The use of algal biomass produced on waste material as substrate for bioethanol production with yeast

Research Project, 2011 – 2014

In this project, we have investigated the possible use of microalgal biomass as substrate in ethanol producing fermentations. For growth and ethanol production the fermenting microorganism (yeast) need sugars, which are today commonly provided from agricultural and forestry products but these have at some points disadvantages. Algal biomass have here been investigated as an alternative sustainable source of raw material since; i) cultivations can be set up in places where food crops cannot grow thus not interfering with food production or leading to increased deforestation, ii) most microalgae do not contain lignin and therefore pretreatment will result in low or no formation of inhibitors, iii) 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. 

From the investigations made in this project it was seen that the algal biomass cultivated on waste material, flue gas and waste water, can be used to provide fermentable sugars as substrates in fermentation. The most promising pretreatment method seemed to be weak acid hydrolysis in a thermal pretreatment process, which released up to 83 % sugars of the total content of carbohydrates. Pretreatment did not lead to formation of the inhibitors furfural or HMF, which is a major issue when dealing with pretreatment of lignocellulosic raw materials.

Variations in species composition of the microalgal community in the production plant was investigated by terminal restriction fragment length polymorphism (T-RFLP) giving a finger print of the composition of the algal community. The T-RFLP analysis showed clear variations of species composition over cultivation season (May to October/November).