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

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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.

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Full scale performance of the aerobic granular sludge process for sewage treatment.

Tila Pronk, M K de Kreuk, Anique B. H. de Bruin … (2015)

Recently, aerobic granular sludge technology has been scaled-up and implemented for industrial and municipal wastewater treatment under the trade name Nereda(®). With full-scale references for industrial treatment application since 2006 and domestic sewage since 2009 only limited operating data have been presented in scientific literature so far. In this study performance, granulation and design considerations of an aerobic granular sludge plant on domestic wastewater at the WWTP Garmerwolde, the Netherlands were analysed. After a start-up period of approximately 5 months, a robust and stable granule bed (>8 g L(-1)) was formed and could be maintained thereafter, with a sludge volume index after 5 min settling of 45 mL g(-1). The granular sludge consisted for more than 80% of granules larger than 0.2 mm and more than 60% larger than 1 mm. Effluent requirements (7 mg N L(-1) and 1 mg P L(-1)) were easily met during summer and winter. Maximum volumetric conversion rates for nitrogen and phosphorus were respectively 0.17 and 0.24 kg (m(3) d)(-1). The energy usage was 13.9 kWh (PE150·year)(-1) which is 58-63 % lower than the average conventional activated sludge treatment plant in the Netherlands. Finally, this study demonstrated that aerobic granular sludge technology can effectively be implemented for the treatment of domestic wastewater.