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The effect of roughness and thickness of biofilms on the dissolved oxygen (DO) concentration boundary layer thickness (DO CBLT) and the external mass transfer process in a biofilm system were investigated using a microelectrode technique.... more
The effect of roughness and thickness of biofilms on the dissolved oxygen (DO) concentration boundary layer thickness (DO CBLT) and the external mass transfer process in a biofilm system were investigated using a microelectrode technique. The experimental results indicated that (a) an increase of biofilm roughness would reduce the external mass transfer resistance; and (b) the absolute roughness increased with an increase in the biofilm maximum thickness, but this increase diminished when the biofilm thickness exceeded 1200 μm. The microelectrode technique is a useful tool to study the external mass transfer process.
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Direct measurement of unsteady-state variation of oxygen concentrations inside deactivated biofilm at intervals of 100 μm was conducted with oxygen microelectrodes. The diffusivity of each layer was estimated using an explicit... more
Direct measurement of unsteady-state variation of oxygen concentrations inside deactivated biofilm at intervals of 100 μm was conducted with oxygen microelectrodes. The diffusivity of each layer was estimated using an explicit finite-difference method. The results show that the distribution of the biofilm effective oxygen diffusivity varies from 25% Dw at the substratum of the biofilm to 90% Dw at the surface of the biofilm. This information provides experimental evidence necessary for biofilm modelling that could not be approached in the past, and will create a new dimension for evaluation of biofilm processes.
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A series of experiments were made in order to compare the removal efficiency of a mixture of four PAHs (naphthalene, phenanthrene, pyrene, and benzo[a]pyrene), under different electron acceptor (NO3-, SO4-2) and hydrodynamic conditions... more
A series of experiments were made in order to compare the removal efficiency of a mixture of four PAHs (naphthalene, phenanthrene, pyrene, and benzo[a]pyrene), under different electron acceptor (NO3-, SO4-2) and hydrodynamic conditions (stagnation and high shear). In all cases naphthalene showed the highest removal efficiency (from 69% up to 100%) as compared with the other PAHs. The fastest rate was obtained for the denitrifying-high shear condition followed by denitrification-no shear, sulfate-reduction-high shear and the lowest for sulfate reduction-no shear. However, most of the perceived removal of the heavier PAHs could be due to aging. No lag time was observed for the denitrifying experiments, and the denitrification rate was the same regardless of the hydrodynamic condition. A lag time of 64 d was observed under conditions of sulfate reduction and high shear. Sulfate reduction did not commence under no shear conditions. No toxic effect was observed for the four PAH mixture under all the conditions tested. Key words: anaerobic systems, biodegradation, denitrification, hydrodynamic conditions, PAH, sulfate reduction.
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The thickness of the dissolved oxygen (DO) concentration boundary layer and the external mass transfer in a biofilm system were investigated using a microelectrode technique. Theoretical analysis was conducted to elucidate the mechanisms... more
The thickness of the dissolved oxygen (DO) concentration boundary layer and the external mass transfer in a biofilm system were investigated using a microelectrode technique. Theoretical analysis was conducted to elucidate the mechanisms of the technique and to interpret the experimental measurements. The measured thicknesses of dissolved oxygen (DO) concentration boundary layers under different conditions demonstrated directly the effect of several factors on external mass transfer resistance. The experimental results indicated that (a) increasing substrate loading rate, (b) increasing fluid streamwise velocity and (c) increasing the roughness of the biofilm surface would decrease the external mass transfer resistance. The measured thickness of the DO concentration boundary layer was not in full agreement with theoretical correlations because the nonuniform biofilm created velocity and concentration fluctuations which resulted in the compression of concentration boundary layers. The microelectrode technique is a useful tool to study the external mass transfer resistance.
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The spatial distributions of properties of biofilms have been investigated by using three different kinds of biofilms as test materials. Biofilms, cultured by laboratory-scale rotating drum biofilm reactors with synthetic wastewater, were... more
The spatial distributions of properties of biofilms have been investigated by using three different kinds of biofilms as test materials. Biofilms, cultured by laboratory-scale rotating drum biofilm reactors with synthetic wastewater, were first cut into 10 to 20 µm thick slices using a microtome, and then apportioned into samples representing 3 or 4 layers. The biofilm properties of each layer were investigated by measuring the densities, phospholipid concentrations, and AR18 dye adsorption abilities. The bacterial population distributions and the metabolically active bacterial distributions were studied by plate count methods or a MPN method, and the tetrazolium dye (INT) reduction method, respectively. Based on statistic evaluations, the micro-slicing technique, the procedure for analyzing phospholipid concentrations of biofilms, and the AR18 dye adsorption tests were suitable to be used in biofilm studies. It was found that the densities of biofilms in the bottom layers were 4 to 7 times higher than those in the top layers. For thick biofilms (thickness > 500 µm), the INT active bacteria decreased from 82-89% in the top layers to 5-11% in the bottom layers. The porosities of thick biofilms changed from 83-92% in the top layers to 56-64% in the bottom layers. For thin biofilms (thickness < 500 µm), the porosities of biofilms changed from 72-75% in the top layers to 35-44% in the bottom layers. Highly spatial distributions of bacterial populations, mean pore radius, and specific surface areas were also observed. As a result of these spatial distributions, the ratio of effective diffusivity to diffusivity in the bulk solution also shows a decrease with depth of the biofilm. Assuming biofilm properties are of a uniform distribution may be an over-simplified assumption, valid only in specific cases.
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The spatial distributions of biofilm properties have been investigated. Heterotrophic biofilms were cultured by using rotating drum biofilm reactors which were fed to a synthetic wastewater. The biofilm was first cut into 1020 μm thick... more
The spatial distributions of biofilm properties have been investigated. Heterotrophic biofilms were cultured by using rotating drum biofilm reactors which were fed to a synthetic wastewater. The biofilm was first cut into 1020 μm thick slices by use of a microtome, and then ...
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Research Interests: Chemistry, Biofilms, Bioremediation, Environmental Chemistry, Environmental Pollution, and 15 moreMedicine, Multidisciplinary, Adsorption, Biodegradation, Biofilm, Micelles, Plants, Sorption, Polycyclic Aromatic Hydrocarbon, Solubility, Environmental Pollutants, Phenanthrene, Pyrene, Soil Pollutants, and Pulmonary Surfactant
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Competitions in biofilms for substrate and space have been studied by using a microelectrode technique and a microslicing technique. Three different kinds of biofilms, cultured by laboratory-scale rotating drum biofilm reactors (RDBR)... more
Competitions in biofilms for substrate and space have been studied by using a microelectrode technique and a microslicing technique. Three different kinds of biofilms, cultured by laboratory-scale rotating drum biofilm reactors (RDBR) with synthetic wastewater, have been used as test materials. Oxygen, ammonium-nitrogen, nitrate-nitrogen, and pH concentration profiles in the biofilms were measured using microelectrodes. Experimental results showed that: 1) an increase of organic loading rate would result in a decrease of DO concentration in the biofilm. However, after the organic loading rate exceeded a certain value, the oxygen profiles within the biofilm did not change any more; 2) Heterotrophs competed for oxygen with nitrifiers, which resulted in the inhibition of nitrification because of the shortage of oxygen. Glucose itself, however, did not inhibit the nitrification processes; and 3) The competition for substrate in biofilms resulted in a stratified biofilm structure. Experiments showed that competition in biofilms resulted in non-uniform spatial distributions of bacterial populations and metabolically active bacteria. The spatial distributions of biotic and abiotic components in turn affected the substrate transfer and substrate competition within the biofilm. Traditional biofilm modelling will fail in many cases if they are based on substrate removal kinetics and uniform distributions of biofilm properties.
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Biofilm in drinking water systems is undesirable. Free chlorine and monochloramine are commonly used as secondary drinking water disinfectants, but monochloramine is perceived to penetrate biofilm better than free chlorine. However, this... more
Biofilm in drinking water systems is undesirable. Free chlorine and monochloramine are commonly used as secondary drinking water disinfectants, but monochloramine is perceived to penetrate biofilm better than free chlorine. However, this hypothesis remains unconfirmed by direct biofilm monochloramine measurement. This study compared free chlorine and monochloramine biofilm penetration into an undefined mixed-culture nitrifying biofilm by use of microelectrodes and assessed the subsequent effect on biofilm activity and viability by use of dissolved oxygen (DO) microelectrodes and confocal laser scanning microscopy (CLSM) with LIVE/DEAD BacLight. For equivalent chlorine concentrations, monochloramine initially penetrated biofilm 170 times faster than free chlorine, and even after subsequent application to a monochloramine penetrated biofilm, free chlorine penetration was limited. DO profiles paralleled monochloramine profiles, providing evidence that either the biofilm was inactivated with monochloramine's penetration or its persistence reduced available substrate (free ammonia). While this research clearly demonstrated monochloramine's greater penetration, this penetration did not necessarily translate to immediate viability loss. Even though free chlorine's penetration was limited compared to that of monochloramine, it more effectively (on a cell membrane integrity basis) inactivated microorganisms near the biofilm surface. Limited free chlorine penetration has implications when converting to free chlorine in full-scale chloraminated systems in response to nitrification episodes.
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A cylindrical model (CM) and a random porous cluster model (RPCM) have been developed in this paper to evaluate tortuosities, tortuosity factors, and effective diffusivities within biofilms, based on measurable biofilm properties. The... more
A cylindrical model (CM) and a random porous cluster model (RPCM) have been developed in this paper to evaluate tortuosities, tortuosity factors, and effective diffusivities within biofilms, based on measurable biofilm properties. The tortuosity factor and the ratio of ...
Research Interests: Materials Science, Chemistry, Water, Modeling, Density, and 4 moreMultidisciplinary, Biofilm, Porosity, and Tortuosity
Microelectrodes, needle-shaped biochemical microsensors fabricated from pulled glass micropipettes, are one of the most prominent, novel methods for studying biofilms. The pulled glass tip can have a diameter of 3–20 μm, allowing for the... more
Microelectrodes, needle-shaped biochemical microsensors fabricated from pulled glass micropipettes, are one of the most prominent, novel methods for studying biofilms. The pulled glass tip can have a diameter of 3–20 μm, allowing for the measurement of the concentrations of specific biological and chemical compounds in microbial communities. Net specific consumption and production rates (i.e., biological activity) at a certain depth can be estimated from the measured concentration profiles. This article is focused on solid-state, needle-type, electrochemical microsensors for detecting important water quality parameters (e.g., oxygen, pH, nitrite, chlorine species, redox, and phosphate). Sensing materials include gold (including a gold-electroplated sensing surface), platinum, carbon-fiber, carbon nanotube, iridium, and cobalt. Emphasis is placed on the material science chemistry behind how electrochemical microelectrode sensors operate. Innovative applications of microsensors, including microelectromechanical systems (MEMS) microelectrode array sensor microfabrication, and three-dimensional microprofile measurement and interpretation will also be demonstrated. Carbon nanotubes (CNTs) are a relatively new member in the carbon family and are being used in biofilm research. Distinctive properties of CNTs and the relationship between structure and their electrochemistry performance are discussed. The electrochemical application of CNTs is focused on nitrite detection.
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Complex mixtures of polycyclic aromatic hydrocarbons and other organic compounds are usually present in contaminated sites. This may influence biodegradation patterns and changes in biofilm growth and development. Biodegradation studies... more
Complex mixtures of polycyclic aromatic hydrocarbons and other organic compounds are usually present in contaminated sites. This may influence biodegradation patterns and changes in biofilm growth and development. Biodegradation studies of naphthalene, phenanthrene and pyrene were conducted in sole-substrate systems and in binary and tertiary mixtures to examine substrate interactions on biofilms in porous media systems. It was shown that phenanthrene and pyrene could not be degraded as sole carbon sources in the system, but binary systems of the 3- and 4-ring PAHs with acetate and naphthalene supplements stimulated their degradation, with up to 87.9% and 70.1% removal efficiencies respectively. However, in the tertiary systems the presence of phenanthrene inhibited pyrene degradation. Adsorption of PAHs to sand media was determined to be negligible. Biofilm growth, development and changes in composition were analyzed over time; these showed increases in both firmly and loosely atta...
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This research investigated the potential for survival of pathogens during and after composting of municipal wastewater sludge by forced aeration, static pile composting method. Both primary and combined primary/secondary sludges were... more
This research investigated the potential for survival of pathogens during and after composting of municipal wastewater sludge by forced aeration, static pile composting method. Both primary and combined primary/secondary sludges were composted.
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THE FEASIBILITY OF WINTER OPERATION OF ANEROBIC DIGESTERS IN HEW HAMPSHIRE AND OTHER NORTHERN AREAS WAS EXAMINED. SMALL-SCALE LABORATORY EXPERIMENTS WERE CONDUCTED USING CONTINUOUS AERATION, ...
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Competitions in biofilms for substrate and space have been studied by using a microelectrode technique and a microslicing technique. Three different kinds of biofilms, cultured by laboratory-scale rotating drum biofilm reactors (RDBR)... more
Competitions in biofilms for substrate and space have been studied by using a microelectrode technique and a microslicing technique. Three different kinds of biofilms, cultured by laboratory-scale rotating drum biofilm reactors (RDBR) with synthetic wastewater, have been used as test materials. Oxygen, ammonium-nitrogen, nitrate-nitrogen, and pH concentration profiles in the biofilms were measured using microelectrodes. Experimental results showed that: 1) an increase of organic loading rate would result in a decrease of DO concentration in the biofilm. However, after the organic loading rate exceeded a certain value, the oxygen profiles within the biofilm did not change any more; 2) Heterotrophs competed for oxygen with nitrifiers, which resulted in the inhibition of nitrification because of the shortage of oxygen. Glucose itself, however, did not inhibit the nitrification processes; and 3) The competition for substrate in biofilms resulted in a stratified biofilm structure. Experi...
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Research Interests:
The spatial distributions of biofilm properties have been investigated. Heterotrophic biofilms were cultured by using rotating drum biofilm reactors which were fed to a synthetic wastewater. The biofilm was first cut into 1020 μm thick... more
The spatial distributions of biofilm properties have been investigated. Heterotrophic biofilms were cultured by using rotating drum biofilm reactors which were fed to a synthetic wastewater. The biofilm was first cut into 1020 μm thick slices by use of a microtome, and then ...
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Research Interests:
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Laboratory scale aerobic digestion experiments were performed and nutrient balances were maintained in order to evaluate nutrient transformations during digestion of waste activated sludge. Reactors loaded at 0.03 ft³ and 0.081 lb... more
Laboratory scale aerobic digestion experiments were performed and nutrient balances were maintained in order to evaluate nutrient transformations during digestion of waste activated sludge. Reactors loaded at 0.03 ft³ and 0.081 lb VS/day/ft³, were operated under both ...
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The treatment of high salinity wastewaters from small island communities by use of rotating biological contactors was evaluated. Domestic wastewaters containing up to full strength seawater were utilized. The effects of salinity, loading... more
The treatment of high salinity wastewaters from small island communities by use of rotating biological contactors was evaluated. Domestic wastewaters containing up to full strength seawater were utilized. The effects of salinity, loading rate and disk media composition on organic removal rate were examined. It was shown that RBCs can treat high salinity wastewaters to the same degree as non-saline wastewaters. The resulting effluent organic content was adequate for discharge into either marine or freshwater receiving waters. Mean COD removals of 61% and 64% were achieved using hydraulic loading rates of 0.04 and 0.08 m³/m²⋅d (1.0 and 2.0 gpd/sq ft), respectively. At higher loading rates, up to 0.33 m³/m²⋅d (8.0 gpd/sq ft), organic removal efficiency was reduced. No difference in treatment efficiency was observed using either plastic or Masonite® as the disk media.
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In this study, the inhibitory effects of acid orange 7 (AO7), a common azo dye, on nitrification in biofilms were investigated in situ using microelectrodes. Biofilms were obtained from laboratory rotating drum biofilm reactor after the... more
In this study, the inhibitory effects of acid orange 7 (AO7), a common azo dye, on nitrification in biofilms were investigated in situ using microelectrodes. Biofilms were obtained from laboratory rotating drum biofilm reactor after the nitrification process reached a pseudo-steady state. Dissolved oxygen, pH, NH4+, NO3−, and redox potential microelectrodes, with tip diameters ranging from 3–15 μm, were used to monitor the spatial distribution and change of microbial activities within nitrifying biofilms. It was found that at lower concentration (1 mg/L), AO7 had only a slight impact on the NH4+-N concentration profiles. The ammonium consumption rate decreased as higher AO7 concentrations (15 mg/L and 25 mg/L) were exposed to the biofilms. A similar trend was observed for the NO3−-N microprofiles. The nitrate production rate decreased as the AO7 concentration in the bulk solution increased. The dissolved oxygen and pH microprofiles also showed oxygen and alkalinity utilization, but ...
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ABSTRACT
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Biofilms play a major role in many water reclamation and reuse technologies. Normally, wherever there is water, a support surface and nutrients available, a biofilm will form. In some cases, this may result in problems for the water... more
Biofilms play a major role in many water reclamation and reuse technologies. Normally, wherever there is water, a support surface and nutrients available, a biofilm will form. In some cases, this may result in problems for the water treatment system, due to biofouling or the growth of pathogenic or other unwanted microbes, but more frequently, the biofilm serves a very useful purpose by biodegrading organic contaminants in the water or by converting unwanted inorganic materials into harmless ones. Biofilms are commonly found associated with membrane reactors and filtration systems used in water reclamation and reuse systems, and are often a critical component. They are also found in soils where they may impact water injection or removal systems, or in situ bioremediation. Knowledge of the way biofilms form, how they grow and how to control them is critical for effective design and operation of many water reclamation facilities. This paper explores the modes of formation and growth o...
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Marine pollution and its control , Marine pollution and its control , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
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ABSTRACT
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Biofilms play a major role in many water reclamation and reuse technologies. Normally, wherever there is water, a support surface and nutrients available, a biofilm will form. In some cases, this may result in problems for the water... more
Biofilms play a major role in many water reclamation and reuse technologies. Normally, wherever there is water, a support surface and nutrients available, a biofilm will form. In some cases, this may result in problems for the water treatment system, due to biofouling or the growth of pathogenic or other unwanted microbes, but more frequently, the biofilm serves a very useful purpose by biodegrading organic contaminants in the water or by converting unwanted inorganic materials into harmless ones. Biofilms are commonly found associated with membrane reactors and filtration systems used in water reclamation and reuse systems, and are often a critical component. They are also found in soils where they may impact water injection or removal systems, or in situ bioremediation. Knowledge of the way biofilms form, how they grow and how to control them is critical for effective design and operation of many water reclamation facilities. This paper explores the modes of formation and growth o...
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In this chapter we describe the fabrication procedure and the evaluation of a solid-state ion-selective sulfide microelectrode for potentiometric measurement of total dissolved sulfide in aqueous solution at neutral pH. The sulfide... more
In this chapter we describe the fabrication procedure and the evaluation of a solid-state ion-selective sulfide microelectrode for potentiometric measurement of total dissolved sulfide in aqueous solution at neutral pH. The sulfide microelectrode was made from a silver wire ...
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The effect of temperature, pH, and Na+/Ca2+ concentration on the adsorptive behavior of organophilic clay used in the solidification/stabilization of hazardous wastes was addressed. The organophilic clay used was montmorillonite type clay... more
The effect of temperature, pH, and Na+/Ca2+ concentration on the adsorptive behavior of organophilic clay used in the solidification/stabilization of hazardous wastes was addressed. The organophilic clay used was montmorillonite type clay modified by cation exchange with a mixed tallow amine as the sorbent. The contaminants used in this work were phenol, 2-chlorophenol, aniline, and chlorobenzene. 2-Butanone (also known as methyl ethyl ketone, MEK) was initially studied, but preliminary work showed that the organophilic clay poorly sorbed it and it was not studied further. A group of isothermal tests were performed to clarify specific sorption behaviors due to temperature effects, high pH, and concentration of the cations Na+ and Ca2+. The adsorption capacity of the organophilic clay decreased as follows: chlorobenzene > 2-chlorophenol > phenol > aniline. Desorption in high pH environments was seen for phenol and 2-chlorophenol. Changes in temperature, rise in the pH, or in...
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A series of experiments were made in order to compare the removal efficiency of a mixture of four PAHs (naphthalene, phenanthrene, pyrene, and benzo[a]pyrene), under different electron acceptor (NO3-, SO4-2) and hydrodynamic conditions... more
A series of experiments were made in order to compare the removal efficiency of a mixture of four PAHs (naphthalene, phenanthrene, pyrene, and benzo[a]pyrene), under different electron acceptor (NO3-, SO4-2) and hydrodynamic conditions (stagnation and high shear). In all cases naphthalene showed the highest removal efficiency (from 69% up to 100%) as compared with the other PAHs. The fastest rate was obtained for the denitrifying-high shear condition followed by denitrification-no shear, sulfate-reduction-high shear and the lowest for sulfate reduction-no shear. However, most of the perceived removal of the heavier PAHs could be due to aging. No lag time was observed for the denitrifying experiments, and the denitrification rate was the same regardless of the hydrodynamic condition. A lag time of 64 d was observed under conditions of sulfate reduction and high shear. Sulfate reduction did not commence under no shear conditions. No toxic effect was observed for the four PAH mixture u...
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ABSTRACT Efforts aimed at reducing pollutant loads from combined sewer overflows (CSOs) on the Muddy Creek receiving waters in Cincinnati, Ohio have been underway in recent years. This includes an investigation of the treatment... more
ABSTRACT Efforts aimed at reducing pollutant loads from combined sewer overflows (CSOs) on the Muddy Creek receiving waters in Cincinnati, Ohio have been underway in recent years. This includes an investigation of the treatment performance of a flow-through wet weather treatment facility (WWTF) using off-line sedimentation tanks, fine screening and chemical disinfection (disinfection was inactive during this study). Calculations using hydrographs and water quality samples collected at the WWTF during rain events established the mass of biochemical oxygen demand (BOD)(5), chemical oxygen demand, and total suspended solids (TSS) removed. Ten storm events sampled from January to September 2002 helped characterize pollutant removal efficiencies for flow-through treatment. Pollutant removal was classified into four components: flow to the wastewater treatment plant (WWTP), sedimentation, storage, and screening. Most pollutant removal was achieved through settling and storage in the treatment tanks, with removal efficiencies of 20-50% for BOD5 and 25-70% for TSS commonly observed. Owing to the high pollutant load in the early portion of the CSO hydrograph, first-flush containment, or capturing and conveying the early portion of the runoff event to the WWTP, was the most efficient treatment method for every storm investigated.
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A new potentiometric sensor electrode for sulfide based on conducting polymer films is introduced. The electrode is formed by electrochemically depositing a film of poly(3-methylthiophene) and poly(dibenzo-18-crown-6) onto an alloy... more
A new potentiometric sensor electrode for sulfide based on conducting polymer films is introduced. The electrode is formed by electrochemically depositing a film of poly(3-methylthiophene) and poly(dibenzo-18-crown-6) onto an alloy substrate. Different methods were used for the electrode preparations. The alloy used has a low melting point, which allowed its use for manufacturing a microsize version of this electrode. The electrode response is stable for 3 days. The working temperature range for this electrode is between 10 and 40°C. The linear dynamic range is 1.0×10−7–1.0×10−2 M and measures total sulfide concentration over a range of pH from 1 to 13. The polymer electrode showed high selectivity for sulfide in the presence of many common interfering anions. The electrode is useful for the measurement of total sulfide in biological environments and can be manufactured in the micron scale. Therefore, it will be useful for the measurement within biofilms.
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ABSTRACT