Biochar facilitates rapid restoration of methanogenesis by enhancing direct interspecies electron transfer after high organic loading shock

This study evaluated the effectiveness of biochar addition against high organic loading shock (OLS) of 80 kg COD/m(3)/d in up-flow anaerobic sludge blanket (UASB) reactors (R1 with biochar; R2 without biochar). After OLS of 24 h, R2 suffered the irreversible acidification (pH of 5.42 +/- 0.07) with low biogas production of 0.08 +/- 0.01 m(3)/kg COD/d. In contrast, the biogas production in R1 restored rapidly to 0.33 +/- 0.04 m(3)/kg COD/d, and effluent pH in R1 returned to 7.01 +/- 0.22. With addition of biochar, potential direct interspecies electron transfer (DIET) partners, including volatile fatty acids (VFAs)-oxidizing bacteria (Bacteroidetes, Smithella, Desulfovibrio, Geobacter) and methanogens (Methanosaeta, Methanosarcina) were enriched in R1, which were conductive to maintain the balance of acidogenesis and methanogenesis. Moreover, the retention of Methanosaeta and Methanosarcina coupled with biochar maintained the structural stability of granular sludge in R1 under the pressure of OLS and VFAs, which guaranteed the stability of anaerobic system.

Automated summary

The study found that the addition of biochar can effectively resist high organic loading shock, with rapid recovery of biogas production and maintenance of the balance between acidogenesis and methanogenesis in R1. Furthermore, the addition of biochar helped retain the structural stability of granular sludge in R1 under pressure, ensuring the stability of the anaerobic system.