Characterization and biodegradation of ibuprofen by Bacillus siamensis strain DSI-1 isolated from wastewater

Abstract

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the emerging class of xenobiotics that were detected in various environmental sources. The monocyclic compound Ibuprofen acts as an emerging micro-pollutant and this has been widely used in the form a pain reliever drug. Microbes have the potential to use this compound as bon and nitrogen source. Hence, this study was conducted in the batch culture with the relevant concentration of Ibuprofen. The active microbial culture was collected from wastewater and this was used to isolate the true degrader of IBU by the addition of IBU during the enrichment process. Therefore, the enrichment culture technique was performed to isolate true Ibuprofen degrading bacterial strain. Haldane’s growth kinetics model was used in order to study the kinetic behaviour of strain. The isolate DSI-1 has been characterized by microscopy, biochemical tests and molecular analysis by using 16S rRNA sequencing. Based on these characterization methods, the isolate DSI-1 was reported as Bacillus siamensis strain DSI-1 (with GenBank accession number MT039503). This strain has degraded the Ibuprofen (up to concentration of 15 mg/L) which was added to wastewater in scale-up bioreactor (5L) study conducted in the present work. Through the batch culture study, it was observed that 20 mg/L of IBU was degraded in 24 h and the maximum specific growth rate (μmax) observed was 0.21/h. The saturation constant (Ks) and inhibition constant (Ki) observed for ibuprofen degradation were 17 ± 5%, and 315 ± 5% mg/L, respectively, with correlation coefficient (R2) of 0.9827. The mathematical modelling was used with the help of Design-Expert® software for the optimization of various physical parameters by experimental design. The correlation coefficient (R2) observed for IBU degradation was 0.8897, Adj R2 (0.7794), and predicted R2 (0.4736). The optimum conditions reported of IBU degradation were temperature (30 °C), pH (7.0), IBU (3.5 mg/L), and agitation speed (165 rpm). This research exemplifies the involvement of bacteria with efficient removal of the relative concentration of Ibuprofen from wastewater. Therefore, the results of this study have indicated the potential for the isolated IBU degrading Bacillus siamensis strain DSI-1 and this strain can be further deployed for bioremediation program by in-situ degradation.