Microalgae have a wide industrial potential because of their high metabolic diversity and plasticity. Selection of optimal cultivation methods is important to optimize multi-purpose microalgal biotechnologies. In this research, Chlorella sorokiniana AM-02 that was isolated from a freshwater lake was cultured under various high photosynthetic photon flux density (PPFD) conditions and CO2 gas levels in standard Bold’s basal medium (BBM). Furthermore, a wide range of nitrate levels (180–1440 mg L−1) was tested on the growth of C. sorokiniana. Microalgae growth, pigment concentration, medium pH, exit gas composition, as well as nitrate, phosphate, and sulfate levels were measured during an experimental period. The preferred high PPFD and optimal CO2 levels were found to be 1000–1400 μmol photons m−2 s−1 and 0.5–2.0% (v/v), respectively. The addition of nitrate ions (up to 1440 mg L−1) to the standard growth medium increased final optical density (OD750), cell count, pigment concentration, and total biomass yield but decreased the initial growth rate at high nitrate levels. Our findings can serve as the basis for a robust photoautotrophic cultivation system to maximize the productivity of large-scale microalgal cultures.
In this work, the impact of granular activated carbon (GAC) on the mesophilic and thermophilic anaerobic digestion of chicken manure and the structure of microbial communities was investigated. These results demonstrated that GAC supplementation effectively enhanced the consumption of produced organic acids in the mesophilic and thermophilic batch tests, accompanied by faster biomethane production in the presence of GAC than from reactors without GAC. However, since the free ammonia level was 3–6 times higher in the thermophilic reactors, this led to the instability of the anaerobic digestion process of the nitrogen-rich substrate at thermophilic temperatures. Bacteroidia and Clostridia were the two main bacterial classes in the mesophilic reactors, whereas the class Clostridia had a competitive advantage over other groups in the thermophilic systems. The archaeal communities in the mesophilic reactors were mainly represented by representatives of the genera Methanosarcina, Methanobacterium, and Methanotrix, whereas the archaeal communities in the thermophilic reactors were mainly represented by members of the genera Methanosarcina, Methanoculleus, and Methanothermobacter. New data obtained in this research will help control and manage biogas reactors in the presence of GAC at different temperatures.
Anaerobic digestion is an important technology to receive energy from various types of biomass. In this work, the impact of granular activated carbon (GAC) on the mesophilic anaerobic co-digestion of sugar beet pulp and distillers grains was investigated. After a short period, anaerobic reactors began to produce biomethane and were ready for completion within 19–24 days. The addition of GAC to reactors (5–10 g L−1) significantly enhanced the methane production rate and consumption of produced volatile fatty acids. Thus, the maximum methane production rate increased by 13.7% in the presence of GAC (5 g L−1). Bacterial and archaeal community structure and dynamics were investigated, based on 16S rRNA genes analysis. The abundant classes of bacteria in GAC-free and GAC-containing reactors were Clostridia, Bacteroidia, Actinobacteria, and Synergistia. Methanogenic communities were mainly represented by the genera Methanosarcina, Methanoculleus, Methanothrix, and Methanomassiliicoccus in GAC-free and GAC-containing reactors. Our results indicate that the addition of granular activated carbon at appropriate dosages has a positive effect on anaerobic co-digestion of by-products of the processing of sugar beet and ethanol distillation process.
The cultivation of microalgae requires the selection of optimal parameters. In this work, the effect of various forms of nitrogen on the growth and productivity of Chlorella sorokiniana AM-02 when cultivated at different temperatures was evaluated. Regardless of the temperature conditions, the highest specific growth rate of 1.26 day−1 was observed in modified Bold’s basal medium (BBM) with NH4+ as a nitrogen source, while the highest specific growth rate in BBM with NO3− as a nitrogen source achieved only 1.07 day−1. Moreover, C. sorokiniana grew well in medium based on anaerobic digester effluent (ADE; after anaerobic digestion of chicken/cow manure) with the highest growth rate being 0.92 day−1. The accumulation of proteins in algal cells was comparable in all experiments and reached a maximum of 42% of dry weight. The biomass productivity reached 0.41–0.50 g L−1 day−1 when cultivated in BBM, whereas biomass productivity of 0.32–0.35 g L−1 day−1 was obtained in ADE-based medium. The results, based on a bacterial 16S rRNA gene sequencing approach, revealed the growth of various bacterial species in ADE-based medium in the presence of algal cells (their abundance varied depending on the temperature regimen). The results indicate that biomass from C. sorokiniana AM-02 may be sustainable for animal feed production considering the high protein yields.
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