Journal of Environmental Engineering

Electrochemical methods such as electrocoagulation (EC), electrooxidation (EO), and electroreduction (ER) are promising technologies to remove organics and heavy metals contained in industrial effluents discharged from numerous industries such as electroplating, textile, and metal processing. EC is widely applicable to treat wastewater that has a wide range of pollutants as well as being applicable to treating organic pollutants having a chemical oxygen demand (COD) range of $\mathrm{1,000}–\mathrm{13,000}\mathrm{mg}/\mathrm{L}$, and metals concentration in the range of $10–\mathrm{2,500}\mathrm{mg}/\mathrm{L}$ depending on the type of pollutants/metals. Several parameters such as pH, current density, electrode gap, electrolysis time, and agitation speed plays a major role during EC. Various laboratory results show that EC works effectively in the pH range 2–8, current density $20–200\mathrm{A}/{\mathrm{m}}^2$, electrode gap 1.5–3 cm, electrolysis time 10–150 min, and stirrer speed 30–200 rpm for the reactor size 1–2.5 L depending on the type of wastewater/effluent. Moreover, this process has been proved to be versatile and environmentally friendly. This review mainly focuses on the separation of heavy metals from electroplating effluent (EPE), including other pollutants removal from various industrial effluents such as textile, distillery, paint, and tannery. EC operation is oriented on the supply of direct current in metal electrodes and, consequently, metal ions released into the solution. This results in an increased metal concentration in the solution that finally precipitates as metal hydroxides along with pollutants. Numerous techniques are available to treat heavy metals bearing effluent, which includes precipitation, adsorption, bioadsorption, ion exchange, and membrane separation. These methods have several limitations in term of high operating costs and a large amount of sludge generation, while the EC process has several advantages over conventional technologies such as requirement of less external chemicals, easier installation, lower secondary pollutants formation, odor and color removal, and lower residence time. However, high electricity consumption due to formation of oxide film on the surface of the electrode is a major drawback of this process because oxide film works as an electric insulator. Overall, the EC method has wide potential to treat different kinds of effluents.

The removal kinetics and mechanism of azo dye Reactive Brilliant Red X-3B (X-3B) by a weak magnetic field (WMF)–enhanced zero-valent iron (ZVI) were explored. The results show that the reaction rate of zero-valent iron removal of X-3B was greatly enhanced by the weak magnetic field, and the removal rate increased with the decreasing of pH and initial dye concentration, and increased with the increasing temperature and ZVI dosage. The effect of common coexisting ions was also studied. In the presence of a magnetic field, ${\mathrm{NO}}_3^{-}$, ${\mathrm{Ca}}^{2+}$, and ${\mathrm{Mg}}^{2+}$ had certain inhibitory effects on the reaction, while anions ${\mathrm{CO}}_3^{2-}$, ${\mathrm{SO}}_4^{2-}$, ${\mathrm{ClO}}_4^{-}$, ${\mathrm{Cl}}^{-}$, ${\mathrm{HCO}}_3^{-}$, and ${\mathrm{PO}}_4^{3-}$ could significantly promote the removal of dye. In contrast, all kinds of anions and cations could promote the reaction without a magnetic field. Expect these, the degradation process was consistent with the pseudo-first-order kinetic model by fitting the experimental data. The activation energy ware $25.7368\mathrm{kJ}{\mathrm{mol}}^{-1}$ in the presence of WMF and $27.9317\mathrm{kJ}{\mathrm{mol}}^{-1}$ in the absence of WMF by using the Arrhenius formula. The degradation process was further analyzed by ultraviolet–visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The main mechanism of this reaction involves free radical oxidation, and the main reaction products were lepidocrocite and $\mathrm{Fe}(\mathrm{OH}{)}_3$.

Potato starch was thermally pretreated and the effect of its solubilization on the production of volatile fatty acids (VFA) using mesophilic anaerobic digestion was investigated in this study. Potato starch with three concentrations (10, 15, and $25\mathrm{g}/\mathrm{L}$) was pretreated at 50°C, 70°C, 80°C, 100°C, 120°C, and 140°C to establish the relationship between temperature and degree of solubilization yielding a linear relationship ($R^2=0.93–0.98$) irrespective of the starch concentration. Anaerobic respirometric studies were performed with raw starch and starches pretreated at 100°C (THP_100) and 140°C (THP_140). The batch reactors were operated in parallel at hydraulic retention times (HRTs) of 0.5, 1, and 2 days and organic loading rates (OLRs) of 6 and $9\mathrm{kg}\text{-}\mathrm{COD}/({\mathrm{m}}^3·\mathrm{day})$. The VFA production from THP_140 starch reduced significantly, but the two other samples did not exhibit changes. A maximum VFA yield of ($0.482\pm 0.054$) ${\mathrm{mg}\text{-}\mathrm{VFA}/\mathrm{mg}\text{-}\mathrm{COD}}_{\mathrm{applied}}$ was obtained at an OLR of $9{\mathrm{kg}\text{-}\mathrm{COD}/(\mathrm{m}}^3·\mathrm{day})$ and an HRT of 2 days. Acetic acid and butyric acid remained the dominant products, irrespective of the operating conditions.

Anaerobic digestion is a method adopted to treat sludge, but its effectiveness is limited by the existence of extracellular polymeric substances (EPSs). For the first time, this study separated sludge into intracellular polymeric substances (IPSs) and EPSs to investigate each of their digestion properties and the influences of EPSs. It was found that (1) EPS anaerobic digestion was completed in 3 days and was much quicker than by IPS; (2) the removal of organic matter in EPSs was higher than in IPSs; and (3) the biogas yield of EPSs [$266.6\mathrm{mL}/\mathrm{g}$ volatile solids (VS)] was higher than that of IPSs ($229.2\mathrm{mL}/\mathrm{g}\mathrm{VS}$). To examine the influences of EPS on sludge anaerobic digestion, an EPS-removal sample was compared with the control sample, and it was found that EPSs could restrict biogas production during sludge anaerobic digestion. After removing EPSs, cumulative biogas production and biogas yield were improved by 9.4% and 28.8%, respectively. The whole biogas production process was also shortened by 7 days after removing EPSs. Future studies could decide whether EPSs should be removed based on their role in anaerobic digestion outcomes (e.g., prioritize the production of biogas or the removal of organic matter).

Volatile organic chemicals (VOCs) are well-known indoor pollutants and are one of the top risks to human health. In this study, we chose commercial activated carbon (CAC) as adsorbents, which are used widely for the removal of indoor formaldehyde. The adsorption equilibria of six VOCs [benzene, toluene, p-xylene, chlorobenzene, acetone, and methyl ethyl ketone (MEK)] onto CAC at the environmentally relevant temperatures [35°C–55°C (308–328 K] were measured, and adsorption isotherms were fitted with the Dubinin-Astakhov (DA) equation. Molar polarizability, molar refraction, molar volume, and parachor were used to calculate the affinity coefficient ($\beta$), with benzene as the reference. The predicted results of the adsorption capacity with calculating characteristic energy ($E$) based on $\beta$ were not applicable well for polar adsorbates because both nonspecific and specific interactions were included during their adsorption. Considering different types of adsorption interaction, we adopted the linear solvation energy relationship (LSER) approach to analyze adsorption interaction and predict $E$ for VOCs adsorption. The results showed that adsorption capacities of VOCs could be predicted effectively, and the average root-mean-square error between the predicted and experimental data was 4.52%. Finally, we further predicted the adsorption capacity of benzene and acetone at a ppb concentration ($<100\mathrm{ug}/\mathrm{L}$), which corresponded to the indoor concentration of VOCs. And the predicted results were verified by adsorption characteristic curves at 155°C and 175°C (428 and 448 K), with data at different temperatures and concentrations falling essentially onto a single curve. This study is meaningful because it presents a useful prediction method of adsorption capacities for VOCs with different properties on CAC more quickly and conveniently.

The aim of this work is to investigate the ability of three agrowaste materials (corncobs, palm tree petioles, and sawdust) to remove diesel motor oil and oily waste from demineralized water and natural seawater. Sorption capacity (SC), reusability, and calorific value (CV) were evaluated. It was found that agrowaste materials have high SC; they are capable of absorbing many times their weight in oil: $12.49–13.56\mathrm{g}/\mathrm{g}$ for palm tree petioles, $6.99–7.56\mathrm{g}/\mathrm{g}$ for corncobs, and $4.19–4.28\mathrm{g}/\mathrm{g}$ for sawdust. The recovery of oils from water surface by sorption on these biomaterials is seen as a quasi-instantaneous mechanism, especially for palm tree petioles and corncobs. However, separation of oils from contaminated water by sawdust can reach its maximum after $15\min$ for diesel motor oil and $20\min$ for oily waste. In water, palm tree petioles, corncobs, and sawdust keep up to 99.34%–99.46%, 94.78%–98.56%, and 72.17%–81.40% of their maximal oil sorption capacities, respectively. Squeezing of saturated sorbents leads to their partial regeneration. Corncobs, palm tree petioles, and sawdust saturated with oils have high calorific values (36.45–38.85, 32.31–34.72, and $28.92–30.86\mathrm{MJ}/\mathrm{kg}$, respectively) and can be considered as combustibles.

Landfill leachate in developing countries is often discharged into the environment without treatment because most treatment technologies have high costs and are highly complex, making their implementation infeasible. This research evaluates the technical feasibility of implementing constructed wetlands with horizontal subsurface flow for the treatment of raw leachate and leachate pretreated with photo-Fenton of the Loma de los Cocos landfill in the city of Cartagena, Colombia. In order to evaluate the vegetation performance, three wetland modules were constructed: one without vegetation (HC), one with Rhizophora mangle (HM), and one with Typha latifolia (HE). Two tests were performed: one with raw leachate and another using pretreated leachate with photo-Fenton, which is considered a suitable treatment for little or moderately biodegradable waters. The modules were operated with a hydraulic retention time of 8 days and an operating time of 16 days. For the photo-Fenton pretreatment, the pH of the leachate was adjusted to values between 2 and 3 using a molar ratio ${\mathrm{Fe}}^{2+}/{\mathrm{H}}_2{\mathrm{O}}_2$ of 0.6 at a retention time of 40 minutes. The raw leachate was characterized as having chemical oxygen demand (COD) concentrations between 3,000 and $\mathrm{4,800}\mathrm{mg}{\mathrm{L}}^{-1}$ and pH values above 7.5. In general, wetlands had higher efficiencies with pretreated leachate. The effluent COD concentrations obtained in all tests complied with the maximum limit established by current Colombian regulations ($\mathrm{2,000}\mathrm{mg}{\mathrm{L}}^{-1}$). During the pretreated leachate test, the HE constructed wetland had pollutant removals that were slightly higher than the mangrove sown wetland (HM): COD (HE: 77%; HM: 73%), chloride (HE: 58%; HM: 50%), sulfate (HE: 58.6%; HM: 54.5%), nitrite (HE: 54.7%; HM: 67%), nitrate (HE: 98.4%; HM: 90.5%), and TDS (HE: 56%; HM: 54%). Although the HM wetland had removal average efficiencies that were slightly lower than those of the HE wetland, it can be concluded that horizontal subsurface-flow constructed wetlands with both vegetation are a viable alternative for the treatment of leachate from the Loma de los Cocos landfill.

At present, the problem of antibiotic contamination has become a global crisis. Some methods on the removal of antibiotics have been reported, and the adsorptive process was an effective approach to the disposal of antibiotics in water. Under mild conditions, carbon nanotubes (CNTs) were synthesized using fallen willow (Salix matsudana Koidz.) leaves as raw materials in this work. Polyurethane (PU)/CNT foams were synthesized using a comixing method. The adsorptive properties of PU/CNT foams for sulfonamides in water were investigated. The results showed that intraparticle diffusion was not the only rate control step, and adsorption was controlled jointly by membrane diffusion and internal diffusion. The adsorption equilibrium time was 8 h. The optimum adsorption conditions of PU/CNT foams for sulfanilamide were as follows: the pH of the sulfanilamide solution was 7, the dosage of PU/CNT foam was 0.02 g, and the initial concentration of sulfanilamide solution was $40\mathrm{mg}·{\mathrm{L}}^{-1}$. In addition, adsorption was affected by electrostatic force, the $\pi \text{-}\pi$ effect, hydrophobic interaction, and hydrogen bond. Moreover, adsorption was heterogeneous in a certain range, and there was an interaction between adsorbent and adsorbate molecules in the adsorption process. Subsequently, the adsorption of PU/CNT foams for sulfonamide was a preferential, spontaneous, and exothermic reaction. In the process of desorption, sulfonamide tended to be retained in the PU/CNT foams.

The widespread use of hazardous organophosphate ester (OPE) flame retardants has led to the contamination of groundwater and drinking water sources. Given the negative impact of OPEs on environmental and human health, there is a critical need to identify effective remediation processes. This study reports that ultrasonic irradiation at 640 kHz leads to effective degradation of tris(2-chloroethyl) phosphate (TCEP), a model organophosphate flame retardant. The concentration of TCEP in an irradiated aqueous solution was monitored by a gas chromatography- nitrogen phosphorus detector (GC-NPD) technique. TCEP has a half-life of less than 1 h under the used experimental conditions. The degradation follows pseudo-first-order kinetics with rate constants varying from 0.09 to $0.02{\min }^{-1}$ depending on initial concentrations ranging from 3.1 to 84 μM. The observed rate constant decreases with the increase in initial TCEP concentration, implying the process likely involves a heterogeneous process controlled by partitioning at the gas–liquid interface during ultrasonic cavitation. The degradation fits the heterogeneous Langmuir-Hinshelwood model, further suggesting the degradation occurs at the gas–liquid interface. Detailed product studies using liquid chromatography orbitrap high-resolution mass spectrometry confirm the primary degradation products are the mono and diester adducts of TCEP, specifically 2-chloroethyl dihydrogen phosphate and bis(2-chloroethyl) hydrogen phosphate. Mineralization of TCEP to chloride and phosphate was monitored by ion chromatography, yielding mass balances of 48% and 32% for chloride and phosphate, respectively, after 6 h of treatment. The results demonstrate that ultrasonic irradiation is effective for the degradation of the halogenated flame retardant TCEP. The results suggest ultrasonic treatment can be used alone or in combination with other methods for the remediation of problematic organophosphorus flame retardants.

Sediment depositions in storm sewer systems have received significant attention due to their implications for urban flooding and environmental impacts. However, only limited attention has been paid to sediment deposition in submerged storm sewers. In this study, a laboratory model was used to study the sediment transport and deposition processes in a submerged storm sewer. The growth of the deposition can be divided into two stages: rapid growth (both deposition height and length increase) and equilibrium growth (only deposition length increases). The sediment loading rate determines the duration of the rapid growth stage, and the equilibrium height increases for larger sediment size and higher sediment concentration. The bed shear stress at the equilibrium stage varies from 1.8 to $8.7\mathrm{N}/{\mathrm{m}}^2$ corresponding to the variation of the bed friction factor from 0.058 to 0.185, which is about 2–4 times that caused by the sediment roughness height alone. This increase in the bed shear stress is mainly due to the significant amount of momentum needed to transport the required sediment loading. A prediction method and its applications are also presented.

Resistant strains of Vibrio cholerae have the potential to reemerge in aquatic reservoirs where they remain in a viable but not cultivable (VBNC) state, or as a rough variant embedded in an exopolysaccharide matrix, which could survive inadequate disinfection processes. This study investigated the chlorine (${\mathrm{Cl}}_2$) and ozone (${\mathrm{O}}_3$) inactivation kinetics for V. cholerae O1 El Tor, VBNC, and rough strains. The effect of both disinfectants was also evaluated at the cellular level using field emission scanning electron microscope (FESEM) micrographs. The $Ct$ ($C$: concentration; $t$: contact time) values for ${\mathrm{Cl}}_2$ and ${\mathrm{O}}_3$ were established. Inactivation kinetics (log10 $N_0/N$) confirmed that ${\mathrm{O}}_3$ is the better water treatment to inactivate VBNC and rough strains of V. cholerae. Compared with the smooth strain, resistant strains require a higher $Ct$ of both ${\mathrm{Cl}}_2$ and ${\mathrm{O}}_3$ to inactivate the same percentage of cells. This study could contribute to preventing the spread of cholera through water consumption, mainly in endemic areas and developing countries, particularly when $Ct$ values of smooth strains are applied in the disinfection of drinking water.

To investigate the effects of different types and concentrations of organic matter on anaerobic ammonium oxidation (anammox), the effects of short-term stresses induced by organic matter on anammox-based nitrogen removal and the associated microbial community were evaluated by adding different organic matter (e.g., glucose, acetic acid, sodium acetate, methanol, and phenol) and concentrations (e.g., $20–250\mathrm{mg}\mathrm{COD}/\mathrm{L}$) into anammox batch reactors (serum bottles) with 46 h. Results indicated that the addition of glucose, acetic acid, and sodium acetate (i.e., at concentrations ranging from 20 to $250\mathrm{mg}\mathrm{COD}/\mathrm{L}$) promoted nitrite removal. Methanol was the most potent inhibitor on ammonium removal, while phenol inhibited ammonium removal even at a low concentration (e.g., $20\mathrm{mg}\mathrm{COD}/\mathrm{L}$). The microbial community structure and composition under organic matter addition was illustrated by high-throughput Miseq sequencing analyses. The phylum Firmicutes was predominant in all samples, followed by Planctomycetes, Proteobacteria, and Chloroflexi, respectively. Planctomycetes, which was related to anammox bacteria, including Candidatus Jettenia and Candidatus Brocadia, dramatically decreased under sodium acetate and methanol stress, respectively.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS), widely used in many commercial and military products, have been notorious due to their environmental persistence. Even radical-based advanced oxidation technologies have been reported to be less effective for decomposition of PFAS, particularly perfluoroalkyl ones, while commonly requiring energy-intensive extreme conditions and tools such as ultraviolet, ultrasound, microwave, electron beam, and high temperatures. Herein, for the first time, the potential of a modified Fenton system, i.e., homogeneous persulfate (PS) conjugated with silver (${\mathrm{Ag}}^{+}$), to decompose PFAS under ambient conditions is communicated. Among many combinations of common oxidants and transition metals tested, only the PS/Ag pair showed significant reactivity at 20°C exclusively toward carboxylic PFAS including perfluorooctanoic acid, resulting in evolution of fluoride ion release and reaction by-product formation. Although sulfonic PFAS still remain challenging, and follow-up assignments are raised to investigate in-depth mechanisms and examine other oxidant and metal pairs, this study offers one step closer to establishing an energy-independent and more practical treatment system for PFAS.