Reactive oxygen species accelerate humification process during iron mineral-amended sludge composting

The production of hydroxyl radicals ((OH)-O-center dot) has been documented during composting. However, the effect of (OH)-O-center dot on composting efficiency remains unclear. Here, iron mineral supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing (OH)-O-center dot production and accelerating the maturation of composting. The results indicated that the maximum (OH)-O-center dot production of imTC was 1922.74 mu mol center dot kg(-1), which increased by 1.39 times than that of ordinary thermophilic composting (oTC). Importantly, the increase of (OH)-O-center dot could greatly enhance organic matter degradation and humic substances formation during imTC, resulting in shorting the maturity time by 25 %. Enrichment of laccase-producing bacteria resulted in higher laccase activity (31.85 U center dot g(-1)) in imTC compared with oTC (23.82 U center dot g(-1)), which may have contributed to the higher level of humifi-cation in imTC treatment. This work, for the first time, proposes a feasible strategy for improving composting efficiency through the regulation of (OH)-O-center dot production during aerobic composting.