Journal of Environmental Engineering

Dissolved oxygen (DO) consumption in the sediments of natural aquatic ecosystems occurs by mass flux across the water-sediment interface. This mass flux is determined as either the rate of oxygen consumption in the sediment or the rate of DO diffusion across the diffusive sublayer. The thickness of the diffusive sublayer is determined by the flow conditions in the turbulent water column. Consequently, feedback occurs between the biochemical consumption that occurs in the sediment and the flow that occurs in the water column. Together, these conditions define the DO flux across the water-sediment interface. Benthic chambers have been used to measure this flux in field and experimental conditions. However, these measurements do not account either for the fact that the flow inside a benthic chamber is not representative of field conditions or for the DO consumption in the water column. Thus, they can provide an inaccurate estimation of the sediment DO demanded in the field. This article aims to present and discuss an approach for analyzing a time series of DO depletion inside a benthic chamber. Based on this approach, the processes related to turbulent water transport in the column are separated from the processes that characterize biochemical consumption in the sediments and the water column. Under these conditions, the parameters related to biochemical consumption in the sediments can be used to compute the expected DO demanded of the sediments in field conditions. Sediment samples from a lagoon near the Universidad de Chile campus in Santiago, the capital city of Chile, were used to illustrate the application of the proposed method. In addition, dimensionless numbers were used to define the method’s validity and limitations.

Accumulation of volatile fatty acids (VFAs) under overloading conditions in anaerobic reactors is a common problem. There is a need to stop this accumulation to improve reactor stability. In this study, propionate-, butyrate-, and acetate-degrading cultures were enriched and used as inocula in a mesophilic two-stage reactor to improve system stability. The performance of a test reactor was compared with that of a control reactor that was not seeded with specific VFA-degrading inocula under normal and overloading conditions. The reactors were fed with simulated wastewater having a chemical oxygen demand (COD) of $\mathrm{10,000}\mathrm{mg}{\mathrm{L}}^{-1}$. The test reactor inoculated with VFA-degrading cultures showed better performance in terms of methane production, COD removal, and VFA degradation. Also, after two consecutive organic shocks (influent COD $\mathrm{20,000}\mathrm{mg}{\mathrm{L}}^{-1}$) the test reactor recovered within four days and low levels of VFAs, especially propionate ($429\mathrm{mg}{\mathrm{L}}^{-1}$), were observed. In contrast, in the control reactor the concentration of VFA did not decline to preshock levels, even after five days of two consecutive shocks. PCR-denaturing gradient gel electrophoresis analysis using 16S rRNA gene amplicons also indicated a significant difference in archaeal community structure in the control and test reactors. Methanosarcinaceae was found dominant in the test reactor whereas in the control reactor an equal abundance of both Methanosaetaceae and Methanosarcinaceae was observed. Specific methanogenic activity also suggested higher acetoclastic and hydrogenotrophic activity of the sludge in the test reactor. Overall, using enriched culture as inocula resulted in a more balanced and robust methanogenic consortium and in improved system stability, with efficient degradation of the high concentration of VFAs.

The United States Army is constructing a new water-treatment facility for Fort Irwin/National Training Center in the Mojave Desert region of southern California to address existing regulatory requirements and to account for anticipated expansion at the installation. The proposed treatment, electrodialysis reversal (EDR), is anticipated to recover 92% of the influent water. The ultimate goal was to achieve 99% recovery, which required additional recovery of the EDR concentrate. This paper describes laboratory testing of conventional water-treatment methods to achieve water recovery beyond standard practice. The effectiveness of lime softening followed by secondary reverse osmosis (RO) was evaluated to treat the concentrate stream and recover additional water to approach 98%. Partial lime softening at dosages of $500-\mathrm{2,000}\mathrm{mg}/\mathrm{L}$ of hydrated lime was capable of removing hardness from simulated EDR concentrate. Adding magnesium chloride to the lime softening step increased silica removal, bringing ${\mathrm{SiO}}_2$ concentrations in the simulated EDR concentrate from 110 to $6.8\mathrm{mg}/\mathrm{L}$ at room temperature. The resulting treated water was suitable for effective reverse osmosis with a standard seawater polyamide membrane. Rejection for all of the dissolved constituents was well above 90% with the exception of arsenic, which was reduced from $50\mathrm{\mu g}/\mathrm{L}$ to levels on the order of $20\mathrm{\mu g}/\mathrm{L}$. To achieve 99% recovery, mechanical vapor recompression is being considered to further recover the concentrate from the RO unit, although this unit process was not evaluated in the research reported in this paper.

An empirical model for monitoring spatiotemporal estuarine chlorophyll concentration is proposed using Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensed data in conjunction with chlorophyll monitoring data and in situ characteristics in the mesohaline segment of the James River, Chesapeake Bay. The spatiotemporal estuarine chlorophyll monitoring model (STE Chl MM) was developed to express chlorophyll concentration with dependent variables of MODIS medium-resolution band (250 m) data and ambient water temperature in the spring (March to May) and fall (July to September). The model includes continuously monitored ambient water temperature as a transfer function representing dissolved oxygen and degree of ambient water kinetics describing fate and utilization of nutrients by the phytoplankton biomass. The STE Chl MM is comparable in performance to the conventional modeling approach that estimates chlorophyll concentration using in situ temperature and dissolved oxygen in terms of root mean square sum for error (RMSE) and $R^2$ (0.880–0.608 and 0.861–0.901, respectively). When high spectral, spatial, and temporal properties of MODIS imagery were joined with in situ data, the meso- and macroscale spatiotemporal characteristics of algal growth in the lowest tributary on the Chesapeake Bay were effectively identified.

Mobile-source emission inventories in countries such as Mexico still require empirical data to complement modeling tools because these tools are based on few local observations. In this study, emission factors (EFs) were determined for 10 light-duty gasoline-powered vehicles as a function of cruising speed under real-world driving conditions typical of the Monterrey metropolitan area, the third largest urban center in Mexico. Greater variability in the EF was found when the vehicles were operated at lower speeds, specifically at $10\mathrm{km}/\mathrm{h}$; however, above $40\mathrm{km}/\mathrm{h}$, the changes were marginal. Engine size was the factor that most influenced the emissions of ${\mathrm{CO}}_2$, which were significantly greater in vehicles with an engine size above 2 L. A reduction trend in the $\mathrm{CO}\text{-}\mathrm{to}\text{-}{\mathrm{NO}}_{\mathrm{x}}$ ratio of newer model vehicles was observed. Upon comparison of the experimental results with the results obtained from the MOBILE6.2-Mexico and the MOVES 2010a models, it was determined that the latter model better described the values of the EFs, the emission profile as a function of speed, and the $\mathrm{CO}\text{-}\mathrm{to}\text{-}{\mathrm{NO}}_{\mathrm{x}}$ ratio of the tailpipe gases.

Process control at older water reclamation plants (WRPs) can be challenging as operators work to balance higher energy costs and more stringent effluent limitations while managing fluctuating loads. To better understand WRP loading characteristics, we developed a classification system for the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) Calumet WRP by combining $k$-means cluster analysis with cross-tabulation analysis. Based on weather and influent composition characteristics, we identified 25 clusters; nine of those clusters are significant (99% confidence level) based on chi-square tests. Dry weather and middle temperature conditions after wet-weather days are common, and compared to cold-weather flows, warm-weather flows are more likely to have large precipitation events and more variation in influent quality. To explore how information about influent scenarios could inform process control and improve process efficiency, we also developed a process simulation model. The model indicates that aeration strategies for each of the nine scenarios could be modified to make it possible for the plant to operate more efficiently while still meeting effluent requirements. The approach described here can provide useful information on the frequency and duration of different types of loading, enabling WRP operators to move toward more flexible and efficient operations.

In this study, batch sorption and desorption experiments were conducted for testosterone using four agricultural soils and five clay minerals. Significant differences in sorption behavior were observed between abiotic and biotic systems. The Freundlich sorption coefficient $K_f{(\mathrm{\mu g}/\mathrm{g})/(\mathrm{\mu g}/\mathrm{mL})}^n$ ranged from 8.53 to 74.46 for soils and from 35.28 to 1,243 for clays. The maximum sorption capacity ($\mathrm{\mu g}/\mathrm{g}$) of soils ranged from 25.25 to 440.61 for soils and from 168.46 to 499.84 for clays. Correlation of the sorption model parameters with the soil properties indicated that both clay content and soil organic matter are important variables in predicting testosterone sorption behavior. Observed testosterone desorption from agricultural soils ranged from approximately 14 to 100% after three desorption cycles, and the desorption percentage decreased as the initial testosterone concentration decreased. It was determined that the temperature, ionic strength, water/soil ratio, and soil depth influenced the sorption and desorption of testosterone. Desorption significantly increased with the soil depth ($p<0.05$) and with the increase in the water/soil ratio. Temperature had an inverse effect on the sorption capacity of the soils tested. Thermodynamic calculations showed that the enthalpy change ($\mathrm{\Delta }{H}^0$) of the soils tested ranged from 12.9 to $20.7\mathrm{kJ}/\mathrm{mol}$, indicating a weak interaction between the testosterone and soil. The authors’ results suggest that additional studies on how soil particles with different size fractions affect hormones’ fate and transport are needed to determine the potential risk of testosterone leaching or runoff.

Seven cycles of operation in relation to the filling ratio, mixed liquor suspended solids (MLSS), hydraulic retention time (HRT), and temperature were studied in a pilot-scale experimental plant of a hybrid moving bed biofilm reactor-membrane bioreactor (MBBR-MBR). The aim of the present research was to study the influence of the operative variables on the behavior of a hybrid MBBR-MBR in relation to organic matter removal and nitrification activity through the kinetic constants for the autotrophic and heterotrophic biomass. Biofilm density during the present research depended on the operative variables changing from $\mathrm{4,403}\pm 188$ to $\mathrm{5,844}\pm 268\mathrm{mg}/\mathrm{L}$ of the carrier, increasing with the increase in MLSS and with the decrease in the HRT. The removal rate was higher than $87.40\pm 4.90$ and $94.88\pm 2.41\%$ for chemical oxygen demand (COD) and biological oxygen demand (BOD) ${\mathrm{BOD}}_5$, respectively, increasing process efficiency with the MLSS, HRT, and temperature. Yield for heterotrophic biomass ($Y_H$) was between $0.506\pm 0.004$ and $0.714\pm 0.076\mathrm{mg}{\mathrm{COD}}_{\mathrm{formed}}/\mathrm{mg}{\mathrm{COD}}_{\mathrm{oxidized}}$, and ${\mu }_{H,\mathrm{máx}}$ of between $0.0245\pm 0.0006$ and $0.056\pm 0.012{\mathrm{h}}^{-1}$. The minimum values of efficiencies obtained for ammonia and total nitrogen were $40.40\pm 20.84$ and $8.75\pm 5.09\%$, respectively, presenting yield for autotrophic biomass (${\mathrm{Y}}_A$) between $0.23\pm 0.01$ and $0.51\pm 0.12\mathrm{mg}$ ${\mathrm{COD}}_{\text{formed}}{/\mathrm{mgN}}_{\mathrm{oxidized}}$, and ${\mu }_{A,\mathrm{máx}}$ varying from $0.0816\pm 0.063$ to $0.3083\pm 0.1199{\mathrm{days}}^{-1}$. Considering the results obtained in this research, hybrid MBBR-MBR could be a reliable technology to reduce the energy demands and fouling problems associated with conventional MBR technology.

A new kind of magnetic porous carrier named magnetic air stone (MAS) was prepared by coating air stone (AS) with ferrofluid nanoparticles. Characterization by X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer reveals that ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles embedded in air stone were paramagnetic with saturation magnetization of $21\mathrm{emu}/\mathrm{g}$. Moreover, an analysis of biofilm formation on MAS was run. The results show that dissolved oxygen increased 50%, mass of the biofilm increased 32%, and biofilm adhesion increased 21%. The main reason for the enhancement of dissolved oxygen was the sorption performance of MAS for removing ions from aqueous solution. Biofilm formation acceleration was due to the ferrofluid nanoparticles used to modify AS into MAS, which are hydrophobic, and hydrophobic cells readily adhere to hydrophobic surfaces. This study demonstrated that the magnetic air stone developed in our research project could be potentially used as a cost-effective carrier for municipal wastewater treatment.

On January 9, 2014, an estimated 37,854 L (10,000 gal.) of 4-methycyclohexane methanol (MCHM) and propylene glycol phenyl ether, solvents used in coal processing, leaked from a ruptured container into the Elk River. The spill, just 1.61 km (1 mi) upstream from a water-treatment plant, forced officials to ban residents and businesses in nine West Virginia counties from using the water for anything other than flushing toilets or fighting fires. An estimated 300,000 West Virginia residents were affected by the spill. This paper reports on the modeling efforts undertaken to forecast time of travel and concentration of MCHM as the plume traveled downstream toward the Greater Cincinnati Water Works (GCWW) intake. The issues addressed include the flow regime, source term describing the spill event, use of real-time and forecast streamflow, and comparison of model results with observations at Charleston (West Virginia), Huntington (West Virginia), and the GCWW intake. The incident-command tool for drinking-water protection (ICWater) was used to model time of travel and concentration of MCHM. Downstream tracing was initiated at the spill site to forecast the location of the leading edge, peak concentration, and trailing edge of the plume for drinking-water intakes as far downstream as 402 km (250 mi).

The effect of nanoparticle silver (AgNP) in a sequencing batch reactor (SBR) removing phosphorus and ammonia was analyzed. The amount of $500\mathrm{\mu g}/\mathrm{L}$ of AgNP did not significantly change the soluble chemical oxygen demand or specific oxygen uptake rates during the batch tests. Furthermore, $300\mathrm{\mu g}/\mathrm{L}$ of AgNP had no effect on phosphorus, ammonia, or chemical oxygen demand removal during continuous dosing. Analysis by inductively coupled plasma-mass spectrometry determined that the lab-scale SBR removed over 80% of influent AgNP during continuous dosing. It was also determined that the North End Water Pollution Control Centre in Winnipeg, Canada, removed just under 50% of influent AgNP, and that half of the reduction occurred before secondary treatment.