Exploring strategies for seaweed hydrolysis: Effect on methane potential and heavy metal mobilisation

Abstract

Energy-rich methane can be harnessed from seaweed deposits by anaerobic digestion. However, the high heavy metal content in the seaweed and its digestates limits their use as fertilisers. Heavy metal contaminants from solid seaweed can be removed by, mobilisation into a liquid phase and subsequent metal ions adsorption. In this laboratory-scale study, pretreatment strategies for enhancing seaweed hydrolysis in relation to metal ions mobilisation were evaluated. Methane potential batch tests were also performed on the resulting treatment leachates. The results show that about 86% of the soluble organic compounds were hydrolysed/solubilised in a leach bed reactor followed by alkaline/autoclave post-treatments. However, Zn ion mobilisation was only 54% from the combined treatments. A 2.8-fold higher methane yield was obtained when the seaweed hydrolysis leachate and the post-treatment leachate were co-digested, compared to raw seaweed. This study demonstrated the efficient utilisation of seaweed for biogas production, and the partial heavy metals mobilisation to enable the metal removal for improved fertiliser quality.