Flue gas Pb0 removal from sludge incineration through biological lead oxidation coupled denitrification

Abstract

Lead (Pb0) in flue gas from sludge incineration can seriously harm human health especially lead poisoning and blood lead increase. Microbial lead (Pb0) oxidation associated with nitrate reduction might be poorly understood in eliminating Pb0 pollution in flue gas from sludge incineration. In this study, a denitrifying bioreactor (DBR) was investigated for Pb0 removal from flue gas. Pb0 removal efficiency achieved 87% in 60-day operation. Dominated Pb0-oxidating-denitrifying bacteria such as Azoarcus, Thauera and Stappia could realize bacterial Pb0 oxidation and nitrate reduction through the regulation of lead oxidation genes (katE, K07217, aoxA, aoxB, moxA) and denitrification gene (napAB and narHGI). The up-regulation of amino acids and polysaccharide biosynthesis, transporters and phosphatase-relevant genes provided evidence of their involvement in the transformation of lead. The bio-oxidation of Pb0 adsorbed on EPS was coupled with denitrification, where Pb0 and nitrate served as the electron donor and terminal electron acceptor, respectively, and thereby formed redox between Pb0 and nitrate. Pb2+ oxidized from Pb0 was intracellularly accumulated, and complexed with EPS by binding with –OH and P = O. Pb0-containing flue gas was bio-stabilized in the form of Pb5(PO4)3Cl and protein/polysaccharide-Pb2+. Pb0 in flue gas was adsorbed by denitrifying bacteria, oxidized to Pb2+ coupling with denitrification, and biostabilized to achieve the removal of Pb0 from flue gas. These results show that the DBR advanced treatmenttechnology is achievable and provide new possibilities for applying the denitrifying bioreactor to remove heavy metals from flue gas.