Nitrate biodegradation by indigenous bacteria strain Bacillus subtilis obtained from eutrophic waters of Dal Lake Srinagar (India): Mechanisms and optimization

Abstract

The presence of elevated nitrate concentrations in natural water bodies is a cause of significant concern, owing to its potential ecological and human health ramifications. Dal lake, a eutrophic lake situated in Srinagar, India, which bears a substantial burden of nutrient pollution stemming from various sources. To tackle high nitrate levels, an indigenous bacterial strain from Dal Lake, Srinagar, India, was used for its biodegradative abilities. To enhance biodegradation, the bacterial strain's efficiency was rigorously tested across various environmental conditions, including temperature, nitrate concentration, pH, contact time, and adsorbent quantity. The active isolate, identified through genetic analysis via 16S rRNA sequencing, was determined to be Bacillus subtilis ON358108. Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), BET (Brunauer–Emmett–Teller) analysis (BET), XRD (X-ray diffraction) was employed.These methodologies were employed to scrutinize various aspects of the adsorbent, including surface area, pore volume, crystalline structure, composition, and internal structure were used in characterizing and elucidating the behaviour of functional groups engaged in the biodegradation process, both prior to and post-nitrate uptake. Adsorption mechanisms were established from experiments using the Langmuir, Freundlich, and Temkin models. We analyzed adsorption kinetics using pseudo-first- and pseudo-second-order models. To optimize the nitrate biodegradation process, we applied Response Surface Methodology (RSM) based on a central composite design approach. This approach successfully removed 91 % (±1.5) of the effluent's nitrate with Bacillus subtilis ON358108.Furthermore, our study demonstrated that the selected isotherm models fit the adsorption process in the following sequence: Langmuir > Temkin > Freundlich. In addition, thermodynamic study revealed the process is spontaneous and endothermic.