Investigation on the improvement of activated sludge dewaterability using different iron forms (ZVI vs. Fe(II))/peroxydisulfate combined vertical electro-dewatering processes

Abstract

The high moisture content (MC) of activated sludge dewatered by traditional vertical electro-dewatering (VED) is unable to meet the disposal requirements. Therefore, different iron forms (ZVI vs. Fe(II))/peroxydisulfate (PDS) combined VED (ZVI/PDS-VED and Fe(II)/PDS-VED) were employed to enhance the dewaterability of activated sludge. The dewatering behaviors of the two combined dewatering processes and the underlying mechanism related to the sludge characteristics were investigated and compared. Sludge was conditioned using ZVI/PDS and Fe(II)/PDS, respectively, and then dewatered by the VED in the experiment. Experimental results showed that with 0.3 g (g dry solids (DS))−1 of iron activators, 0.583 g (g DS) −1 of PDS, and 30 V of voltage, the MC of sludge after ZVI/PDS-VED and Fe(II)/PDS-VED reached the minimum values of 50.6 ± 1.2% and 32.1 ± 1.5%, respectively. ZVI/PDS and Fe(II)/PDS conditioning reduced the MC difference of sludge between the anode and the cathode during the VED, facilitating the water homogenization in the sludge cake. ZVI/PDS-VED and Fe(II)/PDS-VED could effectively reduce the bound water and the free water. Free water had high correlations with α-helix (r = 0.999, p < 0.05) and CO (r = 0.998, p < 0.05). Compared with the traditional VED and the ZVI/PDS-VED, the Fe(II)/PDS-VED had a greater improvement of sludge dewaterability due to the more efficient degradation of extracellular polymeric substances and the increase of sludge surface hydrophobicity. This study promoted the development of the new sludge deep-dewatering technology.