Journal of Environmental Engineering

Decentralized membrane filtration systems (DMFS) have the potential to supply safe drinking water in low-income countries (LICs) where centralized municipal water treatment is practically infeasible. This study aimed at applying an integrated bench-scale and field-testing approach to assess the sustainability of a DMFS in producing safe drinking water in LICs. The state-of-the-art DMFS employed in this study was capable of removing bacteria, surrogate parasites, and viruses at $\log$ reductions above 7, 5, and 4, respectively, from evaluated waters ($n=4$). The technological sustainability of the DMFS was primarily affected by membrane fouling, and a linear correlation was found between the reversible/irreversible fouling rates of a miniature bench-scale system and those of the full-size DMFS caused by representative types of source waters. The total and irreversible fouling rates of the full-size DMFS were approximately 50% of those of the miniature system, regardless of the properties of the source waters. Similar quantitative relationships may be established between the fouling rates of the bench-scale system and those of other full-size DMFS. Overall, easy and cost-effective fouling control is warranted for sustainable application of DMFS in LICs, and bench-scale membrane testing serves as a potential screening tool for this purpose.

Cesium-137 (${}^{137}\mathrm{C}$) is a radioactive source that could be utilized in the construction of a radioactive dispersal device (RDD). The objective of this study was to examine the uptake of ${\mathrm{Cs}}^{+}$ by common structural materials in the presence of water by using batch experiments with nonradioactive cesium chloride (${}^{133}\mathrm{CsCl}$) as a surrogate for the radionuclide. Uptake kinetics and adsorption isotherms of ${\mathrm{Cs}}^{+}$ were measured on a diverse set of building materials, as were the effects of pH on the sorption processes. The results showed that wood materials, metal filings, and organic building materials and supplies did not sorb significant amounts of ${\mathrm{Cs}}^{+}$, but red brick, concrete block, drop ceiling panels, and clay materials retained ${\mathrm{Cs}}^{+}$ strongly. Adsorption kinetics were fast, and sorption isotherms could be characterized as linear. The solution pH did not have a significant effect on ${\mathrm{Cs}}^{+}$ sorption.

Photocatalysis with irradiation of a vacuum ultraviolet (VUV) lamp (VUV-PCO) was used to remove toluene in air. Two parallel reactions with irradiation of a 254 nm lamp (254 nm-PCO) and without ${\mathrm{TiO}}_2$ (i.e., VUV photolysis) were conducted for comparison. The influencing factors of relative humidity, initial toluene concentration, and air flow rate were investigated. The results showed that VUV-PCO achieved much higher toluene removal efficiency and better PCO durability than 254 nm-PCO under different operating conditions. 82.3% toluene conversion was obtained with 1.8 ppm outlet ${\mathrm{O}}_3$ concentration in the former, but only 14.5% with 30 ppm outlet concentration of ${\mathrm{O}}_3$ was obtained in the latter under the conditions of 1% humidity, 50 ppm initial toluene concentration, and $1\mathrm{L}/\min$ flow rate. Energetic photons from the VUV lamp could efficiently destruct toluene directly. ${\mathrm{O}}_3$ formed from VUV irradiation of ${\mathrm{O}}_2$ enhanced the toluene abatement by catalytic ozonation and inhibited the recombination of electron/hole pairs and deactivation of the photocatalyst. VUV-PCO could simultaneously overcome the limitations of the conventional PCO process. It is a promising technology for toluene abatement.

The engineering properties of wastewater residuals (biosolids) can be improved by using waste by-products from local industries. Dewatered biosolids from a wastewater-treatment plant in New Zealand were mixed, on the basis of the dry weight of biosolids, with 30%, 40%, and 50% of fly ash, lime kiln dust (LKD), and two slags [kontinous oxygen blast maxite (KOBM) and work debris (WD)], respectively, together with 0%, 10%, or 20% lime. Changes in the shear strength, measured by using a shear vane and triaxial tests, were obtained after 2 and 8 weeks of curing time. The pH of solids was measured and X-ray diffraction and X-ray fluorescence analyses were performed to determine the mineral and elemental composition of the material. The strain-rate dependency of the strength of biosolids was investigated by performing triaxial tests at different strain rates. The test results yield a logarithmic relation between strain rate and shear strength. Vane strengths of biosolids were found to be a factor of 1.8 higher than the triaxial results. The best performing additives are fly ash in combination with 10% and 20% lime, all LKD mixtures, KOBM with 10% and 20% lime, and WD with 20% lime. These mixtures showed a shear strength equal to or higher than that of biosolids, with 20% lime and a high pH ($>11$) after 8 weeks.

The effects of increasing sonication time (60–150 min), calcium chloride (${\mathrm{CaCl}}_2$; $1–10\mathrm{g}/\mathrm{L}$), ferrous oxide (FeO; $2–10\mathrm{mg}/\mathrm{L}$), aluminium oxide (${\mathrm{Al}}_2{\mathrm{O}}_3$; $2–10\mathrm{mg}/\mathrm{L}$), and ${\mathrm{Na}}_2{\mathrm{CO}}_3$ ($2–12\mathrm{mg}/\mathrm{L}$) on the destruction of six polycyclic aromatic hydrocarbons (PAHs) and acute toxicity in a petrochemical industry wastewater in Izmir (Turkey) were investigated at a sonication intensity and a frequency of $51.48\mathrm{W}/{\mathrm{cm}}^2$ and 35 kHz, respectively. The contribution of $4–6\mathrm{mg}/\mathrm{L}$ ${\mathrm{CaCl}}_2$ to the yields in more hydrophobic PAHs [(benz[a]pyrene (BaP) and indeno[1,2,3-cd]pyrene (IcdP)] was low (6–8%), whereas it was high (21–26%) in less hydrophobic PAHs [acenaphthene (ACT), fluoranthene (FL), benz[a]anthracene (BaA), benz[k]fluoranthene (BkF)] at 30°C after 150 min sonication. $8\mathrm{g}/\mathrm{L}$ ${\mathrm{Na}}_2{\mathrm{CO}}_3$ suppressed the removal of less hydrophobic PAHs (90–96%) although it did not contribute to the yields of more hydrophobic PAHs at 30°C after 150 min sonication. $6\mathrm{g}/\mathrm{L}$ ${\mathrm{Al}}_2{\mathrm{O}}_3$ and $8\mathrm{g}/\mathrm{L}$ FeO increased both less ($E=93–95\%$) and more ($E=90–94\%$) hydrophobic PAH yields. The reason for the decrease in BkF and BaA yields at long sonication time (150 min) was the reformation of these PAHs from their by-products namely, $p$-hydroxybenzoic acid, benzoic acid, Fluoranthene (FL), and Anthracene (ANT). Hydroxylation is the major process for complete sono-degradation of less hydrophobic ACT, FL, BaA, and BkF, whereas the pyrolytic process is the major path for complete degradation of BaP and IcdP. The maximum acute toxicity removal (98%) was provided by $4\mathrm{g}/\mathrm{L}$ ${\mathrm{CaCl}}_2$, $4\mathrm{mg}/\mathrm{L}$ ${\mathrm{Na}}_2{\mathrm{CO}}_3$, $4\mathrm{mg}/\mathrm{L}$ FeO, and $8\mathrm{mg}/\mathrm{L}$ ${\mathrm{Al}}_2{\mathrm{O}}_3$ after 150 min of sonication time at 30°C.

A grit removal process that exploits the phenomenon of secondary currents induced in open-channel flow as water moves around a bend has been investigated by using both physical and computational fluid dynamics (CFD) modeling approaches. The flow field was first validated against a case study by solving the full Reynolds-averaged Navier-Stokes equations and Reynolds stress turbulence models with a finite-volume method. The air-water interaction at the free surface was simulated by using a volume of fluid multiphase model. Discrete phase modeling was then used to calibrate the hydrodynamic interaction with grit particles (varying in size from 63 to 2,000 µm) observed in a physical model with a 30° bend, with respect to particle diameter, flow rate, shape factor, and injection location. This was followed by detailed parametric investigations using the calibrated model at different flow rates, angle of bend, and radius of curvature that showed individual particle trajectories (and consequent grit removal efficiency of the process) for different particle sizes. The CFD model was also used to compare different configurations of receiving sump whereby different outflows and baffles were compared. Overall, the study shows that a very slightly curved channel or straight channel is, in fact, the optimum solution, because the secondary currents in curved channels act to uplift particles away from the sump, thus reducing grit removal efficiency.

Granular media filtration is an important process in drinking water treatment to ensure the adequate removal of particle-bound pathogens (i.e., Giardia and Cryptosporidium). Filtration performance is typically monitored in terms of filtered water turbidity. However, particle counts may provide further insight into treatment efficiency, as they have a greater sensitivity for detecting small changes in filtration operation. Artificial neural networks (ANN) models were applied to optimize filtration at the Elgin Area water treatment plant (WTP) in terms of postfiltration particle counts. Process models were successfully developed to predict postfiltration particle counts. Two inverse-process models were developed to predict the optimal coagulant dosage required to attain target particle counts. Upon testing each model, a high correlation was observed between the actual and predicted data sets. The ANNs were then integrated into an optimization application to allow for the transfer of real-time data between the models and the online supervisory control and data acquisition (SCADA) system.

This paper deals with the adsorption of 4-picoline (4Pi) from aqueous solutions onto bagasse fly ash (BFA) and rice husk ash (RHA) as adsorbents. We discuss the effect of several parameters, such as initial pH, adsorbent dose, contact time, initial concentration, and temperature, on the batch adsorption. We collected equilibrium sorption isotherm data, which could be well-represented by the Redlich-Peterson, Toth, and Radke-Prausnitz isotherm equations. The maximum removal of 4Pi was found to be 46% and 96% by BFA, and 55% and 95% by RHA for lower (50 mg/L) and higher (600 mg/L) concentration of 4Pi, respectively, with sorbent dosages of 5 g/L for BFA and 20 g/L for RHA. Adsorption was found to be very fast, and about 72–90% of 4Pi removal was achieved in the initial 5 min of contact time. We found the sorption of 4Pi on BFA and RHA to be endothermic in nature. The spent adsorbents can be dried and used as a cofuel in boiler furnaces/incinerators.

Hydrocalumite ($[{\mathrm{Ca}}_2\mathrm{Al}(\mathrm{OH}{)}_6{]}_2{\mathrm{CO}}_3·{\mathrm{mH}}_2\mathrm{O}$) was synthesized by precipitation and thermally activated at 300 and 550°C. Its ${\mathrm{CO}}_2$ chemisorption capacity was evaluated and compared with that of calcium oxide (CaO). Initial thermal analyses showed that CaAl-550 sample has better properties as ${\mathrm{CO}}_2$ sorbent than CaO, evaluated under similar conditions. It was determined that both materials (CaAl-550 and CaO) have similar kinetic behavior, and the presence of ${\mathrm{Ca}}_{12}{\mathrm{Al}}_{14}{\mathrm{O}}_{33}$ on the CaAl-550 sample did not reduce or interfere with the ${\mathrm{CO}}_2$ capture. Moreover, when the ${\mathrm{CO}}_2$ absorption-desorption cyclability was analyzed, the CaAl-550 sample apparently possessed better ${\mathrm{CO}}_2$ capture efficiency and thermal stability than CaO. In fact, different characterization analyses (nuclear magnetic resonance and scanning electron microscopy ) suggest that ${\mathrm{CO}}_2$ capture efficiency and thermal stability observed on the CaAl-550 sample can be attributed to the aluminum presence, as ${\mathrm{Ca}}_{12}{\mathrm{Al}}_{14}{\mathrm{O}}_{33}$.

During pollutant transport in a stream, many pollutants get adsorbed in the streambed materials and are subsequently released. A conceptual hybrid-cells-in-series model for adsorption (HCIS-A), which consists of a plug flow zone and two thoroughly mixed zones of unequal residence times, has been developed to simulate adsorption-desorption in addition to advection and dispersion processes. Sorption processes governed by first-order mass exchange kinetics along with advection in the plug flow zone have been solved analytically using the Laplace transform technique. Analytical solutions have been derived for transport of pollutants through the first and second thoroughly mixed zones of the hybrid model considering sorption. Using the convolution technique and ramp kernel coefficients, the pollutants have been routed through all the zones to derive a semianalytical solution at the end of first hybrid unit. The advantages of this conceptual hybrid model are (1) the conversion of the second-order partial differential equation to a first-order ordinary differential equation; (2) the model’s capacity to incorporate variation of stream geometry and flow velocity in different stream reaches; and (3) the model’s capability to incorporate sorption kinetics. The responses of the hybrid model correspond to the finite-difference solutions of the partial differential equation (PDE) that accounts for advection, dispersion, and adsorption. The first arrival time of the pollutant downstream of a point disposal has been estimated. This is not clearly identified in other models. The effect of sorption on pollutant transport was studied and demonstrated in various $C\mathrm{\text{-}}t$ profiles as the pollutant moved downstream of a disposal point. The characteristics of the $C\mathrm{\text{-}}t$ profiles for a conservative pollutant in streams with adsorbing streambed were in the expected trend.

Wet-sieving sand-sized particles from a whole storm-water sample before splitting the sample into laboratory-prepared containers can reduce bias and improve the precision of suspended-sediment concentrations (SSC). Wet-sieving, however, may alter concentrations of total suspended solids (TSS) because the analytical method used to determine TSS may not have included the sediment retained on the sieves. Measuring TSS is still commonly used by environmental managers as a regulatory metric for solids in storm water. For this reason, a new method of correlating concentrations of TSS and SSC by particle size was used to develop a series of correction factors for SSC as a means to estimate TSS. In general, differences between TSS and SSC increased with greater particle size and higher sand content. Median correction factors to SSC ranged from 0.29 for particles larger than 500 µm to 0.85 for particles measuring from 32 to 63 µm. Great variability was observed in each fraction—a result of varying amounts of organic matter in the samples. Wide variability in organic content could reduce the transferability of the correction factors.

The bioretention drainage configuration of raising the outlet to create an internal water storage (IWS) layer in the media was originally intended to promote denitrifying conditions. The goal was to reduce nitrate and total nitrogen concentrations in nutrient-sensitive watersheds. Two field studies in the Piedmont region of North Carolina, where the in situ soils typically have high clay content, showed this design feature had potential to enhance exfiltration and reduce drainage from bioretention. Two bioretention cells in Rocky Mount, North Carolina, were monitored for two year-long periods to measure the impact of varying IWS zone depths over sandier underlying soils. Nearly 99% of runoff entering the bioretention cell with sand underlying soil (sand cell) was never directly discharged to the storm water network. However, the hydraulic retention time (contact time) of runoff in the media was less than 3 h, and except for total suspended solids (TSS), minimal pollutant removal was achieved. The other bioretention cell had a sandy clay loam underlying soil (SCL cell); the percentage of runoff leaving via exfiltration and evapotranspiration from this cell was 87% during the monitoring period with a 1.03-m IWS zone depth and 75% when the IWS zone depth was 0.73 m. The underlying soil of the SCL cell had a lower hydraulic conductivity, so water would remain in the IWS zone for up to 7 days. The increased hydraulic retention time in the media resulted in lower outflow concentrations. For events monitored with drainage from the SCL cell, efficiency ratios of all the nitrogen species and TSS exceeded 0.5. As an additional metric of performance, the parking lot runoff and treated runoff from both the SCL and sand cells were compared to concentrations consistent with “good” and “fair” benthic macroinvertebrate health in streams. Using this metric, the parking lot runoff only met the “fair” standard for total nitrogen (TN) and total phosphorus (TP), and treated runoff from the SCL cell achieved the “good” standard for both TN and TP. However, because of the short hydraulic retention time of runoff in the media for the sand cell, this cell only maintained the “fair” standard for TN and did not achieve the “fair” standard for TP.

A time-dependent system for evaluating the groundwater-contamination hazard rating of uncontrolled municipal solid-waste landfills has been reported elsewhere. While prioritizing uncontrolled landfills for remedial actions, this system (TD-HARAS) accords equal importance to the groundwater contamination caused by a landfill in the past and the contamination to be caused in the future. Some policymakers may like to remediate first those landfills that have greater potential for future contamination; landfill age then becomes an important factor to be taken into consideration for landfill prioritization. In this note, the mathematical framework of TD-HARAS has been extended to allow differential importance to past and future contaminations and to incorporate site age in the assessment of the groundwater-contamination hazard rating of landfill sites. A sensitivity analysis of the extended system (ETD-HARAS) shows that the groundwater-contamination hazard rating of a landfill site decreases with increases in the site age. A comparison of ETD-HARAS with selected existing hazard-rating systems shows that although ETD-HARAS produces significantly differing scores for different landfills and thus responds to varied site conditions, the existing systems individually produce clustered scores and return the same rank to more than one landfill. Thus, ETD-HARAS makes a better basis for site prioritization for taking remedial actions.

This paper describes a framework to determine the total maximum daily flow diversions (TMDFDs) of freshwater from the San Francisco Bay Delta that can be undertaken without causing the extinction of salmon, striped bass, and delta smelt. The framework comprises three models: the watershed analysis risk management framework (WARMF) model of tributary rivers, the Link-Node estuary model of the Bay Delta, and the monthly cohort life-cycle model of fish. The first two models simulate the environmental conditions of river segments and estuary “Nodes” in which fish live. The fish model deposits eggs in river segments on specified months. The eggs become larvae, juveniles, and young as they move downstream to the estuary “Nodes” where they may die, be eaten, or be entrained into pumps that divert water for export to northern and southern California cities and Central Valley farms. Thus, flow diversion is mechanistically connected to fish decline. These models are integrated by the graphical user interface (GUI) of WARMF to serve as a decision support system (DSS). The DSS allows users to enter alternatives of daily flow diversions, including no diversion. The DSS calculates projected fish declines. A stakeholder process is then used to select an acceptable water diversion plan.