Enhanced bio-drying effect in low-temperature: Characteristics of sludge hyperthermophilic aerobic bio-drying by inoculating with thermophilic bacteria and full-scale operation

Abstract Low-temperature environment leads to a weakened ability of sludge bio-drying to drive system evaporation and the system’s water removal capacity of aeration (ΣF·ΔP), significantly reducing water removal rate and consequent decrease of the bio-drying index. The bio-drying system maintains more microorganisms active by inoculating with thermophilic bacteria to produce heat when it reaches above 55 °C to enhance the temperature cumulation and ΣF·ΔP to remove moisture and shorten the bio-drying time rapidly. The results showed that the percentage of the thermophilic period (T ≥ 55 °C) and hyperthermophile period (T ≥ 70 °C) of the hyperthermophilic pile was 67.16% and 30.14%, respectively. In comparison, only the thermophilic period of 5.48% existed in the conventional pile. The moisture content of the hyperthermophilic pile decreased from 51.23% to 41.52% in 12 days and decreased from 50.25% to 41.35% in 21 days that in the conventional pile. Meanwhile, the hyperthermophilic pile had a faster VS consumption rate and higher bio-drying index than the conventional pile. The microbial community composition showed that the hyperthermophilic pile mainly comprised thermophilic bacteria, such as Thermopolyspora, and hyperthermophilic bacteria, such as Thermus. The full-scale operation in the plants showed that the sludge inoculated with thermophilic bacteria reached the bio-drying requirement within 12 days with a maximum temperature of 94 °C, which significantly shortened the time of bio-drying and increased the sludge treatment capacity. Graphical abstract