Hydrothermal deconstruction of local anesthetics (bupivacaine and lignocaine) in pharmaceutical waste

Abstract

Pharmaceutical waste is highly toxic; its disposal is problematic. This study aimed to investigate the non-catalytic hydrothermal deconstruction of local anesthetics and their packaging materials and to gain some insight into the mechanisms of degradation. The widely used local anesthetics bupivacaine and lignocaine with initial concentrations of 400 and 800 mg/L, respectively, were subjected to 60 min hydrothermal treatment at temperatures ranging between 200 and 350 °C. A reduction in the chemical oxygen demand (COD) was observed for the bupivacaine (up to 91.3%), and lignocaine (up to 87.8%) samples. Short-chain and volatile fatty acids, predominantly acetic acid, were produced from the hydrothermal process. Complete degradation of lignocaine was achieved at 200 °C after 30 min, whereas bupivacaine was completely degraded at 250 °C after 10 min. Nitrogen in the form of ammonia (NH3-N) was detected in the degradation products of both bupivacaine (up to 28.2 mg/L) and lignocaine (up to 60 mg/L). Packaging materials make up a substantial part of pharmaceutical waste. Complete deconstruction of packaging waste was achieved by hydrothermal deconstruction, with the resulting mixture having a total chemical oxygen demand (tCOD) of 784 mg/L and soluble chemical oxygen demand (sCOD) of 732.6 mg/L. The total suspended solids (TSS) were reduced by 93%. Complete deconstruction of a mixture of packaging and pharmaceutical waste was achieved at 300 °C after 60 min. The reactive force field (ReaxFF) molecular dynamic simulation suggested that hydroxyl radicals were responsible for the degradation of bupivacaine and lignocaine. The findings indicate the potential for hydrothermal processing to address the problems caused by local anesthetics and the associated packaging materials in pharmaceutical waste.