Efficient pretreatment of industrial estate wastewater for biodegradability enhancement using a...

A self-made micro-electrolysis-circulatory system with the mixture regime of an upflow bed and reactor was tested for the pretreatment of industrial estate wastewater with a low ratio of biological to chemical oxygen demand (BOD₅/COD) at room temperature, 1:1 vol ratio of sponge iron (SFe)/granular activated carbon (GAC), and an intermittent process in aeration and discharge. The system efficiency was evaluated in view of the effects of various processes (hydraulic retention time (HRT), fillers/wastewater ratio (S/L) and aeration). COD reduction of about 51% was obtained for industrial estate wastewater at an S/L ratio of 25%, refluence rate of 16 L/h, HRT of 24 h, and aeration of 60 L/h as the optimal conditions. The considerable change in the calculated BOD₅/COD ratio, from 0.07 to 0.49, showed favorable application of the micro-electrolysis-circulatory system for the reductive and oxidative degradation of organic pollutants to enhance wastewater biodegradability. The reusability of the SFe was also investigated after three successive runs. On the basis of the results of Fe leaching, HRT, S/L ratio, scanning electron microscopy observation, and X-ray photoelectron spectroscopic analysis, the corrosion products facilitated by the inherent porosity of SFe played a significant role due to different oxygen conditions in the surface and internal layers. One result from the removal of organic pollutants dominated by the galvanic cell reactions between SFe and GAC was observed, and the integration coagulation in the bulk solution was mainly attributed to the leaching of Fe. The innovative approach described in this study provides a promising and economical technology for pretreatment of industrial wastewater prior to a biological process.