Total Organic Carbon Reduction Research Articles

Effect of Feeding Rate on the Reduction of Total Volatile Solids and Organic Carbon during Combined Composting and Vermicomposting of Elephant Dung

One of the methods of treatment of animal waste to conserve our nature is vermicomposting in which waste-feeding rate is one of the important parameters to be considered. This paper is concerned with studying and analyzing the effect of feeding rate on the reduction of total volatile solid and total organic carbon during vermicomposting of elephant dung.
 The raw dung collected from the Central Zoo, Jawalakhel, Nepal was composted in a heap on the open ground after removal of inorganic substances by hand sorting and manually breaking of lumps. Composted dung only after two weeks was feed in the circular earthen flower pots having average diameter of 0.15 m and surface area of 0.017 m2 each with small holes at the bottom. The adult healthy Eiseniafetida with a stocking density of 1.6 kg-worm/m2 with feeding rates of 0.75, 1, 1.5 and 2kg-feed/kg worms/day in the batch basis were used in the separate sets for vermicomposting in moisture content of 70 to 80% at normal room condition in two cycles of eight weeks after two weeks of normal composting in a room.
 It was revealed from the experiment that the combined composting and vermicomposting system with feeding rate of 0.75 kg-feed/kg worms/day was more effective in reducing total volatile solids and total organic carbon content to 42.52% and 23.62% respectively after ten weeks.

Treatment Efficiency of Diffuse Agricultural Pollution in a Constructed Wetland Impacted by Groundwater Seepage

Diffuse agricultural pollution degrades water quality and is one of the main causes of eutrophication; therefore, it is important to reduce it. Constructed wetlands (CW) can be used as an effective measure for water quality improvement. There are two possible ways to establish surface flow CWs, in-stream and off-stream. We studied treatment efficiency of the in-stream free surface flow (FSW) Vända CW in southern Estonia from March 2017 until July 2018. The CW consists of two shallow-water parts planted with cattail (Typha latifolia). According to our analyses, the CW reduced total phosphorus (TP) and phosphate (PO4-P) by 20.5% and 16.3%, respectively, however, in summer, phosphorus removal was twice as high. We saw significant logarithmic correlation between flow rates and log TP and log PO4-P removal efficiency (rs = 0.53, rs = 0.63, p < 0.01 respectively). Yearly reduction of total organic carbon was 12.4% while total inorganic carbon increased by 9.7% due to groundwater seepage. Groundwater inflow also increased the concentration of total nitrogen in the outlet by 27.7% and nitrate concentration by 31.6%. In-stream FWS CWs are a promising measure to reduce diffuse pollution from agriculture; however, our experience and literature data prove that there are several factors that can influence CWs’ treatment efficiency.

An integrated approach for efficient conversion of Lemna minor to biogas

Aquatic weed, Lemna minor was evaluated for its potential as a feedstock for gaseous fuel production (biohythane) in an integrated strategy. Three approaches viz., acidogenic fermentation (HAF), electrohydrogenesis (HMEC) and methanogenesis (MAD), were evaluated in single stage as well as in different combinations of two stage (HAF → HMEC, HAF → MAD) and three stage (HAF → HMEC → MAD, HAF → MAD → HMEC) to tap the maximum feasible energy. Compared to single and two-stage operations, three-stage operation evidenced higher biogas (H2 + CH4) yield with remarkable total organic carbon (TOC) reduction. Irrespective of the integration sequence, HAF in first stage depicted the possibility of harnessing higher energy by accumulation of volatile fatty acids (VFA) along with H2 production. Similarly, integration of MAD in second stage showed the possibility of tapping higher energy rather than HMEC due to higher carbon loss as CO2 coupled to more H2 fraction in biogas in case of HMEC. Among, three-stage integrations, higher biogas yield and energy recovery was observed in HAF → MAD → HMEC (38.77 mol biogas/kg TOCR; 25,415 KJ/kg TOCR) as compared to HAF → HMEC → MAD (37.79 mol biogas/kg TOCR; 15,416 KJ/kg TOCR). Along similar lines, analysis of organic carbon flow exhibited significant substrate degradation in three stage integrations (72.5–81.4%) as compared to second (66.2–70%) and first stage (39.7–56.5%).

Electrochemical in-situ hydrogen peroxide generation in a packed-bed reactor for Fenton oxidation of p-nitrophenol in aqueous solution

Advancements in electrochemical generation of hydrogen peroxide (H2O2) in Fenton systems hasten the realization of a “chemical-free” treatment of organic pollutants in water. The present study used a novel air-sparged, packed-bed electrode configuration with reticulated vitreous carbon (RVC) as packing material for electrochemical H2O2 generation. The effects of initial pH, applied current, sparging rate, mass of RVC and electrolyte concentration on cumulative H2O2 generation and current efficiency were evaluated. From the results, the operating conditions that gave the optimal cumulative H2O2 generation and current efficiency were pH0 = 2.0, applied current = 50 mA, air sparging rate = 0.5 L min−1, mass of RVC = 0.75 g, and electrolyte concentration = 100 mM Na2SO4. The same reactor configuration was used for the treatment of the model contaminant from aqueous solution and caused the complete removal of p-nitrophenol (pnP) within a 2 h duration. Mineralization of aromatic intermediates was confirmed by gas chromatography – mass spectroscopy analyses of samples and supported by the reduction in chemical oxygen demand and total organic carbon.

Decolorization of Mono Azo Dye and Textile Wastewater using Nano Iron Particles

Treatment of textile dyeing wastewater using existing physio‐chemical and biological methods is challenging and needs an efficient technique to manage toxic and recalcitrant textile dyes in the environment. As the nano iron particles are highly reactive, nontoxic, and cost‐effective, this study demonstrates the potential of nano iron particles in the decolorization of mono azo methyl orange dye and application to decolorize textile dyeing wastewater. The dye was decolorized 98% within 30 min of reaction time and 54% reduction in total organic carbon was observed. The detected intermediates products such as m/z 149, 128, 84, 73, 56, 55 confirm the efficiency of nano iron particles in degrading textile dyes into lower molecular compounds. The dye decolorization pathway and reaction mechanism are proposed. The treatment of real textile dyeing industry wastewater showed 82% dye color removal and reasonable reduction in the quantity of inorganic pollutants such as chlorides, sulfates. Hence,nano iron particles are highly recommended to remediate textile dyeing wastewater effectively. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S366–S376, 2019

Biodecolourization and biodetoxification of dye-containing wastewaters from leather dyeing by the native fungal strain Trametes villosa SCS-10

The native fungal strain Trametes villosa SCS-10 was investigated for its ability to treat wastewaters from real dyeing of leather produced in pilot-scale. Four types of wastewater using different compositions and dyes (Acid Red 357 and Acid Orange 142) were produced and used in the assays. Three culture conditions were studied. The efficiency of the treatment was assessed in terms of biodecolourization, mycoremediation: reduction of chemical oxygen demand (COD), biological oxygen demand (BOD), total organic carbon (TOC) and biodetoxification. The treatment resulted in between 50–70% of biodecolourization and 40–60% of COD and TOC reduction of the raw wastewater without nutrient addition (N0). However, when wastewaters were supplemented with a high (N1) and a reduced (N0.5) nutrient supply, over 90% of biodecolourization and over 80% of COD and TOC reduction were achieved. The treatment N0.5 allowed the highest values of colour, TOC and COD reduction, which were related to the major peaks of laccase activity (1000–1300 UL−1). The ecotoxicity assays with Raphidocelis subcapitata and Vibrio fisheri demonstrated that the fungal treatment resulted in 50–70% of biodetoxification. The MTT assay revealed that the treated wastewaters did not present cytotoxic effects to the cell line V79. These promising results show that Trametes villosa is suitable for the treatment of wastewater from leather dyeing. Further studies are required to improve the applicability of selected fungal strains in the treatment of wastewater from the tannery industry.

EVALUATION OF DIRECT PHOTOLYSIS, ELECTROOXIDATION AND PHOTOELECTROOXIDATION FOR RHODAMINE-B DEGRADATION

Abstract The focus of this study is to evaluate the efficiency of oxidation processes in the treatment of a solution containing Rhodamine-B (RhB) used in various industrial applications. The advanced oxidation processes of electrooxidation (EO) and photoelectrooxidation (PEO) were used. At the same time, direct photolysis (DP) was also applied. Total organic carbon (TOC) reduction and color removal were evaluated. There was an efficient color removal when DP was performed, and the color removal efficiency was the highest when NaCl was used as supporting electrolyte for PEO and EO. However, the TOC reduction was low, indicating that the degradation of the color does not correspond to the pollutant mineralization.

Selective antibiotic resistance genes in multiphase samples during biofilm growth in a simulated drinking water distribution system: Occurrence, correlation and low-pressure ultraviolet removal

The aim of this study was to gain comprehensive insights into the characteristics of antibiotic resistance genes (ARGs) in multiphase samples from drinking water distribution pipelines using a simulated biofilm reactor. During 120 d of continuous operation, common parameters and six ARGs (ermA, ermB, aphA2, ampC, sulII, and tetO) in samples of three phases (water, particle, and biofilm) from the reactor were investigated, which demonstrated secondary contamination by ARGs. Abundances of the six ARGs in the reactor effluent increased gradually, and in the 120 d effluent, the relative abundances of aphA2 and sulII were the highest, at 9.9 × 10−4 and 1.3 × 10−3, respectively, with a 1.5-fold and 2.8-fold increase, compared with those in the influent. The relative abundances of the six ARGs in the biofilm phase increased significantly (P < 0.05) at 120 d, which was caused by robust bacteria in biofilm that was newly exposed following the detachment of a large piece of aging biofilm. In the particle phase, four of the ARGs did not change significantly during the 120 d period. The six ARGs in the samples of three phases showed a negative correlation with residual chlorine in the pipe water, which demonstrated that low abundance of ARGs in the samples of three phases was related to the improvement of residual chlorine. The proportion of cultivable bacteria illustrated that the robust and active bacteria were negatively correlated with the six ARGs in the biofilm. Total organic carbon (TOC) in the pipeline showed a positive correlation with the proportion of cultivable bacteria in both the water and biofilm phases, which indicated that a TOC reduction in the pipeline contributed to low abundance of ARGs. With low-pressure ultraviolet (LP-UV) irradiation of 20 mJ/cm2, ARGs in the samples of three phases were efficiently controlled, which showed that LP-UV can be used for ARG removal in terminal water for supplemental bactericidal treatment of pipeline effluent.

Fabrication of novel carbon quantum dots modified bismuth oxide (α-Bi2O3/C-dots): Material properties and catalytic applications

The present work reports the facile and the template free sonochemical synthesis of a novel catalyst, α-Bi2O3/C-dots, for the degradation of indigo carmine (IC) dye, its simulated dyebath effluent and levofloxacin under visible light catalysis. The compositional, structural, optical and morphological analysis of α-Bi2O3/C-dots was studied using analytical, spectroscopic and microscopic techniques. X-ray diffraction (XRD) results confirmed the presence of a monoclinic phase of α-Bi2O3 in the nanocomposite and crystallite size of 28.75 nm. Photoluminescence (PL) and UV–vis diffuse reflectance spectra (UV-DRS) studies showed good optical properties and a band gap of 2.49 eV. The synthesized photocatalyst showed superior visible-light driven photocatalytic activity for the degradation of indigo carmine dye (86% dye degradation in 120 min) compared to pure α-Bi2O3 (57%). α-Bi2O3/C-dots also exhibited 79% degradation of antibiotic drug levofloxacin within 120 min, under optimized conditions of pH, catalyst dose and initial dye concentration. Scavenger studies revealed that hydroxyl radicals and electrons played predominant roles in the photocatalytic degradation of IC dye. With respect to total organic carbon (TOC) analysis, 68.8% total organic carbon reduction of the IC dye (10 mg/L) was observed under the same experimental conditions. The catalytic efficiency of C-dots in the photocatalytic process is explained by proposing a degradation mechanism.

Water consumption management in polyethylene terephthalate (PET) bottles washing process via wastewater pretreatment and reuse

The increasing recycling of polyethylene terephthalate (PET) bottles requires more and more fresh water during washing the bottles. The post-washing wastewater is often treated as effluent, whereas it could be reused in the technological process after appropriate pretreatment. In this paper, coagulation together with flocculation is proposed for use in the pretreatment of the wastewater arising during PET bottles washing. Five flocculants and six coagulants were tested. The turbidity and total organic carbon (TOC) were reduced by up to 98% and 69%, respectively. Out of the tested flocculants, Praestol 611 BC at a dose of 2 mg/dm3 had the best performances. The best coagulant in TOC reduction was PIX-123. As for turbidity reduction, ALS was the best, but PIX-123 was comparable, and therefore, PIX-123 was indicated as most suitable in simultaneous reduction of TOC and turbidity. The coagulation and flocculation together reduced the amount of pollutants and contaminants in the post-washing wastewater to the levels allowing the water to be reused in the washing process, which could bring both economical and ecological benefits.

Enhanced synergistic degradation efficiency using hybrid hydrodynamic cavitation for treatment of tannery waste effluent

The treatment of recalcitrant bio refractory pollutants especially common in wastewater emanating from the tannery industries is a major challenge to the industries due to the absence of an efficient treatment technology, high operational costs as well as in view of the stringent rules imposed by the various environmental and governmental regulatory bodies. This study reports the degradation of organic pollutants present in tannery waste effluent (TWE) using hybrid hydrodynamic cavitation (HC) such as HC + ozone (O3), HC + hydrogen peroxide (H2O2) and HC + Fenton's reagent. HC treatment alone caused a reduction of 14.46% chemical oxygen demand (COD), 12.60% total organic carbon (TOC), 10.01% total dissolved solids (TDS) and 34.82% total suspended solids (TSS) of the TWE samples at the optimum inlet pressure of 500 kPa within 120 min. It also caused an increase in biodegradability index (BI) value from 0.33 to 0.43 indicating increased biodegradability, whereas dilution of the TWE samples did not enhance the HC process efficiency. HC combined with O3 was effective as COD and TOC reduction increased to 26.81% and 17.96% respectively at the optimum loading of 7 g/h of O3. HC combined with H2O2 also significantly enhanced the degradation efficiency to a maximum of 34.35% COD and 19.71% TOC reduction due to the enhanced generation of hydroxyl radicals. However, HC combined with Fenton's process was found to be the most efficient hybrid process for the treatment of TWE at a maximum reduction of 50.20% COD and 32.41% TOC respectively at FeSO4.7H2O/H2O2 ratio of 1:3 (w/w). The requirement of H2O2 per g of COD reduction for HC + Fenton reduced to 1.95 g/g compared to the requirement of 3.02 g/g for HC + H2O2 process. Moreover, HC + Fenton's treatment increased the BI value from 0.28 to 0.46, which is an increase by 64% compared to an increase by 30% using HC alone. These hybrid techniques enhanced the BI of treated TWE and therefore may be used as a pre-treatment tool by integrating into existing biological treatment units in the conventional effluent treatment plants, in order to cause enhanced degradation of highly bio-recalcitrant organic pollutants. Other enhanced benefits include higher rate of mineralization of organic matter with lower cost of treatment. Hybrid HC + Fenton was the most energy efficient approach than HC process with a 75% reduction in the energy requirement and 56% reduction in treatment cost per mg of COD reduction of TWE.

Degradation of acetamiprid in UV/H2O2 and UV/persulfate systems: A comparative study

Acetamiprid (ACE) was degraded by using ultraviolet (UV) irradiation and UV based advanced oxidation processes (AOPs) including UV/hydrogen peroxide (UV/H2O2) and UV/potassium persulfate (UV/PS). Among them, UV/PS process exhibited the best performance for the elimination of ACE and reduction of total organic carbon (TOC). The degradation kinetics was comprehensively compared in terms of dose of oxidants, solution pH, and water matrix species. A linear relationship was tentatively developed between the [Oxidant]/[ACE] ratio and the pseudo-first-order kinetic rate constant (k). The degradation was significantly inhibited at basic conditions no matter for UV/H2O2 process or UV/PS process. The effects induced by the water matrix species including inorganic anions and natural organic matter (NOM) were also non-negligible. For UV/PS process, both SO4− and HO contributed to the ACE degradation, whereas only HO participated in the degradation in the UV/H2O2 process. The corresponding second-order rate constants of ACE with HO and SO4− were determined to be 7.59 × 108 and 3.68 × 108 M−1 s−1, respectively. Due to the different active radical species, different degradation products were detected through the HPLC-MS analysis. This work would be meaningful for the remediation of ACE from water by AOPs.

Photocatalytic ozonation under visible light for the remediation of water effluents and its integration with an electro-membrane bioreactor

Photocatalysis and photocatalytic ozonation under visible light have been applied for the purification of a complex aqueous matrix such as the grey water of Masdar City (UAE), by using N-doped brookite-rutile catalysts. Preliminary runs on 4-nitrophenol (4-NP) solutions allowed to test the reaction system in the presence of a model pollutant and to afford the relevant kinetic parameters of the process. Subsequently, the remediation of grey water effluent has been evaluated in terms of the reduction of total organic carbon (TOC) and bacterial counts. The concentration of the most abundant inorganic ionic species in the effluent has been also monitored during reaction. Photocatalytic ozonation under visible light allowed to reduce the TOC content of the grey water by ca. 60% in the optimized experimental conditions and to reduce the total bacterial count by ca. 97%. The extent of TOC mineralization reached ca. 80% when the photocatalytic ozonation occurred downstream to a preliminary electro-membrane bioreactor (eMBR). Coupling the two processes enhanced the global efficiency. In fact, the eMBR treatment lowered the turbidity and the organic load of the effluent entering the photocatalytic ozonation treatment, which in turn enhanced the extent of purification and disinfection.

Assessment of reaction intermediates of gamma radiation-induced degradation of ofloxacin in aqueous solution

Gamma radiolytic degradation of an antibiotic, ofloxacin (OFX) was investigated under different experimental conditions. The parameters such as initial OFX concentration, solution pH, absorbed dose and the concentrations of inorganic (CO32−) and organic (t-BuOH) additives were optimized to achieve the efficient degradation of OFX. The degradation dose constant values of OFX were calculated as 2.364, 1.159, 0.776 and 0.618 kGy−1 for the initial OFX concentrations of 0.05, 0.1, 0.15 and 0.2 mM with their corresponding (G (-OFX)) values of 0.481, 0.684, 1.755 and 1.971, respectively. Degradation rate of OFX was significantly increased with increase in the absorbed dose and decrease in the initial OFX concentration under acidic condition when compared to neutral or alkaline condition. Reaction of OFX in the presence of CO32− and t-BuOH showed that the degradation was primarily caused by the reaction of OFX with radiolytically generated reactive hydroxyl radicals. Mineralization extent of OFX was determined in terms of percentage reduction in total organic carbon (TOC) and results revealed that the addition of H2O2 enhanced the mineralization of OFX from 29% to 36.1% with H2O2 dose of 0.5 mM at an absorbed dose of 3.0 kGy. Based on the LC-QTOF-MS analysis, gamma radiolytic degradation intermediates/products of OFX were identified and the possible degradation pathways of OFX were proposed. Cytotoxicity study of the irradiated OFX solutions showed that gamma radiation has potential to detoxify OFX.

Mechanism and identification of reaction byproducts for the degradation of Chloramphenicol drug in heterogeneous photocatalytic process

The present work investigated the degradation behavior of chloramphenicol (CHPL) drug at a high concentration in the UV-TiO2 photocatalytic (UVPC) process to compare the performance of cleavage of CHPL molecule and total organic carbon (TOC) reduction. The reduction in TOC was mostly resulted from the cleavage of C-C homolytic bond which was in the accordance of LC-MS spectra. The TOC removal was trailed by 23.19% than CHPL with 100 mgL−1 using TiO2 1.25 gL−1, pH 3, and irradiation time of 45 min. The mechanistic routes of CHPL decomposition in the UVPC process are proposed and its synergy in the Fenton oxidation process is also explored. Total seven intermediates appeared in the mass spectra within the mass to charge ratio of 100–400. The proposed mechanism implied that intermediates were mostly originated by the decomposition of amide chain of CHPL molecule. The antimicrobial activity of CHPL towards the inactivation of E. coli XL 10GOLD was decreased by 67.4% after 45 min of decomposition.

Efficiency of a newly established in-stream constructed wetland treating diffuse agricultural pollution

Diffuse agricultural pollution, especially from intensively managed agricultural land is a major cause of eutrophication, therefore it is important to reduce the diffuse load to surface water. Constructed wetlands (CW) are an effective measure for improving water quality and reducing nutrient runoff from agriculture by using natural water treatment mechanisms. We studied treatment efficiency of an in-stream free surface flow (FSW) Vända CW in southern Estonia from 16th of March 2017 till 11th of January 2018. Vända CW has a catchment area of 2.2 km2 and of which approximately 62% is under intensive agricultural management. The CW consists of a sedimentation pond followed by two shallow water wetlands planted with cattail (Typha latifolia). Our analyses showed that the CW retained 17.5 kg phosphorus (P) ha−1 yr−1. During the warm period phosphate removal was up to 41.8% whereas annually it was only 14.4%. Phosphate removal efficiency showed strong negative correlation (R2 = 0.58, p < 0.001) with flow rate and therefore it can be seen that shorter retention time reduces significantly the overall P removal efficiency. The yearly reduction of total organic carbon was up to 3300 kg C ha−1 yr−1 while surprisingly the CW increased total nitrogen up to 1375 kg N ha−1 yr−1. The results demonstrate that the acclimatization period of newly established in-stream FWS CWs in northern countries can be relatively long and after two years of establishment we still cannot see satisfactory treatment processes, especially in nitrogen.

Photocatalytic activity of CuO/Cu(OH)2 nanostructures in the degradation of Reactive Green 19A and textile effluent, phytotoxicity studies and their biogenic properties (antibacterial and anticancer)

In this study, CuO/Cu(OH)2 (denoted as CuONs) nanostructures were synthesized relying to a cheap and rapid chemical co-precipitation method using copper sulfate and liquid ammonia as precursors. Results obtained from X-ray diffraction, and field emission scanning electron microscopy analysis revealed the crystalline nature of synthesized CuONs. Fourier transform infrared spectroscopy and energy dispersive spectroscopy studies showed interactions between copper and oxygen atoms. Synthesized CuONs showed the size in the range of 20–30 nm using high resolution transmission electron microscopy analysis. The photocatalytic degradation performance of Reactive Green 19A (RG19A) dye using CuONs was evaluated. The results showed that CuONs exhibited 98% degradation efficiency after 12 h and also complete mineralization in form of reducing chemical oxygen demand (COD) (84%) and total organic carbon (TOC) (80%). The nanocatalyst was recovered from the dye containing solution and its catalytic activity can be reused up to four times efficiently. CuONs was also able to decolorize actual textile effluent (80% in terms of the American Dye Manufacturers' Institute (ADMI) value) with significant reductions in COD (72%) and TOC (69%). Phytotoxicity studies revealed that the degradation products of RG19A and textile effluent were scarcely toxic in nature, thereby increasing the applicability of CuONs for the treatment of textile wastewater. Additionally, the CuONs showed a maximum antibacterial effect against human pathogens which also displayed synergistic antibacterial potential related to commercial antibiotics. Moreover, CuONs displayed strong antioxidant activity in terms of ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (IC50: 51 μg/mL) and DPPH (1,1-diphenyl-2-picrylhydrazyl) (IC50: 60 μg/mL) radical scavenging. The CuONs exhibited dose dependent response against tumor rat C6 cell line (IC50: 60 μg/mL) and may serve as anticancer agents.

Effective utilization of ozone in plasma-based advanced oxidation process

Decomposition of acetic acid in water was conducted using multiple plasmas generated within oxygen bubbles. Ballast capacitors were used to control the plasma input power, allowing hydrogen peroxide and ozone to be produced at different rates in each plasma by adjusting the capacitance. By using an ozone absorber connected to the plasma reactor, OH radicals, both generated by the plasmas directly and reproduced from hydrogen peroxide through reactions with ozone, could be effectively utilized for the reduction of total organic carbon (TOC). Under the condition with the highest ozone production rate, higher processing speed and energy efficiency for the TOC reduction were achieved compared with other plasma methods.

Electrochemical technology for the treatment of real washing machine effluent at pre-pilot plant scale by using active and non-active anodes

Real effluent of washing machine is one of the major sources of microplastics and fabrics in municipal and surface water. The effluents constitute large volume of wastewater with different surfactants since every household and industries nowadays use washing machine rather than traditional hand washing.In this work, a real effluent of washing machine was treated by electrooxidation (EO) in a pre-pilot plant scale electrochemical flow reactor using active (Ti/Pt) or non-active (boron doped diamond (BDD)) anodes and Ti cathode. The effect of anode material (Ti/Pt or BDD) and the applied current density (16.6, 33.3 and 66.6 mA cm−2) on the decay of the organic matter, in terms of chemical oxygen demand (COD) during the electrochemical treatment was examined using the as-received effluent or by adding Na2SO4 as supporting electrolyte (as auxiliary in the conductivity). A decreased in organic matter (COD) was always observed when an increase on the applied current density was achieved at both anodes; however, BDD anode showed a well-defined trend as well as higher removal efficiency at all current densities studied when compared to Ti/Pt. Besides, faster and higher COD decay was attained by adding Na2SO4 to the real effluent compared to as-received effluent regardless of anode material used. Active chlorine species were also electrochemically produced at both anodes from the Cl− ions in the real effluent, contributing to the elimination of the pollutants. The mineralization of organic matter in the effluent was also determined, obtaining >90% of total organic carbon (TOC) reduction after 360 min with BDD anode at 33.3 and 66.6 mA cm−2. Based on the achieved results, EO is an efficient and effective treatment approach for the remediation of organic micropollutants in washing machine effluent especially with BDD anode.

BDD anodic treatment of 6:2 fluorotelomer sulfonate (6:2 FTSA). Evaluation of operating variables and by-product formation

The concerns about the undesired impacts on human health and the environment of long chain perfluorinated alkyl substances (PFASs) have driven industrial initiatives to replace PFASs by shorter chain fluorinated homologues. 6:2 fluorotelomer sulfonic acid (6:2 FTSA) is applied as alternative to PFOS in metal plating and fluoropolymer manufacture. This study reports the electrochemical treatment of aqueous 6:2 FTSA solutions on microcrystalline BDD anodes. Bench scale batch experiments were performed, focused on assessing the effect of the electrolyte and the applied current density (5–600 A m−2) on the removal of 6:2 FTSA, the reduction of total organic carbon (TOC) and the fluoride release. Results showed that at the low range of applied current density (J = 50 A m−2), using NaCl, Na2SO4 and NaClO4, the electrolyte exerted a minimal effect on removal rates. The formation of toxic inorganic chlorine species such as ClO4− was not observed. When using Na2SO4 electrolyte, increasing the applied current density to 350–600 A m−2 promoted a notable enhancement of the 6:2 FTSA removal and defluorination rates, pointing to the positive contribution of electrogenerated secondary oxidants to the overall removal rate. 6:2 FTSA was transformed into shorter-chain PFCAs, and eventually into CO2 and fluoride, as TOC reduction was >90%. Finally, it was demonstrated that diffusion in the liquid phase was controlling the overall kinetic rate, although with moderate improvements due to secondary oxidants at very high current densities.