Removal of oil from biodiesel wastewater by electrocoagulation method

Treatability of biodiesel wastewaters by using KMnO4 and KMnO4/O3 processes and kinetic analysis

This study aims to investigate the treatability of electrocoagulated biodiesel wastewater (ECBD) by KMnO₄ and KMnO₄/O₃ processes. The ECBD removal efficiencies of both KMnO₄/O₃ and KMnO₄ methods were compared, and the COD and MeOH removal efficiencies with the KMnO₄/O₃ process gave better results than the KMnO₄ process. For the ECBD removal efficiencies, the experimental parameters including pH, KMnO₄ dose, O₃ dose and reaction time were optimized by changing one parameter at a time. As a result of 6 h of KMnO₄ oxidation, 91.74% of COD and 95.93% of MeOH removal was achieved under the optimum conditions. However, the COD and MeOH removal efficiencies have been obtained under optimum conditions for KMnO₄/O₃ as 97.79% and 98.30%, respectively. The second-order kinetic model has been found to be the most suitable model for both processes and the R² has been found as 0.999 and 0.999 for KMnO₄ and KMnO₄/O₃, respectively. The reaction k has also been calculated as 6 × 10^-5 L·mg^-1·min^-1 and 1.63 × 10^-4 L·mg^-1·min^-1 for COD and MeOH in KMnO₄ oxidation, respectively. Furthermore, the k has also been calculated as 6 × 10^-5 L·mg^-1·min^-1 and 1.6 × 10^-4 L·mg^-1·min^-1 for COD and MeOH in KMnO₄/O₃ oxidation, respectively.

A critical review in electrocoagulation technology applied for oil removal in industrial wastewater

EC process, which stands for Electrocoagulation, is considered a widespread wastewater remediation method that is investigated widely for an extensive variety of wastewater resources, based on its flexibility, easy setup, eco-friendly nature, and low footprint. The critical operative factors in the EC process and the crucial relation between EC and the typical chemical coagulation approach had been thoroughly evaluated because they are the main variables that govern the process of contaminant elimination. As a result, the EC process requires further investigations for scale-up simulations in the manufacturing scopes and optimization of operational parameters. Furthermore, the current paper studies the novel integrated separation methods with the combined EC process and also their limitations for improved wastewater remediation process for cleaner wastes, recycling processes, and water recovery. In this paper, the EC enhancement processes toward oil removal from wastewater have been reviewed which includes a concise representation of the source and features of oily wastewater. Additionally, the advanced remediation methods for oil-contained wastewater and the electrocoagulation process are presented. This review summarized the present utilization of electrocoagulation to eliminate oil from wastewater. Besides the process optimization and modeling investigations, the parameters that significantly affect the electrocoagulation remediation effectiveness are evaluated. Finally, the cutting-edge and sophisticated methods of electrocoagulation process for oil removal are presented.

The application of electrochemical processes in oily wastewater treatment: a review

Oily wastewater is becoming a concern worldwide due to its quantities and the presence of contaminants and its sustainable treatment should be cost-effective and meet all requirements so the contaminants are not transferred to the environment. The paper reviews the state-of-the-art in the oily wastewater treatment by electrochemical processes such as electrochemical advanced oxidation processes and electrocoagulation. Efficiency of oily wastewater treatment has been thoroughly investigated with its expression as a function of the main technological (process) parameters. Fe and Al electrodes, as well as their combination have proven to be very effective in oily wastewater treatment with slightly better performance of Al electrodes. Higher current densities and longer reaction times result with higher COD, TOC, turbidity, phenol and oil and grease removal efficiencies, but with resulting increase in wastewater temperature and energy consumption, so there is a strong need for the process optimization. There is a need for further research on the treatment efficiencies of different contaminants (heavy metals, total hydrocarbons, organic halogens, cyanides, etc.). A lack of research is presented on the treatment efficiency with electrodes of different materials as well as the analyses of the sludge production and its further treatment and use or disposal.

Application of coagulation/flocculation in oily wastewater treatment: A review

Volumes of oily wastewater are inevitably generated by every walk of life. The removal of oil particles from oil-contaminated wastewater which is characterized as huge amounts, intricate composition, and great threats to human health and the ecological environment is a research hotspot in water treatment fields. Due to high treatment costs and undesirable treatment efficiencies, oily wastewater treatment remains a topical and urgent issue. At present, coagulation/flocculation as an indispensable oily wastewater treatment technology receives much attention because it is very well established, economical, practical and relatively efficient. The influencing factors of oil wastewater treatment by coagulation/flocculation have also been summarized in-depth, like dosage, pH, etc. In consideration of its complex composition and treatment difficulty, this paper will also compare the treatment effects of different coagulants/flocculants used alone and combined effects in oily wastewater treatment: inorganic coagulants, organic synthetic polymeric flocculants, natural flocculants and modified polymeric flocculants. Additionally, in this review, the mechanisms of removing oily substance by coagulation/flocculation are emphasized. Given strict emission standards and the refractory nature of oily wastewater, the combination process with coagulation/flocculation, such as electrocoagulation, coagulation-membrane filtration hybrid process, and coagulation/flocculation-flotation can present better application potential and are discussed in this review. To provide a proper choice in practical application, the operating cost of coagulation and several conventional technologies are also compared. Finally, the existing challenges in the treatment of oily wastewater by coagulation are analyzed, and the feasible research direction is proposed.

Continuous electrocoagulation degradation of oily wastewater with Fe78Si9B13 amorphous ribbons

The oily wastewater was treated by electrocoagulation with Fe₇₈Si₉B₁₃ amorphous ribbons as anode and graphite plates as cathode under such processing parameters as different pH values and current density, respectively. The degradation effect on the oily wastewater was characterized by chemical demand oxygen (COD), while the ribbons before and after using were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results indicate that under the conditions of pH = 3 and current density being 3.125 A/cm², the optimal COD removal efficiency was obtained to be 73.22%. Compared with the ordinary crystalline iron plate, the COD removal efficiency of resultant wastewater degraded by the amorphous ribbons is more than doubled. Simultaneously, the Fe₇₈Si₉B₁₃ amorphous ribbons exhibit good structural stability even after four cycles of using.

Sewage sludge disintegration by electrocoagulation

In this research, reduction of sludge production and improvement of sludge stabilization degree were aimed, and in this regard, the samples received from an urban wastewater treatment plant were subjected to electrocoagulation (EC) as a disintegration technique. A monopolar EC reactor was designed and iron electrode was used for sludge disintegration. The effect of reaction time, pH and varying current densities on disintegration degree (DD) was determined, and the optimum conditions were found as pH 7, 30 min (reaction time), and 150 A/m² (current density). DD was found as 84.23%, and soluble chemical oxygen demand was found as 675.2 mg/L under optimum conditions. In this research, the disintegration stage of sludge was defined with the best second-order kinetic model. The operating cost was estimated as 0.078 €/m³ for optimum conditions. Also, the EC-induced disintegration ability of sludge was determined using total suspended solids, total organic carbon, capillary suction time, particle size distribution, specific surface area and viscosity. The findings showed that EC technique can be an effective means for sludge disintegration.

Peroxymonosulfate promoted wet air oxidation of a real wastewater from a biodiesel production plant

Wastewater from a real biodiesel plant located in the province of Badajoz (Spain) has been treated by means of the Wet air oxidation (WAO) process. The effluent was slightly acidic (pH = 5.77) with a high content of chemical oxygen demand (COD) (43.1 g L^-1) mainly of organic nature (C_TOC = 10.5 g L^-1). The low biodegradability of this effluent (relation biological-chemical oxygen demand BOD/COD = 8.6 × 10^-3), suggests the suitability to be treated by WAO oxidation. The main WAO operational variables (oxygen pressure, temperature and pH), the use of homogeneous catalysis (Cu²⁺), or the addition of oxidant promoters (H₂O₂ or peroxymonosulfate (PMS)) were explored. From the results obtained, oxygen pressure exerted a positive effect while temperature was a crucial variable in the oxidation of the most recalcitrant organics. Although alkaline pH led to an improved behavior in terms of COD and TOC removals, the lack of aromatic compounds elimination (absorbance at 254 nm) suggests the preference to oxidize non-aromatic compounds. Addition of radical promoters resulted in a positive effect. Peroxymonopersufate was more efficient than H₂O₂ in the promoted experimental series. Under the optimum oxidation conditions used in this study, removals of 55% in COD, 45% in TOC and 86% in aromatic compounds were experienced.

Optimal Hydrogen Production Coupled with Pollutant Removal from Biodiesel Wastewater Using a Thermally Treated TiO₂ Photocatalyst (P25): Influence of the Operating Conditions

This work aimed to produce hydrogen (H₂) simultaneously with pollutant removal from biodiesel wastewater by photocatalytic oxidation using a thermally-treated commercial titanium dioxide (TiO₂) photocatalyst at room temperature (~30 °C) and ambient pressure. The effects of the operating conditions, including the catalyst loading level (1-6 g/L), UV light intensity (3.52-6.64 mW/cm²), initial pH of the wastewater (2.3-8.0) and reaction time (1-4 h), on the quantity of H₂ production together with the reduction in the chemical oxygen demand (COD), biological oxygen demand (BOD) and oil and grease levels were explored. It was found that all the investigated parameters affected the level of H₂ production and pollutant removal. The optimum operating condition for simultaneous H₂ production and pollutant removal was found at an initial wastewater pH of 6.0, a catalyst dosage of 4.0 g/L, a UV light intensity of 4.79 mW/cm² and a reaction time of 2 h. These conditions led to the production of 228 μmol H₂ with a light conversion efficiency of 6.78% and reduced the COD, BOD and oil and grease levels by 13.2%, 89.6% and 67.7%, respectively. The rate of pollutant removal followed a pseudo-first order chemical reaction with a rate constant of 0.008, 0.085 and 0.044 min^-1 for the COD, BOD and oil and grease removal, respectively.

Experimental study on evaluation and optimization of tilt angle of parallel-plate electrodes using electrocoagulation device for oily water demulsification

Tilt angle of parallel-plate electrodes (APE) is very important as it improves the economy of diffusion controlled Electrocoagulation (EC) processes. This study aimed to evaluate and optimize APE of a self-made EC device including integrally rotary electrodes, at a fixed current density of 120 Am^-2. The APEs investigated in this study were selected at 0°, 30°, 45°, 60°, 90°, and a special value (α_(d)) which was defined as a special orientation of electrode when the upper end of anode and the lower end of cathode is in a line vertical to the bottom of reactor. Experiments were conducted to determine the optimum APE for demulsification process using four evaluation indexes, as: oil removal efficiency in the center between electrodes; energy consumption and Al consumption, and besides, a novel universal evaluation index named as evenness index of oil removal efficiency employed to fully reflect distribution characteristics of demulsification efficiency. At a given plate spacing of 4 cm, the optimal APE was found to be α_(d) because of its potential of enhancing the mass transfer process within whole EC reactor without addition, external mechanical stirring energy, and finally the four evaluation indexed are 97.07%, 0.11 g Al g^-1 oil, 2.99 kwhkg^-1 oil, 99.97% and 99.97%, respectively.

Emerging usage of electrocoagulation technology for oil removal from wastewater: A review

Electrocoagulation is a simple and efficient treatment method involving the electrodissolution of sacrificial anodes and formation of hydroxo-metal products as coagulants, while the simultaneous production of hydrogen at the cathode facilitates the pollutant removal by flotation. Oil is one of the most important hydrocarbon products in the modern world. It can cause environmental pollution during various stages of production, transportation, refining and use. Electrocoagulation treatment is particularly effective for destabilization of oil-in-water emulsions by neutralizing charges and bonding oil pollutants to generated flocs and hydrogen bubbles. The development of electrocoagulation technologies provided a promising alternative for oil removal from wastewater. This paper presents a review of emerging electrochemical technologies used for treating oil-containing wastewater. It includes a brief description of the oily wastewater origin and characteristics. The treatment processes developed so far for oily wastewater and the electrocoagulation mechanisms are also introduced. This paper summarizes the current applications of electrocoagulation for oil removal from wastewater. The factors that influence the electrocoagulation treatment efficiencies as well as the process optimization and modeling studies are discussed. The state-of-the-art and development trends of electrocoagulation process for oil removal are further introduced.

Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities

Oily wastewater poses significant threats to the soil, water, air and human beings because of the hazardous nature of its oil contents. The objective of this review paper is to highlight the current and recently developed methods for oily wastewater treatment through which contaminants such as oil, fats, grease, and inorganics can be removed for safe applications. These include electrochemical treatment, membrane filtration, biological treatment, hybrid technologies, use of biosurfactants, treatment via vacuum ultraviolet radiation, and destabilization of emulsions through the use of zeolites and other natural minerals. This review encompasses innovative and novel approaches to oily wastewater treatment and provides scientific background for future work that will be aimed at reducing the adverse impact of the discharge of oily wastewater into the environment. The current challenges affecting the optimal performance of oily wastewater treatment methods and opportunities for future research development in this field are also discussed.

Electrocoagulation treatment of black liquor from soda-AQ pulping of wheat straw

The effect of electrocoagulation treatment was investigated on black liquor from soda-anthraquinone (AQ) pulping of wheat straw. Removal of phenol, chemical oxygen demand (COD), color, total suspended solids (TSS), total dissolved solids (TDS), and total solids (TS) from black liquor was investigated at different current densities by using aluminum electrodes at various electrolysis times (10, 25, 40, 55, and 70 min) and pH levels (3, 5, 7, 9, and 10.5). It was observed that at 16 V, electrolysis time of 55 min and current density of 61.8 mA/cm(2) were sufficient for the removal of the pollutants. Energy consumption was evaluated as an important cost-relation parameter. Results showed that the electrocoagulation treatment reduced color intensity from the high initial value of 18,750 to 220 PCU. This was strongly influenced by the pH level of the wastewater. In addition, it was found that the removal efficiency increased with increasing of current density. The maximum efficiencies for removal were 98.8, 81, 80, 92, 61, and 68 % for color, phenol, COD, TSS, TDS, and TS, respectively. The lowest energy consumption values were obtained at neutral pH after 55 min. Electrocoagulation was found to be an effective, simple, and low-cost technique to treat black liquor.