Deciphering roles and risks of a ternary Zr-MOFs based material in peroxydisulfate enhanced sludge anaerobic fermentation

Though conductive materials can enhance the performance of anaerobic fermentation (AF) for waste activated sludge, challenges such as ineffective heavy metal removal and the unassessed toxicity of both conductive materials and digested sludge hinder its practical application. In this study, a novel composite material, FeM@CS, synthesized from Fe₃O₄@MOF-808 (FeM) and chitosan (CS), was used with sodium persulfate to generate ·SO₄⁻, ·OH, and ¹O₂, significantly enhancing WAS dissolution and hydrolysis. The surface of the material has enriched a large amount of organic substrates and hydrolytic acidogenic bacteria (such as Macellibacteroides) through electrostatic attraction. Under the establishment of a shorter proton/electron transfer distance in FeM@CS, it promotes inter-bacterial syntrophic metabolism and enzyme activity, thereby increasing the production of volatile fatty acids by 184 %. Additionally, FeM and CS facilitated phosphorus and metal adsorption through electrostatic attraction, ligand exchange, and chelation, reducing the concentrations of highly toxic and low-toxicity metals in sludge digestate by 70.51 % and 22.72 %, respectively. Moreover, the toxicity of Chlorella sp., Bacillus subtilis and Thauera aminoaromatica decreased by 24.21 %, 40.00 %, and 43.42 %, respectively. Although FeM@CS exhibits some toxicity, its particulate form makes it easy to recover and difficult to release into the ecological environment. Additionally, FeM@CS demonstrates good recyclability and can desorb high-purity phosphorus and metals, which significantly reduces economic costs and makes it more suitable for large-scale applications. This study provides new insights into a low-toxicity, high-benefit, and sustainable large-scale AF approach.