The most common source of pollution is wastewater that comes from the industrial, agricultural, and household sectors. The aim of this work is to evaluate the impact of a new innovative wastewater treatment technology on the water quality of the Leite River, Lithuania. The Leite River basin receives wastewater from the Leitgiriai agglomeration; it is then released into a channel, which is 73 m away from the river. During the implementation of the BSR Interreg project "Water emissions and their reduction in village communities in the Baltic Sea Region as pilots (VillageWater)," the ineffective Leitgiriai wastewater treatment plant (WWTP) was reconstructed in September and October of 2017. Water samples from Leite River were collected in 2010-2018 in three locations: near the Kulynai, Leitgiriai, and Sausgalviai villages in Lithuania. The results show that the wastewater treatment efficiency is statistically higher than that before the reconstruction of the WWTP. The treated wastewater (before and after reconstruction) is released from the Leitgiriai WWTP into the surface water (channel), which flows into the Leite River. The highest concentrations (according to all examined indicators) have been observed in the channel and in the Leite River 500 m after the release point before the reconstruction. All differences are statistically significant (p < 0.05). According to the 2018 values, the water quality of the Leite River did comply with the good ecological status/potential class indicators near the Leitgiriai village. After the Leitgiriai WWTP reconstruction, the wastewater treatment efficiency increased two times on average. Therefore, the Leite River water quality near Leitgiriai improved.
Keywords: Ammonium nitrogen (NH4-N); BOD7 value; Biogenic material; Chemical/nutrient; Nitrate nitrogen (NO3-N); Total nitrogen (Nt); Total phosphorus (Pt); Wastewater treatment plant.