Optimization of electrochemical activation of persulfate by BDD electrodes for rapid removal of sulfamethazine.

Boron-doped diamond electrodes have been employed for the removal of sulfamethazine (SMZ) from water by electrochemical activation of persulfate (EO/BDD-PS). A set of experiments with a central composite design (CCD) was conducted to optimize the operating parameters such as persulfate dose, solution pH, and current density by response surface methodology (RSM). The experimental results indicated a rapid degradation of SMZ even at high initial concentrations. For instance, complete degradation of 50 mg L-1 of SMZ was attained after 15 min at the optimum operating conditions (persulfate loading = 0.40 g L-1, pH = 4, and current density = 21 mA cm-2). The oxidation mechanism of EO/BDD-PS process was studied based on the reactive oxidant species (ROS) revealing that both (OH) and contributed to the degradation of SMZ in the EO/BDD-PS system. Furthermore, the oxidation pathway has been proposed by the suspect screening and tandem mass spectrometry analysis. The performance of EO/BDD-PS showed faster SMZ degradation than electro-Fenton and anodic oxidation processes using the same BDD electrochemical reactor under the same conditions. Furthermore, we provided a cost estimation study revealing that a full-scale application of the EO/BDD-PS system for the treatment of similar contaminated water costs about $2.23 m-3.

Reuse of adsorption residuals for enhancing removal of ciprofloxacin from wastewater.

Costs of water treatment can be reduced significantly if the spent adsorbents can be reused or regenerated. In this study, two residuals of iron adsorbed onto low-cost activated carbon (Fe-MCAC and Fe-MLAC) are reused as new adsorbents for the removal of ciprofloxacin (CIP) from pharmaceuticals wastewater. The residuals were characterized by SEM, XRD, FTIR, Raman spectra and N2-adsorption desorption. The adsorption mechanisms, performance, kinetics, isotherm, thermodynamic and reusability of residuals for CIP removal were evaluated. The isotherm data were well defined by the Freundlich model for both adsorbents (residuals). Moreover, the CIP adsorption follows the pseudo-second-order kinetic model. The maximum adsorption capacity of CIP on Fe-MCAC and Fe-MLAC was 476.19 and 416.67 mg/g, respectively. The maximum removal of CIP was obtained at pH 7 for both new adsorbents. The optimum contact time was found to be 30 and 60 min for Fe-MCAC and Fe-MLAC, respectively. The values of free energy change and enthalpy change for adsorption of CIP indicated the spontaneous, endothermic nature of the adsorption. In addition, the adsorption process was assisted by increasing randomness due to the value of entropy change. Therefore, the residuals of iron adsorption onto activated carbons could be reused as new low-cost adsorbents for antibiotics removal from wastewater.

Visible-light-driven photocatalytic disinfection of raw surface waters (300-5000 CFU/mL) using reusable coated Ru/WO3/ZrO2.

We selected ruthenium (Ru) to improve the photocatalytic activity of a WO3/ZrO2 composite. The synthesized Ru/WO3/ZrO2 was then compared to a benchmark photocatalyst (S-TiO2) in terms of photocatalytic disinfection of raw surface waters collected from the Nile Delta region, Egypt. The photocatalysts were immobilized on aluminum plates with polysiloxane to test them in repetitive cycles under the irradiation of a metal-halide lamp. Bacterial concentrations in the raw waters ranged from 300 to 5000 CFU/mL (CFU: colony-forming units) and different species and genus were detected including gram-negative (e.g., shigella, salmonella, vibrio parahaemolyticus, and vibrio cholera) and gram-positive bacteria (e.g., enterococcus). Ru/WO3/ZrO2 deactivated over 90 % of the bacterial content within 120 min for most sources, whereas S-TiO2 did not perform as highly. The bacterial count after 240 min of irradiation was below the detection limit for all different water sources. Moreover, the inhabitation of photocatalytic disinfection by natural organic matter (NOM) was investigated. Ru/WO3/ZrO2 was stable for four continuous cycles (960 min in total), suggesting the viability for practical application.

Environmental and cost life cycle assessment of different alternatives for improvement of wastewater treatment plants in developing countries.

Most of wastewater treatment plants (WWTPs) in developing countries comprised primary and secondary treatment without including any tertiary treatment or sludge processing. Decision makers think that additional treatment is costly and the gained environmental benefits are limited. This study aims to investigate the environmental and economic benefits of improving current conventional WWTPs in developing countries by adding tertiary treatment and/or anaerobic digestion of sludge. For this purpose, life cycle assessment (LCA) for four different scenarios was studied for a wastewater plant located in Gamasa, Egypt. The 1st scenario is the plant in its current state. The 2nd scenario is the addition of anaerobic digestion of sludge. The 3rd scenario is the addition of a tertiary treatment stage. The 4th scenario is the addition of anaerobic digestion of sludge and tertiary treatment stage. CML 2000 method was used for assessing the environmental impacts of the four scenarios. The 4th scenario attained maximum environmental benefits for all categories due to the energy saving and the prospect of water reuse. The application of the 4th scenario achieved environmental benefits in some important categories such as ozone layer depletion. According to the economic evaluation, the addition of tertiary treatment leads to gain financial profits due to the value of the reusable produced water. This study underlines the importance of considering LCA in development of WWTPs in developing countries.

Fast adsorption of phosphate (PO4 -) from wastewater using glauconite.

In this study, the removal of phosphate (PO4 -) from wastewater using glauconite was investigated. Glauconite was characterized by N2 adsorption-desorption isotherm, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and Fourier transform infrared (FTIR) spectroscopy. The effects of contact time, pH, initial phosphate concentrations, adsorbent dose, and temperature were investigated by batch experiments. The isotherms, kinetics and thermodynamics for phosphate removal were studied. The results showed that glauconite had a rough surface and abundant pores. The determined Brunauer-Emmett-Teller (BET) surface area was 55 m2/g with a pore radius of 1.99 nm and the pore volume was 0.032 cm3/g. FTIR analysis revealed that the abundance of various functional groups on the surface of glauconite may play an important role for the adsorption process. The optimum pH was 11 with complete removal of phosphate in a short time (nearly 1 min). The experimental data fitted very well with the Langmuir isotherm (R2 = 0.999) with a maximum adsorption capacity of 32.26 mg/g at 50 °C. Adsorption kinetic data were best fitted with the pseudo-second-order kinetic model (R2 = 0.999). Thermodynamic study confirmed the spontaneous, endothermic and irreversible adsorption process. Therefore, glauconite is a promising natural low-cost adsorbent for phosphate removal from wastewater.