Lab-scale Activated Sludge Reactors Research Articles

Microbial density-dependent viral dynamics and low activity of temperate phages in the activated sludge process

The ecological behavior of bacteriophages (phages), the most abundant biological entity in wastewater treatment systems, is poorly understood, especially that of temperate phages. Here, the temporal dynamics of lytic and temperate phages in a laboratory-scale activated sludge reactor with a sludge bulking issue was investigated using coupled sludge metagenomic and viromic analyses. The lysogenic fragments (prophages) identified were widely distributed in the reconstructed metagenome-assembled genomes (61.7%, n = 227). However, only 12.3% of the identified prophages experienced lysogenic-lytic switching, and the abundance contribution of prophages to free virus communities was only 0.02–0.3%, indicating low activity of temperate phages. Although the sludge community changed dramatically during reactor operation, no massive prophage induction events were detected. Statistical analyses showed strong correlations between sludge concentration and free virus and temperate phage communities, suggesting microbial density-dependent virus dynamics in the sludge microbiota.

Acute inhibitory impact of sulfamethoxazole on mixed microbial culture: Kinetic analysis of substrate utilization biopolymer storage nitrification and endogenous respiration

This study explored acute impact of sulfamethoxazole (SMX) on mixed microbial culture by means of respirometric analysis and modeling of process kinetics. The culture was developed in a laboratory-scale activated sludge reactor fed with peptone mixture. The reactor was maintained at steady state at SRT of 10 days allowing the culture to sustain both heterotrophic and autotrophic fractions. Response of biomass under pulse feeding of 50 mg/L and 200 mg/L SMX was determined by monitoring corresponding oxygen uptake rate (OUR) profiles. Model calibration of OUR profiles enabled numerical assessment of the repressive action of SMX on all processes, heterotrophic growth; substrate binding and storage; two-step nitrification; endogenous respiration. The maximum growth rate of Nitrite Oxidizing Bacteria (NOB) was reduced by 35 %, compared to a slight decrease for Ammonia Oxidizing Bacteria (AOB). Upon exposure, significant substrate binding of around 40–50 % by SMX was observed, drastically reducing the amount of available carbon source for microbial growth. Substrate was directed towards storage with a 15–25% increase in the maximum storage rate. Pulse exposure to 200 mg/L of SMX induced a 50 % increase in the endogenous respiration rate, presumably to meet a higher need for maintenance energy potential for resistance and survival.

Effect of oxic/anoxic conditions on the removal of organic micropollutants in the activated sludge process

Among the emerging issues in the field of wastewater treatments, reducing energy consumption and removal of new organic pollutants have become of primary concern. With respect to the first goal, alternating oxic/anoxic conditions in the bioreactor has demonstrated to be a feasible way to ensure the required efficiency of carbon and nitrogen removal along with energy saving. The aim of the present study was to investigate if these alternating oxic/anoxic conditions are also capable of boosting organic micropollutants degradation, by stimulating the appropriate enzymes. Three different aeration frequencies were tested in a laboratory scale activated sludge reactor and the effects evaluated in terms of removal of carbon, nitrogen and a mixture of OMPs (Sulfamethoxazole, Sulfadiazine, Lincomycin, Carbamazepine, Pyrazole, Naproxen, Atrazine and Sucralose). It was also evaluated if these aeration strategies could change the microbial community composition with respect to the control test conducted under continuous air supply. Among the tested strategies, the longest and shortest durations of anoxic conditions promoted the best removal for the majority of OMPs. This enhancement was statistically well correlated to the activity increase of Lignin Peroxidase and Cellulase enzymes whereas the microbial speciation did not change statistically. The same durations were also capable of maintaining high carbon and nitrogen removal rates within the same biological reactor.

Nexus of Stochastic and Deterministic Processes on Microbial Community Assembly in Biological Systems.

Microbial community assembly in engineered biological systems is often simultaneously influenced by stochastic and deterministic processes, and the nexus of these two mechanisms remains to be further investigated. Here, three lab-scale activated sludge reactors were seeded with identical inoculum and operated in parallel under eight different sludge retention time (SRT) by sequentially reducing the SRT from 15 days to 1 day. Using 16S rRNA gene amplicon sequencing data, the microbial populations at the start-up (15-day SRT) and SRT-driven (≤10-day SRT) phases were observed to be noticeably different. Clustering results demonstrated ecological succession at the start-up phase with no consistent successional steps among the three reactors, suggesting that stochastic processes played an important role in the community assembly during primary succession. At the SRT-driven phase, the three reactors shared 31 core operational taxonomic units (OTUs). Putative primary acetate utilizers and secondary metabolizers were proposed based on K-means clustering, network and synchrony analysis. The shared core populations accounted for 65% of the total abundance, indicating that the microbial communities at the SRT-driven phase were shaped predominantly by deterministic processes. Sloan’s Neutral model and a null model analysis were performed to disentangle and quantify the relative influence of stochastic and deterministic processes on community assembly. The increased estimated migration rate in the neutral community model and the higher percentage of stochasticity in the null model implied that stochastic community assembly was intensified by strong deterministic factors. This was confirmed by the significantly different α- and β-diversity indices at SRTs shorter than 2 days and the observation that over half of the core OTUs were unshared or unsynchronized. Overall, this study provided quantitative insights into the nexus of stochastic and deterministic processes on microbial community assembly in a biological process.

Effect of Solids Retention Time on Effluent Dissolved Organic Nitrogen in the Activated Sludge Process: Studies on Bioavailability, Fluorescent Components, and Molecular Characteristics.

Wastewater-derived dissolved organic nitrogen (DON) should be minimized by municipal wastewater treatment plants (MWWTPs) to reduce its potential impact on receiving waters. Solids retention time (SRT) is a key control parameter for the activated sludge (AS) process; however, knowledge of its impact on effluent DON is limited. This study investigated the effect of SRT on the bioavailability, fluorescent components, and molecular characteristics of effluent DON in the AS process. Four lab-scale AS reactors were operated in parallel at different SRTs (5, 13, 26, and 40 days) for treatment of primary treated wastewater collected from an MWWTP. Results showed the positive effect of prolonged SRT on DON removal. AS reactors during longer SRTs, however, cannot sequester the bioavailable DON (ABDON) and occasionally contribute to greater amounts of ABDON in the effluents. Consequently, effluent DON bioavailability increased with SRT ( R2 = 0.619, p < 0.05, ANOVA). Analysis of effluent DON fluorescent components and molecular characteristics indicated that the high effluent DON bioavailability observed at long SRTs is contributed by the production of microbially derived nitrogenous organics. The results presented herein indicate that operating an AS process with a longer SRT cannot control the DON forms that readily stimulate algal growth.

Fate of triclosan in laboratory-scale activated sludge reactors - Effect of culture acclimation

Triclosan (TCS); a widely used antimicrobial biocide, exists in several pharmaceutical and personal care products. Due to its wide usage, TCS is detected in wastewater at varying concentrations. Biological treatability of TCS and its effect on chemical oxygen demand (COD) removal efficiency were investigated running laboratory-scale pulse-fed sequencing batch reactors with acclimated and non-acclimated cultures. The culture was acclimatized to TCS by gradually increasing its concentration in the synthetic feed wastewater from 100 ng/L to 100 mg/L. There were no effects of TCS on COD removal efficiency up to the TCS concentration of 500 ng/L for both acclimatized and non-acclimatized cases. However, starting from a concentration of 1 mg/L, TCS affected the COD removal efficiency adversely. This effect was more pronounced with non-acclimatized culture. The decrease in the COD removal efficiency reached to 47% and 42% at the TCS concentration of 100 mg/L, under acclimation and non-acclimation conditions respectively. Adsorption of TCS into biomass was evidenced at higher TCS concentrations especially with non-acclimated cultures. 2,4-dichlorophenol and 2,4-dichloroanisole were identified as biodegradation by-products. The occurrence and distribution of these metabolites in the effluent and sludge matrices were found to be highly variable depending, especially, on the culture acclimation conditions.

The use of waste mussel shells for the adsorption of dyes and heavy metals

AbstractBACKGROUNDWaste mussel shells present a significant environmental problem in the area of Northern Greece, since they are produced in vast quantities and there is no legislation for their appropriate disposal or use. In the present study the waste shells were used for the removal of dyes and heavy metals from aqueous solutions while powdered mussel shells were added into activated sludge processes for the removal of hexavalent chromium.RESULTSPowdered mussels shells were used in standard adsorption experiments for the removal of methyl blue and methyl red as well as for the removal of Cr (VI), Cd and Cu. Also they were added into laboratory scale activated sludge reactors treating synthetic wastewater with hexavalent chromium, in order to investigate the potential attribution to the treatment efficiency.CONCLUSIONAdsorption experiments indicated almost 100% color removal. High removal efficiencies were observed for the metals, especially in the case of chromium and cadmium reached concentrations even below 1 mg L−1. The addition of powdered mussel shells in the activated sludge processes enhanced the removal of chromium and phosphorus, while enabled the formation of heavier activated sludge flocs and thus enhanced the settling properties of the activated sludge. © 2017 Society of Chemical Industry

Effects of 3,5-dichlorophenol on excess biomass reduction and bacterial community dynamics in activated sludge as revealed by a polyphasic approach

The effects of 3,5-dichlorophenol (DCP) on excess sludge reduction and microbial community dynamics were studied using laboratory-scale activated sludge reactors. The addition of 3,5-DCP at an interval of 7-8 days of operation resulted in effective reduction of growing biomass without a significant decrease in substrate removal activity. However, this uncoupling effect completely disappeared after 30 days of operation. Quinone profiling showed that a drastic component shift from ubiquinone-8 (Q-8) to Q-10 as the major homolog took place during this period of operation, suggesting that Q-10-containing bacteria, i.e., Alphaproteobacteria, became predominant at the uncoupler-ineffective stage. This result was supported by PCR-aided denaturating gradient gel electrophoresis and clone library analyses of 16S rRNA genes and fluorescence in situ hybridization. Among the gene clones detected, those corresponding to Brevundimonas predominated at the uncoupler-ineffective stage. The uncoupler-added reactor yielded 3,5-DCP-resistant Pseudomonas strains as the predominant cultivable bacteria and non-3,5-DCP-resistant Brevundimonas strains as the second most abundant isolates These results suggest that the disappearance of the uncoupling function of 3,5-DCP during the long-term operation of the reactor is related to the drastic community change with increasing populations of Alphaproteobacteria. Most of these alphaproteobacteria represented by Brevundimonas are not resistant to 3,5-DCP but, by an unknown mechanism, may support the bioprotection of the microbial community from the uncoupling effect.

Transformation of pristine and citrate-functionalized CeO2 nanoparticles in a laboratory-scale activated sludge reactor.

Engineered nanomaterials (ENMs) are used to enhance the properties of many manufactured products and technologies. Increased use of ENMs will inevitably lead to their release into the environment. An important route of exposure is through the waste stream, where ENMs will enter wastewater treatment plants (WWTPs), undergo transformations, and be discharged with treated effluent or biosolids. To better understand the fate of a common ENM in WWTPs, experiments with laboratory-scale activated sludge reactors and pristine and citrate-functionalized CeO2 nanoparticles (NPs) were conducted. Greater than 90% of the CeO2 introduced was observed to associate with biosolids. This association was accompanied by reduction of the Ce(IV) NPs to Ce(III). After 5 weeks in the reactor, 44 ± 4% reduction was observed for the pristine NPs and 31 ± 3% for the citrate-functionalized NPs, illustrating surface functionality dependence. Thermodynamic arguments suggest that the likely Ce(III) phase generated would be Ce2S3. This study indicates that the majority of CeO2 NPs (>90% by mass) entering WWTPs will be associated with the solid phase, and a significant portion will be present as Ce(III). At maximum, 10% of the CeO2 will remain in the effluent and be discharged as a Ce(IV) phase, governed by cerianite (CeO2).

Removal and degradation characteristics of quinolone antibiotics in laboratory-scale activated sludge reactors under aerobic, nitrifying and anoxic conditions

This work describes the removal of 6 quinolone antibiotics from wastewaters under different redox conditions (aerobic, nitrifying and anoxic) through batch experiments in laboratory scale activated sludge reactors using mixed liquor from a membrane bioreactor pilot plant (MBR). The main removal pathways for antibiotics from wastewaters involved in each treatment are described. Mass balances indicated that sorption on sludge played a dominating role in the elimination of antibiotics. Sorption potential depended on the redox conditions, being lower in nitrifying (Kd, 414–876 L kg−1) and anoxic (Kd, 471–930 L kg−1) sludge in comparison with aerobic sludge (Kd, 534–1137 L kg−1). Kd was higher for piperazinylic quinolones. Redox conditions also influenced biodegradation, a secondary pathway, which followed first-order kinetics with degradation rates constants ranging from 1.8·10−3 to 8.2·10−3 h−1. Biodegradation rates under anoxic conditions were negligible. The experimental results have also demonstrated much higher removal efficiency by biodegradation (36.2–60.0%) under nitrifying conditions in comparison with aerobic conditions (14.9–43.8%). The addition of allylthiourea, an ammonia monooxygenase inhibitor, inhibited nitrification completely and reduced significantly the biodegradation of target antibiotics (16.5–29.3%). The residual biodegradation in the presence of allylthiourea may be due to the activity of heterotrophs in the enriched nitrifier culture. The removal of the selected antibiotics under the studied redox conditions depended significantly on the bacteria composition of the sludge. These results suggest that despite the known persistence of this group of antibiotics it is possible to enhance their degradation using nitrifying conditions, which at adequate working conditions as high SRT, typical in MBR, become a promising alternative for improving quinolones removal from environment.

Effects of Powdered Kenaf Supplementation on the Performance of Lab-Scale Activated Sludge Reactors

Effects of Powdered Kenaf Supplementation on the Performance of Lab-Scale Activated Sludge Reactors

Dynamics of dewaterability and bacterial populations in activated sludge

Relationships of bacterial populations and extracellular polymer substances (EPS) to dewaterability of activated sludge were studied on three laboratory-scale activated sludge reactors fed with synthetic wastewater. Dewaterability of activated sludge was evaluated by a novel method developed by the authors, in which small amount of sludge was centrifugally dewatered, and its water content was measured. Bacterial populations during the reactor operation were analyzed by the polymerase chain reaction/terminal-restriction fragment length polymorphism (PCR/T-RFLP) targeted at a partial 16S rRNA gene. Extracellular polymeric substances (EPS) were extracted using cation exchange resin (CER), and polysaccharides and total protein in EPS were determined. Some of the dominant terminal-restriction fragments (T-RFs) were observed to have significant relationships with dewaterability of sludge, and it was suggested that bacterial species corresponding to those peaks significantly affected dewaterability. On the other hand, significant relationships were not found between EPS concentration and dewaterability of sludge.

Application of biological indices and a mathematical model for the detection of metal coagulant overload in a laboratory scale activated sludge reactor with phosphate simultaneous precipitation

Phosphorous simultaneous precipitation by coagulants reduces the volatile solids percentage which can be deleterious to the biological process. In this work a mathematical model was developed and biological indices were applied to control Fe(III)-dosed activated sludge systems. A molar ratio Fe:P = 1.9–2.3:1 on the aeration basin of a laboratory-scale activated sludge reactor caused a progressive enrichment of the sludge with inorganic solids deteriorating the system performance. Crawling and attached ciliates were the most sensitive organism groups to these changes. The proposed mathematical model estimated: (i) the threshold concentration of fixed suspended solids, above which the reactor performance deteriorates, and (ii) the decay of the most sensitive organism groups with time. The Shannon–Wiener and sludge biotic indices predicted the decrease of the reactor performance by coagulant overload. The simultaneous application of the mathematical simulation and the biological indices guarantees a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).

Biodegradation of triclosan and formation of methyl-triclosan in activated sludge under aerobic conditions

Triclosan is an antimicrobial agent which is widely used in household and personal care products. Widespread use of this compound has led to the elevated concentrations of triclosan in wastewater, wastewater treatment plants (WWTPs) and receiving waters. Removal of triclosan and formation of triclosan-methyl was investigated in activated sludge from a standard activated sludge WWTP equipped with enhanced biological phosphorus removal. The removal was found to occur mainly under aerobic conditions while under anoxic (nitrate reducing) and anaerobic conditions rather low removal rates were determined. In a laboratory-scale activated sludge reactor 75% of the triclosan was removed under aerobic conditions within 150 h, while no removal was observed under anaerobic or anoxic conditions. One percent of the triclosan was converted to triclosan-methyl under aerobic conditions, less under anoxic (nitrate reducing) and none under anaerobic conditions.

Evaluation of extracellular biopolymer and its impact on bioflocculation in activated sludge bioreactors

The influence and dynamics of bacterial extracellular polysaccharide (EPS) polymer production and its impact on bioflocculation in activated sludge (AS) bench-scale reactors were investigated. The impact of food to microorganism ratio (F/M), reactor configuration and easily biodegradable carbohydrates in influent streams on biological processes that support or weaken good floc formation and the link with EPS quantity was studied. Bioreactors were run as either sequencing batch or continuous systems using wastewater media with glucose or acetate as C source in different F/M ratios. EPS levels were quantified using mid-infrared spectroscopy which provided a rapid technique for monitoring biological processes within AS WWTP. The analysis revealed an interdependent link between EPS production, sludge settling characteristics and mode of reactor operation. An inverse relationship between F/M ratios and EPS quantities was seen but a positive link between EPS levels and aggregation indices, a measure of the efficiency of inter cell attachment and which indicates good settling properties, was also seen. This indicates that during high F/M conditions in lab-scale AS reactors, low levels of EPS may be produced which could have a negative impact on settling of the biomass. Floc architecture was examined under the microscope. Transient growth of filamentous bacteria was seen in the reactors.

Application of a combined biological and chemical system for the treatment of phosphorus-containing wastewater from the food industry

Coagulants can be dosed at different points during the wastewater treatment process to achieve phosphorous removal. Addition of metal coagulants on the aeration basin (simultaneous precipitation) involves lowest cost; however, inert solids reduce the volatile solids percentage which can be deleterious to the biological process. The general objective of the present study was to analyze the feasibility of P removal in a wastewater model system of the dairy industry using simultaneous precipitation in a laboratory-scale activated sludge reactor by addition of ferric chloride. Results showed that the addition of a high dose Fe:P (molar ratio)= 1.9-2.3:1 on the aeration basin of the reactor caused a progressive enrichment of the sludge with inorganic solids. This phenomenon, which involved a gradual deterioration of the environmental quality of the biological system, led finally to a strong decline of the reactor performance. The organisms associated to flocs (crawling ciliates and attached ciliates) were the more sensitive to these changes. A mathematical model allowed the estimation of the concentration of total fixed suspended solids as well as the decrease in the abundance of these organism groups as a function of time of Fe(III) application, considering the influent flow rate, the influent Fe concentration, and the waste flow rate of the sludge. The Shannon-Wiener diversity index and the sludge biotic index (SBI) can early predict the decreasing of the system performance due to metal salts overload. The simultaneous application of the proposed mathematical model and the biological indices guarantee a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).

Treatment efficiency and sludge characteristics in conventional and suspended PVA gel beads activated sludge treating Cr (VI) containing wastewater

Although activated sludge microbial communities are considered stable, the presence of toxic substances, such as Cr, in the influent may induce changes in the activity and the performance of a wastewater treatment plant. The main objective of this study was the determination of Cr effects on the performance and the protistan community of an activated sludge. Six laboratory scale activated sludge reactors, three conventional and three with PVA gel beads, were supplied with synthetic sewage containing Cr (VI), at three concentrations: 1, 5, and 10 mg l−1. The protozoan species were identified, quantified, and correlated to each system's efficiency through microscopic observations. Additionally, the extracellular polymeric substances (EPS) in the form of proteins and polysaccharides were determined. High removal rates of organic compounds (90%), ammonia-nitrogen (95%), total phosphorus (80%), and chromium (90%) were observed even at high Cr dosages. ?he abundance and diversity of the protistans were observed...

Performance and biological indicators of a laboratory-scale activated sludge reactor with phosphate simultaneous precipitation as affected by ferric chloride addition

Iron-base coagulants are widely used for the phosphorous removal from wastewaters. Coagulants may be applied on the secondary treatment (simultaneous precipitation); however, coagulant excess may alter the biological process. The objectives of this work were: (a) to study in a laboratory-scale activated sludge reactor, fed with a model wastewater system from the dairy industry, the feasibility of phosphorous removal by applying simultaneous precipitation using ferric chloride; (b) to assess the effect of different Fe:P (molar ratio) dose ranges: high = 1.9–2.3:1, mean = 1.5–1.9:1 and low = 1.0–1.4:1 on the reactor performance by measuring physical–chemical parameters (pH, COD, TSS, Fe, P), settling properties (DSVI, diluted sludge volume index) and abundance of filamentous microorganisms by microscopic observation; (c) to evaluate the effect of the coagulant on activated sludge microfauna (abundance and morphological–functional groups); (d) to assess the usefulness of these parameters as control tools. A high Fe:P ratio acted as shock load improving the soluble phosphorous and COD removal. Sludge settling properties were rapidly improved due to both a successful control of filamentous bulking and an increase in the flocs density. Prolonged application of high Fe(III) doses negatively affected the reactor performance; a Fe:P ratio = 1.5–1.9:1 achieved an acceptable effluent quality. Changes in the density of Chilodonella sp., Opercularia sp., Vorticella microstoma, Vorticella spp., Colpoda sp. and rotifers were analyzed as a function of the progressive enrichment of Fe(III) in the sludge. Crawling ciliates constituted the most sensitive group to changes in the activated sludge reactor environmental quality, becoming a potential biological indicator of Fe(III) overload.

Zinc-induced antibiotic resistance in activated sludge bioreactors

Increased levels of bacterial resistance to antibiotics noted in recent decades poses a significant obstacle to the effective treatment and prevention of disease. Although overuse of antibiotics in agriculture and medicine is partially responsible, environmental exposure to heavy metals may also contribute to antibiotic resistance, even in the absence of antibiotics themselves. In this study, a series of eight lab-scale activated-sludge reactors were amended with Zn and/or a suite of three antibiotics (oxytetracycline, ciprofloxacin, and tylosin), in parallel with unamended controls. Classical spread-plating methods were used to assess resistance to these compounds in culturable bacteria over 21 weeks. After seven weeks of general acclimation and development of baseline resistance levels (phase 1), 5.0 mg/L Zn was added to half of the reactors, which were then operated for an additional 7 weeks (phase 2). For the final seven weeks (phase 3), two of the Zn-amended reactors and two of the control reactors were amended with all three antibiotics, each at 0.2 mg/L. Zn amendment alone did not significantly change resistance levels at the 95% confidence level in phase 2. However, tylosin resistance increased significantly during phase 3 in the Zn-only reactors and resistance to all three antibiotics significantly increased as a consequence of combined Zn+antibiotic amendments. Ambient dissolved Zn levels in the reactors were only 12% of added levels, indicating substantial Zn removal by adsorption and/or precipitation. These results show that sub-toxic levels of Zn can cause increased antibiotic resistance in waste treatment microbial communities at comparatively low antibiotic levels, probably due to developed cross-resistance resulting from pre-exposure to Zn.

Maintenance of phenol hydroxylase genotypes at high diversity in bioreactors exposed to step increases in phenol loading

To better understand how the composition of bacterial communities changes in response to different environmental conditions, we examined the influence of increasing phenol load on the distribution of the protein-coding functional gene of the largest subunit of phenol hydroxylase (LmPH) and of the 16S rRNA gene in lab-scale activated sludge reactors. LmPH diversity was assessed initially from a total of 124 clone sequences retrieved from two reactors exposed to a low (0.25 g L(-1)) and a high (2.5 g L(-1)) phenol concentration. The quantitative changes in the concentration of the eight detected genotypes accompanied changes in the phenol degradation rates, indicating a community structure-function relationship. Nonmetric dimensional analysis showed that LmPH genotypes and the denaturing gradient gel electrophoresis banding patterns clustered together by phenol concentration, rather than by reactor identity. Seven isolates, representing cultivated strains of each of the observed LmPH genotypes, exhibited a rather narrow range of physiological diversity, in terms of the growth rate and the kinetic parameters of the phenol-degrading activity. We suggest that lab-scale reactors support many ecological niches, which allow the maintenance of a high diversity of ecotypes through varying concentrations of phenol, but the ability of particular strains to become dominant members of the community under the different environmental conditions cannot be predicted easily solely from their phenol-degrading properties.