Temperature Phased Anaerobic Digestion at the Intermediate Zone of 45 °C: Performances, Stability and Pathogen Deactivation

Temperature phased anaerobic digestion (TPAD) systems with conventional sequences (first stage of 55 degrees C and second stage of 35.) have been widely studied. However, very limited studies were available on TPAD system with the first stage operated at the intermediate zone of 45 degrees C, mainly due to the notion that limited microbial activity occurs within this zone. The objective of this research was to evaluate the performance, stability and the capability of 45 degrees C TPAD in producing class A biosolids, in comparison to a conventional TPAD. Four combinations of TPAD systems were studied, 45 degrees C TPAD 2.5/ 10 (1st stage solids retention time (SRT) 2.5 days/2nd stage SRT 10 days), 45 degrees C TPAD 7.5/10, 55. TPAD 2.5/10 and 55. TPAD 7.5/10. Among all, 45. TPAD 7.5/10 was found to have the best performances, attributed to its high volatile solids (VS) destruction (58%), minimal acetate accumulation (127 mg/L), high methane yield (0.58 m(3) CH4/kg VS removed), high COD destruction solid COD (sCOD; 74% and total COD (tCOD) 54%) and minimal free NH3 content (67.5 mg/L). As for stability, stable pH distribution, high alkalinity content and low VFA to alkalinity ratio, indicated a well-buffered system. Additionally, the system had also able to produce class A biosolids. Therefore, proved that TPAD system operated at the intermediate zone of 45 degrees C can perform better than the conventional TPAD, hence, highlighting its economic advantage.

Automated summary

The study evaluated the performance, stability, and capability of a 45 degrees C TPAD system in producing class A biosolids compared to a conventional TPAD system. The 45 degrees C TPAD 7.5/10 combination showed the best performance with high VS destruction rate, minimal acetate accumulation, and high methane yield, indicating its economic advantage over the conventional TPAD system.