This work investigated the effect of additives to sustain the mesophilic AD of FW as sole input. Successive AD batch reactors were conducted at lab-scale, a fraction of the digestate being re-circulated at the beginning of each batch and being fed with fresh substrate. Supplementation of trace elements as well as biochar at doses of 1% and 2% (w:w) was assayed. Addition of trace elements in VFA- and TAN-inhibited reactors had a fast-acting effect and improved the methane production rate. Supplementation in biochar resulted in improved methane yield, increased rate of VFA re‑consumption and prevention of acidosis, even at high TAN levels of more than 4 g/L. This positive biochar effect was linked to the selective enrichment of the archaea genus Methanoculleus, a syntrophic partner of VFA-oxidizing bacteria, together with a reduction of VFA-producing bacterial families such as Porphyromonadaceae.