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Anaerobic co-digestion offers a promising approach to enhancing biogas production from surplus by-products of wastewater treatment plants (WWTPs) and agricultural waste while reducing environmental negative impact. This study investigated the co-digestion of anaerobic thickened sewage sludge (ATSS) and rice straw (RS) under mesophilic conditions (35 ± 1 °C). In phase 1 of the experiment, lab-scale reactors with varying MRs of RS (0 %, 4 %, 8 %, and 16 % based on sludge weight) were employed to determine the optimal MR for maximizing biogas quantity and methane content. Phase 2 examined the impact of mechanical mixing (MM) on biogas production, pathogen and trace element reduction, and the calorific value (CV) of the co-digested mixture compared to the digested thickened sludge (DTS) and RS individually to assess the potential energy of co-digestion. Results revealed that the 8 % MR yielded the highest biogas volume, approximately 2.5 times that of the DTS alone, with methane and carbon dioxide contents within the typical ranges. MM in phase 2 further increased biogas volume by 2.8 times compared to DTS. The CV of the co-digested mixture was 24,937 kJ/kg and 21,929 kJ/kg for the DTS. Pathogens were effectively eliminated, and trace elements remained below the permissible limits. The 8 % MR with MM was identified as the optimal MR that produces the highest biogas quantity before reaching the turning point. Moreover, co-digestion at this MR enhanced the CV of ATSS by 14 %.

The purpose of this study is to investigate the asphalt's surface free energy (SFE) at different mixing ratios (MR) between aged and fresh asphalt using molecular dynamics simulation and contact angle test. According to representative molecular models of fresh and aged asphalt, the asphalt models at different MRs were established based on SARA test results. Then, the models were validated using thermodynamic properties, such as density and cohesive energy density. Subsequently, the SFE of asphalts under different MRs was investigated and compared with the results of contact angle tests. Finally, the change mechanisms of the asphalt's SFE was studied based on the radial distribution function and concentration distribution of asphalt components. The results indicate that the SFE obtained by van der Waals (vdW) surface simulation and by contact angle test both exhibit similar changing trends with increasing MR. They also demonstrate a strong correlation with the colloidal index and resin/asphaltene. The aging effect induces a transition in asphalt from the sol-type and flocculent-type structures to the gel-type structure. The relative component concentration distribution shows that the SFE of asphalt is large when the resin is close to the vacuum surface. This study establishes a consistent relationship between the molecular-level SFE and the macroscopic SFE of asphalt, and reveals the mechanism of asphalt SFE change based on the asphalt component content and distribution. These findings contribute to the understanding of the cohesive properties of asphalt mixtures during the mixing of aged and fresh asphalt. • Five molecular models of fresh-aged asphalt at different mixing ratios are created. • The mechanism of asphalt surface free energy variation with mixing ratios is revealed. • There is a good correlation between SFE of asphalt and colloidal index as well as resin/asphalt. • There is a strong correlation between MD simulations and contact angle test tests. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion offers a promising approach to enhancing biogas production from surplus by-products of wastewater treatment plants (WWTPs) and agricultural waste while reducing environmental negative impact. This study investigated the co-digestion of anaerobic thickened sewage sludge (ATSS) and rice straw (RS) under mesophilic conditions (35 ± 1 °C). In phase 1 of the experiment, lab-scale reactors with varying MRs of RS (0 %, 4 %, 8 %, and 16 % based on sludge weight) were employed to determine the optimal MR for maximizing biogas quantity and methane content. Phase 2 examined the impact of mechanical mixing (MM) on biogas production, pathogen and trace element reduction, and the calorific value (CV) of the co-digested mixture compared to the digested thickened sludge (DTS) and RS individually to assess the potential energy of co-digestion. Results revealed that the 8 % MR yielded the highest biogas volume, approximately 2.5 times that of the DTS alone, with methane and carbon dioxide contents within the typical ranges. MM in phase 2 further increased biogas volume by 2.8 times compared to DTS. The CV of the co-digested mixture was 24,937 kJ/kg and 21,929 kJ/kg for the DTS. Pathogens were effectively eliminated, and trace elements remained below the permissible limits. The 8 % MR with MM was identified as the optimal MR that produces the highest biogas quantity before reaching the turning point. Moreover, co-digestion at this MR enhanced the CV of ATSS by 14 %. [ABSTRACT FROM AUTHOR]