Bifunctional erdite rods as an effective flocculant and catalyst in electro-Fenton systems

Erdite rods were massively produced via a one-step alkaline heating route with the complete recycling of waste waterwork sludge. The sludge was a mixture of Fe, Mn, Al, and Si, but only Fe-bearing substances were converted as erdite rods. The erdite rods had 100 ​nm diameter and 1-5 ​μm length, and was hydrolysed as Fe-SH-rich flocs in wastewater. Its hydrolysis became slow in the presence of electric field but accelerated by adding PMS. p-Nitrophenol was targeted as organic pollutant to determine the rods performance. The removal efficiency of p-nitrophenol was 7.4% by adding erdite rods, but up to 44.6% with the addition of erdite/PMS, and then dramatically increased to 98.7% in the electro-PMS/erdite system. Given that the free Fe was less than 30 ​mg/L, the surface Fe of Fe-SH-rich flocs predominated the PMS activation, in which the surface Fe enriched in electronic field and then was involved in the redox reaction of PMS and then reduced by the adjacent S on flocs. This enabled the recycling of Fe3+/Fe2+ to activate PMS at high level. Thus, the erdite rods showed high p-nitrophenol removal efficiency in the electro-Fenton system in comparison with the other reported reagents, e.g. ferrous sulphate, ferbam, pyrite and FeS.