Characterization of ammonia remover Bacillus albus (ASSF01) in terms of biofilm-forming ability with application in aquaculture effluent treatment

Presence of higher concentration of ammonia (> 0.5 mg/L) as well as nitrite (> 0.2 mg/L) in aquaculture environment create difficulties for fish survival. The existing methods for removal of these pollutants are time-consuming. A stable biofilm-based system for ammonia removal from aquaculture wastewater was developed in the current study to overcome the limitations of conventional treatment processes. In order to do so, initially the bacterial candidate was well characterized and tested for rapid biofilm development. The ammonia bioremediating Bacillus albus (ASSF01), from the activated sludge of shrimp farm, with a generation time of 67 min 12 s in suspension culture, was a structured biofilm former. The staining based measurement showed biofilm initiation from the very first hour of incubation. This finding was further validated using scanning electron microscopy (SEM), profilometry, and ellipsometry with Brewster angular microscopy (BAM). Hurst exponent (H) calculation using the profilometer and ellipsometer data yielded a value of H of above 0.9 and 0.62, indicating positive correlation or persistence behavior, hence a stable biofilm former. Each method of biofilm measurement, in spite of variation in complexity and sensitivity, was equally effective for biofilm progression analysis. The generation time of ASSF01 upon immobilization was 15 min and 36 s, ensuring rapid development of stable system. Response surface methodology (RSM)-based optimization of aquaculture wastewater treatment by the isolate in a biofilm reactor at ambient temperature revealed the optimum influent concentration of ammonia (3.2 mg/L), nitrate (6.89 mg/L), and phosphate (1.17 mg/L) to be reduced to discharge level (as per aquaculture requirement) with 14 h of hydraulic retention time. This study demonstrates the potential of the isolate as an efficient bioremediant for treating ammonia-containing aquaculture wastewater in a single unit biofilm reactor, ensuring rapid stabilization, environmental protection, and aquaculture sustenance.

Near vacuum-ultraviolet aperiodic oscillation emission of AlN films

An accurate measurement of the refractive index is necessary for the optical design of both deep ultraviolet laser diodes and light-emitting diodes. Generally, the refractive indices along different crystallographic axes of anisotropic thin films are measured using variable angle spectroscopic ellipsometry. However, there are still some limitations concerning this method. Here we proposed a potential method to measure the band edge refractive index of wide bandgap semiconductor. An aperiodic oscillation emission phenomenon due to the Fabry-Perot effect was observed in the fluorescence spectrum of an AlN film with a thickness of 1500 nm. Based on the characteristics of the fluorescence spectrum and the definition of Fabry-Perot effect, we obtained the ordinary refractive index of the AlN thin film near the band edge directly. This refractive index measurement method is a supplement to the variable angle ellipsometry, and it is a more direct and effective method for transferred film and thinner samples to measure the fluorescence spectrum.

Immobilization of surface non-affinitive protein onto a metal surface by an external electric field

We investigated an alternate technique to coat the surface with a protein having no surface affinity, without the use of any exotic chemical agents. An external electric field was utilized to prepare the protein coating on a metal substrate. Stainless steel (St) substrate and lysozyme (LSZ) were used as the surface to be coated and the model non-adsorptive protein, respectively. Dynamics of the adsorption of LSZ on the St surface in the presence and absence of an external electric potential (EEP) were monitored by in-situ ellipsometry. Applying negative surface potential (-0.4 V vs Ag/AgCl) forced the adsorption of LSZ onto the St surface where LSZ did not adsorb without applying any EEP. The repetition of the EEP-application and -cut-off indicated the controllability of the LSZ coating amount depending on the total duration of the EEP-application. The coated LSZ largely remained bound to the surface even by the cut-off of the external electric field, the ratio of which to the detached amount was roughly constant (approximately 7:3). Furthermore, the LSZ coated surface on the St substrate was found to be reversibly switched between being affinitive and non-affinitive to a typical model protein adsorbate (bovine serum albumin) by the EEP-application and cut-off.