Nitrogen removal with a dual bag system capable of simultaneous nitrification and denitrification

Abstract

We tested the nitrogen removal ability of a dual bag system. The dual bag was constructed with an outer non-woven fabric bag and an inner non-porous polyethylene film bag. Nitrosomonas europaea and Paracoccus pantotrophus were immobilized on the outer bag and 23 mL of 99.5% ethanol was packed into the inner hermetic bag. The dual bag removes ammonia as follows: ammonia in the solution is oxidized to nitrite, and the produced nitrite is reduced to nitrogen gas by cooperation of the N. europaea and P. pantotrophus on the outer bag. Ethanol as an electron donor for denitrification is supplied to the P. pantotrophus from the inner bag. Ammonia solution (20 mg N L −1) flowed into a reactor tank (200 mL volume) with three dual bags was continuously treated for a hydraulic retention time of 2.6 h at 25 °C. Total nitrogen in the outflow of the reactor was kept below 4.0 mg N L −1 for more than 90 days without accumulating organic carbons. The dual bags removed 80.0% of the nitrogen from the solution without additional operations. The inner bag containing 23 mL of ethanol probably releases ethanol for approximately 1000 days without refilling since the inner bag released only 0.022 mL ethanol per day. The dual bag system would effectively simplify the nitrogen removal system since it is easily installed in vacant spaces of various waterways and tanks.