The effect of backwashing in the structure of microbial community on biological activated carbon (BAC) in a water treatment plant

Biological activated carbon (BAC) filtration has been widely applied for water treatment, in which backwashing is a key process to restore filtration rates or reduce excess head loss. In this study, the alternation of microbial community structure on the BAC samples before and after backwashing were investigated by 16S ribosomal RNA (16S rRNA) gene library and restriction fragment length polymorphism (RFLP) analysis. A total of 27 unique 16S rRNA genes, screened from 266 clones, were obtained from the both samples. The sequenced clones fell into 5 phylogenetic divisions. Phylogenetic analysis indicated that four of them, including β-Proteobacteria, α-Proteobacteria, Planctomycetes and γ-Proteobacteria, were all found before and after backwashing. However, Bacteroidetes only occurred before backwashing. Overall, backwashing led to the reduction of bacterial species on the BAC. The study provides valuable information about the effect of backwashing in the bacterial structure, which may be useful for further explanation of the effects of backwashing and the recovery process of biofilm.