Effects of 1-hydroxyethane-(1,1-bisphosphonic acid) on heterotrophic denitrification performance: Impact of denitrifying microbial communities variation

Abstract

Microbial denitrification can be impaired by the co-existence of organic chelating pollutants; however, information on the potential impacts of nitrate reduction efficiency in response to such pollutants is limited. Herein, 1-hydroxyethane-(1,1-bisphosphonic acid) (HEDP) was selected as a typical pollutant to investigate effects on biological denitrification in an expanded granular sludge blanket (EGSB) reactor. Results showed that 99.5%–99.9% of nitrate was removed after sludge exposure to HEDP (1.5–30 mM). This was due to the protection of microbial cells by an increase in the secretion of extra polymeric substances (EPS) in response to HEDP stress. However, nitrate removal efficiency decreased to 55% with the accumulation of 470 mg L-1 nitrite under 40 mM HEDP. This was due to the dissolution of EPSs, as evidenced by the appearance of humic acid-like substances in the three-dimensional excitation-emission matrix. Furthermore, the removal of 48% of HEDP after exposure of sludge to 5.5 mM HEDP and accumulation of PO43--P in the presence of 8.5–22.5 mM HEDP indicated the adsorption and biodegradation of HEDP in the sludge. Besides, the abundance of genus Desulfurispirillum remained dominant with HEDP concentration. Metagenomic assembly of genomes revealed that the denitrification under HEDP stress was accompanied by an increase in the abundance of Halomonas, containing functional genes (R = 0.97–0.98, P < 0.05). Moreover, the qRT-PCR results demonstrated the up-regulation the narG, nirK, and nosZ genes with HEDP concentration, thus suggesting their major role in the reduction of nitrate.