Magnetite accelerates syntrophic acetate oxidation in methanogenic systems with high ammonia concentrations

Ammonia accumulation is a major inhibitory substance causing anaerobic digestion upset and failure in CH (4) production. At high ammonia levels, CH (4) production through syntrophic acetate oxidization (SAO) pathways is more tolerant to ammonia toxicity than the acetoclastic methanogenesis pathway, but the low CH (4) production rate through SAO constitutes the main reason for the low efficiency of energy recovery in anaerobic digesters treating ammonia‐rich substrates. In this study, we showed that acetate fermentation to CH (4) and CO (2) occurred through SAO pathway in the anaerobic reactors containing a high ammonia concentration (5.0 g l(−1) NH (4) (+)–N), and the magnetite nanoparticles supplementation increased the CH (4) production rates from acetate by 36–58%, compared with the anaerobic reactors without magnetite under the same ammonia level. The mechanism of facilitated methanogenesis was proposed to be the establishment of direct interspecies electron transfer (DIET) for SAO, in which magnetite facilitated DIET between syntrophic acetate oxidizing bacteria and methanogens. High‐throughput 16S rRNA gene sequencing analysis revealed that the bacterial Geobacteraceae and the archaeal Methanosarcinaceae and Methanobacteriaceae might be involved in magnetite‐mediated DIET for SAO and CH (4) production. This study demonstrated that magnetite supplementation might provide an effective approach to accelerate CH (4) production rates in the anaerobic reactors treating wastewater containing high ammonia.