Organics and Nitrogen Removal from Wastewater Across a Plate of entrapped Mixed Microbial Cells

Abstract

This work investigated the concurrent removal of organics and nitrogen from wastewater as it passed through a slab of immobilized activated sludge of different thickness. Removals of chemical oxygen demand (COD) by 90% from feed of 300 mg L^-1 and of ammonia nitrogen (NH₃-N) by 30 to 50% from feed of 27 mg L^-1 in the synthetic wastewater were achieved. Wastewater exited the entrapped mixed microbial cells (EMMC) bed of 0.01 m in depth after a hydraulic retention time of 8 h through the bed. Increasing the thickness by up to 5 folds resulted in no enhancement, indicating aerobic processes ceased within the bed depth. The removal of COD was by aerobic respiration and the removal of nitrogen by oxidation via nitrification, both occurring in the aerobic zone of the EMMC bed near the entrance surface. Denitrification occurred deeper into the anaerobic zone of the bed that removed nitrate, leaving behind <0.75 mg L^-1 of nitrate in the emerging effluent. Apparent first-order rate constants were >0.29 h^-1 and >0.045 h^-1 for COD and NH₃-N removal, respectively.

Key words: Organic and nitrogen removal, entrapped mixed microbial cells, nitrification, dentrification