Biochar enhanced bioaugmentation provides long-term tolerance under increasing ammonia toxicity in continuous biogas reactors

Abstract

Bioaugmentation of ammonia-tolerant methanogens into inhibited anaerobic digestion (AD) reactors was demonstrated as an in-situ remediation strategy to alleviate ammonia toxicity. This study investigated the long-term performance of a novel bioaugmentation strategy, using gel-immobilized ammonia tolerant methanogens (biogel) enhanced with biochar to alleviate ammonia toxicity in thermophilic continuous anaerobic systems. Three ammonia shocks were applied in four continuous stirred-tank reactors, namely by adding biogel (R2), biochar (R3), both biogel and biochar (R4) and control reactor (R1), respectively. The results showed R1, R2, R3 and R4 suffered 31.3%, 28.6%, 26.0% and 17.1% methane production loss, respectively at 5.5 g NH4+-N L−1. R4 achieved 100% methane production recovery compared to 13% of R1. R3 and R4 successfully acclimatized to 6.5 g NH4+-N L−1 with 71.7% and 61.8% original methane yield compared to 36.9% and 35.6% for R1 and R2, respectively. The introduced Methanoculleus thermophilus sp. along with syntrophic partners was protected by the biochar, and its relative abundance in R4 was tenfold than R2. Bioaugmentation developed a long-term ammonia resistance due to the synergistic interaction between biogel and biochar on alleviating ammonia inhibition, securing an additional gross profit of 11.8 $ ton−1 feedstock for the continuous biogas reactor.