Chlorella pyrenoidosa cultivation in outdoors using the diluted anaerobically digested activated sludge

Effect of solar and artificial lighting on microalgae cultivation and treatment of liquid digestate

A comparative study was carried out to assess the effect of two light sources on microalgae cultivation and the treatment of liquid digestate. The R1 photobioreactor operated with LED lightning allowed to achieve moderate nutrient removal rates whereas soluble COD (Chemical Oxygen Demand) was reduced in 90%. After switching this reactor into sunlight, the removal rate of phosphates increased to 66%. However, the greatest removal rate of both nutrients and sCOD of up to 93% was observed in the R2 photobioreactor operated only under sunlight. Microglena sp. was the dominant algae growing in the R1 reactor, and the main bacteria families detected were Chitinophagaceae, Sphingomonadaceae and Xanthobacteraceae. In contrast, Tetradesmus obliquus dominated in the R2 reactor and Rhodanobacteraceae, Chitinophagaceae and A4b were predominant bacteria in this run. Furthermore, much greater biomass productivity as well as overall biomass density was observed in the R2 photobioreactor cultivated exclusively with solar lightning.

Rhizopus oryzae fermentation wastewater nutrient removal coupling protein fodder production by employing Chlorella pyrenoidosa

The scenario was to investigate feasibilities of employing Chlorella pyrenoidosa for Rhizopus oryzae fermentation wastewater nutrient removal coupling protein fodder production. Results stated that TN, TP, NH₃-N, COD, BOD removal reached 99.79%, 94.70%, 98.80%, 97.60%, 99.60% to acquire discharge permit under fed-batch manipulation, whilst the peaked protein yield (19.94 g/L) was 6.04-fold more than batch manipulation. Rhizopus oryzae fermentation wastewater feeding C. pyrenoidosa was praised as high-quality protein not only with 26.78% essential amino acids and essential amino acids/nonessential amino acids value of 0.84 but also pathogenic bacteria and heavy metal loads complying with fodder standards. In vitro digestibility of dry matter, protein, lipid, and starch achieving 80.07%, 92.13%, 95.93%, 91.9% and bioavailability of polypeptides, triglycerides, free fatty acids, and oligosaccharides displaying 98.67%, 87.12%, 93.86%, 30.21%, which were roughly-equivalent to corn/soybean fodder. The findings formed exemplifications in utilizing other microalgal systems for wastewater nutrient removal coupling chemicals production.

Differences in adaptation to light and temperature extremes of Chlorella sorokiniana strains isolated from a wastewater lagoon

Presently, two Chlorella sorokiniana strains sampled during summer (CS-S) and winter (CS-W) from a maturation pond and isolated by dominance were studied on their behavior on temperature and light extremes in batch experiments. Although both strains showed no differences in their tolerance of temperatures up to 45 °C, the growth rates, pigment contents and fatty acid compositions in response to PAR at 700 and 1,500 µmol m^-2sec^-1 differed. CS-W was less affected by photoinhibition and maintained constantly high growth rates. High radiation resulted in both strains in an equivalent decrease of chlorophyll a and accessory pigments indicating that the latter did not function as a light filter. PUFAS (18:3 and 16:3) increased in CS-W at high radiation by > 60% and decreased in CS-S by 8 %. Results indicate that CS-W is highly favorable for mass cultivation particularly in outdoors, in which diurnal variations of solar radiation occur.

Lipids production and nutrients recycling by microalgae mixotrophic culture in anaerobic digestate of sludge using wasted organics as carbon source

Insufficient organics in anaerobic digestate of sludge limited algal mixotrophic culture and caused low lipids production. In this study, enhancing lipids production and pollutants removal by adding acidified starch wastewater was tested for Chlorella pyrenoidosa mixotrophic culture. The results showed that an optimal addition of acidified starch wastewater into anaerobic digestate of sludge (1:1, v/v) improved biomass and lipids production by 0.5-fold (to 2.59 g·L^-1) and 3.2-fold (87.3 mg·L^-1·d^-1), respectively. The acidified starch wastewater addition also improved the quality of algal biodiesel with higher saturation (typically in C16:0 and C18:0). In addition, 62% of total organic carbon, 99% of ammonium and 95% of orthophosphate in mixed wastewater were effectively removed by microalgae. This study provides a promising way to improve biodiesel production and nutrients recovery from anaerobic digestate of sludge using waste carbon source.

Cultivation of Chlorella vulgaris on unsterilized dairy-derived liquid digestate for simultaneous biofuels feedstock production and pollutant removal

In order to assess viability of microalgae cultivation using unsterilized dairy-derived liquid digestate (DLD) for simultaneous biofuels feedstock production and contaminant removal, four DLD concentrations (25%, 50%, 75% and 100%) were used to grow Chlorella vulgaris in batch photobioreactors (PBRs). The 25% DLD was an ideal alternative medium in that high growth rate (0.69 d^-1), high lipid productivity (112.9 mg L^-1 d^-1) as well as high nutrient removal were attained. The high DLD concentration caused inhibition of microalgal growth, where COD was more inhibitive than ammonium. The presence of bacteria did not influence microalgae production because of limited growth. Microalgal growth reduced the richness and diversity of bacterial community. Furthermore, the species of Bacteroidetes, Candidatus Saccharibacteria, and Chlamydiae rather than Proteobacteria benefited microalgal-bacterial symbiosis. These findings contribute to better application of microalgal-bacterial system for large-scale microalgae cultivation as well as environmental sustainability.

Cultivation of Chlorella pyrenoidosa in anaerobic wastewater: The coupled effects of ammonium, temperature and pH conditions on lipids compositions

Anaerobic wastewater potentially was an ideal medium for cultivating microalgae. The coupled effect of ammonium, temperature and pH on lipids accumulation was a core issue during algal culture using anaerobic wastewater. Therefore, their combined effects on Chlorella pyrenoidosa culture and lipids accumulation in anaerobic effluent were investigated. Free ammonia induced from the rising pH and temperature inhibited algal growth, but significantly promoted lipid accumulation. The highest lipids content reached 30.2% when pH rose to 8.3-8.5 (25 °C, ammonium 280 mg/L), which was 1.6-fold higher than that under neutral condition. Moreover, the percentage of unsaturated fatty acids (un-SFAs) increased to 74.8-77.9% at pH 8.3-8.5, whereas it was only 56.1-58.9% under neutral condition. The C18:2 and C18:3 dominated the un-SFAs increase at high pH, typically the percentage of C18:3 increased by 74.5-153.1%. This study provides a potential way for lipid accumulation in algal culture using anaerobic wastewater.

Integrated anaerobic digestion and algae cultivation for energy recovery and nutrient supply from post-hydrothermal liquefaction wastewater

Post-hydrothermal liquefaction wastewater (PHWW), which contains approximately 80% of original feedstock resources, shows great potential to achieve sustainable development of an environment-enhancing energy system. A combination of anaerobic digestion and algae cultivation was proposed for methane recovery and nutrient supply from PHWW. Granular activated carbon (GAC) and ozone were used to enhance energy recovery from the PHWW. The results indicated that with GAC addition, the maximum methane yield increased by 67.7%-228 mL/g COD_removal. In addition, Chlorella vulgaris displayed optimal growth in a 5-fold diluted digestate with a 2.32 g/L maximum biomass content and 180 mg/(L·d) biomass production rate. The total energy yield was 565 kJ/g COD, which was 27.4 times higher than that without GAC. Integration of anaerobic digestion and algae cultivation, particularly with GAC addition during fermentation, is a feasible and advantageous process for energy recovery from PHWW.

Lipid accumulation of Chlorella pyrenoidosa under mixotrophic cultivation using acetate and ammonium

Acetate and ammonium were used as organic carbon and nitrogen sources, respectively, during mixotrophic cultivation of Chlorella pyrenoidosa. Cell growth, content of neutral lipid (NL), productivity of biomass and total lipid, and fatty acid profiles were investigated. Results showed that C. pyrenoidosa could endure high concentrations of NH₄⁺-N (100-200 mg/L) and immediately entered logarithmic growth, when the culture media contained 2.0-10.0 g/L NaAc. The 2.0-10.0 g/L NaAc in the media also resulted in the NL content of 1.87-3.05 mg/10⁹cells, much higher than 0.5 mg/10⁹cells of the controls. The maximum productivities of biomass and total lipid were achieved under 50 and 10 mg/L NH₄⁺-N respectively when the 2.0 g/L NaAc was dosed. The fatty acids were mainly composed of C16:0, C16:1, C18:0, and C18:1 under the mixotrophic cultivation, with the higher saturation compared to the controls.

Utilization of centrate from urban wastewater plants for the production of Scenedesmus sp. in a raceway-simulating reactor

This work investigates the production of the native microalgae strain Scenedesmus sp. in semi-continuous mode at lab scale in open raceway-simulating reactors and using centrate as the culture medium. The biomass productivity and nutrient removal capacity of Scenedesmus sp. at different dilution rates were investigated indoors as well as its tolerance to centrate as the culture medium at different concentrations. A biomass productivity of 7.80 g/m² day was obtained at 200 μE/m² s, 5 cm culture depth, 0.30 1/day of dilution rate and 60% centrate while nitrogen and phosphorus removal rates were 1.50 g/m² day and 0.15 g/m² day, respectively. The produced biomass characterization under these conditions showed a lipid content of 12.60% d wt. along with a favorable fatty acids profile with 57.70% of total fatty acids composed of saturated and monounsaturated fatty acids. Subsequently, the effect of light intensity and culture depth on biomass productivity and nutrient uptake as well as the biochemical composition and fatty acids profile was studied using two irradiance levels (200 and 1000 μE/m² s) and four culture depths (5 cm, 10 cm, 15 cm and 20 cm). Under optimal conditions of 1000 μE/m² s, 60% centrate, 0.30 1/day dilution rate and 15 cm culture depth, a maximum biomass productivity of 22.20 g/m² day was obtained. Nitrogen and phosphorus removal rates of 2.00 gN/m² day and 0.40 gP/m² day, respectively, were recorded. An amount of 11.70% d wt. of lipids was determined along with a suitable fatty acids profile for biofuel production.