Inoculation of granular activated carbon with s-triazine-degrading bacteria for water treatment at pilot-scale

Bacterial strains (SL1: Rhodococcus rhodochrous; WT1: Acinetobacter junii) capable of biodegrading atrazine and simazine in surface water were inoculated into pilot-scale fixed beds of granular activated carbon (GAC, 1 m depth, 15 min empty bed contact time, EBCT). River water was screened, clarified, ozonated and spiked with atrazine and simazine (post-ozonation concentration 0.5–15 μg l−1 of each s-triazine) before entering GAC columns that were monitored for 302 d. Elution of inoculated isolates from GAC columns peaked 15 min (WT1) and 30 (SL1) min after inoculation, but had fallen to 3.8 ± 0.13 × 103ml−1 (WT1) and 3.6 ± 3.37 × 102ml−1 (SL1) by 120 min. During routine operation, elution of SL1 was frequently < 10 ml−1 and less than WT1, and from day 0 to day 119 SL1 was retained on GAC in greater numbers (minimum 8.8 ± 0.32 × 104g−1 dry wt GAC) than indigenous WT1 (1.1 ± 0.16 × 104g−1 dry wt GAC) or introduced WT1 (9.1 ± 0.00 × 103g−1 dry wt GAC). On days 49, 84, 119, 265 and 302 inoculated GAC (SL1 or WT1) had less adsorbed s-triazine per column than non-inoculated GAC. Inoculation of GAC with s-triazine-degrading isolate SL1 reduced transient breakthrough concentrations of atrazine and simazine compared to non-inoculated and WT1-inoculated column effuents on days 21, 84, 140 and 170. However, from day 189 onwards consistent breakthrough occurred in all effluents exceeding the EU maximum admissible concentration (MAC, 0.1 μg l−1).