Characteristics of Biochemical and Fractal Structure of Activated Sludge with Thermochemical Lysis

Abstract

In this study, we investigated the structural characteristic and biochemical properties of waste-activated sludge after thermochemical pretreatment. The results show that with the increase dosage of hydrochloric acid or sodium hydroxide, the concentration of suspended solid (SS) and volatile suspended solids (VSS) declined, especially at pH 12 + H (“H” means heating). At the same time, soluble chemical oxygen demand (SCOD) all increased as well, especially at pH 12, the greatest lysis effect appeared. Protein and polysaccharide presented a similar law with SCOD. Furthermore, the specific surface area (SSA), two-dimensional fractal dimension (D 2), and three-dimensional fractal dimension (D 3) all increased to a certain degree with acid/alkali pretreatment whether or not heating. Otherwise, the median particle size (d 0.5) and zeta potential decreased leading to more compact and stable floc structure and reduction effect compared with the original sludge. In Pearson correlation analysis, SSA and SS, SSA and VSS, zeta potential and SCOD, and zeta potential and protein have significant negative correlations; D 3 and SSA have a significant correlation with SS, VSS, SCOD, and protein. Consequently, measuring the structural parameters D 3 and SSA online can reflect the effects of sludge lysis indirectly, which will be helpful to guide the practical application.