Sustainable Strategy for Enhancing Anaerobic Digestion of Waste Activated Sludge: Driving Dissimilatory Iron Reduction with Fenton Sludge

The Fenton process has been extensively applied for treatment of refractory organic pollutants. The potentially hazardous iron-containing sludge generated from the Fenton process requires proper treatment and disposal, due to its high Fe contents and toxic organic matter involved. Considering that Fe(III) oxides exhibit an ideal potential for enhancing anaerobic digestion (AD), in this study Fenton sludge with a high abundance of Fe(III) was introduced in the AD of waste activated sludge (WAS) with the aim to improve sludge digestion as well as to remove the organic matter in Fenton sludge. Results showed that methane production and sludge reduction of WAS were significantly improved, and the organic matter contained in Fenton sludge was removed by 70.0%. Meanwhile, nearly half of Fenton sludge was converted to Fe2+ via dissimilatory iron reduction during the digestion, in agreement with the microbial community analysis. The study suggests an Fe recycling between AD and the Fenton process and that Fenton sludge can be used as an iron source to enhance AD, during which most of the harmful organic matter in Fenton sludge was removed, and Fe(II) generated can serve as a reactant again for a new Fenton reaction.