Journal of Environmental Engineering

Septic systems can present a risk to human health by releasing highly soluble nitrate–nitrogen into the groundwater. A research and demonstration study undertaken in Black River Falls, Wisconsin, evaluated several promising biofilter technologies for on-site nitrogen removal. Duplicate recirculating sand filter-upflow anaerobic systems with a design hydraulic loading rate of $954\mathrm{L}∕\text{day}$ $(250\mathrm{gal}∕\text{day})$ were used to treat septic tank effluent from a correctional institution and produced a treated wastewater with a total nitrogen concentration of $15.2\mathrm{mg}∕\mathrm{L}$ for System 1 and $18.2\mathrm{mg}∕\mathrm{L}$ for System 2, or 72.0 and 63.0% nitrogen removal, respectively. The differences between the two systems appear to have been the result of process configuration changes made over the duration of the study. This paper evaluates the nitrogen removal performance of the recirculating sand filter-upflow anaerobic systems and the effect of operational and environmental factors, including the recirculation ratio, ${\mathrm{BOD}}_5∕\mathrm{N}{\mathrm{O}}_3^{-}$ , and temperature. Nitrogen removal was limited by the recirculation ratio with the maximum total nitrogen removal of 70.1% when the recirculation $\text{ratio}=3$ . Improved performance was also noted for temperatures $⩾20°\mathrm{C}$ and ${\mathrm{BOD}}_5∕\mathrm{N}{\mathrm{O}}_3^{-}⩾8$ . Low temperatures adversely affected nitrification and low ${\mathrm{BOD}}_5∕\mathrm{N}{\mathrm{O}}_3^{-}$ adversely affected denitrification. The relationships among nitrogen removal, recirculation ratio, ${\mathrm{BOD}}_5∕\mathrm{N}{\mathrm{O}}_3^{-}$ , and temperature are also discussed.

$\mathrm{As}\left(\mathrm{III}\right)$ oxidation by a pure bacterial culture, Alcaligenes faecalis strain O1201, was evaluated using a continuous stirred tank reactor. The bioreactor system was operated for 204 days under a wide range of influent $\mathrm{As}\left(\mathrm{III}\right)$ concentrations $(500–\mathrm{8,000}\mathrm{mg}∕\mathrm{L})$ and hydraulic retention times $(25.6–90.7\mathrm{h})$ with citrate as the sole carbon and energy source at pH 7 and 30°C. Nine steady-state conditions were obtained with $\mathrm{As}\left(\mathrm{III}\right)$ oxidation efficiency exceeding 95%. The system quickly recovered from an $\mathrm{As}\left(\mathrm{III}\right)$ overloading at $\mathrm{15,000}\mathrm{mg}∕\mathrm{day}∕\mathrm{L}$ while it operated at a HRT of $12.8\mathrm{h}$ . A material balance analysis revealed that nearly all the $\mathrm{As}\left(\mathrm{III}\right)$ removed in the continuous stirred tank reactor (CSTR) was oxidized to $\mathrm{As}\left(\mathrm{V}\right)$ and only 3.2% of the $\mathrm{As}\left(\mathrm{III}\right)$ fed to the CSTR was unaccounted for. Biokinetic parameters, $k_{\mathrm{mc}}=0.86\mathrm{mg}∕\mathrm{mg}$ cell dry weight/h and $K_c=70\mathrm{mg}∕\mathrm{L}$ , for $\mathrm{As}\left(\mathrm{III}\right)$ oxidation were obtained using the Monod expression and data obtained at steady-state conditions.

A typical secondary wastewater treatment sludge was digested aerobically in a batch digester in the temperature range of $10–80°\mathrm{C}$ . Reaction rate constants were determined by measuring the amounts of volatile suspended solids removed at different time intervals during the process. The maximum value of the reaction rate constant $\left(0.45{\text{day}}^{-1}\right)$ occurred in the temperature range of $55–60°\mathrm{C}$ . The specific heat of biological oxidation was determined by energy balance calculations in the thermophilic range. Removal of indicator organisms in the sludge during the batch digestion was also studied. Sludge digestion at $60°\mathrm{C}$ resulted in an appreciable reduction of indicator organisms as compared to digestion carried out at $55°\mathrm{C}$ . Sludge digestion at $60°\mathrm{C}$ resulted in more economic energy consumption, better volatile solids reduction, better sludge dewaterability, and more effective pathogen inactivation as compared to digestion of the sludge at $40°\mathrm{C}$ .

Batch studies with an initial phosphorus concentration typical of storm water were conducted at the University of Minnesota on C 33 sand, calcareous sand, limestone, three blast oxygen furnace (BOF) by-products, aluminum oxide, and chopped granular steel wool for the removal of dissolved phosphorus from synthetic storm water runoff. Based on the findings of these batch studies, sand filtration enhanced with steel wool, calcareous sand, or limestone has the potential to be a practical and cost-effective method of removing dissolved phosphorus from storm water runoff. Column studies are then performed on four enhancements with C 33 sand filtration: calcareous sand, limestone, chopped granular steel wool, and steel wool fabric. Synthetic storm water runoff with a variable dissolved phosphorus concentration passed through the columns while the flow rate was measured and effluent samples were taken and analyzed for total and dissolved phosphorus concentration and pH. As found in the batch studies, C 33 sand retained dissolved phosphorus but the capacity was quickly exhausted. Combinations of C 33 sand with limestone or calcareous sand clogged the columns and prevented them from draining completely. Steel wool, however, significantly increased the duration and level of phosphorus retention as compared to C 33 sand alone and did not clog the columns. Between 34 and 81% of the dissolved phosphorus was retained by the six steel-enhanced columns. Fine oxidized iron particles observed in the effluent are too small to be completely captured by typical geotextile fabric and may compromise phosphorus removal performance, but phosphorus adsorbed to iron oxide will be of limited bioavailability. Steel-enhanced sand filtration is modeled with contact time, total mass of phosphorus retained, and influent concentration as variables. Enhancing sand filtration systems with steel wool fabric would minimally increase installation costs and would increase the material cost by 3–5%. Based on these findings, steel-enhanced sand filtration is a potentially cost-effective treatment for removing dissolved phosphorus from storm water runoff.

Water quality impacts of zebra mussel metabolism over an infested $15\mathrm{km}$ reach of the Seneca River, N.Y., are documented, based on vertically and temporally detailed robotic monitoring at the reach boundaries during the summer through early fall intervals of $2\text{years}$ . Substantial reductions over the study reach are documented for dissolved oxygen (DO), pH, fluorometric chlorophyll $a$ , and turbidity, associated with the metabolism of this invader. Violations of New York State water quality standards for DO that would not be resolved by traditional manual monitoring programs were observed. The loss of assimilative capacity caused by the zebra mussel invasion is confounding rehabilitation efforts for a downstream polluted lake that had considered diversion of municipal effluent to the river. The critical role robotic monitoring units would play in an automated control system for an innovative strategy of time-variable river discharge of the effluent is described. Near-real time robotic monitoring provides a more detailed understanding of the impacts of zebra mussels on water quality than traditional less intensive manual measurements.

Cake layer in cross-flow microfiltration can be reduced by coagulation of particles. This is because enlarging particle size by coagulation increases shear induced diffusivity and the back transport of rejected particles. In addition, it is known that flocs can be broken when they are passing through a pump. In light of these facts, this study aims to experimentally look at the floc-breaking phenomenon being related to cake layer reduction. Kaolin is used as particles and aluminum sulfate as a coagulant for the experiment. The results of particle size analyses show that the aggregated particles in feed are completely disaggregated by the pump but reaggregated in the membrane module. This suggests that the reaggregation of particles is critical to cake reduction and flux enhancement. This study proves that most of it occurs around the movable cake layer on membrane where $G$ value is small. Charge neutralization of particles is also proven a dominant coagulation mechanism for reaggregation around the movable cake layer over sweep flocculation. These results suggest that rapid mixing and charge neutralization of particles are more important in reducing cake layer than flocculation. In this reason, in-line mixer is expected to work better with coagulation-cross-flow microfiltration than conventional coagulation tank and this study proved it.

One of the most serious disadvantages of membrane applications in water treatment is the decreasing water permeation rate with time, which is often called fouling. This study investigates surface modification of polyethersulfone (PES) ultrafiltration membranes as a fouling reduction strategy for drinking water treatment applications. Surface modification was achieved through the addition of three different tailor-made hydrophilic surface modifying macromolecules (LSMM200, LSMM400, and LSMM600). Flat sheet membranes were prepared via a single-step casting procedure; their surface hydrophilicity was quantified via contact angle measurements. The incorporation of hydrophilic additives produced slightly more hydrophilic membranes (contact angle reduction of up to $8°$ ) and improved membrane performance compared with the PES membrane without blending. In the treatment of highly colored river water, LSMM400- and LSMM600-modified membranes achieved up to 32% higher final fluxes. Surface modification resulted in significantly decreased flux reductions and natural organic matter accumulation. Dissolved organic carbon removals were approximately 70% for all the membranes studied. No clear correlation between membrane hydrophilicity and fouling reduction was observed.

In this paper, we examine the water quality impacts associated with the reuse of fixated flue gas desulfurization (FGD) material as a low permeability liner for agricultural applications. A $0.457\text{-}\mathrm{m}$ -thick layer of fixated FGD material from a coal-fired power plant was utilized to create a $708{\mathrm{m}}^2$ swine manure pond at the Ohio Agricultural Research and Development Center Western Branch in South Charleston, Ohio. To assess the effects of the fixated FGD material liner, water quality samples were collected over a period of $5\text{years}$ from the pond surface water and a sump collection system beneath the liner. Water samples collected from the sump and pond surface water met all Ohio nontoxic criteria, and in fact, generally met all national primary and secondary drinking water standards. Furthermore it was found that hazardous constituents (i.e., As, B, Cr, Cu, and Zn) and agricultural pollutants (i.e., phosphate and ammonia) were effectively retained by the FGD liner system. The retention of As, B, Cr, Cu, Zn, and ammonia was likely due to sorption to mineral components of the FGD liner, while Ca, Fe, and P retention were a result of both sorption and precipitation of Fe- and Ca-containing phosphate solids.

Parallel to industrial growth and ever increasing use of agrichemicals, environmental resources have been affected and deteriorated by generated pollutants. Groundwater, an important source of fresh water, has not been immune from contamination. Recognition of groundwater vulnerability to pollution will help in managing groundwater quality conflicts. The DRASTIC model (where D=depth to groundwater; R=net recharge; A=aquifer media; S=soil type; T=topography; I=impact of vadose zone; and C=hydraulic conductivity of the aquifer) has been used extensively for assessing the vulnerability of groundwater. It employs a linear combination of some intrinsic properties of aquifers to develop a vulnerability index. As there is no clear boundary for the set of vulnerable aquifers, groundwater vulnerability can be addressed through fuzzy set theory instead of classical set theory. In this study, benefiting from a fuzzy system and a conscious knowledge base, a regional-scale model is developed for groundwater vulnerability assessment that employs DRASTIC parameters. A comparison between the output of the fuzzy model and the DRASTIC index is accomplished. The ability of the fuzzy system to cope with the modeling of a nonlinear system and presentation of the output of the fuzzy system in the framework of a geographical information system are highlighted.

During most of the past century, large quantities of substances were produced and utilized that subsequently proved harmful. This is the case with polychlorinated biphenyls (PCBs) which only became prohibited by law in the 1970s. As a result of their physicochemical properties, these substances are now present everywhere, although they are mainly found in soils, since they are hydrophobic in character. The present study evaluates an innovatory treatment for the remediation ex situ of soils contaminated by PCBs. This treatment consists of a first stage of desorption using a surfactant agent, followed by a second stage of oxidation with the object of transforming the PCBs into innocuous substances through successive oxidations using the photo-Fenton process. The results obtained (87% remediation in the desorption and 100% in the oxidation stages) show this new treatment to be a highly effective alternative, which does not generate dangerous residues of any type.

The effects of the operating conditions, the initial concentrations of marine diesel fuel (MDF) and the coexisting Pb in the soil, and the ethylene diamine tetra acetic salt (EDTA) in solution on MDF removal by sodium dodecyl sulfate (SDS) washing were extensively investigated with the aim of optimizing the process parameters and determining the MDF removal efficiency by SDS under different contamination conditions. The experimental results from batch tests indicated that the majority of MDF was removed by SDS in the first $2\mathrm{h}$ , and its optimal pH was nearly neutral. Increasing the SDS concentration linearly increased the MDF removal efficiency. At a given SDS concentration, the removal efficiency was dependent on the existing forms of MDF in soils, and the free phase of MDF was found to be more easily removed than the adsorbed phase. MDF removal by SDS was significantly reduced by the coexisting Pb in soils, which likely forms a complexation with SDS and thereby enhances the partitioning of MDF in the soil by the re-adsorption of released MDF onto the hydrophobic tails of the adsorbed SDS. EDTA alone, or with SDS, could remove MDF, but the remaining MDF in the contaminated soil after EDTA washing became more difficult to be removed by SDS. Therefore, the EDTA washing followed by SDS washing is not recommended for MDF removal.

The recently introduced ambient air quality standards for fine particulates expand the use of available control system simulation models, from the prediction of total particulate matter removal efficiencies, to the prediction of ${\mathrm{PM}}_{2.5}$ and ${\mathrm{PM}}_{10}$ (particulate matter with diameters less than 2.5 and $10\mathrm{\mu }\mathrm{m}$ ) ones. In order to assess the suitability of cyclone simulation models for this task, the fractional efficiency predictions of six prominent models (Lapple, Leith and Licht, Dietz, Mothes and Loffler, Iozia and Leith, and Mothes and Loffler with the turbulent dispersion coefficient of Salcedo and Coelho) are compared for a number of “standard” cyclone design configurations under a wide range of cyclone diameters and pressure drops. The results reveal a significant discrepancy among model predictions, suggesting that at least some of the models considered are unsuitable for predicting size-specific (e.g., ${\mathrm{PM}}_{2.5}$ and ${\mathrm{PM}}_{10}$ ) cyclone efficiencies. They also show that the sensitivity of fractional efficiencies to changes in the configuration ratios, diameter, and gas pressure drop varies widely, and in some cases even in opposite directions, among models. The above-noted results demonstrate the need for a systematic model validation against credible and sufficiently extensive experimental data sets.