Mass-balance analysis of sulfamethoxazole during extracellular-polymeric-substance extraction from excess sludge

Recycling of biopolymers such as alginate-like extracellular polymers (ALE) and alkaline-extraction extracellular polymeric substances (AEPS) from excess sludge is expected to solve the resource-climate crisis and transform water-resource plants. However, the extracted biopolymers may be contaminated with waste products entering the environment, limiting biopolymer applications and necessitating by-product treatment. This study quantifies the effects of different factors on the occurrence of the antibiotic sulfamethoxazole (SMX) in biopolymers extracted from four sludge categories: conventional activated sludge, anaerobic granular sludge, aerobic digested sludge, and bacterial–algal granular sludge. The mass balance of SMX is analyzed throughout the extraction process. SMX occurrence is higher in the water phase than in the other mass flows and is significantly higher in AEPS than in ALE because ALE contains no humic acids and low amounts of extracted protein. The AEPS level is the highest (~28 %) in aerobic granular sludge. The pH value, which affects the dissociation degree of SMX and the zeta potential of AEPS, potentially affecting the electrostatic interaction, exerts the greatest impact on SMX assignment, followed by temperature and SMX concentration. These results provide a theoretical basis for understanding the interaction between sludge and SMX. They also provide an important reference for optimizing the extracellular-polymeric-substance extraction process and processing the extraction residue.