Biogas yields and composition from oil-extracted halophilic algae residues in conventional biogas plants operated at high salinities.

CO2-induced climate change drives the development of renewable processes for industrial products. Algae processes can actively fix and convert CO2 into value adding products, such as oils. Algae lipids hence counteract climate change and provide access to renewable commodities. In this context, valorization of algal residues remaining after oil extraction is a challenge for the emerging cyclic bioeconomy. This study focuses on the valorization of oil-extracted algae residues derived from the halophilic strain Scenedesmus obliquus via anaerobic digestion. We examined the effect of prior oil extraction on microbial digestibility and increasing salt content in the substrate with regard to biogas yield and composition. Our cumulative data demonstrate that the supercritical CO2 oil extraction acts as a physical pretreatment that facilitates enhanced hydrolysis of both polymeric call wall carbohydrates and cellular proteins, providing methane yields of 213.2 LN kg-1 VS day-1. Methane yields were 20% higher than literature values obtained with the same algae strain in the absence of prior oil extraction. We obtained these superior results albeit all lipids and nonpolar proteins had been extracted from the biogas substrate. Our data indicate that continuous anaerobic digestion without loss of fermentation efficiency is feasible up to a salt concentration of 2% w/v, if conventional, agricultural biogas plants are gradually adapted to the salt content of the substrate. Monofermentation of the investigated oil-extracted algae residue is technically feasible at loading rates of 1.5 kg VS m-3 day-1, but a supplementation with carbohydrate rich biomass would prove beneficial to alleviate ammonia inhibition.

Isolation and Investigation of Natural Rare Earth Metal Chelating Agents From Calothrix brevissima - A Step Towards Unraveling the Mechanisms of Metal Biosorption.

In this study water soluble compounds that form complexes with Rare Earth Elements (REE) and other metals were isolated from Calothrix brevissima biomass with chromatographic methods for the first time. Molecular characterization showed that the isolated compounds are most likely polysaccharides comprised of arabinose, xylose, mannose, galactose and glucose. FT-IR analysis revealed functional groups involved in the binding mechanism of Tb are likely sulfate- and to a lesser extend hydroxyl-groups. The binding specificity of the isolated compounds was investigated with different metal solutions. Here, ions of the alkali and alkaline earth metals Na, K, Mg and Ca showed no competition for Tb-binding even at 10-fold excess concentration. Ions of the elements Co and Pb on the other hand replaced Tb at higher concentrations. Addition of the isolated compounds significantly reduced the precipitation of Eu at pH-values between 6.7 and 9.5, indicating that the interaction between the isolated chelators and Rare Earth Metals is stable even at high pH-values.

Terbium Excitation Spectroscopy as a Detection Method for Chromatographic Separation of Lanthanide-Binding Biomolecules.

Studies of biosorption and bioaccumulation of heavy metals deal mostly with challenging, inhomogeneous, and complex materials. Therefore, most reports describe only application studies, while fundamental research is limited to indirect methods and speculations on the binding mechanisms. In this study, we describe a method for detecting and isolating heavy metal-binding biomolecules directly from crude extracts. The underlying principle is terbium sensitization and fluorescence excitation spectroscopy used offline after a chromatographic run. Compounds interacting with metal ions inevitably change the coordination sphere of terbium, which is reflected in the excitation spectrum leading to metal-specific luminescence. Main advantages of our approach include simple, fast, and inexpensive experiment design, nondestructive measurements, and detection limits far below 1 mg. Here, we have applied our method for three promising biosorbents (green algae, moss, and cyanobacterium) and obtained first information on the character of active compounds isolated from each species.