Investigation on the impact of operation and carbon fractionation on unintended nitrogen and phosphorus removal in wastewater facilities in the San Francisco Bay

In California, the San Francisco (SF) Bay has become one of the most nutrient-enriched estuary in the world due to high nutrient discharges into the watershed (Cloern and Jassby, 2012). Research shows that the SF Bay has been gradually losing its resiliency to nitrogen (N) and phosphorus (P) pollution and may suffer from severe water quality impairment in the near future (Cloern et al., 2020; Novick and Senn, 2014). While wastewater discharges are considered a major contributor of nutrient point-source pollution to the environment (Drolc and Zagorc Koncan, 2002), most municipal wastewater treatment plants (WWTPs) in the SF Bay do not have biological nutrient removal (BNR) processes. In an effort to protect water quality and meet future nutrient discharge limits, 37 WWTPs in the SF Bay have participated in nutrient reduction studies led by the Bay Area Clean Water Agency (BACWA) (Falk et al., 2018). The short-term objective of these studies is to evaluate the current treatment performance and seek opportunities for total nitrogen (TN) reduction via treatment optimization or upgrading. The long-term objective is to incorporate total phosphorus (TP) reduction into the treatment process. Among these 37 WWTPs, several of them have an anaerobic selector in the secondary treatment process. Although the original intent for this design feature was filaments control, some of these facilities have reported unintended N and P removal. This provides an interesting opportunity to evaluate the technical feasibility of optimizing and/or upgrading existing systems to achieve N and P removal. However, to the best of our knowledge, no previous study has examined the carbon fractionation and microbial community compositions in these plants and their influence on nutrients reduction rate. Therefore, the objective of this study is to quantify the impact of operational parameters (e.g., retention times) and influent characteristics (i.e., COD fractions) on N and P reduction capacities in these WWTPs. This may enable us to identify facility specific features that will provide information in the nutrients removal design decision making process. Because this is an ongoing project, only operational and analytical data is presented here. Microbial community characteristics using 16S rRNA gene analysis will be performed to determine the dominant polyphosphate-accumulating organisms (PAOs), ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) communities in these systems.