Comparison of the Performance and Microbial Community Structure of Two Outdoor Pilot-Scale Photobioreactors Treating Digestate

Abstract

This study aimed at examining and comparing the nutrient removal efficiency, biomass productivity and microbial community structure of two outdoor pilot-scale photobioreactors, namely a bubble column and a raceway pond, treating the liquid fraction of an agricultural digestate. Bacterial and eukaryotic communities were characterized using a metabarcoding approach and quantitative PCR. The abundance, composition, diversity, and dynamics of the main microbes were then correlated to the environmental conditions and operational parameters of the reactors. Both photobioreactors were dominated either by Chlorella sp. or Scenedesmus sp. in function of temperature, irradiance and the nitrogen compounds derived by nitrification. Other species, such as Chlamydomonas and Planktochlorella, were sporadically present, demonstrating that they have more specific niche requirement. Pseudomonas sp. always dominated the bacterial community in both reactors, except in summertime, when a bloom of Calothrix occurred in the raceway pond. In autumn, the worsening of the climate conditions decreased the microalgal growth, promoting predation by Vorticella sp. The study highlights the factors influencing the structure and dynamics of the microbial consortia and which ecological mechanisms are driving the microbial shifts and the consequent reactor performance. On these bases, control strategies could be defined to optimize the management of the microalgal-based technologies.

The structure and diversity of microalgae-microbial consortia isolated from various local organic wastes

“…Thus, the results described above seem to suggest that Tetradesmus survived in organic wastes that were not characterized for extreme chemical-biological parameters, unlike Chlorella, which seemed to be much less affected by chemical-biological parameters of the organic wastes. On the other hand, the presence of Tetradesmus excluded (or strongly reduced) the presence of Chlorella, suggesting that in the absence of extreme growing conditions the former, when present, grew better than the latter (Bani et al, 2020). This fact suggested that extreme chemical-biological parameters selected Chlorella.…”

“…The driving forces structuring microbial communities are concurrently regulated by both external factors such as chemical-biological parameters of the growth media and internal factors such as the interaction between eukaryotes and prokaryotes (Bani et al, 2020).…”

Algae as Feedstuff for Ruminants: A Focus on Single-Cell Species, Opportunistic Use of Algal By-Products and On-Site Production

“…The alternative could come in the form of algae by-products sourced from biotechnological industries. Industries of importance include fuel production [8] and when algae are used as biofilters to remove nutrients or contaminants [9,10] or to ameliorate carbon emission from various factories [11]. The concept of biofilters is of particular interest in extensive grazing systems of northern Australia since it has the potential to be linked to the development of silvopastoral plans for rehabilitating mine sites with the algae produced in wastewater being used as feed for livestock or organic fertilizer during the implantation of trees or to increase pastures productivity.…”

Microalgae: A Promising Future

“…Outdoor open systems (i.e., raceway ponds, bubble columns, flat panels) are considered so far as the most viable method of microalgal cultivation on wastewaters [ 13 ], even if complex and dynamic microbial consortia are formed inside [ 14 , 15 ]. A contribution to this field derives from a study, included in this Special Issue, which examined and compared the nutrient removal efficiency, biomass productivity, and microbial community structure of two outdoor pilot-scale photobioreactors (bubble column and raceway pond) [ 13 ].…”

“…Outdoor open systems (i.e., raceway ponds, bubble columns, flat panels) are considered so far as the most viable method of microalgal cultivation on wastewaters [ 13 ], even if complex and dynamic microbial consortia are formed inside [ 14 , 15 ]. A contribution to this field derives from a study, included in this Special Issue, which examined and compared the nutrient removal efficiency, biomass productivity, and microbial community structure of two outdoor pilot-scale photobioreactors (bubble column and raceway pond) [ 13 ]. Data obtained, including the characterization of bacterial and eukaryotic communities using a metabarcoding approach and quantitative PCR, highlighted a different behavior and a different composition of the microbial communities, which were subjected to variations of the environmental conditions as well as of the reactors’ operational parameters.…”