Nitrate removal in an innovative up-flow stirred packed-bed bioreactor

Abstract

The anaerobic removal of nitrates was studied in a continuous up-flow stirred packed-bed reactor (USPBR) containing biological sludge carbonaceous material (BSCM). The carbonaceous material (CM), obtained from exhausted sludge, was used as support to grow the biofilm and solid electron mediator for nitrate reduction in the bioreactor. In a continuous USPBR-BSCM system feed with treated synthetic wastewaters, nitrate removal efficiency was 99% at very short space times (τ) 2min/hydraulic residence times (HRT) 6min. By comparing these results with the hydraulic residence times applied in other classical denitrification technologies, it seems that USPBR-BSCM requires the shortest times to achieve almost complete nitrate removal. In addition, a high denitrification rate of 3.67·10−3mmolNO3−min−1g−1 was observed in the USPBR-BSCM, whilst in the USPBR-biological activated carbon (BAC) it was 2.04·10−3 mmolNO3−min−1g−1. The kinetic analysis of the systems showed a good fit with the Michaelis–Menten model and the kinetic parameters estimated were k1=3.37mmolL−1min−1, k2=0.58mmolL−1 for USPBR-BSCM and k1=2.50mmolL−1min−1, k2=0.27mmolL−1 for USPBR-BAC. Results indicate that SCM is a potentially low cost catalyst and effectively competes with commercial ones; USPBR-BSCM is an inexpensive and advantageous process for nitrate removal and also an effective system for denitrification.