Long-term stability of biological denitrification process for high strength nitrate removal from wastewater of uranium industry

Abstract

The aim of the present study was to biologically denitrify uranium nitrate raffinate (UNR) from nuclear industry, which is a principle source of high strength nitrate waste. To denitrify the high nitrate waste, a pilot-scale continuous stirred tank reactor was designed with two inbuilt settlers. Acclimatization of mixed culture with synthetic waste was carried out prior to the inoculation of the acclimatized sludge into the reactor. Initial concentration of nitrate in uranium raffinate was 77,000 mg/L NO₃. It was diluted and used as a feed to the reactor. Concentration of nitrate in feed was increased gradually from 10,000 mg/L NO₃ to 40,000 mg/L NO₃ with hydraulic retention time (HRT) maintained at 34.4 h. Complete denitrification of 40,000 mg/L NO₃ was achieved in a specified HRT. To facilitate understanding of the treatablity and long-term stability of biological denitrification of UNR, study was carried out for 211 days by periodical perturbation of the system. Furthermore, to find the volume ratio of reactor to settler required for the full-scale design of the denitrification plant, settling of acclimatized sludge was carried out.