A tremendous input of ammonium and rare earth elements (REEs) has entered the surroundings on account of the discharge and leak of leaching agents during rare earth in-suit leaching mining, which has threatened various organisms. Anammox has the potential to release nitrogen contamination, but the potential impacts of REEs on anammox bacteria remain unclear. In this study, La (III) was chosen as a case to explore the long-term impacts on anammox granular sludge. The 5 mg L−1 La (III) which was examined hardly affected the anammox granulates because of the defense of extracellular polymeric substances. The high La concentrations (10–50 mg L−1) caused intercellular accumulation and the significant inhibition of nitrogen removal performance and dehydrogenase activity, especially a decrease in the relative abundance of Ca. Kuenenia. Moreover, it also induced patently oxidative damage and affected cell membrane integrity. Notably, extracellular polymeric substances have a limited defense capability; neither La3+ nor Ca2+/Mg2+ efflux-related genes aggravated the intracellular accumulation of La.
The tremendous input of ammonium and rare earth element (REE) ions released by the enormous consumption of (NH4)2SO4 in in situ leaching for ion-adsorption RE mining caused serious ground and surface water contamination. Anaerobic ammonium oxidation (anammox) was a sustainable in situ technology that can reduce this nitrogen pollution. In this research, in situ, semi in situ, and ex situ method of inoculation that included low-concentration (0.02 mg·L−1) and high-concentration (0.10 mg·L−1) lanthanum (La)(III) were adopted to explore effective start-up strategies for starting up anammox reactors seeded with activated sludge and anammox sludge. The reactors were refrigerated for 30 days at 4 °C to investigate the effects of La(III) during a period of low-temperature. The results showed that the in situ and semi in situ enrichment strategies with the addition of La(III) at a low-concentration La(III) addition (0.02 mg·L−1) reduced the length of time required to reactivate the sludge until it reached a state of stable anammox activity and high nitrogen removal efficiency by 60–71 days. The addition of La(III) promoted the formation of sludge floc with a compact structure that enabled it to resist the adverse effects of low temperature and so to maintain a high abundance of AnAOB and microbacterial community diversity of sludge during refrigeration period. The addition of La(III) at a high concentration caused the cellular percentage of AnAOB to decrease from 54.60 ± 6.19% to 17.35 ± 6.69% during the enrichment and reduced nitrogen removal efficiency to an unrecoverable level to post-refrigeration.
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