The use of sludge as a micronutrient for the improvement of biogas production from seaweed: the integration of two sources of environmental concern to bring new opportunities

Large quantities of seaweed in marine environments and coastal areas can cause serious hygienic and environmental problems. Anaerobic digestion (AD) could provide a solution and could also be useful for the production of bioenergy and fertilizer. However, the AD of algae biomass has some limitations and further work is required on the process. To increase the efficiency of the process, batches of 350 mL feedstock containing seaweed biomass (Sargassum sp.), inoculum, and different dosages of sludge from drinking water treatment (DWTS) as a micronutrient source to improve biogas production were digested in a 500 mL glass reactor and under mesophilic conditions, leading to significantly enhanced methane production. The highest methane yield (199 NmL g−1 VS) was observed when 6 mg L−1 DWTS was added, which showed a 30% improvement compared with the control digester and accounted for a 249.4 kWh increase in net energy per ton. The biodegradability index also increased by 10% compared with the control after the addition of DWTS.