Effect of trace metal bioavailability on the anaerobic digestion of purified terephthalic acid (PTA) production wastewater

The production of purified terephthalic acid (PTA), a precursor for the plastic industry, employs metals-cobalt (Co) and manganese (Mn)-as catalysts, generating wastewater (PTA WW) that contains metals and organic compounds. Co and Mn are essential to microbial necessities during anaerobic digestion (AD), but they can potentially inhibit this process when present in high concentrations. This study investigated the fractionation and bioavailability of Co, Mn, and iron (Fe) in anaerobic sludge from continuous (R1 and R2) and sequential batch reactors (SBR1 and SBR2) treating PTA WW. The modified Tessier sequential extraction procedure showed that Mn was mainly distributed in bioavailable phases, whereas Co and Fe were mainly associated with less mobile, non-bioavailable phases. No Co, Mn, and Fe addition was necessary during the reactors' operation, showing that metals present in PTA WW sustain the AD process, and accumulate in the sludge over time. Notably, SBR1 and SBR2, operated under Co, Mn, and Fe suppression, showed stable performance, indicating that the metal pool accumulated in the granular sludge also sustained the AD process. These findings highlight the potential to operate anaerobic reactors treating PTA WW without continuous trace metal supplementation, which brings beneficial economic implications for the industrial process.