The 6:2 FTS was the substitute for perfluorooctane sulfonate(PFOS) in the chrome plating industry in Japan. Electrochemical oxidation of 6:2 FTS was investigated in this study. The degradabilities of PFOS and 6:2 FTS were tested on the Ti/SnO2–Sb2O5–Bi2O3anode. The effects of current density,potential,and supporting electrolyte on the degradation of 6:2 FTS were evaluated. Experimental results showed that 6:2 FTS was more easily degraded than PFOS on the Ti/SnO2–Sb2O5–Bi2O3anode. At a low current density of 1.42 mA/cm2,6:2 FTS was not degraded on Ti/SnO2–Sb2O5–Bi2O3,while the degradation ratio increased when the current density ranged from 4.25 to 6.80 mA/cm2. The degradation of 6:2 FTS at current density of 6.80 mA/cm2 followed pseudo first-order kinetics with the rate constant of 0.074 hr-1. The anodic potential played an important role in the degradation of 6:2 FTS,and the pseudo first-order rate constants increased with the potential. The surface of Ti/SnO2–Sb2O5–Bi2O3was contaminated after electrolysis at constant potential of 3 V,while the fouling phenomenon was not observed at 5 V. The fouled anode could be regenerated by incinerating at 600°C. The intermediates detected by ultra-performance liquid chromatography coupled with a triple-stage quadrupole mass spectrometer(UPLC–MS/MS) were shorter chain perfluorocarboxylic acids. The 6:2 FTS was first attacked by hydroxyl radical,and then formed perfluorinated carboxylates,which decarboxylated and removed CF2 units to yield shorter-chain perfluorocarboxylic acids.
Electrolysis is a promising technology to improve sludge dewaterability efficiently with negligible environmental impact. To intensify the electrolytic efficiency, the effect of electrolytes(NaCl, Na_2SO_4, NaNO_3, and NaClO_4) on electrolysis pretreatment of municipal sludge and its mechanisms was investigated using Ti/PbO_2 electrodes. The electrolytes,which enhanced the production of oxidative radicals, showed a significant synergetic effect in reducing the capillary suction time(CST) of sludge. NaCl was distinguished from the other electrolytes since it formed a large amount of active chlorine species, which oxidized the sludge cells to improve the sludge dewaterability. The surface morphologies as well as the soluble proteins and polysaccharides were analyzed to unravel the underlying mechanisms of sludge dewaterability. Additionally, an economic assessment showed that NaCl addition in the electrolysis pretreatment can be a suitable technique for enhancing municipal sludge dewaterability.
Ke XiaoJianping DengLi ZengTao GuoYan GongBo YangXu ZhaoHuabo Duan
Electrocoagulation(EC)technique was used to investigate the removal performance of aqueous perfluorooctanoic acid(PFOA)with relatively high concentration as simulating the wastewater from organic fluorine industry.A comparison was done with the similar amount of coagulant between EC and chemical coagulation process.PFOA removal obtained was higher with EC process,especially for Fe anode.Several factors were studied to optimize the EC process.At the optimal operating parameters including 37.5 mA/cm^2 of current density,initial pH 3.77,and 180 rpm of mixing speed,93%of PFOA could be removed with 100 mg/L of initial concentration after 90-min electrolysis.Furthermore,the remove efficiency could be obviously improved by H2O2 intermittent addition,which removed more than 99%of PFOA within 40-min EC.It could be attributed to that H2O2 facilitated the oxidative transformation from ferrous to ferric ion.In addition,the adsorptive removal of aqueous PFOA on Fe flocs during EC was also verified by fourier transform infrared spectra.
Bo YangYanni HanYunpan DengYingying LiQiongfang ZhuoJinhua Wu
