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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.

Both the elemental sulfur-based autotrophic denitrification (ESAD) and the biomass‑sulfur-based mixotrophic (simultaneous autotrophic and heterotrophic) denitrification processes (BSMD) are efficient methods for removing nitrate from wastewater. However, a comparative analysis of the denitrification capacity of the BSMD and ESAD in the packed bed reactors is still lacking. In this paper, corncob powder was selected as the biomass source to prepare biomass‑sulfur-based composite filter (BSCF) for the BSMD process. The denitrification performances of the three identical lab-scale bioreactors packed with varying elemental sulfur-based composite filters (ESCFs) were compared under varying loading conditions, and the optimal ESCF of the ESAD system was 2:1 by weight ratio of sulfur powder to shell powder. In pilot-scale experiments, the results showed that BSCF could decrease the sulfate productivity and gave better denitrification performance than the ESCF with the optimal nitrate removal rate (NRR) of 504 ± 12.3 mg NO

The sulfur-based autotrophic denitrification (SAD) and the solid organic carbon-based denitrification processes are both efficient techniques to remove nitrate from wastewater, and the hydrogen ions generated by the SAD process would be consumed in the heterotrophic denitrification process. Therefore, it is possible to improve the denitrification capacity when the solid organic carbon was added into a SAD reactor. In this study, corncob powder and sawdust powder were selected as solid organic carbon sources, and the sulfur-based autotrophic denitrification integrated biomass-based heterotrophic denitrification system was formed (SBD). The laboratory and field experiments showed that SBD could shorten the start-up period, decrease the sulfate productivity, and maintain a good denitrification performance when treated wastewater. According to the field experiment results, when the HRT was 1 h, the effluent total nitrogen (TN) concentration was always lower than 15 mg L−1. In addition, nitrite inhibition was observed when the concentration of nitrite in the reactors reached above 30 mg L−1. The mixture of elemental sulfur powder, shell powder, corncob powder, and sawdust powder with a mass ratio of 6:2:1:1 was the optimal filter for the SBD system, with an average nitrate reduction rate (NAR) of 420 mg NO3–N·L−1·d−1 obtained at the end of the study. During the whole operation, the major autotrophs in the SBD systems were Thermomonas, Ferritrophicum, and Thiobacillus, while the major heterotrophs were Saprospiraceae, Ferruginibacter, Dokdonella, and Simplicispira. Overall, the SBD system was a feasible and practically favorable way to remove nitrate from wastewater.

Polyacrylamide (PAM) is extensively used in various fields and can often be detected in the corresponding wastewater. Some products can be slowly degraded to an acrylamide (AM) monomer naturally, which poses a threat to human health. In this study, three reactors with different structures were contrasted to investigate the ability to treat PAM production wastewater. Reactor 1 (R1), which was divided into 11 chambers, exhibited the best performance. After the start-up period, the multistage reactor could withstand the substrate shock load well. The changes in viscosity and organic nitrogen show that most of the PAM or AM were treated in R1. The chemical oxygen demand and NH4-N removal efficiency reached 96.4% and 97.2%, respectively. Meanwhile, simultaneous nitrification and denitrification was occurred in R1 and excess sludge production was much lower than the control reactors. Microbial analysis suggests that the independent chambers can form a unique bacterial community. This system could also promote the growth of anaerobic ammonium oxidation (anammox), which increased the total nitrogen removal efficiency to 80%.