Journal of Environmental Engineering

Bioretention is a novel stormwater best-management practice that uses a mixture of soil/sand/mulch as adsorptive filtration media that can capture both urban particulates and dissolved pollutants while promoting infiltration. This study conducted a series of laboratory column experiments and field observations, which showed that: (1) bioretention media stratification occurs with runoff percolation due to particulate deposition; (2) bioretention filter media are clogging limited, instead of breakthrough limited; and (3) both depth filtration and cake filtration significantly contribute to urban particle capture. Because of the fine size of bioretention media, incoming suspended solids cannot significantly penetrate below $5–10\mathrm{cm}$ of the media in the column tests and approximately $20\mathrm{cm}$ in the monitored field facility. Bioretention filters under intermittent flow conditions exhibited higher solids loading capacity (in $\mathrm{kg}∕{\mathrm{m}}^2$ ) before clogging than under continuous flow conditions. The clay components in incoming total suspended solids assume critical responsibility for bioretention media clogging. The media resistance due to solids deposition was estimated through Darcy’s law. The hydraulic conductivity of two media types decreased from $54\pm 23$ and $72\pm 46\mathrm{cm}∕\mathrm{h}$ to less than $10\mathrm{cm}∕\mathrm{h}$ due to particle capture. Experimental results suggest that a $20\text{-}\mathrm{cm}$ media depth is sufficient for bioretention design and maintenance procedures (media replacement) for runoff particle capture.

As a novel stormwater best-management practice, using a soil/sand/mulch mixture to capture urban pollutants while promoting infiltration, the unique media composition renders bioretention significantly different from conventional sand filters. In this work, a three-layer model is presented to describe particulate capture in bioretention media employing parameter calibration and presensitivity analysis. Since the fine size of bioretention media strictly limits the particulate penetration distance, the media column is modeled as a pristine zone (bottom), a working zone (middle), and a cake zone (top). Mechanisms of both depth filtration and cake filtration are examined through mass balances, which show that both are significant. The developed resistance of each layer due to solid deposition was also estimated. Experimental data for different media/TSS-type combinations of selected experimental trials were used in parameter calibration. The calibrated model successfully predicted the effluent TSS and media hydraulic conductivity of subsequent trials with appropriate boundary and initial conditions as input. A weighted combination of calibrated parameters from different TSS types also agreed well with media behavior for treating a complex TSS mixture. The results of media replacement (top removal and refill) simulation also reasonably fit experimental data. Using proper assumptions, a long-term scenario analysis for permeability reduction was performed for a field bioretention facility. Based on modeling results, this study recommends a shallow bioretention media depth design, an annual or biannual field inspection schedule, and periodic media replacement maintenance.

About a billion cubic meters of wastewater effluent are artificially recharged annually in the United States for maintenance of groundwater levels and prevention of seawater intrusion. There is concern that trace contaminants, including various endocrine disrupting compounds (EDCs), are not completely removed during infiltration, leading to deterioration of groundwater quality. In this work, we investigate the mechanisms and efficiency of EDC removal at the Sweetwater Recharge Facility, which is used to recharge secondary effluent from the Roger Road Wastewater Treatment Plant in Tucson, Ariz. Material was collected from the top meter of sediments in two infiltration basins and analyzed for extractable nonylphenol (NP), polybrominated diphenyl ethers (PBDE) and total estrogenic activity. The basins differed significantly in length of service (7 versus 15 years). Nevertheless, profiles of extractable contaminants and estrogenic activity were similar in the two basins. Results suggest that hydrophobic determinants of estrogenic activity are efficiently retained in surface sediments during soil-aquifer treatment. However, measurable levels of PBDEs, NP, and estrogenic activity are present in infiltrate that reaches the local unconfined aquifer at $\sim 40\mathrm{m}$ below land surface.

This work simulated the flow pattern of the sludge blanket clarifier at the Bansin Water Treatment Plant, Taiwan by multiphase flow, three-dimensional analysis. The following three models were developed individually: One-phase flow (water) in the clarifier—this model acquires the basic water-flow pattern; a homogeneous porous medium at the bottom of the clarifier—this porous medium represents the sludge blanket; and, the Eulerian granular multiphase model, which was utilized to obtain solid effluent flux and to determine the effects of particle size and density on sludge blanket stability. Analytical results indicated that the clarifier has two principal circulations inside and outside the reaction well. A plentiful, dense and thick sludge blanket should exist at the clarifier bottom; otherwise particles could flow out through the gap between bottom of the reaction well and top of blanket surface, resulting in poor water quality. In the multiphase flow model, large particles and a high particle density are positively correlated with sludge blanket stability.

Over the past several decades, reductions in phytoplankton stocks and increased water clarity in Lake Erie have resulted from phosphorus load abatement and the introduction of zebra (Dreissena polymorpha) and quagga mussels (D. bugensis). The relative impacts of these developments and their implications for lake management have remained difficult to delineate. To address this issue, we numerically model the complex biophysical interactions occurring in Lake Erie using a two-dimensional hydrodynamic and water quality model that is extended to include dreissenid mussel and zooplankton algorithms. The model reasonably simulates longitudinal trends in water quality as well as the dynamics of central basin hypoxia. Phosphorus is the limiting nutrient through the euphotic zone and its control decreases the algal growth rate and biomass $(\sim 55–60\%)$ . Filter feeding by dreissenid mussels also decreases algal biomass $(\sim 25–30\%)$ , simultaneously stimulating increased net algae growth through enhanced algal consumption and subsequent phosphorus recycling. Effective recycling implies that algae stocks are ultimately regulated by external phosphorus loads. Returning phosphorus loads to pre-abatement 1960s levels, in the presence of dreissenid mussels, results in a western basin algae concentration of $\sim 0.7\mathrm{mg}\text{dry}\text{weight}{\mathrm{L}}^{-1}$ with a potential for nuisance algae growth.

A modified activated sludge process, called the oxic-settling-anaerobic (OSA) process, achieved effective reduction in excess sludge production. Its key feature is the insertion of a sludge holding tank in the sludge return circuit to provide an anaerobic sludge zone. Our previous studies suggested that such excess sludge reduction might be associated with an increased sludge decay rate and the effective consumption of organic substrates generated during the retention of the thickened sludge in the sludge holding tank under a low oxidation-reduction potential (ORP) at $-250\mathrm{mV}$ . To confirm this suggestion, we analyzed the chemical oxygen demand (COD) balance in the sludge holding tank through batch experiments to simulate the sludge concentration, ORP level, and retention time in the sludge holding tank. The COD generated from the sludge reduction in the tank was utilized by organic gas (mainly ${\mathrm{CH}}_4$ ) production, denitrification, sulfate reduction, and phosphorus release, among which the gas production accounted for 50% of the COD utilization. We confirmed that the mechanism of the excess sludge reduction in the OSA process is through enhancement of the sludge decay rate in the anaerobic sludge zone, which increases the soluble COD level, which in turn is mainly transformed into methane gas and carbon dioxide during denitrification.

The effect of chlorine dioxide $\left({\mathrm{ClO}}_2\right)$ pretreatment on subsequent treatment processes (coagulation, flocculation, sedimentation, filtration, and ozonation) was studied at pilot-scale at the Upper San Leandro Water Treatment Plant near Oakland, Calif. Potential impacts of ${\mathrm{ClO}}_2$ on the distribution system were also studied at bench scale using simulated distribution system (SDS) tests. Pilot trials were conducted with one train operating without ${\mathrm{ClO}}_2$ pretreatment (Train 1) and the other with a ${\mathrm{ClO}}_2$ dose of between 0.6 and $1.0\mathrm{mg}∕\mathrm{L}$ (Train 2). Comparison between Trains 1 and 2 showed that ${\mathrm{ClO}}_2$ pretreatment resulted in a 0.1–0.2 NTU decrease in settled water turbidity when compared to no pretreatment. ${\mathrm{ClO}}_2$ pretreatment also resulted in a small $\left(0.01{\mathrm{cm}}^{-1}\right)$ decrease in ultraviolet absorbance at $254\mathrm{nm}$ . Following sedimentation, about 60% of the applied ${\mathrm{ClO}}_2$ formed chlorite $\left({\mathrm{ClO}}_2^{-}\right)$ , with 10–20% forming chlorate $\left({\mathrm{ClO}}_3^{-}\right)$ . Ozonation immediately converted all residual ${\mathrm{ClO}}_2$ and ${\mathrm{ClO}}_2^{-}$ to ${\mathrm{ClO}}_3^{-}$ . There was no significant difference in the performance of the filters between the two trains in terms of headloss, particle count, and turbidity. Bench-scale SDS tests indicated that chlorine dioxide preoxidation did not affect subsequent chloramine stability or concentrations of trihalomethanes, haloacetic acids, or adsorbable organic halides in the distribution system.

Enteroviruses have recently emerged as a concern to health authorities because they are a waterborne nonbacterial cause of gastroenteritis. Forty-six samples of brackish water from two sites upon the Damshui River, Taiwan, were analyzed for the occurrence and serogroups of enteroviruses. The seminested reverse transcriptase polymerase chain reaction was used for detecting enteroviruses. Six of the 23 water samples from one site and eight from the other site tested positive for enteroviruses. Detection results were identified by the nucleic acid sequencing method. Five serogroups of enteroviruses were identified as coxsackievirus A2, coxsackievirus A6, echovirus 11, enterovirus 71, and porcine enterovirus 9. The occurrence of enteroviruses within the water samples shows significant correlations with the occurrence of enterococci and low water temperatures.

In this study, stabilization/solidification (S/S) of refinery oily sludge was applied using two types of cement (I and II), in cement-to-waste ratio from 0.1 to 0.7. The leaching behavior of heavy metals was investigated, by means of a five-point sequential toxicity characteristic leaching procedure (TCLP) test. Sequential TCLP was used to provide an improved assessment of long-term contaminant potential leachability, because the acidic leachant is renewed, whereas in the single TCLP, contaminant leachability is limited by the pH neutralization of the alkaline binder. Cement-based S/S of real refinery oily sludge resulted in very low leachability of heavy metals. Pb and Cd were not detected in any TCLP leachate. The maximum leachability of Fe, Zn, and Ni occurred in the pH range between 5.5 and 6.5. The leachability of Cu and Cr increased with increasing pH. Maximum cumulative percentage of Fe, Ni, and Zn leaching after five consecutive TCLP extractions (for worst case conditions, i.e., 10% II42.5) were 0.01, 22, and 1.2%, respectively, on the basis of metal content of each solidified sample. Further, the leaching behavior of Zn and Ni was modeled using the chemical equilibrium program Visual MINTEQ. Using several combinations of suspected solid phases of Zn and Ni hydroxides, carbonates and sulfides, and surface complexation onto ferrihydrite the diffuse double layer model did not accurately describe the leaching behavior of Zn and Ni.