Showing papers in "Water Environment Research in 1997"
TL;DR: In this paper, the effect of cations on the settling and dewatering of activated sludge was investigated using laboratory scale sludge reactors, and three parameters were investigated, i.e., the calcium to magnesium ratio, increasing divalent cation ratios, and increasing monovalent cation ratio.
Abstract: The effect of cations on the settling and dewatering of activated sludge was investigated using laboratory scale activated sludge reactors. Three parameters were investigated : the effect of the calcium to magnesium ratio ; the effect of increasing divalent cation concentrations ; and the effect of increasing monovalent cation concentrations. The study showed that the settling and dewatering properties of the activated sludge were dependent on both the concentrations and ratios of cations in the feed. Some activated sludge systems required both calcium and magnesium in the feed while others only required one of these cations for good settling and dewatering properties. A minimum of 0.7-2.0 meq/L each of calcium and magnesium was necessary for acceptable settling and dewatering. Increasing the feed concentrations of calcium and magnesium above this level improved floc strength, settling and dewatering properties and increased the bound protein concentration. The poor settling and dewatering of suspensions receiving low divalent cation concentrations in the feed could also be improved by batch addition of calcium and/or magnesium. However, improvements were greater when an equal concentration of the cation was added to the feed. Addition of the monovalent cation, sodium, to the feed resulted in a deterioration in settling and dewatering properties when the monovalent to divalent cation ratio exceeded approximately 2 to 1, expressed on an equivalent basis. However, the deterioration could be reversed by increasing the calcium and magnesium concentration in the feed which reduced the monovalent to divalent cation ratio below 2 to 1.
342 citations
TL;DR: In this paper, the development of a general model for biological nutrient removal in activated sludge systems is discussed, which is a mechanistic model based on the International Association on Water Pollution Research and Control (IAWPRC) (now IAWQ) model for carbonaceous energy removal, nitrification, and denitrification.
Abstract: The development of a general model for biological nutrient removal in activated sludge systems is discussed. The general model is a mechanistic model based on the International Association on Water Pollution Research and Control (IAWPRC) (now IAWQ) model for carbonaceous energy removal, nitrification, and denitrification (Activated Sludge Model No. 1 [ASMI]), and the Wentzel et al. (1989a and b) model for biological phosphorus removal, with a number of modifications. A fermentation process has been included for the conversion of readily biodegradable chemical oxygen demand (COD) to short-chain fatty acids (assuming a loss of COD from the system). Hydrolysis of enmeshed slowly biodegradable COD under anoxic and anaerobic conditions has been incorporated, as well as anoxic growth of polyP organisms. These modifications and others are discussed in this paper. The matrix representation and a description of the model processes are also presented, as well as a brief outline of influent wastewater characterization.
218 citations
TL;DR: In this article, seven mixed liquor samples from full-scale activated sludge systems were analyzed for their settling and dewatering properties, and the calcium, magnesium, sodium, and potassium concentrations were measured.
Abstract: Seven mixed liquor samples from full-scale activated sludge systems were analyzed for their settling and dewatering properties, and the calcium, magnesium, sodium, and potassium concentrations were measured. The soluble cation concentrations were evaluated in terms of the monovalent to divalent cation ratio and the calcium to magnesium ratio. The monovalent to divalent ratio was positively correlated to activated sludge dewatering properties. In batch tests, the addition of calcium or magnesium to samples with a high monovalent to divalent cation ratio improved the dewatering rate of the suspensions by ≤30%. Conditioning and dewatering experiments were performed on thickened sludges from two of the industrial samples. Calcium was added to each sample, in one case, to lower the monovalent to divalent cation ratio and in the second case, to increase the calcium to magnesium ratio. In each case, addition of calcium to the sample reduced the optimum polymer dose for conditioning by 30% compared with control samples with no added calcium. Laboratory reactor studies were performed using mixed liquor and wastewater from three of the activated sludge plants. Two of the systems were deficient in magnesium, and one system was deficient in calcium. In each case, the deficient cation was added to the feed of the reactors, and settling and/or dewatering properties improved. Addition of cations to the feed of two full-scale activated sludge systems improved the settling dramatically, and in one system, the thickened solids content was doubled. These results indicate that cation imbalances are a common cause of sludge settling and dewatering problems in industrial activated sludge plants, and these imbalances can be corrected by addition of the cation deemed to be deficient by analysis of the monovalent to divalent ratio or the calcium to magnesium ratio.
176 citations
TL;DR: In this paper, the toxic effects and degradability of three selected nitrophenols (2-nitrophenol, 4-nithin, and 2,4-dinitrophenolate) in anaerobic acetate and propionate enrichment systems were studied using batch serum bottles.
Abstract: Nitrophenols are among the most important and versatile industrial organic compounds and are widely used in the chemical industry and are listed as priority pollutants by the U.S. EPA. The toxic effects and degradability of three selected nitrophenols (2-nitrophenol, 4-nitrophenol and 2,4-dinitrophenol) in anaerobic acetate and propionate enrichment systems were studied using batch serum bottles. The toxicity to both propionate- and acetate-fed systems decreased in the following order: 2,4-dinitrophenol > 4-nitrophenol > 2-nitrophenol. An up-flow fixed film, acetate-fed reactor was able to acclimate to 20 mg/L of 2-and 4-nitrophenol showing a 95% removal of each nitrophenol. The effect of biomass was studied using serum bottles for anaerobic toxicity assays with the design volatile suspended solids (VSS) concentrations of 500, 1000, and 1 500 mg/L. With higher VSS the toxic effects of nitrophenols on methanogenesis were less severe. Nitrophenols were more inhibitory to acetate utilization than propionate utilization. Under anaerobic conditions, 2-nitrophenol and 2,4-dinitrophenol were transformed both abiotically and biotically to 2-aminophenol and 2-amino,4-nitrophenol, respectively. The presence of propionate in propionate enrichment culture enhanced the removal rates of all three nitrophenols studied.
169 citations
TL;DR: The kinetic growth of unialga Chlorella vulgaris was investigated in mixed-culture fed-batch chemostat reactors, with special reference to temperature and pH as discussed by the authors, and the maximum growth rate of 0.50 day -l was obtained at pH of about 6.31 to 6.84, and the optimum temperature was 32.4°C.
Abstract: The kinetic growth of unialga Chlorella vulgaris was investigated in mixed-culture fed-batch chemostat reactors, with special reference to temperature and pH. The experiments were carried out at 10°C to 40°C, pH was controlled from 3.0 to 11.5 in a series of reactors, and glucose at a concentration of 75 mg/L was fed as the sole source of organic carbon. The maximum growth rate of 0.50 day -l was obtained at pH of about 6.31 to 6.84, and the optimum temperature was 32.4°C. The activation energy of the growth-limiting reaction and the enthalpy change for the enzyme-inactivation reaction were 24.5 and 253.36 kJ/ mole, respectively. The saturation constants for hydrogen ion, K H , and hydroxyl ion, K OH , were temperature-dependent. At temperatures below optimum, K H increased when temperature increased, but K OH decreased. Above the optimum temperature, K H decreased and K oH increased with temperature.
140 citations
TL;DR: In this paper, the authors used activated sludge that had been adapted to a wastewater containing moderately high levels of nitrate (1350 mg/L a/N) and salinity (40000 mg/l total dissolved solids).
Abstract: Nitrite inhibition of denitrification was investigated using activated sludge that had been adapted to a wastewater containing moderately high levels of nitrate (1350 mg/L a/N) and salinity (40000 mg/L total dissolved solids). After adaptation, the activated sludge was used to study pH effects on nitrite inhibition of denitrification over a range of 15 to 2100 mg/L nitrite nitrogen (NO 2 -N). A pH range of 6 to 8 was used. Using a zero-order model, it was found that the denitrification rate for 250 mg/L NO 2 -N increased from 0.001 to 0.02 mg N/mg mixed liquor suspended solids (MLSS).h as pH increased from 6 to 8. Denitrification rate reduction at the lower pH was probably caused by the accumulation of the species nitrous acid (HNO 2 ), and the threshold inhibitory concentration for HNO 2 was estimated to be low : less than 0.02 mg/L HNO 2 -N at pH 6. Mixed liquor suspended solids concentration appeared to have no effect on nitrite inhibition of denitrification.
137 citations
TL;DR: Risk analysis indicates that the contribution of contaminated recreational water to human infections may be higher than previously assumed, and the contributions of viable but nonculturable Campylobacter cells in the contamination cycle has been found to be negligible.
Abstract: Campylobacteriosis is one of the most frequently occurring acute gastroenteritis diseases in humans. Studies have revealed that the main risk factors in contracting campylobacteriosis are eating undercooked poultry meat, drinking raw milk, or drinking untreated water, and to a lesser degree, living in a household with a cat or dog. During the past 5 years many transmission routes of Campylobacter have been elucidated. However, knowledge on the significance of surface waters in causing Campylobacter infections remains scarce. Various reports have shown that the aquatic environment is regularly contaminated with Campylobacter. Risk analysis indicates that the contribution of contaminated recreational water to human infections may be higher than previously assumed. The contribution of viable but nonculturable Campylobacter cells in the contamination cycle has been found to be negligible. Water Environ.
111 citations
TL;DR: In this article, a set of 94 soil water partition coefficients normalized to soil organic carbon content (K oc ) is presented for 11 classes of organic chemicals and three types of descriptors used in predicting K oc were octanol/water partition coefficient (K ow), molecular connectivity (m X t ), and linear solvation energy relationships (LSERs).
Abstract: A critically evaluated set of 94 soil water partition coefficients normalized to soil organic carbon content (K oc ) is presented for 11 classes of organic chemicals. This data set is used to develop and evaluate K oc estimation methods using three different descriptors. The three types of descriptors used in predicting K oc were octanol/ water partition coefficient (K ow ), molecular connectivity ( m X t ), and linear solvation energy relationships (LSERs). The best results were obtained estimating K oc from K ow , though a slight improvement in the correlation coefficient was obtained by using a two-parameter regression with K ow and the third order difference term from m X t , Molecular connectivity correlations seemed to be best suited for use with specific chemical classes. The LSER provided a better fit than m X t , but not as good as the correlation with K ow . The correlation to predict K oc from K ow was developed for 72 chemicals; log K oc = 0.903 log K ow + 0.094. This correlation accounts for 91% of the variability in the data for chemicals with log K ow ranging from 1.7 to 7.0. The expression to determine the 95% confidence interval on the estimated K oc is provided along with an example for two chemicals of different hydrophobicity showing the confidence interval of the retardation factor determined from the estimated K oc . The data showed that K oc is not likely to be applicable for chemicals with log K ow < 1.7. Finally, the K oc correlation developed using K ow as a descriptor was compared with three nonclass-specific correlations and two commonly used class-specific correlations to determine which method(s) are most suitable.
97 citations
95 citations
TL;DR: In this paper, the first-order rate constants for the desorption of 1,3,5-trichlorobenzene, 1,2, 3, 4-tetrachlorobenzenene, and pentachlorabenzene were 0.091, 0.051, and 0.029 hr -1, respectively.
Abstract: The oxidation of 1,3,5-trichlorobenzene, 1,2,3,4-tetra-chlorobenzene, pentachlorobenzene, and hexachlorobenzene sorbed on hematite (α-Fe 2 O 3 ), a naturally occurring soil mineral, by catalyzed hydrogen peroxide was investigated using the hematite as the sole source of the iron catalyst. Partitioning of the chlorobenzenes onto the hematite was documented and essentially each of the chlorobenzenes was initially found in the sorbed state. Subsequent desorption measurements using gas-purge methodology showed that the rate of chlorobenzene desorption decreased as a function of chlorine substitution. The first-order rate constants for the desorption of 1,3,5-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, and pentachlorobenzene were 0.091, 0.051, and 0.029 hr -1 , respectively. Hexachlorobenzene desorption was undetectable over 144 hr. Hematite-chlorobenzene slurries were treated with H 2 O 2 concentrations ranging from 0.1 to 5% at pH 3. The degradation of 1,3,5-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, and pentachlorobenzene using H 2 O 2 concentrations ≤1% proceeded at rates less than their corresponding rates of desorption, suggesting that desorption controlled the rates of oxidation. When H 2 O 2 concentrations ≥2% were used, the degradation rates of the three lower chlorobenzenes exceeded the rates of desorption suggesting that oxidation was occurring, at least in part, in the sorbed state. Hexachlorobenzene was not degraded by H 2 O 2 concentrations ≤5%. Hydroxyl radical generation rates were not significantly different in all of the hematite-catalyzed systems, indicating that surface catalysis mechanisms were saturated with respect to H 2 O 2 (i.e., were characterized by 0-order kinetics), even at the lowest H 2 O 2 concentrations. The data show that sorption significantly affects rates of mineral-catalyzed H 2 O 2 oxidations, and that different mechanisms (e.g., surface-catalyzed oxidation) may be occurring at H 2 O 2 concentrations ≥2%.
87 citations
TL;DR: In this paper, a novel oxidant, periodate (IO_4^−), coupled with ultraviolet (UV) irradiation was used to reduce chemical oxygen demand in industrial wastewater.
Abstract: The rapid reduction of chemical oxygen demand (COD) of industrial wastewater is achieved using a novel oxidant, periodate (IO_4^−), coupled with ultraviolet (UV) irradiation. The wastewater is characterized by a high COD, low total suspended solids, variable triethanolamine (TEA) concentrations, and low concentrations of iron and zinc. The use of periodate and UV irradiation with either aqueous TEA solutions or real wastewater is shown to be effective in reducing the COD to acceptable levels. The optimal pH for COD degradation is determined to be 7.6 because of the combined effects of pH on the speciation of TEA and IO_4^− Increasing the ratio of the initial concentrations of period ate to TEA, [IO_4^−]_0/[TEA]_0, increased the degradation rate up to an apparent saturation value. Irradiation with a 1 000-W mercury-xenon lamp increased the COD pseudo-first-order degradation rate constant by a factor of 5.5 for synthetic TEA solutions and 2.3 for industrial wastewater, compared to irradiation with a 1 000-W xenon lamp.
TL;DR: In this article, the authors compared the performance of a temperature-phased anaerobic process with a conventional single-stage mesophilic system for treating domestic wastewater sludge, and found that the temperature-phase system achieved almost complete destruction of total and fecal coliforms over a range of solids retention times (SRTs) from 10 to 15 days.
Abstract: The temperature-phased anaerobic process involves a two-stage reactor system with the first stage operated at a thermophilic temperature (typically 55°C) and the second stage operated at a mesophilic temperature (typically 35°C). The purpose of this laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage mesophilic system for treating domestic wastewater sludge. Of particular interest in the research was a comparison of the two systems from the standpoint of coliform reduction, volatile solids destruction, and biogas production. The temperature-phased system achieved almost complete destruction of total and fecal coliforms over a range of solids retention times (SRTs) from 10 to 15 days. The concentration of fecal coliforms in the effluent from the temperature-phased system never exceeded 1 000 MPN/g total solids, which can meet the U.S. federal fecal coliform requirements for Class A biosolids. At SRTs ranging from 10 to 15 days, the temperature-phased system achieved an 18% higher destruction of volatile solids and 16% more methane production than was possible with the single-stage mesophilic process.
TL;DR: In this paper, a simple respirometric procedure using an enrichment nitrifying culture was presented for acute nitrification toxicity screening of wastewater, where Allyl thiourea was used as a selective nitrification inhibitor.
Abstract: Current stringent effluent discharge limits for nitrogen and the high sensitivity of nitrifying bacteria to inhibition by toxic compounds encourage the development of methods for acute nitrification toxicity screening of wastewater. For this purpose, a rapid (response time of 14 minutes) and simple respirometric procedure using an enrichment nitrifying culture is presented. Allyl thiourea was used as a selective nitrification inhibitor. The concentration of a toxic compound causing a 50% decrease of nitrifying activity compared to the nontoxic reference measurement with tap water (EC 50 ) was determined for different reference chemicals. The (EC 50 ) values obtained with the nitrifying culture (0.51 mg/L for 3,5-dichlorophenol, 2.67 mg/L for phenol, 0.078 mg/L for CN - , 173 mg/L for Cu ++ , and 8.3 mg/L for Cd ++ ) revealed that the method described combined a high sensitivity with acceptable repeatability. Because of its simplicity and short response time, the proposed procedure seems suitable for on-line acute nitrification toxicity detection at wastewater treatment plants.
TL;DR: In this article, full-scale ultraviolet (UV) light and chlorine disinfection systems were operated in parallel using nitrified and partially denitrified tertiary treated wastewater effluent.
Abstract: Full-scale ultraviolet (UV) light and chlorine disinfection systems were operated in parallel using nitrified and partially denitrified tertiary treated wastewater effluent. A UV dose of 75 mW.s/cm 2 reduced the concentration of fecal coliforms, enterococci, fecal streptococci, MS2 bacteriophage, and poliovirus by four logs. A higher dose was needed to reduce the concentration of heterotrophic plate count (HPC) by four logs and to achieve a total coliform value <2.2 MPN per 100 mL within a consecutive 7-day period as required by the most restrictive California Wastewater Reclamation Criteria (CWRC). The cleaning frequency needed to maintain a minimum operational UV dose was assessed by constructing a lamp fouling curve describing reduction in UV intensity as a function of elapsed time since lamp cleaning. Substitution of UV light for chlorine disinfection eliminated formation of trihalomethanes, reduced formation of aldehydes, and formed a mid-polarity unidentified peak at a bench-scale dose of 2 800 mW s/cm 2 . The unidentified UV peak was not detected at a full-scale dose of 188 mW.s/cm 2 . No chronic toxicity was observed for the full-scale UV irradiated effluent ; a decline in the reproductive rate of Ceriodaphnia dubia was observed for the full-scale chlorinated effluent.
TL;DR: A free water surface constructed wetlands has been in operation at the Sacramento Regional Wastewater Treatment Plant treating municipal secondary effluent since the spring of 1994 as mentioned in this paper, and data on removal of 13 metals and ammonia are presented for the operating period from July 1994 to December 1995.
Abstract: Constructed wetlands have the potential to trap and remove metals contained in wastewater. Long-term removal is expected to occur by accumulation and burial in the plant detritus in a manner similar to the removal of phosphorus. A free water surface constructed wetlands has been in operation at the Sacramento Regional Wastewater Treatment Plant treating municipal secondary effluent since the spring of 1994. Data on removal of 13 metals and ammonia are presented for the operating period from July 1994 to December 1995. Significant removal of copper, lead, and zinc is indicated from preliminary results. Water quality profiles for copper, lead, nickel, and zinc are presented for a plug flow cell.
TL;DR: In this paper, the authors studied disinfection byproduct (DBP) formation in non-nitrified and nitrified secondary effluents from several treatment plants and renovated water following soil aquifer treatment.
Abstract: Disinfection byproduct (DBP) formation was studied in nonnitrified and nitrified secondary effluents from several treatment plants and renovated water following soil aquifer treatment. The wastewater was chlorinated using different concentrations of chlorine. The study included formation of trihalomethanes (THM), haloacetic acids (HAA), and total dissolved organic halogens (DOX). In ammonia-containing effluents (nonnitrified), where stable chloramine is formed, applying a chlorine dose of 0.34 (weight ratio of Cl/C) produced an average ratio of DOX to dissolved organic carbon (DOC) of 8.5 μg Cl/ mg C, and insignificant concentrations of THM and HAA. In nitrified-effluents forming free chlorine residual, a Cl/C dose of 0.34 (weight ratio) yielded an average DOX/DOC of 49 μg Cl/mg C. The THM formation varied widely with the effluent source and HAA/DOC formation was 2 to 3 μg Cl/mg C. The DOX formation potential (DOXFP) per mg carbon averaged 28 μg Cl/mg C for ammonia-containing effluents and 147 μg Cl/mg C for completely nitrified effluents. The THM formation potential (THMFP) constituted 13 to 56% and HAAFP constituted 10 to 17% of the DOXFP, respectively. The results indicated that high concentrations of DBP are formed during chlorination of effluents, posing a contamination problem. Reduction of DBP formation can be achieved by applying treatment processes producing low-DOC effluents and leaving a small concentration of residual ammonia.
TL;DR: In this paper, an exergy analysis has been performed for Lulea WWTP in Northern Sweden, where the main flows included in the analysis are the wastewater heat, precipitants and other chemicals, organic matter and nutrients in the wastewater and biosolids, and electricity used for operation and maintenance.
Abstract: The objective of this article is to exemplify how an exergy analysis could be used to estimate the consumption of physical resources at a wastewater treatment plant (WWTP). The exergy analysis has been performed for Lulea WWTP in Northern Sweden. About 60,000 population equivalents are connected to the WWTP, which has mechanical and chemical treatment. Flows included in the analysis are the wastewater heat, precipitants and other chemicals, organic matter and nutrients in the wastewater and biosolids, and electricity used for operation and maintenance. One conclusion is that the value of the heat is overestimated in a conventional energy analysis. Also, the organic matter probably represents the largest technical exergy flow. It is not clear how the exergy value of nutrients should be estimated.
TL;DR: The fundamental principles of a steady‐state model for biological excess phosphorus removal (BEPR) that is based on the current understanding of the mechanisms of BEPR are described and can be used for design and to predict the expected system response under constant flow and load conditions.
Abstract: The function of the single-sludge activated-sludge system has expanded from chemical oxygen demand (COD) removal to include, progressively, nitrification, denitrification, and phosphorus removal, all biological. With such complexity, design procedures based on fundamental behavioral patterns are required. The fundamental principles of a steady-state model for biological excess phosphorus removal (BEPR) that is based on the current understanding of the mechanisms of BEPR are described. The model can be used for design and to predict the expected system response under constant flow and load conditions. With the aid of the model, the influence of various parameters on the magnitude of phosphorus removal and the interactions between BEPR and nitrification and denitrification are examined. Principle variables that influence phosphorus removal are an influent wastewater characteristic-readily biodegradable chemical oxygen demand Concentration - and process design parameters-anaerobic mass fraction and its subdivision and sludge age. Also, the model indicates that, in agreement with observations, preventing recycling of nitrate to the anaerobic reactor is one of the main considerations in design.
TL;DR: In this paper, a 5670m 2 wet detention pond draining a predominantly residential urban area was monitored for flow, suspended solids, bedload, particle-size distribution, and selected pollutants during 16 storm events.
Abstract: A 5670-m 2 wet detention pond draining a predominantly residential urban area was monitored for flow, suspended solids, bedload, particle-size distribution, and selected pollutants during 16 storm events. Both suspended solids concentrations and particle-size distribution of the suspended solids in runoff water exhibited large variations between storms. Though a portion of particles larger than the pond's critical particle size left the pond, the pond removed 87% of the total suspended solids entering the pond. The relative proportion of clay-size particles increased from 36 to 72%. Sand- and silt-size fractions both decreased. Heavier particulate material saltating along the channel bottom, termed bedload, composed an average of 14% of the total particulate mass or load to the pond. The pond's sediment and associated pollutant removal efficiencies were influenced by influent particle-size distribution.
TL;DR: In this article, an extensive assessment was made of nine common similarity measures on the basis of their discriminative ability and bias in weighting of different types of variation in species abundance between samples, by using sets of river macroinvertebrate samples.
Abstract: An extensive assessment was made of nine common similarity measures on the basis of their discriminative ability and bias in weighting of different types of variation in species abundance between samples, by using sets of river macroinvertebrate samples. Seven agglomerative hierarchical clustering methods were applied to these measures. Successful site discrimination is defined as grouping of all replicate samples from a particular site. Major differences existed in the discriminative ability between the similarity measures. The measures overweight some types of variation and underweight the others to varying extents, which is closely related to their discriminative ability. A new dissimilarity-similarity measure was devised to respond to all types of variation with minimum bias. This measure yielded a higher percentage of correct site discrimination than the others tested. Use of an extra data set confirmed the superior performance of the new measure and also indicated that it could discriminate between sites of different water quality.
TL;DR: The shortcomings of total chlorine residual as a measure of wastewater disinfection are discussed in this paper, where the effect of pH is significant in the toxicity of chlorine compounds and the formation of organic chloramines made the residual measurement technique more difficult to use in wastewater disinfections.
Abstract: The shortcomings of total chlorine residual as a measure of wastewater disinfection are discussed The effect of pH is significant in the toxicity of chlorine compounds Recent investigation to the formation of organic chloramines made the residual measurement technique more difficult to use in wastewater disinfection Redox potential (or oxidation-reduction potential-ORP) is studied as an alternative way of assessing the efficacy of disinfectants through theoretical consideration and literature review Experiments performed using wastewater samples showed that ORP is better correlated to the inactivation of coliform than total chlorine residual Also illustrated is a case study carried out at a municipal wastewater treatment plant in California (US) By replacing conventional methods for establishing chlorine and sulfur dioxide dosage with a system that automatically modulates chemical feed by ORP, the plant reduced chemical use for chlorination and dechlorination by 47 and 62%, respectively, while consistently maintaining compliance with stringent disinfection requirements (22 MPN coliform per 100 mL) and chlorine discharge limits (less than 01 mg/L)
TL;DR: In this article, the authors presented results from bench-scale pilot tests of membrane ultrafiltration of produced water obtained from three operating oil and gas wells, which reduced concentrations of grease and oil in the produced waters evaluated in this work to below current and anticipated regulatory limits.
Abstract: Produced water from gas and oil operations is purportedly the largest single source of waste generated in the U.S., with an annual production rate of more than 2.7 bil t (3 bil ton). Results are presented from bench-scale pilot tests of membrane ultrafiltration of produced water obtained from three operating oil and gas wells. Ultrafiltration (UF) reduced concentrations of grease and oil in the three produced waters evaluated in this work to below current and anticipated regulatory limits. Permeation flux varied from one produced water to another. Because membrane cost is influenced by permeate flux, generalizations regarding the economic or technical feasibility of UF treatment of produced water based on the limited number of laboratory and field tests performed to date do not appear to be warranted.
TL;DR: In this article, a longitudinal dispersion model was proposed to estimate the discrepancy between this model and natural processes, and an estimate of the Lagrangian spatial scales was proposed, and it was shown that those scales are as large as two to four times the length of alternate bars.
Abstract: Contaminant transport in natural streams is considered on the basis of tracer studies in Moldovian small lowland rivers. Theories describing the spread of conservative and passive pollutants in the context of a longitudinal dispersion model, as well as attempts to estimate the discrepancy between this model and natural processes, are discussed. It is shown that the model agrees with experimental data, with an accuracy ranging from 15 to 20%, at least in the upper [C(t) > 0.5C max ] concentration distributions. The process behaves in a quasi-Fickian manner only at distances greater than 80 to 100 times the river width. Primarily, the nonuniformity of the average velocities over cross sections affects the process. An estimate of the Lagrangian spatial scales was proposed, and it was shown that those scales are as large as two to four times the length of alternate bars.
TL;DR: In this article, ground tires were used as a supplement to the engineered landfill clay liner system in order to retard VOC transport to a greater degree than that which occurs in the traditionally constructed engineered containment system.
Abstract: Bentonite slurry cut-off walls, have been used under site-specific conditions as an alternative to substantially reduce the spreading of groundwater contamination. Shredded tires were found to be used as a supplement to the engineered landfill clay liner system in order to retard VOC transport to a greater degree than that which occurs in the traditionally constructed engineered containment system. Laboratory-scale column permeameter tests were conducted to investigate the retardation of volatile organic compound (VOC) movement through a bentonite slurry cut-off wall amended with ground tires, which were found to sorb a significant amount of VOCs. The hydraulic conductivity was not affected by addition of ground tires but was affected by addition of VOCs at 10{approximately}15 mg/L. The hydraulic conductivity increased immediately after addition of VOCs but remained relatively constant throughout the test period. A typical slurry cut-off wall does not appear to be a good barrier for the containment of organic compounds. The organic compound breakthrough times were significantly prolonged by addition of ground tires. For example, m-xylene did not breakthrough in ground tire amended permeameters over 450 days but broke through in the silty-sand and bentonite mixed permeameter. Ground tires had a great deal of organic compound sorption capacitymore » without deteriorating the performance of slurry cut-off walls. It appears that addition of ground tire to slurry cut-off walls significantly improve the efficiency of organic compound containment with minimal additional construction costs.« less
TL;DR: In this paper, the effects of sample size (the number of replicates) on 11 similarity measures were investigated using a set of freshwater macroinvertebrate samples and a randomization procedure for resampling.
Abstract: The effects of sample size (the number of replicates) on 11 similarity measures were investigated using a set of freshwater macroinvertebrate samples and a randomization procedure for resampling. Most of these indices were strongly affected by sample size. However, as sample size increased, species composition and relative abundance changed significantly and the real similarity between two replicate samples increased substantially. Responsiveness to sample size dictates the sensitivity of a similarity measure to community change. The relative independence of sample size of some similarity measures results from strongly overweighting abundant species. CY dissimilarity-similarity measure showed the highest sensitivity, followed by Canberra metric.
TL;DR: In this paper, a variable-order kinetic model for sizing the second-stage cells of a series system yielded a coefficient of determination, r 2, of 0.94 for the summer NH4 removal data.
Abstract: Research was conducted on pilot-scale, subsurface flow constructed wetland systems treating municipal wastewater. Increasing the hydraulic retention time (HRT) from 1.7 days to 4.3 days reduced the mean effluent NH 4 concentration by 2.7 mg N/L. Hydroperiod manipulation caused a 2.9-mg N/L decrease in effluent NH 4 . The influent NH 4 concentration for the 9-month study period averaged 21 mg N/L. The lowest average effluent NH 4 concentration observed in single-stage treatment cells was 13 mg N/L. The mean effluent NH 4 concentration from the second-stage cells of two wetland cells in series was 10 mg N/L. During the period from May through September, the second-stage cells produced an effluent NH 4 concentration of 6 mg N/L. A variable-order kinetic model for sizing the second-stage cells of a series system yielded a coefficient of determination, r 2 , of 0.94 for the summer NH4 removal data. The predicted HRT to reduce NH 4 from 20 mg N/L to 5 mg N/L was 3.9 days, if the cells were subjected to cyclic draw and fill.
TL;DR: A sampling program was conducted to assess the quality of first flush storm water runoff from 10 industrial groups typical of many businesses located in North Carolina as discussed by the authors, which indicated that zinc and copper were the most common of the eight metals measured in runoff from the 20 industrial sites monitored.
Abstract: A sampling program was conducted to assess the quality of first flush storm water runoff from 10 industrial groups typical of many businesses located in North Carolina. Analysis of samples collected during the first 30 min of runoff (first flush) indicated that zinc and copper were the most common of the eight metals measured in runoff from the 20 industrial sites monitored. Ten volatile organic, semivolatile organic, or pesticide compounds were found at eight different sites, with the most common being methylene chloride (three sites). Conventional pollutants such as nutrients and solids were measured at varying levels at every site, but were generally the highest where a significant amount of biological waste or exposed soil was present.
TL;DR: In this article, the removal of ammonia from coke-plant effluents by using synthetic zeolites has been investigated using the 13x molecular sieve and showed that the ammonium adsorption rate increases with an increase in the contact time of zeolite with ammonia solution.
Abstract: Ammonia is discharged at significant concentrations in coke-plant effluents and can adversely impact freshwater-receiving streams. This article reports on the removal of ammonia from such wastewaters by using synthetic zeolites. Factors affecting the ammonium exchange capacity included the contact time, the concentration of ammonia in the solution, the particle size of the zeolites, the loading flow rates, and the number of regenerations of zeolite, the 13x molecular sieve has also been tested for its capacity to remove ammonia from coke-plant secondary wastewater.
Results indicate that the ammonium adsorption rate increases with an increase in the contact time of zeolite with ammonia solution. Smaller particle size of the zeolite, increase in ammonium concentration, and lower loading flow rate elevate ammonium exhange capacity for the zeolite. Column, and repeated column regeneration of the zeolite with NaCl solution reactivates the zeolite column, and repeated column regeneration is possible without loss of ammonium uptake capacity.
TL;DR: In this article, the relative rates of volatile fatty acid (VFA) production and VFA uptake were quantified through separation of fermentation step from the phosphorus-accumulating bacteria (Bio-P removal process).
Abstract: In this research, the relative rates of volatile fatty acid (VFA) production and VFA uptake were quantified through separation of fermentation step from the phosphorus-accumulating bacteria (Bio-P removal process). Furthermore, the effect of prefermentation of raw wastewater on Bio-P removal was evaluated. Degritted raw wastewater was fermented under different conditions in bench-scale anaerobic sequencing batch reactors called primary acid fermenters (PAFs). Specific rates of VFA production were measured under different solids retention times (4, 8, 12, and 13 days), two pH levels (natural pH of wastewater and pH of 6.1 to 6.4), two regimens of mixing (6 h/cycle versus 0.25 h/cycle), and hydraulic retention times of 9 and 12 hours. Experiments were conducted at room temperature (20 ± 2°C). Specific rate of VFA production ranged from 0.3 to 3.0 mg VFA/g VSS. h under investigated conditions while the volumetric rate of production varied from 4 to 54 mg VFA/L. d depending on the conditions of the reactors. The rate of VFA uptake was measured in a subsequent biological nutrient removal sequencing batch reactor fed with fermented wastewater. The rate was 28.5 mg VFA/g VSS h. Phosphorus release was found to be 18.8 mg ortho-P/g VSS h (primary release) during the period of VFA uptake and 1.8 mg ortho-P/g VSS.h (secondary release) when VFA were depleted in the environment. Bio-P removal improved significantly as the result of prefermentation of degritted raw wastewater.
TL;DR: In this article, a Langmuir-Hinshelwood (L-H) rate form is used to describe the kinetics of the photocatalytic oxidation of these compounds.
Abstract: The photocatalytic oxidation rates of nitrotoluene (2-NT and 3-NT) and dinitrotoluene (2,4-DNT and 2,6-DNT) in aqueous suspensions of Degussa P-25 were found to be pH independent because these compounds do not exhibit any pH-dependent speciation. The reaction rates of mononitrotoluenes were found to be 60 to 80% greater than those of dinitrotoluenes. A Langmuir-Hinshelwood (L-H) rate form is used to describe the kinetics of the photocatalytic oxidation of these compounds. The L-H constant k 1 has been found to be essentially independent of the compound being degraded. At low concentrations, the reaction rates of nitrotoluenes decrease with increasing nitration. This has been explained through the electron-withdrawing characteristics of the nitro group, employing the Hammett relationship, with the reaction rates following the sequence Toluene > 3-NT > 2-NT > 2.4-DNT > 2,6-DNT > TNT (trinitrotoluene, predicted) The photocatalytic oxidation of 2,6-DNT produces ammonium and nitrate ions. Attempts at augmenting the reaction rate by addition of hydrogen peroxide or Cu 2+ ions did not significantly increase the reaction rate.