Redox zones stratification and the microbial community characteristics in a periphyton bioreactor

• Periphyton bioreactor greatly improved water quality of a water tank.
• Stratification of five redox zones was observed from top to bottom in a water column.
• Periphyton auto regulated its structure to adapt to aerobic/anaerobic environments.
• Periphyton kept high species richness and metabolic activity at various redox zones.

Bioremediation techniques based on microorganisms have been widely applied to treat polluted surface water, but the efficiencies have been limited, especially in deep and static waters. Microbial aggregates, known as periphyton, were introduced into a tank bioreactor to improve pollutants removal and a periphyton bioreactor with an 84 cm column was built to investigate microbe–wastewater interactions. Periphyton greatly improved water quality and produced a distinct stratification in the water column into five redox zones with slight overlaps. From top to bottom these were: oxygen reduction, nitrate reduction, iron reduction, sulfate reduction and methanogenic zone. Periphyton communities had high species diversities (767–947 OTUs) with the facultative zone (middle layer) having higher species richness and functional diversity than the aerobic (top layer) and anaerobic zones (bottom layer). A good knowledge of interactions between periphyton and water column stratification could benefit from integration of periphyton to improve bioremediation of deep and static water.