Main Influencing Factors and Strengthening of Anaerobic Transformation of Excess Sludge in China

Abstract

The anaerobic conversion efficiency of excess sludge in China is significantly lower than that in developed countries. Sludge characteristics are important influencing factors in the anaerobic degradability of sludge. The typical differences between excess sludge in China and in developed countries are mainly reflected in three aspects:long sludge age, high content of micro-sized grits, and high content of metal ions. Therefore, the effects of sludge age, micro-sized grits (represented by silica particles), and metal ions on the anaerobic digestion (AD) of excess sludge were studied systematically. Quantified comparison and targeted enhancement research were also carried out. The results showed that the negative effect of grit in the influent on VS reduction of sludge during AD was not obvious, while sludge age and metal ions were the main inhibitory factors. In addition, the inhibition level of sludge age was significantly higher than that of metal ions (P<0.05). With an increase in sludge age, the inhibition level of metal ions showed a further strengthening trend. Therefore, it could be concluded that long sludge age was the most important factor limiting the degradability of excess sludge. Moreover, with thermal hydrolysis pretreatment (160℃, 0.55 MPa, 30 min), the cumulative methane yield and VS reduction of sludge with long sludge age (40 d) almost increased to the values of sludge with a sludge age of 5 d. That is, thermal hydrolysis pretreatment has the potential to break through the bottleneck of degradability of sludge caused by long sludge age.