Chemical Engineering Journal 94 (2003) 155–159 The denitrification treatment of low C/N ratio nitrate-nitrogen wastewater in a gas–liquid–solid fluidized bed bioreactor Wen Jianping ∗ , Pan Lei, Du Liping, Mao Guozhu Department of Biochemical Engineering, School of Chemical Engineering, Tianjin University, Tianjin 300072, PR China Accepted 29 January 2003 Abstract A 12 l gas–liquid–solid three-phase fluidized bed bioreactor in which biomass supported on activated charcoal was used to remove nitrate-nitrogen from wastewater and its performance was considered. The effects of temperature, pH, C/N ratio, gas flow rate and hydraulic residence time (HRT) on nitrate-nitrogen reduction were investigated and discussed. The optimum operated conditions such as temperature of 20–35 ◦ C, pH value of 6.5–7.5, HRT of 3 h, C/N of 0.95–1 and gas influx of 0.3 m 3 /h were found. Under optimum operated conditions, the average removal ratios of COD and NO x -N are higher than 92% and 96%, respectively. In addition, the radial and axial positions have little influence on the local profiles of COD and NO x -N. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Gas–liquid–solid three-phase fluidized bed bioreactor; Nitrate-nitrogen; Wastewater; Bio-denitrification 1. Introduction After biochemical treatment of ammonia containing wastewater from the fertilizer production, the effluent with COD <50 mg/l and NH 4 -N <10 mg/l and NO x -N <500 mg/l can meet the national primary discharge stan- dard of PR China for ammonia industry wastewater. But the nitrate-nitrogen in low C/N ratio wastewater, which was transformed from ammonia-nitrogen, still does rather serious harm to the environment [1–3]. It is very necessary to remove the nitrate-nitrogen from effluent. As a pow- erful tool for wastewater processing, bio-denitrification, which was used at municipal treatment plants to treat wastewater after ammonia was converted to nitrate via nitrification, has attracted biochemical and environmen- tal scientists and engineers’ attentions [4–8]. Especially, the bio-denitrification technology based on some new liquid–solid fluidized bed reactors was developed in recent years for the removal of nitrate-nitrogen from wastewater [9]. However, little is known about the bio-denitrification treatment of low C/N ratio nitrate-nitrogen wastewater in a gas–liquid–solid three-phase fluidized bed bioreactor, characterized by the higher operational flexibility, shorter reaction time and greater processing capability. There- ∗ Corresponding author. Tel.: +86-22-2740-1664; fax: +86-22-2350-1622. E-mail address: jpwen@tju.edu.cn (W. Jianping). fore, objective of the present study is to both develop a gas–liquid–solid three-phase fluidized bed bioreactor and acquire the optimum operated parameters for removing nitrate-nitrogen from wastewater. 2. Materials and methods 2.1. Reactor design and other apparatus Experiments were performed in the apparatus shown in Fig. 1. The fluidized bed section (5), constructed from the plexiglass, had a 100 mm i.d. and was 1200 mm high. It was ended by a disengaging cap with 160 mm i.d. and a height of 200 mm. A growing medium, stored in reservoir (1), was pumped into the bottom of the bioreactor using a peristaltic pump (2) flux of which ranges from 600 to 10,000 ml/h. The nitrogen gas was introduced to the bed through a distributor with 0.1 mm diameter holes. The role of baffle plate sepa- rator (7) was to separate the carriers from the liquid in the effluent leaving the bioreactor and send the carriers back to the bioreactor. The liquid flow rate was measured with a ro- tameter (4) and was controlled by a cutoff valve (3). The flow rate of nitrogen gas, which is very convenient for fer- tilizer plant with air separation devices, was measured with a rotameter (8) and was control by a needle valve (9). The temperature controlled system (10) consisted of a coil with cold water and an electric heater coupled with a contact 1385-8947/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1385-8947(03)00049-4