Characterization of microbial communities associated with advanced wastewater treatment for water reuse

In many regions of the world, conventional water resources are not sufficient to meet the needs due to growing populations and progressive land use. Growing scarcity of potable water supplies and a decrease in water quality as shown by increased eutrophication related to agriculture are important issues facing many aired regions globally. Accordingly, projects that integrate water reuse via the engineered treatment of wastewater have become more desirable. Reuse of municipal wastewater safely, reliably, and economically expands the water supply for communities. Therefore, planned water reuse is being implemented more than in any time in our history to help meet the needs of societies. While inherent reuse is a natural part of the earth's water cycle, human intervention via new technologies, engineering, and knowledge speeds up this process, making it possible to produce highly purified water directly from wastewater for potable and agricultural uses.

One option for advanced wastewater treatment is to employ treatment technologies that can include some of the following technologies: microfiltration (MF), reverse osmosis (RO), granular activated carbon (GAC), ozone treatment (O₃), biological aerated filter (BAF), ultraviolet light advanced oxidation process (UV/AOP) for both indirect potable reuse (IPR) and direct potable reuse (DPR). Despite the rapid growth of these technologies in the water reclamation industry, understanding of the microbial communities related to enhanced water is currently limited and challenging. To date, a great effort has been made to understand the composition of types microorganisms in treated wastewater to assess treatment performance based on the total number of microorganisms removed. However, identification and understanding of specific pathogens and indicator bacteria is limited and characterization of the microbial communities present at various levels of advanced water treatment remains largely unknown. Lack of rapid, accurate, and sensitive methods is one important reason for this important knowledge gap. Polymerase chain reaction (PCR) based methods are rapid but target a limited number of known organisms. Next generation sequencing (NGS) combined with bioinformatics is a multidirectional technique that offers a powerful, high throughput, culture-independent analysis of the microbial communities and their attenuation through advanced water treatment. NGS and bioinformatics were used to identify microbial communities comprised of fungi, protozoa, bacteria, viruses, and antibiotic resistance genes (ARGs) in water and biofilm matrices retrieved from various unit processes in an advanced treatment train. As expected, diverse communities of fungi, bacteria, viruses, and antibiotic resistance genes (ARGs) were temporally monitored and identified in the influent water with stepwise reduction in species diversity and richness as advanced treatment progressed. Microbial load and species diversity within all identified taxonomic levels, including fungi, bacteria and viruses, decreased at each stage of advanced treatment. Following ozone, GAC, and RO advanced treatment, most of the viral DNA identified in the water and biofilm samples was identified as bacteriophage and not human viruses. Specific species of protozoa most likely related to ozone-GAC treatment were also identified but were removed post-ozone, suggesting that specific microbial species and genes related to ozone-GAC advanced treatment can be identified. It is concluded that NGS combined with bioinformatics is an innovative approach that is multidirectional community analysis technique for accurate detection and characterization of microbial communities in influent water and biofilms related to advanced wastewater treatment. This permits engineers to understand precisely the performance of each unit process so that they can select the appropriate configurations that will provide the necessary water quality at the appropriate cost. This approach can be applied to various water matrices to address the safety of reuse water of both IPR and DPR.