Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2 and Ti/SnO2-Sb/MnO2 anodes

Electrochemical decomposition of environmentally persistent perfluorooctanoic acid (PFOA) in aqueous solution was investigated over Ti/SnO₂-Sb, Ti/SnO₂-Sb/PbO₂, and Ti/SnO₂-Sb/MnO₂ anodes. The degradation of PFOA followed pseudo-first-order kinetics. The degradation ratios on Ti/SnO₂-Sb, Ti/SnO₂-Sb/PbO₂, and Ti/SnO₂-Sb/MnO₂ anodes achieved 90.3%, 91.1%, and 31.7%, respectively, after 90 min electrolysis at an initial 100 mg/L PFOA concentration at a constant current density of 10 mA/cm² with a 10 mmol/L NaClO₄ supporting electrolyte solution. The defluorination rates of PFOA on these three anodes were 72.9%, 77.4%, 45.6%, respectively. The main influencing factors on electrochemical decomposition of PFOA over Ti/SnO₂-Sb anode were evaluated, including current density (5-40 mA/cm²), initial pH value (3-11), plate distance (0.5-2.0 cm), and initial concentration (5-500 mg/L). The results indicated that PFOA (100 mL of 100 mg/L) degradation ratio and defluorination ratio achieved 98.8% and 73.9%, respectively, at the optimal conditions after 90 min electrolysis. Under this optimal condition, the degradation rate constant and the degradation half-life were 0.064 min⁻¹ and 10.8 min, respectively. The intermediate products including short-chain perfluorinated carboxylic acids (PFCAs, C₂∼C₆) and perfluorocarbons (C₂∼C₇) were detected by electrospray ionization (ESI) mass spectrum. A possible electrochemical degradation mechanism of PFOA including electron transfer, Kolbe decarboxylation, radical reaction, decomposition, and hydrolysis was proposed. The electrochemical technique could be employed to degrade PFOA from contaminated wastewater as well as to reduce the toxicity of PFOA.     

Experimental studies on the performance,emission and combustion characteristics of a biodiesel-fuelled (Pongamia methyl ester) diesel engine with diethyl ether as an oxygenated fuel additive

This paper investigates the combustion, performance and emission characteristics of a single-cylinder diesel engine using neat biodiesel (Pongamia methyl ester) with two different blends (10% and 15% diethyl ether [DEE]) at different load conditions. The measured values of brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), exhaust gas temperature (EGT), carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NO) and smoke were calculated and analysed and compared with diesel fuel. The results showed that a significant reduction in NO and smoke emissions for neat biodiesel with 15% DEE blend compared with neat biodiesel at full load conditions. The peak pressure and heat release rate were decreased, and maximum rate of pressure rise and ignition delay were also decreased with DEE blends at full load. On the whole, it is concluded that the biodiesel with 15% DEE blend showed better results with respect to efficiency and emissions point of view compared with biodiesel.     

Short-term adhesion and long-term biofouling testing of polydopamine and poly(ethylene glycol) surface modifications of membranes and feed spacers for biofouling control

Ultrafiltration, nanofiltration membranes and feed spacers were hydrophilized with polydopamine and polydopamine-g-poly(ethylene glycol) surface coatings. The fouling propensity of modified and unmodified membranes was evaluated by short-term batch protein and bacterial adhesion tests. The fouling propensity of modified and unmodified membranes and spacers was evaluated by continuous biofouling experiments in a membrane fouling simulator. The goals of the study were: 1) to determine the effectiveness of polydopamine and polydopamine-g-poly(ethylene glycol) membrane coatings for biofouling control and 2) to compare techniques commonly used in assessment of membrane biofouling propensity with biofouling experiments under practical conditions. Short-term adhesion tests were carried out under static, no-flow conditions for 1 h using bovine serum albumin, a common model globular protein, and Pseudomonas aeruginosa, a common model Gram-negative bacterium. Biofouling tests were performed in a membrane fouling simulator (MFS) for several days under flow conditions similar to those encountered in industrial modules with the autochthonous drinking water population and acetate dosage as organic substrate. Polydopamine- and polydopamine-g-poly(ethylene glycol)-modified membranes showed significantly reduced adhesion of bovine serum albumin and P. aeruginosa in the short-term adhesion tests, but no reduction of biofouling was observed during longer biofouling experiments with modified membranes and spacers. These results demonstrate that short-term batch adhesion experiments using model proteins or bacteria under static conditions are not indicative of biofouling, while continuous biofouling experiments showed that membrane surface modification by polydopamine and polydopamine-g-poly(ethylene glycol) is not effective for biofouling control.