Activated Sludge Reactor Research Articles

Activated sludge pilot plant: Comparison between experimental and predicted concentration profiles using three different modelling approaches

This paper presents an experimental and numerical study of an activated sludge channel pilot plant. Concentration profiles of oxygen, COD, NO 3 and NH 4 have been measured for several operating conditions. These profiles have been compared to the simulated ones with three different modelling approaches, namely a systemic approach, CFD and compartmental modelling. For these three approaches, the kinetics model was the ASM-1 model ( Henze et al., 2001). The three approaches allowed a reasonable simulation of all the concentration profiles except for ammonium for which the simulations results were far from the experimental ones. The analysis of the results showed that the role of the kinetics model is of primary importance for the prediction of activated sludge reactors performance. The fact that existing kinetics parameters in the literature have been determined by parametric optimisation using a systemic model limits the reliability of the prediction of local concentrations and of the local design of activated sludge reactors.

Hybrid activated sludge/biofilm process for the treatment of municipal wastewater in a cold climate region: a case study

A hybrid activated sludge/biofilm process was investigated for wastewater treatment in a cold climate region. This process, which contains both suspended biomass and biofilm, usually referred as IFAS process, is created by introducing plastic elements as biofilm carrier media into a conventional activated sludge reactor. In the present study, a hybrid process, composed of an activated sludge and a moving bed biofilm reactor was used. The aim of this paper has been to investigate the performances of a hybrid process, and in particular to gain insight the nitrification process, when operated at relatively low MLSS SRT and low temperatures. The results of a pilot-scale study carried out at the Department of Hydraulic and Environmental Engineering at the Norwegian University of Science and Technology in Trondheim are presented. The experimental campaign was divided into two periods. The pilot plant was first operated with a constant HRT of 4.5 hours, while in the second period the influent flow was increased so that HRT was 3.5 hours. The average temperature was near 11.5°C in the overall experimental campaign. The average mixed liquor SRT was 5.7 days. Batch tests on both carriers and suspended biomass were performed in order to evaluate the nitrification rate of the two different biomasses. The results demonstrated that this kind of reactor can efficiently be used for the upgrading of conventional activated sludge plant for achieving year-round nitrification, also in presence of low temperatures, and without the need of additional volumes.

Partial Nitrification in an Airlift Activated Sludge Reactor with Experimental and Theoretical Assessments of the pH Gradient inside the Sponge Support Medium

An airlift-type activated sludge reactor using a sponge support medium was fed with wastewater containing 500 mg-N/L of NH4 +-N. In order to establish partial nitrification, the reactor was kept at 35°C. Moreover, the reactor was started up with the NaHCO3 solution as an alkali agent to supply inorganic carbon for enhancement of partial nitrification. The partial nitrification was established during the period when NaHCO3 was used as an alkali agent. However, soon after changing the alkali agent to a mixture of Na2HPO4 and NaOH, the production of NO2 --N started to decrease. The change in pH inside the sponge medium revealed by the model simulation and microelectrode study showed relatively high free ammonium concentration inside the medium. Thus, partial nitrification was proved to be affected by inorganic carbon in the alkali agent. Furthermore, it was suggested that the establishment of partial nitrification in this study was due to the combination of high operating temperatures, addition of inorganic carbon, and the inhibition of NOB by the free ammonium concentration.

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).

The Different Metabolic Activity of Activated Sludge Samples Taken from Reversed A<sup>2</sup>/O Process and Conventional A<sup>2</sup>/O Process

The metabolic activity of sludge samples taken from two pilot scale activated sludge reactor was studied. The two reactors were of the same size and structure. One was operated according to the reversed A2/O process (R-reactor) and another was operated according to conventional A2/O process (C-reactor). The activities of dehydrogenase (DHA) and electron transport system (ETS) and the specific oxygen uptake rate (SOUR) of sludge taken from R-reactor were 34.98%, 22.44% and 12.70% higher than those of the sludge taken from C-reactor. As for the R-reactor, the sludge undergoes aerobic condition right after anaerobic experience. Compared to entering aerobic stage from anoxic stage (C-reactor), entering aerobic stage from anaerobic stage can significantly enhance the activity of microbes, accelerate the decomposition of organics and improve the SOUR of the sludge.

Performance of enhanced biological SBR process for aniline treatment by mycelial pellet as biomass carrier

Mycelial pellet of Aspergillus niger Y3 was used as a biomass carrier to immobilize the aniline-degrading bacterium, Acinetobacter calcoaceticus JH-9 and the mix culture of the COD rapid degradation bacteria. In order to investigate its removal effect on aniline and COD, the combined mycelial pellets were applied in the SBR. Comparison of the performances was conducted between another SBR inoculated with sole strain JH-9 and the above SBR. The results showed that the stable degradations of aniline and COD were observed in both reactors. In the SBR with combined mycelial pellet, the biological removal efficiency was about 0.9 mg aniline/(L·d). It was much higher than that in the activated sludge reactor. Meanwhile, the performances of the sedimentation velocity, liquid–solid phase separation and the effluent quality were better in the SBR. According to SEM images and PCR–DGGE analysis, the species immobilized on the biomass carrier were more predominant in this system.

Treatment of oilfield wastewater containing polymer by the batch activated sludge reactor combined with a zerovalent iron/EDTA/air system

Laboratory-scale experiments were conducted in order to evaluate the performance of a novel treatment process for oilfield wastewater based on combining chemical oxidation, performed by a zerovalent iron (ZVI), ethylenediamine tetraacetic acid (EDTA) and air process, with biological degradation, carried out in a batch activated sludge reactor. The influence of some operating variables was studied. The results showed that the optimum pretreatment conditions were 150 mg/L EDTA, 20 g/L ZVI, and a 180-min reaction time, respectively. Under these conditions, removal efficiencies for hydrolyzed polyacrylamide (HPAM), total petroleum hydrocarbons (TPH), and chemical oxygen demand (COD) were 66%, 59%, and 45%, respectively. During the subsequent 40 h of bioremediation, the concentrations of HPAM, TPH, and COD were decreased to 10, 2 and 85 mg/L, respectively. At the end of experiments, the total removal efficiencies of HPAM, TPH, and COD were 96%, 97% and 92%, respectively.

Diagnosis and Quantification of Glycerol Assimilating Denitrifying Bacteria in an Integrated Fixed-Film Activated Sludge Reactor via13C DNA Stable-Isotope Probing

Glycerol, a byproduct of biodiesel and oleo-chemical manufacturing operations, represents an attractive alternate to methanol as a carbon and electron donor for enhanced denitrification. However, unlike methanol, little is known about the diversity and activity of glycerol assimilating bacteria in activated sludge. In this study, the microbial ecology of glycerol assimilating denitrifying bacteria in a sequencing batch integrated fixed film activated sludge (SB-IFAS) reactor was investigated using (13)C-DNA stable isotope probing (SIP). During steady state SB-IFAS reactor operation, near complete nitrate removal (92.7 ± 5.8%) was achieved. Based on (13)C DNA clone libraries obtained after 360 days of SB-IFAS reactor operation, bacteria related to Comamonas spp. and Diaphorobacter spp. dominated in the suspended phase communities. (13)C assimilating members in the biofilm community were phylogenetically more diverse and were related to Comamonas spp., Bradyrhizobium spp., and Tessaracoccus spp. Possibly owing to greater substrate availability in the suspended phase, the glycerol-assimilating denitrifying populations (quantified by real-time PCR) were more abundant therein than in the biofilm phase. The biomass in the suspended phase also had a higher specific denitrification rate than the biofilm phase (p = 4.33e-4), and contributed to 69.7 ± 4.5% of the overall N-removal on a mass basis. The kinetics of glycerol based denitrification by suspended phase biomass were approximately 3 times higher than with methanol. Previously identified methanol assimilating denitrifying bacteria were not associated with glycerol assimilation, thereby suggesting limited cross-utilization of these two substrates for denitrification in the system tested.

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.

Biological treatment of natural rubber latex centrifugation effluent using activated sludge system enriched with Bacillus sp. SBS25

Natural rubber latex centrifugation effluent is highly polluting and it is difficult to process because of its high COD and BOD coupled with the excessive amounts of suspended solids. A bacterial strain Bacillus sp. SBS25, isolated from soil, was found to possess natural rubber latex degrading ability. It was exploited in the treatment of the latex centrifugation effluent along with the native flora of the effluent. The treatment with free cells of selected bacteria showed 68% reduction in COD while the fill and draw treatment method in an activated sludge reactor using the consortia and the selected isolate resulted in 92.5% reduction. The performance of the activated sludge reactor was evaluated in terms of reduction in COD, MLSS and SVI.

Impacts of single-walled carbon nanotubes on microbial community structure in activated sludge

Single-walled carbon nanotubes (SWNTs) are likely to become increasingly widespread and yet their environmental impact is not well understood. The purpose of the current study was to evaluate the impact of SWNTs on microbial communities in a 'sentinel' environmental system, activated sludge batch-scale reactors. Triplicate batch reactors were exposed to SWNTs and compared to control reactors exposed to impurities associated with SWNTs. Automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterial community structure in each reactor. SWNT exposure was found to impact microbial community structure, while SWNT-associated impurities had no effect, compared to controls. 16S rRNA gene sequence analysis indicated that dominant phylotypes detected by ARISA included members of the families Sphingomonadaceae and Cytophagacaceae and the genus Zoogloea. ARISA results indicated an adverse impact of SWNTs on the sphingomonad relative to other community members. Changes in community structure also occurred in both SWNT-exposed and control reactors over the experimental time period and with the date on which activated sludge was obtained from a wastewater treatment facility. These results indicate that SWNTs differentially impact members of the activated sludge reactor bacterial community. The finding that community structure was affected by SWNTs indicates that this emerging contaminant differentially impacted members of the activated sludge bacterial community and raises the concern that SWNTs may also affect the services it provides.

Evaluating the influence of process parameters on soluble microbial products formation using response surface methodology coupled with grey relational analysis

Soluble microbial products (SMPs) present a major part of residual chemical oxygen demand (COD) in the effluents from biological wastewater treatment systems, and the SMP formation is greatly influenced by a variety of process parameters. In this study, response surface methodology (RSM) coupled with grey relational analysis (GRA) method was used to evaluate the effects of substrate concentration, temperature, NH4+-N concentration and aeration rate on the SMP production in batch activated sludge reactors. Carbohydrates were found to be the major component of SMP, and the influential priorities of these factors were: temperature>substrate concentration>aeration rate>NH4+-N concentration. On the basis of the RSM results, the interactive effects of these factors on the SMP formation were evaluated, and the optimal operating conditions for a minimum SMP production in such a batch activated sludge system also were identified. These results provide useful information about how to control the SMP formation of activated sludge and ensure the bioreactor high-quality effluent.

Influence of the employment of adsorption and coprecipitation agents for the removal of PPCPs in conventional activated sludge (CAS) systems

Three activated sludge reactors were operated to improve the removal of organic micropollutants such as Pharmaceutical and Personal Care Products (PPCPs). Reactor 1 (R1) was operated as a Conventional Activated Sludge reactor (CAS), Reactor 2 (R2) consisted of a CAS unit that was continuously fed with FeCl3 whereas granular activated carbon (GAC) was fed directly into the mixed liquor of Reactor 3 (R3) in order to attain concentrations in the range 100-1,000 mg/L. PPCPs removal rates varied depending on the compound present in each reactor during the entire 220 days of operation. Some substances showed the same behaviour in all reactors, such as the acidic pharmaceuticals naproxen and ibuprofen, which were almost completely removed (> 90%). More hydrophobic organic substances, like musk fragrances, were about 90% removed after 40 days of operation in all of the reactors. The main difference between the three reactors was obtained in R3 when the GAC concentrations in the aeration tank were around 500-1,000 mg/L. Under these conditions, the more recalcitrant compounds like diazepam and carbamazepine could be removed by up to 40%, and diclofenac up to 85%. Adsorption isotherms for PPCPs were obtained with activated carbon, and the results were successfully fitted to the Freundlinch equation. The more recalcitrant compounds (carbamazepine, diazepam and diclofenac) had the highest adsorption capacities onto GAC, which is consistent with the behaviour observed in R3 and helps to identify the removal mechanism (adsorption for these compounds, whereas absorption for fragrances).

Simultaneous Organic Matter Removal in a Cyclic Activated Sludge Reactor from Municipal Waste Water

The aerobic and anaerobic cyclic activated sludge reactor of A/O process was separated into an A/O domestication segments and organic matter removal ability strengthen segments. In the A/O disposal system, organic carbon degradation, nitrogen and phosphorus removal from municipal waste water in reactor were investigated. Results showed that good performance of the A/O disposal system was achieved and the highest removal efficiencies of COD, TN and TP were 96%, 50% and 75%, respectively. When organic loadings varied from low to high, the removal ability increased and then the hybrid microbe in activated sludge degradation ability became strong. So the cyclic activated sludge was a useful method for eliminate organic matter removal from municipal waste water.

N2O Emissions from Activated Sludge Processes, 2008−2009: Results of a National Monitoring Survey in the United States

Despite recognition of the possible role of biological nitrogen removal (BNR) processes in nitrous oxide (N(2)O) emission, a measured database of N(2)O emissions from these processes at the national scale does not currently exist. This study focused on the quantification of N(2)O emissions at 12 wastewater treatment plants (WWTPs) across the United States using a newly developed U.S. Environmental Protection Agency (USEPA) reviewed protocol. A high degree of variability in field-scale measurements of N(2)O was observed, both across the WWTPs sampled and within each WWTP. Additionally, aerobic zones, which have hitherto not been considered in the USEPA approach of estimating N(2)O emissions, generally contributed more to N(2)O fluxes than anoxic zones from BNR reactors. These results severely qualify the conventional use of a single emission factor to "estimate" N(2)O emissions from BNR processes, solely by virtue of denitrification. Upon subjecting the nationwide data set to multivariate regression data mining, high nitrite, ammonium, and dissolved oxygen concentrations were positively correlated with N(2)O emissions from aerobic zones of activated sludge reactors. On the other hand, high nitrite and dissolved oxygen concentrations were positively correlated with N(2)O emissions from anoxic zones. Based on these results, it can be argued that activated sludge processes that minimize transient or permanent build up of ammonium or nitrite, especially in the presence of dissolved oxygen, are expected to have low N(2)O emissions.

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.

Microbial succession in response to 1,4-dioxane exposure in activated sludge reactors: Effect of inoculum source and extra carbon addition

Bacterial community succession related to 1,4-dioxane exposure was investigated in two different activated sludge-inoculated reactors (municipal wastewater and dye industrial wastewater sludge), with or without additional carbon source, for 7 weeks. The denaturing gradient gel electrophoresis (DGGE) analysis revealed that microbial succession varied according to the inoculum sludge sources and the presence or absence of the extra carbon source. In the reactor inoculated with the municipal sludge, bacterial species belonging to α - and γ -Proteobacteria and Nitrospira class were dominant over time. On the other hand, bacterial species showing significant homology to β -Proteobacteria (e.g., Methylibium petroleiphilum PM1) and Actinobacteria class, who have been reported to have 1,4-dioxane degradation potential, were found in the industrial sludge-inoculated reactors. The appearance of these bacteria demonstrates that the microbial community structure of the inoculum and the presence of an extra carbon source affect the microbial succession in the system exposed to 1,4-dioxane.

Biodegradation and Adsorption of Antibiotics in the Activated Sludge Process

The removal of 11 antibiotics of 6 classes, that is, two beta-lactams (ampicillin and cefalexin), two sulfonamides (sulfamethoxazole and sulfadiazine), three fluoroquinolones (norfloxacin, ofloxacin, and ciprofloxacin), one tetracyclines (tetracycline), two macorlides (roxithromycin and anhydro-erythromycin), and one others (trimethoprim), in activated sludge process was investigated using two series of batch reactors treating freshwater and saline sewage respectively. At environmental relevant concentrations tested in this study, biodegradation and adsorption were the major removal routes for the target antibiotics, where volatilization and hydrolysis were neglectable. Among the 11 target antibiotics, cefalexin and the two sulfonamides were predominantly removed by biodegradation in both freshwater and saline sewage systems. Ampicillin, norfloxacin, ciprofloxacin, ofloxacin, tetracycline, roxithromycin, and trimethoprim were mainly removed by adsorption. Divalent cations (Ca(2+) and Mg(2+)) in saline sewage significantly decreased the adsorption of the three fluoroquinolones onto activated sludge. These three fluoroquinolones also exhibited certain biodegradability in the saline activated sludge reactor. Erythromycin-H(2)O was persistent in both saline and freshwater systems under the experimental conditions and could not be removed at all. Kinetics study showed that biodegradation of cefalexin, the two sulfonamides and the three fluoroquinolones followed first-order model well (R(2): 0.921-0.997) with the rate constants ranging from 5.2 x 10(-3) to 3.6 x 10(-1) h(-1).