Optimisation of Ultrasound Pretreatment of Microalgal Biomass for Effective Biogas Production through Anaerobic Digestion Process

Abstract

The anaerobic digestion, AD, process presents a solution for sustainable waste management, greenhouse gas mitigation and energy production for growing population needs and requirements. Adopting a biorefinery approach that utilises different feedstock may enhance energy production and support optimisation of the anaerobic digestion process. Algae is a promising feedstock that could be used for energy production via the anaerobic digestion process. Microalgal biomass is rich in carbohydrates and lipids; however, many species of algae exhibit tough cell walls that could also be difficult to digest and may influence or inhibit the efficiency of the AD process. This study concentrated on the comparison of AD remediation of two marine algal biomass species, Tetraselmis suecica and Nannochloropsis oceanica. The two species were pre-treated with an ultrasound technique and compared for their methane production using biochemical methane potential tests. For Tetraselmis, a specific methane production of 0.165 LCH4/KgVS was observed; however, for Nannochloropsis, a value of 0.101 LCH4/KgVS was observed for the samples treated with ultrasound. The BMP results from this study show that among the two micro-algae species tested, Tetraselmis suecica is found to be a better substrate for methane production potential. Contrary to increasing the specific methane production, ultrasound cavitation caused a slight decrease in the specific methane production values for both Nannochloropsis oceanica and Tetraselmis suecica biomass residues. The pre-treatment of the biomass using ultrasound techniques provided comparable results and can be recommended for effective bioenergy production. However, further research is required for the optimisation of the pre-treatment of microalgae and for the integration of microalgal biorefineries for circular economy.

Cell destruction level and metabolites green-extraction of Tetraselmis suecica by low and intermediate frequency ultrasound

“…The majority of these studies focused on lipid extraction at very low frequencies, commonly 20 kHz [43] , [42] or 40 kHz [3] . A recent study focused on determining if US could be used as a pre-treatment to break down T. suecica cells more easily, again at 20 kHz and keeping the US power fixed at 500 W [44] .…”

A Review of Aquatic Plant Biomass Pretreatment Methods for Biogas Production

“…These studies, which focus on the physical aspect of pretreatment, demonstrate that ultrasound is not the only method for preparing microalgae cells for subsequent use. This variety of results emphasizes the complexity of the mechanisms of interaction of ultrasound with microbiological biomass and indicates the need for a deeper understanding of these processes (Paul et al, 2023). It is important to consider that the effectiveness of ultrasound pretreatment can vary significantly depending on the specific experimental conditions, including the type and condition of microalgae biomass, ultrasound parameters and treatment environment.…”

The Influence of the Ultrasound Disintegration of Microalgal–Bacterial Granular Sludge on Anaerobic Digestion Efficiency

“…The amounts of soluble COD and TOC were 771 ± 83 mgO 2 /L (solubilization degree 72.4 ± 7.3%) and 560 ± 42 mg/L (solubilization degree 77.5 ± 8.5%), respectively (Table 4). Ultrasonication is a very popular and effective mechanical pretreatment method used for treating different kinds of biomass prior to AD [44][45][46][47][48]. This method improves the biodegradability of biomass by disrupting its structure, thus changing its physical, chemical, and biological properties [45,49].…”