Comparative evaluation of the nutrient and cod removal performances of various sequentially operated biofilm reactors

In this paper, the performances of Fixed Bed (FXB), Fluidized Bed (FLB), and Hybrid (HYB, i.e. fluidized bed followed by fixed) operational conditions of biofilm reactors were investigated. The COD (chemical oxygen demand), TN (total nitrogen) and TP (total phosphorus) were taken as performance-indicator parameters. For that purpose, a pilot experimental setup allowing FXB, FLB and HYB operations in a single reactor was run under varying COD (between 500 to 2000 mg COD l(-1)), TN (between 25 to 100 mg l(-1)) and TP (between 5 to 20 mg l(-1)) influent concentrations. The system was operated as sequentially batch (SBR) and a filtering process was added at the end of each operational phase in order to achieve liquid-solid separation. Results indicated that FXB and FLB are two upper and lower cases, and HYB plays a role between them and respond as a best alternative. For example, for the lower influent concentrations (around 500 mg l(-1)), 84% of COD was removed to final averages of 78 +/- 15.4 mg l(-1); simultaneously, TN reduced to 18.55 +/- 3.48 mg l(-1) (corresponding to 31 TN removal) and 60%. of TP was treated to final averages of 1.9 +/- 20.2 mg l(-1) in the HYB operation. When the influent concentrations were increased to 1000 mg l(-1),COD removal efficiency of the HYB reactor was reduced to 73% (COD reduced from 1005.3 +/- 6.13 mg l(-1) to 270.57 +/- 13.18 mg l(-1)) and, due to incomplete organic matter degradation and oxygen deficiency, 40% of TN was removed to final averages of 34.03 +/- 5.04 mg l(-1) and 56% of TP treated to final averages of 3.98 +/- 0.28 mg l(-1). Performance of the HYB reactor was decreased when influent concentration increased to 2000 mg COD 1(-1)