An activated sludge-based biosensor for rapid IC50 estimation and on-line toxicity monitoring

Antimicrobial activity of pharmaceutical cocktails in sewage treatment plant effluent - An experimental and predictive approach to mixture risk assessment

Municipal wastewater contains multi-component mixtures of active pharmaceutical ingredients (APIs). This could shape microbial communities in sewage treatment plants (STPs) and the effluent-receiving ecosystems. In this paper we assess the risk of antimicrobial effects in STPs and the aquatic environment for a mixture of 18 APIs that was previously detected in the effluent of a European municipal STP. Effects on microbial consortia (collected from a separate STP) were determined using respirometry, enumeration of culturable microorganisms and community-level physiological profiling. The mixture toxicity against selected bacteria was assessed using assays with Pseudomonas putida and Vibrio fischeri. Additional data on the toxicity to environmental bacteria were compiled from literature in order to assess the individual and expected joint bacterial toxicity of the pharmaceuticals in the mixture. The reported effluent concentration of the mixture was 15.4 nmol/l and the lowest experimentally obtained effect concentrations (EC₁₀) were 242 nmol/l for microbial consortia in STPs, 225 nmol/l for P. putida and 73 nmol/l for V. fischeri. The lowest published effect concentrations (EC₅₀) of the individual antibiotics in the mixture range between 15 and 150 nmol/l, whereas 0.9-190 μmol/l was the range of bacterial EC₅₀ values found for the non-antibiotic mixture components. Pharmaceutical cocktails could shape microbial communities at concentrations relevant to STPs and the effluent receiving aquatic environment. The risk of antimicrobial mixture effects was completely dominated by the presence of antibiotics, whereas other pharmaceutical classes contributed only negligibly to the mixture toxicity. The joint bacterial toxicity can be accurately predicted from the individual toxicity of the mixture components, provided that standardized data on representative bacterial strains becomes available for all relevant compounds. These findings argue for a more sophisticated bacterial toxicity assessment of environmentally relevant pharmaceuticals, especially for those with a mode of action that is known to specifically affect prokaryotic microorganisms.

Adaptive use of a personal glucose meter (PGM) for acute biotoxicity assessment based on the glucose consumption of microbes

In this study, a new method for acute biotoxicity assessment was proposed by measuring the glucose consumption of microbes with a personal glucose meter (PGM).

Toxicity measurement in biological wastewater treatment processes: a review

Biological wastewater treatment processes (WWTPs), by nature of their reliance on biological entities to degrade organics and sometimes remove nutrients, are vulnerable to toxicants present in their influent. Various toxicity measurement methods have been adopted for biological WWTPs, but most are performed off-line, and cannot be adapted to on-line monitoring tools to provide an early warning for WWTP operators. However, the past decade has seen a rapid expansion in the research and development of biosensors that can be used for toxicity assessment of aquatic environments. Some of these biosensors have also been shown to be effective for use in biological WWTPs. Nevertheless, more research is needed to: examine the sensitivity of assays and sensors based on single organisms to various toxicants and develop a matrix of biosensors or a biosensor incorporating multiple organisms that can protect WWTPs; test the micro fuel cell (MFC)-based biosensors with real wastewaters and correlate the results with the well-established oxygen uptake rate (OUR)-based or CH4-based toxicity assay; and, develop advanced data processing methods for interpreting the results of on-line toxicity sensors in real WWTPs to reduce the noise due to the normal fluctuation in influent quality and quantity.

A novel integrated biosensor based on co-immobilizing the mediator and microorganism for water biotoxicity assay

A novel integrated biosensor for biotoxicity assay has been developed by co-immobilizing microorganisms and mediators within a novel redox hydrogel.

Long-term effects of Ni(II) on the performance and activity of activated sludge processes

The long-term effects of Ni(II) on substrate removal and microorganism activities were investigated by operating sequencing batch reactors (SBRs). Compared to the control system lacking Ni(II), the removal efficiencies of total organic carbon (TOC) and ammonium nitrogen (NH4(+)-N) in SBR system loading with 10mgL(-1) Ni(II) decreased drastically from 90.2±3.6 percent to 75.0±8.9 percent, and 99.2±0.6 percent to 50.8±11.5 percent, respectively. As compared to the control system, a inhibitory rate of more than 50 percent for the 2,3,5-triphenyltetrazolium chloride electron transport system (TTC-ETS) and the 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride electron transport system (INT-ETS), and 43 percent for the specific oxygen uptake rate (sOUR) were detected in SBR system loading with 20mgL(-1) Ni(II). TTC-ETS, INT-ETS, and sOUR were significantly correlated with substrate removal efficiencies, suggesting that they could all serve as effective indicators of the performance of activated sludge processes. Additionally, INT-ETS is superior to sOUR and TTC-ETS in detecting the toxic effects of Ni(II) on sludge microorganism activity.

Effects of Cr(VI) on the performance and kinetics of the activated sludge process

The substrates removal performance, removal kinetics and the electron transport system (ETS) of sludge were investigated by sequencing batch reactors (SBR) and batch assays, respectively. Compared to the control system, significant decreases were observed in substrate removal efficiency with the Cr(VI)-feeding concentration up to 5 mg L(-1) in SBR system. And the recovery for NH4+-N removal were more difficult than that of COD after the termination of Cr(VI)-feeding. Significant inhibitory effects of Cr(VI) on the ETS activity and substrate removal kinetics were observed in the batch assays. The inhibitory effects of Cr(VI) would be overestimated on COD removal and underestimated on NH4+-N removal by the short-term batch assay as compared to the long-term operations. Additionally, significant correlations between the ETS activity and the inhibitory rates of Cr(VI) on substrate removal indicated the ETS activity can provide effective predictions on the potential performance of substrate removal in activated sludge.

Estimating the toxicities of organic chemicals in activated sludge process

The experimental logEC50 toxicity values of 104 compounds causing bioluminescent repression of the bacterium strain Pseudomonas isolated from an industrial wastewater were studied. Using the Best Multilinear Regression method implemented in CODESSA PRO, models with up to 8 theoretical descriptors were obtained. Utilizing a rigorous descriptor selection and validation procedure a reliable QSAR model with four parameters was selected as best. The proposed model emphasizes the importance of the halogen atoms presented in each compound, the possibility of H-bond formation and the flexibility and degree of branching of the molecules. As pointed out by many researchers, the contribution of the octanol-water partition coefficient to the explanation of the toxicity effect was also found to be significant. In addition, the model currently proposed was compared to those reported earlier and its advantages were discussed in detail.

New concept for a toxicity assay based on multiple indexes from the wave shape of damped metabolic oscillation induced in living yeast cells (part I): characterization of the phenomenon

The damped glycolytic oscillation phenomenon occurring in starved cells of the yeast Saccharomyces cerevisiae (NBRC 0565) was characterization for application to a toxicity bioassay. S. cerevisiae was grown under semi-anaerobic conditions. The transient oscillations were observed photometrically as the time course of the fluorescent intensity of reduced pyridine nucleotide resulting from instantaneous addition of glucose to a cell suspension. In this study, simple and reproducible conditions inducing damped oscillations were obtained by modifying a literature method. For estimation of the wave shapes of the damped oscillations we used six indexes. To investigate the total reproducibility as the averaged relative standard deviation (RSD(av)) for the six indexes obtained from the wave shapes, the damped oscillations were induced under the optimum conditions and the RSD(av) values were calculated as 14% in a buffer cell suspension (n = 62) and 22% in a water cell suspension (n = 78). Finally, the effects of glucose concentration on the six indexes were examined, and all the indexes changed when the glucose concentration was changed. Excellent correlations were obtained between the index of oscillation-state time and the concentration of glucose in a buffer cell suspension (r = 0.9985, 0.5-250 mmol L(-1), 10 points) and in a water cell suspension (r = 0.9989, 2.5 micromol L(-1)-250 mmol L(-1), 12 points), respectively.

A simple and highly repeatable colorimetric toxicity assay method using 2,6-dichlorophenolindophenol as the redox color indicator and whole eukaryote cells

A simple and highly reproducible toxicity assay method was studied by employing 2,6-dichlorophenolindophenol (DCIP) as a redox color indicator, baker's yeast Saccharomyces cerevisiae, and a thermostable three-consecutive-stir unit. The absorbance of DCIP was decreased by increasing the metabolism activity of S. cerevisiae to intake glucose as an organic substance. By optimizing the measurement conditions, we obtained highly sensitive responses to glucose between 0.75 and 30 mg/L (eight points, n = 3) with an incubation time of the reaction mixture of 10 min at 30 degrees C. An excellent value of 1.15% was obtained as the average of the repeatability from eight points. Next, for the characterization of this method, we investigated the influence on the colorimetric response of dissolved substances, such as inorganic ions and surfactants, in natural water. Furthermore, the colorimetric responses to several toxicants were examined using Cu2+, Mn2+, Zn2+, Cr3+, and Fe3+ as heavy-metal ions and simazine as an agricultural chemical. As a result, notable colorimetric responses were obtained for Cu2+ and Mn2+ at several concentrations, and the results were compared with those obtained using river water as a real sample. In the stability test, responses to 30 mg/L glucose were obtained for 28 days when the yeast cell suspension was stored at 4 degrees C (response reduction, 43.9%; average of the relative standard deviation for nine testing days, 22.7%; average of repeatability, 1.01%).

New concept for a toxicity assay based on multiple indexes from the wave shape of damped metabolic oscillation induced in living yeast cells (part II): application to analytical toxicology

An ideal toxicity assay should utilize multiple indexes obtained from transient changes of metabolic activities. Here, we demonstrate the possibility for a novel toxicity bioassay using the damped glycolytic oscillation phenomenon occurring in starved yeast cells. In a previous study, the phenomenon was characterized in detail. Under optimum conditions to induce the phenomenon, the wave shapes of the damped glycolytic oscillations were changed by the instantaneous addition of both glucose and chemicals and by changing the chemical concentration. We estimated the changes in the oscillation wave shapes as six indexes, i.e., the number of wave cycles, maximum amplitude, oscillation frequency, attenuation coefficient, initial peak height, and non-steady-state time. These index changes were obtained from several kinds of chemicals. The chemicals, especially those for acids (0.01-100 mM HCl and 0.01-50 mM citric acid), bases (0.001-50 mM KOH), heavy metal ions (1-1,000 mg L(-1); Cu(2+), Pb(2+), Cd(2+), Hg(2+)), respiratory inhibitors (3-500 mg L(-1) NaN(3)), dissolved oxygen removers (10-300 mg L(-1) NaSO(3)), surfactants (10-200 mg L(-1) benzalkonium chloride), and aldehyde (10-1,000 mg L(-1) acetaldehyde), showed characteristic patterns depending on each chemical and its concentration. These significant results demonstrate the possibilities of new methods for both toxicity qualification and quantification.

Rapid activated sludge respiration inhibition test performed by CO2 producing rate using a carbon dioxide sensor

The rapid activated sludge inhibition test (rapid ASRI) is one of the promising bioassays to evaluate environmental risk to the ecosystem caused by various pollutants. To improve the sensitivity and stability of ASRI, the CO2 producing rate (CPR) using a carbon dioxide gas sensor was employed to examine the respiration activity of activated sludge and to compare it to that by the conventional activated sludge respiration inhibition test using oxygen uptake rate (OUR) by EC50 values derived from dose response curve. Detection of respiratory activity based on CPR has higher reliability and sensitivity than that of OUR. It should be noted that the sensitivity of CPR for evaluating toxicity is sufficiently high in terms of derived dose response curve of some model environmental pollutants and the resultant EC50 values.

Assessing wastewater toxicity to activated sludge: recent research and developments

Toxicants in municipal sewage treatment plant (STP) influent wastewater may inhibit the biological activity of the activated sludge and cause treatment plant process upsets. Such process upsets may be avoided if influent wastewater is monitored for toxicity and protective actions are taken when toxicity is detected. A comprehensive review of the methods that can be used for assessing wastewater toxicity to biological treatment systems was conducted several years ago and the resultant report was published in 2000 by Water Environment Research Foundation (WERF). The WERF report also specified the criteria for influent wastewater toxicity monitoring methods and suggested research needs to be addressed. A significant amount of effort was made since the publication of the WERF report to develop new assays or devices and to improve existing ones. In this manuscript, recent research and developments in methods for assessing wastewater toxicity to activated sludge were reviewed. The literature indicates that bioluminescence- and respirometry-based methods received much attention in recent research. A comparison of the new/improved methods with the criteria described in the WERF report reveals that none of these methods has been shown to meet all the specified criteria. The present review also indicates that research efforts since 2000 have not fully taken into account the criteria for influent wastewater toxicity monitoring methods and have not addressed the research needs proposed in the WERF report.

Toxicity assessment of common xenobiotic compounds on municipal activated sludge: comparison between respirometry and Microtox

The toxicity of four xenobiotic compounds 3,5-dichlorophenol, formaldehyde, 4-nitrophenol and dichloromethane, representative of industrial wastewater contaminants was evaluated by a simple respirometric procedure set up on the basis of OECD Method 209 and by the Microtox bioassay. Very good reproducibility was observed for both methods, the variation coefficients being in the range of 2-10% for the respirometric procedure and 6-15% for Microtox, values that can be considered very good for a biological method. Comparison of EC(50) data obtained with the two methods shows that in both cases 3,5-dichlorophenol is more toxic than other compounds investigated and dichloromethane has a very low toxicity value. Intermediate EC(50) values were found for the two other chemicals, formaldehyde and 4-nitrophenol. Moreover, the Microtox EC(50) values are generally lower (except for dichloromethane) than the respirometric ones: these differences could be explained by the fact that the Microtox method uses a pure culture of marine species and, therefore, should not necessarily be expected to behave like a community of activated sludge bacteria. In conclusion, both methods can be usefully applied for toxicity detection in wastewater treatment plants but it is advisable to take into account that Microtox is more sensitive than respirometry in estimating the acute toxicity effect on the biomass operating in the plant.

Microbial sensors on a respiratory basis for wastewater monitoring

In respect of their rapidity, their online capabilities, and their moderate costs, biosensing systems generally offer an attractive alternative to the existing methods of water analysis. Additionally, one particular advantage of microbial biosensors is the ability to measure direct effects on living cells, e.g., their respiratory activity and its alteration caused by environmental pollutants. It is true that microbial sensors, often do not provide the optimum solution for the determination of individual analytes when compared to established physico-chemical analysis methods. However, these biosensing devices are predestined for the summary determination of environmentally relevant compounds and their complex effects, respectively. For this reason, microbial sensors allow an integral evaluation of the degree of environmental pollution including the interaction of various compounds. Moreover, in some cases specific metabolic pathways in microorganisms are used, resulting in the development of microbial sensors for the more selective analysis for those compounds or pollutants, which cannot be measured by simple enzyme reactions, e.g., the determination of aromatic compounds and heavy metals. This chapter gives an overview of microbiological biosensors on respiratory basis for the measurement of the following environmentally relevant compounds: inorganic N-compounds, heavy metals, organic xenobiotics and the estimation of sum parameters or so-called complex parameters such as BOD, ADOC, N-BOD, and the inhibition of nitrification.

Monitoring the toxicity of phenolic chemicals to activated sludge using a novel optical scanning respirometer

This paper reports the development of optical scanning respirometer for determining the toxicity of chemicals to activated sludge. The respirometer is used to measure the dissolved oxygen concentration by monitoring the luminescence intensity of ruthenium dye immobilized in a polymer film in contact with the wastewater sample. The intensity is related to the extent of oxygen quenching of luminescence. The toxicity of chemicals can be evaluated by measuring the inhibition on respiration rate of microorganism using the scanning respirometer. The IC50 values (concentration of a chemical that exhibits 50% respiration inhibition) of various phenolic chemicals in activated sludge were determined. The performance of this method is compared with other toxicity methods. The experimental results indicate that the reproducibility and sensitivity of this respirometer are reasonably good.

A microbial sensor for detecting inhibitors of nitrification in wastewater

A biosensor for rapid and reproducible measurements of inhibitors of nitrification in environmental samples has been developed. The biosensor is mainly designed to be used for wastewater control and consists of a Clark oxygen probe as a transducer and an immobilised mixed nitrifying culture as the microbial component. The measuring principle is based on the direct determination of bacterial metabolic activity by measuring the oxygen consumption rate of the microbial immobilisate. Both the prototype of a laboratory device and a field device have been realised. The laboratory device can be used to determine the nitrification inhibiting effect of individual chemical compounds as well as of environmental samples. The field device was constructed for on-line monitoring of inhibitors in sewage systems.

Microbial cyanide sensor for monitoring river water

A microbial cyanide sensor using Saccharomyces cerevisiae for monitoring a river water is described. This sensor is based on the inhibition of S. cerevisiae's respiration by cyanide. This sensor is a reactor type flow system and composed of two oxygen electrodes and a reactor which contains S. cerevisiae immobilized beads. The S. cerevisiae's respiration activity is measured using the oxygen electrodes. The sensor showed a linear response in the range from 0 to 15 microM and maintained stable response for 9 days at ambient temperature. The sensor was optimized for the monitoring of river water and was applied to river water analysis.