Bioethanol production using algal biomass produced on waste material as substrate

Conference poster, 2012

For growth and ethanol production, microorganisms need sugars, which commonly are provided from agricultural and forestry products containing starch or cellulose. There are several drawbacks with those substrates for fuel ethanol production, such as interference with food production when using agricultural crops, or high formation of inhibitory compounds from pretreatment of lignin-containing forestry products. Algae biomass could be an alternative sustainable raw material since cultivations can be set up in places where food crops cannot grow thus not interfering with food production. Most microalgae cells do not contain lignin and therefore pretreatment will result in less formation of inhibitors. Microalgal cultivations can contribute to environmental benefits by capturing carbon dioxide from flue gas and utilize nutrients such as nitrogen and phosphorus from municipal waste water, resulting in purification of such waste streams together with production of energy-rich biomass. The feed of municipal waste water results in a continuous addition of algal species and microorganisms other than the initial alga of the inoculum which gives a mixed population in the cultivation system. This, together with seasonal variations, may cause changes in the population dynamics; hence different times of harvesting may result in different microbial composition. This project investigates the potential of using microalgal biomass produced on waste streams as substrate in ethanol production. The algae used were produced in the development plant in Umeå run by SLU, using flue gas of the heat and power plant (Umeå Energi) as carbon source, municipal waste water from the waste water treatment plant (Umeva) as nutrient source and sunlight as energy source. Algal biomass from 8 time points of a cultivation season were used for i) determination of macromolecular composition in biomass, ii) investigation of different biomass pretreatment processes to yield fermentable sugars, iii) analysis of fermentability and ethanol production in algal hydrolysates and vi) investigation of changes in species composition during the cultivation season. Both enzymatic and acid hydrolysis were investigated as pretreatment process and so far the best results have been obtained with acid hydrolysis. Additionally, small scale fermentations in acid pretreated algal hydrolysates were performed to study fermentability and ethanol production. Variations in species composition of the community at different sampling times will be investigated by terminal restriction fragment length polymorphism (T-RFLP) based on species variations in the 18S rDNA gene.