Report No FR/K0002

May 1994


Members of FWR expressed concern about the contamination of source waters by s-triazine herbicides and the difficulties of ensuring their removal in water treatment to the levels required by legislation on drinking water quality (0.1 g l-1 individual p esticides, 0.5 g l-1 total pesticides, Council of the European Communities, 1980). As a consequence, FWR commissioned the Research School of Biosciences, University of Kent, to investigate the potential for microbiological degradation of the two most common s-triazine herbicides, atrazine and simazine. The contract began in November 1990 and has continued for 3 years and 5 months and has been funded outside the core programme from FWR's investment income.

Bacterial strains were isolated capable of biodegrading atrazine and simazine at low concentrations (1-10g l-1) in surface water at a temperature of 10C. Biodegradation was increased (20-30%) by the addition of 1g GAC l-1 in batch experiments. The inoculation of fixed bed GAC at laboratory-scale demonstrated that inoculation did not reduce microbial water quality (no sustained increases in bacterial elution) whilst it regenerated GAC by reducing the amount of adsorbed s-triazine (biodegradation of 53-58% of 13.9 g g-1 of each herbicide). Inoculation also significantly improved treated water quality by reducing the concentration of s-triazines in product water.

When tested at pilot-scale there was again no reduction in microbial water quality (no sustained increases in bacterial elution). Inoculation of GAC with WT1 or SL1 significantly reduced the amount of adsorbed atrazine and simazine on GAC and reduced breakthrough concentrations of atrazine and simazine (in the case of SL1 up to day 189). Reductions in the numbers of s-triazine-degraders maintained on the GAC, and a subsequent insufficient rate of biodegradation, prevented the extension of these beneficial effects on treated water quality beyond the first 6 months of operation.

The results demonstrate that inoculation of GAC with s-triazine-degrading bacteria is compatible with current water treatment technologies for pesticide removal (ozonation and GAC adsorbtion) and reduces transient breakthrough concentrations of the s-triazines within the first 6 months of operation. These beneficial affects were not extended beyond 6 months because s-triazine degrading bacterial species were not present at high enough density (i.e. less than 1 x 105 cells g-1 GAC). This may be overcome by more frequent inoculation (e.g. every 3 months) or by altering operational parameters (e.g. increasing EBCT up to 30 minutes).

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