Journal of Environmental Engineering

Tetramethylammonium hydroxide (TMAH) is widely used in manufacturing thin-film transistor liquid crystal displays (TFT-LCD) and semiconductors. Because of its toxicity and nitrogen content, TMAH-containing wastewater has to be properly treated before discharge. In this study, several commercial activated carbons were characterized and used for TMAH adsorption. Activated carbon with micropores showed higher adsorption capacity for TMAH. The adsorption kinetics could be represented by pseudo-second-order model, and the Langmuir model fitted the adsorption of TMAH on activated carbon under different pH adsorption well. Higher pH was favorable for TMAH adsorption, while there was no TMAH adsorption at pH $4.7\pm 0.2$. The adsorption was spontaneous and exothermic. Exhausted carbon could be easily regenerated by 0.1 N HCl, with no considerable reduction in performance even after five cycles of adsorption-desorption. It was proposed that electrostatic interaction was the main mechanism of TMAH adsorption on the activated carbon.

A novel wastewater treatment configuration—the Baffled Bioreactor (BBR)—was tested for municipal wastewater treatment at pilot-scale. This patented BBR is characterized by a hydraulically driven sludge recycling mechanism in the aerobic zone that eliminates the need for sludge return from a final clarifier, which significantly reduces the overall maintenance needs. Throughout 2009, a pilot-scale BBR with a total effective volume of $8.1{\mathrm{m}}^3$ (2,153 gallons) was operated at the Southeast Wastewater Treatment Plant in Rolla, Missouri. An annual average mixed-liquor suspended-solids (MLSS) concentration of $3.2\mathrm{g}/\mathrm{L}$ was maintained in the aerobic zone without a return pump. During the summer, the treatment capacity reached $37.9{\mathrm{m}}^3/\mathrm{d}$ (10,000 gpd), with average effluent concentrations of ${\mathrm{BOD}}_5$, SS, and ${\mathrm{NH}}_4^{+}\mathrm{\text{-}}\mathrm{N}$ of lower than $10\mathrm{mg}/\mathrm{L}$, $10\mathrm{mg}/\mathrm{L}$, and $1\mathrm{mg}/\mathrm{L}$, respectively. At $37.9{\mathrm{m}}^3/\mathrm{d}$ (10,000 gpd), the total hydraulic retention time in the anoxic and aerobic zones was approximately 4.5 h. However, a significant reduction of biological activity was observed in winter in the above-grade system. At a water temperature in the range of 8–10°C, the treatment capacity decreased to $11.4–15.1{\mathrm{m}}^3/\mathrm{d}$ (3,000–4,000 gpd), with average effluent concentrations of ${\mathrm{BOD}}_5$, SS, and ${\mathrm{NH}}_4^{+}\mathrm{\text{-}}\mathrm{N}$ of $8.8\mathrm{mg}/\mathrm{L}$, $10.8\mathrm{mg}/\mathrm{L}$, and $4.2\mathrm{mg}/\mathrm{L}$, respectively. An anoxic selector significantly improved the sludge settling characteristics in summer and fall, thereby increasing the total MLSS in the BBR. This research demonstrates that this patented BBR technology can effectively remove BOD, SS, and nitrogen throughout the year with minimal maintenance requirements.

This paper used a sonication-cryptic growth technique in sequencing batch reactor (SBR) to reduce sludge yield and then analyzed the accumulation of eight typical heavy metals in sludge, namely, Hg, Cr, Ni, Cu, Zn, As, Cd, and Pd. SBR-1 was blank, SBR-2 used sonication, SBR-3 was dosed with heavy metals, and SBR-4 had both sonication and heavy metals. Artificial wastewater dosed with $12.5\mathrm{mg}/\mathrm{L}$ heavy metals was used for SBR-3 and SBR-4. Results showed that the addition of heavy metals in influent caused the latter to accumulate in sludge and that each metal exhibits different behavior. Heavy-metal addition dropped sludge bioactivity by 53% and decreased the effluent chemical oxygen demand (COD) (SBR-3 versus SBR-1). Application of sonication (each day, 15% sludge was treated for 15 min by $1.2\mathrm{W}/\mathrm{ml}$ ultrasound) decreased the excess sludgy by almost half; however, it increased sludge heavy-metal concentration only by 3.5% (SBR-4 versus SBR-3). Furthermore, sonication benefited sludge bioactivity and thus improved the effluent COD quality. It also significantly changed the individual accumulation patterns of eight heavy metals.

Phosphate removal from aqueous solutions was investigated using chemically modified sugarcane bagasse. The modified sugarcane bagasse (MSBG) is an agricultural by-product adsorbent with anion exchange functionality MSBG and raw sugarcane bagasse (SBG) were characterized by elemental analysis, zeta-potential analysis surface-area determination, and SEM. Adsorption kinetics and the equilibrium of phosphate between aqueous solutions and MSBG were studied. The adsorption capacity of MSBG was $21.3\mathrm{mg}·{\mathrm{g}}^{-1}$ at natural pH when $50\mathrm{mg}{\mathrm{L}}^{-1}$ of phosphate solution was adsorbed by 0.100 g of sorbent. The kinetic data was fitted using a pseudo-first-order equation and a pseudo-second-order equation. Among the kinetic model studies, the pseudo-second-order equation was the best-fit model for describing the adsorption process. Equilibrium data were modeled using the Langmuir and the Freundlich isotherms. The Langmuir isotherm model fits much better than the Freundlich model. The desorption study indicated that the sorbent could be recovered in 0.05 M NaOH solution within 30 min.

Bi-based oxyhalide ${\mathrm{Bi}}_4{\mathrm{TaO}}_8\mathrm{X}$ ($X=\mathrm{Cl}$, Br, I) photocatalysts have been prepared by the combined method of liquid phase and solid state reactions and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). Using the azo dye wastewater simulated by aqueous methyl orange (MO) solutions, photocatalytic activity of these catalysts was studied under ultraviolet light, visual light, and solar irradiation. All of the samples had high photocatalytic activity. After 2 h of ultraviolet radiation, the degradation efficiency of methyl orange by ${\mathrm{Bi}}_4{\mathrm{TaO}}_8\mathrm{X}$ ($X=\mathrm{Cl}$, Br, I) was as high as 100%. Under visible-light and solar irradiation, the photocatalytic activity decreased in the order ${\mathrm{Bi}}_4{\mathrm{TaO}}_8\mathrm{I}>{\mathrm{Bi}}_4{\mathrm{TaO}}_8\mathrm{Br}>{\mathrm{Bi}}_4{\mathrm{TaO}}_8\mathrm{Cl}$. More than 90% degradation efficiency was observed for ${\mathrm{Bi}}_4{\mathrm{TaO}}_8\mathrm{I}$ after 12 h of solar irradiation. Furthermore, the photocatalytic degradation kinetics of methyl orange have been investigated under different types of light irradiation.

Performance of a membrane bioreactor (MBR) in removal of formaldehyde from synthetic wastewater was investigated. Batch tests for biodegradation of formaldehyde indicated that bioreactors containing acclimated sludge were able to remove up to 99.9% of the formaldehyde from solution. The 12-L MBR was equipped with a submerged hollow-fiber ultrafiltration (UF) membrane with $0.85{\mathrm{m}}^2$ filtration area. The unit was operated at a hydraulic retention time of 10 h in aerobic mode with formaldehyde as the sole carbon source for microbial growth. The results revealed that the MBR reduced formaldehyde concentration from $526\pm 30$ to a $1.39\pm 0.73\mathrm{mg}/\mathrm{L}$, corresponding to a removal efficiency of $99.73\pm 0.14\%$. Increasing solid retention time (SRT) resulted in an increase in mixed liquor suspended solids (MLSS), leading to improved efficiency in removal of formaldehyde from the MBR. Flux decline during MBR operation was caused by accumulation of MLSS on the membrane surface. SRT did not affect flux decline, but did affect flux recovery after cleaning. Long SRT (60 days) led to greater flux recovery than shorter SRTs (30 and 10 days).

This study assessed the potential of ozone for the degradation of nine commonly used veterinary antibiotics (five sulfonamides, three tetracyclines, and one macrolide) in swine wastewater pretreated by sequencing batch reactor (SBR). The apparent second-order rate constants for the reactions of selected antibiotics toward ozone in Milli-Q water ($k_{{\mathrm{O}}_3}$ at pH 7.0 and $T=20°\mathrm{C}$) were determined by competition kinetics as follows: sulfonamides [$(1.9–6.2)\times {10}^6{\mathrm{M}}^{-1}{\mathrm{s}}^{-1}$], tetracyclines ($6.9\times {10}^6\mathrm{\text{to}}1.7\times {10}^7{\mathrm{M}}^{-1}{\mathrm{s}}^{-1}$), and tiamulin ($3.8\times {10}^5{\mathrm{M}}^{-1}{\mathrm{s}}^{-1}$). The antibiotics could be quickly degraded by ozone in the SBR effluent with degradation rates following the order of their $k_{{\mathrm{O}}_3}$ values. In the SBR effluent, the dissolved organic materials strongly competed for oxidants against antibiotics, while the suspended solids had insignificant influence on antibiotics degradation. The reaction mechanism was primarily direct oxidation via ozone rather than indirect oxidation via hydroxyl radicals. Overall, ozonation is a feasible polishing process, subsequent to biological treatment, for removal of residual antibiotics from swine wastewater.

The influence of different variables in the photoelectro-Fenton process for the treatment of landfill leachate was investigated using an experimental design methodology. The variables considered in this study include ferrous ion dosage, hydrogen peroxide concentration, and current density. Response factors were color removal and chemical-oxygen demand (COD) removal efficiency after a 90-min reaction. The response surface methodology models were derived based on the results of color removal and COD removal, and the response surface plots were developed accordingly. The organic components before and after application of the photoelectro-Fenton process were investigated by gas chromatography-mass spectroscopy.

The present study investigates the adsorption characteristics of Cu(II) onto a low-cost biosorbent, pineapple leaf powder (PLP). Results of batch adsorption experiments showed that PLP could effectively remove Cu(II) from aqueous solution. Functional groups of PLP responsible for binding the ${\mathrm{Cu}}^{2+}$ were identified. The uptake of ${\mathrm{Cu}}^{2+}$ by PLP was very rapid, and 90% of Cu could be removed within the first 20 min. A pseudo-second-order equation could describe the kinetic data well. Copper adsorption was highly dependent on solution pH, and the removal efficiency was greater at a higher pH and low ionic strength. The apparent activation energy was calculated to be $6.99\mathrm{kJ}{\mathrm{mol}}^{-1}$. The adsorption increased with temperature, suggesting an endothermic reaction. The maximum adsorption capacities calculated from Langmuir isotherms was $9.28\mathrm{mg}{\mathrm{g}}^{-1}$ at pH 5.0. From the perspective of waste utilization, high copper adsorption capacity, and freely abundant availability of this low-cost adsorbent, PLP is potentially useful for future practical applications.

Humic acid (HA) removal from water with inorganic polyaluminum coagulants is reported in this paper. Polyaluminum chloride (PAC) and three kinds of polyaluminum chloride sulfate (PACS) with a $[{\mathrm{SO}}_4^{2-}]/[{\mathrm{Al}}^{3+}]$ ($S$) molar ratio of 0.02, 0.06, and 0.10 were prepared. The coagulation behaviors of these coagulants were investigated in the view of coagulant dosage, initial pH, and aging time. PACS ($S=0.06$) showed the best HA removal efficiency, and there was no restabilization within a broad effective dosage range. The proper initial pH range was broad and was 4.0–9.0 for PACS ($S=0.06$). The stability of PACS ($S=0.06$) reduced with a long aging time, so the proper aging time should not exceed 1 month. The aluminum species distribution, particle mean size, charge neutralization, and infrared spectrum of prepared coagulants were tested. Results showed that $\mathrm{S}{\mathrm{O}}_4^{2-}$ addition promoted the hydrolysis/polymerization of aluminum and reduced the charge neutralization capacity of PACS. Besides charge neutralization, the bridge-aggregation and sweep-flocculation mechanisms may play important roles for HA removal. The coexisting ${\mathrm{Ca}}^{2+}$ and kaolin slightly promoted the HA removal with polyaluminum coagulants.

Some paddy rice fields in central Taiwan had been exposed for more than 20 years to irrigation water containing metal. This study was carried out to evaluate the spatial distribution of heavy metal in soils exemplified by Cr, Cu, and Zn. Four sites were studied, and each site was divided into a regular grid of $5\mathrm{m}\times 5\mathrm{m}$ in the sampling process. At the surface, total metal concentrations were not normally distributed, showing a rather positively skewed profile. The concentration of Cr, Cu, and Zn away from the irrigation channel inlet, around 20 m, decreased by approximately more than 40 % with respect to that at the entrances. Findings revealed that a linear relationship between the logarithm of the metal concentration and the irrigation distance for each site was found. Vertically, the content of Cr, Cu, and Zn in soil decreased in two stages with respect to depth. The first stage was from the surface ($0–15\mathrm{cm}$ depth), to the bottom horizon ($15–30\mathrm{cm}$ depth) and the second stage was from the bottom horizon to the deeper horizon ($30–45\mathrm{cm}$ depth). The highest concentrations were observed at the irrigation inlets, and the concentration decreased with increasing distance from the irrigation inlet until 40 m. The lowest concentrations were found at the irrigation outlets. A linear relationship between the logarithmic metal concentration and irrigation distance for each site was found. In the case of soil exposed to irrigation water containing metal, the patent of water flow on the soil surface and in the subsurface was a determining factor in the redistribution of Cr, Cu, and Zn within the sites studied.

To control eutrophication in receiving water bodies, biological nutrient removal (BNR) of nitrogen and phosphorus has been widely used in wastewater treatment practice, both for the upgrade of existing wastewater treatment facilities and the design of new facilities. However, implementation of BNR activated sludge AS systems presents challenges attributable to the technical complexity of balancing influent chemical oxygen demand (COD) for both biological phosphorus (P) and nitrogen (N) removal. Sludge age and aerated/unaerated mass fractions are identified as key parameters for process optimization. Other key features of selected BNR process configurations are discussed. Emerging concerns about process sustainability and the reduction of carbon footprint are introducing additional challenges in that influent COD, N, and P are increasingly being seen as resources that should be recovered, not simply removed. Energy recovery through sludge digestion is one way of recovering energy from influent wastewater but which presents a specific challenge for BNR: generation of sidestreams with high nutrient and low COD loads. Technologies designed specifically to treat these side-stream loads are overviewed in this paper. Finally, relatively high levels of nitrous oxide emissions, a powerful greenhouse gas, have been shown to occur in the BNR process under certain conditions, particularly in the presence of high nitrite concentrations. The advantages of using process modeling tools is discussed in view of optimizing BNR processes to meet effluent requirements and to meet goals of sustainability and reducing carbon footprints.

Urban stormwater runoff has been implicated as a major source of excess nutrients to surface waters, contributing to the development of eutrophic conditions. Bioretention, a promising technology for urban stormwater pollution treatment, was investigated to determine whether an aluminum-based water treatment residual (WTR) amended bioretention soil media (BSM) could adsorb sufficient $P$ at low concentrations ($120\mu {\mathrm{g}\mathrm{P}\mathrm{L}}^{-1}$), extrapolated for a 20-year facility lifetime. Batch and minicolumn studies were employed to determine both an optimal BSM mixture and media performance. Media tests demonstrated $P$ adsorption proportional to WTR addition. Additional amendments such as quartz sand and hardwood bark mulch produced further significant variations in adsorptive behavior. WTR-amended media showed excellent $P$ removal, meeting the developed benchmark for adsorptive behavior. Predominantly, media met minimal $P$ adsorption requirements when it contained at least 4 to 5% WTR by mass (air dried). The use of an oxalate-extractable aluminum-, iron-, and phosphorus-based metric to predict media $P$ adsorption capacity, the oxalate ratio, is proposed. A media oxalate ratio of 20–40 is expected to meet the $P$ adsorption requirement.

Bioretention is an EPA-designated best management practice developed to mitigate negative ecological effects from urban storm-water. However, while these facilities perform well for the removal of a multitude of pollutants, in many cases they are ineffective in treating excessive storm-water nutrients such as phosphorus (P) that may induce surface water eutrophication. This work builds on the results of a previous paper, which describe initial studies on the use of aluminum-based water treatment residual (WTR) as a bioretention soil media (BSM) amendment. A 5% WTR-, 3% triple-shredded hardwood bark mulch-amended loamy sand BSM was investigated in a large-scale (0.9 m) column to determine the media P adsorption performance under varying hydrologic and pollutant concentration conditions. Results indicate that the WTR-amended media adsorbed 88.5% of the applied P mass, relative to a non-WTR-amended control media for which effluent P mass increased by 71.2%. The amended media consistently produced total phosphorus effluent event mean concentrations $<25\mu \mathrm{g}{\mathrm{L}}^{-1}$ and exhibited a maximum effluent concentration of only $70\mu \mathrm{g}{\mathrm{L}}^{-1}$. Media oxalate ratio (OR) correlated well with the observed media P adsorption performance, providing additional support for the effectiveness of this metric in predicting media P adsorption capacity.

Precoagulation is one of the effective pretreatments in membrane filtration. This process mitigates membrane fouling, which is the major drawback of membrane technology in drinking water and wastewater treatment. This study investigated the effects of precoagulation under different coagulation mechanisms on membrane fouling. Use of ultrasound in polytetrafluoroethylene (PTFE) membrane cleaning was also evaluated. In precoagulation, synthetic raw water was precoagulated using aluminum sulfate at different coagulation mechanisms, named electrostatic patch effect (EPE), charge neutralization (CN), and sweep flocculation (SW). Flocs produced from different coagulation mechanisms exhibited different sizes, structures, and strengths. Likewise, the fouling type generated from each mechanism was demonstrated as pore blocking for EPE, cake formation for SW, and combination phenomenon for CN. Moreover, this study indicated that the membrane flux was enhanced in the sequence of $\mathrm{EPE}>\mathrm{CN}>\mathrm{SW}$. The flux recovery rate after ultrasonic cleaning was in the sequence of $\mathrm{SW}>\mathrm{CN}>\mathrm{EPE}$. Finally, this study evidenced that the floc characteristics from various coagulation mechanisms affected membrane performance, fouling types, and ultrasonic cleaning efficiency.

Membrane bioreactors (MBRs) have attracted widespread attention in advanced water treatment because of their production of consistent and high-quality effluent. However, membrane fouling during operation has greatly hindered their application. Studies have suggested that a coating of ${\mathrm{TiO}}_2$ nanoparticles on membranes may reduce membrane fouling by enhancing the hydrophilicity of the membrane. In this study, two membranes were coated with ${\mathrm{TiO}}_2$ nanoparticles for membrane fouling mitigation. To evaluate the filtration performance of the ${\mathrm{TiO}}_2$ composite membranes, a synthetic wastewater was prepared to model the municipal wastewater for the MBR operation. The mixed liquor from the MBR was used in the filtration test to evaluate the performance of the ${\mathrm{TiO}}_2$ composite membrane. Filtration tests showed that membrane fouling was reduced substantially, which was attributable to the increased hydrophilicity of the membrane. Results also shows that optimal amount of coating is important in fouling mitigation. An ultrasonic washing test suggests that most of the ${\mathrm{TiO}}_2$ particles were firmly coated on the surface of the composite membrane.

A total of 11 boreholes were drilled at depths of 20–500 m to investigate the geochemical characteristics of groundwater at the KAERI Underground Research Tunnel (KURT) site. The groundwater chemistry up to a depth of 500 m at the KURT site was divided into $\mathrm{Ca}\mathrm{\text{-}}{\mathrm{HCO}}_3$ and $\mathrm{Na}\mathrm{\text{-}}\mathrm{Ca}\mathrm{\text{-}}{\mathrm{HCO}}_3$ types in the groundwater system. $\mathrm{Ca}\mathrm{\text{-}}{\mathrm{HCO}}_3$ and $\mathrm{Na}\mathrm{\text{-}}\mathrm{Ca}\mathrm{\text{-}}{\mathrm{HCO}}_3$ types showed that the geochemistry of the groundwater was influenced by weathering, dissolution, or precipitation of minerals in the system. The $\mathrm{Na}\mathrm{\text{-}}\mathrm{Ca}\mathrm{\text{-}}{\mathrm{HCO}}_3$ type of groundwater resulted from water-rock interaction such as weathering of plagioclase and dissolution of carbonate minerals. The $\mathrm{Na}/\mathrm{Cl}$ ratios increased at depths in the groundwater, implying that the weathering reaction of plagioclase occurred in the system, which released Na ions into the groundwater. Also, $\mathrm{Ca}/\mathrm{Cl}$ ratios showed a similar pattern in the groundwater, indicating a weathering reaction of carbonate minerals such as calcite that adds ${\mathrm{Ca}}^{2+}$ to the groundwater. The scattered distribution of ${\mathrm{Cl}}^{-}$ and tritium values indicated that a mixing process occurred in the groundwater system, which new water recharged into the system and mixed with old groundwater formation in the deeper part of groundwater system. The results from geochemical modeling showed reasonable fits in major ion profiles from observed values at groundwater sampling points. The model indicated that the simulated major processes, including major parameters used in the modeling, reflected the actual groundwater condition well. This study showed that the geochemical characteristics of the groundwater were controlled by various factors including the weathering of minerals such as plagioclase and K-feldspar, dissolution or precipitation of calcite, a mixing process, and, possibly, ion exchange.

Trimethoprim (TMP) is a widely prescribed antibiotic frequently detected in the aquatic environment. This study investigates the reactions of TMP and two sub structure model compounds [2, 4-diamino-5-methylpyrimidine (DAMP) and 3, 4, 5-trimethoxytoluene (TMT)] with chlorine dioxide (${\mathrm{ClO}}_2$), one of the common water disinfection oxidants, in batch reactors. A second-order kinetic model that incorporates the organic compounds’ acid-base speciation can sufficiently describe the reaction kinetics and is used to evaluate molecules’ reactive sites. TMP’s apparent second-order rate constant ($k_{\mathrm{app}}$) with ${\mathrm{ClO}}_2$ ranges at $5–33{\mathrm{M}}^{-1}·{\mathrm{s}}^{-1}$ from pH 2.7 to 9.1, corresponding to a half-life of 40.8 min at pH 7 and $1\mathrm{mg}/\mathrm{L}$ of ${\mathrm{ClO}}_2$. The reaction’s pH dependence is linked to protonation of the ring nitrogens on TMP’s 2, 4-diaminopyrimidinyl moiety. Comparison among TMP, DAMP, and TMT reveals that the reactivity of TMP to ${\mathrm{ClO}}_2$ resides mostly in its diaminopyrimidinyl moiety at neutral to alkaline pH, but centers in its trimethoxybenzyl moiety at acidic conditions. LC/MS analysis shows that oxidation of TMP by ${\mathrm{ClO}}_2$ generates Cl and OH substitutions at both diaminopyrimidinyl and trimethoxybenzyl moieties and other products. The reaction rate constants obtained in clean water matrix can be used to model the decay of TMP by ${\mathrm{ClO}}_2$ in surface water samples, but overestimate the decay in wastewater samples. Overall, transformation of TMP by ${\mathrm{ClO}}_2$ can be expected under typical ${\mathrm{ClO}}_2$ disinfection conditions.

Irrigation reuse of municipal effluents conserves freshwater resources and avoids direct nutrient discharges to surface waters. The sustainability of agricultural reuse programs, however, may be challenged by evolving phosphorus (P)-based nutrient management policies. This paper assesses the agricultural and environmental implications of soil P accumulation from effluent irrigation and discusses sustainability under guidelines to control P export in agricultural runoff and drainage. For typical regulatory maximum irrigation rates ($5.1\mathrm{cm}{\mathrm{wk}}^{-1}$), secondary effluents containing $3–4\mathrm{mg}\mathrm{P}{\mathrm{L}}^{-1}$ provide $\sim 90\mathrm{kg}\mathrm{P}{\mathrm{ha}}^{-1}{\mathrm{yr}}^{-1}$ and cause soil P enrichment beyond levels needed for optimum crop yields. Applied P potentially falls short of crop needs for advanced wastewater treatment processes with low ($<0.5\mathrm{mg}{\mathrm{L}}^{-1}$) effluent P or where hydraulic rates are restricted by soil, climatic, or regulatory conditions. Except for some locations where well-drained low P-retention soils overlie shallow groundwater, effluent-irrigated P has minimal impact on water quality. Most site assessment tools (P indices) were developed to identify fields with high P loss vulnerability from manure and commercial fertilizer application and do not explicitly address effluent-applied P. Adoption of P-management regulations not accounting for the differential behavior of P in effluent-irrigated fields may unnecessarily restrict agricultural irrigation of reclaimed water.

The indirect electrochemical oxidation of chlorophenols was studied. The process involved the simultaneous reduction of water to produce protons that were used for the subsequent electrochemical reduction of oxygen to generate hydrogen peroxide. In the presence of ferrous ions, a Fenton’s reagent was produced. In the process, upon reaction with hydrogen peroxide, ferrous ions were converted to the ferric state and were then regenerated at the cathode to recover ferrous ion—an important reactant in Fenton’s reagent. A series of chlorophenols, including 4-mono-, 6-dichloro-, and 4-trichlorophenol, were studied. The degradation of monochlorophenols proceeded in decreasing order: $3\mathrm{\text{-}}\mathrm{\text{chlorophenol}}>2\mathrm{\text{-}}\mathrm{\text{chlorophenol}}\sim 4\mathrm{\text{-}}\mathrm{\text{chlorophenol}}$; for dichloerophenols, the order was: 3, $5\mathrm{\text{-}}\mathrm{\text{dichlorophenol}}>3$, $4\mathrm{\text{-}}\mathrm{\text{dichlorophenol}}>2$, $3\mathrm{\text{-}}\mathrm{\text{dichlorophenol}}>2$, $5\mathrm{\text{-}}\mathrm{\text{dichlorophenol}}>2$, $4\mathrm{\text{-}}\mathrm{\text{dichlorophenol}}>2$, $6\mathrm{\text{-}}\mathrm{\text{dichlorophenol}}$;and for trichloro-phenols, the order followed: 2, 3, $5\mathrm{\text{-}}\mathrm{\text{trichlorophenol}}>2$, 3, $6\mathrm{\text{-}}\mathrm{\text{trichlorophenol}}>2$, 4, $5\mathrm{\text{-}}\mathrm{\text{trichlorophenol}}>2$, 4, $6\mathrm{\text{-}}\mathrm{\text{trichlorophenol}}$. The results indicated that the number and the relative locations (i.e., ortho, meta, or para) of chlorine substitution on the benzene ring played an important role in determining the rate and extent of chlorophenol oxidation. Regardless of the type of chlorine-substituted phenol, two major reaction pathways were responsible for the intermediate degradation of chlorophenols: hydroxyl radical attack (hydroxylation) and dechlorination. The detailed kinetics of the degradation of chlorophenols was studied in detail using 2-chlorophenol. Formic acid and acetic acid were the major end products that, in combination, contributed to 70% of the residual total organic carbon (TOC). Three other minor intermediates, 2-chloro-hydroquinone (2-Cl-HQ), 2-chloro-catechol (2-Cl-CA), and 4-hydroxyl,2,2’-dichlorodiphenyl ether (HDCDH), were observed; each contributed to a small percentage of the residual TOC.

In this study, the adsorption performance of elemental mercury onto commercially produced Thief carbons (TCs) and TCs modified with ferric chloride and sodium chloride were investigated. The results indicate that the modifications of Thief carbons not only considerably enhanced their mercury sorption capacities but also change their mercury sorption mechanism. For example, modification of a Thief carbon with ferric chloride can increase its mercury sorption capacity from $21\mu \mathrm{g}/\mathrm{g}$ to $206\mu \mathrm{g}/\mathrm{g}$ (nearly a ten times increase), whereas reducing its surface area from $326{\mathrm{m}}^2/\mathrm{g}$ to $217{\mathrm{m}}^2/\mathrm{g}$. Ferric chloride is a better modification agent than sodium chloride. Analyses of the sorption mechanism with different tools, including X-ray photoelectron spectroscopy (XPS), indicate that physical sorption dominates raw Thief-carbons-based mercury sorption, whereas chemical sorption plays a much more important role in modified Thief-carbon-based mercury sorption. The reaction order and activation energy of ferric chloride modified Thief-carbon-based mercury chemisorption are 1 and $85.6\mathrm{kJ}/\mathrm{mol}·\mathrm{K}$, respectively.