Improving the performance of thermophilic anaerobic digester through recirculation of low hydrogen biogas

Abstract

Biogas recirculation was conducted to improve the performance of two thermophilic anaerobic sequenced batch reactors (ASBRs), in which high concentrations of volatile fatty acids (VFAs) were accumulated. To accelerate degradation of VFAs, facilitating acetate consumption via syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis (SAO-HM) was expected to be effective. Hence, to promote the SAO-HM pathway, hydrogen was removed to create low hydrogen partial pressure (pH₂) in reactor RH, yet in reactor RB, hydrogen was not treated. The performance of RB and RH on VFAs degradation and methane production processes was compared at steady stage; the VFAs and soluble microbial products (SMP) in the effluents were monitored. The results showed that low pH₂ intensified the SAO reaction, thereby accelerating conversion of acetate to methane, as well as acetate production from glucose and VFAs. Glucose fermentation type was also influenced. VFAs and SMP in the effluents were reduced after the introduction of biogas mixing, which proceeded much faster in RH with low pH₂. Recirculation of low hydrogen biogas with SAO-HM pathway being promoted should be more effective to alleviate high acid level stress and to improve the reactor performance.

Keywords:

• Anaerobic digestion
• waste treatment
• hydrogen
• biogas recirculation
• soluble microbial product

Acknowledgments

This research was partially sponsored by National Basic Research Program of China (973 Program, No. 2012CB719801), National Natural Science Foundation of China (No. 51178327; 21177096), Innovation Program of Shanghai Municipal Education Commission (13ZZ030), the Shanghai Pujiang Program (No. 11PJ1409200), Fundamental Research Funds for the Central Universities (No. 0400219195), State Key Laboratory of Pollution Control and Resource Reuse Foundation (PCRRY11008).