Drip irrigation with treated wastewater: sanitary issues of biofouling

Drip irrigation techniques provide water-saving irrigation solutions that deliver water in controlled quantities for the plant's optimal growth. Nonetheless, biofilm development in these systems fed with treated wastewater induces biofouling and reduces the benefit of this system. Several experiments were performed in order to characterize the factors affecting biofouling in these systems. In the first study, the influence of dripper hydraulic parameters on biofilm development and on the presence of bacterial genera of health interest was tested. Three types of drippers with different hydraulic parameters and flow rates (1, 2 and 4 L.h-1) have been installed on irrigation pipes supplied with lagoon-treated wastewater for 3-4 months. The biofilm development was followed by Optical Coherence Tomography. Bacterial communities of dripper biofilms were characterized by 16S rDNA high throughput sequencing over time. The biofilm development was higher in the 1 L.h-1 drippers. The structure of the bacterial communities in the dripper biofilms and the abundance of genera associated with opportunistic pathogens (Legionella, Acinetobacter, Aeromonas, Pseudomonas, Mycobacterium or Stenotrophomonas) were different according to the dripper type, which could be explained by hydraulic flow changes. Moreover, the abundance of some of these genera (Acinetobacter, Aeromonas) in dripper biofilms decreases over time while the bacterial diversity increases. In a second experiment, the effect of treatments (water purge and chlorination) to limit the biofilm development were studied for 1 L.h-1 drippers. The dripper biofilm development was slower for the chlorinated irrigation pipes. The impact of the treatment on the bacterial communities and on the removal of genera containing opportunistic species will be characterized (analyses in progress).