Microalgae community shifts during the biogas upgrading in an alkaline open photobioreactor

Abstract

Aims: To achieve the functional specialization of a microalgae community through operational tuning of an open photobioreactor used for biogas upgrading under alkaline conditions.

Methods and results: An open photobioreactor was inoculated with an indigenous microalgae sample from the Texcoco Soda Lake. A microalgae community was adapted to fix CO₂ from synthetic biogas through different culture conditions reaching a maximum of 220 mg CO₂ l^-1 per day. Picochlorum sp. and Scenedesmus sp. were identified as the prominent microalgae genera by molecular fingerprinting (partial sequencing of 16S rRNA and 18S rRNA genes) but only the first was detected by microscopy screening. Changes in the microalgae community profile were monitored by a range-weighted richness index, reaching the lowest value when biogas was upgraded.

Conclusions: A robust microalgae community in the open photobioreactor was obtained after different culture conditions. The specialization of microalgae community for CO₂ fixation under H₂ S presence was driven by biogas upgrading conditions.

Significance and impact of the study: The alkaline conditions enhance the CO₂ absorption from biogas and could optimize specialized microalgae communities in the open photobioreactor. Denaturing gradient gel electrophoresis fingerprinting and richness index comparison are useful methods for the evaluation of microalgae community shifts and photosynthetic activity performance, particularly in systems intended for CO₂ removal from biogas where the CO₂ assimilation potential can be related to the microbial richness.

Keywords: CO2 fixation; DGGE fingerprinting; alkaline photobioreactor; biogas; microalgae.