A bottom-up approach to select microbes from textile wastewater for detoxification of aromatic amine and azo dye in a single stage

Abstract

Biological processes show great promise for treating textile wastewater, but the complexity and high energy needs limit their industrial applications. Complete dye degradation involves physiologically distinct bacteria in a two-stage process. First, anaerobic bacteria cleave azo dyes into hazardous aromatic amines, whereas its further degradation requires aerobic bacteria. We propose strategic microbial selection based on their physiological capabilities while developing a bioremediation design to detoxify aromatic amines and dyes in a single stage. Bacillus firmus PM1, the amine degrader, and Serratia liquefaciens PM2, the helper strain, were isolated from textile wastewater. B. firmus PM1 completely degraded 4-Nitroaniline (4-NA), a common dye intermediate, under a range of physicochemical conditions prevalent in textile effluent viz. varying pH (7–11), oxygen availability (static/shaking), temperature (30–40 °C), and 4-NA concentrations (200–1000 μM). Along with 4-NA degradation (100 %), B. firmus PM1 could also efficiently degrade co-contaminants, aniline (35 %), and phenols (45 %). UPLC, FTIR, and LC-MS analysis suggested that when B. firmus PM1 is used in co-culture with S. liquefaciens PM2, it efficiently mineralizes 4-NA (95 %) and reduces Acid Black 1 (AB1) (80 %) dye both in synthetic and the real textile effluent. Further, the co-culture could also significantly reduce 4-NA and AB1 mixture induced phytotoxicity/cytogenotoxicty in Vigna mungo and Allium cepa. Thus, the study demonstrates a novel bottom-up approach that relies on isolating bacteria degrading the penultimate toxic dye metabolite and developing a co-culture for degrading the parent dye. The study demonstrates that detoxification-centric use of specialized microbes has potential to evolve sustainable industrial practices.