Journal of Environmental Engineering

For most piping systems the maximum and minimum operating pressures occur during transient operations. Therefore it is essential to good design and operation to perform a transient analysis for normal startup and shutdown and for unplanned events such as a pump trip associated with a power outage. This author also claims that waterhammer (transient) analysis is easy. Hydraulic engineers who have studied the traditional approach to transient analysis might dispute this claim but, in fact, carrying out an analysis using the concept of pressure wave action provides an accurate, intuitive, and simple method for transient pipe system analysis of simple or complex pipe systems. Not only is this approach simple, it is extremely efficient producing accurate solutions with far fewer calculations making this approach suitable for analyzing large pipe distribution systems.

Conditioning of either wastewater biosolids or water treatment residuals conventionally utilizes a single polymer to improve subsequent dewatering. The sequential addition of two polymers has been reported to enhance biosolids dewaterability, but comparable benefits have not been demonstrated for water treatment residuals. This paper evaluated the use of cationic and nonionic polymers, singly and in combination (dual), to investigate whether dual polymer conditioning of residuals offers any advantages, and to determine whether the results could be accommodated by current mechanistic understandings. For this purpose, lab-scale tests used capillary suction time (CST), supernatant viscosity, zeta potential, streaming current, turbidity, floc size, and rheometric analyses. Comparisons of CST and viscosity results for single and dual polymer additions indicated that dual polymer use gave moderately improved dewaterability, possibly due to the increased mixing utilized for dual polymer addition. Using a cationic polymer produced a less turbid supernatant. Zeta potential and streaming current were not good indicators of conditioning efficacy when a nonionic polymer was used. Rheometric analyses were only meaningful in one selected method for treatment of the data: the area under the rheogram up to a shear rate of $30\text{inverse}\mathrm{s}$ . Overall, implementation of dual polymer use does not appear warranted.

Researchers Örmeci and Abu-Orf used rheology; a fundamental character of sludge, to arrive at a standard protocol for measuring network strength in terms of energy required to break up the structure of a certain volume of sludge. A mathematical derivation showed that the area under the rheograms indicated energy dissipation within the sludge system, which was related to the network strength. The research described in this paper investigates the use of this protocol for measuring sludge network strength at different polymer doses and relates the results to filtration, thickening, and dewatering. Laboratory tests used anaerobically digested sludge and both capillary suction time and filtration tests to indicate dewaterability and filtration. Network strength measurements used a torque rheometer. At full scale, dose response testing was used to correlate the measured network strength of the conditioned sludge to both centrifugation and gravity belt thickening performance as indicated by solids output. Both laboratory and full-scale testing showed that the network strength could be used to identify the optimum polymer conditioning to achieve good water removal from the sludge. The network strength increased with increasing the polymer dose, however, within the optimum dose range, a “drop” in the network strength occurred. This paper also discusses how to use the sludge network strength information to achieve the desired dryness from a dewatering device, and ultimately automate conditioning and dewatering processes.

Aeration experiments, based on dimensional analysis, were conducted in brick masonry tanks of dimensions $2.9\times 2.9\times 1.6{\mathrm{m}}^3$ and $5.9\times 2.9\times 1.6{\mathrm{m}}^3$ to study the design characteristics of a single hub paddle wheel aerator. A generalized equation has been developed to estimate the optimum volume of water to be aerated at a given paddle wheel diameter $\left(d\right)$ and speed $\left(N\right)$ . A simulation equation with $E$ [nondimensional number characterizing standard aeration efficiency (SAE)] and $P^{*}$ (nondimensional number characterizing power input per unit volume) provided a correlation better than that with $E$ and $\mathsf{F}$ (Froude number) and $E$ and $\mathsf{R}$ (Reynolds number) only. A simplified generalized equation correlating $E$ and $P^{*}$ was developed which can be used to predict aeration efficiency for $P^{*}⩽6.56$ . Similarly, a simulation equation with $N_e$ [(power number)(nondimensional number charcterizing power consumption)] and $P^{*}$ provided a correlation better than that with $N_e$ and $\mathsf{F}$ and $N_e$ and $\mathsf{R}$ only. The optimum dynamic condition at which maximum SAE is produced has also been presented. All the above results are valid subject to $1.47⩽P^{*}⩽15.54$ .

Modification of rainfall-runoff processes by urban infrastructure and anthropogenic activities impacts receiving waters and the surrounding terrestrial environment. Infiltration–exfiltration systems such as a partial exfiltration reactor (PER) when loaded by transient sheet flow have the potential to attenuate the impact of both the quantity and quality of urban runoff. These in situ systems are subject to highly variable water quality and quantity while functioning under variably saturated flow conditions. To improve the understanding of field-scale PER performance as a rainfall-runoff unit operation and process, a two-dimensional (2D) numerical model was used to simulate the effluent hydrograph and water content profiles under transient hydraulic loadings. Richard’s equation was applied in the 2D model using parameters estimated from laboratory experiments and hydrographs measured for an in situ PER. The temporal dynamics of the water content illustrated the ability of the PER to lower peak flow, redistribute volume, and attenuate temporal aspects of the inflow hydrograph. Results demonstrated the role of the PER to attenuate runoff water quantity, while also providing water quality improvements, as illustrated for suspended solids and dissolved Cu. Simulation of historical events for different surrounding soils illustrated the critical role of surrounding soil conditions on PER performance. While the PER demonstrated water quantity attenuation benefits for design storms (1, 2, $5\text{year}$ return periods), results also illustrate how a given PER design for clayey soils conditions can be limiting for intense events. Evaporation was a dominant mechanism for the drying process in the PER upper layer; with a residual moisture content in the porous pavement layer achieved in less than $2\text{days}$ in summer for Cincinnati, Ohio.

A manganese oxide-coated polymeric media (MOPM) utilized in sorptive filtration systems as a rainfall-runoff or snowmelt unit operation and process media was characterized using scanning electronic microscopy and adsorption kinetics were studied using a flow-through batch reactor. Results indicated the MOPM adsorption kinetics can be described as a fast adsorption reaction occurring within $30\min$ followed by a slower reaction that continued from $5\text{to}15\mathrm{h}$ , as a function of initial pH and sorbent dosages. A potential driving kinetic model was developed based on an elementary second-order rate law. Modeled results were compared to experimental data using this model and a series of comparative kinetic models. Manganese oxide surface morphology and the ability of a parabolic diffusion model to predict the adsorption kinetics of MOPM suggest diffusion-controlled adsorption for divalent heavy metals on MOPM. Based on a goodness of fit test, the potential driving model best represented the experimental data. Using the potential driving model, it was found that rate constants increased with increasing solution pH, but were independent of sorbent dosages. Results indicated that metal ions with the highest adsorption affinity had the highest rate constants. Observed porosity, the excellent fit of the potential driving model, and breaks in Elovich model plots all suggest a complex adsorption mechanism. Results suggest MOPM can be an effective media for rainfall-runoff and snowmelt metal adsorption.

Rainfall runoff and snowmelt impacted by anthropogenic activities can transport significant loads of metals. Ecological concerns and recent regulatory guidance have spurred development of unit operations such as ex situ sorptive filters and engineered media infiltration systems with the intent of including sorption mechanisms for metals as compared to conventional filter media. Applications of sorptive media for rainfall or snow unit operations include infiltration systems, sorptive clarifiers, separation systems, and deformable, cartridge, or tubular filters. Column breakthrough experiments were conducted for selected sorptive filter media and compared to conventional filter media. Comparing plain sand, granular activated carbon, and cementitious media to oxide coated/admixture media, manganese oxide coated media (MOCM) had the best overall operational behavior with 10% breakthrough bed volumes $\left(V_b\right)$ , breakthrough capacity $(X∕M_b)$ , and exhaustion capacity $(X∕M_{\mathit{exh}})$ two times higher than those of iron oxide coated sand (IOCS). As the empty bed contact time (EBCT) for MOCM increased from $0.5\text{to}1.1\min$ ; the values of $V_b$ , $X∕M_b$ , and $X∕M$ increased by a factor of 2. Compared to metal breakthrough for uncoated sand or polymeric media, manganese oxide polymeric media (MOPM) as well as bench scale partial exfiltration reactor media (combining uncoated cementitious media and oxide coated media) provided significant capacities for Pb, Cu, Cd, and Zn. Removal mechanisms for MOCM include adsorption, surface complexation, ion exchange, and filtration, accounting for MOCM’s high capacity. Although uncoated cementitious media also had a significant capacity for metals through precipitation and filtration, breakthrough instability of metal precipitates and high effluent pH can limit application in monomedium applications.

Flow cytometry was applied in the study of bacteria and phytoplankton populations in five tropical reservoirs. Water quality between different reservoirs was compared and correlation analyses were carried out to investigate how the biomass of bacteria and phytoplankton related to other water quality parameters measured (i.e., temperature, dissolved oxygen, pH, conductivity, water transparency, turbidity, chlorophyll $a$ , and total nitrogen and phosphorus). Average chlorophyll $a$ concentrations were typically greater than $20\mu \mathrm{g}∕\mathrm{L}$ . Bacteria populations detected with flow cytometry were generally small in size (typically $<0.08\mu {\mathrm{m}}^3$ or $0.3\mu \mathrm{m}$ equivalent spherical diameter) and contributed less than 13% of the total microbial biomass. Subpopulations of pico-, ultra-, and net phytoplankton were discriminated flow cytometrically by their red and orange autofluorescence. Cyanobacteria dominated four out of the five reservoirs in terms of numbers but only contributed more than 50% of the microbial biomass in two of the reservoirs. In general, local reservoirs were found to be phosphorus limited and alkaline conditions favored the growth of phytoplankton and bacteria.

A conventional tracer study using ${\mathrm{Li}}^{+}$ and ${\mathrm{Cl}}^{-}$ was conducted on four ${\mathrm{Fe}}^0$ -packed column reactors for nitrate removal. Both ${\mathrm{Li}}^{+}$ and ${\mathrm{Cl}}^{-}$ showed strong adsorption onto iron media and thus were not ideal tracers for the study. Tests using an impulse loading of nitrate were then innovated to investigate the transport and reduction of nitrate in the reactors. The impulse loading was superposed on a continuous constant feeding of nitrate which generated a steady effluent baseline. A multivariable model incorporating hydraulic dispersion, adsorption/desorption, and reduction of nitrate was developed and numerically solved. Both Langmuir adsorption and linear adsorption isotherms were separately applied to describe nitrate adsorption on the reactive surface. The parameters of the model were estimated by fitting the model with the response curves from the impulse loading tests. These estimated parameters were consistent with previous studies. Specifically, the modeling results suggest a significant adsorption of nitrate by the iron media, causing an evident retardation effect. The research may lead to new methods for studying the fate of contaminants in porous reactive environments.

Potassium permanganate was encapsulated in various polymers to create microcapsules with slow-release properties. Batch tests were conducted to evaluate the rates at which the microcapsules release permanganate. The release histories of 18 different polymer formulations varied strongly, but average initial release rate was $2.70\mathrm{g}$ $\mathrm{K}\mathrm{Mn}{\mathrm{O}}_4$ released g $\mathrm{K}\mathrm{Mn}{\mathrm{O}}_4$ ${\text{initial}}^{-1}{\mathrm{d}}^{-1}$ , and the release rate typically decreased with time. The total duration of release ranged from $3\text{to}80\text{days}$ , with an average of $27\text{days}$ . In other batch tests trichloroethene (TCE) was degraded to below detectable amounts by the microcapsules. The degradation rate for TCE was three to four times faster during the initial reaction period than predicted based on permanganate release rates. There appear to be several promising environmental applications for this method of creating a slow-release oxidant.

Porous reactive barriers containing metallic iron and hydrogenotrophic denitrifying microorganisms may potentially be suitable for in-situ remediation of nitrate-contaminated groundwater resources. The main objective of the research described here was to determine the type and concentration of metallic iron to be used in such reactive barriers so that ammonia formation through metallic iron-assisted abiotic nitrate reduction was minimized, while a reasonable rate of biological denitrification, sustained by hydrogen produced through metallic iron corrosion, was maintained. Initial experiments included the demonstration of autotrophic denitrification supported by externally supplied hydrogen, either from a gas cylinder or generated through anaerobic corrosion of metallic iron. Next, the effect of iron type on abiotic nitrate reduction was studied, and among those types of iron tested, steel wool, with its relatively low surface-area-to-weight ratio, was identified as the material that exhibited the least propensity to abiotically reduce nitrate. Further, long-term experiments were carried out in batch reactors to determine the effect of steel wool surface area on the extent of denitrification and ammonia production. Finally, experiments carried out in up-flow column reactors containing sand and varying quantities of steel wool demonstrated biological denitrification occurring in such systems. Based on the results of the final set of experiments, it appeared that to minimize ammonia production, the steel-wool concentration up-flow columns must be even below the lowest value—0.5 g steel wool added to $125{\mathrm{cm}}^3$ of sand—used during this study. To counter any detrimental effect of lowered steel wool concentration on the extent of hydrogenotrophic denitrification, increase of the retention time in the columns to values higher than 13 days (the maximum value investigated in this study) may be necessary.

Acid mine drainage is a serious environmental problem caused by the oxidation of sulfide minerals that releases highly acidic, sulfate, and metals-rich drainage. In this study, alkaline industrial wastes were mixed with acid mine tailings in order to obtain neutral conditions. A series of column leaching tests were performed to evaluate the behavior of reactive mine tailings amended with alkaline-additions under dynamic conditions. Column tests were conducted of oxidized mine tailings combined with cement kiln dust, red mud bauxite, and mixtures of cement kiln dust with red mud bauxite. The pH results show the addition of 10% of alkaline materials permits the maintenance of near neutral conditions. In the presence of 10% alkaline material, the concentration of toxic metals such as Al, Cu, Fe, Zn are significantly reduced as well as the number of viable cells (Thiobacillus ferrooxidans) compared to control samples.

This paper presents a laboratory investigation to evaluate the capacity of alkaline residues to inhibit acid mine drainage. Column tests were used to evaluate the geochemical behavior of cement kiln dust (CKD) and red mud bauxite (RMB) used as covers, liners, or mixed with acid producing tailings and waste rocks. The most important indicators of neutralization are pH and the concentrations of metals in solution. Initial leachate pH of samples with an alkaline cover composed of 10% CKD or 10% of a mixture of CKD and RMB was low, but rapidly increased to near 7.0 and stabilized for the duration of this study. The use of alkaline materials as a liner had a positive effect on the reduction of Fe, $\mathrm{S}{\mathrm{O}}_4$ and other metals such as Cu and Zn concentrations and the number of viable bacteria. In the cases where the alkaline layer was used as a liner or mixed with the waste rocks, near neutral pH values were rapidly reached in the leachate. However, in these columns the leachate pH values decreased over time.