Activated Sludge Reactor Research Articles

Treatment of low-strength municipal wastewater containing phenanthrene using activated sludge and biofilm process

The main objective of this study was the comparison of activated sludge reactors with reactors containing biocarriers using a wastewater containing phenanthrene as a model compound simulating the presence of toxic substances. Five sequencing batch reactors were used. One contained a porous polyvinyl alcohol gel (PVA-gel) biocarrier and another had a high-density polyethylene biocarrier, while the other three reactors consisted of conventional activated sludge. The addition of phenanthrene at low concentration (15 μg/L in influent wastewater) did not adversely affect the removal efficiencies of chemical oxygen demand (COD) and ammonium (i.e. nitrification performance). However, with a higher addition of phenanthrene (150 μg/L in influent wastewater), a reduction in COD removal efficiency and an inhibitory effect on denitrification was observed. Generally, nutrient removal was poor, with the exception of denitrification in the reactor containing the PVA-gel. It seems that PVA-gel beads allow the formation of a stable anoxic zone in the protective core of the gel beads.

Accurate assessment of the biodegradation of cationic surfactants in activated sludge reactors (OECD TG 303A)

The continuous-fed activated sludge test (OECD TG 303A) was used to predict the removal of cationic surfactants from wastewater in activated sludge plants. However, a method to differentiate between adsorption and biodegradation is not provided in these guidelines. Assessment of removal by biodegradation was possible with analysis of the surfactant present in mixed liquid suspended solids in combination with a simple equation. This equation was derived from the mass balance of the activated sludge unit in steady state. The removal by biodegradation of decylamine, tetradecylamine, octadecylamine, dioctadecylmethylamine and dioctadecyldimethylammonium chloride that have different capacities to adsorb was >99.9%, >99.9%, 98.2%, 94.2%, and 69.0%, respectively. The total removal of all five cationic surfactants from the influent was ≥98.8%. The removal of octadecylamine spiked at different influent concentrations indicated first order kinetics.

Treatment of Nitrate-Rich Saline Effluent by Using Citrate-Rich Waste as Carbon Source and Electron Donor in a Single-Stage Activated Sludge Reactor

Disposing of nitrate-containing effluents from seawater-fed intensive aquacultural applications is a major environmental problem. A possible solution is to mix nitrate-rich effluents from marine recirculating aquaculture systems (RASs) with citrate-rich liquid wastes (CLW), a common by-product of the food industry. Where possible, such strategy can alleviate two environmental problems simultaneously, in a cost-effective fashion. However, concerns are often raised regarding secondary pollution stemming from the use of CLW, particularly related to phosphorus and heavy metals. This work showed that both phosphorus and heavy metal were completely absorbed by the bacterial sludge generated in the process, indicating low environmental risk associated with the disposal of the treated effluent to the environment. Operation of continuous stirred-tank reactor (CSTR) single-sludge denitrification reactor with CLW as electron and carbon donor resulted in high nitrate removal efficiency (>95 %) and denitrification rate of up to 1.6 g NO3-N L−1 reactor day−1 along with low bacterial biomass yield [0.23 g chemical oxygen demand (COD) new cells g−1 COD citrate]. Moreover, the use of CLW was found to be environmentally safe and equally efficient to the use of traditional, costly carbon sources such as methanol and acetic acid, rendering this alternative attractive for treatment of nitrate-rich saline effluents.

Bifurcation and chaotic in a model for activated sludge reactors

A dynamical model of an activated sludge process system is considered and analyzed. Numerical techniques are used to show when the system exhibits chaos. Three choices of bifurcation parameters produce different pictures of solution behavior in the form of limit cycles, two-torus and chaotic behavior. For some range of the reactor residence time the model exhibits chaotic behavior as well. Practical criteria are also derived for the effects of feed conditions and purge fraction on the dynamic characteristics of the bioreactor model.

Integrated fixed-biofilm activated sludge reactor as a powerful tool to enrich anammox biofilm and granular sludge

A pilot-scale activated sludge bioreactor was filled with immobile carrier to treat high ammonium wastewater. Autotrophic nitrogen elimination occurred rapidly by inoculating nitrifying activated sludge and anammox biofilm. As the ammonium loading rate increased, nitrogen removal rate of 1.2kgNm−3d−1 was obtained with the removal efficiency of 80%. Activated sludge diameter distribution profiles presented two peak values, indicating simultaneous existence of flocculent and granular sludge. Red granular sludge was observed in the reactor. Furthermore, the results of morphological and molecular analysis showed that the characteristics of granular sludge were similar to that of biofilm, while much different from the flocculent sludge. It was assumed granular sludge was formed through the continuous growth and detachment of anammox biofilm. The mechanism of granular sludge formation was discussed and the procedure model was proposed. According to the experimental results, the integrated fixed-biofilm activated sludge reactor provided an alternative to nitrogen removal based on anammox.

Simultaneous biodegradation of bisphenol A and a biogenic substrate in semi-continuous activated sludge reactors.

In this work, the simultaneous degradation of BPA and cheese whey (CW) in semi-continuous activated sludge reactors was studied. The acclimation process and microbial growth on BPA, CW and BPA + CW were analyzed. In addition, the effect of increasing CW concentration on the BPA degradation by acclimated activated sludge was also studied. In order to reduce the factors involved in the analysis of the simultaneous degradation of BPA and CW, the effect of bisphenol A (BPA) on activated sludge not previously exposed to BPA (native activated sludge) was studied. Results demonstrate that BPA concentrations lower than 40 mg l(-1) had a negligible effect on the growth of native activated sludge. In the semi-continuous reactors, the presence of CW increased the acclimation time to 40 mg l(-1) of BPA. Once the capability of degrading BPA was acquired, the removal of BPA was not affected by the presence of CW. Increasing the CW concentration did not affect the removal of BPA by the acclimated activated sludge. Additionally, the CW consumption was not modified by the presence of BPA. Kinetic and stoichiometric coefficients reported in the present work can be useful in developing mathematical models to describe the simultaneous aerobic biodegradation of a biogenic substrate, such as CW, and BPA by activated sludge.

Gravitational Search Algorithm Optimization for PID Controller Tuning in Waste-water Treatment Process

This paper presents a new approach of optimization technique in the controller parameter tuning for waste-water treatment process (WWTP) application. In the case study of WWTP, PID controller is used to control substrate (S) and dissolved oxygen (DO) concentration level. Too many parameters that need to be controlled make the system becomes complicated. Gravitational Search Algorithm (GSA) is used as the main method for PID controller tuning process. GSA is based on Newton's Law of Gravity and mass interaction. In this algorithm, the searcher agents survey the masses that interact with each other using law of gravity and law of motion. For WWTP system, the activated sludge reactor is used and this system is multi-input multi-output (MIMO) process. MATLAB is used as the platform to perform the simulation, where this optimization is compared to other established optimization method such as the Particle Swarm Optimization (PSO) to determine whether GSA has better features compared to PSO or vice-versa. Based on this case-study, the results show that transient response of GSA-PID was 20%-30% better compared to transient response of the PSO-PID controller.

English

The objective of this study was to assess a cattle manure treatment system with aerated tanks in a “free-stall” confinement system, where the recycled wastewater was used to clean the facilities and the effluent was applied to forage cultivation areas. A batch activated sludge reactor with a prolonged intermittent aeration system scaled to a 24-day hydraulic retention time was used, and the wastewater was diluted at a volume ratio of 1:1. Samples were taken at the input and interior of the aeration tanks, at the irrigation pipe exit, and from pure animal waste. The following parameters were determined: pH, temperature, oil and grease, total biochemical oxygen demand (BOD) and chemical oxygen demand (COD), total solids, total nitrogen and ammoniacal nitrogen, potassium, phosphorus, and magnesium. The results indicated that the aerobic biological treatment is effective in reducing and stabilising organic matter in wastewater.

Production of protein‐ and carbohydrate‐EPS in activated sludge reactors operated at different carbon to nitrogen ratios

AbstractBACKGROUNDThis study aimed to clarify how a variation in the carbon to nitrogen (C/N) ratio in influent wastewater affects the production and composition of extracellular polymeric substances (EPS) in activated sludge. In the literature such a comparative analysis is rarely presented, most studies on EPS focus on simultaneous organic carbon removal and nitrification whereas little attention is paid to the case of low organic load or separate‐stage nitrification.RESULTSAmong the very loosely bound, loosely bound and tightly bound EPS fractions, tightly bound EPS prevailed in semi‐continuously fed batch activated sludge reactors that were fed at a C/N ratio of 10, 5 and 0, respectively. The C/N ratio had no clear effect on total EPS production, however it changed the proportion of proteins and carbohydrates. In each sludge proteins constituted the dominant part of EPS, but the EPS of the nitrifying sludge (C/N = 0), had a definitely higher protein content. As evidenced by HPSEC fingerprints, in all EPS fractions most proteins had MWs ≤16 kDa. Depending on the C/N ratio in a reactor, high MW proteins in EPS shifted from tightly bound fractions to others.CONCLUSIONThe study is among the few that highlight how the protein and carbohydrate content in EPS changes at different C/N ratios. Since wastewater composition in a treatment system affects the chemical composition of EPS, each sludge might have different responses to uptake of xenobiotics such as metals. Further, this difference in composition might affect sludge settling, dewatering and membrane fouling. © 2014 Society of Chemical Industry

Mitigation of nitrous oxide (N2 O) emission from swine wastewater treatment in an aerobic bioreactor packed with carbon fibers.

Mitigation of nitrous oxide (N2 O) emission from swine wastewater treatment was demonstrated in an aerobic bioreactor packed with carbon fibers (CF reactor). The CF reactor had a demonstrated advantage in mitigating N2 O emission and avoiding NOx (NO3 + NO2 ) accumulation. The N2 O emission factor was 0.0003 g N2 O-N/gTN-load in the CF bioreactor compared to 0.03 gN2 O-N/gTN-load in an activated sludge reactor (AS reactor). N2 O and CH4 emissions from the CF reactor were 42 g-CO2 eq/m(3) /day, while those from the AS reactor were 725 g-CO2 eq/m(3) /day. The dissolved inorganic nitrogen (DIN) in the CF reactor removed an average of 156 mg/L of the NH4 -N, and accumulated an average of 14 mg/L of the NO3 -N. In contrast, the DIN in the AS reactor removed an average 144 mg/L of the NH4 -N and accumulated an average 183 mg/L of the NO3 -N. NO2 -N was almost undetectable in both reactors.

Biosorption and biodegradation of polyacrylate/nano-ZnO leather finishing agent and toxic effect on activated sludge

The removal of polyacrylate/nano-ZnO (PA/ZnO) from water by simultaneous biosorption and biodegradation was investigated using an activated sludge (AS) unit. About 90.9%, 93.2% and 95.1% of the total PA/ZnO was removed when the AS biomasses were 2.5, 5.0 and 10.0 g, respectively. The removal efficiency increases with the increase of initial AS concentration. More than 74.5% of the total PA/ZnO was removed in the first day, implying that biosorption was the dominant removal route. The adsorption process fitted well to the Langmuir model rather than Freundlich model. Kinetics data showed better correlation with pseudo-second order than pseudo-first order models. PA/ZnO also exhibited certain biodegradability in the activated sludge reactor. Biodegradation mechanisms of PA/ZnO were studied by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and gel permeation chromatography (GPC). The results showed that the biodegradation process occurs in the AS microorganisms mainly though chain scission. Microbial community analysis by 16S rRNA based PCR-DGGE revealed little shift in the community structure and diversity, suggesting that PA/ZnO exhibits little toxicity to microorganisms.

Upgrading the performances of ultrafiltration membrane system coupled with activated sludge reactor by addition of biofilm supports for the treatment of hospital effluents

Abstract The biological treatment of an hospital effluent has been monitored during 150 days in an activated sludge system followed by an ultrafiltration membrane (BBR-UF). After 75 days, support media was added into the bioreactor to develop a biofilm and to compare process performances of the two reactor configurations: activated sludge (AS-UF) or biofilm biological reactor (BBR-UF). The removal efficiencies of (chemical oxygen demand) COD, (total suspended solids) TSS, (volatiles suspended solids) VSS, and (total nitrogen) TN with the BBR-UF were 93.2%, 100%, 99.9% and 91.3%, respectively, compared to 87.9%, 99.6%, 97.5% and 91.1% with the AS-UF. Codeine, ketoprofen, diclofenac, naproxen, roxithromycin, metronidazole, hydrochlorothiazide, furosemide, gemfibrozil, pravastatin, and iohexol were highly removed by BBR-UF, while low removal was observed for the same molecules in the AS-UF. This could be attributed (1) to the increase of biomass concentration, (2) to the increase of sludge resident time or (3) to sorption on the biofilms. During continuous reactor operation, (trans membrane pressure) TMP increase in BBR-UF was negligible whereas membrane module in AS-UF required a regular physical maintenance. In the last case, membrane fouling was attributed to the modification of the concentration of the produced exopolymeric substances like protein and polysaccharide. The addition of biofilm supports media improved the performances of AS-UF and also decreased the negatives effects of the biomass on the membrane for the treatment of hospital wastewaters.

Monitoring the abundance and the activity of ammonia-oxidizing bacteria in a full-scale nitrifying activated sludge reactor.

Cell-specific ammonia oxidation rate (AOR) has been suggested to be an indicator of the performance of nitrification reactors and to be used as an operational parameter previously. However, published AOR values change by orders of magnitude and studies investigating full-scale nitrification reactors are limited. Therefore, this study aimed at quantifying ammonia-oxidizing bacteria (AOB) and estimating their in situ cell-specific AOR in a full-scale activated sludge reactor treating combined domestic and industrial wastewaters. Results showed that cell-specific AOR changed between 5.30 and 9.89 fmol cell(-1) h(-1), although no significant variation in AOB cell numbers were obtained (1.54E + 08 ± 0.22 cell/ml). However, ammonia-removal efficiency varied largely (52-79 %) and was proportional to the cell-specific AOR in the reactor. This suggested that the cell-specific AOR might be the factor affecting the biological ammonia-removal efficiency of nitrification reactors independent of the AOB number. Further investigation is needed to establish an empirical relationship to use cell-specific AOR as a parameter to operate full-scale nitrification systems more effectively.

Hydrodynamic Mathematical Modelling of Aerobic Plug Flow and Nonideal Flow Reactors: A Critical and Historical Review

Existing mathematical models of wastewater treatment plants focus primarily on the bioconversion processes and often do not cope with the reactor hydrodynamics. However, in the literature several aerobic plug flow bioreactors with both kinetics modelling and hydrodynamics description are reported. The authors review mathematical models of aerobic plug flow reactors, such as activated sludge reactors, fluidized bed reactors, biofilters, and trickling filters focusing on their hydrodynamic approach and on the role of the reactor configuration on the process performance. For each reactor type the following modelling approach is compared: (a) ideal model, such as plug flow or complete mixed, (b) tank in series model, (c) dispersion model and (d) computational fluid dynamic model.

Simulation and calibration of a full-scale sequencing batch reactor for wastewater treatment

The aim of this study is to apply the main mathematical models used in activated sludge reactors, the Activated Sludge Model No. 1 (ASM1) and its variations (ASM2d and ASM3), to predict the behavior of a full-scale sequencing batch reactor (SBR) used for the treatment of domestic wastewater employing the software ASIM®. Two cycles were studied, the step-feed cycle and conventional filling. Samples were taken from the raw influent, from the reactor and from the treated wastewater, and these data were used to calibrate the models. The ASM1 model was the best model to represent the cycle with only an input, while model ASM3 was the best for simulating the scaled filling cycle. This work presents calibrated parameters for the two kinds of filling. The results of these simulations indicate that the calibration process succeeded and can be used as a model for future studies.

Removal of trace organic chemicals and performance of a novel hybrid ultrafiltration-osmotic membrane bioreactor.

A hybrid ultrafiltration-osmotic membrane bioreactor (UFO-MBR) was investigated for over 35 days for nutrient and trace organic chemical (TOrC) removal from municipal wastewater. The UFO-MBR system uses both ultrafiltration (UF) and forward osmosis (FO) membranes in parallel to simultaneously extract clean water from an activated sludge reactor for nonpotable (or environmental discharge) and potable reuse, respectively. In the FO stream, water is drawn by osmosis from activated sludge through an FO membrane into a draw solution (DS), which becomes diluted during the process. A reverse osmosis (RO) system is then used to reconcentrate the diluted DS and produce clean water suitable for direct potable reuse. The UF membrane extracts water, dissolved salts, and some nutrients from the system to prevent their accumulation in the activated sludge of the osmotic MBR. The UF permeate can be used for nonpotable reuse purposes (e.g., irrigation and toilet flushing). Results from UFO-MBR investigation illustrated that the chemical oxygen demand, total nitrogen, and total phosphorus removals were greater than 99%, 82%, and 99%, respectively. Twenty TOrCs were detected in the municipal wastewater that was used as feed to the UFO-MBR system. Among these 20 TOrCs, 15 were removed by the hybrid UFO-MBR system to below the detection limit. High FO membrane rejection was observed for all ionic and nonionic hydrophilic TOrCs and lower rejection was observed for nonionic hydrophobic TOrCs. With the exceptions of bisphenol A and DEET, all TOrCs that were detected in the DS were well rejected by the RO membrane. Overall, the UFO-MBR can operate sustainably and has the potential to be utilized for direct potable reuse applications.

Quorum quenching is responsible for the underestimated quorum sensing effects in biological wastewater treatment reactors

Quorum sensing (QS) and quorum quenching (QQ) are two antagonistic processes coexisting in various bacterial communities in bioreactors, e.g., activated sludge for biological wastewater treatment. Although QS signal molecules are detected in activated sludge reactors and known to affect sludge properties and reactor performance, there has been no direct evidence to prove the endogenous existence of QQ effects in activated sludge. In this study, for the first time, acyl homoserine lactones-degrading enzymatic activity, a typical QQ effect, was discovered in activated sludge and found to considerably affect the QS detection results. The coexistence of QS and QQ bacteria in activated sludge was further confirmed by bacterial screening and denaturing gradient gel electrophoresis analysis. The method developed in this study could also be used to evaluate QQ activities in bioreactors, and a possible way is provided to tune bioreactor performance through balancing the QS and QQ processes.

Decolorization and biodegradation of the azo dye Congo red by an isolated Acinetobacter baumannii YNWH 226

A strict aerobic Acinetobacter baumannii YNWH 226, isolated from an activated sludge reactor treating textile wastewater, was able to grow on Congo red as the sole carbon source under aerobic conditions. The decolorization and TOC reduction efficiency were 99.1 and 93.72%, respectively. The effects of the Congo red concentration were studied. The environmental factors (i.e., pH, temperature and agitation speed) on the biodegradation of Congo red in aqueous phase were studied and evaluated using response surface methodology. The results indicated that when the Congo red concentration was 100 mg/L, the optimal decolorization conditions were as follows: 37°C, pH 7.0 and 180 rpm. The single A. baumannii YNWH 226 was able to form aromatic amines by reductive breakage of the azo bond and then oxidize them into non-toxic metabolites.

Integration of Chlorella protothecoides production in wastewater treatment plant: From lab measurements to process design

The exploitation of microalgae in a wastewater treatment process is currently an open issue, and its actual applicability is still under investigation. In this work the effects of temperature, day/night irradiation and bacterial competition were studied on growth and nutrient removal of Chlorella protothecoides cultivated in real and unsterilized primary urban wastewater. C. protothecoides showed a linear dependence of growth rate on temperature under continuous irradiation with a maximum at 30°C. Continuous flow experiment under day–night irradiation condition showed that a cyclic steady state was achieved, with significant differences in biomass concentration and nutrient removal after dark and light periods. The presence of a native microflora in wastewater did not affect the microalgal growth, both in batch and continuous flow experiments. N and P were efficiently removed in all conditions tested, while the COD was not consumed by microalgal biomass. Thus, in view of a large scale application, a two step depuration process would be required, where the photobioreactor will remove nutrients as N and P and an activated sludge reactor downstream will reduce the organic matter. The experimental data obtained were used to design a possible process of this type.

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).