Comprehensive evaluation of a cost-effective method of culturing Chlorella pyrenoidosa with unsterilized piggery wastewater for biofuel production

Simultaneous bioremediation of petroleum hydrocarbons and production of biofuels by the micro-green alga, cyanobacteria, and its consortium

There are two major problems in the world, fuel deficiency and environmental pollution by fossil fuels. Microalgae are regarded as one of the most feasible feedstocks for the manufacturing of biofuels and are used in the degradation of fossil fuel spills. The present study was possessed to investigate the ability of green alga Chlorella vulgaris, blue-green alga Synechococcus sp, and its consortium to grow and degrade hydrocarbon such as kerosene (k) with different concentrations (0, 0.5, 1, and 1,5%), and also using algal biomasses to produce biofuel. The algal growth was estimated by optical density (O.D) at 600 nm, pigment contents such as Chlorophyll a,b carotenoid, and dry weight. The kerosene degradation was estimated by FT-IR analysis after and before the cultivation of algae and its consortium. The components of the methanol extract were determined by GC-MS spectroscopy. The results denote the best growth was determined by O.D, algae consortium with 1.5% Kerosene after ten days, meanwhile, the highest dry weight was with C. vulgaris after ten days of cultivation. The FT-IR demonstrated the algae and consortium possessed high efficacy to degrade kerosene. After 15 days of algae cultivation with 1% K, C.vulgaris produced the maximum amount of lipids (32%). The GC-MS profile of methanol extract of two algae and consortium demonstrated that Undecane was presented in high amounts, C.vulgaris (19.9%), Synechococcussp (82.16%), algae consortium (79.51%), and also were presented moderate amounts of fatty acid methyl ester in Synechococcus sp. Overall, our results indicate that a consortium of algae can absorb and remove kerosene from water, and at the same time produce biofuels like biodiesel and petroleum-based fuels.

A Low-Cost Fertilizer Medium Supplemented with Urea for the Lutein Production of Chlorella sp. and the Ability of the Lutein to Protect Cells against Blue Light Irradiation

This study aimed to investigate the use of organic fertilizers instead of modified f/2 medium for Chlorella sp. cultivation, and the extracted lutein of the microalga to protect mammal cells against blue-light irradiation. The biomass productivity and lutein content of Chlorella sp. cultured in 20 g/L fertilizer medium for 6 days were 1.04 g/L/d and 4.41 mg/g, respectively. These values are approximately 1.3- and 1.4-fold higher than those achieved with the modified f/2 medium, respectively. The cost of medium per gram of microalgal biomass reduced by about 97%. The microalgal lutein content was further increased to 6.03 mg/g in 20 g/L fertilizer medium when supplemented with 20 mM urea, and the cost of medium per gram lutein reduced by about 96%. When doses of ≥1 μM microalgal lutein were used to protect mammal NIH/3T3 cells, there was a significant reduction in the levels of reactive oxygen species (ROS) produced by the cells in the following blue-light irradiation treatments. The results show that microalgal lutein produced by fertilizers with urea supplements has the potential to develop anti-blue-light oxidation products and reduce the economic challenges of microalgal biomass applied to carbon biofixation and biofuel production.

Effects of C/N ratio on the growth and protein accumulation of heterotrophic Chlorella in broken rice hydrolysate

BACKGROUND

Microalgae protein is considered as a sustainable alternative to animal protein in the future. Using waste for microalgal culture can upgrade low-value raw materials into high-value products, helping to offset the cost of microalgal protein production. In this study we explored the feasibility of using microalgae heterotrophic fermentation to convert broken rice hydrolysate (BRH) into protein.

RESULTS

The results showed that the increase of BRH supplemental ratio was beneficial to the increase of biomass production but not beneficial to the increase of intracellular protein content. To further improve protein production, the effect of C/N ratio on intracellular protein accumulation was studied. It was found that low C/N ratio was beneficial to the synthesis of glutamate in microalgae cells, which in turn promoted the anabolism of other amino acids and further the protein. When the C/N ratio was 12:1, the biomass productivity and protein content could reach a higher level, which were 0.90 g/L/day and 61.56%, respectively. The obtained Chlorella vulgaris biomass was rich in essential amino acids (41.80%), the essential amino acid index was as high as 89.07, and the lysine content could reach up to 4.05 g/100 g.

CONCLUSIONS

This study provides a theoretical basis and guidance for using Chlorella vulgaris as an industrial fermentation platform to convert broken rice into products with high nutritional value.

Performance and mechanism of Chlorella in swine wastewater treatment: Roles of nitrogen-phosphorus ratio adjustment and indigenous bacteria

The effects of adjusting the nitrogen-phosphorus (N/P) ratio of wastewater and indigenous bacteria on swine wastewater treatment by Chlorella sp. HL were investigated. The optimal N/P ratio of Chlorella in swine wastewater was 20 by adjusting the phosphorus concentration. The participation of indigenous bacteria increased total extracellular polymeric substances content, which was beneficial to maintain the stability of the algal-bacterial consortium, and improved the algal density and the removal rate of total nitrogen, total phosphorus, and chemical oxygen demand by 47.8%, 24.0%, 30.7%, and 326.7%, respectively. Proteobacteria was the dominant phylum with the relative abundance of 71.58% in the algal-bacterial system at optimal N/P ratio, and Brevundimonas, Chryseobacterium, and Pseudomonas played positive roles in the establishment of symbiotic systems at the genus level. These results provide a theoretical basis for the construction of an efficient algal-bacterial symbiotic system in swine wastewater treatment and support for commercial scale-up.

Mixotrophic microalgal-biofilm reactor augmenting biomass and biofuel productivity

The present work aimed to evaluate the mixotrophic growth of Chlorella pyrenoidosa in a microalgal-biofilm reactor (MBR) using waste glycerol as an organic carbon source. The biomass productivity of C. pyrenoidosa (10.14 g m^-2 d^-1) under the mixotrophic mode was remarkably higher than that observed during the phototrophic mode (4.16 g m^-2 d^-1), under similar incubation conditions. The hydraulic retention time (HRT) of 6 d was found optimal for the higher productivity of microalgae in the MBR. Notably, based on biofuel quality, mixotrophically grown microalgal biomass was noted to have better suitability for biomethane production compared to biodiesel. Besides, up to 98.09, 75.74, and 55.86% removal of phosphate, nitrate, and COD, respectively, was recorded within 6 d under mixotrophic growth. Overall, the present findings magnificently demonstrate the efficient recycling of waste glycerol for higher biomass production coupled with phycoremediation using mixotrophic MBR.

Bioethanol production from Chlorella vulgaris ESP-31 grown in unsterilized swine wastewater

The potential of microalgae to remove nutrients from swine wastewater and accumulate carbohydrates was examined. Chlorella sorokiniana AK-1 and Chlorella vulgaris ESP-31 were grown in 10% unsterilized swine wastewater and obtained a maximum carbohydrate content and productivity of 42.5% and 189 mg L^-1d^-1, respectively. At 25% wastewater and 25% BG-11 concentration, the maximum carbohydrate productivity and total nitrogen removal efficiency of C. vulgaris ESP-31 were improved to 266 mg L^-1d^-1 and 54.2%, respectively. Further modifications in light intensity, inoculum size, and harvesting period enhanced the biomass growth, carbohydrate concentration, and total nitrogen assimilation to 3.6 gL^-1, 1.8 gL^-1, and 92.2%, respectively. Ethanol fermentation of the biomass resulted in bioethanol yield and concentration of 84.2% and 4.2 gL^-1, respectively. Overall, unsterilized swine wastewater was demonstrated as a cost-effective nutrient source for microalgal cultivation which further increases the economic feasibility and environmental compatibility of bioethanol production with concomitant swine wastewater treatment.

Screening of the dominant Chlorella pyrenoidosa for biofilm attached culture and feed production while treating swine wastewater

This research 12 microalgal species were screened for biofilm attached culture in the treatment of anaerobically digested swine wastewater (ADSW). The influence of ADSW on biomass productivity and removal efficiencies were evaluated using biofilm attached culture with the selected Chlorella pyrenoidosa. The variation of nutritional components from algal cells were further analysed to evaluate the potential applications of C. pyrenoidosa. The results showed that C. pyrenoidosa had the highest tolerance to ADSW, and the highest removal efficiencies for wastewater pollutants were reached when cultured in 5 times diluted ADSW. These test conditions resulted in an algal cell biomass composed of 57.30% proteins, 14.87% extracellular polysaccharide, 3.08% crude fibre, 5.57% crude ash, 2.85% moisture. Amino acids in proteins contained 21.73% essential amino acids and the EAA/NEAA value was 0.64. The essential amino acid score indicates that the selected C. pyrenoidosa could be a good protein source for feed addition.

Microbial interspecific interaction and nitrogen metabolism pathway for the treatment of municipal wastewater by iron carbon based constructed wetland

In order to explore the pollutant removal performance and interspecific interaction in constructed wetland (CW) with Fe₀-C filler, constructed wetland with Fe₀-C filler (CW-Fe) and with ceramsite filler (CW-C) were set up. Besides, the nutrients removal and interspecific interaction were analyzed, and the results showed that total nitrogen (TN) removal efficiency of CW-Fe system without carbon source was lower than that in CW-C system though CW-Fe system could convert macro-molecular organic matter into micro-molecular organic matter. However, ammonia nitrogen (NH₄⁺-N) increase was observed in CW-Fe system with better total phosphorus (TP) removal performance. High-throughput sequencing showed that the microbial richness and abundance of Bacteroides, Firmicutes, Chlorofeli and Actinobacteria in the CW with Fe₀-C filler was significantly higher than with ceramsite filler. The interaction between two CWs was significantly different, and the functional enzymes abundance of nitrate nitrogen (NO₃^--N) to NH₄⁺-N transformation in CW-Fe system significantly increased.

Cultivating Chlorella sorokiniana AK-1 with swine wastewater for simultaneous wastewater treatment and algal biomass production

Swine wastewater is rich in nitrogen and organic carbon which are essential macronutrients for microalgal growth. Three indigenous microalgal strains (Chlorella sorokiniana AK-1, Chlorella sorokiniana MS-C1, and Chlorella sorokiniana TJ5) were examined for their growth capability in untreated swine wastewater. C. sorokiniana AK-1 showed the best tolerance towards swine wastewater, and obtained the highest biomass concentration (5.45 g/L) and protein productivity (0.27 g/L/d) when grown in 50% strength swine wastewater. Cell immobilization using sponge as the solid carrier further enhanced maximal biomass concentration and protein productivity to 8.08 g/L and 0.272 g/L/d, respectively. Reuse of microalgae loaded sponge resulted in an average biomass production and protein productivity of 6.51 g/L and 0.15 g/L/d, respectively. The COD, TN and TP removal efficiency for the swine wastewater was 90.1, 97.0 and 92.8%, respectively. This innovative swine wastewater treatment method has demonstrated excellent performance on simultaneous swine wastewater treatment and protein-rich microalgal biomass production.

Tribonema sp. and Chlorella zofingiensis co-culture to treat swine wastewater diluted with fishery wastewater to facilitate harvest

Cultivating microalgae on wastewaters is an effective way to produce algal biomass whereas harvesting microalgae is a costly operation. This study we examined the feasibility of co-culturing a high-value microalga with an auto-flocculating strain to enable efficient recovery of biomass. Experiments were conducted to co-cultivate Chlorella zofingiensis with Tribonema sp. on swine wastewater diluted by fishery wastewater under different conditions. The result showed the optimal inoculum ratio of Tribonema sp. to Chlorella zofingiensis was 1:1. The removal efficiencies of pollutants (NH₄⁺-N, TN, TP, and COD) and lipid content were high when the co-culture ratios of Tribonema sp. were high. Also, some larger chain fatty acids, specifically C20:5 and C22:6 were present when the two strains co-culture. The recovery efficiency increased with the increasing proportion of auto-flocculating Tribonema sp.. Algae co-culture has the potential to address limitations in substrate utilization by individual strains, also improve the recovery of biomass.

Evaluation of filamentous heterocystous cyanobacteria for integrated pig-farm biogas slurry treatment and bioenergy production

The study evaluates 36 filamentous heterocystous cyanobacteria for the treatment of biogas slurry from pig farm and the accumulation of biomass for bioenergy production. The results showed that only the strains B, J, and L were able to adapt to a 10% biogas slurry. The removal rates of ammonia nitrogen, total nitrogen, and total phosphorus for strains J and L were 92.46%-97.97%, 73.79%-79.90%, and 97.14%-98.46%, respectively, higher than that of strain B. Strain J had the highest biomass productivity and lipid productivity. Based on the biodiesel prediction results, it was concluded that strains J and L are more suitable for biodiesel production. The estimation of theoretical methane potential suggests that the algal biomass of strain J also have the desirable possibility of biogas generation. In summary, algal strain J (Nostoc sp.) offers great potential for biogas slurry treatment and for the production of bioenergy.

Simultaneous nutrition removal and high-efficiency biomass and lipid accumulation by microalgae using anaerobic digested effluent from cattle manure combined with municipal wastewater

BACKGROUND

Microalgae as a viable biodiesel feedstock show great potential to approach the challenges of energy shortage and environment pollution, but their economic feasibility was seriously hampered by high production cost. Thus, it is in urgent need to reduce the cost of cultivation and improve the biomass and lipid production of microalgae. In this work, anaerobic digestion effluent from cattle manure combined with municipal wastewater was used as a cost-effective medium for cultivating microalgae and expected to obtain high biomass. The pretreatment of anaerobic digested effluent containing dilution rate, sterilization and nutrient optimization was investigated. Then, initial pH and light intensity for algal growth, lipid production and wastewater purification were optimized in this study.

RESULTS

Scenedesmus sp. could grow rapidly in 10% anaerobic digestion effluent from cattle manure combined with secondary sedimentation tank effluent without sterilization. Optimum nutrient additives for higher biomass were as follows: glucose 10 g/L, NaNO₃ 0.3 g/L, K₂HPO₄·3H₂O 0.01 g/L, MgSO₄·7H₂O 0.075 g/L and trace element A5 solution 1 mL/L. Biomass of 4.65 g/L and lipid productivity of 81.90 mg/L/day were achieved during 7-day cultivation accompanying over 90% of COD, NO₃ ^--N, NH₄ ⁺-N, and 79-88% of PO₄ ^3--P removal with optimized initial pH of 7.0 and light intensity of 5000 l×. The FAME profile in ADEC growth medium consisted in saturated (39.48%) and monounsaturated (60.52%) fatty acids with the 16- to 18-chain-length fatty acids constituting over 98% of total FAME.

CONCLUSIONS

This study proves the potential of anaerobic digested effluent combined with municipal wastewater for microalgae culture, and provides an effective avenue for simultaneous microalgal lipid production and treatment of two kinds of wastewater.