Cultivation of Chlorella vulgaris in sludge extracts: Nutrient removal and algal utilization

Algal-mediated nitrogen removal and sustainability of algal-derived dissolved organic matter supporting denitrification

Algae-mediated nitrogen removal from low carbon vs. nitrogen (C/N) wastewater techniques has garnered significant attention due to its superior autotrophic assimilation properties. This study investigated the ammonium-N removal potential of four algae species from low C/N synthetic wastewater. Results showed that 95 % and 99 % of ammonium-N are eliminated at initial concentrations of 11.05 ± 0.98 mg/L and 42.51 ± 2.20 mg/L with little nitrate and nitrite accumulation. The compositions of secreted algal-derived dissolved organic matter varied as C/N decreased and showed better bioavailability for nitrate-N removal by Pseudomonas sp. SZF15 without pre-oxidation, achieving an efficiency of 99 %. High-throughput sequencing revealed that the aquatic microbial communities, dominated by Scenedesmus, Kalenjinia, and Micractinium, remain relatively stable across different C/N, aligning with the underlying metabolic pathways. These findings may provide valuable insights into the sustainable elimination of multiple nitrogen contaminants from low C/N wastewater.

pH-Responsive Eco-Friendly Chitosan–Chlorella Hydrogel Beads for Water Retention and Controlled Release of Humic Acid

For improving the mechanical strength of controlled release fertilizer (CRF) hydrogels, a novel material of Chlorella was employed as a bio-based filler to prepare chitosan–chlorella hydrogel beads with physical crosslink method. Here, the synthesis mechanism was investigated, and the chitosan–chlorella hydrogel beads exhibited enhanced mechanical stability under centrifugation and sonication than pure chitosan hydrogel beads. Chlorella brought more abundant functional groups to original chitosan hydrogel, hence, chitosan–chlorella hydrogel beads represented greater sensitivity and controllable response to external factors including pH, salt solution, temperature. In distilled water, the hydrogel beads with 40 wt% Chlorella reached the largest water absorption ratio of 42.92 g/g. Moreover, the mechanism and kinetics process of swelling behavior of the chitosan–chlorella hydrogel beads were evaluated, and the loading and releasing of humic acid by the hydrogel beads as a carrier material were pH-dependent and adjustable, which exhibit the potential of chitosan–chlorella hydrogel beads in the field of controlled release carrier biomaterials.

Application of phagotrophic algae in waste activated sludge conversion and stabilization

Phagotrophic algae can consume bacteria that are the predominant microorganisms present in the waste activated sludge (WAS) generated from municipal wastewater treatment processes. In this study, we developed a combined ultrasonication-phagotrophic algal process for WAS conversion. The ultrasonic pretreatment released small volatile solids (VS) including bacteria from WAS flocs. A phagotrophic alga Ochromonas danica then grew by consuming more than 80% of the released VS, with approximately 30% (w/w) algal cell yield. The process reduced the overall WAS VS by 42.4% in 1 day, comparing very favorably with the 27% reduction in 10 days by aerobic digestion. For stabilizing the solids remaining from the ultrasonic step, the total oxygen uptake required was 65%-92% lower than that for the original WAS, indicating substantially reduced aeration cost. Overall, this novel process enhanced the WAS digestion at lower energy requirements and produced microalgae for other potential uses. © 2021 Water Environment Federation PRACTITIONER POINTS: At least 80% of released VS from WAS can be processed by phagotrophic algae. Significant amounts of algae can be produced from WAS. Ultrasonication-phagotrophic algal process can make sludge management more sustainable.

Auto-flocculation microalgae species Tribonema sp. and Synechocystis sp. with T-IPL pretreatment to improve swine wastewater nutrient removal

It is recognized coupling microalgae, which is rich in lipids or protein with wastewater treatment offers extra economic benefits that can potentially make microalgal production feasible by reducing production costs and providing environmental benefits. However, the pretreatment of high concentration nutrients such as ammonia nitrogen (NH₃-N), total phosphorus (TP) and chemical oxygen demand (COD) in swine wastewater is the premise of application for microalgae in wastewater treatment. This study two auto-flocculation microalgae Tribonema sp. and Synechocystis sp. were selected for evaluation; they were cultivated in diluted swine wastewater together after it was pretreated with titanium dioxide (TiO₂) plus intense pulsed light (T-IPL). The results showed that the growth of the two strains in the wastewater pretreated with T-IPL grew better than when grown without the pretreatment. The content of lipid in the two algae, cultured in the pretreated wastewater, was also higher than the lipid content from the un-pretreated wastewater; but protein content was lower. Overall, the removal efficiencies of pollutants NH₃-N, TP, and COD by the two microalgae in anaerobic digestion of swine wastewater (ADSW) with T-IPL pretreatment, were higher than the removal efficiencies without pretreatment. This research also indicates that these two auto-flocculation microalgae have the potential to reduce harvesting costs. And, using T-IPL to pretreat wastewater could provide a promising method for the pretreatment of wastewater.

Bioremediation and biomass production of microalgae cultivation in river watercontaminated with pharmaceutical effluent

This work evaluated the potential of microalgae of Chlorella sp., SL7A, Chlorococcum sp., SL7B and Neochloris sp.,SK57 cultivated in river water contaminated with pharmaceutical effluent for biomass and lipid production. It has been observed that fast growing algae in this medium is Neochloris sp.SK57. Maximum biomass and lipid yield was obtained from Neochloris sp. SK57 (0.52 g/l) and Chlorococcum sp. SL7B (0.129 g/l)along with drycell weight of lipid was 28%.The increased in biomass and lipid in this media is could due to assimilation of organic nutrients and stress due to other components present in the river water. Fatty acid profile of algal biomass showed that saturated fatty acids production is enhanced in oils of Neochloris sp. SK57, and its suitability in food and fuel applications. Water quality of the river water was monitored before and after algal cultivation. Results showed that quality of river water was improved after algal cultivation.

Recent advances in downstream processing of microalgae lipid recovery for biofuel production

The world energy system faces two major challenges: the requirement for more energy and less carbon. It is important to address biofuels production as an alternative to the usage of fossil fuel by utilizing microalgae as the potential feedstock. Yet, the commercialization of microalgae remains contentious caused by factors relating to the life cycle assessment and feasibility of microalgae-based biofuels. This present review starts with an introduction to the benefits of microalgae, followed by intensive elaboration on microalgae cultivation parameters. Subsequently, the fundamental principle along with the advantages and disadvantages of various pretreatment techniques of microalgae were reviewed. In addition, the conventional and recent advances in lipid extraction techniques from microalgae were comprehensively evaluated. Comparative analysis regard to the gaps from previous studies was discussed point-by-point in each section. The effort presented in this review will provide an insight for future researches dealing with microalgae-biofuel production on downstream processing.

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.

Hydrothermal pretreatment of salvaged cyanobacteria and use of pretreated medium for cultivating Scenedesmus obliquus

This work studied the hydrothermal Pretreatment of Salvaged Cyanobacteria and used the pretreated slurry as medium for cultivating Scenedesmus obliquus. The cyanobacterial slurry was pretreated by chemical oxidation, hydrothermal treatment and hydrothermal oxidation, and then the cultivation experiment of oil-producing microalgae (Scenedesmus obliquus) was carried out. The results showed that hydrothermal oxidation could transform the hard-to-treat salvaged cyanobacteria into culture medium for microalgae. The oil yield from S. obliquus cultured in that was higher than that in conventional BG11 medium.

High-value chemicals from Botryococcus braunii and their current applications - A review

Botryococcus braunii is known for its high yield of extracellular hydrocarbons and polysaccharides. Hydrocarbons, especially botryococcenes and squalene can be used as not only fuels but also alternative feedstock for other fossil-based products. Exopolysaccharides excreted from B. braunii can be used as scaffolds for polyesters production, and have a notable potential for synthesis of nanoparticles. B. braunii is also a rich source of carotenoids, especially the unique secondary carotenoids such as botryoxanthins that have never been found in other microalgae. The morphology, physiology, and outer cell walls of B. braunii are complex. Understanding the colony structure shall provide insights into the mechanism of cell growth and chemicals secretion. It is possible to improve the production economics of the alga with advanced culture systems. Moreover, investigation of metabolic pathways for B. braunii may help us understand their regulation and provide valuable information for strain selection and optimal production of high-value chemicals.