Waste activated sludge disintegration with free nitrous acid – Comprehensive analysis of the process parameters

Disintegrated Waste-Activated Sludge (NO2/FNA Method) as a Source of Carbon for Denitrification in the Mainstream of a WWTP

“…Moreover, the addition of NO 2 /FNA could not overcome a shorter retention time, as the value recorded for R7 (255 mgN-NO 2 /L, pH 5, 24 h) was lower than that observed for the reactors with only pH control (no nitrite addition, but a retention time of 48 h). Overall, the obtained results are in accordance with previous studies, which indicates that the obtained disintegrated streams are reliable [16,17].…”

“…The exposition of WAS to pH 7 (R4) and 5 (R5) without the addition of nitrite resulted in comparable increases in the SCOD concentration of 160 and 157 mgSCOD/gVS, respectively, which indicated that pH had no influence. The lowest tested NO 2 /FNA concentration (R6, 123 mgN-NO 2 /L, pH 5) after 48 h of exposure resulted in a 14% higher SCOD release than when there was only the pH control (R5), which confirms previous studies stating that the implementation of FNA increases the effectiveness of sludge disintegration [17]. The highest SCOD release (200 mgO 2 /gVS, R8) occurred when the NO 2 /FNA concentration (264 mgN-NO 2 /L, pH 5) was in the range reported in the previous study as being most beneficial [17].…”

“…The lowest tested NO 2 /FNA concentration (R6, 123 mgN-NO 2 /L, pH 5) after 48 h of exposure resulted in a 14% higher SCOD release than when there was only the pH control (R5), which confirms previous studies stating that the implementation of FNA increases the effectiveness of sludge disintegration [17]. The highest SCOD release (200 mgO 2 /gVS, R8) occurred when the NO 2 /FNA concentration (264 mgN-NO 2 /L, pH 5) was in the range reported in the previous study as being most beneficial [17]. The exposure of WAS to a concentration of 255 mgN/L for 24 h resulted in a 25% lower SCOD release when compared to 48 h of exposure to a comparable NO 2 /FNA concentration (264 mgN/L).…”

“…The characteristics of the substrates used in this study, including those of the total solids (TS), volatile solids (VS), total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), and soluble total nitrogen (TN), are presented in Table 1. The FNA disintegration tests were conducted according to the methodology presented in our previous study [17]. Two concentrations and two retention times were tested (R6-R8; Table S2).…”

“…The WAS from a full biological nutrient removal plant (operated at a high SRT) is exposed to NO 2 /FNA concentrations selected according to previous studies (123, 255, and 264 mgN-NO 2 /L; 2.8 and 5.8 mgN-HNO 2 /L, pH 5) [16,17].…”