Simplified denitrification system using ethanol released from non-porous polyethylene-film bag

A holding bag fabricated using non-porous low-density polyethylene (LDPE) film was examined to simplify a denitrification system for nitrate-containing wastewater without organic carbon. The LDPE-film bag filled with ethanol released ethanol slowly. The amount of the released ethanol could be controlled by changing the film thickness. A dual bag was constructed with an outer non-woven fabric bag on which Paracoccus denitrificans cells were immobilized and the inner LDPE-film bag filled with ethanol. When the dual bag was immersed in a nitrate solution under agitation of N2 gas or air, the nitrate content of the solution decreased irrespective of the agitating conditions. The maximum nitrogen removal rate was 5.94 g N d−1 m−2 of the outer bag's surface. This value corresponded to the volumetric nitrogen removal performance of 0.1 kg N m−3 d−1, though the packed ratio of the dual bag in the solution was below 10%. The dual bag could remove nitrogen from nitrate solution without an additional apparatus. The bioreactor using the dual bag would be extremely effective as an additional denitrification system, since they can be easily installed in the vacant spaces of various tanks.