Effect of chlorination and pressure flushing of drippers fed by reclaimed wastewater on biofouling

Dripper clogging reduces the performance and service life of a drip irrigation system. The impact of chlorination (1.5 ppm of free chlorine during 1 h application) and pressure flushing (0.18 MPa) on the biofouling of non-pressure-compensating drippers fed by real reclaimed wastewater was studied at lab scale using Optical Coherence Tomography. The effect of these treatments on microbial composition (bacteria and eukaryotes) was also investigated by High-throughput DNA sequencing. Biofouling was mainly observed in inlet, outlet and return areas of the drippers. Chlorination limited biofilm development mainly in the mainstream of the milli-labyrinth channel. It was more efficient when combined with pressure flushing. Moreover, chlorination was more efficient in maintaining the water distribution uniformity. It reduced the bacterial concentration and the diversity of the dripper biofilms compared to the pressure flushing method. This method strongly modified the microbial communities, promoting chlorine-resistant bacteria such as Comamonadaceae or Azospira. Inversely, several bacterial groups were identified as sensitive to chlorination such as Chloroflexi and Planctomycetes. Nevertheless, one month after stopping the treatments the bacterial diversity re-increased and the chlorine-sensitive bacteria such as Chloroflexi phylum and the Saprospiraceae, Spirochaetaceae, Christensenellaceae and Hydrogenophilaceae families re-emerged with the growth of biofouling, highlighting the resilience of the bacteria from drippers. Based on PCoA analyses, the structure of the communities still clustered separately from never-chlorinated drippers, showing that the effect of chlorination was still present one month after stopping the treatment. HighlightsO_LIThe fouling of drippers is a bottleneck for drip irrigation using reclaimed wastewater C_LIO_LIBiofouling was lowest when chlorination was combined with pressure flushing C_LIO_LIThe {beta}-Proteobacteria and Firmicutes contain chlorine resistant bacteria C_LIO_LIThe decrease of Chloroflexi by chlorination was transitory C_LIO_LIThe bacterial community was resilient after the interruption of cleaning events C_LI