Impact of Depuration Plants on Nutrient Levels in the North Adriatic Sea

Abstract

Macronutrients (nitrogen—N; phosphorus—P; silicon—Si) play a crucial role in ocean surface waters stimulating the planktonic primary production; in fact, their concentrations are fundamental for the evaluation of the trophic status of the water body and eutrophication phenomena. Loads of nutrients into the sea are mainly represented by river runoff and depuration plant outflows. For this purpose, in the framework of the AdSWiM project, “Managed use of treated urban wastewater for the quality of the Adriatic Sea” levels of N-NO3, N-NO2, N-NH4, Si-Si(OH)4, P-PO4 (dissolved inorganic phosphorus—DIP) and total dissolved phosphorus (TDP) were determined colorimetrically at two sites in the Gulf of Trieste: Lignano Sabbiadoro and San Giorgio di Nogaro. For each site, during the bathing seasons of 2019 and 2020, a sample from the depuration plant (DP) outflow and another one in the bottom seawater near the discharging pipelines were collected. Results showed a strong dilution effect on nutrient levels passing from DPs to the sea, from one to three orders of magnitude and a low and not harmful concentration in seawater. The outflow composition of the two DPs showed that the main fraction of dissolved inorganic nitrogen (DIN) was represented by N-NO3 for Lignano, while in San Giorgio the major contribution came from N-NH4. Concerning phosphorus, Lignano showed a higher content (about 3 times) of P levels than San Giorgio, but a similar percentage composition, DIP:DOP (77:23), compared to the seawater site one DIP:DOP (2:98). Despite the difference between the DPs, no substantial differences were found in the sea sites, demonstrating the negligible effect of the DP outflows in the nutrient levels in the study area.

The Interreg Project AdSWiM: Managed Use of Treated Wastewater for the Quality of the Adriatic Sea

“…PTE concentration did not significantly differ between wastewater and seawater samples, although other parameters (e.g., nutrient concentration and microbial indicators) need to be investigated to identify possible synergistic effects. Some differences were observed in the composition of the WWTP effluents between Italian and Croatian plants because of the different source of waters converging to the depuration plants [41][42][43].…”

“…In this study, a plastic electrode based on graphite, a PVC binder [49,50], and an in-house synthesized organic derivative of molybdate anion (MOP) [51] was prepared as the first approach to develop an electrochemical DIP sensor (Figure 4A). Prior to electrode preparation, surface waters of the northern Adriatic Sea were characterized, and nutrient concentrations were measured during a whole season using classical analytical techniques [41,42]. After determination of the baseline nutrient content, the electrode was prepared and optimized for its use as a phosphate sensor.…”

Dissolved Potentially Toxic Elements (PTEs) in Relation to Depuration Plant Outflows in Adriatic Coastal Waters: A Two Year Monitoring Survey

“…In particular, the Adriatic Sea is considered further vulnerable to contamination due to its semi-enclosed morphological structure, low bathymetry, and high river inputs. Moreover, several studies have reported that the sea zones close to the wastewater outfall pipelines are particularly sensitive and vulnerable to pollution such as high concentrations of nutrients, fecal indicator bacteria (FIB), and pharmaceutically active compounds [20][21][22][23][24][25].…”