Abstract
BACKGROUND
The present study compared the performance and capability of thermophilic–mesophilic, temperature‐phased anaerobic digestion (TPAD) of wastewater sludge at 45 and 55 °C in terms of rate of hydrolysis and methanogenesis at two point interval times – December and January – with operational conditions kept constant (total solid content 6.5%, solids retention time 12.5 days).
RESULTS
The reduction of volatile solids (VS) was 77% at 45 °C TPAD‐1 and 72% at 55 °C TPAD‐II. The accumulation of ammonia and volatile fatty acids (VFAs; propionic acid) were observed to be below the inhibitory range (>3000 mg L−1), whereas the methane (CH4) production (45 °C, 3.55 ± 0.47 L CH4 L−1 day−1; 35 °C, 1.44 ± 0.12 L CH4 L−1 day−1) remained considerably higher in TPAD‐I than TPAD‐II. Furthermore, the TPAD‐II system suffered from certain degree of instability due to high level of total VFAs (6087 ± 1578 mg L−1), low buffering capacity, increased level of total NH3 (2982 ± 219 mg L−1) and free NH3 (246 ± 25 mg L−1), and relatively reduced CH4 production (1.69 ± 0.1 L L−1 day). The bacterial and archaeal population of the TPADs investigated by 454 pyrosequencing and Illumina sequencing showed, in both TPAD systems, a bacterial community dominated by Firmicutes, followed by Bacteriodetes, Proteobacteria, Synergistetes and Actiniobacteria. The archaeal community was dominated by Methanimicrobia (74–84% Methanosarcina) and Methanobacteria (15–27% Methanobacterium). A progression from genus Clostridium to Coprothermobacter and Tepidanaerobacter, and Methanocarcina to Methanothermobacter and Methanobacterium was observed in TPAD‐II.
CONCLUSIONS
This study proved the processes driving the dynamics of key microbial population and its correlation with hydrolytic functionality of TPAD systems. © 2019 Society of Chemical Industry