The conversion of nitrate in water to diatomic nitrogen gas by immobilized Pseudomonas stutzeri on vermiculite

Denitrification is a reduction of nitrate by heterotrophic and autotrophic bacteria that may ultimately produce molecular nitrogen (N2) through a series of intermediate nitrogen compounds.Vermiculite is a hydrous phyllosilicate mineral (Mg, Fe+2,Fe+3)3[(Al,Si)4O10](OH)2·4H2O with several layers for bacterial immobilization. The goal of this study was removal of nitrate from water with vermiculite and bacterial bio-film. In this process, 2×107 of bacteria were trapped in one gram vermiculite with resting cells and growing cells and nitrate removal were compared by free cells. The data showed that the un-immobilized cell in resting state could only remove 45 mg nitrate in 5 days, however nitrate removal by resting cell on vermiculite was 180 mg in 10 days, while in free resting cells this removal was poor. The maximum removal of 450 mg nitrate occurred after 25 days with feeding of biofilm. The intermediate product of nitrate removal was nitrite and in all data, the end product was nitrogen.   Highlights Immobilization of P. stutzeri in resting cell status,improved nitrate removal efficiency versus un-immobilized bacteria. Feeding the immobilized bacteria, improved nitrate removal efficiency. Vermiculite introduced as a beneficial support media for immobilization of bacteria.