Revalorization of solid waste microalgae biomass from pig manure water treatment towards fertilizers production.

Abstract

The use of microalgae is growing in different applications in the last decades. Pharmaceuticals, cosmetics, animal feed, biofuels, chemicals, wastewaters treatment and fertilizers production are several fields that they are being applied. This is not only due to the current oil crisis, but also to the necessity of new energy sources with the aim of having feasible and environmental friendly processes. The microalgae seem to be an effective option for the agro-food wastewater treatment with high nutrient contents. The wastewater is treated and converted into an effluent that could be returned with minimal environmental issues or reused. The nutrients accumulation (N and P) in the biomass, which was produced in this process of treatment, becomes an attractive residue for its possible valorization (Singh et al., 2016).

The production of biogas is one of the tendency for this biomass, and the maximum theoretical yield is 0.40L CH4/g SV, considering the whole microalgae biomass. This reduced digestibility is attributed to the strong structure of its cell wall and to the presence of recalcitrant compounds, hence, it is necessary to apply different pretreatments to break the cell wall and increase the biomass biodegradability. The use of obtained digestate solid (after the anaerobic digestion) as a fertilizer is an interesting alternative. Europe requires annually of 11 Mton N, 2.8 Mton phosphorus and 2.6 Mton of potassium, of which a significant percentage is imported. The use of microalgae for the fertilizers production could generate new business opportunities and would be an important advantage for the European economic sector (BBI, 2016).

Therefore, this work aims at implementing the biorefinery concept by valorizing the microalgae biomass produced from pig manure wastewater treatment as a substrate for biogas production through anaerobic digestion. Furthermore, several pretreatments are applied to improve the CH4 methane production. The obtained digestate solid is used in a new subsequent revalorization for fertilizer production.