<p>The anaerobic digestion (AD) of swine wastewater (SWW) is challenged by high concentrations of organic matter and nitrogen, often resulting in volatile fatty acid (VFA) accumulation and ammonia inhibition. This study evaluated the effect of three lignocellulosic biochars, derived from olive wood (BO), walnut wood (BWW), and walnut shell (BWS), on methane production, nutrient removal, VFA dynamics, and ammonia recovery via struvite precipitation. Batch incubations were performed using raw SWW and biochar-pretreated SWW, with and without additional biochar addition. Wood derived biochar’s (BWW and BO) enhanced methane production and reduced the microbial lag phase, whereas BWS showed no improvement. Pre-treatment with BO achieved high P-PO₄³⁻ (93.8%) and ammonia (34.7%) removal but did not enhance methane production. Precipitation from the post-digestion liquid achieved up to 93% ammonia removal in raw SWW with slightly lower efficiencies in pre-treated samples. XRD confirmed the formation of struvite and hazenite, with morphology depending on treatment conditions. The findings highlight that the effectiveness of biochar in AD systems is strongly feedstock-dependent. Under the tested conditions, pretreatment of swine wastewater with BWW and BWS improved AD performance, while the high pH of BO limited its suitability. These findings support biochar selection strategies to optimize AD and nutrient recovery in sustainable wastewater treatment systems.</p> Graphical Abstract <p></p>