Enhanced refractory organics removal by sponge iron-coupled microbe technology: performance and underlying mechanism analysis

Sponge iron (SFe) is a zero-valent iron (Fe 0 ) composite with a high-purity and porous structure. In this study, SFe was coupled with microorganisms that were gradually domesticated to form a Fe 0 /iron-oxidizing bacteria system (Fe 0 -FeOB system). The enhancement effect of the Fe 0 -FeOB system on refractory organics was verified, the mechanism of its strengthening action was investigated, and the relationship and influencing factors between the Fe 0 and microorganisms were revealed. The average removal rates of the Fe 0 -FeOB system were 8.98%, 5.69%, and 40.67% higher than those of the SBR system for AF, AN, and NB wastewater treatment, respectively. With the addition of SFe, the microbial community structure was gradually enhanced with a large number of FeOB were detected. Moreover, the bacteria with strong iron corrosion and Fe(II) oxidation abilities plays a critical role in improving the Fenton-like effect. Interestingly, the variation trend of ⋅OH was fairly consistent with that of Fe(II). Thus, the main drivers of the Fenton-like effect are biological corrosion and metabolism. Consequently, microbial degradation and Fenton-like effect contributed to the degradation performance of the Fe 0 -FeOB system. Among them, the microbial degradation accounted for 96.09%, of which the biogenic Fenton effect accounted for 8.9%, and the microbial metabolic activity accounted for 87.19%. However, the augmentation of the Fe 0 -FeOB system was strongly dependent on SFe for the strengthening effect of microorganisms disappeared after leaving the SFe 35 days. Graphic abstract