In this study, the effects of free nitrous acid (FNA) pre-treatment on the rheological properties of digested sludge were investigated at a pilot-scale, along with the improvement in volatile solids (VS) destruction and biogas production. Two pilot-scale anaerobic sludge digesters were operated for one year, one receiving thickened waste activated sludge (TWAS) without pre-treatment (control) and one receiving TWAS pre-treated for 24 h at an FNA concentration of 4.9–6.1 mgN/L (nitrite = 250 mgN/L, pH = 5.0, T = 22–30 °C). The results confirmed the enhancing effect of FNA pre-treatment on methane production (37 ± 1%), consistent with previous laboratory studies. Equally importantly, FNA pre-treatment substantially reduced the shear viscosity of TWAS by 51 ± 8% at 100 s⁻¹ and 49 ± 7% at 250 s⁻¹, likely due to the solubilization of the TWAS (11.1 ± 0.8%). Similarly, FNA pre-treatment also reduced these viscosity parameters of the digested sludge by 80 ± 4% and 78 ± 4%, respectively, caused by both enhanced VS destruction and disintegration of the digested sludge. The dewaterability of digested sludge, assessed by dewatered solids content, capillary suction time and specific resistance to filtration, was not improved by FNA pre-treatment. The polymer requirement for dewatering was reduced by 24 ± 0.6% due to the lower solids concentration in the digested sludge achieved with FNA pre-treatment. The changes to sludge rheological properties revealed in this study further enhances the business case for the FNA pre-treatment technology.

在这项研究中，在试验规模上研究了游离亚硝酸（FNA）预处理对消化污泥流变特性的影响，并改善了挥发性固体（VS）的破坏和沼气的产生。两个中试规模的厌氧污泥消化池运行了一年，其中一个未经处理（对照）的增稠废物活性污泥（TWAS），一个接受了FNA浓度为4.9–6.1 mgN / L的TWAS预处理的24小时（亚硝酸盐= 250 mgN / L，pH = 5.0，T = 22–30°C）。结果证实了FNA预处理对甲烷产生的增强作用（37±1％），与以前的实验室研究一致。同样重要的是，FNA预处理可使TWAS的剪切粘度在100 s ^-1时显着降低51±8％，在250 s ^-1时显着降低49±7％，可能是由于TWAS（11.1±0.8％）的溶解。类似地，FNA预处理还可以将消化污泥的这些粘度参数分别降低80±4％和78±4％，这是由于VS破坏增强和消化污泥的分解所致。通过脱水固体含量，毛细抽吸时间和特定的过滤阻力评估的消化污泥的脱水性没有通过FNA预处理得到改善。脱水所需的聚合物量减少了24±0.6％，这是因为通过FNA预处理可以降低消化污泥中的固体含量。这项研究揭示的污泥流变特性的变化进一步增强了FNA预处理技术的商业案例。