Effect of cell wall weakening on microalgae chlorella vulgaris for energy and cost effective biomethane production

Abstract

In recent years, most of the developed and developing countries step forward to minimize the use of conventional Petroleum Based Fuels (PBF), as continuous burning of PBF cause several negative impacts on the environment. On the other hand, increasing the global population leads to lack of PBF for our day today life. To balance the global energy demand, many developed and developing countries start searching alternative source of bioenergy using renewable waste biomass. In order to overcome this issue, many researchers and policymakers are suggesting Microalgae Biomass (MB) as renewable feedstock for bioenergy production. Deriving bioenergy from microalgae has several benefits than conventional PBF such as eco-friendly nontoxic and pollution free. Microalgae contains three key biopolymers such as protein, carbohydrate and lipids, which are completely utilized by anaerobic microbes to produces bio-based valuable product. Anaerobic Digestion (AD) is the oldest and profitable technique followed for cost effective biomethane recovery from microalgae. The cell wall of microalgae is complex and rigid in nature, which lowers the anaerobic biodegradability (Abio) of feedstock and Biomethane Yield (BMY). Many researchers have suggested disintegration of microalgae prior to AD, enhances the Abio and BMY. Bearing all these in mind, in the present study a novel two-phase disintegration of MB was employed to improve Abio and BMY. In two-phase disintegration, initially the cell wall of MB was weakened using four different techniques (Ultrasonic US, Low Thermochemical LTC, Citric Acid CA and Titanium Dioxide TD) followed by Biological Disintegration (BD) using cellulase-secreting bacteria. At first phase, 101.27 kJ/kg TS of US input energy was employed for cell wall weakening (CWW). The results of two-phase disintegration process (US mediated BD) showed higher algal liquefaction (AL) of about 34.8 % comparatively higher than BD (23.8%) and control (6.9%). A maximal Volatile fatty acids (VFA) production of about 3069 mg/L was achieved in US-BD. The outcomes of biochemical methane potential (BMP) assay reveal that US-BD showed higher BMY of about 0.3035 L/g COD than BD (0.208 L/g COD) and control (0.0682 L/g COD) respectively newline