Packed-Bed Reactors for Nitrification and Denitrification of Secondary Effluents.

摘要

Upflow packed-bed reactors (PBR) have been investigated to determine their usefulness as a tertiary treatment process to further reduce biochemical oxygen demand (BOD) and suspended solids (SS) from secondary effluents and to remove nitrogen by biological nitrification and denitrification. Laboratory-scale units were used to help identify system design parameters and to study the effect of such variables as temperature,detention time,oxygen concentration and packing material. Pilot-scale studies using secondary effluent were performed to help identify operating problems and to determine PBR performance in a more realistic treatment situation. These tests have shown that the PBR process can remove about 50% of the carbonaceous BOD and suspended solids from a secondary effluent. Another 20% to 30% can be removed by granular-media filtration. Biological nitrification could be achieved at flow rates below about 0.5gpm/sq ft (1.25 m/h) and denitrification could be achieved at flow rates less than about 1.0gpm/sq ft (2.5 m/h). Granular media such as crushed sand or coal or modular plastic media provided about equal performance,but were subject to plugging especially when using the PBR for denitrification. A complete tertiary treatment system consisting of packed-bed reactors for BOD removal,nitrification and denitrification and granular-media filters for final polishing can provide an effluent with BOD,SS and nitrogen concentrations comparable to that which can be achieved by physical-chemical treatment including activated carbon adsorption for removal of organic materials.