Treatment effect on degradation compounds production of microalgal-bacterial biomass grown in photobioreactors for pig manure remediation

Abstract

The development of efficient and inexpensive methodologies for the treatment of all types of wastewater (manure, municipal wastewaters, etc.) is an increasing need. One of the most promising methods is the usage of photobioreactors. Biomass produced, composed by microalgae and bacteria, use the nutrients present in all types of wastewater to generate carbohydrates, proteins and lipids. These products can be further processed and revalorized. The use of the different fractions of the biomass, applying the concept of biorefinery, improves the economic and environmental viability of the global process. Certain aspects of the valorization of the carbohydrate fraction of algae and bacteria biomass grown in pig slurry treatment plants in the form of fermentable sugars were studied in this work. Algal biomass samples, obtained from pig manure treatment in a pilot plant, were subjected to several physical and chemical treatments, followed by an enzymatic hydrolysis step. Sugar release entails co-solubilization of other fractions of biomass (proteins and lipids) and generation of degradation byproducts, which can reduce the efficiency and inhibit further processes. The aim of the study is to identify the most efficient method to maximize sugars production while simultaneously minimizing their degradation. The effect of treatments on the generation of degradation byproducts has been investigated. To deepen the understanding of the processes of nutrient degradation and differentiate degradation due to pretreatment and due to biological action, some treatments (acid hydrolysis, alkaline hydrolysis and bead mill grinding) were applied to pure sources of carbohydrates (cellulose), gelatin (proteins) and lipids (vegetable oil). The concentrations of inhibitors obtained were studied by using multivariate statistical analysis (principal component analysis and hierarchical cluster analysis), demonstrating the effect of the different physical, chemical and enzymatic treatments in the type and concentration of degradation products released. Obtained results revealed that even though high byproduct yields, hydrochloric acid treatment is the most suitable method due to the highest monosaccharide recovery. Chemical treatments resulted in higher degradation, while in physical treatments inhibitors were mainly produced during enzymatic hydrolysis as a result of bacteria metabolism.