USING LOW-COST, IN SITU MEASUREMENTS OF OPTICAL BRIGHTENERS TO IDENTIFY WASTEWATER INPUTS TO STREAMS

Untreated wastewaters can enter waterbodies through sewer overflows and leaking infrastructure, threatening human and aquatic health. Water managers need low-cost field methods to quickly identify wastewater contamination and plan mitigation strategies. Wastewater can be distinguished from natural water using a variety of biological or chemical tracers (e.g., E. coli, F, B) present in different proportions in the two endmembers. Many traditional wastewater tracers require expensive lab analyses, making them less feasible for rapid and inexpensive detection of infrastructure issues. In contrast, optical brighteners (OB), synthetic compounds present in detergents and paper products added to wastewater during water use, can be detected quickly and inexpensively with handheld field fluorometers. To determine if field OB measurements alone can be used to detect wastewater inputs onsite and identify infrastructure in need of repair, OB concentrations were compared with more traditional wastewater indicators (e.g., E. coli) in a suburban watershed (Fishpot Creek, Valley Park, Missouri). Stream samples were collected at high spatial (26 sites) and temporal (monthly) resolution with monthly samples of wastewater influent to understand patterns of wastewater inputs to the basin. For monthly stream samples collected from June 2019 to July 2020, OB values ranged from 6.9 to 31.7 RFU (arithmetic mean: 14.1 RFU), while recreational season E. coli levels ranged from 3.1 to >2419.6 CFU/100 mL (geometric mean: 254.9 CFU/100 mL). Wastewater OB values averaged at 219.8 RFU. Stream OB values positively correlated with both E. coli levels and wastewater infrastructure density, indicating that field OB measurements could be used for finding wastewater releases. Wastewater contributions for each site were calculated using OB concentrations and a two-component mixing model. While the stream outlet had median wastewater inputs of <5%, upstream wastewater loads could be as high as 18% of the flow, suggesting infrastructure failures in these areas. Some of these upstream sites have already been targeted for sewer repairs by water managers. Ongoing work will characterize additional samples and wastewater tracers (e.g., F, B, microbial source tracking) to validate OB readings and quantify wastewater inputs to the stream.