Influent salinity conditions affect the bacterial communities of biofouling in hybrid MBBR-MBR systems

The system performance, biomass kinetics and microbial community structure in biofouling and suspended biomass of a hybrid MBBR-MBR system operating at 6 h of hydraulic retention time subjected to four different scenarios of salinity wastewater - constant 6.5 mS cm(-1), and tidal-like variable at 4.5, 6.5 and 8.5 mS cm(-1) was studied. The performance of the bioreactors in terms of organic matter removal was efficient, nevertheless only the scenario of variable 4.5 mS cm(-1) showed good nitrogen removal (59.59%). The salinity conditions exerted an effect over the kinetics of the system, with rates of substrate utilization dependent on substrate for variable salinity conditions and non-dependent for constant salinity conditions. Also, higher peak salinities lead to lower rates of substrate utilization. Massive parallel sequencing showed that Xanthomonadaceae family (2.57-33.00%) and Mycobacterium genus (4.70%) dominated biofouling under variable and constant salinity conditions, respectively. Principal component analyses showed higher community similarity between biofouling and suspended biomass under variable salinity conditions than for constant salinity. However, differences in biofouling-related OTUs were observed between attached and suspended communities by the means of effect size quantification. The composition of oligotypes of OTUs important for biofouling showed no differences between biofouling and suspended biomass at all salinity scenarios. The results suggested that biofouling process could be mainly determined by increases in relative abundance of biofouling-related OTUs in the attached biomass with respect to suspended biomass (25.76-204.63% increase). The results obtained will be of importance for future design and implementation of strategies for operation and biofouling control of salinity wastewater treatment systems.