Trace elements enhance biofilm formation in UASB reactor for solo simple molecule wastewater treatment

► Biofilm boosting with sufficient trace elements (TE) was achieved in one UASB reactor treating solo simple molecule in this study. ► Rather than biocatalyst enhancing biofilm formation was convincing. ► Black PVA-gel beads with a ranking average settling velocity 322 m/h (9 cm/s) and 0.24 g VSS/g PVA gel were got.