Responses of anaerobic hydrogen-producing granules to acute microplastics exposure during biological hydrogen production from wastewater

Anaerobic hydrogen-producing granule (AHPG) has been successfully applied in hydrogen production from wastewater. While various types of microplastics in large amounts are readily detected in both municipal and industrial wastewaters, however, to date the response of AHPG to multiple coexisting microplastics in wastewater is unknown yet. Herein, this study provided a first insight into the acute exposure-response relationship between multiple coexisting microplastics and the AHPG during biological hydrogen production from wastewater. Fluorescence tagging found that many microplastics accumulated and covered on the surface of the whole granule. Morphology and particle size of microplastics-bearing AHPG were characterized by microscopic observation, showing that the shock load of microplastics in the wastewater at the studied concentrations (40 and 80 mg/L) made the granule loose and even break down with the decreased particle size. The visualization of extracellular polymeric substances (EPS) structure revealed that microplastics decreased EPS production by 8.8-16.7%. Microbial community analysis demonstrated that the acute exposure of microplastics did not drive the change in the microbial community diversity and composition. However, toxic leachates and upgraded oxidative stress induced by microplastics increased cell death up to 14.7% and decreased hydrogen production by 18.7%, when the AHPG exposed to 80 mg/L of microplastics. This work gained a new insight into the response of anaerobic microorganisms to coexisting microplastics in the real environment.