Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater.

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 109 and 3.2 × 108 copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

Reduction of antibiotic resistome and integron-integrase genes in laboratory-scale photobioreactors treating municipal wastewater.

Wastewater treatment systems receiving municipal wastewater are major dissemination nodes of antibiotic resistance genes (ARGs) between anthropogenic and natural environments. This study examined the fate of antibiotic resistome and class 1-3 integron-integrase genes in photobioreactors that were treating municipal wastewater diluted (70/30) with lake or tap water for the algal biomass production. A combined approach of metagenomic and quantitative (qPCR) analysis was undertaken. Municipal wastewater treatment in the photobioreactors led to reduced antibiotic resistome proportion, number of ARG subtypes, and abundances of individual ARGs in the bacterial community. The ARGs and intI1 gene abundances and relative abundances in the discharges of the photobioreactors were either comparable or lower than the respective values in the effluents of conventional wastewater treatment plants. The reduction of the resistome proved to be strongly related to the changes in the bacterial community composition during the wastewater treatment process as it was responding to rising pH levels caused by intense algal growth. Several bacterial genera (e.g., Azoarcus, Dechloromonas, and Sulfuritalea) were recognized as potential hosts of multiple antibiotic resistance types. Although the lake water contributed a diverse and abundant resistome and intI genes profile to the treatment system, it proved to be considerably more beneficial for wastewater dilution than the tap water. The diversity (number of detected resistance types and subtypes) and proportion of the antibiotic resistome, the amount of plasmid borne integron-integrase gene reads, and the abundances and relative abundances of the majority of quantified ARGs (aadA, sul1, tetQ, tetW, qnrS, ermB, blaOXA2-type) and intI1 gene as well as the amount of multi-resistance determinants were significantly lower in the discharges of photobioreactors where lake water was used to dilute wastewater.