Journal of Environmental Engineering

One potential beneficial reuse of high-carbon-content (HCC) fly ashes is in reactive barrier applications for remediation of contaminated groundwater. However, leaching of metals from coal fly ashes into the environment is of concern. A series of column leach tests (CLTs) and batch water leach tests (WLTs) were performed to investigate the potential leaching of metals from HCC fly ashes during reactive barrier applications. Fly ash content and pH were two key factors affecting the amount leached in WLTs. Leaching of metals in CLTs exhibited a first flush, followed by a tailing elution pattern, for all fly ashes. Attempts to correlate the WLT and CLT data indicated that scale-up of the WLT results to the column experimental setup provided a better prediction of the leachable amount in CLTs compared with a direct comparison of concentrations. Nevertheless, caution should be exercised when building correlations because of the different testing conditions in the two test setups.

The release of nonaqueous-phase liquids (NAPLs) from porous media to groundwater is a widespread environmental problem. The mass transfer of individual NAPL components controls both the extent of groundwater contamination and the persistence of the residual NAPL phase. In order to quantify this key process, small-scale experimental studies on NAPL-water mass transfer were performed in a dynamic system mimicking environmental conditions with “clean” water continuously flowing through the NAPL pool. To describe this process, a modified simulation method was developed and validated by the experimental data. The experimental system consisted of a custom-designed flow cell (with NAPL and water) connected to the peripheral equipment (e.g., pump, water source). This continuously stirred flow-through reactor was used to perform mass transfer experiments with simple and complex model NAPL–water systems. To simulate the experimental data (concentration versus time profiles of individual NAPL compounds), an analytical solution of a standard mass transfer model was adapted in simple model NAPL systems, and a numerical method was employed for complex multicomponent model NAPL–water systems containing phenols, heteroaromatic compounds, and polycyclic aromatic hydrocarbons (PAHs). The numerical model was developed based on a mass balance equation and a general form of Raoult’s law. The simulated concentration profiles of the various solutes matched well the experimental data only if the nonideal behavior of the more polar solutes was accounted for. Using the developed numerical mode simulated mass transfer coefficients for individual NAPL components compared well with previously published values if available.

The accumulation of organic contaminants in process-affected (PA) water represents an environmental liability for oil sands operators. Oil sands coke is a promising adsorbent for removing dissolved organic carbon (DOC), which includes toxic acid-extractable oil sands tailings organics (AEOSTO) found in PA water. The ability of raw and activated delayed and fluid coke to remove DOC and AEOSTO from PA water was assessed. Treatment with $5\mathrm{g}/\mathrm{L}$ of activated delayed and fluid coke removed 91% of DOC and 92% of AEOSTO at levels of $36\mathrm{mg}/\mathrm{L}$ and $60\mathrm{mg}/\mathrm{L}$, respectively. Heavy metal leaching of vanadium at $5.9\mathrm{mg}/\mathrm{L}$ was observed for a $5\mathrm{g}/\mathrm{L}$ application of activated delayed coke, representing a challenge to the approach. Microtox testing indicated that higher carbon doses of activated cokes were effective in reducing toxic the biological response caused by organic compounds; however, exposure to heavy metals increased the toxic effect with time. The proposed methodology should be coupled with an inorganic treatment technique for complete oil sands tailings water treatment.

Extensive living roof substrate design to promote storm-water management while balancing structural load and maintaining $>60\%$ nonirrigated plant cover is investigated through linked laboratory and field experiments in Auckland, New Zealand. Setting quantifiable goals for the 2002 FLL guidelines and agronomic testing methods resulted in successful design of multiple nonproprietary substrates. Particle size distribution and quality control in the materials’ supply chain are critical. Additional work is required to define a meaningful standard permeability test for living roofs. While the maximum water capacity guideline provides a conservative estimate for structural loading when a substrate is wet, it should not be used to predict storm-water retention. Agronomic measures of readily available water (10–100 kPa suction) plus plant stress water (100–1,500 kPa suction) provide a reasonable estimate for the maximum potential rainfall storage during individual storm events. Subject to Auckland’s frequent rainfall, an extensive living roof with 70% v/v 4–10 mm pumice, 10% v/v 1–3 mm zeolite, and 20% organic matter at a 100-mm depth is recommended to maintain plants without irrigation (excluding drought conditions) and minimize weeds while preventing runoff from storms with less than 25 mm of rainfall.

Photocatalytic nitrate reduction was examined in a model water and in groundwater by using three commercially available titanium dioxide photocatalysts (Evonik P25, Evonik P90, and Sachtleben Hombikat UV100). The photocatalysts were characterized using uniform methods (TEM, XRD, surface area, UV-VIS, surface charge) and their photocatalytic activity was differentiated using these results. Under all experimental conditions, P25 and P90 were superior to UV100, and P90 outperformed P25 with nitrate reductions as high as 77% at the maximum irradiance level used ($6.46\times {10}^{22}\mathrm{photons}/\mathrm{L}$). The photocatalytic nitrate reduction activity was found to be dependent on the rate of recombination, pH, and the total photocatalyst surface area, with the recombination rate being the limiting variable. Nitrate reduction was more efficient in model water than in groundwater that contained constituents capable of occupying photocatalyst surface sorption sites or scavenging conduction band electrons. The greater efficiencies of P25 and P90 compared with UV100 were attributed primarily to the mixed-phase nature of the photocatalysts, which allow for better charge separation, and the greater activity of P90 over P25 was attributed to a larger surface area. The results should be helpful in the selection of these commercially available photocatalysts to treat a wide range of pollutants other than nitrate.

Hydraulic fracturing (or fracking) of substrates and proppants into contaminated soils is a developing, but understudied, practice of stimulating in situ bioremediation. In this work, three different purities of the substrate crab shell chitin (SC-20, SC-40, and SC-80), two proppant loadings (sand:chitin mass ratios of $5:1$ and $15:1$), and three chloroethene concentrations (1 and $10\mathrm{mg}/\mathrm{L}$ trichloroethene, and $1.5\mathrm{mg}/\mathrm{L}$ cis-1,2-dichloroethene) were experimentally and statistically examined to determine their effects on halorespiration. The least refined crab shell, SC-20, produced the greatest variety of electron donors, converted the highest percentage of contaminant mass to ethene, and supported a significantly greater Dehalococcoides population than the other substrates. Although influent chloroethene concentration and proppant loading did not significantly affect halorespiration ($p$-values $>0.079$), decreasing the proppant loading from $15:1$ to $5:1$ increased the longevity of electron-donor production. These results indicate that funds need not be expended for purification of crab shell substrates, and that SC-20 should be used with proppant loadings of $5:1$ or lower to maximize the duration of electron-donor production at sites with potential biodegradation rate limitations.

Tetracycline antibiotics have been extensively used in pharmaceutical and veterinary therapies, and they are widely present in natural waters. Although Fe(III)-citrate complexes are known to be highly photoreactive, the optimal conditions for treatment of pollutants at near-neutral pH are not fully understood. In this study, the photochemical removal of tetracycline (TC) in the Fe(III)-citrate solution under simulated sunlight was investigated. A central composite design was employed to explore the effects of the initial concentrations of TC (0–90 μM), Fe(III) (0–40 μM), citrate (0–400 μM), and pH (5.0–9.0) on the photodegradation of TC in aqueous solution. Five levels of each factor were included in the design. The photodegradation of TC in the Fe(III)-citrate solution was observed to follow pseudo-first-order kinetics. According to the multivariate effects analysis, the optimal photodegradation condition was achieved at pH 6.9 and $[\mathrm{Fe}(\mathrm{III}){]}_0/(\mathrm{citrate}{)}_0=33.8/324$ (μM), with the corresponding rate constant $0.0323\stackrel{-1}{min}$ ($t_{1/2}=21.5\min$). The quenching experiments verified that up to 74.5% degradation of TC was attributed to the attack of $•\mathrm{OH}$ formed in the Fe(III)-citrate solution. The results indicated that Fe(III)-citrate complexes were a highly effective catalyst for the elimination of TC at near-neutral pH under simulated sunlight.

Cationic surfactants were employed to modify granular activated carbon (GAC) for the purpose of improving GAC’s adsorption of arsenate from water. Rapid small-scale column tests (RSSCTs) were set up to test the adsorption capacities. Results indicated that surfactant cetyltrimethylammonium chloride (CTAC) modification manifested the highest improvement in GAC’s adsorption for arsenate. GAC modified by $2\mathrm{mmol}/\mathrm{L}$ of CTAC was able to operate approximately 64,000 bed volumes before $10\mu \mathrm{g}/\mathrm{L}$ of arsenate breakthrough as compared with 2,100 bed volumes for virgin GAC. GAC also performed much better than zeolite and bentonite both in surfactant retention and arsenic removal. Arsenate adsorption was affected by influent concentration, pH, and presence of other anions. The effect of competitive anions on arsenate adsorption was in the order of ${\mathrm{PO}}_4^{3-}>{\mathrm{SO}}_4^{2-}>{\mathrm{NO}}_3^{-}$. Breakthrough tests on tap water spiked with arsenate indicated that the modified GAC had high selectivity for arsenate and considerable amount of arsenate was removed though the influent contained interfering anions and total organic carbon (TOC) in concentrations of magnitude higher than that of arsenate.

A novel approach for setting thermal habitat recommendations for an endangered aquatic species will be proposed in this paper. The method, uniform continuous above-threshold (UCAT) analysis, evaluates the duration and frequency of continuous events in which the temperature is higher than a specified value and identifies temperature levels that, because of their rare occurrence in the past, can be considered stressor thresholds. The UCAT analysis was applied to set thermal habitat recommendations for Alasmidonta heterodon, an endangered mussel species in the Upper Delaware River. It was found that a maximum daily water temperature of 26.5°C lasting for more than 7 days is a rare event in the A. heterodon population centers in Upper Delaware River and consequently this condition should be avoided by adjusting already regulated cold-water releases from upstream reservoirs. Knowledge of temperature thresholds and their relationship with persistent low-flow periods provided further decision support for the development of flow management recommendations for species protection. The case study of A. heterodon in the Upper Delaware River demonstrates that in the absence of laboratory research on physiological temperature tolerance of a species, UCAT analysis provides an effective way to approximate habitat conditions that fall within thermal tolerances. Because of quick and easy preparation and analysis, this method may also have a broader application to habitat studies of other animal groups.

Naegleria species (spp.) is a free-living amoeboflagellate that is widespread in natural environments. Some Naegleria spp. cause fatal human infections, and the most important source of these infections is water. This genus is recognized as a potential human pathogen that causes primary amoebic meningoencephalitis. In this study, 211 water samples were collected from two watersheds in Taiwan. The Naegleria spp. on the basis of polymerase chain reaction (PCR) amplification with a genus-specific primer pair and an investigation of Naegleria spp. in the Puzih Rivers and Kaoping Rivers in Taiwan. The percentage of positive samples obtained from the Kaoping River (21.8%) was higher than that from the Puzih River (0.6%). The presence/absence of Naegleria spp. within the water samples showed a significant difference with levels of water temperature and pH value. The most frequently identified Naegleria spp. was N. philippinensis ($n=3$), followed by N. clarki ($n=2$), N. gallica ($n=2$), and N. americana ($n=2$). N. australiensis, N. dobsoni, N. gruberi, and N. schusteri were each detected once. The presence of Naegleria spp. should be considered a potential public health threat; therefore, regularly maintaining normally operated water treatment facilities and implementing effective management strategies are critical for protecting public health.

The EPA method 1623 is designed specifically for the detection of Cryptosporidium and Giardia, but the method has some issues with low and variable recoveries. Ultrafiltration has been used effectively for microorganism recovery from water samples but is not approved by the EPA. To determine the efficacy of using ultrafiltration, 10-L tap water and surface water samples were seeded with Cryptosporidium and Giardia and concentrated with either a pleated capsule filter or a hollow-fiber ultrafilter. For Cryptosporidum, oocyst recovery in tap water was significantly higher for ultrafiltration (68%) versus the capsule filter (37%); ultrafiltration recovered 65% of oocysts in surface water versus 61% for the capsule filter. However, Giardia cyst recovery was mixed. In tap water, the capsule filter produced a significantly better recovery (85%) of Giardia compared with ultrafiltration (63%), but the surface water ultrafiltration recovery (81%) was significantly better than the capsule filter recovery (40%). Overall, ultrafiltration recoveries were equal to or better for Cryptosporidium, but recoveries of Giardia were varied depending on the filter used and the type of water analyzed.