Microbial community in packed bed bioreactor involved in nitrate remediation from low level radioactive waste

Abstract

Nitrate is the second largest contaminant of agriculture soil after pesticides. It also is a major pollutant from nuclear and metallurgical operations. Conventional methods for nitrate removal suffers from high cost and complexity leaving bioremediation as a viable alternative strategy. A pilot plant of 2.5 m(3)/day capacity has been functioning since 2005 based on microbial consortia treating actual effluent from nuclear power plant having pH of 7-8.5 (optimum) with N:C ratio of 1:1.7. The maximum biodegradable nitrate concentration of 3000 ppm could be reduced to below permissible limit (44.2 ppm) within 24 h in presence of sodium acetate as carbon source. Culture independent analysis (16S rDNA based) revealed clones having closest identity with uncultured bacterium, Pseudomonas stutzeri and Azoarcus sp. The existence of dissimilatory pathway of nitrate reduction in the community DNA is indicated by presence of nirS and nirK gene. Though the microbial mass was developed using municipal sewage, absence of Mycobacterium sp was confirmed using PCR. The understanding of the molecular identification of the consortium would help in developing the preservation strategy of the microbial mass for replication and perpetuation of the system.

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

“…The problem in hand was to develop a microbial process, which could efficiently treat low-level radioactive waste containing nitrate generated from ore enrichment. Nitrate being a common pollutant in municipal as well as agricultural waste water, municipal sewage was passed through corrugated sheets of a packed bed reactor to develop a biofilm-based bioreactor that could treat low-level radioactive effluent within 24 h on a continuous basis [5] using acetate as the sole carbon source. However, dead mass was generated during the operation.…”

“…However, dead mass was generated during the operation. The biomass was characterized [5] and further enrichment in nitrate broth (HiMedia M439) resulted in isolation of the fastest nitrate removing consortium. This consortium was further characterized to yield the world's first nitrate accumulating pure culture [11] of a Bacillus sp.…”

Microbe-Based Strategy for Plant Nutrient Management

“…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.…”

“…In order to study the leaching process, outlets were made along the breadth of the tub at diferent heights of 3, 7, 11, 15 and 17 cm from the surface of the soil which facilitated in sample collection which in turn were assessed for the nitrate concentration [37,38].…”

“…For this, water was poured into the soil illed tub. As the water seeped down, samples were collected from each outlet and analyzed for nitrate concentration [37,38]. For the second and third set, the soil was inoculated with 100 ml of seed culture of BN7 and NB1, respectively.…”