Flocculation of oleaginous green algae with Mortierella alpina fungi.

Microalgae are promising sources of valuable bioproducts such as biofuels, food, and nutraceuticals. However, harvesting microalgae is challenging due to their small size and low biomass concentrations. To address this challenge, bio-flocculation of starchless mutants of Chlamydomonas reinhardtii (sta6/sta7) was investigated with Mortierella alpina, an oleaginous fungus with high concentrations of arachidonic acid (ARA). Triacylglycerides (TAG) reached 85 % of total lipids in sta6 and sta7 through a nitrogen regime. Scanning electron microscopy determined cell-wall attachment and extra polymeric substances (EPS) to be responsible for flocculation. An algal-fungal biomass ratio around 1:1 (three membranes) was optimal for bio-flocculation (80-85 % flocculation efficiency in 24 h). Nitrogen-deprived sta6/sta7 were flocculated with strains of M. alpina (NVP17b, NVP47, and NVP153) with aggregates exhibiting fatty acid profiles similar to C. reinhardtii, with ARA (3-10 % of total fatty acids). This study showcases M. alpina as a strong bio-flocculation candidate for microalgae and advances a mechanistic understanding of algal-fungal interaction.

Nanobubble technology in anaerobic digestion: A review.

Nanobubble technology has significant potential to improve the anaerobic digestion (AD) process by ameliorating the rate-limiting steps of hydrolysis and methanogenesis, as well as providing process stability by reducing sulfide and volatile fatty acid (VFA) levels. Nanobubbles (NB) can enhance substrate accessibility, digestibility, and enzymatic activity due to their minuscule size, high electrostatic interaction, and ability to generate reactive oxygen species. Air- and O2-NB can create a microaerobic environment for higher efficiency of the electron transport system, thereby reducing VFAs through enhanced facultative bacterial activity. Additionally, H2- and CO2-NB can improve hydrogenotrophic methanogenesis. Recently, several studies have employed NB technology in the AD process. There is, however, a lack of concise, synthesized information on NB applications to the AD process. This review provides an in-depth discussion on the NB-integrated AD process and the putative mechanisms involved. General discussions on other potential applications and future research directions are also provided.