Sludge bio-drying is an approach for biomass energy utilization, in which sludge is dried by
means of the heat generated by aerobic degradation of its organic substances. The study
aimed at investigating the interactive influence of air-flow rate and turning frequency on
water removal and biomass energy utilization. Results showed that a higher air-flow rate
(0.0909 m3 h1 kg1) led to lower temperature than did the lower one (0.0455 m3 h1 kg1) by
17.0% and 13.7% under turning per two days and four days. With the higher air-flow rate
and lower turning frequency, temperature cumulation was almost similar to that with the
lower air-flow rate and higher turning frequency. The doubled air-flow rate improved the
total water removal ratio by 2.86% (19.5 g kg1 initial water) and 11.5% (75.0 g kg1 initial
water) with turning per two days and four days respectively, indicating that there was no
remarkable advantage for water removal with high air-flow rate, especially with high
turning frequency. The heat used for evaporation was 60.6e72.6% of the total heat
consumption (34,400e45,400 kJ). The higher air-flow rate enhanced volatile solids (VS)
degradation thus improving heat generation by 1.95% (800 kJ) and 8.96% (3200 kJ) with
turning per two days and four days. With the higher air-flow rate, heat consumed by
sensible heat of inlet air and heat utilization efficiency for evaporation was higher than the
lower one. With the higher turning frequency, sensible heat of materials and heat
consumed by turning was higher than lower one.