Journal of Environmental Engineering

The synthetic strong base anion-exchange resin Amberlite IRA-900 was investigated for its adsorption capacity to simultaneously remove selenate (${\mathrm{SeO}}_4^{2-}$) and sulfate (${\mathrm{SO}}_4^{2-}$) from single and binary anion solutions at pH 7.5 and 20°C. At an initial ${\mathrm{SeO}}_4^{2-}$ and ${\mathrm{SO}}_4^{2-}$ concentration of 428.9 and $\mathrm{1,441.1}\mathrm{mg}/\mathrm{L}$, respectively, IRA-900 adsorbed 85 ($\pm 1$)% ${\mathrm{SeO}}_4^{2-}$ and 75 ($\pm 5$)% ${\mathrm{SO}}_4^{2-}$ from single anion solutions at 2% ($w/v$) resin dosage. In binary anion solutions, a 20% decrease for both the ${\mathrm{SeO}}_4^{2-}$ and ${\mathrm{SO}}_4^{2-}$ adsorption efficiency was observed. Batch kinetic experimental data indicated that the adsorption rate of IRA-900 for both ${\mathrm{SeO}}_4^{2-}$ and ${\mathrm{SO}}_4^{2-}$ in the single and binary anion solutions fitted well to the pseudo-second-order kinetic model ($R^2=0.99$). The modified Langmuir isotherm complete competition model best fitted the experimental data for binary anion solutions, showing 24% and 10% average relative error from theoretical calculations for ${\mathrm{SeO}}_4^{2-}$ and ${\mathrm{SO}}_4^{2-}$, respectively. Exhausted resin was regenerated for the next cycle of adsorption using either 0.25 or 0.5 M HCl for 20 min and was tested for 30 adsorption-desorption cycles. Results showed that the resin was suitable for reuse at an optimal adsorption-desorption of 6 cycles without compromising the removal efficiencies. Efficient and fast adsorption of both ${\mathrm{SeO}}_4^{2-}$ and ${\mathrm{SO}}_4^{2-}$ is promising for developing an IRA-900 based ion-exchange process for the remediation of Se-contaminated (waste)waters.

Bacterial profile, nutrients removal performance, and membrane fouling behavior were evaluated in an anoxic/oxic electro-membrane bioreactor (A/O e-MBR) treating municipal wastewater at different hydraulic retention times (HRTs) (30, 20, and 15 h). The results demonstrated that HRT reduction from 30 to 15 h had a negligible effect on chemical oxygen demand (COD), ammonium (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$), and total phosphorus (TP) removal, showing efficiencies above of 98%, 99%, and 95%, respectively, for any experimental runs. On the other hand, total nitrogen (TN) removal improved significantly from 80.7% to 90.5% as the HRT was reduced from 30 to 15 h. Activity batch assays have shown a higher specific nitrate uptake rate (SNUR) at the shorter HRT. Results of DNA sequencing analysis indicated a larger amount of denitrifying bacteria genus and a greater relative abundance of Nitrospira genus at shorter HRTs, supporting the higher SNUR and the greater TN removal. The membrane fouling rate increased by about 16 times during the period with HRT of 15 h. Besides, some fouling propensity parameters have shown a worse mixed liquor filterability in this period.

This study investigates the performance of laboratory-scale vegetative biofiltration systems in reducing five heavy metals [cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn)] from synthetic graywater. Thirty-six biofiltration columns of the same design were constructed, and twelve species of ornamental plants were planted, with three specimens from each species being planted in a single column. The study was conducted for six months in an arid climate. The overall removal efficiency for Zn and Cu was found to be about 98% and 75%, respectively. It was observed that soil Zn and Cu concentrations increased from 11.24 to $26.13\mathrm{mg}/\mathrm{L}$ and from 11.09 to $12.12\mathrm{mg}/\mathrm{L}$, respectively, after irrigation with graywater. Zn and Cu were mainly removed by soil accumulation and plant uptake, respectively. Both Pb and Cr increased in effluent (about 29% and 6.5%, respectively) and in soil (about 12% and 63%, respectively) after irrigation with graywater, whereas Cd increased in effluent (about 7.6%) but decreased in soil (about 46%). Finally, the plants were ranked and recommended for application based on their performance consistency and effectiveness. The species Alternanthera ficondea topped the ranking, followed by the species Ixora coccinaea, Vitex agnus, Rhoeo discolor, and Jasmine sambac.

NO and ${\mathrm{SO}}_2$ oxidization by ${\mathrm{H}}_2{\mathrm{O}}_2$ in coal-fired flue gas was modeled, and the effects of temperature and ${\mathrm{H}}_2{\mathrm{O}}_2$ concentration on NO and ${\mathrm{SO}}_2$ oxidization were investigated. The pathways of NO and ${\mathrm{SO}}_2$ oxidization were as follows: ${\mathrm{H}}_2{\mathrm{O}}_2\to \mathrm{OH}\to {\mathrm{HO}}_2+\mathrm{NO}\to {\mathrm{NO}}_2$ and ${\mathrm{SO}}_2+\mathrm{OH}\to {\mathrm{HOSO}}_2+{\mathrm{O}}_2\to {\mathrm{SO}}_3$, respectively. There were optimal temperature ranges of NO and ${\mathrm{SO}}_2$ oxidization, and the ranges were 650–920 K and 650–750 K, respectively. In the optimal temperature ranges, the ${\mathrm{NO}}_2$ conversion rate was greater than 0.9 at ${MR}_{\mathrm{H}2\mathrm{O}2/\mathrm{NO}}>1.9$, and the ${\mathrm{SO}}_3$ conversion rate reached about 0.3 at ${MR}_{\mathrm{H}2\mathrm{O}2/\mathrm{SO}2}=0.1–0.4$. ${\mathrm{SO}}_2$ oxidization could promote ${\mathrm{HO}}_2$ formation to oxidize NO.

In this research, carboxylated multiwalled carbon nanotubes (c-MWCNTs) were improved with 5-amino-3-(2-thienyl) pyrazole (p-MWCNTs) for adsorption of ${\mathrm{Cd}}^{2+}$ and ${\mathrm{As}}^{3+}$ from aqueous solutions. Field emission scanning electron microscopy, Fourier transform infrared spectra spectroscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis were employed to characterize the p-MWCNTs. The central composite design inspected the effects of the pH, adsorbent dose, and initial metal ions concentration on the adsorption process. Further, the optimum adsorption conditions were acquired as 20 mg of the adsorbents, $\mathrm{pH}=7–8$, and $20\mathrm{mg}·{\mathrm{L}}^{-1}$ of metal ions concentration. Furthermore, for analysis of variance, the quadratic model was applied and indicated that pH was the most effective parameter in the adsorption process. Also, various adsorption isotherm models were examined. The results showed that the Langmuir isotherm correlated the experimental results in this work well, while kinetic data could be characterized by the pseudo-second-order adsorption rate kinetics. Moreover, the thermodynamic evaluations discovered that the sorption process was spontaneous and endothermic in nature. Finally, the adsorption–desorption study demonstrated a good regeneration capacity of the adsorbent for considering wastewater containing ${\mathrm{Cd}}^{2+}$ and ${\mathrm{As}}^{3+}$.

Perfluorinated chemicals (PFCs) are highly persistent organic contaminants that have become a global health concern. Few studies so far have demonstrated successful decomposition of PFCs under ambient condition. As a result, this feasibility study aimed to quickly examine whether palladium-doped nanoscale zerovalent iron (nZVI/Pd), known to dehalogenate many halogenated chemicals, can remove perfluorooctanoic acid (PFOA) in water, one of the most widely used PFCs. Batch experiments were performed to evaluate the effects of various operation parameters, including reaction pH, nZVI/Pd dose, and PFOA concentration, to find best treatment options for PFOA. Significant removal of PFOA was observed at low pH and high nZVI/Pd dosage while nZVI/Pd was superior to micron-size ZVI and nZVI without Pd. However, the decrease in total organic carbon was very similar to PFOA removal, negligible amounts of fluoride ions were detected in water, and mass spectrometry analysis indicated no significant formation of reaction intermediates. The results implied that the observed PFOA removal was more closely associated with adsorption than reaction (i.e., defluorination). Kinetic models and adsorption isotherm models were employed to explain the PFOA removal and obtain insights on the physicochemical processes around nZVI/Pd interacting with PFOA.

Microalgae can be used as a promising biofuel material that offers a high amount of lipid production and fast growth rate. Nutrient compositions and concentrations are important factors related to the lipid production and accumulation in many algae species. In this work, nutrient availabilities with different concentrations of nitrogen, phosphorus, and carbon were studied in a single impact factor experiment to investigate their effects on the algal biomass and lipid production of Chlorella sp. The results indicate that lowering the nitrogen concentration could maximize the lipid production, and appropriate ${\mathrm{K}}_2{\mathrm{HPO}}_4$ and ${\mathrm{Na}}_2{\mathrm{CO}}_3$ concentration could have benefits for lipid content production. Therefore, the effects of nutrient availabilities on lipid productivity were concluded in the order of N (nitrogen concentration) > C (carbon concentration) > P (phosphorus concentration), with nitrogen playing the biggest role in lipid production activities. The results can provide a fundamental understanding of nutrient availabilities’ effects on cell growth and lipid production in the algae Chlorella sp.

Fluoride uptake by porous hydroxyapatite ceramics is investigated through batch adsorption studies to determine the effect of varying the size of hydroxyapatite grains and pore size. It is found that ceramics made from fine hydroxyapatite ($d_{50}=100\mathrm{\mu m}$) have higher fluoride uptake and smaller pores compared with ceramics made from coarse ($d_{50}=240\mathrm{\mu m}$) hydroxyapatite ($18.2\mathrm{mg}/\mathrm{g}$ versus $12.4\mathrm{mg}/\mathrm{g}$, respectively). Fewer processing steps are required for ceramics made from fine hydroxyapatite. This ceramic has high selectivity for fluoride relative to anions commonly found in groundwater and natural organic matter (NOM) and can be regenerated for up to five adsorption cycles using 0.05 and 0.1 M sodium hydroxide.

This paper explores sorption of human adenovirus 40 (HAdV40) to wastewater solids in primary and secondary sludge samples. To measure kinetics and isotherms of adsorption, serial dilutions of HAdV40 (${10}^5–{10}^9\mathrm{GC}/\mathrm{mL}$) are mixed with sludge samples. Real-time polymerase chain reaction (qPCR) is used for virus quantification. For both types of sludge, HAdV40 adsorption is strong ($K_P>{10}^4\mathrm{L}/\mathrm{kg}$). There is no statistically significant difference ($p>0.05$) in $K_P$ values measured for the primary sludge and the mixed liquor sludge. Sequential desorption experiments with deionized water as the liquid phase show poor reversibility of HAdV40 adsorption. More HAdV40 is desorbed from primary sludge solids than from secondary sludge solids, but the difference is not statistically significant ($p>0.05$). Future research is needed to evaluate the impact of main wastewater components on virus adsorption and desorption.