Assessment of a Novel Microalgae-Cork Based Technology for Removing Antibiotics, Pesticide and Nitrates from Groundwater

Groundwater pollution has increased in recent years due to the intensification of agricultural and livestock activities. This results in a significant reduction in available freshwater resources. Here, we have studied the long term assessment of a green technology (1-4 L/day) based on a photobioreactor (PBR) containing immobilized microalgae–bacteria in polyurethane foam (PF) followed by a cork filter (CF) for removing nitrates, pesticides (atrazine and bromacil), and antibiotics (sulfamethoxazole and sulfacetamide) from groundwater. Gene-based metataxonomic assessment showed that whereas green algae where most abundant species on the PBR foam, a greater bacterial alpha diversity was observed in the CF (Shannon: 5.58 ± 0.08) compared with the PBR (Shannon: 3.86 ± 0.11). Interestingly, a high denitrifying potential was detected in both materials (nosZ), whereas fungal populations were only detected in the CF (ITS2). The prototype was moderately effective for removing nitrates (58%) at an HRT of 8 days, while its efficiency decreased at a HRT of 4 and 2 days (<20% removal). The combined use of PBR-CF enabled antibiotics and pesticides to be attenuated up to 95% at an HRT of 8 days, but their attenuation decreased with shorter HRT, pesticides being the compounds most affected (reducing from 97–98% at an HRT of 8 days to 23–45% at an HRT of 2 days). Pesticide transformation products were identified after the CF, supporting biodegradation as the main attenuation process and linked to the presence of specific pesticide biodegradation species (genus Phenylobacterium). Therefore, the results show a very promising use of the combined application of microalgae and cork for treating agriculturally polluted groundwater