Toxicity in different molecular-weight fractions of sludge treating synthetic wastewater containing 4-chlorophenol

Abstract This study investigated sludge toxicity in removal of 4-chlorophenol (4-CP) in reactor system with addition of methanol. The toxicity was evaluated in two sequential batch reactors (SBRs), namely acclimated sludge reactor with addition of 10 mg l −1 4-CP and control sludge reactor without 4-CP addition. Results showed that even though 4-CP both in aqueous and sludge phases was undetectable, the toxicity of the acclimated sludge was still higher than the control sludge, which was assessed with Photobacterium phosphoreum ( P. phosphoreum ). Adsorption and biodegradation assays indicated that secondary metabolites from microorganism also contributed to sludge toxicity in addition to 4-CP itself. The different molecular-weight (MW) distribution of organic substances in sludge analysis validated that the mass fractions of TOC at >10 K and 10 K-500 were significantly related to the sludge toxicity.