Abstract
The emergence and spread of antibiotics resistance in wastewater treatment systems have been pointed as a major environmental health problem. Nevertheless, research about adaptation and antibiotics resistance gain in wastewater treatment systems subjected to antibiotics has not been successfully developed considering bioreactor performance, microbial community dynamics and microbial activity dynamics at the same time. To observe this in autotrophic nitrogen removal systems, a partial-nitritation biofilter was subjected to a continuous loading of antibiotics mix of azithromycin, norfloxacin, trimethoprim, and sulfamethoxazole. The effect of the antibiotics mix over the performance, bacterial communities and bacterial activity in the system was evaluated. The addition of antibiotics caused a drop of ammonium oxidation efficiency (from 50 to 5%) and of biomass concentration in the bioreactor, which was coupled to the loss of ammonium oxidizing bacteria Nitrosomonas in the bacterial community from 40 to 3%. Biomass in the partial nitritation biofilter experienced a sharp decrease of about 80% due to antibiotics loading, but the biomass adapted and experienced a growth by stabilization under antibiotics feeding. During the experiment several bacterial genera appeared, such as Alcaligenes, Paracoccus, and Acidovorax, clearly dominating the bacterial community with >20% relative abundance. The system reached around 30% ammonium oxidation efficiency after adaptation to antibiotics, but no effluent nitrite was found, suggesting that dominant antibiotics-resistant phylotypes could be involved in nitrification–denitrification metabolisms. The activity of ammonium oxidation measured as amoA and hao gene expression dropped a 98.25% and 99.21%, respectively, comparing the system before and after the addition of antibiotics. On the other hand, denitrifying activity increased as observed by higher expression of nir and nos genes (83.14% and 252.54%, respectively). In addition, heterotrophic nitrification cyt c-551 was active only after the antibiotics addition. Resistance to the antibiotics was presumably given by ermF, carA and msrA for azithromycin, mutations of the gyrA and grlB for norfloxacin, and by sul123 genes for sulfamethoxazole. Joined physicochemical and microbiological characterization of the system were used to investigate the effect of the antibiotics over the bioprocess. Despite the antibiotics resistance, activity of Bacteria decreased while the activity of Archaea and Fungi increased.
Highlights
Several human and animal wastes, such as pharmaceutical industry effluents or livestock wastes, are treated through anaerobic digestion processes
It is possible that the addition of antibiotics triggered denitrification metabolisms from nitrite when the antibiotics or other organic matter within the biofilm were used as organic matter
Metatranscriptomics analysis demonstrated that dominant bacterial genera after the antibiotics addition expressed proteins that develop heterotrophic nitrification and aerobic denitrification metabolism, which contrasted with the high activity of ammonium oxidation found in the biofilter after the antibiotics addition
Summary
Several human and animal wastes, such as pharmaceutical industry effluents or livestock wastes, are treated through anaerobic digestion processes. The anaerobic digestion systems have shown poor antibiotics removal treatment in the range of 1–10 mg L−1 concentrations (Massé et al, 2014; Wang et al, 2015). In the last 10 years, autotrophic nitrogen removal technologies have been developed for an efficient, cheap bioremediation of this waste (van der Star et al, 2007). These technologies rely on the unique metabolism of “Candidatus Brocadiales” bacteria, named as anaerobic ammonium oxidation, in which ammonium is oxidized using nitrite as terminal electron acceptor, yielding molecular nitrogen as a result (van Teeseling et al, 2016). In order to develop and control separately the partial-nitritation and anaerobic ammonium oxidation, the partial-nitritation/anammox technology has been developed
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