Processing of brewery wastes with microalgae for producing valuable compounds

Publishable summary: 

GREENBIOREFINERY is focused to develop new strategies to generate valuable bioproducts by integrating the treatment of brewery wastes with the production of microalgae biomass and derivate products. This integration allow transforming the wastes from breweries into valuable biomass, thus not only reducing the environmental impact of breweries activities but also recovering nutrients contained on these wastes, and producing valuable compounds. To achieve this goal, the first task has been to characterize wastes (liquids and gases) generated from breweries located in countries of partners involved into the project (Spain, Portugal, Colombia and Argentina). Results confirm that in spite to be the same industry, the distinct operation schemes used by the different industries produce diverse effluents with large changes into its composition. Focusing in liquid wastes the Chemical Oxygen Demand (COD) values ranged from 241 to 40520 mg/L, whereas the nitrogen (N) and phosphorous (P) concentration values ranged from 23 to 1238 and from 15 to 95 mg/L, respectively. All of them are higher than limits defined by EU directive (COD/N/P below 100/10/2) thus additional treatments being necessary prior to release the water to the environment. Most of the companies perform this treatment out of the brewery in agreement with wastewater treatment plants, thus this treatment representing a

relevant cost for the brewery because large volumes of liquid wastes have to be treated, from 100 to 2500 t/month. According to the performed analysis all the effluents analysed contains enough nutrients (C/N/P) to be used for the production of microalgae, thus from 0.5 up to 14 kg of biomass can be produced per cubic meter of liquid effluent. Considering a minimum value of the biomass of 1 €/kg (actual price of microalgae biomass worldwide exceeds 5 €/kg) to integrate microalgae biomass production schemes into breweries allow to minimize the release of valuable nutrients at the same time that increasing the profitability and sustainability of breweries. Experiments have been performed at laboratory scale but simulating outdoor real conditions, with different microalgae strains, using identified wastes as culture medium. Robust strain as Scenedesmus and Chlorella habitually used in wastewater treatment schemes were used, in addition to high potential strains as Botryococcus and Euglena, but also new strains with large lipids contents as Neochloris, and the most largely produced strain in worldwide as Spirulina. Results demonstrate that all the tested strains can be produced in brewery wastes the major factor determining the operation and performance of the system being the composition of the waste instead the microalgae strain. COD was the major factor influencing the performance of the systems, the lower the COD content the better was the performance of microalgae cultures and the quality of final biomass produced. When the COD is excessive (upper than 1000 mg/L) the growth of bacteria is enhanced whereas the growth of microalgae is reduced, by excess of turbidity into the culture medium. At these conditions large hydraulic retention times (larger than 5 -7 days) are requested to remove the COD and produce valuable microalgae biomass containing low proportion of bacteria (lower than 25%). In front, when the COD is low (lower than 1000 mg/L) the growth of bacteria is limited the performance of microalgae being maximal if enough light is provided. At these conditions the hydraulic retention time can be largely reduced (up to 1 -3 days) thus increasing the treatment capacity at the same time that removing all the contaminants (N/P) from the waste, and producing high quality microalgae biomass containing less than 5% of bacteria. Microalgae biomass produced from brewery wastes is being used to produce biofertilizers by enzymatic hydrolysis as main valorisation route, but also alternatives uses as to produce biofuels as BioHydrogen through dark fermentation with Enterobacter aerogene s, and of bio - oil through pyrolysis are being studied. All of them demonstrated to be feasible now the optimal schemes being evaluated to compare the best alternative to be validated at pilot scale.