Journal of Environmental Engineering

The present study describes the effects of initial alkalinity and various solid alkalinity sources such as calcite, dolomite, and oyster shell on nitrate removal in a sulfur-oxidizing autotrophic denitrification process. The results showed that denitrification rate increased as the initial alkalinity present in the system increased. Denitrification rates determined by a half-order kinetic model were 0.269, 0.976, 2.631, and $3.110\mathrm{mg}\mathrm{N}{\mathrm{O}}_3–{\mathrm{N}}^{1∕2}∕{\mathrm{L}}^{1∕2}\bullet \text{day}$ corresponding to the initial alkalinity of 300, 600, 1,200, and $\mathrm{1,800}\mathrm{mg}\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3∕\mathrm{L}$ , respectively. This amount of consumed alkalinity closely matched the theoretical alkalinity requirement. However, when $300\mathrm{mg}\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3∕\mathrm{L}$ of alkalinity was initially present the sulfur-based denitrification was greatly inhibited. The data indicate that approximately two times initial alkalinity of theoretically required alkalinity is needed for a desirable sulfur-based denitrification reaction. The initial alkalinity dissolution rates were 88, 38, and $14\mathrm{mg}\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3∕\mathrm{L}\bullet \text{day}$ from $5\mathrm{g}$ of oyster shell, calcite, and dolomite, respectively. Accordingly, only 1.6 and 5% of initial nitrate remained in $7\text{days}$ for oyster shell and calcite, respectively, but about 15% was still detected when dolomite was used.

A three-dimensional computational fluid dynamics model is used to estimate the hydraulic residence time for a portion of the Wachusett Reservoir in central Massachusetts. The basin under consideration has several major inflows and exhibits complex flow patterns. The basin is modeled using the FLUENT software package with particles used to track travel time in a steady-state flow field. A tetrahedral mesh with over 1.6 million cells is used with accurate depiction of basin bathymetry and inlet and outlet geometries. Modeling is performed to simulate behavior during a period when conditions are isothermal. It is determined that mean hydraulic residence time is $3–4\text{days}$ ; approximately half of what would be expected assuming strictly plug flow. The presence of a primary flow path, large scale eddies and stagnation zones contribute to the faster travel times. Reductions in inflow rates produce increased residence times and significant changes in flow patterns.

For determining the accumulated pollutant mass on highways, two years of monitoring data were used from eight highway sites in southern California. Buildup over antecedent dry days was calculated from mass washed off from the following storm and retained pollutant mass. Mass accumulation rates were determined for total suspended solids (TSS), chemical oxygen demand (COD), oil and grease, total Kjeldahl nitrogen, and total phosphorus, and are reported in $\mathrm{g}∕{\mathrm{m}}^2\text{-}\text{day}$ . A revised buildup model is proposed using an alternative modeling approach to describe buildup during dry days between storms. The result shows that, between 1 and 10 antecedent dry days, the pollutant mass buildup rates are determined to be $0.544\mathrm{g}∕{\mathrm{m}}^2\text{-}\text{day}$ for TSS, $0.114\mathrm{g}∕{\mathrm{m}}^2\text{-}\text{day}$ for COD, and $0.0113\mathrm{g}∕{\mathrm{m}}^2\text{-}\text{day}$ for oil and grease. Buildup rates decline in subsequent periods rates decreased by 79% for TSS, 78% for COD, and 61% less for oil and grease in the following $10–70\text{day}$ period.

The main objective of this study was to determine the optimum composition of a reactive porous medium containing sand and metallic iron, to be used for $\mathrm{Fe}\left(0\right)$ -assisted hydrogenotrophic denitrification. This determination is important to ensure that the end-product distribution after such treatment is acceptable, i.e., ammonia formation due to abiotic nitrate reduction by metallic iron in such media is minimized, while a reasonable rate of biological denitrification is maintained. Based on a previous study it was established that steel wool, with its relatively low specific surface area, exhibited the least propensity to abiotically reduce nitrate. It was also established that to achieve acceptable end-product distribution, the steel wool concentration in the reactive porous media has to be lowered even below the lowest value, i.e., $4.0\mathrm{g}$ steel wool/ ${\mathrm{m}}^3$ of sand, used during that study. It was further hypothesized that to counter any detrimental effect of lower steel wool concentration on biological nitrate removal rate, increase of the retention time in porous media to values higher than 13 days, the maximum value investigated in that study, may be necessary. In the present study, experiments were conducted in batch reactors containing denitrifying microorganisms and various concentrations of steel wool and in semibatch reactors containing sand seeded with denitrifying microorganisms and various concentrations of steel wool. Based on the results of the semibatch experiments, it appears that to achieve acceptable end-product distribution, the steel wool concentration in the reactive porous media has to be maintained around $2.0\mathrm{g}$ steel wool/ ${\mathrm{m}}^3$ sand and the corresponding retention time in the reactive media must be around 26 days.

Filamentous bulking can be controlled by the addition of oxidant chemical agents such as ozone. To evaluate the ozone effect on activated sludge from a laboratory scale reactor, different techniques were applied: Settleability test, respirometry (oxygen uptake rate), and the INT-dehydrogenase activity test carried out both by spectrophotometry $\left({\mathrm{DHA}}_{\mathrm{a}}\right)$ and image analysis $\left({\mathrm{DHA}}_{\mathrm{i}}\right)$ . In activated sludge, the respirometric technique and the spectrophotometric ${\mathrm{DHA}}_{\mathrm{a}}$ quantified ozone action on the total respiratory activity of flocs; in contrast, the image ${\mathrm{DHA}}_{\mathrm{i}}$ test was applied to evaluate the specific action of ozone on filamentous microorganisms. The conditions for application of the INT-dehydrogenase activity test were standardized using pure cultures of a filamentous microorganism (Sphaerotilus natans) and a floc-forming bacterium (Acinetobacter anitratus). For activated sludge with filamentous bulking, ozone doses and treatment times necessary to improve settleability were established. Ozone dose levels and contact times influence the viability of bacteria in flocs and filaments and the finding of appropriate parameters to preserve floc viability and, at the same time, inhibiting filaments is essential to filament control by ozonation.

A mathematical model to predict the performance of a membrane pervaporation unit directly placed in the soil to reuse wastewater for agricultural microirrigation was presented. The model was formulated by combining the solution–diffusion and the resistance-in-series model for mass transport across the membrane thickness, the Richard’s equation for soil water movement and the van Genuchten function for soil hydraulic properties to predict the water permeate flux for different types of test soil over a wide range of process operating conditions. Its applicability was assessed by comparing to the experimental data collected using both hollow fiber (HF) bundles and corrugated sheets (CS) membrane modules made of a hydrophilic dense polymer. A good agreement was observed between the model predictions and the experimental measurements. Further analysis concluded that the water permeate flux were mainly controlled by the porosity, the particle-size distribution, and the residual water of the soil. The overall mass transfer resistances were estimated to be $1.2\times {10}^{14}$ and $5.6\times {10}^{13}\mathrm{s}\mathrm{Pa}∕\mathrm{m}$ for the HF and CS modules buried in loam soil, respectively, which are different from those measured in sweeping air pervaporation tests. The soil resistance for water transport was $7.1\times {10}^{13}\mathrm{s}\mathrm{Pa}∕\mathrm{m}$ . It is believed that the model could be a valuable tool to refine the design and optimize the operation of the proposed membrane pervaporation system.

Implications of conventional activated sludge (CAS) process modification to a low sludge production (LSP) process have been studied for treating pulp and paper wastewaters. The activated sludge process is modified to a two-stage design to establish a microbial food chain that would result in reduced sludge production. The return activated sludge in the LSP process bypasses the first (dispersed growth) stage to be received only by the second (predatory) stage. The resulting once-through operation of the dispersed growth (DG) stage makes it potentially susceptible to bacterial washout under hydraulic shock conditions. A sensitivity analysis of the DG stage operation was performed by varying its hydraulic residence time. The experimental data revealed that the optimal DG stage hydraulic residence is between 3 and $5\mathrm{h}$ , with bacterial washout likely to be initiated within $2\mathrm{h}$ . Based on laboratory results, it appears that a well-designed LSP system is likely to be able to handle day-to-day variations in hydraulic and organic loading rates. The LSP process produced 36% less sludge than the CAS process while consuming approximately 25% more oxygen. The treatment performance of the two systems was comparable except that the LSP sludge had much better settling and dewatering properties.

This study investigated the kinetics and emission factor for 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) on the combustion of liquid crystal display components. In addition, chemical characteristics and structure of the liquid crystal sample were also investigated. The evaporation and gas diffusion of liquid crystals occur in the early stage of the combustion process (at $<545\mathrm{K}$ ). Continuously, the liquid crystal molecules may be oxidized to form $\mathrm{C}{\mathrm{O}}_2$ , CO, $\mathrm{C}{\mathrm{H}}_4$ , ${\mathrm{C}}_2{\mathrm{H}}_6$ , and PAHs. The activation energy $(18.9\mathrm{Kcal}∕\mathrm{mol})$ , preexponential constant $({10}^{13.9}\mathrm{L}∕\min )$ and reaction order (3.1) of the combustion of liquid crystal display components were also determined. On the other hand, the analytic results indicated that the emission factor for 16 USEPA priority PAHs in particulate and gas phase is not determined (n.d.)-25.19 and n.d.- $31.48\mu \mathrm{g}∕\mathrm{g}$ , respectively. The emission factor is approximately 390 and 1,520 times higher, respectively, than that of waste terephthalic acid and biological sludge combustion. Results of this work suggest that the combustion of liquid crystal display components should emphasize the air pollution control.

Laboratory and field studies were conducted to elucidate heavy metal removal by three wetland grasses and sediments in storm water detention pond. The removal of heavy metals including Cd, Cu, Pb, and Zn was mediated by fluid-flow intensity in the reactors. The growth of plants and the removal rates of contaminants were plant species dependent. All three wetland grasses removed contaminants from the spiked nutrient solutions. A first-order kinetic model adequately represented the removal of contaminants by plants. The analyses of undisturbed sediment cores in detention pond revealed strong stratification of heavy metal concentrations at the sediment–water interface. A simple model that integrates heavy metal removal by aquatic plants and sediments in storm water detention ponds is proposed. The model provides an estimate of contaminant residence time which can be related to hydraulic residence time in storm water detention ponds.

The removal of 2,4-dinitrotoluene (2,4-DNT), a munitions waste constituent and an industrial intermediate, from contaminated soils was evaluated using enhanced electrokinetic (EK) remediation. Two model soils were spiked with $480\mathrm{mg}$ of 2,4-DNT/kg of dry soil for the EK experiments. The spiked soils were kaolin, a low-buffering clayey soil, and glacial till, a high-buffering silty soil. The glacial till was obtained from a field site and contained 2.8% organic matter. Deionized (DI) water and cyclodextrin solutions were used as the EK purging solutions. Cyclodextrin was selected as a nonhazardous solubility enhancer for enhancing the desorption and removal of 2,4-DNT from soils in EK remediation. Two aqueous solutions of hydroxypropyl $\beta$ -cyclodextrin (HPCD) at concentrations of 1 and 2% were selected for kaolin and glacial till, respectively, based on results for batch extraction of 2,4-DNT from the same soils. During the EK experiments, greater current and electro-osmotic flow were observed for HPCD solutions than for DI water. After the completion of the EK experiments, the soils in the EK cell were extruded and the residual 2,4-DNT in the soils was determined. Less 2,4-DNT remained in the kaolin soil (up to 94% transformed) than in the glacial till soil (20% transformed) due to strong retention of 2,4-DNT by the soil organic matter in glacial till. For kaolin, less 2,4-DNT remained in the soil using HPCD solutions than using DI water. For glacial till, comparable levels of 2,4-DNT remained in the soil for both EK solutions. Since no 2,4-DNT was detected in the effluents from the EK cells, the decrease in 2,4-DNT concentration in the kaolin and glacial till soils was attributed to electrochemical transformation of 2,4-DNT to other species.

The development of water quality models, and also the nature of water quality impairment, is uniquely presented in the point source dissolved oxygen (DO) modeling completed in the Jackson River (Virginia) over the past $50\text{years}$ . Various water quality modeling studies have been completed in the Jackson River over the years starting with the earliest of modeling frameworks, the Streeter–Phelps equation (1950s and 1960s); progressing to a biochemical oxygen demand–DO model (1970s and 1990s) including diurnal photosynthetic effects (DIURNAL); a Monte Carlo DO analysis using the DIURNAL model (1990s); to the most recent modeling that is currently developing a periphyton model to assess the impact of nutrient loadings on the periphyton community and ultimately DO levels (2000). These early modeling studies were completed by such modeling forefathers as Clarence J. Velz and Donald J. O'Connor, both completing their work at academic institutions (Manhattan College and the University of Michigan) and private consulting firms (Hydroscience and HydroQual, Inc.). Interesting to note is that Earle B. Phelps taught Clarence J. Velz, Donald J. O’Connor’s eventual professor at Manhattan College. Other work completed on the river by early environmental engineers included reaeration studies by Ernest C. Tsivoglou (1966) and the first activated sludge wastewater treatment design for a pulp and paper mill by Wesley Eckenfelder (1950s). The studies investigated: how to improve existing DO conditions in the river; the effects of color reductions on diurnal DO swings; proposed upstream flow regulation effects on water quality and river temperature; and the impact of instream oxygen addition.

The potential benefits prefermentation can provide to biological nutrient removal are measured and compared to the costs of excess oxygen consumption and sludge production incurred by an activated sludge system that utilizes prefermentation, instead of primary clarification. Prefermentation was found to produce superior performance in regards to enhanced biological phosphorus removal. A lower soluble orthophosphorus effluent value [ $3.2\mathrm{mg}∕\mathrm{L}$ for the prefermented activated sludge (PAS) train versus $4.6\mathrm{mg}∕\mathrm{L}$ for the control train with primary clarification (PCAS)] and a higher percent phosphorus (% P) content of the biomass (9.0% for the PAS train versus 7.8% for the PCAS train) were both found to be statistically significant (P values of $4.26\times {10}^{-5}$ and 0.0082, respectively). In addition statistically significant improvements in denitrification rates and reduced observed yields were observed due to prefermentation. However statistically significant increases in solids inventory and in particular oxygen uptake rates offset these improvements. Waste activated sludge production was slightly higher in the PAS train but was not found to be statistically significant.

Sulfur–limestone autotrophic denitrification (SLAD) processes are very efficient for treatment of ground or surface water contaminated with nitrate. However, detailed information is not available on the interaction among some major variables on the design and performance of the SLAD process. In this study, the response surface method was used by designing a rotatable central composite test scheme with 12 SLAD column tests. A polynomial linear regression model was set up to quantitatively describe the relationship of the effluent and influent nitrate–nitrogen concentration and hydraulic retention time (HRT) in the SLAD column reactors. This model may be used for estimating the effluent nitrate–nitrogen concentration when the influent nitrate–nitrogen concentration ranges between 20 and $110\mathrm{mg}∕\mathrm{L}$ and the HRT ranges between 2 and $9\mathrm{h}$ . Based on our model and the requirement for nitrite control, we recommend that the HRT of the SLAD column reactor be kept $⩾6\mathrm{h}$ and the nitrate loading rate less than 200 g $\mathrm{N}{\mathrm{O}}_3^{-}–\mathrm{N}∕\text{day}{\mathrm{m}}^3$ media to achieve high nitrate removal efficiency $(>99\%)$ and prevent nitrite accumulation from being $>1\mathrm{mg}∕\mathrm{L}$ $\mathrm{N}{\mathrm{O}}_2^{-}–\mathrm{N}$ .

Phenol and nitrate are two major pollutants simultaneously occurring in several industrial wastewaters. In this study, a 110-day gradual enrichment of an anaerobic culture has been carried out at $25°\mathrm{C}$ in an anaerobic bioreactor for continuously treating a synthetic wastewater containing $600\mathrm{mg}∕\mathrm{L}$ phenol and $430\mathrm{mg}∕\mathrm{L}{\mathrm{NO}}_3^{-}–\mathrm{N}$ . The results showed that the enriched culture can utilize phenol as a sole electron donor and nitrate as a sole electron acceptor. At the end of the enrichment (on Day 110), 93.3% of phenol and 98.0% of ${\mathrm{NO}}_3^{-}–\mathrm{N}$ were simultaneously removed at a hydraulic retention time of $20.25\mathrm{h}$ in the anaerobic bioreactor. The removal of $1\mathrm{g}{\mathrm{NO}}_3^{-}–\mathrm{N}$ required about $3.19\mathrm{g}$ chemical oxygen demand as the electron donor. Batch tests further revealed that cresol, nitrophenol, and monochlorinated phenol (MCP) could exert detrimental influences on the treatment abilities of the enriched culture. However, the inhibitory effects of cresol were impermanent, as compared to those of nitrophenol and MCP. In order to operate the anaerobic bioreactor steadily, high concentrations of cresol should be diluted before being fed while the existence of nitrophenol and MCP in the bioreactor should be avoided.

Crude oil spillage is a major environmental pollution in the Niger–Delta area of Nigeria. The use of recycled rubber from enormous available scrap tires for pollution control of oil-polluted fresh and marine water and the attendant survival of aquatic organisms (fish) in these polluted waters was investigated. The absorption capacity of rubber particles for the oil was the same in both the oil-polluted fresh and marine waters and depended on the rubber particle size and temperature of absorption. The survival time of the fish depended on the amount of rubber added to and the dissolved oxygen (DO) concentration in the oil-polluted waters. The survival time increased from 3.5 to $7.25\mathrm{h}$ as the rubber to oil ratio was increased from 0.5 to 2.5. At a ratio of 3, the oil film on the water was no longer continuous and the survival time increased to $6,000\mathrm{h}$ . The survival time increased with the DO concentration in polluted water. In the absence of added rubber particles, the DO concentration decreased within $2\mathrm{h}$ from $5.27\mathrm{mg}∕\mathrm{L}$ to less than $3\mathrm{mg}∕\mathrm{L}$ , a value below the limit required for aquatic organism survival.