Comparing pretreatment methods to improve the methane yield of microalgae grown in wastewater

Abstract

Microalgae have recently drawn attention as a potential resource for biofuels generation. In the short term, anaerobic digestion seems the most viable downstream process. Still, microalgae cell wall restrains the hydrolysis, hampering the methane production potential. This work aimed at improving the anaerobic biodegradability of microalgae through different pretreatment methods: microwave, low temperature and high temperature. For the microwave pretreatment, the specific energy was the main parameter affecting biomass solubilisation, increasing up to 800 % compared to untreated biomass. For the low and high temperature pretreatments, temperature was the most important factor, increasing biomass solubilisation up to 1190 and 2140 % in each case. BMP tests showed an increased methane yield after all pretreatments (40-80 %), with the highest results for the microwave pretreatment. In semi-continuous reactors operated at 15 days HRT, the methane production was increased by 30 and 33 % after microwave and low temperature pretreatment, respectively. When increasing the HRT to 20 days, the methane yield was further enhanced by 60 and 52 % after microwave and low temperature pretreatment, respectively. Therefore, initial results showed pretreatment potential for microalgae solubilisation and methane yield improvement.