Total Organic Carbon Decay Research Articles

Electrocoagulation using aluminum electrodes as a sustainable and economic method for the removal of kinetic hydrate inhibitor (polyvinyl pyrrolidone) from produced wastewaters

Electrocoagulation is a water treatment technology capable to remove a variety of organic pollutants from water. It is advantageous compared to chemical coagulation due to the controlled dissolution of coagulants by regulating the current density and pH. In this work, the removal of kinetic hydrate inhibitor (KHI) (polyvinyl pyrrolidone, PVP) from water by electrocoagulation using Al electrodes was investigated. The effects of several experimental conditions including the nature of the supporting electrolyte, the current density, and the initial pH value on the electrochemical dissolution of aluminum was evaluated. The findings of the experiments revealed that both chemical and electrochemical dissolution play important roles in the generation of hydroxo-aluminum species. Corrosion studies demonstrated that the presence of chloride ions in water promotes aluminum dissolving via pitting corrosion, whereas the presence of phosphate ions inhibits aluminum corrosion by the deposition of a thick passive layer of aluminum hydroxide/phosphate on the metal surface. The theoretical and experimental amounts of aluminum, increase linearly with increasing specific electrical charge for Q< 2.5 Ah/L, which correlates well with Faraday's Law. The removal of KHI from 0.1M NaCl aqueous solutions by electrocoagulation using aluminum electrodes achieved high removal efficiency in terms of total organic carbon (TOC) up to 95%. TOC decay during galvanostatic electrolysis confirmed the removal of KHI molecules by Al-electrocoagulation at different current densities and pH conditions. The primary mechanism involved in eliminating KHI from water by electrocoagulation using Al electrodes includes mainly the adsorption of PVP molecules on the surface of Al(OH)3 flocs and their enmeshment inside the solid coagulants.

Enhanced catalyst-free degradation and mineralization of ceftriaxone by UV/H2O2 and UV/S2O82− processes using KrCl excilamp (222 nm)

Ceftriaxone (CEF), a cephalosporin antibiotic, has been widely used in the treatment of complex bacterial infections and frequently detected in the aquatic environment. This study is the first to explore the degradation and mineralization of CEF in aqueous solution by UV/H2O2 and UV/S2O82- processes using KrCl excilamp (222 nm). CEF was degradable under direct photolysis (∼80 %), but not mineralized in terms of total organic carbon (TOC) decay. The degradation rate constants and mineralization up to 98 % decreased in the order: UV/S2O82- ≫ UV/H2O2 > UV. Radical scavenging tests showed the involvement of SO4•− and HO• as primary reactive oxygen species (ROS). Addition of Cl-, SO42-, NO3– and HCO3– anions in the range of 1–100 mM promoted the degradation in most cases, but the TOC decay in this concentration range was enhanced only by sulfates. High concentrations of NO3– and HCO3– inhibited the mineralization. The impact of anions as radical promoters in relation with generation of secondary ROS and their selectivity towards CEF and it intermediates is discussed. Finally, testing tap water as a real matrix showed complete degradation of CEF with a limited mineralization by UV/S2O82- process. This study demonstrates the great potential of mercury-free KrCl excilamp in catalyst-free persulfate oxidation system for effective elimination of antibiotics, such as CEF, from aqueous media.

Osmotic dewatering accelerates inherent sluggish kinetics of electro-Fenton process: Toward sustainable removal of organic contaminants

Refractory organic pollutants, especially at low concentrations, are very slowly degradable through a heterogeneous electro-Fenton (EF) process. This drawback, caused by limited mass transfer between in-situ produced oxidizing agents and organic molecules, negatively affects the overall performance of EF and thus restricts its large-scale deployment. In this study, we provided an innovative solution by integrating the EF process with an osmotically driven membrane technology to overcome this challenge. Osmotic dewatering was conducted to extract water continuously from the EF cell and keep the kinetics of oxidation reaction in its fast state. The hybrid process was operated in two different modes, EF – Forward osmosis (FO) and EF – pressure retarded osmosis (PRO), where the membrane active layer and underlying support faced the feed solution, respectively. Rhodamine B (RhB) and Reactive Red 120 (RR120) were utilized as probe organic contaminants and their degradation rate, total organic carbon (TOC) decay, mineralization current efficiency (MCE), and specific energy consumption (SEC) were evaluated for a single EF and hybrid EF-FO and EF-PRO processes. Comparing with a single EF reaction, TOC decay improved by 57.9 ± 2% and 70.4 ± 6% using EF-FO and EF-PRO processes, respectively. Overall, MCE of hybrid processes surpassed 100% while it remained under 50% for a single EF reaction. SEC calculations showed a significant reduction in energy consumption, by almost one-third, when the EF reaction is integrated with the FO process. To demonstrate the practicality of our hybrid process at a very low concentration of organic pollutants, RhB-containing solution with an initial concentration of 2 ppm was subjected to EF and EF-PRO processes. EF-PRO system demonstrated 88.1% TOC removal which was 3-fold higher than that of a single EF process.

Treatment of olive oil mill wastewater by single electrocoagulation with different electrodes and sequential electrocoagulation/electrochemical Fenton-based processes

The treatment of olive oil mill wastewater (OOMW) by novel sequential processes involving electrocoagulation (EC) followed by electro-Fenton (EF) or photoelectro-Fenton (PEF) under UVA irradiation has been studied using a boron-doped diamond anode and an air-diffusion cathode for H2O2 electrogeneration. Their performance was monitored from the removal of total organic carbon (TOC), chemical oxygen demand, turbidity, total solids and total nitrogen, as well as from the energy consumption. Preliminary EC assays were performed with one pair of electrodes made of Al, Fe, AISI 304 or AISI 316L. The Fe/Fe cell showed the best performance, yielding 40% TOC decay in 20 min. Subsequent EF or PEF at natural pH 7.2 performed similarly, whereas PEF became superior at pH 3.0 due to the action of UVA photons. Comparison between EC/PEF and single EF or PEF at pH 3.0 and 25 mA cm−2 with 0.50 mM Fe2+ revealed the positive outcome of the sequential process, attaining 97.1% TOC abatement after 600 min. GC–MS analysis of the raw wastewater allowed identifying 18 cyclic and 27 aliphatic compounds, most of which could not be removed by EC. The final solutions in EC/EF and EC/PEF contained a large plethora of persistent long-chain aliphatic acids and alkanes.

A Kinetic and Mechanismic Study of Plasma-Induced Degradation of Monochloropropionic Acids in Water by Means of Anodic Contact Glow Discharge Electrolysis

Decomposition of aqueous monochloropropionic acids (MCPAs) was investigated by means of anodic contact glow discharge electrolysis (CGDE). With the decay of MCPAs, the corresponding total organic carbon (TOC) also decreased smoothly. Furthermore, it was found that chlorine atoms in the MCPAs were released as chloride ions. As the main by-products, oxalic acid and formic acid were detected. The acetic acid (CA), monochloroacetic acid (MCA), and propanedioic acid (PDA) were also detected as the primary intermediates for decomposition of the corresponding MCPAs. The decay of both MCPAs and TOC obeyed the first-order kinetics, respectively. The apparent rate constant for the decay of MCPAs increased with the increase inpKavalues of MCPAs, while that for the decay of TOC was substantially unaffected. The reaction pathway involving the successive attack of hydroxyl radical and the carbon chain cleavage were discussed based on the products and kinetics.

Degradation of trans-ferulic acid in acidic aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

Solutions of pH 3.0 containing trans-ferulic acid, a phenolic compound in olive oil mill wastewater, have been comparatively degraded by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Trials were performed with a BDD/air-diffusion cell, where oxidizing OH was produced from water discharge at the BDD anode and/or in the solution bulk from Fenton’s reaction between cathodically generated H2O2 and added catalytic Fe2+. The substrate was very slowly removed by AO-H2O2, whereas it was very rapidly abated by EF and PEF, at similar rate in both cases, due to its fast reaction with OH in the bulk. The AO-H2O2 process yielded a slightly lower mineralization than EF, which promoted the accumulation of barely oxidizable products like Fe(III) complexes. In contrast, the fast photolysis of these latter species under irradiation with UVA light in PEF led to an almost total mineralization with 98% total organic carbon decay. The effect of current density and substrate concentration on the performance of all treatments was examined. Several solar PEF (SPEF) trials showed its viability for the treatment of wastewater containing trans-ferulic acid at larger scale. Four primary aromatic products were identified by GC–MS analysis of electrolyzed solutions, and final carboxylic acids like fumaric, acetic and oxalic were detected by ion-exclusion HPLC. A reaction sequence for trans-ferulic acid mineralization involving all the detected products is finally proposed.

Cathodic polarization effect on the electro-Fenton regeneration of activated carbon

The regeneration of dye-adsorbed activated carbon (AC) using an electro-Fenton approach was studied and compared with typical regeneration methodologies (thermal, solvent extraction, and Fenton). The cathodic polarization effect of the electro-Fenton process on the AC surface was compared based on the textural and structural properties surface via physicochemical characterization techniques. The total organic carbon decay and color removal of a dye-contaminated model solution were also studied using the different methodologies, and several regeneration cycles were employed for each methodology in order to assess the regeneration efficiency and correlate it with AC structural changes. The results show that the electrochemical process is the best method to regenerate AC because it maximizes the adsorption efficiency (approximately 80–90 %) compared to other methods of regeneration (<20 %) after 10 working cycles. These results led us to conclude that cathodic polarization regenerates the AC more efficiently than conventional methods.

Electrochemical Treatment of Biotreated Landfill Leachate Using a Porous Carbon Nanotube-Containing Cathode: Performance, Toxicity Reduction, and Biodegradability Enhancement

Abstract The electrochemical treatment of biotreated landfill leachate was carried out using a Ti/SnO2-Sb2O5-IrO2 anode and a porous carbon nanotube-containing cathode. The ideal pollutant removal has been achieved by the electrochemical treatment evaluated by the decay of total organic carbon (TOC), chemical oxygen demand (COD), ammonia nitrogen (NH3-N), and total nitrogen (TN). The influences of cathodic potential and external addition of Fe2+ on TOC decay evidenced that both electro-Fenton oxidation and anodic oxidation were accounted for pollutant degradation. Cl− can play an important role in the removal of NH3-N and TN. The determination of dehydrogenase activity and BOD5/COD showed that the leachate toxicity became weaker and the biodegradability was enhanced after the electrochemical treatment. These results suggest that the electrochemical process may present a promising alternative for the advanced treatment of biotreated landfill leachate.

Kinetic modeling of electrochemical oxidation of phenol on boron-doped diamond anode in the presence of some inorganic species

Phenolic wastewater from many industries contains inorganic species such as cyanide, sulfide, ammonium, thiocyanate, etc. Presence of these inorganic pollutants in phenolic wastewater could hinder the proper understanding of phenol oxidation kinetics when chemical oxygen demand (COD) decay data are used in the kinetic modeling, because these inorganic species exert oxygen demand as phenol. Unlike COD decay data, total organic carbon (TOC) decay data does not have any correlation with such inorganic species, and also available TOC measurements techniques are currently better in terms of automation, accuracy, and reliability compared with COD measurement techniques. In the present study, the kinetics of electrochemical oxidation of phenol on boron-doped diamond anodes in synthetic wastewater containing sulfide, cyanide, and ammonia species in single, binary, tertiary, and quaternary mix matrixes were modeled via employing current limiting modeling (CLM) using TOC in addition to traditional COD decay data. For all the different mix matrixes investigated, comparable trends describing the kinetics of electrochemical oxidation process were obtained for both the COD and the TOC decay models. Statistical diagnostics of the developed COD and TOC decay models parameters revealed that the operating regimes of the oxidation processes were accurately predicted to be limited by mass transfer. These results establish the suitability of using TOC decay for the CLM of phenol oxidation kinetics both in the presence and absence of the inorganic species. Based on these results in relation to the disparity between COD and TOC as parameters for evaluating phenol oxidation kinetics, it was concluded that TOC decay data are more appropriate compared with COD decay data for the CLM of kinetics of electrochemical oxidation of phenol in wastewater containing inorganic species that exert oxygen demand.

Behavior of dioxin like PCBs and PBDEs during early diagenesis of organic matter in settling material and bottom sediments from the sewage impacted Buenos Aires' coastal area, Argentina.

Settling particles (SPs) and sediments collected in the Buenos Aires sewer area were analyzed for dioxin like polychlorinated biphenyls (dlPCBs) and polybrominated diphenyl ethers (PBDEs) to follow early diagenetic changes during transport and deposition of organic matter. SP showed a temporal trend of higher total organic carbon (TOC) and fresher dlPCBs and PBDEs signatures during warm-rainy months related to more efficient washout of residues. TOC-normalized sediment trap concentrations suggest a diagenetic magnification of dlPCBs during cold-dry months due to enhanced decomposition of TOC, whereas most labile PBDEs appear to follow TOC decay. The diagenetic behavior of individual congeners along seasonal changes (cold/warm) and during deposition (bottom sediment/SP) shows the selective preservation of heavier, more persistent congeners with a positive relationship with sediment half-lives. The 3-4 times diagenetic magnification of heavier congeners observed in bottom sediments would be a prevailing long-term pathway for dlPCBs and PBDEs bioaccumulation in detritus feeding organisms.

Plasma-Induced Decomposition of Dichlorophenols and Trichlorophenols in Water by Means of Anodic Contact Glow Discharge Electrolysis

Decomposition of aqueous dichlorophenols and trichlorophenols was investigated by means of contact glow discharge electrolysis. With the decay of chlorophenols (CPs), the amount of total organic carbon (TOC) in water also decreased smoothly, indicating that carbon atoms of benzene nucleus could be eventually converted to inorganic carbons. And, it was found that chlorine atoms in the CPs were released as chloride ions. As the by-products, oxalate and formate were formed. The chlorine derivatives of 1,4-hydroquinone and 1,4-benzoquinone were detected as the primary intermediates in the initial stage of decomposition of each of CPs. The decay of both CPs and TOC obeyed the first-order rate law, respectively. The apparent rate constants for the decay of CPs increased with the decrease in pKa values of CPs, while those for the decay of TOC were substantially unaffected.

Destruction of 4-phenolsulfonic acid in water by anodic contact glow discharge electrolysis

Destruction of 4-phenolsulfonic acid (4-PSA) in water was carried out using anodic contact glow discharge electrolysis. Accompanying the decay of 4-PSA, the amount of total organic carbon (TOC) in water correspondingly decreased, while the sulfonate group of 4-PSA was released as sulfate ion. Oxalate and formate were obtained as minor by-products. Additionally, phenol, 1,4-hydroquinone, hydroxyquinol and 1,4-benzoquinone were detected as primary intermediates in the initial stages of decomposition of 4-PSA. A reaction pathway involving successive attacks of hydroxyl and hydrogen radicals was assumed on the basis of the observed products and kinetics. It was revealed that the decay of both 4-PSA and TOC obeyed a first-order rate law. The effects of different Fe ions and initial concentrations of 4-PSA on the degradation rate were investigated. It was found that the presence of Fe ions could increase the degradation rate of 4-PSA, while initial concentrations lower than 80 mmol/L had no significant effect on kinetic behaviour. The disappearance rate of 4-PSA was significantly affected by pH.

Plasma-induced complete destruction of tetrachlorophenols in an aqueous solution

The complete destruction of tetrachlorophenols (TCPs) in water irradiated with a dc plasma was carried out. The plasma was generated locally between an electrolytic solution and the tip of an anode in contact with the surface by means of contact glow discharge electrolysis. From the beginning of the reaction, the TCPs were smoothly degraded. With the disappearance of the TCPs, the amount of total organic carbon (TOC) in water concurrently decreased, which signified the effective conversion of organic carbons to inorganic ones. In addition, all the chlorine atoms of the TCPs were eventually liberated as chloride ions. Thus, it was shown that TCPs could be thoroughly mineralized under these conditions. Furthermore, it was revealed that the decay of both the TCPs and TOC obeyed the first-order rate law. The apparent rate constant for the decay of TCPs rose with a decline in the pKa values of the TCPs, while for the decay of TOC the rate was substantially unchanged. The kinetic behaviour associated with the relative reactivity of TCPs could be interpreted on the basis of a reaction scheme involving successive attacks by the hydroxyl radicals generated in water by the action of the plasma.

Degradation of 4-chloro-2-methylphenol in aqueous solution by electro-Fenton and photoelectro-Fenton processes

Degradation of 4-chloro-2-methylphenol (PCOC), a refractory toxic chemical emitted to the environment from the industrial production of phenoxy herbicides was studied in aqueous solution. Electro-Fenton and photoelectro-Fenton processes were used as the degradation methods. H2O2, produced by the reduction of oxygen at carbon cathode reacted with dissolved metal ions to form hydroxyl radicals, which in turn reacted with PCOC sequentially to degrade the aromatic ring. The effects of using different [Fe2+]/[PCOC]0 and the effect of replacing Fe2+ by Mn2+ ion have been examined. It was found that degradation rate was increased with increasing [Fe2+]/[PCOC]0 ratio from 2 to 4. However, the total charge utilized during the treatment was also increased. The efficiency of PCOC degradation was observed to be higher when Mn2+ was used as the catalyst. The mineralization of aqueous solutions of PCOC, withdrawn from the reactor at certain time interval, has been followed by total organic carbon (TOC) decay and dechlorination. A fast and complete degradation of the aromatic ring was achieved in photoelectro-Fenton system. 41.7% TOC decay and complete dechlorination were observed by consuming only 141.4C electrical charge during a 300min photoelectron-Fenton treatment. In the case of electro-Fenton system, 280.7C electrical charge was consumed during 450min of electrolysis to attain a similar degradation of PCOC. 14.9% TOC removal and 89.3% dechlorination have been obtained in this system under the applied conditions.

Phenol and substituted phenols AOPs remediation

The oxidation of phenol and two substituted species (4-nitrophenol and 4-chlorophenol) has been carried out by means of the O 3, UV–vis, O 3 + UV–vis, TiO 2 + UV–vis, O 3 + UV–vis + TiO 2 and O 3 + TiO 2 systems. From UV–vis experiments, the quantum yield of these organics has been calculated (0.018, 0.005 and 0.017 mol per Einstein for phenol, 4-nitrophenol and 4-chlorophenol, respectively). Broadly speaking, the addition of titania powder results in a slight inhibition of the parent compound degradation rate, although a positive effect is experienced when measuring the chemical oxygen demand (COD) and total organic carbon (TOC) removals. Amongst the technologies investigated, those combining ozone and radiation show the best efficiency in terms of phenols elimination and also COD and TOC decay rates. A simple economy analysis of the processes illustrates how the combinations O 3 + UV–vis and O 3 + UV–vis + TiO 2 are the most attractive technologies, although some additional considerations have to be taken into account.

Study of Herbicide Alachlor Removal in a Photocatalytic Process through the Examination of the Reaction Mechanism

The reaction mechanism and intermediates of the photocatalytic degradations of alachlor in TiO2 suspensions using narrow-band UV radiation with a peak at 300 nm were investigated. The direct photolysis of alachlor was found to be an insignificant and slow process, but the addition of TiO2 enhanced the reaction rates by about 12 times. Intermediates were identified using liquid chromatography−electrospray ionization−mass spectrometry and MS/MS. A total of 8 major intermediates were identified. The evolution profiles of different intermediates were quantified and the reaction mechanism was proposed accordingly. The major degradation mechanisms of alachlor photocatalysis include dechlorination, dealkylation, hydroxylation, scission of the C−O bond, and N-dealkylation. Both the decay of alachlor and the total organic carbon (TOC) increased slightly with initial pH levels. The TOC analysis revealed the different degradation stages of the reaction, where a lag phase with very low TOC decay was followed by a mil...