Journal of Environmental Engineering

The behavior of a University of Cape Town (UCT) membrane bioreactor (MBR) system was investigated for use in biological nutrient removal from real wastewater. The pilot plant was in operation for a period of 165 days, during which an extensive data gathering campaign was conducted. The pilot plant was started up by inoculating it with activated sludge from a nearby wastewater treatment plant, and it was fed by real municipal wastewater characterized by high organic nitrogen concentrations attributable to discharges from industrial wastewater and sporadic landfill leachate. Carbon and biological nutrient removal processes, a sludge production process, and a membrane fouling mechanism were analyzed and discussed. The organic nitrogen levels, which were higher than typical values for municipal wastewater, caused ammonification phenomena. This led to intense nitrification and denitrification activities. The pilot plant showed satisfactory efficiency in terms of average removal efficiencies for both carbon and nitrogen. However, lower efficiencies were recorded for phosphorus removal as an indirect effect of the intense denitrifying activity of the phosphorus-accumulating organisms in the anoxic tank. Membrane fouling was mainly of reversible nature, and low values of soluble microbial product were measured.

The transport of proteinate-capped silver nanoparticles (AgNPs) was evaluated in well-defined water-saturated Ottawa sand over a range of water chemistry conditions and sand particle sizes. AgNP retention in the columns increased with solution ionic strength and reductions in mean sand particle diameter, with the influence from ionic strength having the more significant effect on AgNP retention. Increased retention of AgNPs in the porous media with increasing ionic strength appears to be caused by increased nanoparticle–sand interaction rather than increased aggregation of nanoparticles with a resulting increase in physical filtration. Effluent AgNP concentrations over time were effectively simulated using the transient, one-dimensional advection–dispersion equation with maximum attachment capacity ($S_{\max }$) and attachment/detachment coefficients ($k_{\mathrm{att}}$ and $k_{\det }$). In almost all cases, significant amounts of AgNPs exited the columns, suggesting that AgNPs are relatively mobile in sand. At ionic strengths typical of natural groundwater (e.g., 10 mM), only 30–50% of the AgNPs were retained.

The purpose of this research is to evaluate the aptitude of two residual soils for the remediation of groundwater contaminated by arsenic (As). Batch and soil column tests were performed to evaluate removal of As from water. Permeable soil columns were prepared with mixtures of sand (90%) and two lateritic soils (10%). Results showed that removal of As in batch tests ranged from 95–99% when using a solid-liquid ratio equal to $1:10$. Experimental results obtained in the soil column tests and calibrated simulation models showed that the amount of water that can be decontaminated depends on the initial As concentration and the flow rate. Maximum adsorption capacities in bath test and removal efficiency in soil columns tests clearly relates with the amount of iron compounds in the solid phase. The quality of residual soil samples are related to a high iron content to favor As removal and low clay-size particle content to achieve acceptable flow rates for water purification in low-cost permeable filters and permeable reactive barriers.

Two conceivable types of mathematical model, i.e., exponential or hyperbolic, that describe the sequential pickup of a contaminant from a substrate upon successive treatment with magnetic particles have been developed and tested. The models were applied to sets of experimental data spanning extremes of system behavior. Allowance was made within each model to account for departure from ideality. The nonideal hyperbolic model was identified as being the one that can be better applied to the experimental data. The successful application of this model to a given data set enables a pickup efficiency that is based on all of the available experimental data to be accurately determined. Thus, it was found that the pickup efficiency is highly correlated with one of the fitting parameters introduced to account for nonidealized behavior. The ability to accurately assess removal efficiency in the sequential pickup of chemical contaminants by magnetic particles is essential for the optimization of this technology for practical application in the field, particularly with respect to environmental remediation.

Tetrachloroethylene (PCE) is a common contaminant in the groundwater. The mechanism and pathway of PCE dechlorination by zero-valent iron (Fe) in the presence of Cu (Fe–Cu), alone or with powdered activated carbon ($\text{Fe–Cu}/\mathrm{C}$) were studied. The experimental results have demonstrated that (1) $\text{Fe–Cu}/\mathrm{C}$ produced higher PCE removal efficiency than adsorption by C or dechlorination by Fe or Fe–Cu due to adsorption and the synergetic effects of Fe–Cu and Fe–C microelectrodes, (2) the batch PCE dechlorination was most rapid at the neutral pH, (3) $\text{Fe–Cu}/\mathrm{C}$ dechlorination resulted in smaller and more porous Fe particles, and (4) PCE was sequentially dechlorinated to form trichloroethylene, dichloroethylenes (cis, 1,1, and trans isomers), methylene chloride, and vinyl chloride. $\text{Fe–Cu}/\mathrm{C}$ dechlorination is an attractive technology for the remediation of PCE-contaminated groundwater.

The degradation of chlortetracycline hydrochloride in aqueous medium (initial concentration of $10\mathrm{mg}/\mathrm{L}$) has been studied by electrooxidation process using $\mathrm{Ti}/{\mathrm{PbO}}_2$ and $\mathrm{Ti}/{\mathrm{IrO}}_2$ anode electrodes. The performance of the electrolytic cell resulted from its capability of reacting on pollutants by using both effects of electrolysis. Indeed, the organic pollutants can be destroyed at the electrode surface where hydroxyl radicals are generated (direct effect), and they can be simultaneously oxidized in solution by means of active chlorine (indirect effect). Different operating parameters, such as current density, reaction time, and temperature, were investigated. The optimal experimental parameters for chlortetracycline degradation have been investigated by using a central composite design (CCD) methodology. It has been demonstrated that under the optimal conditions determined by this method, electrooxidation can economically be applied to oxidize chlortetracycline (96% of degradation for a total cost of US$3.23 per gram of chlortetracycline removed).

Green roofs are a technology used to control the quantity of the storm-water runoff and reduce energy consumption. Questions remain about their effect on water quality. Total suspended solids and turbidity are of the main parameters for water quality. This study investigated whether turbidity could produce a satisfactory estimation for total suspended solids (TSS) in the storm-water runoff from green roofs. Measuring turbidity is much faster than measuring TSS; a log-linear model showed strong positive correlation between TSS and turbidity ($R^2=0.9374$) with a regression equation of [$\ln (\mathrm{TSS})=0.979\ln (\mathrm{Turb}\mathrm{.})+0.574$]. This equation shows that turbidity is a suitable monitoring parameter for TSS when TSS sampling and testing are impractical or not feasible.

Fertilized highway slopes constitute nonpoint sources of nitrogenous nutrients that are degrading the surface water and groundwater resources. This paper presents the results of simulated rainfall experiments conducted on a plot-scale test bed (slope-adjustable) that was fully exposed to weather for closely representing the conditions of a fertilized turf-covered highway slope in Florida. Thirty-six tests were conducted on three slopes (25, 33, and 50%), simulating two rainfall intensities (12.5 and $25\mathrm{mm}/\mathrm{h}$). The soils used were fine sand (AASHTO A-3 class) and silty sand (AASHTO A-2-4 class). Following the local highway practices, the tests were conducted after compacting the soils and establishing Argentine Bahia turf over A-3 soils and Pensacola Bahia turf over A-2-4 soils. Two fertilizers were used: a quick release (QR) 10-10-10 and a slow release (SR) 16-0-8. Weather conditions varied considerably during the duration of the project, affecting soil moisture, soil—grass—nutrient interactions, and the distribution of applied rainfall. These weather effects and differences in soil and turf properties resulted in variations of surface runoff percentages and total nitrogen (TN) concentrations in surface runoff and seepage. Because of the differences in the availability of washable TN, the A-3 soil (fine sand) resulted in lower TN losses than the A-2-4 soil (silty sand). The losses of TN were influenced by the intensity and slope of the rainfall, but the differences were significant ($\alpha =0.05$) in only three of the eight cases analyzed. In the case of A-3 soils, the test series conducted during late fall resulted in higher TN losses than in the test series conducted during early fall season. These results suggest that the TN losses were lower where the soil allowed ready entry of the TN into soil, and in cases of less runoff. The fertilizer type did not result in a significant difference ($\alpha =0.05$) in TN loss. The results of all test series and ANOVA suggest that the slow release fertilizers did not result in lower TN losses than the QR fertilizers.

Sedimentation-filtration (SedFil) basins are one of the storm-water best management practices (BMPs) that are intended to mitigate water quality problems in urban creeks and rivers. A new physically based model of variably saturated flows was developed for simulating flow and sediment in SedFils within the Soil and Water Assessment Tool (SWAT). The integrated SWAT-SedFil model allows for simulation of unsaturated flow in the filtration basin during small storms and fully saturated flow. Unsaturated flow was modeled using a modified Green and Ampt equation, and saturated flow was simulated with Darcy’s Law. Unsaturated flow comprises only a small fraction of large storm events; however, many regular storms are small and may not generate sufficient runoff to create a saturated flow in the filtration basin. Therefore, the combined unsaturated/saturated flow approach for modeling SedFils improved the accuracy of the model, especially in long-term evaluations. The model performs well with respect to estimating storm-water and sediment at the inlet and outlet of a SedFil.

A computational model was developed to study the hydrodynamic characteristics of a new multienvironment air-lift bioreactor. This model study considerably expands on the laboratory experiments by exploring the hydrodynamic characteristics of multiple combinations of geometries and operating conditions and by providing a visual illustration of the liquid-phase flow patterns. The model was first tested against preliminary laboratory results to ensure its validity. This included comparing two simplified geometries for the three-disc prototype air sparger assembly to determine which led to results closer to laboratory measurements. A torus geometry was found to better represent the prototype than a single disc. The model was modified to evaluate the hydrodynamic characteristics of alternative operating conditions and physical geometries beyond what would be possible in the laboratory. The flow pattern in the outer clarifier zone was shown to be very sensitive to the geometry of the bioreactor wall separating the clarifier from the inner microaerophilic zone. Establishing a smooth, upward flow pattern in the clarifier was shown to be possible only when the clarifier was sufficiently shielded from the circulation in the anoxic cone below. Further research is needed to quantify the effect of hydrodynamic characteristics on contaminant removal efficiency.

The provision of technologies that can meet increasingly stringent wastewater discharge standards while reducing energy, operation, and maintenance costs is vital to government, local authorities, industry, and the public at large. The air suction flow biofilm reactor (ASF-BR) is a novel batch biofilm technology suitable for treating wastewaters from municipal, industrial, and agricultural sources. This paper presents an investigation into the performance of a laboratory-scale ASF-BR in treating municipal-strength wastewater over two operational periods—Phase 1 and Phase 2. Phase 1 concentrated on organic carbon removal and nitrification, whereas Phase 2 included an anoxic step to achieve denitrification. The operation of the unit was also investigated by monitoring organic carbon and nitrogen in the reactors during a number of treatment cycles. In Phases 1 and 2 (29 and 124 days of steady-state operation, respectively) of this laboratory study, using a municipal-strength synthetic wastewater, the average influent total chemical oxygen demand (${\mathrm{COD}}_t$) was 288 and $313\mathrm{mg}/\mathrm{L}$, whereas the average influent filtered COD (${\mathrm{COD}}_f$) was 127 and $148\mathrm{mg}/\mathrm{L}$, respectively. The average ${\mathrm{COD}}_f$ removal rates were 92 and 79% during Phases 1 and 2, respectively. Average nitrogen removals during Phases 1 and 2 of greater than 95% ammonium nitrogen (${\mathrm{NH}}_4\text{-}\mathrm{N}$) were achieved. By reducing the number of pumping cycles during the aerobic step, the overall energy consumed was reduced by 37.5% during Phase 2 while achieving similar results. On the basis of these positive initial results, a pilot-scale reactor has been constructed at a local wastewater-treatment facility, and commissioning of the unit is currently underway.

This study aims to establish a new technology for the advanced treatment of vitamin C (VC) wastewater by coupling electrochemical oxidation (EO) and an integrated bioreactor. Characteristics of organic compounds in the effluent from biotreatment of VC wastewater were analyzed. EO was used to break the chromophore functional groups of these organic compounds and improve biodegradability of the effluent. The subsequent integrated bioreactor was proposed to further degrade organic compounds in the effluent from the EO. The optimum operation parameters of this combined technology and the effect of cosubstrate on the removals of color, chemical oxygen demand (COD), and nitrogen were investigated. EO could remove color with the maximum removal of 183° and improve the biochemical oxygen demand-to-COD ratio effectively from 0.07 to 0.24. Effluent COD and color of the integrated bioreactor decreased from $111.4\mathrm{mg}/\mathrm{L}$ and 60° without glucose addition to $100.9\mathrm{mg}/\mathrm{L}$ and 50° with glucose addition. Concomitantly, total nitrogen removal efficiency increased sharply from 20.2% to 84.2%. Infrared spectra showed that the combined technology removed COD and color by breaking chromophoric functional groups. The combination of EO and integrated bioreactor could be an effective, sustainable, and nonsecondary pollution technology for the advanced treatment of VC wastewater.

Vinegar fermentation wastewater with an initial chemical oxygen demand (COD) content of $33.16\mathrm{g}·{\mathrm{L}}^{-1}$ was subjected to electrohydrolysis using aluminium, copper, and stainless-steel electrodes for hydrogen gas production. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (2,098 ml), hydrogen yield ($\mathrm{1,210}\mathrm{ml}{\mathrm{H}}_2{\mathrm{g}}^{-1}\mathrm{COD}$), hydrogen formation rate ($525\mathrm{ml}·{\mathrm{d}}^{-1}$), percent hydrogen (99.5%) in the gas phase, percent COD removal (12%), and energy efficiency (21.3%) was obtained with the aluminium electrode. Hydrogen gas production by water electrolysis was 260 ml with the Al electrode, and wastewater control resulted in nearly $23\mathrm{ml}{\mathrm{H}}_2$ in 96 h. Hydrogen gas was produced by reaction of ($\mathrm{H}+$) ions released from acetic acid and electrons provided by DC current. Aluminium electrode was the most suitable one among the others tested.

Biosorption is an effective and economic method to treat wastewater containing low concentrations of uranium pollutants. In this study, banyan leaves (BLs) were used as a biosorbent to adsorb uranium ions. The biosorption behavior, thermodynamics, and kinetics of this adsorption process, as well as its mechanism, were investigated. The results indicated that the optimal adsorption effect was achieved when the initial pH was 3.0, the initial uranium concentration was $100\mathrm{mg}{\mathrm{L}}^{-1}$, the absorbent dosage was $5\mathrm{g}{\mathrm{L}}^{-1}$, and the temperature was chosen to be 293 K. The biosorption rate could be described better by a pseudo-second-order model than a pseudo-first-order model, an Elovich kinetic model, and a double-constant speed kinetic model. The adsorption of uranium(VI) ions proceeded very rapidly in the first 30 min, which subsequently slowed down, and finally reached equilibrium after 50 min. The biosorption isotherm of uranium adsorbed onto BLs could be described better by Freundlich isotherm than Langmuir and Temkin isotherms. This pattern of uranium adsorption onto BL was not achieved by single-molecule form, but rather by multiple forms of adsorption. The thermodynamics parameters, namely, $\mathrm{\Delta }{H}^0$, $\mathrm{\Delta }{S}^0$, and $\mathrm{\Delta }{G}^0$, of adsorption of uranium(VI) ions onto BLs were calculated according to the results of the experiment, which revealed that the biosorption processes were both endothermic and spontaneous. The authors investigated the active sites of BLs for biosorption, and the results proved that $-\mathrm{OH}$, $\mathrm{C}=\mathrm{O}$, $\mathrm{P}-\mathrm{O}$, and $\mathrm{Si}=\mathrm{O}$ played an important role in biosorption.

The coal mining operation in the Razi mine of the Golestan Province, northeast Iran, has slightly disturbed the balance of the existing geowater system, which may have a long-term environmental impact if no attempt is made at considering such environmental problems. Prediction of rare earth elements (REEs) in mine drainages is a major task in developing an appropriate remediation strategy because high concentrations of REEs may be harmful to human beings and animals. Expert systems are broadly used in many applications. In this paper, a general regression neural network (GRNN) method has been chosen as an easy-to-use tool in order to predict REEs in neutral alkaline mine drainage (NAMD) of the Razi coal mine that contains a low concentration of REEs (varying between 2.0 and $3.09\mathrm{\mu }\mathrm{g}/\mathrm{L}$) and high levels of sulphate ($2,100\mathrm{mg}/\mathrm{L}$), bicarbonate ($1,575\mathrm{mg}/\mathrm{L}$), and pH (about 9). The pH and ${\mathrm{SO}}_4^{2-}$ concentration of NAMD were the main constituents used for REE prediction. To evaluate the accuracy of the GRNN method, the hydrogeochemical data measured in the study area and those data sets available in the literature were considered, and the results were compared with the ones obtained by using the multiple linear regression (MLR) technique. The results show that the GRNN method gives better and more realistic results than the MLR method. The correlation coefficients between the predicted and measured REEs by the GRNN method for train and test data sets were 0.99 and 0.99; describing the high capability of the GRNN method in REE prediction. However, the MLR method results in physically meaningless negative predictions and low correlation coefficient.

Dissolved oxygen (DO) concentration is an important water quality parameter. This paper studies the increase of DO concentration in water by air injection into a horizontal pipe flow. A 3D computational fluid dynamics model was employed to compute the water and bubble mixture flow with a DO transport model. Experiments were also conducted to validate the mathematical model. A relative saturation coefficient relationship was developed with air bubble volume fraction and travel time. An oxygen absorption efficiency is defined, and its relationship with the inlet DO concentration, air bubble volume fraction, and travel time was discussed.

Relatively high concentrations of antibiotic-resistant bacteria are often found in the anthropogenically impacted aquatic environment. This is an emerging concern, and it is not clear which mechanism is responsible: external input, selection by antibiotics, or coselection by metals. To explore these hypotheses, a simple mechanistic mathematical model is developed, which includes state variables for antibiotic and metal toxicants, susceptible and resistant bacteria, and particulate and dissolved organic matter (DOM). The toxicants partition to solids and DOM. Bacteria growth is limited by DOM, susceptible bacteria are inhibited by toxicants, and resistant bacteria incur a metabolic cost of carrying the resistance. Tetracycline resistance in the Poudre River in Colorado is considered as a case study. The model is used to predict the concentration of resistant bacteria, and the output is compared with observations from the literature. External input and selection by tetracyclines cannot explain the observed density of resistant bacteria. Comparison of observed ambient concentrations and bacteria chronic toxicity values suggests that Cu, Zn, and Se may exert significant toxicity on the susceptible bacteria. Model simulations with Cu and Zn reproduce the magnitude and general spatial pattern of the observations, which shows that coselection by those metals is plausible; Se does not exert sufficient toxicity. Coselection of antibiotic resistance by metals may be significant, considering the widespread pollution of surface waters by metals.