Chemical Oxygen Demand Abatement Research Articles

Optimization of Fenton process conditions in winery wastewaters treatment followed by ion exchange process to recover iron

Fenton’s oxidation has been widely studied for treatment of winery wastewater (WW). However, the generation of iron sludges imposes a significant drawback for this treatment process. Consequently, an integrated methodology was tested involving the application of ion exchange resins that recover dissolved iron without sludge production in Fenton’s Process. The aim of this study is optimizing Fenton oxidation for the abatement of COD in WW. Using a methodology design of experiments (DOE), Fenton process was able to remove up to 57% of chemical oxygen demand (COD) when pH 3, reaction time 1 h, [H2O2] = 0.15 molL−1 and [H2O2]/[Fe2+] = 15 were applied. A cationic ion-exchange resin, Dowex Marathon C, was able to recover iron present in the effluent after the oxidation process. Continuous and discontinuous trials were conducted in this scope for the synthetic solution and the real effluent after Fenton. The innovative methodology of using IE to circumvent Fenton's peroxidation limitation will surely lead to a widespread application of IE in the treatment of industrial effluents.

Decentralized environmental applications of a smartphone-based method for chemical oxygen demand and color analysis

This study is focused on a proposal of a smartphone imaging-based quantification for providing a simple and rapid method for the analysis of chemical oxygen demand (COD) and color throughout the use of the HSV and/or RGB model in digital devices. For COD, calibration curves were done based on the theoretical values of potassium biphthalate for a proper comparison between the spectrophotometer and the smartphone techniques. The smartphone camera and application attain an average accuracy higher than the analysis in the spectrophotometer (98.3 and 96.2%, respectively). In the color analysis, it was demonstrated that only the UV–vis bands measurement is not feasible to perform the real abatement of the dye in the water because the limiting concentration that allows obtaining a linear relationship in this equipment related to the dye concentration is about 10 mg L−1. Above this value, the spectrophotometer can not reach the real difference of color in the solution. Meanwhile, the smartphone method by using the camera reaches linearity until 50 mg L−1. From an environmental point of view, smartphones have been used for monitoring several organic and inorganic pollutants, however, no attempts have been published related to their use to evaluate the color and COD during wastewater treatment. Therefore, this investigation also aims to assess the utilization of these methods, for the first time, when high-colored water polluted by methylene blue (MB) was electrochemically treated by using a boron-dopped diamond (BDD) as the anode, with different current densities (j = 30, 45, 60, and 90 mA cm−2). COD and color abatement results clearly showed that different organic matter/color removal efficiencies were achieved, depending on the j used. All the results are aligned with the studies already available in the literature, with the total removal of color in 120 min of electrolysis with 60 and 90 mA cm−2, and almost 80% of COD abatement with the higher j. Moreover, samples of real effluent from beauty salons were compared, with standard deviation varying from only 3 to 40 mg O2 L−1, which is acceptable for COD values close to 2000. Finally, the methods here presented can be a great benefit for public water monitoring policies, since it is cheap and has a decentralized characteristic, given that smartphones are very common and portable devices.

Optimization of textile effluent bacterial treatment and improvement of the process efficiency through SPB1 biosurfactant addition.

The current work aims to optimize biological textile effluent treatment through the use of newly selected bacterial consortia composed of two strains: Citrobacter sedlakii RI11 and Aeromonas veronii GRI. We assessed the effect of SPB1 biosurfactant addition on color removal (CR). The process was optimized by a Box-Bhenken by examining the effect of pH, consortia density and biosurfactant value on treatment efficiency. Firstly, physicochemical analyses of the studied effluent revealed an alkaline pH along with a high content of suspended materials and large amounts of organic matter. Optimal CR and a chemical oxygen demand abatement of about 94 and 86% were obtained when treating the textile effluent at pH 5 with a total optical density of 0.4 and by incorporating 0.01% SPB1 biosurfactant. Additionally, an abolishment of phytotoxicity was registered after treatment optimization. The evaluations of the action mode of both selected bacteria during textile effluent treatment suggested the occurrence of biodegradation phenomena of dyes through enzymatic activities.

The adsorption mechanism of sludge-based biochar toward highly concentrated organic membrane concentrates from landfill leachate.

In this study, the sludge-based biochar (BC) was prepared by dewatered sludge from a membrane bioreactor to treat the membrane concentrate. Then, the adsorbed and saturated BC was regenerated (RBC) by pyrolysis and deashing treatment to further treat the membrane concentrate. Afterward, the composition of membrane concentrate before and after BC or RBC treatment was detected, and the biochars' surface characteristics were characterized. The results showed that RBC outperformed BC in the abatement of chemical oxygen demand (CODCr), ammonia nitrogen (NH3-N), and total nitrogen (TN), with their removal rates of 60.07%, 51.55%, and 66.00%, respectively, an improvement of 9.49%, 9.00% and 16.50% of the removal rate compare to BC. The specific surface area of BC and RBC was about 109 times as much as the original dewatered sludge, and the pore size of BC and RBC belonged to mesopore which was a benefit for removing small and mediate size pollutants. The increase of the oxygen-containing functional group in RBC and the ash abatement contributed much to the improvement of RBC adsorption performance. In addition, cost analysis showed that BC+RBC had a cost of 0.76$/kg for COD removal, which was a lower cost than other common membrane concentrate treatment technologies.

Degradation of Orange G by UV/TiO2/IO4 ‾process: Effect of operational parameters and estimation of electrical energy consumption

In the present study, the degradation of an azo dye Orange G (OG) by the UV/TiO2/periodate (IO4‾) process has been investigated. OG was totally disappears within 10 min by the UV/TiO2/IO4‾compared to UV alone, UV/TiO2 or UV/IO4‾. A synergistic effect has been obtained when combining the UV/TiO2 and the UV/IO4‾systems, resulting in positive interactions between both processes. Experiments conducted with specific hydroxyl radical scavengers, show that despite the inhibition effect observed, complete degradation has been achieved beyond 10 min, demonstrating that the degradation is not only initiated by hydroxyl radical, but also by other reactive entities; the involvement of iodate radical is confirmed with the use of chromium species as a competitor with periodate ions for the photogenerated electron at the conduction band. The operating parameters influencing the degradation process such as initial dye concentration, initial periodate concentration, light intensity/wavelength and initial pH solution have been explored. The presence of inorganic ions such as chloride, bromide, sulphate, carbonate and bicarbonate ions in the irradiated solution show reverse effects depending on the concentration used. The OG degradation in different water matrices is found to be sensitive to the presence of different species and their nature. Chemical oxygen demand (COD) has been partially removed after 10 min of treatment, and then this COD abatement stabilized, indicating the strength of the by-products from dye degradation by the UV/TiO2/IO4‾ system during the treatment time. The electrical energy consumption is estimated at 2.21kWhm‾3/Order. The results obtained indicate that the UV/TiO2/IO4‾ process could be used as a hybrid process to the treatment of dye contaminated water.

The Electrochemical Reaction Kinetics during Synthetic Wastewater Treatment Using a Reactor with Boron-Doped Diamond Anode and Gas Diffusion Cathode

A system of boron-doped diamond (BDD) anode combined with a gas diffusion electrode (GDE) as a cathode is an attractive kind of electrolysis system to treat wastewater to remove organic pollutants. Depending on the operating parameters and water matrix, the kinetics of the electrochemical reaction must be defined to calculate the reaction rate constant, which enables designing the treatment reactor in a continuous process. In this work, synthetic wastewater simulating the vacuum toilet sewage on trains was treated via a BDD-GDE reactor, where the kinetics was presented as the abatement of chemical oxygen demand (COD) over time. By investigating three different initial COD concentrations (C0,1 ≈ 2 × C0,2 ≈ 4 × C0,3), the kinetics was presented and the observed reaction rate constant kobs. was derived at different current densities (20, 50, 100 mA/cm2). Accordingly, a mathematical model has derived kobs. as a function of the cell potential Ecell. Ranging from 1 × 10−5 to 7.4 × 10−5 s−1, the kobs. is readily calculated when Ecell varies in a range of 2.5–21 V. Furthermore, it was experimentally stated that the highest economic removal of COD was achieved at 20 mA/cm2 demanding the lowest specific charge (~7 Ah/gCOD) and acquiring the highest current efficiency (up to ~48%).

Environmental application of a cost-effective smartphone-based method for COD analysis: Applicability in the electrochemical treatment of real wastewater

This study aims to develop a cheap method for the evaluation of quality of water or the assessment of the treatment of water by chemical oxygen demand (COD) measurements throughout the use of the HSV color model in digital devices. A free application installed on a smartphone was used for analyzing the images in which the colors were acquired before to be quantified. The proposed method was also validated by the standard and spectrophotometric methods, demonstrating that no significant statistical differences were attained (average accuracy of 97 %). With these results, the utilization of this smartphone-based method for COD analysis was used/evaluated, for first time, by treating electrochemically a real water matrix with substantial organic and salts content using BDD and Pt/Ti anodes. Aiming to understand the performance of both anodes, bulk experiments were performed under real pH by applying current densities (j) of 15, 30, and 60 mA cm−2. COD abatement results (which were achieved with this novel smart water security solution) clearly showed that different organic matter removal efficiencies were achieved, depending on the electrocatalytic material used as well as the applied current density (42 %, 45 %, and 85 % for Ti/Pt while 93 %, 97 % and total degradation for BDD by applying 15, 30, and 60 mA cm−2, respectively). However, when the persulfate-mediated oxidation approach was used, with the addition of 2 or 4 g Na2SO4 L−1, COD removal efficiencies were enhanced, obtaining total degradation with 4 g Na2SO4 L−1 and by applying 15 mA cm−2. Finally, this smartphone imaging-based method provides a simple and rapid method for the evaluation of COD during the use of electrochemical remediation technology, developing and decentralizing analytics technologies for smart water solutions which play a key role in achieving the Sustainable Development Goal 6 (SDG6).

Heterogeneous Photodegradation for the Abatement of Recalcitrant COD in Synthetic Tanning Wastewater

Tannery wastewater is considered one of the most contaminated and problematic wastes since it consists of considerable amounts of organic and inorganic compounds. These contaminants result in high chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS). In this work, the heterogeneous photodegradation of recalcitrant COD in wastewater from the tanning industry was investigated, in particular the recalcitrant COD due to the presence of vegetable tannins extracted from mimosa and chestnut and from synthetic tannins based on 4,4′ dihydroxy phenyl sulfone. TiO2 Aeroxide P-25 was employed to study the photodegradation of model molecules in batch conditions under different parameters, namely initial concentration of COD, temperature, and catalyst dose. The maximum COD abatement reached was 60%. Additionally, preliminary kinetic investigation was conducted to derive the main kinetic parameters that can be useful for process scale-up. It was found to be independent of the temperature value but linearly dependent on both catalyst loading and the initial COD value.

Micro-meso structure NaP zeolite @TiO2 nanocomposite: eco-friendly photocatalyst for simultaneous removal COD and degradation of methylene blue under solar irradiation.

A low-cost NaP zeolite@TiO2 nanocomposite catalyst with zeolite Si/Al ratio lower than three were synthesized for the first time under hydrothermal condition. The nanocomposites were characterized by different methods such as Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), N2 physisorption, NH3 temperature-programmed desorption (NH3-TPD), fluorescence microscopy, thermal analysis (TGA/DTA) and zeta potential analysis. The results showed that a micro-meso structure NaP zeolite with higher surface area and acidity with respect to pure zeolite was prepared. TiO2 nanoparticle was dispersed over the whole of zeolite without aggregation. A reduction of the TiO2 bandgap nanoparticle was observed from DRS spectra. The photocatalytic activity of low-cost NaP zeolite@TiO2 nanocomposite was tested for simultaneous methylene blue dye (MB) and chemical oxygen demand (COD) under solar and ultraviolet light. The result showed that the nanocomposite catalyst has great potential (above 90%) for COD removal discolouring of MB (about 99.6%) at room temperature. The optimum amount of some parameters such as the loaded amount of TiO2 (0.36g), catalyst dosage (0.1g), time (2h), initial dye concentration (100mg/L), solution pH value (about 7) under solar light were considered. In addition, present negative charge in the surface that show in zeta potential confirm the high activity of catalyst to interaction with cationic dye. As a further advantage, the NaP zeolite@TiO2 nanocomposite was easier to be separated in aqueous media than the pure TiO2 powders, making possible the reuse several times (over five runs) without using oxidant. Finally, the NaP zeolite@TiO2 nanocomposite was used for COD abatement in wastewater from two real industrial streams. The MB degradation kinetics were fitted by a pseudo-first-order model with K = 0.534h-1.

Leachate degradation using solar photo-fenton like process: Influence of coagulation-flocculation as a pre-treatment step

The effectiveness of using solar photo-Fenton-like processes to degrade sanitary landfill leachates was investigated. Leachate samples exhibited varying composition, owing to a mixture of older and younger effluents from a former dump site subsequently converted into a sanitary landfill. Coagulation assays (jar test) using Al3+, Fe2+, and Fe3+ in the 240–800 mg L–1 range were performed to evaluate optimal coagulant concentration for abatement of chemical oxygen demand (COD) and dissolved organic carbon (DOC). A high COD (53%) and DOC (72%) removal rates were obtained for Al3+ but there was a very substantial increase in the turbidity. Optimal coagulant concentration was then adopted, and the effluents were subjected to photo-Fenton processes at laboratory scale. At this scale, coagulation by Fe3+ at 240 mg L–1 combined with a photo-Fenton-like method exhibited superior performance, with 66% DOC removal by coagulation and over 70% DOC removal using the photo-Fenton-like process. Solar photodegradation was conducted for 180 min at [Fe3+] ≈ 100 mg L–1, pH = 3.0 ± 0.3, and [H2O2] = 50–250 mg L–1 at a solar pilot plant. Use of solar photo-Fenton-like processes improved effluent biodegradability, irrespective of coagulation pretreatment, and also reduced leachate toxicity, as shown by acute ecotoxicity tests using Lactuca sativa seeds, Allium cepa bulbs, and Artemia salina, proving to be a promising treatment method in line with the National Solid Waste Policy, which promotes and encourages non-generation, reduction, reuse, recycling, the treatment of solid waste, and the environmentally appropriate final disposal of tailings.

Performance investigation of electrochemical assisted HClO/Fe2+ process for the treatment of landfill leachate.

The feasibility of removal of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) from landfill leachate by an electrochemical assisted HClO/Fe2+ process is demonstrated for the first time. The performance of active chlorine generation at the anode was evaluated in Na2SO4/NaCl media, and a higher amount of active chlorine was produced at greater chloride concentration and higher current density. The probe experiments confirmed the coexistence of hydroxyl radical (•OH) and Fe(IV)-oxo complex (FeIVO2+) in the HClO/Fe2+ system. The influence of initial pH, Fe2+ concentration, and applied current density on COD and NH4+-N abatement was elaborately investigated. The optimum pH was found to be 3.0, and the proper increase in Fe2+ dosage and current density resulted in higher COD removal due to the accelerated accumulation of •OH and FeIVO2+ in the bulk liquid phase, whereas, the NH4+-N oxidation was significantly affected by the applied current density because of the effective active chlorine generation at higher current but was nearly independent of Fe2+ concentration. The reaction mechanism of electrochemical assisted HClO/Fe2+ treatment of landfill leachate was finally proposed. The powerful •OH and FeIVO2+, in concomitance with active chlorine and M(•OH), were responsible for COD abatement, and active chlorine played a key role in NH4+-N oxidation. The proposed electrochemical assisted HClO/Fe2+ process is a promising alternative for the treatment of refractory landfill leachate.

Advanced treatment of hydraulic fracturing flowback water using a novel combined process

A novel process was proposed for treating heavily polluted hydraulic fracturing flowback water from oil/gas production with an initial chemical oxygen demand (COD) of 8850 mg/L. The process was comprised of gel breaking, cavitation-impinging stream/iron-carbon micro-electrolysis (CIS/ICME) and electro-Fenton. The viscosity of the wastewater was reduced from 6.20 to 1.09 mPa•s after 90 min of gel breaking treatment using sodium hypochlorite at a dosage of 3.0 g/L. The CIS technology solved the passivation and hardening problems of traditional ICME technology, enhancing COD abatement by 48.2% points and increasing iron utilization from 36.8% to 82.4%. The results show that, under the optimum conditions, the effluent COD was reduced to around 170 mg/L with a removal efficiency of 98.1%, and the reduction ratios of oil, color, corrosion rate and suspended solids reached 100%, 95.2%, 94.0% and 97.7%, respectively. The quality of final effluent could meet the national discharge standard of China. The CIS/ICME process removed a considerable proportion of COD and oil, while the electro-Fenton unit played an important role in post-polish of final effluent. This study shows that the hybrid system has the potential to be applied for the advanced treatment of high-strength oilfield wastewater.

Optimization of the operating parameters and their effects on the degradation of Naphthol Blue Black by the Fenton process

The objective of this work was to model and optimize the degradation of black azo dye Naphthol Blue Black (NBB) by the Fenton process (advanced oxidation) using a minimum of experiments. A Plackett-Burman screening design was first applied to determine the main factors influencing the process. The dye discoloration efficiency gave a yield approximately equal to 97% in the best conditions of several operating parameters used. The variance analysis (ANOVA) showed the effects of all different factors and deduced the most important ones. Subsequently, a second quadratic design of experiments central composite type (CCD) was applied using the response surface methodology (RSM) to optimize the most important parameters deduced by the first design cited above, in order to obtain the best performance of the discoloration of NBB with this process. So from the contour plots and the response surfaces, the discoloration yield enhanced to the maximum and the optimization plot given by the Mnitab software, showed the following optimized parameters [NBB]=37.5 mg/L, [H2O2]=66.5 mg/L, [Iron]=3.5 mg/L and pH=3.4 for a yield of 100% with a desirability of 1.0000. At last, to confirm that the discoloration was due to the degradation of the dye, the chemical oxygen demand (COD) was studied and in the optimized conditions, the degradation reached 94.78% after 120 min of treatment. The kinetics of the dye degradation showed by the COD abatement was relatively slow compared to the kinetics of the dye discoloration.

Biological treatment of Hydrothermal Liquefaction (HTL) wastewater: Analytical evaluation of continuous process streams

In order to deal with hydrothermal liquefaction wastewater (HTWW), a new anaerobic-aerobic continuous process was developed. The process, which included a sequence of Up-Flow Anaerobic Sludge Blanket (UASB) and downstream aerobic Continuously Stirred Tank Reactor (CSTR), was tested on the HTWW obtained from Waste to Fuel® demo plant developed by ENI s.p.a. [1]. Performance of the system was evaluated in term of methane yield and chemical oxygen demand (COD) abatement capability. Detailed fate of organic compounds was evaluated through different analytical techniques, highlighting main issues and potential of HTWW biological treatment. The system was fed with neat HTWW (189 gCOD L−1) for 2.5 y, with variable organic loading rate (OLR) and minimal external inputs. UASB reactors converted most of HTWW organics into volatile fatty acids (VFA) and methane with concurrent precipitation of oily like insoluble, whereas aerobic CSTR removed VFA from anaerobic effluent. Under regime conditions (ORL equal to 0.5 gCOD L−1 d−1) COD decreased from 189 to 6.6 gCOD L-1, showing 97 % COD abatement with the coupled anaerobic-aerobic treatment. Such a COD abatement was obtained by means of multiple effects, namely biomethanation, precipitation of organic matter and aerobic oxidation of fermentation products (VFA produced in anaerobic digestion) and subsequent aerobic oxidation (in downstream aerobic reactor). These effects accounted for 43, 40 and 17 % of the total COD decrease, respectively. Inhibition phenomena were the key challenge for improving methane yields and system productivities. The overall results confirmed that valorization of HTWW is a feasible task, albeit rather challenging.

Low energy electrochemical oxidation efficiently oxidizes a common textile dye used in Thailand

Organic dyes are extensively used worldwide in the textile industry. Thailand's textile industry, which is mostly composed of small- and mid-sized factories that produce wastewater streams, would benefit from efficient, small-sized, and easy to operate treatment technologies. Electrochemical oxidation (ECO) is an alternative to historic solutions (e.g., biological treatment, coagulation, membranes, ozone) to treat dyebath effluents and reuse the water for secondary, non-potable purposes. ECO is an advanced oxidation process capable of in-situ electrogeneration of hydroxyl radical to completely mineralize organic pollutants. This work demonstrates the capability of electrochemically-driven systems to efficiently decolorize and mineralize dyebath effluents containing anthraquinone dye Acid Green 25. Achieving color and chemical oxygen demand abatement to below effluent discharge limits was attained using only 100 mA cm−2. Breaking the aromatic rings successfully produced readily biodegradable, low molecular weight carboxylic acids and inorganic (ammonium, nitrate) total nitrogen below 7 mg-N L−1, which can be readily discharged to sewers or even urban surface waters. The competitiveness of the electrochemical system is analyzed using engineering figures of merit, and the impacts of operational variables are discussed in terms of removal percentage, efficiency, and electrical energy per order. Results suggest wide applicability as an alternative for treating textile manufacturing waste streams.

Solar-Light-Responsive Titanium-Sheet-Based Carbon Nanoparticles/B-BiVO4/WO3 Photoanode for the Photoelectrocatalytic Degradation of Orange II Dye Water Pollutant.

We report the preparation and application of a heterostructured photoelectrocatalyst comprising carbon nanoparticles (CNPs) and boron codoped BiVO4 and WO3 for the removal of an organic dye pollutant in water. The materials, synthesized by hydrothermal method, were characterized by X-ray diffraction, diffuse reflectance UV–visible spectroscopy, energy-dispersive X-ray spectroscopy, and electron microscopy. The catalysts were immobilized on treated titanium sheets by drop-casting. The fabricated electrodes were characterized by linear sweep voltammetry (LSV) and chronoamperometry. Diffuse reflectance spectroscopy of the catalysts reveals that the incorporation of CNPs and B into the structure of monoclinic BiVO4 enhanced its optical absorption in both UV and visible regions. The LSV measurements carried out in 0.1 M Na2SO4 showed that the BiVO4- and WO3-based photoelectrode demonstrated significant photoactivity. CNP/B-BiVO4 and CNP/B-BiVO4/WO3 photoanodes gave photocurrent densities of approximately 0.83 and 1.79 mA/cm2, respectively, at 1.2 V (vs 3 M Ag/AgCl). The performance of the electrodes toward degradation of orange II dye was in the order BiVO4 < B-BiVO4 < WO3 < CNP-BiVO4 < CNP/B-BiVO4 < CNP/B-BiVO4/WO3, and the apparent rate constants obtained by fitting the experimental data into the Langmuir Hinshelwood kinetic model are 0.0924, 0.1812, 0.254, and 0.845 h–1 for BiVO4, WO3, CNP/B-BiVO4, and CNP/B-BiVO4/WO3, respectively. The chemical oxygen demand abatement after 3 h of electrolysis at the best performing photoanode was 58%. The study showed that BiVO4 and WO3 are promising anodic materials for photoelectrocatalytic water treatment plant.

Proposal for highly efficient electrochemical discoloration and degradation of azo dyes with parallel arrangement electrodes

In this research, different electrochemical advanced oxidation processes (EAOPs), such as electro-oxidation (EO), electro-Fenton (EF) and photoelectro-Fenton (PEF) were aimed to enhance the degradation efficiency of two azo dyes: Chocolate Brown HT (CB) and Eriochrome Black (EB), as model industrial dyes. Boron doped Diamond (BDD) electrodes were used as an anode and a cathode for EAOPs production. The capacity of individual effects of each process and coupling were evaluated as functions of the decolorization and mineralization of industrial dye solutions. The azo dye solutions were completely decolorized under acidic conditions pH2.8–3.0. The mineralization of the mixture of solutions was improved in the following order: EO<EF<PEF, due to the gradual increase in the production of free hydroxyl radicals (OH), PEF is more potent due to the photolysis of the oxidation products. Chemical oxygen demand abatement of 91% for EO, 95% for EF and 98% for PEF processes were obtained, when using an applied current density (j) of electrolyzed solution of 20 mAcm−2. The azo dye decolorization for all treatments followed pseudo-first-order kinetics, suggesting the attack of a constant production of OH radicals in the solution under EF and PEF, and EO at the anode surface.

Fluidized-bed Fenton treatment of imidacloprid: Optimization and degradation pathway

Abstract Environmental impact of pesticides is one of the great concerns being addressed by water-food nexus research. Imidacloprid is one of the most used insecticides as an alternative for carcinogenic organochloride insecticides. Even though Imidacloprid has lower toxicity for mammals, its fate and incomplete degradation by conventional wastewater treatment technologies are worrisome when considering continuous environmental exposure. Application of fluidized-bed Fenton process is proposed as an alternative treatment to mitigate the impact of imidacloprid in water. The consequence of different experimental parameter variations such as Fe2+ catalyst concentration, H2O2 concentration and propylene glycol (a common excipient in commercial pesticides) was evaluated. Experimental results under optimized conditions demonstrate almost complete removal of imidacloprid and abatement of chemical oxygen demand and total organic carbon. The intermediates of oxidized imidacloprid yield during fluidized-bed Fenton treatment were identified using GC–MS and a reaction sequence for imidacloprid degradation was proposed.

Optimization of operating conditions for the valorization of olive mill wastewater using membrane processes.

The main goal of this work was to assess the performance of an integrated membrane system for the treatment and valorization of wastewater generated from an olive mill (OMW) coming from a traditional extraction press. Two different lots of this effluent were firstly processed in an ultrafiltration (UF) pilot unit after a pretreatment by screening. The effect of transmembrane pressure (TMP) and temperature on the chemical oxygen demand (COD) reduction and removal of total phenolic (TPh) content was investigated. Under optimal conditions (TMP = 1.5bar and T = 20°C), 20.6 and 26.8% for COD and TPh removal were achieved, respectively. The permeate from UF was then treated by nanofiltration (NF) in order to obtain a retentate enriched in phenolic compounds. The influence of pressure drop (ΔP), temperature, and pH on the removal of COD, TPh, and permeate flow was examined using a 23 full-factorial experimental design. The effect of the independent variables and their interactions on the process performance was analyzed with Pareto charts. Multivariable regression models allowed to built 3D surface plots. The best conditions that maximize the COD abatement (83.3%) and TPh removal (93.1%) were ΔP = 18bar, T = 20°C, and a pH2.7. It can be concluded that the integration of UF and NF processes investigated in this work is a promising strategy for the treatment and valorization of OMW.

The combination of photocatalysis process (UV/TiO2(P25) and UV/ZnO) with activated sludge culture for the degradation of sulfamethazine

ABSTRACTThe major factors affecting the removal efficiency of sulfamethazine (SMT) by photocatalysis process in the presence of TiO2 P25 or ZnO, namely the pH, the amount of catalyst and the initial SMT concentration were examined. The obtained results showed the absence of adsorption of SMT on the catalysts and the absence of degradation of SMT by direct photolysis under UV light in the absence of catalyst. The variation of the pH solution in the range 4–9 did not cause any significant degradation of SMT. The optimal amounts of each catalyst were, respectively, 0.5 and 0.25 g/L for TiO2 P25 and ZnO. Increasing the initial SMT concentration impacted negatively the removal efficiency, which decreased from 31% to 13% and from 100% to 27% in the presence of TiO2 P25 and ZnO in the presence of 10 mg/L and 50 of SMT after 30-min reaction time, respectively. The obtained results showed better efficiency of ZnO than TiO2 P25 regarding both removal efficiency and chemical oxygen demand (COD) abatement. However, removal efficiency and COD abatement were not complete, even after 7 h of photocatalysis, about 92% and 41%, respectively. The biodegradability was examined after photocatalysis performed in the following conditions: [SMT]0 = 50 mg/L, pH = 6, T = 25°C, ω = 360 rpm and 0.5 g/L of TiO2 P25 or 0.25 g/L of ZnO. In these conditions, the removal efficiencies were, respectively, 26% and 41% in the presence of TiO2 P25 and 55 and 92% in the presence of ZnO after 4 and 7 h of pretreatment times, respectively. The BOD5/COD ratio increased substantially and, respectively, from 0 to 0.25 and from 0 to 0.16 in the presence of TiO2 P25 and ZnO after 7 h of irradiation. Even if the limit of biodegradability (0.4) was not achieved, a subsequent biological treatment was considered in the presence of TiO2 P25, leading to 58% COD abatement after a 28-day culture.