Electrochemical pretreatment of coking wastewater by Ti/BTN/RuO2-IrO2-TiO2: Selectivity of chloridion oxidation and multi-response optimization

Electrocatalysis degradation of biochemical tail water from coking wastewater using particle electrode with persulphate

Due to the intricate composition and recalcitrant nature of coking wastewater, the biochemical effluent often fails to meet standards. This study explored the preparation of particle electrodes, utilizing activated carbon powder (PAC) loading single-element Fe, Co, and Ni, as well as dual-element Ni-Fe and Co-Fe as catalyst. The particle electrode system was integrated with persulphate (PS) activation to enhance its performance. The effects of potassium persulphate (KPS) dosages, currents, and Ni:Fe ratios were investigated. The results showed that bimetallic particle electrodes outperformed their monometallic particle electrodes. Among the five electrode materials, Ni-Fe/PAC achieved the best degradation efficiency of 84.4% and the lowest energy consumption of 19.73 kW·h·kg-1 COD. When the initial concentrations of TOC and COD were set at 300 and 280 mg L-1, the Ni-Fe/PAC with 5 mmol L-1 KPS achieved removal efficiencies of 61.7 and 84.4%, respectively. The metals on Ni/PAC and Co/PAC existed in the zero-valent state, while Fe on Fe/PAC was present as Fe2O3. Co-Fe/PAC exhibited the formation of CoFe2O4 oxides. Ni-Fe/PAC possessed the lowest hydrogen evolution reaction potential (-0.28 V), and the highest oxygen evolution potential (2.4 V), and reached an electrochemical active surface area (ECSA) of 236.3 cm2. Cyclic voltammetry (CV) curves indicated that the direct redox reactions and indirect oxidation of pollutants occurred concurrently. Both •OH and ⋅ SO 4 - radicals played crucial roles during the degradation processes. The degradation efficiency of organic matter was as follows: benzene compounds (88.4%) >heterocyclic compounds (75.3%) >polycyclic aromatic hydrocarbons (53.9%).

Electrochemical chlorine evolution reaction to improve the desalination of sea sand

Sea sand, a vital sand and gravel resource, is rich in chloride, which causes corrosion of steel reinforcements. This study investigates the effect of the electrochemical chlorine evolution reaction (CER) on the desalination of sea sand. The results indicate that the chlorine removal efficiency (RE) of sea sand increased from 48.76 to 56.40 % under optimal conditions: a current density of 15 mA/cm2, an electrolysis time of 1 min, and a sodium sulphate-supported electrolyte concentration of 0.05 mol/L. After 30 days of resting, the dissolved chlorine content in sea sand was 0.154 %, which was 21.03 % lower than that of the control group. The electrically active chlorine-mediated desalination process demonstrated excellent dechlorination ability, facilitated the transformation of metal and organic chlorine into liquid and gaseous forms, and reduced the slow release of chloride from sea sand. Therefore, CER is expected to be an efficient method for sea sand desalination.

Variation of current density with time as a novel method for efficient electrochemical treatment of real dyeing wastewater with energy savings

Electro-oxidation is a promising technology for wastewater treatment with biorefractory organic and nitrogen pollutants; however, the high energy demand hinders its wide application. In this study, a novel method by regulating significant parameter during the electro-oxidation process in a timely manner for real dyeing wastewater treatment with energy savings was studied. Operating factors (i.e., flow rate, initial pH value, electrode distance, and current density) were investigated for chemical oxygen demand (COD) and ammonia removal, and the results indicated that current density was the key factor that obviously influenced the electrochemical performance. Indirect oxidation by active chlorine was then confirmed as the main reaction pathway for pollutant oxidation, and the relationship between the current density and the generation of active chlorine was established, suggesting that a large part of the generated active chlorine was not utilized effectively. Subsequently, a novel method of varying the current density in a timely manner based on the reaction mechanism was proposed; the results indicated that, with similar pollutant removal efficiencies, energy consumption could be reduced from 31.6 to 20.5 kWh/m3. Additionally, the novel system was further optimized by Box-Behnken design: The COD removal efficiency could reach 71.8%, and the energy demand could be reduced by 45.6%.