Journal of Environmental Engineering

The Monod method is widely used to model nutrient limitation and primary productivity in water bodies. It offers a straightforward approach to simulate the main processes governing eutrophication and it allows the proper representation of many aquatic systems. The Monod method is not able to represent the nutrient luxury uptake by algae, which consists of the excess nutrient uptake during times of high nutrient availability in the water column. The Droop method, which is also used to model nutrient limitation and primary productivity, takes into account the luxury uptake of nutrients. Because of the relative complexity of the Droop method, it has not been systematically adopted for the simulation of large stream networks. The Water Quality Analysis Simulation Program (WASP) version 7.1 was updated to include nutrient luxury uptake for periphyton growth. The objective of this paper is to present the new nutrient limitation processes simulated by WASP 7.1 and to compare the performance of the Droop and the Monod methods for a complex stream network where periphyton is the main organism responsible for primary productivity. Two applications of WASP 7.1 with the Droop and Monod methods were developed for the Raritan River Basin in New Jersey. Water quality parameters affecting the transport and fate of nutrients were calibrated based on observed data collected for the Raritan River total maximum daily load. The dissolved oxygen and nutrients simulated with WASP 7.1, obtained with the Droop and Monod methods, were compared at selected monitoring stations under different flows and nutrient availability conditions. The comparison of the WASP 7.1 applications showed the importance of using the Droop method when periphyton was the main organism responsible for primary productivity. The data simulated with the Droop method resulted in good agreement with the observed data for dissolved oxygen, ammonia-nitrogen, nitrate-nitrogen, and dissolved orthophosphate at the selected stations. The Monod method was not able to capture the diel dissolved oxygen variation when nutrients were scarce, and it resulted in unrealistic diel variations of nutrients at times of strong primary productivity at some locations.

This study aims at coupling a hybrid genetic algorithm (HGA) and a neural network (NN) model for the multiobjective calibration of surface water quality models. The HGA is formed as a robust optimization algorithm through combining a real-coded genetic algorithm with a local search method, i.e., the Nelder-Mead simplex method (NMS). The NN model is developed to approximate the input-output response relationship underlying a numerical water quality model, and is then incorporated into the HGA framework, which results in the HGA-NN approach. This approach has the advantage of evaluating the objective function of the calibration model in a more efficient way. The HGA-NN approach is tested in the calibration of a CE-QUAL-W2 model which is set up to simulate the hydrodynamic process and water quality conditions in Lake Maumelle in central Arkansas. It is found that the HGA-NN approach can improve the computational efficiency. However, it does not guarantee the finding of the parameter values with a low objective function value. An adaptive HGA-NN approach is then proposed to improve its performance. In this adaptive approach, both the water quality model and the NN model are incorporated into the HGA framework. They are executed adaptively to evaluate the objective function. The application results demonstrate that the adaptive approach can be applied to the calibration of water quality models.

Environmental Fluid Dynamics Code, a numerical estuarine and coastal ocean circulation hydrodynamic and eutrophication model, was used to simulate the distributions of dissolved oxygen (DO), salinity, water temperature, and nutrients in the Caloosahatchee River Estuary. Modeled DO, salinity, and water temperature were in good agreement with field observational data from the Florida Department of Environmental Protection and South Florida Water Management District. Sensitivity analyses identified the effects of river discharge, atmospheric winds, and tidal forcing on the spatial and temporal distributions of DO. Simulation results indicated that vertical mixing due to wind forcing increased the bottom DO concentration. River discharge enhanced stratification in deep locations but propagated vertical mixing in the shallow upper estuary. Finally, tidal forcing heavily influenced bottom layer DO concentrations throughout the whole river estuary.

The objective of this study was to investigate the mechanisms and extent of bauxite residue (red mud) neutralization at the residue surface in field impoundments as a result of long-term reaction with atmospheric ${\text{CO}}_2$ and addition of amendments to promote vegetation. The results showed that carbonation from atmospheric carbon dioxide reduces the pH of red mud from 12.5 to about pH 9.3 at the surface of storage cells, with the depth of neutralization dependent on the age of the stored residue (up to 1.2 m in 35 years). The presence of vegetation further lowered residue pH to about pH 8.5, with the depth of neutralization dependent on depth of root penetration. Sewage and yard-waste amendments accelerated neutralization and the establishment of vegetation and further lowered the residue pH to about pH 6.7, likely due to organic acid leaching. For vegetated areas, the root density (g roots/g soil) was proportional to the extent of neutralization of residue, with root density higher in near-surface residue than in deeper residue.

Passive reactive barriers (PRBs) are commonly used to treat groundwater that is contaminated with chlorinated solvents such as trichloroethylene (TCE). A number of PRBs have been constructed with plant mulch as the reactive medium. The TCE is removed in these barriers through adsorption, biological reductive dechlorination, and abiotic reactions with reduced iron minerals that are formed in the barrier. Generally speaking, adsorption has limited capacity for TCE removal and abiotic dechlorination is dependent on metal sulfides of biogenic origin. Therefore, the long-term performance of these barriers will be controlled by their capacity to support biological activity. Laboratory batch experiments were inoculated with an enrichment culture of dechlorinating microorganisms. Dechlorination of TCE to ethylene was achieved using plant mulch; however, neither water extractable nor organic-solvent extractable components of the mulch could sustain dechlorination of TCE. This indicates that biodegradation of organic wood fibers in the plant cell wall provides electron donors for dechlorination of TCE. Kinetic analysis of the methane production in the batch tests provides supporting evidence that the plant mulch is able to sustain long-term biological activity in a typical barrier constructed with plant tissues. The recognition of the intact plant tissues as a long-term electron donor expands the knowledge about the microbial dechlorination under natural conditions. In addition, the production of dissolved inorganic carbon (DIC) observed in a column study was used to estimate the life cycle of a full-scale biowall installed at Altus AFB, Oklahoma. Based on a consistent downward trend in DIC concentrations in the effluent and a stable concentration in the influent over time, the mulch in the biowall is expected to support microbial activity for 10 years.

A soil decontaminating process has been studied at laboratory scale for the treatment of one soil polluted by both polycyclic aromatic hydrocarbons (PAHs) and lead (Pb). This process first includes attrition and sieving steps to separate the coarse $\left(>2\text{mm}\right)$ from the fine $\left(<2\text{mm}\right)$ fractions, followed by a flotation step using an amphoteric surfactant in acid and saline conditions for the treatment of the fine contaminated particles. Electrodeposition and chemical precipitation using sodium hydroxide have been compared to ensure a possible reuse of wastewaters without disturbing the efficiency of the process. The performance of the process has been estimated considering soil quality after treatment with respect to the limit regulatory levels for commercial or industrial use in Quebec (Canada). Precipitation of lead hydroxides was efficient after five cycles of wastewaters reuse, while electrodeposition did not maintain efficiency of the flotation step with regard to PAH levels in soil after treatment. The complete process including Pb precipitation ensured the removal of $89\pm 8$ and $76\pm 10\mathrm{\%}$ of total PAH, respectively, for the coarse $\left(>2\text{mm}\right)$ and fine $\left(<2\text{mm}\right)$ fractions, while Pb was removed at $88\pm 10$ and $65\pm 2\mathrm{\%}$ , respectively, for the same fractions of the soil.

Nanoparticles have emerged as promising adsorbents for water purification. In this study, nanoscale carbon black was employed to remove natural organic matter (NOM) from water in the presence and absence of coagulation. Standard Suwannee River NOM was employed as the targeted pollutant. In the absence of coagulation, more than 60% NOM removal was achieved by carbon black adsorption. A higher hydrogen ion concentration (pH) (3–5) was favorable for NOM removal. More than 35% NOM was removed by carbon black adsorption in the first 20 min, and the adsorption of NOM onto carbon black occurred within about 2 h. Proper stirring was essential for the mixture of NOM and carbon black, while insufficient stirring or overstirring decreased NOM removal efficiency. When low dosages of coagulants were used in combination with carbon black at pH 6–7, the removal efficiency of NOM increased significantly. Depending on the coagulant, the sequencing of adsorption and coagulation can be important. Almost 90% NOM was removed in 15 min by carbon black adsorption and alum coagulation, which is a higher removal than for conventional treatment. This study indicated that carbon black might be an important adsorbent for NOM removal in water treatment in combination with low doses of alum.

Due to California’s stringent hazardous waste (HW) classification regulations, high-capacity adsorptive media (AM) used for the removal of arsenic from potable water are likely to be classified as HW if operated to breakthrough. An alternative is to prematurely retire the AM, avoiding generation of HW. The impact of waste classification of spent AM on annual costs for arsenic systems was investigated. For a typical small water system (SWS), the media replacement cost alone was predicted to range from $0.80 to $2.00 per 1,000 L treated, in comparison to the average cost of tap water in the U.S. of $0.53 per 1,000 L treated, highlighting the financial burden for SWS. The costs of media replacement dominated over costs for transport and disposal regardless of whether spent media were designated as HW or non-HW. Media costs and influent arsenic concentration were more significant factors than transport distance or disposal fees. Under typical conditions for SWS, it was found to be cost effective to load the media to exhaustion as long as the arsenic loading at replacement was greater than 560-mg arsenic/kg AM, a situation readily obtained with commercially available high-capacity iron oxide adsorbents.

Selenate removal by adsorption using iron-coated granular activated carbons (Fe-GACs) is reported in this study. Adsorption kinetics and equilibrium experiments with initial selenium concentration of 1 mg/L were conducted under three different ionic strengths to study selenate adsorption behavior. Selenate adsorption reached equilibrium within 48 h with more than 85% of the equilibrium capacities being obtained within the first 6 h. High removal efficiency (i.e., $>75\mathrm{\%}$ ) was achieved for pH range of 2–5. Acid-base titration experiments showed point of zero charge $\left({\text{pH}}_{\text{pzc}}\right)$ at pH 7.5 for the tested Fe-GAC. Pseudo-second-order kinetic model characterized selenate adsorption kinetics well $\left(R^2=0.999\right)$ and the rate constant decreased with ionic strength. Adsorption capacity decreased significantly with increasing ionic strength, which was not observed in selenite adsorption with the same adsorbent. Competitive adsorption with other four oxyanions ( ${\text{SiO}}_3^{2-}$ , ${\text{SO}}_4^{2-}$ , ${\text{PO}}_4^{3-}$ , and ${\text{CO}}_3^{2-}$ ) showed that selenate removal efficiency was reduced to various degrees in the presence of each individual anion. Competitive adsorption of binary adsorbates (selenite and selenate) showed a decreasing trend of selenite adsorption capacity with decreasing ionic strength, indicating stronger competition of selenate against selenite under the low ionic strengths. The Sheindorf-Rebuhn-Sheintuch multiadsorbate competitive adsorption model was applied to quantify the binary competitive adsorption between selenate and selenite.

This paper presents competitive sorption of coexisting pesticides onto treated wood charcoal and describes the effect of various water quality parameters, viz., pH, ionic strength, chloride concentration, presence of calcium and magnesium, fertilizers, humic acid, polyacrylic acid, and also the effect of coexisting pesticides on the sorption of endosulfan onto treated wood charcoal. The coexisting pesticides were found to hinder the performance of wood charcoal in removing endosulfan. Competitive uptake study revealed that endosulfan occupies more sites followed by atrazine and monocrotophos. Solubility in water could be one of the major reasons for this preferential order. The presence of humic acid was found to show much more significant influence on the performance of wood charcoal than the presence of polyacrylic acid. Among fertilizers, single superphosphate was found more influential. Most of it, among the other reasons, could be due to the competition of the coexisting molecules for the available adsorption sites on wood charcoal. Other parameters have resulted in some fluctuations in performance, but the effects are not significant. Endosulfan removal efficiency faltered at higher pH values, and ionic species did not affect the sorption as endosulfan is nonionic under neutral conditions.

This research evaluated nitrogen-removing bioretention systems for control of nutrients, organics, and solids in agricultural runoff. Pilot-scale experiments were conducted with bioretention systems incorporating aerobic nitrification and anoxic denitrification zones with sulfur or wood chips as denitrification substrates. Varying hydraulic loading rates (HLRs), influent concentrations, and wetting and drying periods were applied to the units during laboratory and two seasons of field tests with dairy farm runoff. Total N removal efficiencies greater than 88% were observed in both units with synthetic storm water. In first-season field tests, moderate removal efficiencies were observed for chemical oxygen demand (46%), suspended solids (69%), total phosphorous (TP) (66%), and total N (65%). During the second season, operational changes in the farm resulted in lower organic, solids, and nutrient loadings resulting in improved effluent quality, especially for suspended solids (81% removal) and total N (82% removal). The systems were not hydraulically overloaded even at 20 times the normal HLR.

The possibility of using the sorption technology to reduce the levels of metal ions present in urban storm-water runoff was investigated in this study. Seven sorbent materials including Amberlite XAD7, chitosan, crab shell, peat, Sargassum, sawdust, and sugarcane bagasse were initially examined for removal of 11 metal ions (Na, K, Ca, Mg, Mn, Co, Ni, Cu, Zn, Cd, and Pb) from simulated storm-water runoff at different concentrations. Among these sorbents, crab shell performed well with removal efficiencies exceeding 93% for all heavy metal ions examined and thus selected for further studies. Based on scanning electron microscopy/energy-dispersive x-ray analysis, microprecipitation of metal carbonates followed by adsorption onto the surface of crab shell was identified as the major mechanism responsible for removal of heavy metal ions by crab shell. Crab shell exhibited rapid removal of meal ions with attainment of biosorption equilibrium within 20 min. A crab-shell-packed column was used to study the continuous metal retention process. The column performed very well in the removal of heavy metal ions and was able to operate up to 192 h at a flow rate of 10 mL/min before outlet concentrations of Mn and Co reached 0.3 times of their respective inlet concentrations. Other metal ions such as Pb, Zn, Ni, Cd, and Cu were only in trace levels in the final effluent until 192 h. These findings would form the basis for the future development of crab-shell-based biofilters for removal of dissolved heavy metal ions from storm-water runoff.

As(III) oxidation by a chemoautotrophic bacterium, Thiomonas arsenivorans strain b6, was evaluated in a continuous stirred tank reactor (CSTR) under a range of influent As(III) concentrations (2,000–4,000 mg/L) and hydraulic retention times (HRTs) (21.7–74.9 h). Five steady states were obtained after the CSTR was continuously operated for 115 days with over 99% As(III) oxidized under the optimal growth conditions for strain b6 at pH 6 and $30°\text{C}$ . The culture exhibited strong resilience by recovering from an As(III) overloading of $4,847.4\pm 290.9\text{mg}/\text{day}/\text{L}$ operated at a HRT of 21.7 h. Arsenic mass balance analysis revealed that As(III) was mainly oxidized to As(V), with unaccounted arsenic well within the analytical error of measurement. The best estimates of biokinetic parameters for As(III) oxidation were obtained using the steady-state data and the Monod expression based model [ $k=5\text{mg}$ As(III)/mg dry cell weight/h; $K_s=20.1\text{mg}/\text{L}$ ; $k_d=0.008{\text{h}}^{-1}$ ; and $Y=0.011\text{mg}$ cell dry weight/mg As(III)]. The Monod model and the reactor mass balance successfully simulated both the steady-state and transient phases of CSTR operation. Sensitivity analyses defined $Y$ and $k$ to be the most sensitive to model predictions, whereas $k_d$ and $K_s$ were least sensitive to model simulations of As(III) oxidation under steady-state conditions.

This work advances the mathematical modeling of ion exchange treatment in completely mixed flow reactors in which there is recycle and regeneration of the ion exchange resin. The most common application of this process is magnetic ion exchange resin to remove dissolved organic carbon from raw drinking water. The motivation for this work was the complex distribution of resin particle ages and sizes that result from the recycle and regeneration processes. The newly developed model uses a single “age-averaged” diffusion equation to represent resin particle age as compared with the previous Monte Carlo model that uses a large number of diffusion equations to represent various resin particle ages. Advantages of the age-averaged model over the Monte Carlo model include a closed-form analytical solution for the steady-state case of the model, advanced numerical techniques used for the nonsteady-state case of the model, and model simulations require much less computational time and yield more accurate results. The age-averaged model is a robust numerical tool that can be used to evaluate a range of treatment scenarios as a result of these advancements.

The static granular bed reactor (SGBR) is a unique high-rate anaerobic reactor designed to operate in a simple downflow manner, offering high chemical oxygen demand (COD) removal efficiencies (greater than 90%) resulting from high biomass retention in the system. A study was performed to evaluate the SGBR versus a control system, the upflow anaerobic sludge blanket (UASB) reactor, and to evaluate performance idiosyncrasies of the SGBR and the control. The two reactors were operated at three different hydraulic retention times (HRTs): 8, 16, and 24 h. The reactors treated synthetic wastewater, intended to simulate food industry waste, composed of sucrose and nonfat dry milk. Overall, COD removal was higher for the SGBR than for the UASB reactor. In particular, at a HRT of 8 h, the SGBR achieved a COD removal of 90.7% and the UASB reactor reduced the COD concentration by 77.5%. The UASB reactor’s specific COD loading factor proved rate limiting with values ranging from 0.19 to $0.94\text{gCOD}/\left(\text{gVS}\cdot \text{d}\right)$ versus 0.11 to $0.34\text{gCOD}/\left(\text{gVS}\cdot \text{d}\right)$ for the SGBR. A tracer study idealized hydraulics within the two systems, and the results showed minimal dead volume and 4–6% short circuiting for both reactors.

The effect of reagent pH and ionic strength was evaluated on the horseradish peroxidase (HRP)-luminol- $p$ -iodophenol enhanced chemiluminescence assay. This assay was optimized for HRP and ${\text{H}}_2{\text{O}}_2$ quantification during enzyme-mediated remediation of groundwater or wastewater contaminated with phenolic chemicals. The maximum chemiluminescence intensity $\left(I_{\text{CLmax}}\right)$ and total area under the chemiluminescence intensity profiles were measured as a function of $p$ -iodophenol concentration, reagent solution pH, and reagent ionic strength. $I_{\text{CLmax}}$ values were optimum at pH 8.5 and increased linearly with reagent ionic strength. Optimum chemiluminescence enhancement was produced at a $p$ -iodophenol concentration of 0.3 mM under the reaction conditions. $I_{\text{CLmax}}$ values were linearly correlated with HRP and ${\text{H}}_2{\text{O}}_2$ concentrations within the ranges of 0.1–1 activity units/mL and 0.1–1 mM, respectively. Results indicate that the HRP-luminol- $p$ -iodohenol enhanced chemiluminescence assay has a potential to be used for quantification of HRP activity and ${\text{H}}_2{\text{O}}_2$ concentration in aqueous solutions encountered in groundwater remediation or wastewater treatment scenarios.

A model is presented to quantify microbial occlusion in effluent particles and improve understanding of the removal and inactivation of occluded microorganisms in filtration and disinfection systems. Microbial occlusion in particles is described in the model as a function of the particle size distribution, the microbial density $\left(N_1\right)$ , which is the average quantity of target microorganisms within the subset of particles that contain microorganisms, and the frequency of association $\left(N_2\right)$ , which is the ratio of particles that contain at least one target microorganism. To demonstrate the model, undisinfected secondary effluent samples were collected from an extended aeration treatment facility and analyzed to determine values for the model variables, $N_1$ and $N_2$ for heterotrophic bacteria and aerobic endospores and $N_2$ for total coliform bacteria. Heterotrophic bacteria were present in most effluent particles (73–100%) at high densities (7–93 per particle), whereas aerobic endospores and total coliform bacteria were only present in a small percentage of effluent particles (0.1–6%) and the density of aerobic endospores in effluent particles was not appreciably higher than one per particle.

Membrane cleaning is critical to the operation of membrane processes. This paper studies the impact of using four different types of bench-scale membrane systems to assess the effectiveness of different cleaning steps after the filtration of colored river water. The systems are a stirred ultrafiltration (UF) cell, a SEPA cell, a small cross-flow (CF) cell, and a six-CF-cell-in-parallel system. The effect of cleaning frequency was also investigated. The comparison was implemented in terms of flux recovery, solute removal, solute resistance removal, and changes of contact angles. The stirred UF cell was only reliable and comparable in terms of flux and flux recovery results. The six-cell-in-parallel system requires further development due to their much lower flux. For cleaning at 30-min intervals, the cleaning efficiency of membranes was similar for the three CF systems. For cleaning intervals of 2 and 4 h did not statistically affect the flux recovery for the stirred UF cell and SEPA cell. There was some irreversible fouling that could not be restored completely by clean-in-place method even with rigorous chemical treatment.

Reactor experiments were conducted to study aerobic sulfide oxidation in pulp and paper wastewaters under typical operating conditions. Data produced from these experiments were used to develop a set of sequential rate equations that describe the significant sulfide and oxygen processes in the reactors. Model parameters were estimated for three different pulp and paper wastewaters using a multiresponse procedure. The sulfide oxidation rate coefficients for the wastewaters ranged from 0.108 to $0.155{\text{min}}^{-1}$ at $35°\text{C}$ and approximately neutral pH. The reaction order with respect to oxygen could not be precisely estimated but appeared to be near the lower boundary for the fitting procedure (essentially zero order). Modeling of the oxygen depletion data provided evidence that the first sulfide oxidation reaction product consumed 0.5 mg of oxygen per mg of sulfide oxidized, suggesting polysulfides and elemental sulfur as the initial reaction products. The oxygen depletion modeling also suggested oxidation of the initial reaction product to a more stable intermediate which is postulated to be thiosulfate.

The addition of ferrous salts is a commonly used strategy for sulfide control in sewer networks. The ${\text{Fe}}^{2+}$ dosing requirement in rising main sewers which takes into account of the effect of anaerobic sewer biofilms on the dosing demand is investigated. A laboratory-scale rising main sewer, consisting of four biofilm reactors in series and fed with real sewage, was operated for over 12 months, during which ${\text{FeCl}}_2$ was dosed at several locations and at various dosing rates. The experimental results consistently revealed that approximately 0.7 mol of ${\text{Fe}}^{2+}$ was required to precipitate sulfide formed from the reduction of 1 mol of sulfate by anaerobic sewer biofilms. This ratio is significantly lower than the ratio expected from reaction stoichiometry (molar ratio of 1:1), and also the ${\text{Fe}}^{2+}$ to sulfide ratio (1.07–1.10 mol:1 mol) observed in batch tests conducted with real wastewater in the absence of sewer biofilms. Biofilms adapted to ${\text{Fe}}^{2+}$ addition were found to contain a substantially higher amount of elemental sulfur than biofilms not receiving ${\text{Fe}}^{2+}$ dosage. This suggests ${\text{Fe}}^{2+}$ addition might have altered the final product of sulfate reduction by anaerobic sewer biofilms. The study also showed that the addition of ferrous salts at the inlet of a rising main sewer can effectively control sulfide throughout the whole system despite of the presence of competing anions in wastewater. Phosphate precipitation with ferrous iron in anaerobic rising main sewers is negligible.