Chlorate reduction capacity and characterisation of chlorate reducing bacteria communities in sediments of the rio Cruces wetland in southern Chile

This study investigated chlorate reduction kinetics in multiple samples of sediments from a longitudinal profile of a wetland located downstream of the effluent discharge of a cellulose plant, including characterisation of the bacterial communities involved. The sediments were exposed to different initial chlorate concentrations in microcosm tests, with and without the addition of acetate as an external electron donor, and in a matrix of natural water or a defined medium. At a high initial chlorate concentration of 100 mg/L, in the absence of an external electron source, the degradation curves presented first-order kinetics, influenced by electron donor availability. The first-order kinetic constant varied between 0.05 and 0.17 day⁻¹. Subsequently, when the initial chlorate concentration was reduced to 7 mg/L, a zero-order kinetic was obtained, with the kinetic constant presenting values between 1.1 and 1.3 mg/L-day. No correlation was observed between chlorate degradation kinetics and the location of the sampling points or the previous history of exposure to chlorate. Other factors evaluated, such as the availability of organic matter or the chlorate reducing bacteria count, also proved not to have any incidence on the results. The richness of chlorate reducing bacteria species in the different samples analysed were also similar, with the greatest similarity being found between cld genes in the samples from the upstream or downstream sampling points. Additionally, cld genes most similar to those present in PCRB like Dechlorospirillum sp., Alicycliphilus denitrificans, Dechloromonas agitata, Dechloromonas sp. LT1 and Ideonella dechloratans were detected. This study showed that the anaerobic sediments of the Cruces river wetland present a high potential for chlorate natural attenuation, regardless of the previous history of exposure to chlorate. This capacity is associated with the presence of a diverse community of chlorate reducing bacteria.