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As the implementation of full advanced treatment with reverse osmosis (RO) grows in response to water scarcity, the effects of RO brine disposal to sewersheds on wastewater treatment will become an increasingly important consideration. Unfortunately, there is little existing literature on the actual effects of brine augmentation on wastewater flocculation and settling. In this study, RO brine from a wastewater reuse system was blended into raw wastewater. Jar tests of chemically enhanced primary treatment (CEPT) were conducted with varying brine blends and ferric chloride coagulant doses. Brine augmentation, at volumetric fractions ranging from 2.7% to 54% of the primary influent, was observed to affect CEPT performance, as removal of turbidity and total suspended solids (TSS) decreased in response to increasing brine share. Control jars with 0% brine generally had greater than 80%–90% TSS removal at the baseline coagulant dose of 12.5 mg/L, and this decreased to around 70% at 27% brine and less than 70% at 54% brine. This effect was observed to be roughly proportional to the level of brine addition, and it appears to be driven by changes to the properties of the fluid and primary particles as a result of brine addition. Adding brine both increases the density and viscosity of the fluid through higher total dissolved solids and decreases the density of the primary particles that make up the floc by contributing dissolved organics rejected by RO. CEPT performance was restored to its current baseline of around 80%–90% removal of TSS and turbidity by increasing ferric chloride dose (and thus floc density), with 17 mg/L required at 2.5% brine share and 30 mg/L required at 15% brine share. Overall, there was a roughly linear relationship between influent brine proportion and additional coagulant required to bring CEPT performance back up to brine‐free levels. The impact observed in this study suggests a topic for future research with other sources of brine and other coagulants. Article Impact Statement: By investigating primary settling affected by RO brine, this work addresses a topic of current interest that has not been widely studied. [ABSTRACT FROM AUTHOR]

Summary: Trait‐based approaches are increasingly gaining importance in community ecology, as a way of finding general rules for the mechanisms driving changes in community structure and function under the influence of perturbations. Frameworks for life‐history strategies have been successfully applied to describe changes in plant and animal communities upon disturbance. To evaluate their applicability to complex bacterial communities, we operated replicated wastewater treatment bioreactors for 35 days and subjected them to eight different disturbance frequencies of a toxic pollutant (3‐chloroaniline), starting with a mixed inoculum from a full‐scale treatment plant. Relevant ecosystem functions were tracked and microbial communities assessed through metagenomics and 16S rRNA gene sequencing. Combining a series of ordination, statistical and network analysis methods, we associated different life‐history strategies with microbial communities across the disturbance range. These strategies were evaluated using tradeoffs in community function and genotypic potential, and changes in bacterial genus composition. We further compared our findings with other ecological studies and adopted a semi‐quantitative competitors, stress‐tolerants, ruderals (CSR) classification. The framework reduces complex data sets of microbial traits, functions and taxa into ecologically meaningful components to help understand the system response to disturbance and hence represents a promising tool for managing microbial communities. [ABSTRACT FROM AUTHOR]