Effects of light intensity on biomass, carbohydrate and fatty acid compositions of three different mixed consortia from natural ecological water bodies

Bio-coatings in permeated cultivation systems: Unprecedented impacts on microalgal monoculture growth and organic matter yield

Bio-coating, a recent and promising approach in attached microalgal cultivation systems, has garnered attention due to its efficiency in enhancing immobilized algal growth, particularly in submerged cultivation systems. However, when the cells are cultured on thin solid microporous substrates that physically separate them from the nutrient medium, it remains unclear whether the applied bio-coatings still have a significant impact on algal growth or the subsequent rates of algal organic matter (AOM) release. Therefore, this current work investigated the role of bio-coatings on the microalgal monoculture growth of one freshwater species, Chlorella vulgaris ESP 31, and one marine species, Cylindrotheca fusiformis on a hydrophilic substrate, polyvinylidene fluoride membrane in a permeated cultivation system. Wide range of bio-coating sources were adapted, with the result demonstrating that bacteria-derived coating promoted algal growth by as high as 140% when compared with the control group for both species. Interestingly, two distinct adaptation mechanisms were observed between the species, with only C. fusiformis demonstrating a positive correlation between cell growth and AOM productivity, particularly in its extracellularly bound fractions. It is worth noting that despite this specific fraction exhibiting the lowest content among all; it displayed significant relevance in terms of AOM productivity. High extracellular protein-to-polysaccharide ratio (>5.7 fold) quantified on bacterial intracellular exudate-coated membranes indirectly revealed an underlying symbiotic microalgal-bacterial interaction. This is the first study showing how bio-coating influenced AOM yield without any physical interaction between microalgae and bacteria. It further confirms the practical benefits of bio-coating in attached cultivation systems.

Comprehensive modeling and predicting light transmission in microalgal biofilm

Biofilm-based microalgae culture combined with wastewater treatment is a promising biotechnology for environmental management. Light availability influences the accumulation of microalgal biomass and nutrient removal. A light attenuation model which comprehensively considered microalgal biofilm structure (density and biofilm thickness), pigments content, and extracellular polymeric substances content was developed to predict the light attenuation in biofilm according to the simplification of the radiative transfer equation. The predicted results were in good overall agreement with the experiment, with an average error of less than 9.02%. These factors (biofilm density, thickness, pigments content, and extracellular polymeric substances content) all contributed to the light intensity attenuation, but biofilm thickness caused the most dramatic attenuation under the same increment of relative change in actual culture. The scattering coefficient of the biofilm (0.433 m²/g) was less than that of the suspension (1.489 m²/g) under white incident light. It suggests that the dense structure of cells allows much light to be concentrated in the forward direction when transmitting. This model could be adopted to predict the light distribution in microalgal biofilm for the further design of efficient photobioreactors and the development of light optimization strategies.

Regulation of carbon source metabolism in mixotrophic microalgae cultivation in response to light intensity variation

Microalgae are one of the promising sources for renewable energy production, and the light intensity variation can affect the biofuel generation and carbon assimilation of mixotrophic microalgae. To reveal the response of carbon assimilation to light intensity, the effect of light intensity on the carbon source metabolism of Chlorella vulgaris under mixotrophic cultivation was investigated in this study. Moreover, the optimal carbon source composition for mixotrophic microalgae cultivation was evaluated using bicarbonate (HCO₃^-) and carbonate (CO₃^2-) as inorganic carbon sources, and glucose and acetate as organic carbon sources. The optimal light intensity for Chlorella vulgaris growth was at the range of 8000-12000 lux. For the accumulation of biochemical components, low light intensity was beneficial to protein accumulation, and high light intensity was advantageous for carbohydrate and lipid accumulation. With HCO₃^- and glucose, the maximum lipid content reached 37.0% at a light intensity of 12000 lux. The citrate synthase activity was negatively correlated with light intensity, showing an opposite trend to biomass production. High light intensity had a positive impact on Rubisco expression, which promoted the microalgae growth and carbon fixing. The energy produced by heterotrophic metabolic activities increased at low light intensity, and the enhancement of biomass production with high light intensity was mainly caused by the improved photoreaction efficiency during the mixotrophic cultivation.

Use of biomass-derived adsorbents for the removal of petroleum pollutants from water: a mini-review

Over the past decades, a large amount of petroleum pollutants has been released into the environment resulting from various activities related to petrochemicals. The discharge of wastewater with petrochemicals can pose considerable risk of harm to the human health and the environment. The use of adsorbents has received much consideration across the environmental field as an effective approach for organic pollutant removal. There is a particular interest in the use of biomass adsorbent as a promising environmentally-friendly and low-cost option for removing pollutants. In this article, we present a review of biomass-derived adsorbents for the removal of petroleum pollutants from water. The features of different adsorbents such as algae, fungi, and bacteria biomasses are summarized, as is the process of removing oil and PAHs using biomass-derived adsorbents. Finally, recommendations for future study are proposed.

Microbial co-culturing strategies for the production high value compounds, a reliable framework towards sustainable biorefinery implementation - an overview

The microbial co-cultures or consortia are a natural set of microorganisms formed from different species or the same species but different strains, in which members can interact with each other. The co-culture systems have wide variety of technological applications such as the production of foods, treatment of wastewater, removal of toxic substances, environmental recovery, and all these without the need to work in sterile conditions. Therefore, the need of understanding communication mechanisms between cell-to-cell within co-culture will allow to construct and to program their biological behavior from the use of complex substrates to produce biocompounds. The technology of co-culture systems enables the development of biorefinery platforms to obtain biofuels, and high value compounds through biomass transformation by sustainable process. This review focuses on understanding the roles of consortia microbial to design and built co-culture systems to produce high value compounds in terms a sustainable biorefinery.

Strategic implementation of phosphorus repletion strategy in continuous two-stage cultivation of Chlorella sp. HS2: Evaluation for biofuel applications

Lipid production in microalgae under nitrogen (N) starved condition can be enhanced by excess phosphorus (P) supply in the second stage of two-stage cultivation strategy. However, implementing two-stage cultivation is difficult in large-scale cultivation system as it requires high energy of transferring large algal biomass from first stage to second stage. To address this problem, we have optimized a continuous two-stage (CTS) cultivation strategy using Chlorella sp. HS2, where nitrogen in the growth environment is depleted naturally via consumption. To enhance both biomass and lipid productivity this strategy explored supplementation of additional P from 50% to 2500% of the initial concentration at the start of N-limited second stage of growth. The results of the optimization study in photobioreactor (PBR) showed that supplementing 500% of initial P and 100% of initial other nutrients (O) (N₀-P₅₀₀-O₁₀₀) on 5th day showed the maximum biomass productivity of 774.4 mg L^-1 d^-1. It was observed that Chlorella sp. HS2 grown in PBR yielded higher biomass (3.8 times), lipid (6.1 times) and carbohydrate (5.5 times) productivity in comparison to the open raceway ponds (ORP) study, under optimum nutrient and carbon supply condition. The maximum lipid (289.6 mg L^-1 d^-1) and carbohydrate (219.2 mg L^-1 d^-1) productivities were obtained in TPBR-3, which were 1.9 and 1.3 times higher than that of TPBR-2 (+ve control) and 9.6 and 3.7 times higher than that of TPBR-1 (-ve control), respectively. Fatty acid mainly composed of C₁₆/C₁₈ (84.5%-85.7%), which makes the microalgal oil suitable for biofuel production. This study concluded that feeding excess amount of P is an effective and scalable strategy to improve the biomass and lipid productivity of CTS cultivation.

Critical processes and variables in microalgae biomass production coupled with bioremediation of nutrients and CO2 from livestock farms: A review

Development of renewable and clean energy as well as bio-based fine chemicals technologies are the keys to overcome the problems such as fossil depletion, global warming, and environment pollution. To date, cultivation of microalgae using wastewater is regarded as a promising approach for simultaneous nutrients bioremediation and biofuels production due to their high photosynthesis efficiency and environmental benefits. However, the efficiency of nutrients removal and biomass production strongly depends on wastewater properties and microalgae species. Moreover, the high production cost is still the largest limitation to the commercialization of microalgae biofuels. In this review paper, the state-of-the-art algae species employed in livestock farm wastes have been summarized. Further, microalgae cultivation systems and impact factors in livestock wastewater to microalgae growth have been thoroughly discussed. In addition, technologies reported for microalgal biomass harvesting and CO₂ mass transfer enhancement in the coupling process were presented and discussed. Finally, this article discusses the potential benefits and challenges of coupling nutrient bioremediation, CO₂ capture, and microalgal production. Possible engineering measures for cost-effective nutrients removal, carbon fixation, microalgal biofuels and bioproducts production are also proposed.

Optimisation of the production of fermentable monosaccharides from algal biomass grown in photobioreactors treating wastewater

Biomass grown in wastewater treatment photobioreactors is a cheap raw material with high contents of carbohydrates, proteins and lipids. This work studies the production of fermentable monosaccharides from three biomasses grown in piggery wastewater (P), domestic wastewater (W) and synthetic medium (S) by applying chemical pretreatment and enzymatic hydrolysis, using a Taguchi design. ANOVA identified temperature, chemical reagent type and chemical reagent concentration as significant operational parameters. However, the biomass concentration, pretreatment time, enzyme dosage and enzymatic hydrolysis time had no remarkable effect. The bacterial content of the biomass had no relevant impact on carbohydrate and protein solubilisation but had a remarkable effect on the degradation of the released carbohydrates (57, 60 and 37% for P, W and S), while also affecting lipid solubilisation. Pretreatment with HCl 2 M at 120 °C resulted the optimal conditions, achieving a monosaccharide recovery of 53, 59 and 80% for P, W and S biomasses, respectively.