Journal of Environmental Engineering

Environmental pollution has now become a potential problem that restricts stable economic growth. As an effective way to measure sustainable development, ecological efficiency can comprehensively reflect the actual level of coordinated economic and environmental development. This paper established a data envelopment analysis (DEA) evaluation model using environmental pollution and resource consumption as input indicators and total economic output as the output indicator. Eco-efficiency evaluation empirical research was carried out on 27 coal resource–dependent cities divided into eastern, central, and western regions in China to establish the eco-efficiency of these cities. The results show that technical efficiency, pure technical efficiency, and scale efficiency are relatively low in resource-dependent cities. The technical efficiency values for three regions were 0.506, 0.402, and 0.439, and the overall level was considerably low, which shows that the regional differences of ecological efficiency are obvious. High ecological efficiency is mainly concentrated in the eastern cities, but the ecological efficiency levels in the central and western regions are relatively low. The main factors affecting eco-efficiency include solid waste, waste gas, and resource consumption. Finally, the development countermeasures of coal resource–dependent cities’ eco-efficiency, such as industrial structure transformation, developing circular and low-carbon economies, and implementation of environmental protection measures for boosting economic growth were given based on the empirical research results.

The focus of this study was to investigate the fate and transport of toluene, a light nonaqueous-phase liquids (LNAPLs) in the subsurface region under dynamic groundwater table conditions. A series of experiments were conducted using two-dimensional (2D) sand tank setup having dimensions $125\times 90\times 10\mathrm{cm}$ ($\mathrm{L}\times \mathrm{H}\times \mathrm{W}$) and integrated with an auxiliary column of inner diameter 14 cm and height 120 cm. Initially, a steady-state flow and LNAPL transport experiment was conducted under stable groundwater table condition. Thereafter, three groundwater table fluctuation experiments were conducted on a rising and falling groundwater table in 2, 4, and 8 h to maintain rapid, general, and slow fluctuation conditions, respectively. The pure phase of toluene was injected at a rate of $1\mathrm{mL}/\min$ for a total duration of 5 min. Soil-water and soil-vapor samples were periodically collected and analyzed for toluene concentrations. Later, the representation of the 2D sand tank setup was numerically simulated to obtain the response of flow and the LNAPL transport under varying groundwater table conditions. Analysis of the results shows that a large LNAPL pool area ($250{\mathrm{cm}}^2$) develops under rapidly fluctuating groundwater conditions, which significantly enhances the dissolution rate and contributes to a high concentration of dissolved LNAPLs at the receiving receptors. Estimated values of Sherwood and Peclet numbers show that the dissolution rates were highly affected by groundwater table dynamics, which may cause loss of pure-phase pollutant mass around the pollutant source. The concentration isolines of toluene show that the transport of dissolved LNAPL plumes was also comparatively fast in the case of rapidly fluctuating groundwater. A high biodegradation rate was observed in plume regions having concentration ranges of 140–160 ppm, while it decreases in plume regions having very high ($>160\mathrm{ppm}$) and low concentrations ($<140\mathrm{ppm}$) of dissolved LNAPL. In the sand tank, microbial growth was found to increase as the plume moved away from the LNAPL pool toward a low gradient, which intensifies the detrimental impact of toluene on the survival of indigenous microorganisms near the LNAPL pool. The results of this study may help in implementing effective remediation techniques to decontaminate LNAPL polluted sites under fluctuating groundwater table conditions, especially in (semi)-arid coastal aquifers.

The effects of an operating water head (OWH) and reduced graphene oxide (RGO) addition on the pervious concrete filter (PCF) and heavy metals interaction were investigated in the present study. Five simulated wastewaters containing Cd, Zn, Cu, Pb, and these four ions mixed together were filtered by PCF monoliths, considering the influence of three OWHs, viz. 30 cm, 7.5 cm, and trickling water head. The metal ions fixation degree increased with decreasing levels of OWH, which indicates that empty bed contact time influences PCF performance. Additionally, heavy metals removal and leaching from 0.06 wt% RGO modified PCF (G-PCF) and plain PCF were examined by first passing the five wastewater samples, immediately followed with strong acidic water, while maintaining the same flow and time. As a consequence of acid water passage, the fixated ions were seen to leach out from PCFs, but the RGO’s strong reinforcement substantially reduced such leaching degree and additionally improved the simultaneous removal of four heavy metals. Although the estimated cost of G-PCF was relatively higher than plain PCF, both these filters appear highly efficient and inexpensive, unlike treatment units that are currently used by the electroplating industry for heavy metals removal.

In this paper, the impact of pH, ionic strength, and dissolved organic matter [humic acid (HA) and tannic acid (TA)] on graphene oxide (GO) stability was investigated. The results showed that the GO is negatively charged over a pH range from 2 to 11. pH did significantly affect GO stability at a level of 4 or higher, but the particles became unstable below pH 3 due to protonation of $-\mathrm{COOH}$ at the edge. Ionic strength (IS) and salt type had observable effects on stability as a result of electrical double layer compression and specific interactions. ${\mathrm{CaCl}}_2$ affects GO more noticeably than NaCl because of the binding ability of ${\mathrm{Ca}}^{2+}$ ions with carboxyl and hydroxyl functional groups. pH had negligible effects in the presence of 10 mM NaCl, but 1 mM ${\mathrm{CaCl}}_2$ decreased GO stability as pH increased owing to the adsorption of ${\mathrm{Ca}}^{2+}$ ions on the surface functional groups of GO and the consequent decrease of surface charge. The applicability of DLVO theory as a predictive tool was investigated by modeling GO sheets in two different geometries; three-dimensional spherelike particles and two-dimensional particles at different values of pH and IS. Overall, the specific interactions and chemical structure of adsorbed organics had a dominant role in GO stability.

High-volume blast furnace (BF) slag resulting from iron-making activities has long been considered a burden on the environment. Despite a high number of investigations, aspects of the transformation of BF slag into high value-added products for environmental remediation are still challenging. This work presents a feasible solution toward layered double hydroxides $[{\mathrm{Ca}}_{1.89}{\mathrm{Mg}}_{0.89}{\mathrm{Al}}_{1.0}(\mathrm{OH}{)}_{7.5}{\mathrm{Cl}}_{0.83}({\mathrm{CO}}_3{)}_{0.11}·{\mathrm{yH}}_2\mathrm{O}]$ and the formation of its oxide derivatives (${\mathrm{Ca}}_{1.91}{\mathrm{Mg}}_{0.98}{\mathrm{Al}}_{1.0}{\mathrm{Cl}}_{0.12}{\mathrm{O}}_{4.33}$) by taking advantage of proper cationic composition in BF slag. The adsorption kinetics and isotherms of adsorbents for Cr(VI) removal were investigated in detail. The adsorption kinetic data for layered double hydroxides (S-LDHs) and oxide derivatives (S-LDOs) agreed well with pseudo-second-order kinetic equations. The adsorption activation energies for Cr(VI) adsorption on S-LDHs and S-LDOs were 41.84 and $60.50\mathrm{kJ}/\mathrm{mol}$, respectively. Thermodynamic studies demonstrated that the adsorption was a spontaneous and endothermic chemical process, and the better-fitted Langmuir model revealed that the adsorption reaction was monolayer adsorption. S-LDOs exhibited good adsorption capacity ($55.37\mathrm{mg}/\mathrm{g}$), which could be attributed to more active sites with increased specific surface area and a memory effect after calcination. This paper provides highlights regarding the utilization of metallurgical wastes for environmental remediation.

Clogging of leachate collection systems (LCSs) can cause potentially catastrophic failures in landfill operation. The primary cause of clogging is calcium carbonate precipitation, which forms inside the pipe around a nucleus of silt, sand, microbial colonies, or other particles. One approach that has been proposed to prevent clogging in LCS is electronic scale control (ESC) technology. To quantify the effectiveness of ESC to reduce clogging within a gravity LCS pipe network, a field-scale pipe network was constructed with side-by-side flow of composite leachate treated electronically on one side and untreated leachate on the other. Water quality parameters, saturation indices, and solids composition were compared for any differences between the treated and untreated leachate. With respect to water quality of leachate, no statistically significant differences were observed. Neither the Langelier Saturation Index (LSI) nor the Ryzner Index (RI) changed toward neutrality after treatment. X-ray diffraction/X-ray fluorescence (XRD/XRF) analysis of precipitates in the pipe network identified calcite (${\mathrm{CaCO}}_3$) to be the predominant phase present, and there were no observed differences in composition between the treated and untreated precipitates.

Catalytic wet peroxide oxidation (CWPO) of dichlorophenols (DCPs) over Fe-Cu-pillared clay (PILC) without and with NaCl was investigated. Concentration change dynamics in ${\mathrm{H}}_2{\mathrm{O}}_2$, ${\mathrm{Cl}}^{-}$, and hydroxyl radicals ($·\mathrm{OH}$) during DCP oxidation were also studied. Additionally, the intermediates formed were detected by liquid chromatography-mass spectroscopy (LC-MS). The results showed that the presence of NaCl inhibited the DCP oxidation rate to some extent, where induction time ($T_I$) was lengthened from 75.9 to 93.6 min, and half-decomposition time ($T_{1/2}$) was extended to 20.6 min (from 86.6 to 107.2 min) as compared with control (without NaCl addition). However, NaCl only strongly inhibited the oxidation rate of ortho-substituted DCPs such as 2,6-DCP, where $T_I$ was lengthened to 80 min (from 290.7 to 370.4 min), but not meta-DCPs or para-DCPs. Further investigation showed that NaCl did not affect the conversion (dechlorination and hydroxylation) of DCPs and also did not change the DCP oxidation path. It was hypothesized that the inhibitory mechanism of NaCl on ortho-DCP oxidation was mainly due to inhibiting the rate-limiting step of ${\mathrm{H}}_2{\mathrm{O}}_2$ decomposition (lengthening the induction period from 350 to 510 min) by competing with ${\mathrm{H}}_2{\mathrm{O}}_2$ for the complexation of Fe (III), secondary due to scavenging of $·\mathrm{OH}$ (about 21%) to form chlorine radicals such as $·{\mathrm{Cl}}_2^{-}$.

In order to better understand the performance, anaerobic treatment of spent wash with very high chemical oxygen demand (COD) ($\mathrm{110,000}–\mathrm{140,000}\mathrm{mg}/\mathrm{L}$) and biochemical oxygen demand (BOD) ($\mathrm{55,000}–\mathrm{65,000}\mathrm{mg}/\mathrm{L}$) was studied on a full-scale continuous stirred-tank reactor (CSTR). Under variable organic loading rates (OLRs), optimum conditions for maximum COD removal and biogas generation were found to be $\mathrm{OLR}=\mathrm{60,000}–\mathrm{65,000}\mathrm{kg}\mathrm{COD}/\mathrm{day}$, $\mathrm{hydraulic}\mathrm{retention}\mathrm{time}(\mathrm{HRT})=22–17\mathrm{days}$, and volatile fatty acids (VFA) to alkalinity ratio of around 0.12. Maximum COD removal efficiency was found to be around 71% when operated in the pH range of 7–8 with stable temperature of 37°C–38°C with biogas conversion coefficient of 0.4. These figures are particularly significant when operating the anaerobic biodigesters for treatment of spent wash and to produce biogas as an energy source. An anaerobic CSTR can successfully be employed for the treatment of distillery spent wash, but postmethanation effluent still contains a high COD concentration and needs to be treated further to meet the pollution norms and standards.

Emerging contaminants are a global concern, as Directive 2013/39/UE shows. Given the possible consequences that may lead to the presence of these compounds in water resources, different proposals are being evaluated to avoid their discharge into the environment. This study focuses on the use of a biological and physicochemical combined treatment formed by a membrane bioreactor with an ${\mathrm{H}}_2{\mathrm{O}}_2/\text{UltraViolet}(\mathrm{UV})$ advanced oxidation process coupled subsequently to degrade contaminants of emerging concern in real urban wastewater. The membrane bioreactor operated at 16 h of hydraulic retention time and $\mathrm{4,250}\mathrm{mg}/\mathrm{L}$ of mixed liquor suspended solids. Different hydrogen peroxide dosages (25, 50, and $100\mathrm{mg}/\mathrm{L}$) were tested in the photoreactor at 20°C and the natural pH of the wastewater. Different initial concentrations of a mix of pharmaceuticals (carbamazepine, ciprofloxacin, and ibuprofen) were tested. Removal efficiencies obtained in the biological stage ranged from 66.23%–96.18%, 90.63%–100%, and 90.04%–96.48%, respectively. However, complete removal was achieved after the physicochemical stage when the concentrations of contaminants in the mix were similar to current concentration levels in urban wastewater.

Formaldehyde (FA) is considered a toxic and mutagenic compound that is suspected to be carcinogenic for humans. FA is widely emitted to the atmosphere by several chemical industries. Therefore, it is important to have an effective system to remove it from air. Although biotrickling filter (BTF) has been introduced as a suitable method to remove FA from air, the optimum conditions have not yet been fully investigated in a satisfactory way. Here, the authors want to find the optimum conditions for effective factors, including pH, retention time, operation time, bed length, and volumetric air flow rate (VAFR) on a BTF. In this study, BTF was applied for treatment of FA from synthetically contaminated air. In order to predict FA removal efficiency (RE), artificial neural network (ANN) was used for simulation of BTF and for analyzing empirical data. ANN assessed RE and predicted data with acceptable root-mean-square error (RMSE) and correlation coefficient ($R^2$). Moreover, a sensitivity analysis (SA) was performed showing that pH and operation time are effective at changing the amount of FA elimination. The results of this study can be used to operate BTF in the optimum conditions for obtaining high RE.