Combined electrocoagulation processes as a novel approach for enhanced pollutants removal: A state-of-the-art review.

A novel approach using the integration of electrocoagulation, with one or more treatment processes has been recently practiced to improve the removal of colloidal and non-biodegradable pollutants. Several treatment processes including adsorption, chemical coagulation, magnetic field, reverse osmosis, and membrane filtration have been combined with electrocoagulation treatment step to improve pollutants removal efficiency. These combined systems showed the potential to improve the performance of the treatment process. This paper presents a state-of-the-art review for the recent processes available in the literature that combine treatment electrocoagulation with one of the previously mentioned treatment processes. It is found that the removal efficiency of any combined processes is higher than that of any single treatment process and the combined process has up to 20% higher removal efficiency compared to electrocoagulation alone. However, most reported studies were conducted at bench-scale level with synthetic wastewater instead of real wastewater. The main aspects of these combined systems including process mechanism, kinetic models, cost and the scale up of combined processes were discussed and summarized. Finally, several concluding remarks were drawn in view of the literature investigations and the gaps that suggest more studies and insights for future development were addressed.

Optimal conditions for olive mill wastewater treatment using ultrasound and advanced oxidation processes.

The treatment of olive mill wastewater (OMW) in Jordan was investigated in this work using ultrasound oxidation (sonolysis) combined with other advanced oxidation processes such as ultraviolet radiation, hydrogen peroxide (H2O2) and titanium oxide (TiO2) catalyst. The efficiency of the combined oxidation process was evaluated based on the changes in the chemical oxygen demand (COD). The results showed that 59% COD removal was achieved within 90 min in the ultrasound /UV/TiO2 system. A more significant synergistic effect was observed on the COD removal efficiency when a combination of US/UV/TiO2 (sonophotocatalytic) processes was used at low ultrasound frequency. The results were then compared with the COD values obtained when each of these processes was used individually. The effects of different operating conditions such as, ultrasound power, initial COD concentration, the concentration of TiO2, frequency of ultrasound, and temperature on the OMW oxidation efficiency were studied and evaluated. The effect of adding a radical scavenger (sodium carbonate) on the OMW oxidation efficiency was investigated. The results showed that the sonophotocatalytic oxidation of OMW was affected by the initial COD, acoustic power, temperature and TiO2 concentration. The sonophotocatalytic oxidation of OMW increased with increasing the ultrasound power, temperature and H2O2 concentration. Sonolysis at frequency of 40 kHz combined with photocatalysis was not observed to have a significant effect on the OMW oxidation compared to sonication at frequency of 20 kHz. It was also found that the OMW oxidation was suppressed by the presence of the radical scavenger. The COD removal efficiency increased slightly with the increase of TiO2 concentration up to certain point due to the formation of oxidizing species. At ultrasound frequency of 20 kHz, considerable COD reduction of OMW was reported, indicating the effectiveness of the combined US/UV/TiO2 process for the OMW treatment.

Bioconversion of paper mill sludge to bioethanol in the presence of accelerants or hydrogen peroxide pretreatment.

In this study we investigated the technical feasibility of convert paper mill sludge into fuel ethanol. This involved the removal of mineral fillers by using either chemical pretreatment or mechanical fractionation to determine their effects on cellulose hydrolysis and fermentation to ethanol. In addition, we studied the effect of cationic polyelectrolyte (as accelerant) addition and hydrogen peroxide pretreatment on enzymatic hydrolysis and fermentation. We present results showing that removing the fillers content (ash and calcium carbonate) from the paper mill sludge increases the enzymatic hydrolysis performance dramatically with higher cellulose conversion at faster rates. The addition of accelerant and hydrogen peroxide pretreatment further improved the hydrolysis yields by 16% and 25% (g glucose / g cellulose), respectively with the de-ashed sludge. The fermentation process of produced sugars achieved up to 95% of the maximum theoretical ethanol yield and higher ethanol productivities within 9h of fermentation.

Mass transport enhancement in annular-shaped lid-driven bioreactor.

The current study investigated numerically the two-dimensional (2D) incompressible flow and mass transfer in a lid-driven cavity of annular geometry accompanied by enzymatic surface-reactions. The lid-driven bioreactor had a square cross-section of (H × H) and a radius of curvature of r (c). This flow configuration gives the opportunity to evaluate effects of curvature as well as operational parameters on the bioreactor performance. For forced-convection, conservation equations were solved numerically, using fourth-order finite volume schemes, to identify the 2D flow structure and concentration distribution of substrate within the bioreactor. For pure diffusion, analytical solution was obtained. Substrate transfer rates were presented in terms of Sherwood number. While, effectiveness factor was computed to evaluate the force-convection contribution over pure molecular diffusion. Mass-transfer against surface-reaction resistance was estimated via Damkohler number. Results indicate the positive role of increasing Peclet number, Reynolds number, and radius of curvature in enhancing the substrate transport process.

Impact of Fenton and ozone on oxidation of wastewater containing nitroaromatic compounds.

Fenton and ozone treatment was investigated at laboratory scale for the degradation of aqueous solutions of nitrobenzene (NB). Effects of reactants concentration (03, H2O2, and Fe(II)), temperature, and pH on NB degradation were monitored. Reaction kinetic of these processes was also assessed. A rapid reaction took place for Fenton process at higher initial concentration of H2O2, higher temperatures, and more acidic conditions (pH 3). Similarly, ozonation reaction exhibited rapid rates for higher ozone dose, higher temperatures, and more basic conditions (pH 11). Complete NB degradation in 65 min was achieved using Fenton process. The conditions of complete elimination of 100 mgfL of initial NB concentration, were 250 mg/L of H2O2 concentration, pH 3, and 10 mg/L of Fe(II) concentration. Under these conditions, 55% organic carbon elimination was achieved. Total organic carbon mineralization was attained in 240 min reaction time by Fenton process with 900 mg/L of H2O2 concentration, and 30 mg/L of Fe(II) concentration. Fenton reaction showed a pseudo-first order kinetic; the reaction rate constant was ranged from 0.0226 to 0.0658 min(-1). Complete NB degradation was also achieved for an ozone dose of the order of 2.5 g/L. The ozonation was studied at different ozone doses, different initial pH (7-11) and at different temperatures (15-35 degrees C). NB ozonation kinetic was represented by a bi-molecular kinetic model which was reduced to pseudo-first order kinetic. The pseudo-first order reaction rate constant was determined to increase at 20 degrees C from 0.004 to 0.020 min(-1) as the used ozone increased from 0.4 to 1.9 g/L.

Degradation of dissolved diazinon pesticide in water using the high frequency of ultrasound wave.

This article aims to apply the ultrasound technique in the field of clean technology to protect environment. The principle of sonochemistry is conducted here to degrade pesticides in simulated industrial wastewater resulted from a factory manufacturing pesticides namely diazinon. Diazinon pesticide selected in this study for degradation under high frequency ultrasound wave. Three different initial concentrations of diazinon (800, 1200, and 1800 ppm), at different solution volumes were investigated in to degrade dissolved diazinon in water. Ultrasound device with 1.7 MHz, and 0.044 cm diameter, was used to study the degradation process. It is found that as the concentration of diazinon increased, the degradation is also increasing, and when the solution volume increases, the ability to degraded pesticides decreases. The experimental results showed an optimum condition achieved for degradation of diazinon at 1200 ppm as initial concentration and 50 ml solution volume. Kinetic modeling applied for the obtained results showed that the degradation of diazinon by high ultrasound frequency wave followed a pseudo-first-order model with apparent rate constant of around of 0.01 s(-1).