Calcium-rich bone biochar boosts fat, oil, and grease (FOG) biodegradability: Methane maximization and microbial community pattern

The present study evaluated calcium-rich bone biochar, derived from pig and chicken bones, for enhanced anaerobic digestion of FOG (fat, oil, grease). The study aimed to maximise energy recovery by reducing the negative impact of long-chain fatty acids (LCFAs) and to evaluate the subsequent effect on the microbial community structure. A series of 2.0 ​% FOG batch trials was prepared, adding pig bone biochar (PB) and chicken bone biochar (CB) based on their calcium (Ca) content to maintain (0.1, 0.5, and 1.0 ​% Ca concentrations). Parallelly, Ca was used at the same concentrations without biochar. Supplementation of 0.5 ​% PB, CB, and Ca individually enhanced LCFAs degradation up to 81.6 ​%, 81.0 ​%, and 84.8 ​%, respectively. Therefore, the accumulative methane yield increased by 4-, 3.9-, and 5.2-fold over the control FOG2.0 ​%. Reduction in methane production was observed at 1.0 ​% PB, CB, and Ca compared with 0.5 ​% but, interestingly, 1.0 ​% PB and CB showed higher accumulative methane yield of 135.6 ​mL ​g⁻¹ VS and 125.3 ​mL ​g⁻¹ VS, respectively, in comparison to Ca (60.7 ​mL ​g⁻¹ VS). There was enhancement in Firmicutes and Campylobacteriotes, accompanied by a simultaneous rise in Methanosarcina at 0.5 ​% PB (from 23.7 ​% to 78.1 ​%) and Methanoculleus at 0.5 ​% Ca (from 41.3 ​% to 50.0 ​%). Ca-rich PB and CB biochar significantly enhanced FOG anaerobic digestion through synergistic mechanisms, including reducing inhibition, stimulating microbes, facilitating electron transfer, and improving nutrient supply. Using animal bone residues for FOG anaerobic digestion provides both a sustainable waste management route and an efficient calcium-rich material to boost energy recovery.