Effects of ultrasonic pretreatment on quantity and composition of bacterial DNA recovered from granular activated carbon used for drinking water treatment

Effects of ultrasonic pretreatment on bacterial DNA recovery from granular activated carbon (GAC) were investigated. GAC (Calgon F400), biologically activated, was sampled from an actual drinking water plant. Different ultrasonic energy densities (0-400 J·cm^-3) were applied with agitation (250 rpm for 30 min), and recovered bacterial DNA was quantified using quantitative PCR. Energy density was linearly correlated with the concentration of carbon fines produced from GAC during ultrasonication. Ultrasonication alone had no effect on DNA recovery at ≤60 J·cm^-3, but a strongly adverse effect at >67 J·cm^-3 due to the produced carbon fines. Agitation along with ultrasonication strongly enhanced the bacterial DNA recovery when ≤40 J·cm^-3 was applied, although it did not affect the production of carbon fines. Ribosomal tag pyrosequencing was used to compare recovered bacterial communities (0, 20 and 30 J·cm^-3 with or without agitation). Ultrasonication allowed for obtaining a more diverse and richer bacterial community from GAC, compared with the control. Agitation did not show a positive effect on community organization (richness and diversity). Consistently, canonical correspondence analysis indicated that the energy density was associated with the relative abundances of particular bacterial members (P < 0.05), while agitation did not. Correspondence analysis revealed that the recovered bacterial communities were grouped according to the applied energy densities. In conclusion, ultrasonication and agitation influence the recovered DNA in quality and quantity, respectively, and carbon fines as a by-product by ultrasonication interfere with the DNA recovery.