Journal of Environmental Engineering

The potential effectiveness and time scales for monitored natural attenuation of polychlorinated biphenyl (PCB)-contaminated sediments are difficult to predict. Little is known about the depth- and time-dependent dechlorination of PCBs and the microbial communities that give rise to dechlorination processes. The present work describes evaluation of a single sediment core from the Grasse River (Massena, New York) using a combination of molecular techniques to provide detailed insight of dechlorination potential. Primers specific for 16S rRNA genes from the bacterial domains, putative dechlorinating organisms in the phylum Chloroflexi, the Dehalococcoides genus, and two PCB degrading organism strains, o-17 and DF-1, were used to construct phylogenetic microbial community profiles using denaturing gradient gel electrophoresis (DGGE). Further, quantitative polymerase chain reaction (Q-PCR) was used to estimate population numbers of putative PCB-related organisms in the sediments along the depth of the core. PCB congener analysis was used in conjunction with Molar Dechlorination Product Ratio (MDPR, the sum of five PCB end products over total PCBs), chlorine content, chlorine per biphenyl (CPB), and PCB composition changes with depth in the core to evaluate the extent of dechlorination. All core samples contained populations of Chloroflexi, Dehalococcoides, and o-17/DF-1 related organisms, representing the first report of putative dechlorinating organisms with depth in PCB-contaminated sediment. A clear pattern of dechlorination was observed, with deeper (older) sediments showing more extensive dechlorination and middle sediments showing less dechlorination. The evaluation of putative dechlorinating bacterial populations in conjunction with congener shifts resulting from dechlorination enables a critical association that may lead to better prediction of successful natural attenuation of PCB-contaminated sediment.

Simulated groundwater solutions contaminated with trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound (US) and ultraviolet light (UV) sources. The treatment process was operated using UV or US individually, and UV and US concurrently (UVUS). The solutions contaminated with TCE or PCE were exposed to UV light emitted from Hg-arc lamps surrounding the quartz reactor vessel, and to acoustic waves from a US horn located at the bottom of the reactor vessel. The rate constants ($k$) of photolysis by UV, sonolysis by US, and photosonolysis by UVUS were evaluated using a mathematical model in conjunction with a nonlinear regression analysis. The removal efficiencies ($E$) for the UV, US, and UVUS treatments were also determined. For TCE, the US rate constant ($k_{\mathrm{us}}=0.016\pm 0.010{\min }^{-1}$) and the UV rate constant ($k_{\mathrm{uv}}=0.076\pm 0.004{\min }^{-1}$) yield the theoretical additive rate constant ($k_{\mathrm{ad}}$) of $0.092{\min }^{-1}$, whereas the observed UVUS rate constant ($k_{\mathrm{uvus}}$) is $0.110\pm 0.002{\min }^{-1}$. Furthermore, the efficiency of the US treatment ($E_{\mathrm{us}}=0.299$) and of the UV treatment ($E_{\mathrm{uv}}=0.664$) gives the theoretical additive efficiency ($E_{\mathrm{ad}}$) of 0.706, whereas the observed UVUS efficiency ($E_{\mathrm{uvus}}$) is 0.741. For PCE, $k_{\mathrm{ad}}$ and $k_{\mathrm{uvus}}$ are 0.324 and $0.698{\min }^{\mathrm{-1}}$, respectively, whereas $E_{\mathrm{ad}}$ and $E_{\mathrm{uvus}}$ are 0.894 and 0.948, respectively. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is likely synergistic.

A new sample collection system was developed to improve the representation of sediment entrained in urban storm water by integrating water quality samples from the entire water column. The depth-integrated sampler arm (DISA) was able to mitigate sediment stratification bias in storm water, thereby improving the characterization of suspended-sediment concentration and particle size distribution at three independent study locations. Use of the DISA decreased variability, which improved statistical regression to predict particle size distribution using surrogate environmental parameters, such as precipitation depth and intensity. The performance of this statistical modeling technique was compared to results using traditional fixed-point sampling methods and was found to perform better. When environmental parameters can be used to predict particle size distributions, environmental managers have more options when characterizing concentrations, loads, and particle size distributions in urban runoff.

In a pulp and paper mill, the highly colored wastewater generated from the pulping process requires pretreatment before the biological purification process because of the presence of recalcitrant lingo-cellulosic compounds. For the present study, the black liquor was prepared in the laboratory by digesting the sugarcane baggase using the soda process, which was further diluted before use in the experimental study. The wastewater [$\mathrm{pH}=13.0$, chemical oxygen demand $(\mathrm{COD})=5,120\mathrm{mg}/\mathrm{L}$] was treated by two processes: wet oxidation (WO) (both noncatalytic and catalytic) and coagulation. Catalytic WO (CWO) experiments were conducted in the presence of 60% $\mathrm{CuO}/40\%$ ${\mathrm{CeO}}_2$ at temperatures ranging from 130 to 170°C and total pressures of 0.95 MPa. During the CWO process, the maximum COD and color removals were found to be approximately 51 and 71%, respectively. Coagulation followed by noncatalytic WO exhibited the best performance with overall COD and color reductions of approximately 77.5 and 87%, respectively. The biodegradability of the wastewater was increased to 0.60 and 0.96 after CWO and combined treatment, respectively, from an initial value of 0.22.

With an ever-increasing demand for phosphate-based fertilizer, new sustainable sources of phosphorus are warranted. Recent technologies have successfully demonstrated the possibility of recovering phosphorus from wastewater-treatment plants as struvite, which is also a ready-made, slow-release fertilizer. However, process parameters that influence the operation of crystallizers and production of good-quality struvite pellets have yet to be fully understood. This paper discusses the influence of process parameters on the characteristics of struvite pellets. Among the various process parameters, upflow velocity and flow patterns in the crystallizer were found to influence the size and shape of the pellets. In the range (1.5–7.1) tested, supersaturation ratio did not appear to influence the crushing strength of the pellets formed. Midsized pellets, in the 2.0–2.5-mm range, exhibited the highest crushing strengths. Higher magnesium concentration in the crystallizer was able to increase the crushing strength of struvite pellets by as much as 15–27%.

Forty-three bioretention cells (BRCs) throughout North Carolina were assessed for maintenance needs, soil media composition, and as-built surface storage volume to determine whether BRCs are typically constructed per their intended design specifications. Visual inspections identified hydric soils and redoximorphic features (indicators of prolonged anaerobic conditions) and quantified the occurrence of issues requiring maintenance. Particle-size distribution and permeability of soil media were measured at multiple locations within each cell, and topographic surveys were performed to calculate as-built surface storage volumes. Field drawdown tests were used to verify permeability measurements and assess overall BRC function. Of the studied cells, 22% contained redoximorphic features in the upper 30 cm, and 53% were in need of maintenance due to one or more factors. Although 71% of assessed cells failed to meet soil media particle-size distribution specifications, 98% of BRCs contained media with adequate or high permeability. Over half (65%) of cells were undersized vis-à-vis intended design, with 53% exhibiting moderately or severely undersized surface storage capacity. Discrepancies in average ponding depth and incorporation of inspection/maintenance programs significantly influenced the accuracy of as-built BRC storage volume; therefore, it is important for inspectors to verify that the bed elevations of BRCs have been accurately graded. Despite being typically undersized, it was concluded that most observed bioretention cells are meeting the hydrologic goals of North Carolina standards.

The operating energy efficiency of the Ulu Pandan membrane bioreactor plant is optimized by artificial neural network (ANN) and bioprocess models. The ANN model mines historical plant data to uncover optimal operating settings. Historical plant data indicate that adjusting the membrane scouring aeration cycle will lead to direct energy savings. The ANN model concurs and shows the same correlation. Changes to plant operations carry substantial risks to the stability of the plant and place limitations on the range of operational variations. A plant risk assessment is conducted to ascertain the risk proposition for the adjustment of operating parameters. The bioprocess model investigates the underlying biological treatment mechanisms to identify the impact of the solids retention time on the volatile suspended solids, soluble microbial products, and endogenous decay coefficient. Results of the modeling show qualitatively good agreement with measured operating data. The concentrations of volatile suspended solids, soluble microbial products, and endogenous decay coefficient are shown to be sensitive to the system solids retention time.

Vertical-flow constructed wetlands were investigated for ammonium and nitrate removal from synthetic wastewater in bench-scale wetland columns. Total ammonia and nitrate were measured as wastewater and fed through planted and unplanted columns over three 4-week phases: downflow, upflow, and downflow-upflow in series. Mass balance results showed that downflow columns removed $>90\%$ of influent ammonium, regardless of vegetation. Unplanted downflow columns removed 15% of nitrate and 14% of total nitrogen. Planted downflow columns removed only 1% of nitrate and total nitrogen. Unplanted upflow columns removed 55% of ammonium, 50% nitrate, and 31% of total nitrogen, whereas planted upflow columns removed 59, 60, and 40% of nitrogen species, respectively. For downflow-upflow columns in series, unplanted columns removed 79% of the ammonium, 1% of nitrate, and 4% of total nitrogen. In-series planted columns removed 93, 62, and 59%, respectively. These results suggest that downflow wetlands may be more appropriate for ammonium removal. Upflow wetlands achieve the best nitrate removal. For total nitrogen removal, downflow-upflow in-series wetlands may be better. Plants significantly improve nitrogen removal rates.

Urban runoff adversely impacts cold-water stream environments due to sporadic fluxes of thermally enriched runoff. This adversely impacts tourism in regions that support trout and salmon streams. Research on storm water control measures (SCMs) has shown that meeting the 21°C trout threshold is not consistently feasible with current SCM technologies. Thus, it is important to consider other factors in storm water temperature management, such as catchment characteristics. Median and maximum runoff temperatures from a shaded parking lot were consistently lower than those from a nearby unshaded lot. This suggests the need to implement a tree canopy cover in trout-sensitive catchments. A light-colored chip seal pavement was compared to a traditional hot-mix asphalt pavement; the light-colored chip seal produced median storm water temperatures that were 1.4°C lower than the standard hot-mix asphalt. It was shown that runoff temperature measurement location is critical when evaluating SCM performance, and that underground conveyances can substantially reduce runoff temperature.