Downstream evolution of wastewater treatment plant nutrient signals using high‐temporal monitoring

Abstract

Wastewater treatment plants are major point-sources of nutrients to streams globally, but the impact on receiving streams is not always clear. Previous research has shown mixed responses in receiving streams, with some showing no net retention through instream processing for large distances below plants and some showing high rates of processing and retention. This study focuses on Sandy Run, a small, suburban stream in Montgomery County, PA, that receives effluent from two plants, where effluent makes up an estimated 50% of outlet discharge at baseflow. Two sites were monitored in late summer baseflow using high-temporal loggers to evaluate nitrate and phosphate retention with distance below the plants. Effluent quantity was monitored immediately below the effluent outfalls using specific conductivity as a conservative signal of solute fluctuations throughout the day. A site 1 km downstream showed diel nitrate changes, but despite moderate gross primary productivity and ecosystem respiration rates, there was little net retention of nutrients and the diel nitrate signal can be attributed to advection and dispersion of variable upstream effluent. A site 5.4 km below the plant showed a diel nitrate signal as well, but baseflow daily hysteresis plots of nitrate and specific conductivity showed the effluent and nitrate peaks did not coincide. Instead, the effluent input signal was seen overnight, but there was in-stream removal and release processes during the day. Over the distance to this site, the stream was metabolizing some of the high nutrient loads, although gross primary productivity and ecosystem respiration rates were lower. It is important to understand subdaily changes in nutrient processing to fully quantify the impacts of effluent on small streams at different scales. Furthermore, looking at the diel signal without considering conservative transport would overestimate in-stream processing. K E Y W O R D Sdaily hysteresis, ecosystem respiration (ER), gross primary productivity (GPP), high-temporal sensor, in-stream metabolism, nitrogen cycling, urban stream, wastewater treatment plant

Contrasting Raz–Rru stream metabolism and nutrient uptake downstream of urban wastewater effluent sites

“…S1A). Similar high nutrient loads and longitudinal changes in nutrients have been observed in the downstream reaches below 2 of the other WWTPs in the watershed (Ledford and Toran 2020). In contrast, neither nitrate nor phosphorus show a decrease in concentration downstream of Ambler WWTP, which is ∼10 km downstream Figure 1.…”

Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring

“…Hence, WWTPs may create nodes of high metabolic variability in the network that turn on during critical biogeochemical windows of opportunity ( sensu [ 54 ]; compare upstream-downstream variances in Fig 4 ). Sub-daily changes in effluent quantity and quality combined with hydrologic and biogeochemical diel cycles create highly complex systems that are difficult to piece apart [ 33 , 47 ].…”

“…For example, the first site downstream of all four WWTPs (D-All-16.5) sustained a relatively high summer GPP but was further than any other downstream site from an effluent source. Previous work suggests that the effluent signature arriving at this site from the WWTPs on Sandy Run has already been attenuated [ 47 ]. However, there is a distinct shift in bed material between Sandy Run (sand) and D-All-16.5 (gravel, cobbles, and boulders).…”

“…When the Ambler WWTP discharges, concentrations of NO 3 –N increase by 1–5 mg L -1 . Along Sandy Run, NO 3 –N is attenuated over the 5.5 km downstream of the upper plant, with the lower plant adding minimal load to the stream [ 47 ]. At the confluence with Sandy Run, NO 3 –N is similar in both reaches so there is little or no change in concentration, but total dissolved phosphorous (TDP) increases by 0.1–0.2 mg L -1 .…”

Ion Selective Amperometric Biosensors for Environmental Analysis of Nitrate, Nitrite and Sulfate

“…Due to enzyme degradation or leaching, NR based biosensors often have short shelf lifetimes varying from 1-2 [21] to 7 days by dry storage [24], but appropriate immobilization in polymers such as pyrrol-pyridium and PVA may extend shelf lifetime to 3 weeks [25] and even 1 month [28]. It was not possible to find reports of extensive use of NR based biosensors for environmental monitoring, indicating that their measuring characteristics fall short of potentiometric ionophore-based electrodes (that have widespread applications in waste water treatment [29]), UV-absorption based optical sensors from for example Sea-Bird Scientific (that can be used in transparent freshwater and seawater environments [30]) and bacteria-based biosensors (see below).…”