Moisture evaporation effect on pore structure and microbial distribution during sludge biodrying

Abstract

Biodrying of dewatered sludge is an eco-friendly and efficient technology to decrease the sludge moisture content (MC) by metabolic heat generated from sludge organic matter degradation. By analyzing the water states and visualizing the sludge pore structure during the biodrying process, it was found that the bound water accounted for 96.5–97.9% of the sludge water and interstitial water was only 2.0–3.5%. The microscopic and dispersed sludge pores were transformed into larger and linked ones by the transformation of bound water into interstitial water and the subsequent evaporation. As a result, the depth of live bacteria distribution thickened, reaching 0–180 µm, 0–330 µm, and 0–350 µm during the temperature ramp-up to 45.6 °C, the peak temperature of 70.7 °C, and the cool-down to 45.6 °C, respectively. Briefly, as moisture evaporated, the pore structure of the sludge expanded and the microbial distribution deepened. Moreover, the phylum of anaerobic bacteria was drastically decreased.