Novel Microbial System Developed from Low-Level Radioactive Waste Treatment Plant for Environmental Sustenance

Abstract

A packed bed bioreactor efficiently treated low-level radioactive waste for years with a retention time of 24 h using acetate as the sole carbon source. However, there was generation of dead biomass. This bioreactor biomass was used to develop a bacterial consortium, which could perform the function within 4 h while simultaneously accumulating nitrate and phosphate. The dead mass was negligible. Serial dilution technique was used to isolate the world's first pure culture of a nitrate accumulating strain from this consortium. This isolate could simultaneously accumulate nitrate and phosphate from solution. Its ability to form biofilm helped develop a packed bed bioreactor system for waste water treatment, which could optimally remove 94.46% nitrate within 11 h in batch mode while 8 h in continuous mode from waste water starting from 275 ppm of nitrate. The conventional approach revealed the strain to be a member of genus Bacillus but showed distinct differences with the type strains. Further insilico analysis of the draft genome and the putative protein sequences using the bioinformatics tools revealed the strain to be a novel variant of genus Bacillus. The sequestered nitrate and phosphate within the cell were visualized through electron microscopy and explained the reason behind the ability of the isolate to accumulate 1.12

Microbe-Based Strategy for Plant Nutrient Management

“…NB1 reduced 75-90% nitrate within a pH range of 5-12 with the maximum at pH 10 while that of BN7 was a range of 6-11 [39]. The optimum temperature range for NB1 was 30-40°C and that for BN7 was 25-37°C [39].…”

“…Of the four diferent combinations tested, two consortia were found to be eicient: anaerobic consortium from ECW (NB1) and aerobic consortium from bioreactor biomass (BN7). They demonstrated 96 and 97.44% nitrate removal in 12 and 4 h by NB1 and BN7, respectively [39]. Another interesting feature of BN7 was its simultaneous accumulation of nitrate and phosphate from medium.…”

“…Since cultivation is the ongoing practice in this area, eicient strains with potential for promoting plant growth are expected to inhabit this area. The other inoculum was the biomass from a low-level radioactive waste treating microbial bioilm bioreactor removing mainly nitrate [38,39]. This was expected to contain eicient nitrate reducers/accumulators due to its constant exposure to nitrate.…”

“…The experiments were repeated thrice. The aerobic culture exhibiting growth along with nitrate reduction in the presence of different metal salts was checked for metal accumulation within the biomass using energy-dispersive X-ray fluorescence (EDXRF) analysis [39,40]. While chromium (Cr), strontium (Sr) and cadmium (Cd) salts were inhibitory for the growth of the anaerobic consortium NB1 even at a concentration of 0.1 mM, the consortium showed growth in up to 0.5 mM concentration of copper (Cu), lead (Pb), cobalt (Co) and zinc (Zn).…”

“…While chromium (Cr), strontium (Sr) and cadmium (Cd) salts were inhibitory for the growth of the anaerobic consortium NB1 even at a concentration of 0.1 mM, the consortium showed growth in up to 0.5 mM concentration of copper (Cu), lead (Pb), cobalt (Co) and zinc (Zn). Being an anaerobic consortium, it was better preserved as glycerol stock while retaining its nitrate removal activity up to 24 days rather than stab or lyophilized culture as compared to BN7 [39].…”