The ability of macroalgae to stabilise and optimise the anaerobic digestion of household food waste

Abstract

This study investigated the potential of seaweed waste (SW) as a sustainable feedstock for anaerobic co-digestion with food waste (FW). The study was conducted at laboratory scale using a batch test approach run over 34 days. Methane (CH4) potential assays were conducted at the following FW to SW dry mass ratios: 100:0, 90:10, 75:25, 50:50 and 0:100. Results indicated that anaerobic co-digestion of FW and SW at a mixture ratio of 90:10 produced the highest methane yield (252 cm3 g−1 of volatile solids (VS)), rates of reaction (0.08 d−1) and resulted in a better stability of the process. Predictions based on the Buswell formula suggested that all reactors were performing below the theoretical (maximum) with a greater disparity at increasing levels of seaweed in the feed, likely due to high levels of sulphur in the SW (1.73% mass fraction). The analysis of heavy metals in SW and final digestate indicated that using SW for anaerobic co-digestion with FW enhanced the process by providing trace nutrients without impacting the heavy metal content of the digestate. The analysis of carbon (C) and nitrogen (N) indicated that by using SW for co-digestion with FW, C:N optimal mass ratios were achieved. It was concluded that the addition of SW for anaerobic co-digestion of FW can be used to accelerate the bioenergy production from FW. An additional benefit will be the abatement of the negative impacts of SW in coastal areas, making the overall process more sustainable.