Treatment of 2-Mercapto-5-methyl-1,3,4-thiadiazole (MMTD) wastewater by bipolar membrane electrodialysis: MMTD migration, process factors and implications

2-Mercapto-5-methyl-1,3,4-thiadiazole (MMTD), an important intermediate of widely used cefazolin and cefazedone antibiotics, was hardly decyclized during conventional wastewater treatment, raising a great risk to the environment. In this study, a new strategy for treating MMTD wastewater at the source by bipolar membrane electrodialysis (BMED) was proposed, realizing a material closed loop in the processes of MMTD production. Meanwhile, a laboratory-scale BMED system was set up for exploring MMTD migration, process factors, and technology implications. The results revealed that MMTD in the feed compartment may migrate into the acid/base compartment by electromigration and diffusion, the electromigration process of MMTD microspecies was controlled by its ionization, and the diffusion process of MMTD microspecies was influenced by its chemical potential on both sides of the membranes and the types of membranes. The analysis of the BMED process factors showed that these factors such as the initial pH of the feed solution, current density, flow velocity, and initial acid/base concentration affected the acid/base concentration, MMTD leakage, current efficiency, energy consumption, electric field intensity, ion flux, electrical resistance, head loss, and proton leakage. Based on these effects of the BMED process factors, some new strategies were proposed to optimize BMED process. Besides, the implications of BMED technology were affirmed by surveying the feasibility of BMED product recycling. Furthermore, this type of new strategy could be applied to the treatment of other similar wastewater at the source, realizing a closed loop in its production.