Waste iron shavings to advance anaerobic treatment of acidic poly (butylene adipate-co-terephthalate) wastewater in submerged anaerobic membrane reactor.

The wastewater generated during the synthesis of biodegradable plastics, namely poly (butylene adipate-co-terephthalate) (PBAT), is greatly acidic and contains various toxic pollutants. Adding waste iron shavings (WIS) into the submerged anaerobic membrane bioreactor to construct the coupled reactor (WIS-Reactor) holds promise for improving the treatment efficiency of acidic PBAT wastewater. The results showed that the chemical oxygen demand (COD) and volatile fatty acids (VFAs) removal efficiencies of WIS-Reactor were increased by 2.36 and 9.92 times, respectively, compared with the control. Even under strongly acidic influent conditions (pH = 4.0), the methane conversion efficiency (227.07 mLCH/gCODr) and COD removal rate (51.80 %) in WIS-Reactor were maintained consistently. The pH value in WIS-Reactor increased to around 6.0, the alkalinity increased by 1.5 times due to hydrogen evolution corrosion, and the sludge concentration increased by 19 % without a substantial increase in membrane fouling. Further analysis showed that iron ions released by WIS promoted the secretion of coenzyme F, enhanced electron transfer between microorganisms, and accelerated CH production through enhancing the hydrogenotrophic methanogenesis pathway. Additionally, WIS promoted the enrichment of acidogenic bacteria (Corynebacterium) and electroactive microorganisms (Synergistaceae), and may accelerate the electron transfer efficiency between Syntrophomonas and Methanosaeta through direct interspecies electron transfer, thereby improving the anaerobic digestion of acidic PBAT wastewater.