinetic parameters. The estimated μ values by the best model were 0.57, 0.11, and 0.15 d−1 for AOB, NOB, and comammox bacteria, respectively.

Bioleaching of toxic metals from anaerobically digested sludge without external chemical addition

Anaerobically digested (AD) sludge is widely applied to agricultural land as fertilizer. However, heavy metals in AD sludge potentially pose a significant threat to environment. This study reports a novel bioleaching approach, with no need for externally added chemicals. Sludge acidification was achieved using the protons produced from microbial oxidation of the inherent ammonium in AD sludge. An acid-tolerant microbial consortium, dominated by ammonia-oxidizing bacteria from the genus Candidatus Nitrosoglobus (i.e. relative abundance of 72.5 ± 2.3% based on 16S rRNA gene sequencing), was enriched after 120 days incubation in a laboratory sequencing batch reactor. The consortium oxidizes ammonium even at pH 2.5, at approximately 30% of its maximum rate, measured at pH 5.5. Inoculating the consortium at a solid ratio of 1:20, caused the pH of the AD sludge to decrease from 7.5 to 2.0 over five days under aerobic conditions. As a result, metals in the AD sludge were efficiently extracted into the liquid phase. In particular, two of the most abundant toxic metals, Cu and Zn, were solubilized with high efficiencies of 88 ± 4% and 96 ± 3%, respectively. Overall, the results of this study enable the economical and safe reuse of excess sludge generated during biological wastewater treatment.

Investigation of Formation and Development of Anammox Biofilms by Light, Epifluorescence, and Electron Microscopy

The stages of formation and development of activated sludge biofilm carrying out the anammox process in a laboratory sequencing batch reactor (SBR) with complete biomass retention on the carrier were investigated using light, epifluorescence, and electron microscopy. Light microscopy revealed biofilm formation on the carrier to occur within one week. Rod-shaped and filamentous microorganisms were the first to attach on the carrier and acted as a skeleton for biofilm formation, thus playing an important role in colonization of the carrier. Epifluorescence microscopy revealed physiologically active anammox bacteria of the genera Candidatus “Brocadia” and Ca. “Jettenia” in the biofilms. Selective autofluorescence of the colonies of anammox bacteria Ca. “Jettenia” was observed. This autofluorescence was probably caused by specific proteins in the extracellular polymeric substances (EPS), their synthesis and/or amount depending on the colony age and the physiological state of the cells. Structural organization of the colonies of anammox bacteria was investigated by electron microscopy. High-throughput sequencing of the 16S rRNA gene fragments revealed the presence of sequences affiliated with members of the phyla Chloroflexi, Bacteroidetes, Planctomycetes, and Proteobacteria in the biofilms. Apart from anammox bacteria, anaerobic and facultatively anaerobic organotrophs, stage I nitrifiers, denitrifiers, and sulfate reducers were detected. Members of the genus Ca. “Brocadia” were predominant among the anammox bacteria, probably due to better adhesion of their cells to the carrier or to their competitive advantage over Ca. “Jettenia” in the presence of organic acids (acetate and formate) in the medium.

Impact of the Biological Cotreatment of the Kalina Pond Leachate on Laboratory Sequencing Batch Reactor Operation and Activated Sludge Quality

Hauling landfill leachate to offsite urban wastewater treatment plants is a way to achieve pollutant removal. However, the implementation of biological methods for the treatment of landfill leachate can be extremely challenging. This study aims to investigate the effect of blending wastewater with 3.5% and 5.5% of the industrial leachate from the Kalina pond (KPL) on the performance of sequencing batch reactor (SBR) and capacity of activated sludge microorganisms. The results showed that the removal efficiency of the chemical oxygen demand declined in the contaminated SBR from 100% to 69% and, subsequently, to 41% after the cotreatment with 3.5% and 5.5% of the pollutant. In parallel, the activities of the dehydrogenases and nonspecific esterases declined by 58% and 39%, and 79% and 81% after 32 days of the exposure of the SBR to 3.5% and 5.5% of the leachate, respectively. Furthermore, the presence of the KPL in the sewage affected the sludge microorganisms through a reduction in their functional capacity as well as a decrease in the percentages of the marker fatty acids for different microbial groups. A multifactorial analysis of the parameters relevant for the wastewater treatment process confirmed unambiguously the negative impact of the leachate on the operation, activity, and structure of the activated sludge.

Towards a cleaner wastewater treatment: Influence of folic acid addition on sludge reduction and biomass characteristics

Reduction of sludge production is one of the most desired goals in the wastewater treatment plants operation. Alternatives like the enhancement of metabolism uncoupling or the increase of endogenous respiration by different chemicals have been reported in the bibliography. In this work, two folic acid concentrations (0.8 and 1.6 mg L−1) added to a laboratory sequencing batch reactor were tested in order to assess the effect of this vitamin on the biological treatment. For this purpose, in addition to study sludge reduction and organic matter removal, an exhaustive biomass characterization including soluble microbial products, cellular viability, adenosine triphosphate (ATP), microbial hydrolytic enzymatic activities and bacterial community analysis have been performed. Results indicated that a concentration of 0.8 mg L−1 led to the greatest sludge reduction (44.7%), due to the increase of endogenous respiration. In the reactor with folic acid addition, higher soluble microbial products, enzymatic activities, cellular viability and lower cellular ATP was observed. Regarding the microbial community, folic acid addition did not affect nitrifying bacteria although it did reduce the abundance of denitrifying, increased the amount of filamentous bacteria (Caldilineacaeae and Haliscomenobacter) and enhanced Bacteriodetes and Chloroflexi phyla. A continuous addition of folic acid drove to biomass adaptation that caused a diminution of folic acid activity after 40 days.

The Effect of Bioaugmentation with Archaea on the Oxygen Uptake Rate in a Sequencing Batch Reactor

The aim of this study was to evaluate the effect of bioaugmentation with Archaea domain organisms on the activated sludge (AS) expressed by the oxygen uptake rate (OUR) in a laboratory sequencing batch reactor (SBR). The influence of depletion of the external substrate in bioaugmented (SBR-A) and non-bioaugmented (SBR-B) activated sludge during aerobic stabilization was investigated. The experiment was divided into two steps. First, the OUR was measured in the standard conditions of biological treatment. Second, AS was only aerated in the absence of the substrate. It was observed that bioaugmentation with Archaea had an increasing effect on the endogenous and exogenous OUR of the sludge in both phases. In the first phase, the average endogenous OUR was 28.70 ± 2.75 and 21.63 ± 0.9 mgO2·dm−3·h−1 in the SBR-A and SBR-B, respectively. Regarding the exogenous OUR, the average values were 95.55 ± 11.33 and 57.15 ± 24.56 mgO2·dm−3·h−1 for the SBR-A and SBR-B, respectively. Archaea enhancing its biological activity, expressed as the OUR, exert a stabilizing effect on this parameter of AS and ensure its lower sensitivity to changes in the process conditions, substrate supply disruption and prolonged aeration.

Changes in the process performance, sludge production and microbial activity in an activated sludge reactor with addition of a metabolic uncoupler under different operating conditions

Sludge production in wastewater treatment plants is nowadays a big concern due to the high produced amounts and their characteristics. Consequently, the study of techniques that reduce the sludge generation in wastewater treatment plants is becoming of great importance. In this work, four laboratory sequencing batch reactors (SBRs), which treated municipal wastewater, were operated to study the effect of adding the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS) on the sludge reduction, the SBRs performance and the microbial hydrolytic enzymatic activities (MHEA). In addition, different operating conditions of the SBRs were tested to study the effect of the TCS on the process: two dissolved oxygen (DO) concentrations (2 and 9 mg L−1) and two F/M ratio (0.18 and 0.35 g COD·g MLVSS−1·d−1). The sludge production decreased under high DO concentrations. At the same time, the DNA and EPS production increased in the four SBRs. After these stress conditions, the performance of the reactors were recovered when DO was around 2 mg L−1. From that moment on, results showed that TCS addition implied a reduction of the adenosine triphosphate (ATP) production, which implied a decrease in the sludge production. In spite of this reduction, the SBRs performances did not decay due to the increase in the global MHEA. Additionally, the sludge reduction was enhanced by the increase of the F/M ratio, achieving 28% and 60% of reduction for the low and the high F/M ratio, respectively.

Biological treatment of hypersaline wastewater from table olive processing: Process performance and protist population under different operating conditions

Biological treatment of fermentation brines from table olive processing (FTOP) entails many difficulties due to their very high salinity and high COD concentration, which include some phenolic compounds. These extreme conditions limit the biodiversity of the microbial population. Experiments treating FTOP were performed in laboratory sequencing batch reactors (SBR) changing operating conditions during their operation, in order to study the effects on the SBR performance and on the protist population. The statistical study showed that the SBRs with high influent COD, pH and volatile solids and low influent phenol concentration, hydraulic retention time and temperature achieved the highest COD removal efficiencies. These operational conditions also provided the highest ciliate population and the lowest flagellate presence.

Short-term Influence of Drilling Fluid on Ciliates from Activated Sludge in Sequencing Batch Reactors.

Spent drilling muds are the liquid residues of rock drilling operations. Due to a high concentration of suspended solids and potentially detrimental chemical properties, they can negatively affect microorganisms participating in wastewater treatment processes. We evaluated the addition of a potassium-polymer drilling fluid (DF) to activated sludge in laboratory sequencing batch reactors (SBRs) for municipal wastewater treatment. Ciliate assemblage, the most dynamic component of eukaryotes in activated sludge, and which is highly sensitive to changes in the system, was evaluated. The average ciliate abundance dropped by about 51% (SBR 2; 1% DF added) and 33% (SBR 3; 3% DF added) in comparison to the control (SBR 1; wastewater only). A decrease in the total number of ciliate species during the experiment was observed, from 25 to 24 in SBR 2 and from 17 to 13 in SBR 3. Moreover, a drop in the number of dominant (>100 individuals mL) ciliate species was observed during the experiment-from eight in the control to five in SBR 2 and four in SBR 3-signaling noticeable changes in the quantitative structure of ciliate species. The species analyzed showed different responses to DF addition. The most sensitive was , which is bacteriovorus. In contrast, two predators, and , showed no reaction to DF addition. Our results indicate that addition of potassium-polymer DF, in doses of 1 to 3% of the treated wastewater volume, had no toxic effects on ciliates, but qualitative and quantitative changes in their community were observed.

Brine recovery from hypersaline wastewaters from table olive processing by combination of biological treatment and membrane technologies

The fermentation brines from table olive processing (FTOP) are hypersaline effluents (conductivities higher than 75 mS cm−1) with high organic matter concentrations (COD around 10 g L−1), which also include phenolic compounds (between 700 and 1500 mg TY·L−1). In this work, an integrated process for the FTOP reuse as brine in the table olive processing has been evaluated. This integrated process consisted of a biological treatment followed by a membrane system, which included ultrafiltration (UF) plus nanofiltration (NF). The biological treatment was carried out by 6 L laboratory sequencing batch reactor (SBR). UF and NF were performed in laboratory plants for flat membranes of 0.0125 and 0.0072 m2, respectively. Each stream generated during the FTOP treatment (SBR effluent, and UF and NF permeates) were evaluated. The SBR eliminated around 80% of COD and 71% of total phenols concentration. In the final NF permeate the COD concentration was lower than 125 mg L−1; while the turbidity, colour and phenolic compounds, were completely removed.

Sludge reduction by uncoupling metabolism: SBR tests with para-nitrophenol and a commercial uncoupler

Nowadays cost reduction is a very important issue in wastewater treatment plants. One way, is to minimize the sludge production. Microorganisms break down the organic matter into inorganic compounds through catabolism. Uncoupling metabolism is a method which promote catabolism reactions instead of anabolism ones, where adenosine triphosphate synthesis is inhibited. In this work, the influence of the addition of para-nitrophenol and a commercial reagent to a sequencing batch reactor (SBR) on sludge production and process performance has been analyzed. Three laboratory SBRs were operated in parallel to compare the effect of the addition of both reagents with a control reactor. SBRs were fed with synthetic wastewater and were operated with the same conditions. Results showed that sludge production was slightly reduced for the tested para-nitrophenol concentrations (20 and 25 mg/L) and for a LODOred dose of 1 mL/day. Biological process performance was not influenced and high COD removals were achieved.

Biological Treatment of Poultry Slaughterhouse Wastewater by Using Different Fibers

This study evaluated the performance of sequencing batch reactor (SBR) with and without the fibers of poultry slaughterhouse wastewater (PSWW). The fibers act as attachment materials to the suspended solids, which are considered as pollutant in PSWW. PSWW contains high-pollutant concentrations. Experiments were conducted using two 60 L laboratory SBR reactors at room temperature (25 °C) and pH 7±0.5. The removal percentage of SBR with and without the fibers was compared in terms of chemical oxygen demand and biological oxygen demand. The removal percentage of SBR with fibers showed higher overall performance, which was approximately 90%. Meanwhile, the removal of SBR without fibers achieved an average percentage of about 70%, which was slightly lower compared with SBR reactor with fibers.

Impact of substrate feed patterns on solids reduction by the Cannibal process.

A biological solids reduction process that uses a side-stream anaerobic reactor (Cannibal process) was investigated to better understand why variations in solids reduction occur in field installations. Field observations indicated that single stage, high sludge age processes would frequently not provide a low solids yield. To study this, laboratory sequencing batch reactors were operated, one as a conventional activated sludge system and the other two with a side-stream anaerobic reactors. The control and one anaerobic side-stream system were operated with a 5-minute feed cycle to mimic a plug flow system. The other anaerobic side-stream system operated with a 4-hour feed cycle to simulate complete mix. The 5 minutes feed Cannibal system generated up to 80%. less biological solids than the control. The 4 hours feed Cannibal system produced less biological solids than the conventional activated sludge system but remained higher than for system with a 5-minute feed time.

Integration of biopolymer production with process water treatment at a sugar factory

The present investigation has focused on generating a surplus denitrifying biomass with high polyhydroxyalkanoate (PHA) producing potential while maintaining water treatment performance in biological nitrogen removal. The motivation for the study was to examine integration of PHA production into the water treatment and residuals management needs at the Suiker Unie sugar beet factory in Groningen, the Netherlands. At the factory, process waters are treated in nitrifying-denitrifying sequencing batch reactors (SBRs) to remove nitrogen found in condensate. Organic slippage (COD) in waters coming from beet washing is the substrate used for denitrification. The full-scale SBR was mimicked at laboratory scale. In two parallel laboratory scale SBRs, a mixed-culture biomass selection strategy of anoxic-feast and aerobic-famine was investigated using the condensate and wash water from Suiker Unie. One laboratory SBR was operated as conventional activated sludge with long solids retention time similar to the full-scale (SRT >16 days) while the other SBR was a hybrid biofilm-activated sludge (IFAS) process with short SRT (4-6 days) for the suspended solids. Both SBRs were found to produce biomass with augmented PHA production potential while sustaining process water treatment for carbon, nitrogen and phosphorus for the factory process waters. PHA producing potential in excess of 60 percent g-PHA/g-VSS was achieved with the lab scale surplus biomass. Surplus biomass of low (4-6 days) and high (>16 days) solids retention time yielded similar results in PHA accumulation potential. However, nitrification performance was found to be more robust for the IFAS SBR. Assessment of the SBR microbial ecology based on 16sDNA and selected PHA synthase genes at full-scale in comparison to biomass from the laboratory scale SBRs suggested that the full-scale process was enriched with a PHA storing microbial community. However, structure-function relationships based on RNA levels for the selected PHA synthases could not be established and, towards this ambition, it is speculated that a wider representation of PHA synthesases would need to be monitored. Additionally at the factory, beet tail press waters coming from the factory beet residuals management activities are available as a carbon source for PHA accumulation. At pilot scale, beet tail press waters were shown to provide a suitable carbon source for mixed culture PHA production in spite of otherwise being of relatively low organic strength (≤ 10 g-COD/L). A copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV with 15% HV on a molar basis) of high thermal stability and high weight average molecular mass (980 kDa) was produced from the beet tail press water. The mixed culture accumulation process sustained PHA storage with parallel biomass growth of PHA storing bacteria suggesting a strategy to further leverage the utilization of surplus functional biomass from biological treatment systems. Integration of PHA production into the existing factory water management by using surplus biomass from condensate water treatment and press waters from beet residuals processing was found to be a feasible strategy for biopolymer production.

Strong selection pressures impact the capacity of flocculating activated sludge bacteria to granulate

The capacity of activated sludge (AS) microbial populations to form dense granules offers the potential to establish efficiently settleable biomass. This has the potential to circumvent problems around ineffective solids-liquid separation and sensitivity to variable chemical oxygen demand (COD) loads. Although a number of studies have evaluated aerobic laboratory granulation reactors as high-rate treatment systems, the biological processes involved in aerobic granulation are not fully understood. Concomitantly, the impact of operation parameters such as organic loading rates is also important for granulation. The ability of a flocculating AS community to granulate under different selection pressures was evaluated in a laboratory sequencing batch reactor by determining levels of extracellular polymeric substances (EPS) and particle size fractions that developed under feast (4.74 g COD L(-1)) and famine (0.42 g COD L(-1)) nutrient regimes. The efficiency of solid-liquid separation was also measured. Aggregation indices showed levels >94% and a sludge volume index factor of up to 0.94, which strongly suggested granule formation; however, microscopy evaluation showed a mixture of flocs and granules. Particle size analysis revealed binomial distribution patterns of particles in the reactor which shifted to smaller tightly bound particles (<200 μm) although large particles (>600 μm) were also measured during famine conditions. This coincided with increases in EPS levels although EPS quantities were low and it is postulated that this could have impacted granule formation: the EPS in the bacterial aggregates were consumed since the AS community was starved.

Low Acetate Concentrations Favor Polyphosphate-Accumulating Organisms over Glycogen-Accumulating Organisms in Enhanced Biological Phosphorus Removal from Wastewater

Glycogen-accumulating organisms (GAOs) are thought to compete with polyphosphate-accumulating organisms (PAOs) in enhanced biological phosphorus removal (EBPR) wastewater treatment systems. A laboratory sequencing batch reactor (SBR) was operated for one year to test the hypothesis that PAOs have a competitive advantage at low acetate concentrations, with a focus on low pH conditions previously shown to favor GAOs. PAOs dominated the system under conventional SBR operation with rapid acetate addition (producing high in-reactor concentrations) and pH values of 7.4-8.4. GAOs dominated when the pH was decreased (6.4-7.0). Decreasing the acetate addition rate led to very low reactor acetate concentrations, and PAOs recovered, supporting the study hypothesis. When the acetate feed rate was increased, EBPR failed again. Dominant PAOs and GAOs were Candidatus Accumulibacter phosphatis and Defluviicoccus Cluster 2, respectively, according to fluorescent in situ hybridization and 454 pyrosequencing. Surprisingly, GAOs were not the immediate causes of PAO failures, based on functional and population measurements. Pyrosequencing results suggested Dechloromonas and Tetrasphaera spp. may have also been PAOs, and additional potential GAOs were also identified. Full-scale systems typically have lower in-reactor acetate concentrations than laboratory SBRs, and so, previous laboratory studies may have overestimated the practical importance of GAOs as causes of EBPR failure.