Journal of Environmental Engineering

Unabated runoff from impervious surfaces after rain events is considered a major source of impairment of receiving water bodies. Bioinfiltration storm-water control measures (SCM) have been shown to be effective in reducing runoff and pollutants from urban areas and thus provide a mechanism for protecting downstream sources from erosion and contamination from suspended solids, metals, and nutrients. However, less is known about the loss mechanisms responsible for contaminant removal and the long-term performance of such SCMs. Even less is known of the performance from a vadose zone perspective. The research presented herein examines the long-term (9 year) performance of a bioinfiltration rain garden with specific emphasis on the removal of orthophosphate. Field data indicated clear removal trends for orthophosphate (${\mathrm{PO}}_4^3\text{−}\mathrm{P}$), the bioavailable form of phosphorus, as the storm water infiltrated into the infiltration bed of the rain garden. The median ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ concentration decreased from $0.21–0.25\mathrm{mg}/\mathrm{L}$ in the ponded water to $0.03\mathrm{mg}/\mathrm{L}$ in the pore water at the bottom of the infiltration bed. Overall, the rain garden showed no sign of decreased ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ removal performance over 9 years of monitoring. In addition to monitoring dissolved ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ concentrations over time, soil samples were collected throughout the rain garden to quantify the accumulation of ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ in the soil. Results show that ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ was uniformly distributed throughout the top layer of the ponded area of the infiltration bed ($0.13\pm 0.03\mathrm{mg}/\mathrm{g}$ dry soil, $n=4$) and then decreased with depth between 0 and 10 cm. The sorbed ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ concentrations remained relatively constant between the depths of 10 to 30 cm throughout the infiltration bed ($0.05\pm 0.02\mathrm{mg}/\mathrm{g}$ dry soil, $n=20$). A mass balance comparing the mass of ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ entering and leaving the rain garden to the mass sorbed to the soil suggested that the extraction procedure used to remove the ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ from the soil (0.5 N HCl for 24 h) provided a rough estimate of the ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ that accumulated during the 9 years of operation. Comparison of the ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ sorbed to the first 30 cm of soil over the 9 years (1.58 kg or $176\mathrm{g}/\text{year}$) to the maximum amount of ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ that the soil can hold if in equilibrium with dissolved ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ concentrations typical of the rain garden ($0.05–0.11\mathrm{mg}/\mathrm{g}$ dry soil, based on batch sorption experiments) indicated that the top 10 cm of the infiltration bed was saturated with ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ but saturation of deeper depths would not occur for $>20\text{years}$. This led to the conclusion that, in regards to the soil, infrequent maintenance is needed with respect to ${\mathrm{PO}}_4^3\text{−}\mathrm{P}$ removal during the long-term operation of the rain garden.

Rapid sand filters are a familiar and mature technology, but the mechanical sophistication they incorporate in industrialized nations limits their sustainable application in developing countries. Conventional rapid sand filters require pumps, elevated tanks, or multiple filter units to generate high flow rates for backwashing. Stacked rapid sand filtration is introduced here as a more robust and sustainable alternative. A stacked rapid sand filter can backwash itself with no additional flow, which eliminates the need for pumps or other expensive equipment. This study presents laboratory and field proof-of-concept demonstrations of this novel technology. The multilayer configuration of stacked rapid sand filters allowed a laboratory unit to be loaded at $1.4–1.83\mathrm{mm}/\mathrm{s}$ ($120–160\mathrm{m}/\mathrm{day}$) per layer and backwashed at $10–11\mathrm{mm}/\mathrm{s}$ ($860–950\mathrm{m}/\mathrm{day}$) with the same or similar total flow rate. The filtered effluent met U.S. Environmental Protection Agency drinking water standards. The backwash cycle was also demonstrated, and flushing of contaminants from the sand bed was effective even with 5–10 NTU backwash water. A test stacked filter unit also demonstrated satisfactory filtration performance and effective backwashing at several water treatment plants in Honduras.

Multiple regression models, principal component analysis, redundancy analysis, and the self-organizing map (SOM) model were applied to assess the effects of physico-chemical parameters on the treatment performance of contaminated wetland sediments in replicate integrated constructed wetland (ICW) mesocosms treating either farmyard runoff or domestic wastewater. Dissolved oxygen concentration and conductivity were correlated with the reduction of ammonia–nitrogen (${\mathrm{NH}}_4–\mathrm{N}$) and/or molybdate reactive phosphorus (MRP), and the redox potential and conductivity were related to chemical oxygen demand (COD) removal. SOM was selected as the prediction model to provide numerical estimations for the performance of ICW mesocosms. The model was validated, indicating that ${\mathrm{NH}}_4–\mathrm{N}$, MRP, and COD removal can be predicted by input variables that are quick and cost-effective to measure. The SOM model is an appropriate method for monitoring the performance of mature ICWs as a source of contaminants such as nitrogen and phosphorus. Although no reduction in the overall performance was observed for ICW Sites 7 and 11, this laboratory-scale study provides valuable warning signs regarding the loss of contaminant removal for ICW systems that have been in operation for a relatively long time.

Suspended solids in highway storm water runoff create a wide range of water quality problems; their removal lessens the deleterious impact of storm water runoff on aquatic ecosystems. In this study, three geotextiles were tested in a laboratory setup with influent suspensions having a hydraulic loading rate, total suspended solids (TSS) concentration, and particle size distribution similar to those reported for urban highway storm water runoff. Results indicated that after a short ripening period, a geotextile with an apparent opening size of 150 μm can effectively remove suspended solids to below a target concentration of $30\mathrm{mg}/\mathrm{L}$. The results also showed that the change in hydraulic conductivity of the geotextile filter system can be related to suspended solids captured via a power function, which may be used to predict the flow rate through the filter during its life span. New retention criteria specifically for storm water filtration are introduced for geotextiles.

At-grade distribution systems for wastewater treatment represent potential sources of nutrient input to the environment. The efficacy of nutrient treatment in the vadose zone below an at-grade distribution system receiving secondary treated municipal wastewater effluent was studied on silt loam soil at a site in Calgary, Alberta, Canada, where there are large seasonal temperature fluctuations and cold winter conditions. In addition to wastewater effluent characterization, field monitoring of pore water chemistry, soil temperature, and interstitial soil gas concentrations was conducted at five different depths (up to 150 cm below surface) over the 47-week effluent dosing period. Results showed that ammonium-N from the applied effluent was effectively nitrified in the top 30 cm of the soil profile. While there was evidence for subsequent nitrate removal by denitrification in this same zone, it was limited to the warm summer months and did not appear to result in significant nitrogen mass removal (5–15%) at greater depths in the soil profile. Phosphate was rapidly attenuated in the top 60 cm of the soil profile. This study demonstrated the importance of climatic conditions on biochemical nitrogen transformations in the shallow subsurface and suggested a greater potential for nitrate leaching to groundwater in the winter.

Simulation-based design and analysis of biotreatment systems depends to a great extent on the accuracy of the model parameters used. In many cases, site-specific parameter estimates are not available and parameter values recommended in the literature are adopted along with a measure of judgment to account for bioprocess uncertainty. To better quantify process certitude associated with this approach and thus provide guidance to process designers lacking site-specific parameter values, stochastic simulations were conducted and the empirical frequency distributions derived from the simulation results were interpreted in terms of process certitude. In general, the simulation results confirmed field experience and current practice in biotreatment from a probabilistic standpoint and provided context in terms of process certitude. The certitude of achieving specific treatment levels increased with sludge age, validating the application of a design safety factor on the minimum solids retention time. The increase in process certitude was not substantial, however, beyond a sludge age of about 4 days for the removal of organic material or about 10 days for the removal of ammonia. Process certitude was also declined when the hydraulic behavior of the treatment system approached complete mixing, which could result from such operational strategies as increasing the recycle ratio or the utilization of step feed.

Chrome tanneries generate large quantities of chromium-laden sludge that require proper disposal in engineered landfills to prevent contamination of subsurface soils and groundwater and reduce the risk to public health and the environment. This study investigates the feasibility of using a fine-grained soil as a suitable landfill liner material for the effective containment of chromium in the sludge leachate. Several series of laboratory permeability, adsorption, and column tests were conducted using soil without and with selected additives (rice husk, bentonite, and fly ash) to determine permeability and adsorption and transport of chromium in the soil. Permeability tests showed that the field soil amended with 17% rice husk and 2% bentonite provides the desired hydraulic conductivity of ${10}^{-7}\mathrm{cm}/\mathrm{s}$ (or less) to minimize the leachate migration into the surrounding subsurface environment. The rice husk and bentonite admixtures significantly reduced the hydraulic conductivity of the soil from $3\times {10}^{-7}$ to $2.8\times {10}^{-9}\mathrm{cm}/\mathrm{s}$, and this admixture was further tested for its effect on the adsorption and transport of chromium in the soil. The batch kinetics and column tests results showed that the soil possesses relatively high chromium adsorption capacity under natural or slightly alkaline condition. The batch tests showed that the amendment marginally improved the chromium adsorptive capacity of the soil. The column tests showed a slight increase in breakthrough time due to the presence of the amendment. The inclined base column tests showed that a mildly inclined liner configuration has a marginal effect on the chromium attenuation in the soil. Overall, this study showed that soil amended with 17% rice husk and 2% bentonite significantly decreased the hydraulic conductivity of the soil and slightly increased the adsorption of chromium, and therefore, has the potential for usage as a landfill liner in a landfill system to contain chromium contamination.

For the design and analysis of an ion exchange (IEX) process, it is necessary to know the minimum IEX resin usage defined thermodynamically. Anion exchange resin sorption of dissolved natural organic matter (NOM) may follow an isotherm of either Type I or Type II, which are noticeably different at high surface coverage. The charge density of NOM, which monotonically increases with the pH, appears to play a critical role. Basic pH (high charge density) favors a Type I isotherm and acidic pH (low charge density) may change the isotherm to Type II. The Langmuir equation and the Wiegner-Jenny-Summers-Roberts (WJSR) equation can be used to quantify the Type I and Type II isotherms, respectively. Explicit relationships between minimum resin usage and desired level of removal are subsequently developed and the isotherm constants, along with the non-removable NOM fraction, are simultaneously estimated by an innovative least-squares regression (LSR) approach. The Langmuir isotherm-based model accurately describes the sorption removal of Type I isotherm, and the WJSR isotherm-based model accurately describes the sorption removal of Type II isotherm. At removals $>30\%$, however, the two sorption models offer comparable minimum IEX resin usages. The sorption models and LSR methods developed herein are applicable to resin slurry contactors, including batch reactors, plug flow reactors, or continuous-flow stirred tank reactors.

Sorption and biotransformation of six endocrine disrupting compounds (EDCs) [estrone (E1), $17\beta$-estradiol (E2), estriol (E3), $17\alpha$-ethynylestradiol (EE2), 4-tert-octylphenol (4-t-OP), and bisphenol A (BPA)] and two pharmaceutically active compounds (PhACs) [ibuprofen (IBU) and naproxen (NAP)] were studied in microcosms and columns under conditions that simulate the percolation of effluent through sandy soil on reclaimed land in Singapore. Sorption isotherms followed a linear model, except for IBU and BPA, for which a Freundlich model was used, and for NAP, which sorbed too little to be measurable. Degradation experiment results showed that aerobic conditions were more favorable for the degradation of EDCs than anaerobic or anoxic conditions. E3 and 4-t-OP were totally removed within 40 days, whereas EE2, BPA, IBU, and NAP were persistent. However, under anaerobic conditions, E1 was formed from E2 and vice versa, reaching steady-state conditions after approximately 15 days. To simulate the groundwater (GW) recharge condition, eight laboratory-scale soil aquifer treatment (SAT)–saturated sand columns (each with a length of 1.0 m) were operated in series. Secondary effluent (SE) and ultrafiltered effluent augmented with the target compounds was applied to two identical sets of eight columns, respectively. With secondary effluent and ultrafiltered SE as the feed, the target compounds were completely removed after 8 m of infiltration, with the exception of NAP, which persisted at $1\mathrm{\mu }\mathrm{g}/\mathrm{L}$ in the effluent of recharged columns after an operating time of 3 pore volumes (PV). The higher removal rate in SE recharged columns is attributed to the higher nutrient content, microbial populations, and a longer period of acclimatization. Small-scale batch studies showed that E2, EE2, IBU, and NAP removal was primarily a result of biological transformation that was faster under aerobic than anaerobic conditions.

Mushroom compost, wood chips, sawdust, cow manure, and rice straw were characterized and tested in three combinations as prospective substrates during the treatment of acidic (pH 3) and moderate (pH 6) mine drainage in 3.5 L column bioreactors operated for 167 days, at 3 days of hydraulic retention time. Mixtures gave comparable performances in each pH condition with satisfactory efficiencies. After less than a 2-week acclimation period, bacteria became active, as indicated by a pH increase and sulfide production. Dissolved organic carbon (DOC) consumption was higher in acidic condition, whereas sulfate removal mainly occurred in the early reaction period. There were significant differences in the sulfate and DOC results from acidic relative to moderate mine drainage columns. Aluminum was readily removed (nearly 100%) by all the reactors. Iron removal was better for acidic (98–99%) than for moderate (73–85%) mine drainage. Manganese, mostly leached out from substrate materials, prevailed in early reaction times, followed by a steady decrease toward the end. Results demonstrate the potential utility of mixed substrates for enhancing the performances of bioreactors for mine drainage treatment. However, longer lasting times of DOC would characterize the moderate mine drainage condition.