The influence of thermal treatment on recirculating two phase anaerobic digestion system

Recirculated two-phase anaerobic digestion (RTAD) is a recent technique to improve biogas production. Recirculating the effluent of two-phase anaerobic system has a methanogens invasion risk to dark fermentation. Hot compressed water is possible to reduce the methanogens invasion. The objectives of this study are identifying the effect of hot com-pressed water pretreatment on RTAD and evaluating the fermentation system during the change of hydraulic retention time and effluent recirculation ratio. The RTAD system was built and operated with 4 different conditions, those are hydraulic retention time 2-day (HRT 2d), HRT 3d, Effluent Ratio 1:5 (R1:5) and R2:5. The result shows that the shorter HRT increase the biogas production. The pH in the reactor is more stable after the recir-culation process. In bioreactor performance, the hot compressed water treatment increased the COD removal at all conditions. The highest COD removal achieved at con-dition of HRT 2-day with removal up to 94.5%. The system that using hot compressed water treatment has the higher energy potential at HRT 2-day, R 1:5 and R 2:5 compared with no hot compressed water treatment. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study found that hot compressed water treatment can increase biogas production and COD removal efficiency in RTAD system, especially with shorter hydraulic retention time. The recirculation process can improve the stability of pH in the reactor.