Agri effluents such as winery or olive mill wastewaters are characterized by high phenolic
concentrations. These compounds are highly toxic and generally refractory to biodegradation.
Biological sand filters (BSFs) represent inexpensive, environmentally friendly and sustainable
wastewater treatment systems which rely vastly on microbial catabolic processes. This study
aimed to assess the impact of increasing concentrations of synthetic phenolic-rich wastewater,
ranging from 96 mg.L-1 gallic acid and 138 mg.L-1 vanillin (i.e. a total chemical oxygen demand
(COD) of 234 mg.L-1) to 2400 mg.L-1 gallic acid and 3442 mg.L-1 vanillin (5842 mg COD.L-1), on
bacterial communities from BSF mesocosms. This amendment procedure instigated
adaptation of the bacterial communities, notably leading to the selection of a resistant
diazotrophic community. This suggests that functional alterations in the bacterial communities
in BSFs ensure provision of sufficient bioavailable nitrogen for the degradation of wastewater
with a high C:N ratio.