Journal of Environmental Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

The aim of this work was to study the supercritical water (SCW) regeneration of phenol-saturated activated carbon (AC) with the ${\mathrm{H}}_2{\mathrm{O}}_2$ and alkali metal catalyst (${\mathrm{Na}}_2{\mathrm{CO}}_3$, NaOH, ${\mathrm{K}}_2{\mathrm{CO}}_3$, and KOH) addition. The results showed that SCW could effectively regenerate AC in the 385–425°C range without any additives, but large and small amounts of phenol and dibenzofuran were present in the liquid phase, respectively, which would result in secondary pollution. The ${\mathrm{H}}_2{\mathrm{O}}_2$ addition enhanced the decomposition of phenol and increased the ${\mathrm{CO}}_2$ yield. With the addition of ${\mathrm{H}}_2{\mathrm{O}}_2$ and an alkali metal catalyst, SCW further decreased the phenol and dibenzofuran yields but increased the ${\mathrm{H}}_2$ and ${\mathrm{CO}}_2$ yields. Active component-supported (Cu-Ce-O, Fe-Ce-O, Ni-Zn-Pt, and Ni-Co-Pt) AC adsorbents might have decomposed some of the phenol during the phenol adsorption process, which resulted in relatively small amounts of phenol adsorbed on the AC and a decrease of the liquid (phenol and dibenzofuran) and gaseous (${\mathrm{H}}_2$ and ${\mathrm{CO}}_2$) yields. SCW regeneration increased the surface area and pore volume of the AC and raised the adsorption capacity. The ${\mathrm{H}}_2{\mathrm{O}}_2$ and alkali metal catalyst addition can be used to achieve the rapid, efficient, and harmless regeneration of AC in SCW at a lower temperature (385°C).

The Persian Gulf (also known as Arabian Gulf) is surrounded by desalination plants with about 50% of worldwide capacity to desalinate seawater. Most of these plants dispose of hypersaline effluent (brine) via surface and nearshore outfall into the Gulf. Because energy for desalination increases with seawater salinity, buildup of salt in brine endangers potable water supply there. Brine also contains metals and chemicals (foreign to the marine environment) that have adverse effects on marine ecosystems. Here, for the first time, brine is introduced into Gulf evaporation-driven residual circulation, which controls subbasin flushing, to quantify brine impact on salinity at basin and regional scales. Salt buildup increased mean annual basin salinity ($40.5\mathrm{g}/\mathrm{kg}$) by only $0.43\mathrm{g}/\mathrm{kg}$, which confirms that basin salinity is insensitive to brine. But regional sensitivity to brine is significant, especially in the southwestern Gulf region near the Arabian coast, where the largest salt buildup raised salinity by about $4.3\mathrm{g}/\mathrm{kg}$. The results of this study suggests a significant role for brine outfall position in determining brine impact on regional salt levels.

Water quality is a critical factor in the treatment of Microcystis aeruginosa–contaminated water sources. In this paper, we report on a pressure pretreatment method that is safer than the traditional preoxidation treatment for the removal of Microcystis aeruginosa from water obtained from Taihu Lake in China. The experimental results indicated that the removal efficiency of Microcystis aeruginosa was significantly improved when the water was pressurized at 0.3–0.7 MPa for 1 min, and the optimal removal efficiency was obtained at a pressure of 0.7 MPa. The removal efficiency of Microcystis aeruginosa by direct coagulation and sedimentation without a pretreatment was only 56.3%, whereas the pretreatments of $2\mathrm{mg}·{\mathrm{L}}^{-1}$ chlorine oxidation for 30 min, $2\mathrm{mg}·{\mathrm{L}}^{-1}{\mathrm{KMnO}}_4$ oxidation for 30 min, and a prepressure treatment at 0.7 MPa for 1 min resulted in an increase in the removal efficiency to 68.4%, 72.1%, and 90.5%, respectively. The chlorine preoxidation increased the concentrations of the microcystins, dissolved organic carbon (DOC), and disinfection byproducts of the treated water; the ${\mathrm{KMnO}}_4$ preoxidation slightly increased the DOC and byproducts of the treated water; whereas the prepressure treatment did not increase the microcystin concentration but reduced the concentrations of the DOC and disinfection byproducts in the treated water. Therefore, the relative ranking of the methods in terms of water quality based on the concentration change of the microcystins, DOC, and byproducts following treatment was prepressure coagulation and sedimentation (PCS) > direct coagulation and sedimentation without a pretreatment (CS) > ${\mathrm{KMnO}}_4$ preoxidation coagulation and sedimentation (${\mathrm{KMnO}}_4$ OCS) > chlorine preoxidation coagulation and sedimentation (chlorine OCS).

The selection of a natural bacterial consortium from an activated sludge system and the verification of the capability of these organisms for hormone biodegradation are important to the wastewater treatment process. An enrichment aerobic reactor was seeded with activated sludge and synthetic wastewater with estrone, 17β-estradiol, and 17α-ethynylestradiol, and hormones were used as the sole external carbon sources. From 16S rRNA sequencing analyses, the entire structure of the bacterial community and the bacterial genera present in the system were identified. The enrichment, obtained from the supply of hormones in the system, made it possible to obtain a bacterial consortium able to perform the degradation of hormones. Aerobic bacteria were highly capable of degrading the natural hormones (24 h); synthetic hormone was degraded by 84.5% (34 days), and bacteria were selected in the presence of 17α-ethynylestradiol. The authors suggest that Emticicia, Nubsella, and Sphingobacterium, bacteria from the Bacteroidetes phylum, were responsible for 17α-ethynylestradiol biodegradation. Emticicia was first reported as being supposed to be a hormone-degrading bacterium.

The Mn-based denitration catalyst has problems such as structural instability and poor poison resistance. In this work, Ce-modification improved the ${\mathrm{NO}}_x$ conversion and sulfur resistance of Mn-based catalysts. The ${\mathrm{TiO}}_2\text{-}{\mathrm{CeO}}_2$, ${\mathrm{ZrO}}_2\text{-}{\mathrm{CeO}}_2$ and ${\mathrm{TiO}}_2\text{-}{\mathrm{ZrO}}_2\text{-}{\mathrm{CeO}}_2$ (molar ratio of $4:1:n$) carriers were prepared by the sol–gel method, then ${\mathrm{MnO}}_x$ was impregnated on ${\mathrm{TiO}}_2\text{-}{\mathrm{ZrO}}_2\text{-}{\mathrm{CeO}}_2$ to investigate the catalytic activity and ${\mathrm{SO}}_2$ resistance at low temperature. The as-synthesized catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry (TG) to show the microstructure of the catalyst and the effect of Ce on the denitration performance. The results demonstrated that the addition of Ce into the ${\mathrm{TiO}}_2\text{-}{\mathrm{ZrO}}_2$ carrier inhibited the growth of ${\mathrm{TiO}}_2$ grains, formed ${\mathrm{CeTi}}_2{\mathrm{O}}_6$ crystals, improved the content of ${\mathrm{Mn}}^{4+}$, and increased the adsorption of ${\mathrm{NH}}_3$, and thus the ${\mathrm{NO}}_x$ conversion efficiency was improved. In the presence of both ${\mathrm{SO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$, the addition of Ce lowered the formation amount of ammonium sulfate and avoided the sulfation of manganese. The results suggest that Ce improved the structural instability and poison-resistance of Mn-based catalysts.

Activated phenol-formaldehyde (PF) beads were successfully synthesized using waste bamboo tar as the raw material via suspension polymerization method and adequate carbonization and activation. The activated PF beads were then examined by toluene adsorption tests at 2,500–20,000 ppmv by using a thermogravimetric system at operating temperatures between 25°C and 90°C. Saturated activated PF beads were also regenerated under 150°C for five cycles to understand their feasibility for adsorption-desorption applications. The experimental results showed that the activated PF beads with specific surface area $>600{\mathrm{m}}^2/\mathrm{g}$ were achieved, mostly contributed by micropores. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models could well fit the toluene adsorption data, with the Langmuir isotherm being the most suitable ($R^2>0.999$). Superior thermal regeneration efficiency after five adsorption-desorption cycles further suggests that the activated PF beads derived from waste bamboo tar have great potential to recover volatile organic compounds from solvents for industrial applications.

Emissions from organic liquids stored in atmospheric tanks were estimated using semiempirical equations developed by the USEPA and implemented in Microsoft Excel^® in order to study the effect of averaging time and meteorological data on estimated emissions. Annual emissions based on average annual weather data were typically lower than the sum of emission estimates based on average monthly weather data. However, some weather conditions displayed the opposite relationship, so the comparison of average time effects must be location specific. For both fixed and floating roof tanks, uncertainty in temperature data had the largest impact on calculated emissions. Solar insolation had little or no impact on emissions, and only external floating roof tank emissions showed a small dependence on wind speed. Trends were the same for the five locations used in the study. Finally, it was shown that the dimensionless pressure function used to calculate emissions from floating roof tanks is nearly proportional to the vapor mole fraction for liquids with vapor pressures appropriate for storage in atmospheric tanks, enabling emission estimates based on vapor mole fraction.

Although electrochemical treatment has received increased attention with respect to treating poly- and perfluoroalkyl substances (PFAS), studies assessing treatment longevity for the wide range of PFAS present in water impacted by aqueous film-forming foam (AFFF) are lacking. A 21-day study was performed in which electrochemical treatment using boron-doped diamond (BDD) anodes was performed in successive 24-h batch cycles on groundwater impacted with AFFF. Results showed substantial defluorination of both the perfluoroalkyl acids (PFAAs) and defluorination of polyfluoroalkyl compounds (based on fluoride generation). Substantial perchlorate generation was observed throughout the study. PFAS treatment effectiveness diminished over time due to scaling, resulting in decreased removal of the PFAAs and generation of perfluorobutanoic acid (PFBA). Based on measured generation of fluoride relative to the concentrations of the PFAAs, defluorination of the polyfluoroalkyl acids decreased 2–3 times more than the PFAAs due to this scaling. This suggests that defluorination of the polyfluoroalkyl acids occurred via a mechanism different from that of the PFAAs. Acid cleaning to remove the accumulated scale resulted in restoration of PFAS treatment. Together, these results suggest that electrochemical treatment of AFFF-impacted waters shows promise. Polyfluorinated compounds and PFBA showed greater adverse impacts from the mass transfer and/or residence time decreases associated with the scaling than what was observed for the other PFAAs. This implies that these compounds may prove to be the greater challenge in long-term full-scale applications.