Journal of Environmental Engineering

Cyanotoxins released from cyanobacteria (or blue-green algae) pose an increasing public health risk worldwide. In this study, the release of the cyanotoxin microcystin, from Microcystis aeruginosa due to oxidative, ultraviolet (UV), and physical impacts during water treatment was studied. Additionally, the relative and absolute rates of chemical oxidation of the six microcystins were determined for selected oxidants. Cell viability was measured based on treatment dosage using a fluorescence method. The specific chemical oxidants studied were free chlorine $\left(\text{HOCl}/{\text{OCl}}^{-}\right)$ , chlorine dioxide, ozone, permanganate, and monochloramine. UV energy was at 254 nm. For chemical oxidants and UV, the exposures or doses examined were selected based on typical disinfection dosages. Other treatments examined included low and high salinity, ultrasonics, and physical blending. Free chlorine, permanganate, chlorine dioxide, monochloramine, and ozone were observed to at least partially disinfect the cyanobacteria, while the other disinfectants used as treatments did not. Significant concentrations of microcystin-LR (MC-LR) were observed in treated water after treatment of Microcystis aeruginosa with chlorine dioxide, low salinity, sonication, and blending. In these cases, the rate of cell lysis due to treatment was greater than the subsequent removal of the chemical from solution. For the other oxidants and UV, no significant buildup of the cyanotoxin was observed. These results suggest that permanganate was shown to be the most effect disinfectant for achieving both disinfection and removal of the released cyanotoxins with typical disinfectant dosages. However, it should be noted that the use of permanganate leads to the formation of particulate manganese dioxide in solution which can cause potential problems in treated drinking water.

A population balance model was developed to simulate simultaneous precipitation and flocculation during precipitative softening. Rate coefficients for nucleation, crystal growth, and flocculation were extracted from experimental particle-size distribution (PSD) data based on changes in the total number and total volume of particles. Three models of flocculation were evaluated: rectilinear, curvilinear, and an empirical size-independent model. Model simulations were compared with experimental PSD data to test which model was most appropriate. The curvilinear precipitative flocculation model was superior when seeded precipitation occurred at moderate mixing intensities $\left(G=50–100{\text{s}}^{-1}\right)$ . However, the curvilinear model overpredicts the formation of very large particles and requires values of the collision efficiency greater than 1.0, suggesting a more complicated dependence of the PSD dynamics on mixing intensity and saturation ratio than presently included in the model. At higher mixing intensities $\left(G=300{\text{s}}^{-1}\right)$ , flocculation exhibited size-independent behavior, indicating that physical/chemical aspects of the precipitation process are altering or overshadowing the physics described in the curvilinear flocculation model.

Three-dimensional numerical analyses of flow and transport characteristics in two representative multichamber ozone contactor models with different chamber width were conducted using large eddy simulation (LES). Both time-averaged and instantaneous flow patterns suggest that the flow is characterized by the occurrence of large turbulent structures leading to extensive short-circuiting between chambers and internal recirculation inside the chambers. The flow is also found to be highly three-dimensional, as secondary vortices and recirculation zones develop. The simulation results further suggest that the hydrodynamics in ozone contactors can be improved by reducing the chamber width. The results of the LES are qualitatively verified using previously reported tracer test results obtained from laboratory experiments. The LES technique, applied to the ozone contactor flow and transport of a tracer for the first time, is expected to serve as a powerful tool for existing reactor flow diagnosis, reactor retrofitting as well as for new reactor design.

Generally, the flow in settling tanks is stratified, but the effect of buoyancy force on the flow field depends on the inlet concentration of particles and flow bulk velocity. A common approach for increasing settling tanks performance is to use baffles which can reduce effects of the unfavorable phenomena such as short circuiting between inlet and outlet and density currents in primary and secondary settling tanks, respectively. The suitable position of the baffles is related to the importance of buoyancy force. As a result, effects of inlet Reynolds and Froude numbers on the strength of buoyancy force are studied for a secondary settling tank and the results show that neither Reynolds nor Froude numbers are sufficient to be considered alone. Effect of buoyancy force on the suitable baffle position is also investigated. Results show that in high Reynolds numbers, the flow field and baffle position are not affected by the inlet Froude number.

Batch ozone-photocatalytic oxidation $\left({\text{O}}_3/\text{UV}/{\text{TiO}}_2\right)$ and biological remediation by macroalgae were performed in a laboratory-scale reactor to evaluate the efficiency of these processes in the degradation of contaminants and/or decrease in the ecotoxicity of produced waters of petroleum refineries. The effectiveness of the hybrid advanced oxidation process followed by biological treatment was evaluated through the physicochemical time-course analysis and ecotoxicological tests. The results showed that after 5 min of treatment the ${\text{O}}_3/\text{UV}/{\text{TiO}}_2$ combination was very effective and phenol concentration decreased by 99.9%, sulfide by 53.0%, COD by 37.7%, O&G by 5.2%, and ammonia by 1.9%. The following reductions in contaminants were obtained after 60 min of oxidation treatment: phenols 99.9%, O&G 98.2%, sulfide 97.2%, COD 89.2%, and ammonia 15%. The acute toxicity tests with the bacterium Vibrio fischeri (Lumistox) and the fish Poecilia vivipara showed a high toxicity of the raw effluents ( $E\left(L\right)C_{50}<1.55\%$ for both species), while after 60 min of treatment effluents showed lower acute toxicity toward bacteria $\left(E{C}_{50}=30.9\%\right)$ , but toxicity toward fish remained high $\left(E{C}_{50}=1.9\%\right)$ . Additional wastewater biotreatment with macroalgae Ulva spp. for wastewater depuration showed a significant toxicity reduction ( $E{C}_{50}=89.2\%$ for bacteria and $E{C}_{50}=85.7\%$ for fish), which was due to the biosorption/transformation of metals and ammonia compounds during the biological treatment. Thus, the physicochemical results showed that a combination of ${\text{O}}_3/\text{UV}/{\text{TiO}}_2$ for 10 min followed by macroalgae depuration seems to be a good option for cost effective treatment of produced water streams.

The single Fenton or the Fenton process implemented in combined scheme as a posttreatment after the ferric chloride coagulation was applied for leachate collected from a real waste disposal site. Depending on the ratios of ${\text{H}}_2{\text{O}}_2$ /chemical oxygen demand, ${\text{H}}_2{\text{O}}_2/{\text{Fe}}^{2+}$ , and pH, the Fenton oxidation or both the Fenton oxidation and the Fenton coagulation were involved in chemical oxygen demand reduction. The implementation of ferric chloride coagulation as a pretreatment stage or acidification of raw leachate did not result in the improvement of chemical oxygen demand reduction efficacy of the following Fenton process comparing with that obtained by the direct Fenton treatment of raw leachate. The direct Fenton treatment with a higher (3/1) ${\text{H}}_2{\text{O}}_2$ /chemical oxygen demand ratio applied to raw leachate without pH preadjustment $\left({\text{H}}_2{\text{O}}_2/{\text{Fe}}^{2+}=10/1\right)$ , produced more oxidized organic compounds (measured as dissolved organic carbon/chemical oxygen demand ratio), more biodegradable by-products (measured as a 7-day biological oxygen demand/chemical oxygen demand ratio), and required a considerably lower dosage of NaOH for neutralization, making it preferable for the leachate treatment. Although up to a twofold reduction in the toxicity was observed after the overall Fenton process application, the treated leachate remained extremely toxic to Daphnia magna.

Natural attenuation is a passive remedial approach that depends upon natural processes to degrade and dissipate contaminants in soil and groundwater. Intrinsic bioremediation is believed to be the major process among the natural attenuation mechanisms that account for the reduction of contaminant concentrations. In this study, a mass flux approach was used to calculate the contaminant mass reduction at a petroleum-hydrocarbon spill site. The mass flux technique is a simplified mass balance procedure, which is accomplished using the differences in total contaminant mass flux across two cross sections of the contaminant plume. The mass flux calculation results show that up to 86% of the dissolved total benzene, toluene, ethylbenzene, and xylene (BTEX) isomers removal was observed via natural attenuation at this site. Evidence for the occurrence of natural attenuation was the decreased contaminant mass flux through the plume cross sections along the transport path and limited spreading of the BTEX plume. Evidences for the BTEX biodegradation include: (1) decreased BTEX concentrations along the transport path; (2) depletion of dissolved oxygen, nitrate, and sulfate; (3) production of dissolved ferrous iron, sulfide, methane, and ${\text{CO}}_2$ ; (4) deceased pH in the spill source area and increased pH in iron-reducing area; (5) increased alkalinity and microbial populations; and (6) preferential removal of certain BTEX components along the transport path. The effectiveness of intrinsic bioremediation on BTEX removal was evaluated by the in situ tracer method. Results reveal that approximately 74% of the BTEX removal was due to the intrinsic biodegradation process. The first-order decay model was applied for the natural attenuation and intrinsic bioremediation rates calculation. Results show that the biodegradation capacity (34.5 mg/L) for BTEX was much higher than the detected contaminants within the plume. The calculated total BTEX first-order natural attenuation and intrinsic bioremediation rates were 0.025 and 0.017% 1/day, respectively. Results of polymerase chain reaction, denaturing gradient gel electrophoresis, and nucleotide sequence analysis reveal that some petroleum-hydrocarbon degraders (Flavobacterium capsulatum, Xanthobacter sp., Xanthobacter flavus, Xanthomonas codiaei, Pseudomonas boreopolis, Methylobacterium sp., Reichenowia pictae) might exist at this site, which might contribute to the BTEX biodegradation. Results suggest that the natural attenuation mechanisms can effectively contain the plume, and the mass flux method is useful in assessing the occurrence and efficiency of the natural attenuation and intrinsic bioremediation processes.

A mathematical and statistical model for simulating contaminant removal from a surface sand filter is reported. The model was based on a mass balance equation and an advection-dispersion transport model. The unknown parameters of the model were the deposition rate and the hydrodynamic dispersion. Changes in space were allowed within the filter media depth and time variability of flow and influent contaminant concentration were taken into account. System field monitoring was performed between 2004 and 2006. A total of 17 storms were selected for the study. Runoff constituent analyses included: total suspended solids, total petroleum hydrocarbons-diesel range hydrocarbons, and zinc. The objective was to explore the capabilities of a two parameter model for predicting effluent contaminant concentrations. Optimized model parameter values were calculated on a storm by storm basis. Thereafter, a gamma distribution was fitted to the optimized values. A Monte Carlo simulation was performed to explore the predicting capabilities of the model by using two storms left for validation. Results of the validation phase show an acceptable performance of the model since, in general, estimated effluent concentrations fell within the uncertainty limits.

Sediment oxygen demand (SOD) and nutrient flux studies were conducted for a tropical reservoir in Singapore in order to determine the approximate SOD and nutrient release rates from the sediments. SOD values obtained from laboratory experiments ranged from 1.4 to $3.3\text{g}{\text{O}}_2/{\text{m}}^2\text{-day}$ . Similar results were also obtained by calculating SOD values from in situ DO measurements taken in the field. The nutrient flux study was performed in the laboratory at a constant temperature of $25°\text{C}$ in oxic and anoxic columns. Except for $\text{nitrate}+\text{nitrite}$ , higher nutrient release rates were generally observed under anoxic conditions. The ammonium release rate was $0.06\text{g}{\text{O}}_2/{\text{m}}^2\text{-day}$ under oxic conditions and $0.117\text{g}{\text{O}}_2/{\text{m}}^2\text{-day}$ under anoxic conditions. The nitrate flux rate was $0.17\text{g}{\text{O}}_2/{\text{m}}^2\text{-day}$ under oxic conditions but was negligible under anoxic conditions. Orthophosphate flux results were negative throughout the oxic incubation implying that sediments acted as a sink. The release rate of orthophosphate was $0.0076\text{g}{\text{O}}_2/{\text{m}}^2\text{-day}$ under anoxic conditions.

Discoloration in water distribution systems has been studied in partnership with a number of U.K. water companies by measuring the turbidity response to changes in hydraulic conditions induced by systematic flushing. The resulting data was used to verify a predictive empirical model and hence the underlying assumptions made in its development. Model simulations, made using previously established parameters defined solely by pipe diameter and pipe material, are presented alongside measured data to demonstrate this verification. The primary cause of discoloration observed is the mobilization of material from cohesive layers bonded to pipe walls. These layers demonstrate a profile of increasing shear strength with increasing degree of discoloration. Differences are demonstrated in the layer and ultimate shear strength characteristics of the discoloration layers formed in iron and plastic pipes, with a modeled shear stress of $1.2\text{N}/{\text{m}}^2$ shown to exhaust material layers in plastic pipes. Based on the observed data it is theorized that accumulation of material to the pipe walls is primarily dependent on two mechanisms; ubiquitous background concentrations in the bulk water, and if present corrosion by-products from iron pipes and fittings. A consequence of this is that all pipes within a water distribution system are susceptible to the development of material layers. In the formulation of operation and maintenance strategies it is suggested that iron and plastic pipes should be treated differently to obtain optimum operational effectiveness and minimize discoloration risk.

The kinetics, equilibriums, and thermodynamics of metal ion ( ${\text{Pb}}^{2+}$ , ${\text{Ag}}^{2+}$ , ${\text{Cu}}^{2+}$ , ${\text{Zn}}^{2+}$ , ${\text{Co}}^{2+}$ , ${\text{Sr}}^{2+}$ , and ${\text{Cs}}^{+}$ ) biosorption by the waste yeast cells of Saccharomyces cerevisiae from a local brewery were investigated. The results showed that the biosorption of these metal ions on the biomass was a very rapid process, following the pseudo-second-order equation gave the better fitting results in describing the kinetic data than the pseudo-first-order equation. The equilibrium data could be fitted well with the Langmuir model. The maximum sorption capacity obtained from the Langmuir model followed $\text{Pb}>\text{Ag}>\text{Cu}>\text{Zn}>\text{Co}>\text{Sr}>\text{Cs}$ (based on $\text{mmol}{\text{g}}^{-1}$ ). The biosorption process by the yeast was favorable for these metal ions removal according to the constant separation factor $\left(0<R_L<1\right)$ from the Langmuir model. The dried yeast cells showed high affinity for ${\text{Pb}}^{2+}$ uptake as soft ion and low affinity for ${\text{Cs}}^{+}$ as hard ion biosorption. The calculated values of the thermodynamic constants demonstrated that the biosorption process of ${\text{Ag}}^{+}$ , ${\text{Cu}}^{2+}$ , ${\text{Zn}}^{2+}$ , or ${\text{Co}}^{2+}$ was spontaneous and the entropy increased. pH increased during the metal biosorption by the yeast cells. ${\text{Pb}}^{2+}$ , ${\text{Ag}}^{2+}$ , ${\text{Cu}}^{2+}$ , ${\text{Zn}}^{2+}$ , or ${\text{Co}}^{2+}$ exhibited a certain degree of covalent binding with the waste yeast cells. ${\text{Cs}}^{+}$ , as a typical hard ion, showed ionic binding with the biomass.

In order to optimize the efficiency of the removal of volatile organic compounds (VOCs) by adsorption onto activated carbon beds, process simulations taking into account exothermicity effects are helpful. Significant temperature increases may arise in the bed during the VOC adsorption cycle, especially when high concentrations have to be treated. Consequently, reliable and easy-to-handle isotherms remain a key hurdle to build realistic models. In this study, adsorption models were tested to describe a set of experimental data obtained for three VOCs (acetone, ethyl formate, and dichloromethane) adsorbed onto five commercial activated carbons at four different temperatures (20, 40, 60, and $80°\text{C}$ ). A new expression of the Freundlich equation $\left[q_e=\left(a_{1}T+a_2{T}^2\right)C_e\left(1/n_f\right)\right]$ was shown to be statistically the most efficient to describe the adsorption isotherms of VOCs, single or in mixtures. A second-order polynomial temperature-dependence was introduced in this expression. The so-adapted Freundlich relationship gave a mean coefficient of determination of 0.97 for single-component adsorption and a correlation coefficient of 0.98 for binary mixtures.

The objective of this study was to use thermal treatment to treat soil contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). The emissions of lead (Pb) and PAHs during the thermal treatment process were evaluated. The parameters included pretreatment, temperature, and speed of the rotary kiln. Cadmium (Cd) had a higher mobility in thermally treated contaminated soil slag than other heavy metals because the primary fraction of Cd was the exchangeable fraction (90%). Of the temperatures tested in this study, the highest emission concentration of Pb occurred at $700°\text{C}$ . The Pb emission concentrations in the gas phase and solid phase were $44\mu \text{g}/\text{N}{\text{m}}^3$ and $138.35\mu \text{g}/\text{N}{\text{m}}^3$ , respectively. In PAHs emissions, naphthalene, acenaphthene (Acp), and fluorene were the main species in the gas phase, at different operating temperatures. The concentrations of these species ranged from 615.5 to $2,002.3\mu \text{g}/\text{N}{\text{m}}^3$ . Acp and chrysene were the main species in the solid phase at different temperatures, and the concentrations of these species ranged from 25.5 to $113\mu \text{g}/\text{N}{\text{m}}^3$ .

Measurement of particulates [respirable particulate matter (RPM or ${\text{PM}}_{10}$ ), fine RPM $\left({\text{PM}}_{2.5}\right)$ , non-RPM (NRPM), and total suspended particulate matter (TSPM)] were carried out on a campaign basis over a period of 3 years (2003–2006) at Kaikhali (22.022°N and 88.614°E) inside one of the world’s largest mangrove delta region—“The Sundarbans.” Considering the toxic potential of the particulate fractions, the foremost objective of this study was to determine the particulate concentrations during different parts of the year as well as to ascertain the trend of occurrence of the particulate fractions in an area of rich and unique biodiversity. Moreover, as the area had no past records on particulate data over a decade, the other important objective of the study was to prepare substantial database for the area for the present time. The average range of ${\text{PM}}_{10}$ , ${\text{PM}}_{2.5}$ , NRPM, and TSPM for the period from 2003–2006 has been found to be (57–118), (35–80), (10–25), and $\left(73–135\right)\mu \text{g}{\text{m}}^{-3}$ respectively. The data obtained for the finer particulate fractions have been compared with some previous studies in India. In addition to the particulate fractions, meteorological parameters such as wind speed, wind direction, and temperature were also recorded to accomplish proper interpretation of the data. The requisite statistical parameters (standard deviation, average, and range) for the particulate fractions have also been calculated.

Many stream restoration projects do not include a requirement for long-term monitoring after the project has been completed, resulting in a lack of information about the success or failure of certain restoration techniques. The National Risk Management Research Laboratory, part of the U.S. EPA Office of Research and Development, evaluated the effectiveness of stream bank and channel restoration as a means of improving in-stream water quality and biological habitat in Accotink Creek, Fairfax City, Va., using discrete sampling and continuous monitoring techniques before and after restoration. This project monitored the effects of a 549 m (1,800 linear-ft) restoration of degraded stream channel in the North Fork of Accotink Creek. Restoration, which was intended to restore the stream channel to a stable condition, thereby reducing stream bank erosion and sediment loads in the stream, included installation of native plant materials along the stream and bioengineering structures to stabilize the stream channel and bank. Results of sampling and monitoring for 2 years after restoration indicated a slight improvement in biological quality for macroinvertebrate indices such as Virginia Stream Condition Index, Hilsenhoff Biotic Index, and Ephemeroptera, Plecoptera, Trichoptera taxa; the differences were statistically significant at 90% level of confidence with the power of greater than 0.8. However, indices were all below the impairment level, indicating poor water quality conditions. No statistically significant differences in chemical constituents and bacteriological indicator organisms were found before and after restoration as well as upstream and downstream of the restoration. The results indicated that stream restoration alone had little effect in improving the conditions of in-stream water quality and biological habitat, though it has lessened further degradation of stream banks in critical areas where the properties were at risk. Control of storm-water flows by placing best management practices in the watershed might reduce and delay discharge to the stream and may ultimately improve habitat and water quality conditions.

Three storm-water wetlands in series were monitored in a heavily urbanized 12.5 ha watershed in Mooresville, North Carolina. Monitoring of this system allowed an examination of the diminishing returns provided by three successive best management practices (BMPs) of a similar type. At least 80% of the total concentration reduction for all pollutants occurred within the first wetland cell. Only the first wetland cell significantly $\left(p<0.05\right)$ reduced all pollutants tested. No pollutant was significantly reduced from the outlet of Wetland Cell 2 to the outlet of Wetland Cell 3 $\left(p<0.05\right)$ . Median complete system (outlet of Wetland Cell 3) effluent concentrations for total suspended solids, total phosphorus, total nitrogen, and turbidity were 8, 0.09, 0.73 mg/L, and 10 NTU, respectively, which compared favorably to published results. Organic nitrogen generated from wetland vegetation seemed to result in a background source of nitrogen in the wetlands, supporting the idea of an irreducible concentration for nitrogen in these systems. The results indicate that the successive BMPs in a series do not perform as well as the first when each BMP uses similar removal mechanisms.

Lab flotation in artificial sea water was used to separate sand-oil mixtures prepared by mixing crude oil with quartz-dominated beach sands. Major factors affecting the separation efficiency for three representative oils (light, waxy, and heavy viscous) were examined through lab flotation tests, vortex experiments, and oil viscosity measurements. Results showed that flotation in sea water can effectively separate the tested sand-oil mixtures which had large contrast in physicochemical properties: (1) aging of sand-oil mixtures reduced the separation efficiency; (2) both the viscosity of crude oil and its adhesion to sand surfaces had major impacts on separation efficiency; (3) addition of small amounts of surfactants could substantially improve the separation efficiency; and (4) for heavy viscous oil, hydrocarbon solvents needed to be added to improve separation because of their solvency and capability in reducing oil viscosity.

In this work the photodegradation of orange II was carried out in the presence of iron-rich montmorillonite (MMt) (2.24% ${\text{Fe}}_2{\text{O}}_3$ ) using a 15-W low-pressure ultraviolet lamp $\left(\lambda =254\text{nm},I=48.4\mu \text{W}/{\text{cm}}^2\right)$ . The effects of pH, MMt dose, and dye concentration were studied. A low pH value is favorable for the decolorization of orange II. The hydroxyl radical $\left({}^{•}\text{O}\text{H}\right)$ concentration increased with increasing concentration of MMt in aqueous solutions in the range of 0–1.5 g/L. Concentrations higher than 5.0 g/L MMt inhibited the ${}^{•}\text{O}\text{H}$ production. There was no significant decrease in photocatalytic activity when the catalyst was reused. Hydroxyl radicals were detected by tert-butyl alcohol in aqueous MMt suspensions under ultraviolet irradiation and were responsible for the degradation of orange II. Free iron ions dissolved in MMt suspensions, structural iron in the MMt structural and the charged surface of nanoclay are responsible for the hydroxyl radical $\left({}^{•}\text{O}\text{H}\right)$ production. Free iron ions dissolved in solution plays a predominant role in the degradation of orange II. This study shows that iron-rich MMt is a potential photocatalyst for dye wastewater treatment.