Anaerobic digestion (AD) is a promising bio-technology for energy recovery from organic wastes. This study
provides a novel method for the enhanced AD of dairy manure (DM) without pre/post-treatment by the direct
supplementation of special natural ash from soil called Mineraso (MS) to the feed of lactating Holstein dairy
cattle (HDC). MS is chiefly composed of approximately 84.8% of iron hydroxide. MS was supplemented at
rates of 0 (F1), 25 (F2), and 50 (F3) g/head of HDC/day for two months. Thereafter, the manure of each
group of HDC was collected and examined for iron concentrations prior to the batch AD experiments. The
results revealed that the amounts of iron excreted in manure were reduced by 63.64% and 68.42%,
respectively. Interestingly, the supplementation of MS at concentrations of 25 and 50 g/head of HDC
improved biogas yields from DM by 21.90% and 40.05%, respectively than the control (no MS
supplementation). Additionally, the equivalent dosages of MS improved methane yield by 25.87% and
46.51%, respectively. The highest cumulative production of biogas and CH4 was 1.11 and 0.63 L/gVS
removed, respectively, which was achieved by F3 supplement, while the corresponding values in the case of
F1 were 0.79 and 0.43 L/gVS removed. Therefore, the supplementation of animals with iron-containing MS
might represent a sustainable and practical approach to enhancing CH4 yields.