Removal and toxic forecast of microplastics treated by electrocoagulation: Influence of dissolved organic matter.

In recent years, the break of COVID-19 makes the large use of disposable products, which causes the removal of microplastics become an imperative problem. Electrocoagulation is one of the effective removal technologies, but there is hardly research concentrating on the effect of substrate in the actual water on the microplastics removal with electrocoagulation. As an important role of water bodies, dissolved organic matter (DOM) has a vital and inevitable effect on the efficiency of electrocoagulation. In this study, the effect of DOM in tailwater on microplastics during electrocoagulation is elucidated by comparing the electrocoagulation treatment results between simulated wastewater and tailwater, using parallel factor analysis (PARAFAC), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometer (FTIR) and zeta potential analyzer. Three kinds of microplastic particles (i.e. polypropylene, polyethylene, and polymethyl methacrylate) were added into each of the two kinds of wastewaters to form six electrocoagulation systems. Results show that DOM in tailwater promotes the production of flocs and free radicals during electrocoagulation process. Fe2+ and Fe3+ are adsorbed on the surface of DOM molecules and combined with •OH form flocs. Although DOM accelerates the production of free radicals and thus promotes the aging of microplastics, flocs with DOM as crystal nucleus can prevent toxic substances and small-sized microplastics from leaching into water again. Therefore, electrocoagulation is preferred to removal microplastics in water with high concentration of DOM. This study provides a significant reference for microplastics removal by electrocoagulation in actual water, and promote the practical application of electrocoagulation for microplastics removal in water treatment.

Sulfur-zinc modified kaolin/steel slag: A particle electrode that efficiently degrades norfloxacin in a neutral/alkaline environment.

In this work, sulfur and zinc were used to modify the steel slag/kaolin particle electrodes. Sulfur-zinc modified kaolin/steel slag particle electrodes (S-Zn-KSPEs) was successfully prepared. In a wide pH range (pH 3-10), S-Zn-KSPEs could efficiently degrade norfloxacin at low voltage (4 V) within 90 min. The removal rate of NOR by S-Zn-KSPEs was about 100% in acidic environment, more than 90% in neutral environment, and more than 80% in alkaline environment. And S-Zn-KSPEs could also efficiently degrade methylene blue, diuron, levofloxacin and other refractory pollutants under neutral conditions. S-Zn-KSPEs showed good stability and recyclability, and could maintain high catalytic activity after 8 cycles in a neutral or alkaline environment. The possible degradation mechanism and the degradation pathway of norfloxacin are proposed. In addition, S-Zn-KSPEs also showed a higher treatment effect in the treatment of actual surface water bodies. And S-Zn-KSPEs had a strong acid-base buffering capacity, which could avoid some pretreatment measures of wastewater in practical applications.