MICROBIAL ATRAZINE MINERALIZATION UNDER CARBON LIMITED AND DENITRIFYING CONDITIONS

A microbial enrichment culture was able to mineralise atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) supplied as sole carbon and energy source. The microorganisms were immobilised in a non-aerated fixed bed reactor with sintered glass beds as carrier matrix. Atrazine elimination was rapid, efficient and quantitative. With feed rates of up to 15.51 d(-1) of medium containing 7.5 mg l(-1) atrazine, the hydraulic retention time in the 300 mi reactor decreased to below 30 min. Atrazine effluent concentrations under these conditions were in the 10-100 mu g l(-1)-range. The mineralisation of atrazine became incomplete under oxygen deficient conditions observed with atrazine feed concentrations of 15 mg l(-1). However, complete atrazine conversion was regained and the effluent levels dropped to below 10 mu gl(-1) when NO(3)(-)ions (66 mg l(-1)) were supplemented to this medium. When [U-ring-C-14]atrazine (7-15 mg l(-1)) was used in the feed medium and a hydraulic residence time of 3.6 h was applied, atrazine was not detectable (< 0.2 mu gl(-1)) in the effluent. The yield of (CO2)-C-14, in relation to the radioactivity applied to the system was 33% under C-Limited and 44% under denitrifying conditions, respectively. Under low oxygen concentrations, only 77% of the atrazine was converted, and only 12% of the radioactivity was obtained as (CO2)-C-14,, whereas a total of 61% of the radioactivity could be attributed to two water soluble metabolites, 2-hydroxy-4-ethylamino-6-isopropylamino-1,3,5-triazine and 2-chloro-4-amino-6-isopropylamino-1,3,5-triazine.