Biological Denitrification by Chalk-Fixed Biofilms: Laboratory Studies

Abstract

Waste water with high nitrate (1000 – 2500 mg NO₃ ⁻ l⁻¹) and ammonia (> 200 mg NH₄ ⁺ l⁻¹) contained denitrifying bacteria (10³ CFU ml⁻¹). Laboratory experiments were done using chalk-fixed biofilms reactors, that simulated the natural pathway of the polluted aquifer, to define a suitable in situ treatment. The inoculum adapted well to the very high nitrate volumetric loads when the amounts of electron donor (0.4 g ethanol g⁻¹ NO₃ ⁻ removed) and phosphorus ([PO₄ ²⁻] > 5 mg l⁻¹) were adequate. Adding metals reduced the nitrite residual concentration below the EC standard values and enhanced denitratation and ammonia elimination.

Keywords:

• Biofilm
• biological treatment
• denitrification
• ethanol
• groundwater