• Energy Research

The biomass of the cyanobacterium Spirulina platensis was used for metal removal from four industrial effluents with different chemical composition. The process of metal bioaccumulation (alive biomass) and biosorption (dry biomass) was studied at the native effluents pH as well as the pH 9.5. Metal uptake by S. platensis biomass was determined by means of neutron activation analysis (NNA). The obtained results show different affinity of biomass to metals presented in effluents. The results of this study have indicated that S. platensis is a very good candidate for the removal of heavy metals from complex industrial effluents.

The goal of the present work was to investigate the physicochemical and radiochemical conditions and the microbial diversity in groundwater collected near the Lake Karachai (Russia), which was formerly used for the disposal of liquid radioactive waste, to isolate the dominant bacteria, and to determine their taxonomy and the physiological characteristics responsible for their adaptation to this environment. Groundwater samples contained high concentrations of acetate, oxalate, nitrate, and sulfate, as well as radionuclides. High-throughput sequencing and analysis of the clone libraries revealed lower microbial diversity in the most strongly contaminated groundwater and a predominance of bacteria of the genera Polynucleobacter, Pusillimonas, Candidatus Pelagibacter, and of the candidate phylum Parcubacteria; these groups include species with an ultra small cell size. Archaeal sequences in the libraries belonged to ammonium oxidizers of the phylum Thaumarchaeota and methanogens of the phylum Euryarchaeota. Pure cultures of obligate and facultative ultramicrobacteria belonging to the genera Chryseobacterium, Microbacterium, Salinibacterium, Pusillimonas, Roseomonas, and Janibacter were isolated from water samples. In genomes of Pusillimonas and Roseomonas strains the genes associated with nitrate reduction, resistance to heavy metals and metalloids were revealed. Several isolates are able to participate in the geochemical process of nitrate conversion to N2 using acetate; this results in decreasing redox potential, which in turn may stimulate radionuclide reduction and decrease radionuclide migration in groundwater.

The chemical and physical methods of controlling microbiological processes during long-term storage of nitrate-containing radwastes in the liquid form in deep reservoir beds as well as incorporated in a cement matrix in surface storage facilities are examined. It is shown that irrespective of the final method used for disposal of radwastes biogenic processes are best controlled by directed suppression or stimulation, which can be accomplished by adjusting the ratios of the physical and chemical storage parameters: temperature, pH, ionizing radiation, concentration of nitrate ions and other potential substrates for culturing bacteria as well as action by adding biocidal agents.

The article deals with the problem of managing liquid nitrate-containing radioactive waste. A fundamentally new method for preliminary treatment that allows one to decrease the volume of these waste based on denitrification or anaerobic nitrate respiration (reducing nitrates to molecular nitrogen) has been developed. Microorganisms isolated from repository radioactive waste that is resistant to high salinity and ionizing radiation were used in the work. Based on laboratory studies on denitrification in model solutions of liquid radioactive waste, a design for a denitrifying reactor was developed and its basic parameters were calculated.