Journal of Environmental Engineering

In water distribution systems, valves play a crucial role in system reliability and security by providing a shutoff function when it is necessary to isolate subsystems. In this paper failure of shutoff valves to close is considered. The failure impact is quantified in terms of the expanding subnetwork and the increased number of customers out of service. To evaluate a system-wide valve failure impact, three methods are suggested: segment–valve matrix, decision tree analysis, and simulation. The segment–valve matrix shows the propagation of failure through the network as valves fail to close. The decision tree enumerates all possible valve failure combinations and corresponding event probabilities. Because the complete enumeration can be unwieldy, simulation procedures are offered that approximate the enumeration results closely. The details of the methods are illustrated with the aid of an example.

Characterization of the particle population for a location in a water supply reservoir, Kensico Reservoir, N.Y., is documented for a high turbidity event, from its onset, through alum treatment and its waning. Supporting in situ measurements included the beam attenuation coefficient at $670\mathrm{nm}$ $\left(c_{670}\right)$ and $660\mathrm{nm}$ $\left(c_{660}\right)$ [surrogates of turbidity $\left(T_n\right)$ ], particle concentrations $\left(N\right)$ and size distributions (PSDs), and size class specific settling velocities (SVs). Laboratory measurements included chemical and morphometric analyses of individual particles, and routine measurements of $T_n$ . The turbidity is shown to be primarily derived from clay minerals, mostly in the size range of $1.5–6\mu \mathrm{m}$ . An initial high $c_{670}$ level $(40{\mathrm{m}}^{-1};T_n\sim 100\mathrm{NTU})$ decreased sevenfold in less than $1\text{week}$ in response to alum treatment that largely eliminated the particle size classes responsible for the elevated turbidity. Successful SV experiments, made using a laser in situ scattering and transmissometry (LISST) instrument, for seven particle size classes in the range of $1.25–129\mu \mathrm{m}$ yielded SV values of $0.17–69.4\mathrm{m}{\text{day}}^{-1}$ . Size classes larger than $\sim 5\mu \mathrm{m}$ settled much slower than Stokes law predictions, before alum treatment, indicating that these classes existed as porous flocs or aggregates. Decreases in SVs following treatment suggest changes in floc character consistent with increased porosity. In situ measurements of $c_{670}$ , $N$ , PSDs, and SVs can contribute to the development and testing of a multiple particle size class model to simulate fate, transport, and impacts of suspended particles.

The present work proposes that the incorporation of granular activated carbon (GAC) treatment model that accounts for nonequilibrium adsorption into the optimal design of pump-and-treat systems will result in more realistic costs and better-engineered remediation systems. It was found that, when nonequilibrium GAC adsorption effects are considered, the predicted cost of optimal remediation strategies increases consistently when compared to costs obtained assuming equilibrium GAC adsorption, for a wide range of cleanup goals. This finding implies that when simpler equilibrium models are used for GAC adsorption, cleanup costs will be underestimated. GAC treatment costs are shown to be particularly sensitive to the degree of mass transfer limitations in the aquifer–contaminant system, especially when nonequilibrium GAC adsorption is accounted for. Time-varying pumping rates are shown to produce more efficient remediation solutions; the increase in efficiency is even more pronounced when nonequilibrium GAC adsorption is accounted for. Further results show that the optimal remediation designs can be significantly more efficient when the number of GAC adsorber units is selected through optimization.

The potential for degradation of two important endocrine disrupting chemicals, 17 $\beta$ -estradiol (E2) and estrone (E1) in a wastewater effluent recharged aquifer system was assessed using lab scale microcosms. Biotransformation by microorganisms present in the aquifer material was found to be the major mode of removal for both organic contaminants in the microcosms. The addition of ultrafiltered secondary effluent, simulating recharge of aquifer, did not significantly alter the behavior of both E2 and E1 in the aquifer microcosms. A significant difference in E2 removal rates in microcosms that received E2 as a concentrated stock in methanol as opposed to direct dissolution of E2 into groundwater shows that the presence of methanol could alter the biodegradation kinetics of the organic pollutant of interest. The rapid utilization of methanol by indigenous methanol degraders, which was present as an alternative carbon substrate, caused rapid depletion of oxygen and, hence, development of anoxic conditions in the microcosms. Increased oxygen supply led to corresponding improved E2 biotransformation rates, indicating that E2 degradation under anoxic conditions was much slower than under aerobic conditions. On the other hand, in the presence of a high initial concentration of methanol, E1 was more persistent in the medium under aerobic conditions than under anoxic conditions. Apparently, the initial high concentration of methanol had an inhibitory effect on aerobic E1 degraders in the microcosms.

The fuel additive methyl tert-butyl ether (MTBE) is sometimes considered to be a recalcitrant compound in groundwater. Due to MTBE’s relatively poor adsorption and low volatility, interest is growing in new remediation methods which provide an alternative to using activated carbon or stripping techniques. This study addresses the abiotic degradation (hydrolysis) of MTBE to the intermediate tert-butanol (TBA). Two selected materials with acidic properties were shown to hydrolyze MTBE in batch tests at moderate pH values. The sorption of MTBE and TBA was estimated with Freundlich isotherms. Isotherms and TBA formation were used to calculate MTBE degradation. In another experiment, TBA was degraded aerobically by microorganisms. Since TBA seems to be more easily available as a carbon source to microorganisms than MTBE, the catalytic transformation of MTBE to TBA and methanol could enhance the natural attenuation of MTBE.

Quaternized poly(4-vinylpyridine) coated activated carbon has been proven to be successful in removal and recovery of $\mathrm{Cr}\left(\mathrm{VI}\right)$ from aqueous solution. However, the key component of the mass transfer operations and the diffusion coefficient has not been determined. In this study, adsorption of $\mathrm{Cr}\left(\mathrm{VI}\right)$ was investigated at different initial concentrations. A finite bath diffusion control model with changing bulk concentrations was derived analytically, and a constant related to radius of the absorbent particle and the fractional attainment of adsorption was first introduced into this model. Results indicated that the adsorbent provided fast adsorption kinetics and the modified diffusion-control model fitted the experimental data well. The observed sorption kinetics was consistent with the finite bath diffusion, with an average value of $4.10\times {10}^{-6}{\mathrm{cm}}^2∕\mathrm{s}$ for the product of the distribution coefficient and the effective diffusivity in the adsorption of $\mathrm{Cr}\left(\mathrm{VI}\right)$ on the quaternized poly(4-vinylpyridine) coated activated carbon.

Most commonly used river water quality models for biochemical oxygen demand (BOD) and dissolved oxygen (DO) simulations are mainly based on advection, decay, settling, and loading functions. Using these concepts, refined river water quality models for BOD and DO simulations are developed in the present work considering a large number of physically based parameters and input variables. The refined models developed can be transformed to some of the commonly used river water quality models, if physically based parameters and input variables are omitted or removed. To test the applicability of the refined models developed and commonly used models, a total of 732 water quality and flow data sets are collected during March 1999–February 2000 from 22 sampling stations of the River Kali in India. River Kali is a highly polluted river in India and receives continuous inflow of untreated point source pollution from municipal and industrial wastes and nonpoint source pollution from agricultural areas. Newton–Raphson technique is used to optimize the model parameters during calibration and the performance of different models are evaluated using error estimation, viz. standard error and mean multiplicative error, and correlation statistics $\left({\mathrm{r}}^2\right)$ . The results indicate that the BOD–DO models proposed by Camp in 1963 provide better results in comparison to other commonly used models. Moreover, the refined models developed for BOD and DO simulations minimize error estimates and improve correlation between observed and computed BOD and DO values of River Kali.

Rapid hydrogen peroxide $\left({\mathrm{H}}_2{\mathrm{O}}_2\right)$ decomposition is a significant limitation of catalyzed ${\mathrm{H}}_2{\mathrm{O}}_2$ propagations (i.e., modified Fenton’s reagent) for the remediation of contaminated soil and groundwater by in situ chemical oxidation. Rates of ${\mathrm{H}}_2{\mathrm{O}}_2$ decomposition mediated by seven trace minerals and four iron and manganese oxides were evaluated in batch reactors containing slurries of ${\mathrm{H}}_2{\mathrm{O}}_2$ and each of 11 minerals. At pH 3, the dominant catalysts in the decomposition of ${\mathrm{H}}_2{\mathrm{O}}_2$ on a per surface area basis were the manganese and iron oxides pyrolusite, goethite, and hematite, while decomposition rates in the presence of the manganese oxyhydroxide manganite and the trace mineral siderite were one to two orders of magnitude lower. At pH 7, the dominant catalysts were hematite and pyrolusite, and decomposition rates were one to two orders of magnitude lower in the presence of goethite, manganite, and siderite. The trace minerals anatase, bauxite, cuprite, ilmenite, magnesite, and willemite provided the least activity for decomposing ${\mathrm{H}}_2{\mathrm{O}}_2$ at both pH regimes. The results of this study document that the trace minerals anatase, bauxite, cuprite, ilmenite, magnesite, siderite, and willemite do not provide a significant pathway for ${\mathrm{H}}_2{\mathrm{O}}_2$ decomposition in the subsurface, and efforts to stabilize ${\mathrm{H}}_2{\mathrm{O}}_2$ for ISCO should focus on reactions occurring on the surfaces of iron and manganese oxides.