Accumulation of TiO2 nanoparticles in the anammox bioreactor: Their effects on treatment performance and microbial dynamics

Nanotechnology applications have significant beneficial impacts on society however, the possible adverse effects of nanoparticles (NPs) lead to great concern from the environmental perspective because of their overproduction, overconsumption, and unintentional release to the wastewater. The main goal of the study was to investigate the long-term effects of titanium dioxide (TiO2) NPs on the Anammox process, considering the accumulation of NPs on biological systems over time, in terms of nitrogen treatment capacity, extracellular polymeric substances content, and microbial dynamics. Anammox population was found to be vulnerable to the elevated TiO2 NPs concentration. Persistent deterioration on nitrogen removal was observed at 200 mg/L NPs dose upon following 585 days of exposure. NH4+-N and NO2--N removal efficiencies decreased from 97.65 % +/- 1.63 to 15.84 % and 98.7 % +/- 1.84 to 8.69 %, respectively. At the inhibition dose, total Ti content was found to be 1.9 g/L Ti and 65.24 % of which was associated to the biomass. It reveals that, most of the accumulated Ti within the bioreactor deposited on the microorganisms, which may decrease substrate utilization. During the exposure period, relative abundance of Candidatus Brocadiaceae was almost stable up to 200 mg/L NPs dose and at this dose, its abundance decreased by 9.75 %.