Mehmet KOBYA

Article | 2023 | Journal of Water Process Engineering56

The near-widespread presence of poly- and perfluoroalkyl substances (PFASs) in humans has generated concerns regarding the potential negative impact of these chemicals on human health, as some PFASs are exceedingly persistent and bioaccumulative. Among the perfluorinated PFASs, which exhibit high polarity and strong carbon–fluorine bonds, perfluorooctanesulfonate (PFOS) is one of the frequently encountered species. In this study, the efficiency of electrooxidation (EO) and its application in groundwater simulation were first evaluated as a realistic approach to PFOS removal. After optimizing EO parameters including the solution pH, . . .current density, and the effects of inlet concentration and the anode material, 83 total organic carbon (TOC) removal was obtained. In groundwater experiments, in which the infiltration of PFOS from soil layers into groundwater was simulated, 79 TOC removal efficiency was achieved in the more complex groundwater; moreover, an F− ion concentration of 8.78 mg/L was obtained from the decomposition of PFOS. To increase the realism of the simulation, the leachate process was repeated four times, and the EO process was applied to each sequential leachate. In addition, the process efficiency was studied in real landfill leachate wastewater to which PFOS had been added. Despite the challenging wastewater composition, 84 TOC removal efficiency was achieved. Together, these results indicate that BDD-anodic oxidation may be a practical method to treat PFOS-contaminated groundwater and wastewater. Keyword: electrochemical treatment; groundwater treatment; landfill leachate treatment; PFAS More less

Mehmet KOBYA

Article | 2023 | Journal of the Professional Association for Cactus Development ( 25 )

The electrocoagulation (EC) treatment process was aided by the cladode mucilage of Opuntia ficus-indica (OFI) to improve chemical oxygen demand (COD) removal efficiency () of wastewater from a plant producing flavoring and food additives. The studied variables included initial pH, current density, types of electrodes (Fe and Al), mucilage concentration, and charge loading. The EC treatment using Al electrodes, assisted by an optimum concentration of 200 mg L-1 OFI mucilage, a current density of 60 A/m2, and an initial pH equal to 3, improved the COD removal efficiency (69.77) at an EC treatment time of 40 min. The EC operating costs . . ., energy, and electrode consumptions values were equal to 3.809 US /m3, 0.810 kWh/kg COD removed, and 0.7898 kg/m3, respectively. However, no improvement was noted when Fe electrodes were used with or without adding OFI mucilage (under conditions of pH 6, current density of 50 A/m2, and EC time of 120 min), and COD removal efficiency () was equal to 41.5. The operational costs, energy and electrode consumptions were equal to 4.2201 US /m3, 2.8 kWh/kg COD removal and 3.0964 kg/m3, respectively. The OFI mucilage could be used as a promising bio-coagulant with EC treatment using Al electrodes, to treat the plant producing flavoring and food additives wastewater. Keyword: COD; electrocoagulation process; food production; mucilage; opuntia ficus indic More less

Mehmet KOBYA

Article | 2021 | Chemosphere286 ( 2 )

Herein, ZnCr layered double hydroxide (ZnCr LDH), and its nanocomposites with GO and rGO were synthesized using the co-precipitation method. The samples were characterized using XRD, FT-IR, SEM, TEM, BET, and XPS techniques. The sonophotocatalytic activity of the ZnCr LDH, ZnCr LDH/GO, and ZnCr LDH/rGO was investigated via the degradation of rifampicin (RIF) in the ultrasonic bath under visible light irradiation. The synergy index of more than 1 determined for ZnCr LDH/rGO indicated the positive interaction of sonocatalysis and photocatalysis resulted by hybridizing the LDH nanosheets with rGO. The maximum sonophotocatalytic degrada . . .tion efficiency of 87.3?as achieved in the presence of ZnCr LDH/rGO nanocomposite with the concentration of 1.5 g L-1 for degradation of RIF with an initial concentration of 15 mg L-1 within 60 min sonication under visible light irradiation. The addition of different scavengers indicated that hydroxyl radicals, superoxide anion radicals, and the generated holes played a dominant role in the degradation of the pollutant molecules. A possible degradation mechanism was suggested based on the intermediates. The antibacterial tests confirmed the higher antibacterial activity of ZnCr LDH/GO compared with ZnCr LDH and ZnCr LDH/rGO against Grampositive Staphylococcus aureus More less

Mehmet KOBYA

Article | 2024 | Journal of Chromatography A1715

This study investigated the removal of Reactive Blue 21 (RB 21) dye from aqueous solutions by adsorption, evaluating the waste fly ash (FA). The effects of the parameters, such as initial dye concentration (100–750 mg/L), initial pH (2.0–8.0), adsorbent dose (1.0–4.0 g/L), and temperature (298–323 K) on the adsorption process were investigated. The optimum initial pH value was 2.0 for the highest RB21 dye removal (75.2 mg/g). At optimized conditions (pH 2.0, an adsorbent dosage of 1.0 g/L, a dye concentration of 750 mg/L, and an equilibrium time of 72 h), the highest adsorption capacity was found to be 105.2 mg/g. Moreover, the resu . . .lts of the kinetic studies fitted the pseudo-second-order kinetic model. Equilibrium data were best represented by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 103.41 mg/g at 323 K. ΔGads0 values were negative and varied from 11.64 to 9.50 kJ/mol in the temperature range of 298–323 K, the values of enthalpy (ΔHadso) and entropy (ΔSadso) of thermodynamics parameters were calculated as 37.62 kJ/mol and 86.67 J/mol K, respectively, indicating that this process was endothermic. Furthermore, the adsorbent costs for powdered activated carbon (PAC) and FA to remove 1 kg of RB 21 dye from aqueous solutions are calculated as 2.52 U.S. and 0.34 U.S. , respectively. It is seen that the cost of FA is approximately 7.4 times lower than PAC. The results showed that FA, a low-cost industrial waste, was promising for the adsorption of RB 21 from aqueous solutions. Keyword: adsorption; fly ash; isotherm; kinetics; reactive blue 2 More less

Mehmet KOBYA

Article | 2021 | Journal of Environmental Engineering and Science17 ( 2 )

The aim of this study was the optimisation of the activated carbon (C) production process by dehydration-carbonisation using concentrated sulfuric acid (H2SO4) from hazelnut shells found locally and readily available agricultural waste and the adsorption of chromium (III) (Cr3) on the activated carbon produced by this method. An adsorption experiment was carried out at conditions of 25 degrees C and initial concentration of 30 mg chromium (III)/l. The optimum process conditions for ensuring maximum adsorption capacity were investigated by means of statistically designed experiments and steepest ascent experiments. The optimum values . . . found were an impregnation ratio of 4.5 ml sulfuric acid/g hazelnut shells, an oven temperature of 50 degrees C, a holding time in the oven of 19.8 h and a maximum adsorption capacity of 14.76 mg chromium (III)/g hazelnut shell activated carbon (HSAC). The surface properties of HSAC were investigated by scanning electron microscopy and Fourier transform infrared spectroscopy and agreed with the outcomes. The adsorption mechanism could be rapid ion exchange and slow chemisorption and/or an outer-sphere complexation at pH 3.5-6.0 during the process More less

Mehmet KOBYA

Article | 2022 | Chemosphere309 ( 1 )

In this study, a ternary layered double hydroxide containing Zn, Co, and Fe transition metals (ZnCoFe LDH) was developed using a co-precipitation procedure. The as-synthesized photocatalyst was evaluated for its perfor-mance in the degradation of methylene blue (MB) under visible light irradiation. The effects of various process conditions including photocatalyst dosage, pollutant concentration, pH, lamp distance, and lamp power were investigated. The ZnCoFe LDH achieved approximately 74 photodegradation efficiency owing to the narrow bandgap of 2.14 eV. The Langmuir-Hinselwood rate constants were calculated as 1.17 min-1 and 3.55 m . . .in-1 for photolysis by LED lamp alone and for photocatalysis by LED/ZnCoFe LDH, respectively. The photocatalytic ability of the LDH was attributed to the generation of radical species like center dot OH and O2 center dot-. The photocatalytic degradation intermediates of MB were determined by GC-MS analysis. The catalyst retained its performance throughout seven reuse cycles with only a 4.17 reduction in removal efficiency. The energy per order EEO of the ZnCoFe/LED process in 180 min treatment time was determined as 5.41 kWh.m- 3. order-1. This study shows that ZnCoFe LDH has sufficient activity and photostability for long-term application in photocatalytic water treatment More less

Mehmet KOBYA

Article | 2022 | Chemosphere307 ( 3 )

This study compares the efficiencies of active (Ti/TiO2-RuO2-IrO2 (TIR)) and inactive (Ni/Boron Doped Diamond (BDD)) anodes in terms of pollutant treatment and by-product formation in pretreated (chemical coagulation) landfill leachate nanofiltration membrane concentrate (PLNC). PLNC has high chemical oxygen demand (COD:4900 mg/L), total organic carbon (TOC: 1874 mg/L), total Kjeldahl nitrogen (TKN: 520 mg/L), ammonium nitrogen (NH3-N: 21.35 mg/L), chloride (5700 mg/L) and sulfate (9000 mg/L - due to coagulant type). The parameters of COD, TOC, NH3-N, TKN, free and combined chlorine species, halogenated organic compounds (HOCs), ads . . .orbable organic halogens (AOX), and nitrate at different current density (J: 111-555 A/m(2)) and initial pH (pH(i):3.5-7) were compared for both anodes. The removal efficiencies at the optimum conditions (pH(i) 5.5, 333 A/m(2) and 8 h) were obtained as 86.4 COD, 77.4 TOC, 93.4 TKN, 94.4 NH3-N with BDD and 34.3 COD, 27.3 TOC, 93.7 TKN, 97.4 NH3-N with TIR. According to gas chromatography-mass spectrometry (GC-MS) results obtained under optimum conditions, haloalkane/alkene, halonitroalkane, halonitrile, haloketone, haloalcohols, haloacids, haloaldehydes, haloamines/amides on both electrodes were detected as species of HOCs. In addition, the highest nitrate concentration was observed at the TIR anode, while the highest AOX concentration was observed at the BDD anode More less

Mehmet KOBYA

Article | 2021 | Process Safety and Environmental Protection152

Phosphates are a major cause of eutrophication and growth of algal blooms in surface waters. The current study investigated phosphorus removal from sludge centrate effluent (SCE) of a municipal wastewater plant by packed-bed electrocoagulation (EC) reactor. Distinctively, iron (Fe), aluminum (Al) and Al-Fe hybrid scrap anodes were used. The influence of initial pHi, applied current and packed anode bed density were evaluated. Phosphorous removal efficiency of 99.99 ?as obtained at applied current of 0.20A with anode bed densities of 0.18 kg Al/m3 (pHi 5.0) and 0.48 kg Fe/m3(pHi 7.0). Optimum operating costs entailing sludge disposal . . ., chemical, energy and electrode consumption were calculated as 0.379 US $/m3 (6.04 $/kg PO4-P) for Fe scrap, 0.494 US $/m3 (9.46 $/kg PO4-P) for Al scrap and 0.501 US $/m3 (9.59 $/kg PO4-P) for Al-Fe hybrid scraps. Phosphorus removal per electrochemically generated metal was 191.22 mg P/g Al, 104.88 mg P/g Fe, and 61.08 mg P/g (Al Fe). The molar metal to phosphorus ratio at optimum conditions were calculated as 5.41, 3.97 and 7.65 mol/mole for Al, Fe and Al-Fe, respectively. The key mechanisms for phosphorus removal were metal-phosphorus precipitation and adsorption. Herein, metal scrap anodes have been proved effective for phosphorous removal from SCE. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved More less

Mehmet KOBYA

Article | 2022 | Journal of Environmental Chemical Engineering10 ( 6 )

Heterogeneous electro-Fenton (EF) is a powerful technology for the removal of emerging organic pollutants from wastewater. However, the development of catalysts with high activity towards the production of •OH by decomposing H2O2 remains a challenge. Herein, Co-doped ZnFe LDH as a heterogeneous catalyst with 2D plate-like morphology was produced by a co-precipitation method. Co-doping increased the pore volume of ZnFe LDH from 0.188 cm3/g to 0.2711 cm3/g and pore diameter from 5.305 nm and 9.39 nm. EF process consisted of a hydrothermally activated graphite felt cathode and a platinum plate anode. The Phenazopyridine (PHP) removal e . . .fficiency of the EF process in the presence of Co-doped ZnFe LDH is twice that of the electrochemical process. Additionally, Co-doping increased the performance of ZnFe LDH from 60 to 82 due to a synergistic effect of redox couples of Fe2/Fe3 and Co2/Co3. The Co-doped ZnFe LDH/EF process achieved complete removal of PHP in real wastewater in 4 h and at natural pH. After 7 reuse cycles, the catalyst retained 91 of its performance. The eight by-products of PHP were determined by GC–MS. This work provides a way sustainable approach for the efficient removal of organic pharmaceuticals from wastewaters.Keyword: Emerging pollutants; Graphite felt; Hydrotalcite; Nanomaterials; Wastewater treatmen More less

Mehmet KOBYA

Article | 2023 | Ultrasonics Sonochemistry95

This study is the first to explore the possibility of utilizing CuCr LDH decorated on reduced graphene oxide (rGO) and graphene oxide (GO) as sonophotocatalysts for the degradation of dimethyl phthalate (DMP). CuCr LDH and its nanocomposites were successfully fabricated and characterized. Scanning electron microscopy (SEM) along with high-resolution transmission electron microscope (HRTEM) both evidenced the formation of randomly oriented nanosheet structures of CuCr LDH coupled with thin and folded sheets of GO and rGO. The impact of diverse processes on the degradation efficiency of DMP in the presence of the so-prepared catalysts . . . was compared. Benefiting from the low bandgap and high specific surface area, the as-obtained CuCr LDH/rGO represented outstanding catalytic activity (100 ) toward 15 mg L−1 of DMP within 30 min when subjected to light and ultrasonic irradiations simultaneously. Radical quenching experiments and visual spectrophotometry using an O-phenylenediamine revealed the crucial role of hydroxyl radicals compared to holes and superoxide radicals. Overall, outcomes disclosed that CuCr LDH/rGO is a stable and proper sonophotocatalyst for environmental remediation. Keywords: Layered double hydroxide, Graphene, Advanced oxidation processes, Sonophotocatalysis, Dimethyl phthalat More less

Mehmet KOBYA

Article | 2021 | Water Science & Technology84 ( 9 )

Reverse osmosis concentrate (ROC) is one of the major drawbacks in membrane treatment technologies specifically due to the scale-forming ions. It is important to remove these ions from ROC to enhance total water recovery and reuse in the textile industry that is the largest water-consumer and polluter industry. In this work, coagulation/high pH precipitation (CP) integrated with ceramic microfiltration (CMF) was studied as a pretreatment method followed by nanofiltration (NF) to increase the efficiency of water recovery. To prevent organic fouling, ferric chloride (FeCl3) was applied at a concentration of 3 mM, and ceramic membranes . . . were used for the removal of non-precipitating crystals and/or suspended solids (at high pH) before the NF processes. The CP-CMF method successfully removed calcium (Ca2+), magnesium (Mg2+), silica (SiO2), and TOC up to 97, 83, 92, and 87% respectively, which resulted in higher performance of the NF process. Moreover, this method provided higher flux at lower pressure that ultimately increased overall water recovery of the NF process to achieve near-zero liquid discharge (n-ZLD). A cost-benefit estimation showed that a high-quality effluent (CO More less

Zarlık MAYMEKOV | Canarbek İZAKOV | Nurzat ŞAYKİYEVA | Mustafa DOLAZ | Mehmet KOBYA

Article | 2023 | Theoretical Foundations of Chemical Engineering57 ( 2 )

Under practical conditions, one of the possible solutions to the problem of treatment of hydrogen-sulfide-containing industrial wastewater is the electrochemical oxidation of sulfides. In this work, the model system Fe-NaCl-Na2S-H2SO4-H2O is considered, an experimental setup is constructed, and the electrocoagulation process is studied in a wide (288-308 K) range of temperatures of an aqueous solution of hydrogen sulfide. The optimal ratios between the initial components in the system are determined. The experimental and calculated pH of the solution are found. The system is thermodynamically modeled by minimizing the Gibbs energy, . . .and the concentration distribution of individual molecules and other species (cations, anions) in the solution is characterized. Possible chemical reactions in the system Fe-NaCl-Na2S-H2SO4-H2O during the electrocoagulation of hydrogen-sulfide-containing wastewater are identified. Eh-pH diagrams are constructed to compare the redox potentials of the systems Fe-H2O, Fe-H2O-S, and Fe-NaCl-Na2S-H2SO4-H2O based on the determined concentrations of iron- and sulfur-containing particles in the solution. A calculation formula for the redox potential Eh of the system is obtained. Keyword: distribution; electrocoagulation; hydrogen sulfide; iron; particle; sodium chloride; sodium sulfide; wate More less