Fraction Of Suspended Solids Research Articles

The effect of fine grits and fine debris concentrations on the MLVSS/MLSS ratio of an activated sludge system

This study embarks on an explorative investigation into the effects of typical concentrations and varying particle sizes of fine grits (FG, the involatile portion of suspended solids) and fine debris (FD, the volatile yet unbiodegradable fraction of suspended solids) within the influent on the mixed liquor volatile suspended solids (MLVSS)/mixed liquor suspended solids (MLSS) ratio of an activated sludge system. Through meticulous experimentation, it was discerned that the addition of FG or FD, the particle size of FG, and the concentration of FD bore no substantial impact on the pollutant removal efficiency (denoted by the removal rate of COD and ammonia nitrogen) under constant operational conditions. However, a notable decrease in the MLVSS/MLSS ratio was observed with a typical FG concentration of 20 mg/L, with smaller FG particle sizes exacerbating this reduction. Additionally, variations in FD concentrations influenced both MLSS and MLVSS/MLSS ratios; a higher FD concentration led to an increased MLSS and a reduced MLVSS/MLSS ratio, indicating FD accumulation in the system. A predictive model for MLVSS/MLSS was constructed based on quality balance calculations, offering a tool for foreseeing the MLVSS/MLSS ratio under stable long-term influent conditions of FG and FD. This model, validated using data from the BXH wastewater treatment plant (WWTP), showcased remarkable accuracy.

Spatial and temporal distribution of geochemical elements and their processes in different size fractions–Miri River (NW Borneo)

The toxicity, persistence, and propensity for accumulation of metals in aquatic environments have raised significant concerns globally. Expansion of urbanization with the growth of industrial and agricultural sectors in Miri City results in a high concentration of pollutants that flow directly into the Miri River. Hence, this study provides a comprehensive analysis of the Miri River water quality, focusing on spatial and temporal variations. River water samples were collected in two different time periods and analysed for physico-chemical parameters includes major ions, nutrients, metals and isotopes. Particularly, the metals were analysed in different size fractions (particulate and colloid) of the suspended solids. Geochemical plots, pollution index, geochemical modelling and factor analysis were used for the data analysis. Interpretation of data reveals that the mean concentration of metals in river water were increased from downstream to the upstream of the river irrespective of the seasons. Major ions were mostly derived from the chemical weathering of source rocks, which was supported by the Gibbs plot. Piper plot indicates the seasonal shifting of water types from Ca–Mg to Na–Cl. Isotopic signatures reveal direct atmospheric precipitation and evaporation were the major origins of river water. Fe was the dominant metal concentration in river water irrespective of the seasons (mean concentration 1.05 mg/L). Fe and Zn were the dominant metal concentration observed in all the 3 size fractions of suspended solids. Industrial activities and seawater influx dominate in the downstream, whereas weathering and agricultural inputs are significant in the upstream of the river. Particulate and colloidal fractions are the major contributors for the metal transport in the midstream and downstream of the river. The outcome of this study offer a thorough understanding of the seasonal elemental distribution at different size fractions, geochemical behaviour and the pollution status of the Miri River. With this knowledge, sustainable management strategies can be developed for this crucial water resource to the benefit of Miri community.

Aquatic particulate absorption coefficient combining extraction and bleaching optimized for inland waters

AbstractThe particulate absorption coefficient is one of the fundamental inherent optical properties describing interactions of light with material in water. Its spectral properties contain important information about chemical and biological constituents. It is often partitioned into algal and non‐algal fractions which provide useful information describing phytoplankton. Particulate absorption coefficient has been routinely measured in the ocean particularly to calibrate remote sensing algorithms. However, the methods to measure marine algal and non‐algal absorbing fractions might fail in freshwaters due to difficulties extracting green‐algae pigments and cyanobacterial phycocyanin and the high organic content of the non‐algal particles, making direct bleaching biased. In this work, we describe a method with sequential extraction, bleaching, and post‐processing to obtain unbiased pigments and non‐algal absorption fractions in freshwater environments, and we compare it against the resulting fractions obtained by only extraction or bleaching, using samples collected from 649 lakes across Canada. The resulting non‐algal particles spectra from our method appear free of interfering pigments while maintaining spectral shapes, as verified by the higher correlation coefficient between the 400 and 700 nm exponential coefficient (S, often referred to as slope) of the non‐algal particles spectra and the organic fraction of total suspended solids, and by having a better correlation between the ratio of absorption coefficient of phytoplankton at 620 and 676 nm and cyanobacterial biomass percentage. Overall, this method solves the two problems in freshwater particulate absorption partitioning associated with (1) unextracted pigments with methanol extraction methods and (2) bias introduced to non‐algal absorption spectra from NaOH bleaching.

Enhanced Sewage Sludge Drying with a Modified Solar Greenhouse

This work reports the results obtained with an innovative configuration of a closed-static solar greenhouse for sludge drying. The novelty of the solar greenhouse configuration consisted in using a forced ventilation system to provide hot air for sludge drying and the utilization of solar irradiation for energy supply. Wet sewage sludge (97% humidity) was successfully dried up to a residual humidity close to 5% after 25 days during wintertime. The increase of the airflow rate supplied under the sludge bed improved the sludge drying rate. Moreover, the fraction of volatile suspended solids decreased from 70% to 41% after 13 days, indicating that air supply promoted the simultaneous stabilization of the sludge as a side-effect to the drying process. Overall, the specific energy consumption per ton of evaporated water was estimated to approximately 450 kWh/t, resulting in about 55% of energy demand lower than a conventional thermal drying system, while using only free solar energy. The achieved high weight reduction of up to 99% implies a noticeable reduction of the excess sludge handling costs, indicating that solar greenhouse drying is a highly interesting opportunity for sludge drying in medium-small sized WWTPs.

Light availability regulated by particulate organic matter affects coral assemblages on a turbid fringing reef

Recently, increasing evidence suggests that reef-building corals exposed to elevated suspended solids (SS) are largely structured by changes in underwater light availability (ULA). However, there are few direct and quantitative observations in situ support for this hypothesis; in particular, the contribution of SS to the diffuse attenuation coefficient of the photosynthetically active radiation (Kd-PAR) variations is not yet fully understood. Here, we investigated the variations in ULA, the structure of coral assemblages, and the concentration and composition of SS on the Luhuitou fringing reef, Sanya, China. Light attenuation was rapid (Kd-PAR: 0.60 ± 0.39 m-1) resulting in a shallow euphotic depth (Zeu-PAR) (<11 m). Benthic PAR showed significant positive correlations with branching and corymbose corals (e.g. Acropora spp.), while massive and encrusting species (e.g. Porites spp.) dominated the coral communities and showed no significant correlations with PAR. These results indicate that the depth range available for coral growth is shallow and the tolerance to low-light stress differs among coral species. Notably, Kd-PAR showed no significant correlations with the grain size fractions of SS, whereas significant positive correlations were found with its organic fraction content, demonstrating that the light attenuation of SS is mainly regulated by particulate organic matter (POM). Intriguingly, our isotopic evidence revealed that POM concentration contributed the most to changes in Kd-PAR, with its source being slightly less important. Combined, our results highlight ULA regulated by POM is an important factor in contributing to changes in coral assemblages on inshore turbid reefs, and reducing the input of terrestrial materials, especially POM, is an effective measure to alleviate the low-light stress on sensitive coral species.

Computational prediction of the just-suspended speed, Njs, in stirred vessels using the lattice Boltzmann method (LBM) coupled with a novel mathematical approach

The determination of the minimum agitation speed, Njs, to achieve the just-suspended off-bottom solid suspension state in liquids in stirred vessels is an issue of significant importance in industrial processes. Here, Njs was computationally predicted for a stirred, fully baffled vessel provided with different axial or radial impellers using an LBM-based CFD model coupled with a novel method to extract Njs from the computational results. Accordingly, the number of solid particles in a very thin control volume near the bottom of the vessel were computationally predicted over a range of agitation speeds, N, to determine the mass fraction of suspended solids, Xm. A regression analysis based on the logistic equation was then applied to the Xm-N curves and a simple, derivative-based mathematical method was applied to predict Njs. The results obtained with this novel computational approach were found to be in good agreement with previous experimental data.

The COVID-19 Pandemic: New Knowledge on the Impact of Air Quality on the Spread of Coronavirus Infection in Cities.

—Suspended substances in the air form clusters with coronavirus particles and spread up to 10 m from the source of infection. The importance of taking air pollution into account when simulating the spread of the COVID-19 pandemic is due to the similarity in the health impacts made by the coronavirus and the respirable fraction of suspended solids. In Europe, up to 6.6% of deaths and in China up to 11% of deaths from COVID-19 are due to ambient air pollution. In epidemiological models, this factor must be considered along with other reasons for the development of coronavirus infection. In Russian cities, increased air pollution can be one of the risk factors for the development of an epidemic.

Sludge Production Characteristics of SedimentationㆍDissolved Air Flotation (SeDAF) Process for Enhanced Phosphorus Removal

Objectives : In order to prevent eutrophication and algal blooms, Ministry of Environment in Korea reinforced the effluent standards of wastewater treatment facilities. As a result, many advanced wastewater treatment processes have been implemented nationwide. Current conventional treatment systems have usually been facing high operational costs and large sludge production problems. Therefore, it is essential to develop more economic and efficient process to cope with these issues.Methods : The sedimentation and dissolved air flotation (SeDAF) process has been developed, that integrates sedimentation and dissolved air flotation. Several simulation experiments were carried out to verify and optimize the operation conditions of the SeDAF process. Removal efficiencies of each water quality item and sludge mass balance were analyzed intensively in the SeDAF process using the modified jar-test.Results and Discussion : Removal efficiencies of the SeDAF process were higher and more stable than those of sedimentation process. Several ‘sludge production / coagulant dosage’ ratios were analyzed and the representative value of 4 mg･L-1 as SS / mg･L-1 as Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; was obtained in the SeDAF process. Fractions of suspended solids (SS) and total phosphorus (T-P) in sludge were measured; the ratios of flotation sludge to sedimentation sludge and fractions of flotation sludge in total sludge had their typical convergence ranges for the conditions of optimal coagulant dosage.Conclusions : The ratios or fractions of SS and T-P in sludge could be applied as the evaluation indicators of the SeDAF process. The reduction of coagulant dosage could be corresponded directly to the reduction of sludge production.

Insights into total estrogenic activity in a sewage-impacted urban stream assessed via ER transcriptional activation assay: Distribution between particulate and dissolved phases

Endocrine disrupting chemicals (EDC) are exogenous substances that can potentially mimic hormonal substances and cause adverse effects on the endocrine system of living beings. The behavior and fate of these compounds in the environment is directly related to their physical-chemical properties, which indicate great affinity for solid and organic particles and suggest an inherent mechanism of fractionation between dissolved and particulate phases of aqueous matrices. However, few studies have been considering this fact when quantifying these pollutants and their effects through bioassays. In this study, the fractionation of estrogenic substances between dissolved and particulate phases in an urban stream was investigated via estrogenic activity evaluation by the YES assay. Two fractions of suspended solids (< 0.7 µm and between 0.45 and 0.7 µm) and the dissolved phase were considered and two approaches of SPE percolations were applied. Total estradiol equivalent (E2-Eq) values were observed in the 29–65 ng L−1 range, of which 35–62% were associated with the particulate phase. Most of the estrogenicity was associated with particles between 0.45 and 0.7 µm, whereas cytotoxicity was induced by extracts of particles greater than 0.7 µm. Results demonstrated the importance of solid fractions analysis towards the quantification of total estrogenic activity from aqueous environmental matrices and highlights the relevance of controlling fine suspended solids in sewage treatment plant effluents, regarding the control of endocrine disrupters in the environment.

Drugs in the environment: Do we know the risks?

Abstract The occurrence of residual drugs in sewage and natural waters is an important international topic. The behavior of compounds in the environment and sewage treatment plants (ETEs) is influenced by their physicochemical properties, which govern partition in water, soil or biota. The present study aims to identify the presence of clonazepan, simvastatin, paracetamol, atenolol, carbamazepine and fluoxetine drugs in biosolid from TEE before and after the composting process. Based on the Environmental Protection Agency's Structure-Activity Relationship Model (ECOSAR) Program (EPA), and according to ZAGATTO (2006), the octanol/water partition coefficient (Kow) observed for ibuprofen drugs, fluoxetine and sinvastanin was 3.97, 3.82 and 4.68, respectively, denoting its bioaccumulation potential, which does not happen with the other compounds, as they present logKow &amp;lt; 3, being log kow = 0.03 for atenolol; 2.3 for carbamazepine; 0.49 for paracetamol and 2.53 for clorazepam. AQUINO, 2013, mentions that drugs with logKow &amp;lt; 2.5 have high hydrophylycity and low absorption trend in biomass and lipid fractions of suspended solids. For Log Kow values between 2.5 and 4.0, there is a moderate tendency of absorption in these matrices. Data on ecotoxicity, provided by the ECOSAR program, indicate the effects observed in fish, at the concentration of 30 μg/L for Sinvastatin and 20 μg/L for Fluoxetine. The agricultural use of biosolids is a controversial subject due to the potential adverse impacts on human health. In the name of safety, strict standards, high quality criteria and restrictions on use are imposed, and standards should be based on risk assessment, but there is a lack of data on the subject, and there is still no clarity as to what constitutes tolerable risk in the brazilian context for the composition of a pattern. Key messages According to the results obtained, it is verified that the studied compounds have the potential to cause deleterious effects on the evaluated organisms, according to the ECOSAR model. Considering the little information available on the subject, especially in relation to the incidence and persistence of drugs in the environment, the continuity of studies is necessary.

Development of a treatment train for the remediation of a hazardous industrial waste landfill leachate: A big challenge

This study focuses on the development of a treatment train for a leachate from a hazardous industrial waste landfill (HIWL) previously treated by: (i) catalytic oxidation with hydrogen peroxide (H2O2) for sulphide and sulphite conversion into oxidized sulphur species, including sulphate, and (ii) chemical precipitation of sulphate as barite. The complete treatment line counted on four more stages: (iii) 1st biological oxidation for removal of biodegradable organic compounds and nitrogen species, (iv) coagulation with ferric chloride (coagulant dose of 100 mg Fe L−1, pH 2.8) for removal of a fraction of recalcitrant organics and suspended solids, (v) photo-Fenton oxidation using ultraviolet A (UVA) radiation (PF-UVA) (pH 2.8, initial total dissolved iron content of 140 mg L−1, treatment time of ~4 h) for recalcitrant organics degradation and biodegradability improvement, and (vi) 2nd biological oxidation for removal of the biodegradable organic matter resulting from the PF-UVA process. The use of anodic oxidation or photoelectro-Fenton processes in stage (v) demonstrated to be unfeasible. A chemical oxygen demand (COD) below 1000 mg O2 L−1, a common limit imposed by municipal wastewater treatment plants (MWWTPs) to effluents discharged into the municipal sewer, was achieved after a feasible treatment time (~4 h) using the multistep approach. The remediation of the HIWL leachate proved to be a big challenge.

Simulation and computational study of U-mold membrane components by CFD multiphase flow Euler model

When treating waste water with MBR system, the function of membrane module is to filter suspended solids (SS) in sewage. In the MBR waste-water treatment system, due to the U-shaped hollow fiber membrane module is one of the commonly used membrane modules, the CFD multi-phase flow Euler model is used to simulate and calculate the U-type hollow fiber membrane module in this paper. In the research process, the geometric model of the single U-shaped membrane tube was firstly established by ICEM CFD pre-processor, and structured meshing this geometric model. Then set the FLUENT solver to calculate the mesh file and monitor the volume fraction of the SS at the exit of the geometry model. Because the research object of this paper is solid-liquid separation, the multi-phase flow Euler model is enabled in the solver. Finally, the calculation result is graphically presented by the CFD-Post post-processor. On this basis, this paper selects the sewage with different SS concentration for experimental analysis: we use the SS concentration of waste-water as the secondary boundary condition of the solver to calculate, and compare the calculation results with the MBR system operation results in actual production. The comparison results show that the volume fraction of SS at the exit of U-shaped membrane tube is almost zero after calculation by the solver, which is basically the same as the actual MBR system. It solves the problem of using CFD to simulate U-shaped membrane module to filter sewage process, and has certain reference value for MBR simulation research.

Limitations imposed by conventional fine bubble diffusers on the design of a high-loaded membrane bioreactor (HL-MBR).

The operation of membrane bioreactors (MBRs) at higher than usual mixed liquor suspended solids (MLSS) concentrations may enhance the loading rate treatment capacity while minimizing even further the system's footprint. This requires operating the MBR at the highest possible MLSS concentration and biomass activity (e.g., at high loading rates and low solid retention times (SRTs)). Both a negative effect of the MLSS concentrations and a positive effect of the SRT on the oxygen transfer have been reported when using conventional fine bubble diffusers. However, most of the evaluations have been carried out either at extremely high SRTs or at low MLSS concentrations eventually underestimating the effects of the MLSS concentration on the oxygen transfer. This research evaluated the current limitations imposed by fine bubble diffusers in the context of the high-loaded MBR (HL-MBR) (i.e., high MLSS and short SRT-the latter emulated by concentrating municipal sludge from a wastewater treatment plant (WWTP) operated at a short SRT of approximately 5days). The high MLSS concentrations and the short SRT of the original municipal sludge induced a large fraction of mixed liquor volatile suspended solids (MLVSS) in the sludge, promoting a large amount of sludge flocs that eventually accumulated on the surface of the bubbles and reduced the free water content of the suspension. Moreover, the short SRTs at which the original municipal sludge was obtained eventually appear to have promoted the accumulation of surfactants in the sludge mixture. This combination exhibited a detrimental effect on the oxygen transfer. Fine bubble diffusers limit the maximum MLSS concentration for a HL-MBR at 30gL-1; beyond that point is either not technically or not economically feasible to operate; an optimum MLSS concentration of 20gL-1 is suggested to maximize the treatment capacity while minimizing the system's footprint.

The influence of particle size on the first flush strength of urban stormwater runoff.

The presence of a first flush (FF) of suspended solids (SS) in stormwater runoff has important implications for the design of treatment facilities, as does the particle size of solids. Whilst numerous studies have examined the FF behaviour of SS, few have disaggregated FF trends by particle size. In this study, the FF behaviour of SS was investigated in five size ranges, sampled from an urban stormwater drainage system located in Dublin, Ireland. A weak FF was exhibited in the gross fraction of SS, with just two events from 14 transporting more than 50% of the SS mass in the first 25% of runoff, implying that treatment structures should be capable of removing SS throughout the storm event. In the majority of rain events, the FF strength increased with decreasing particle size, probably related to the lower intensities required to dislodge solids at the onset of rainfall. Although FF strength was correlated with rain event characteristics, prediction intervals were too broad to confirm FF presence based on rainfall data alone. Therefore, the design of smaller treatment volumes based on an assumption of FF must be justified by local monitoring data.

CFD-DEM simulations of early turbulent solid–liquid mixing: Prediction of suspension curve and just-suspended speed

Solid–liquid mixing as a unit operation still faces considerable challenges, notably regarding the prediction of the impeller speed required to suspend the particles (Njs), the fraction of suspended solids and the homogeneity of the suspension at a given speed. In this work, we extend to the turbulent regime, by means of large eddy simulation (LES), a CFD-DEM model developed recently in our group for solid–liquid mixing. The resulting model is used to study the mixing of glass particles in a baffled stirred tank equipped with a down-pumping pitched blade turbine. Various characteristics of the liquid dynamics as well as the distribution and motion of the solids are investigated. The fraction of suspended solid particles predicted by the model is validated against experimental data obtained via the pressure gauge technique (PGT). Two new methods to calculate the fraction of suspended particles in a Euler–Lagrange simulation, the so-called Lagrangian suspended fraction analysis (LSFA) and the decorrelated fraction analysis (DFA) techniques are introduced. The results obtained with these two methods, as well as with many others taken from the literature, are compared to the Zwietering correlation and to the results obtained by the PGT. It is found that some techniques proposed in the literature, namely the local concentration, the power consumption and the transient solids concentration analysis techniques, cannot be applied adequately in this case. On the other hand, the LSFA, DFA and PGT techniques are observed to predict accurately the fraction of suspended solids when compared to experimental PGT data.

Prediction of coagulation and flocculation processes using ANN models and fuzzy regression.

Coagulation and flocculation are two main processes used to integrate colloidal particles into larger particles and are two main stages of primary water treatment. Coagulation and flocculation processes are only needed when colloidal particles are a significant part of the total suspended solid fraction. Our objective was to predict turbidity of water after the coagulation and flocculation process while other parameters such as types and concentrations of coagulants, pH, and influent turbidity of raw water were known. We used a multilayer perceptron (MLP), a radial basis function (RBF) of artificial neural networks (ANNs) and various kinds of fuzzy regression analysis to predict turbidity after the coagulation and flocculation processes. The coagulant used in the pilot plant, which was located in water treatment plant, was poly aluminum chloride. We used existing data, including the type and concentrations of coagulant, pH and influent turbidity, of the raw water because these types of data were available from the pilot plant for simulation and data was collected by the Tehran water authority. The results indicated that ANNs had more ability in simulating the coagulation and flocculation process and predicting turbidity removal with different experimental data than did the fuzzy regression analysis, and may have the ability to reduce the number of jar tests, which are time-consuming and expensive. The MLP neural network proved to be the best network compared to the RBF neural network and fuzzy regression analysis in this study. The MLP neural network can predict the effluent turbidity of the coagulation and the flocculation process with a coefficient of determination (R2) of 0.96 and root mean square error of 0.0106.

Development of an unresolved CFD–DEM model for the flow of viscous suspensions and its application to solid–liquid mixing

Although viscous solid-liquid mixing plays a key role in the industry, the vast majority of the literature on the mixing of suspensions is centered around the turbulent regime of operation. However, the laminar and transitional regimes face considerable challenges. In particular, it is important to know the minimum impeller speed ( N j s ) that guarantees the suspension of all particles. In addition, local information on the flow patterns is necessary to evaluate the quality of mixing and identify the presence of dead zones. Multiphase computational fluid dynamics (CFD) is a powerful tool that can be used to gain insight into local and macroscopic properties of mixing processes. Among the variety of numerical models available in the literature, which are reviewed in this work, unresolved CFD-DEM, which combines CFD for the fluid phase with the discrete element method (DEM) for the solid particles, is an interesting approach due to its accurate prediction of the granular dynamics and its capability to simulate large amounts of particles. In this work, the unresolved CFD-DEM method is extended to viscous solid-liquid flows. Different solid-liquid momentum coupling strategies, along with their stability criteria, are investigated and their accuracies are compared. Furthermore, it is shown that an additional sub-grid viscosity model is necessary to ensure the correct rheology of the suspensions. The proposed model is used to study solid-liquid mixing in a stirred tank equipped with a pitched blade turbine. It is validated qualitatively by comparing the particle distribution against experimental observations, and quantitatively by compairing the fraction of suspended solids with results obtained via the pressure gauge technique.

Modelling total suspended solids, E. coli and carbamazepine, a tracer of wastewater contamination from combined sewer overflows

Summary Urban source water protection requires knowledge of sources of fecal contamination upstream of drinking water intakes. Combined and sanitary sewer overflows (CSOs and SSOs) are primary sources of microbiological contamination and wastewater micropollutants (WWMPs) in urban water supplies. To quantify the impact of sewer overflows, predictive simulation models are required and have not been widely applied for microbial contaminants such as fecal indicator bacteria and pathogens in urban drainage networks. The objective of this study was to apply a simulation model to estimate the dynamics of three contaminants in sewer overflows – total suspended solids, Escherichia coli ( E. coli ) and carbamazepine, a WWMP. A mixed combined and pseudo-sanitary drainage network in Quebec, Canada was studied and modelled for a total of 7 events for which water quality data were available. Model results were significantly correlated with field water quality data. The model confirmed that the contributions of E. coli from runoff and sewer deposits were minor and their dominant source was from sewage. In contrast, the main sources of total suspended solids were stormwater runoff and sewer resuspension. Given that it is not present in stormwater, carbamazepine was found to be a useful stable tracer of sewage contributions to total contaminant loads and also provided an indication of the fraction of total suspended solids originating from sewer deposits because of its similar response to increasing flowrates.

Identification of compounds bound to suspended solids causing sub-lethal toxic effects in Daphnia magna. A field study on re-suspended particles during river floods in Ebro River

Identifying chemicals causing adverse effects in organisms present in water remains a challenge in environmental risk assessment. This study aimed to assess and identify toxic compounds bound to suspended solids re-suspended during a prolonged period of flushing flows in the lower part of Ebro River (NE, Spain). This area is contaminated with high amounts of organochlorine and mercury sediment wastes. Chemical characterization of suspended material was performed by solid phase extraction using a battery of non-polar and polar solvents and analyzed by GC–MS/MS and LC–MS/MS. Mercury content was also determined for all sites. Post-exposure feeding rates of Daphnia magna were used to assess toxic effects of whole and filtered water samples and of re-constituted laboratory water with re-suspended solid fractions. Organochlorine and mercury residues in the water samples increased from upstream to downstream locations. Conversely, toxic effects were greater at the upstream site than downstream of the superfund Flix reservoir. A further analysis of the suspended solid fraction identified a toxic component eluted within the 80:20 methanol:water fraction. Characterization of that toxic component fraction by LC–MS/MS identified the phytotoxin anatoxin-a, whose residue levels were correlated with observed feeding inhibition responses. Further feeding inhibition assays conducted in the lab using anatoxin-a produced from Planktothrix agardhii, a filamentous cyanobacteria, confirmed field results. This study provides evidence that in real field situation measured contaminant residues do not always agree with toxic effects.

Accumulation of Chemical Oxygen Demand in Membrane Bioreactors at Pilot-Scale and Full-Scale Conditions

AbstractThe accumulation of high-molecular-weight organic compounds is a common phenomenon in membrane bioreactors (MBRs). It is currently not known to what extent accumulation occurs in full-scale plants because relevant tests were mostly performed in experimental plants. To overcome the lack of practical experience, a measurement campaign was carried out including four municipal wastewater treatment plants and two pilot plants [one MBR and one conventional wastewater treatment plant (WWTP)]. The results clearly showed that accumulation depends on sludge retention time (SRT), temperature, sludge volume index (SVI), and the fraction of volatile suspended solids (VSS). As a result of biological processes, the chemical oxygen demand (COD) accumulation may increase for a limited period of time and amounts 10–120 mg/(PE·d). The introduction of sludge from a municipal MBR into the system of conventional activated sludge plants (CAS) for external sludge handling does not affect the treatment efficacy of the la...