Characterization of Biofilm Bacterial Communities in a Vertical Unsaturated-Flow Bioreactor Treating Domestic Greywater

Greywater (GW) is wastewater generated from domestic activities without the input of toilet and kitchen. Its reuse can help to reduce the overall potable water consumption in urban areas. In the current study, an extensive greywater treatment unit consisting of an attached growth unsaturated-flow bio-reactor, with “BIOROCK”® medium, was developed. Its performance was studied and the bacterial communities of the BIOROCK® biofilm were characterized through 454-pyrosequencing of 16S rRNA genes. The medium physical properties (porosity and high specific surface) made it possible to support highly diverse and relatively long-term stable bacterial communities that showed spatial variations in their relative abundance. The bacterial communities were dominated by genera previously associated with wastewater environments and that present some kind of degrading activities. Consequently, after treatment, water turbidity was reduced by 83 % and COD removal efficiency was 80 %, demonstrating that most of the biodegradable matter had been removed. Some pathogens were detected, but usually at low abundances. With some minor adjustments and the addition of a chlorination step, the treated greywater generated by this system can be used for non-potable purposes, such as irrigation and toilet flushing.