Nitrification of industrial nuclear effluent using whole bacterial cell immobilization

VENTURINI, M; SILVA PAULO, P.; CURUTCHET, G.; PIZARRO, R.

Environmental Biotechnology and Engineering Advances 2016

CINVESTAV

Año: 2018; p. 716 - 726

In the nuclear industry, ammonia-derived compounds are used in the processes ofmanufacture of uranium concentrates (known as ?yellow cake?) which are used as rawmaterial to obtain nuclear fuels. For this reason, the effluent of this process containshigh concentration of ammonium, and consequently, high levels of uranium. Therefore,these effluents must be treated to diminish the concentrations of NH4 (4g/l N-NH4+) andU (300ppm UO2+2) in order to fulfill local environmental laws. Ammonium is a verysoluble ion and it is difficult to precipitate, meaning, it is not easy to eliminate. Theuranium has several oxidation states and this depends on the leachant composition andsubsequent precipitating conditions; the soluble forms is uranyl ion (UO2+2).In this work, we studied and applied the nitrification process, by an autotrophic aerobicoxidation bacterial community, to oxidize the ammonium to nitrate. Due to thecomplexation and the long time taken to generate the appropriate amount of biomass,the key point in this process is the bacterial cells immobilization to a solid support, toavoid biomass loss and also to enhance the performance in kinetic and effectivenessterms. Hence, we worked with copolymeric hydrogels previously developed, which wereobtained by gamma irradiation of 2-hydroxyethyl methacrylate. These hydrogels wereinoculated with the bacterial community and then visualized by electronic microscopyand also kinetically compared. The elastic properties of this material avoideddeformations in time, and also prevented the development of anaerobic zones in theinternal zone, though inside the hydrogel anaerobic environment was denoted byaccumulation of nitrate, which did not appeared in studies without solid supports.The study was performed at laboratory scale of 5 liters of effluent during 100 days, withan ammonium concentration reduction of 90% (initial value: 4000ppm). The kinetic rateof consumption was 350mg/l.day. The treatment was also evaluated in terms of externalparameters (rO2 and CO3- consumption), which are stoichiometric reactant in thenitrification process. Obtained results showed to be a viable process for the treatment ofeffluents from nuclear industry. The uranyl ions at the end of process were not detected.