Lighting the way to sustainable development: Physiological response and light control strategy in microalgae-based wastewater treatment under illumination

The effect of different light spectra on selenium bioaccumulation by Spirulina platensis cyanobacteria in flat plate photobioreactors

Selenium (Se) plays a crucial role in human health, influencing conditions such as cancer, diabetes, and neurological disorders. With global population growth and unequal nutrient distribution threatening food security, new approaches are needed to meet the nutritional needs of the world. Se is essential for immune function, metabolism, and antioxidant defense, and in regions suffering from food insecurity and malnutrition, selenium-enriched food could offer an affordable solution. Spirulina platensis, microalgae, can bioaccumulate Se from its environment, enhancing its nutritional value. This study explores how different light spectra (red, white, yellow, and blue LEDs) affect Se bioaccumulation in Spirulina when Na2SeO3 is added to the culture medium in photobioreactors. The results show that red light made the highest Se bioaccumulation (0.118 mg.L-1), followed by white, yellow, and blue light. Se addition also increased cell dry weight by 46%, 33%, 22%, and 60%, respectively, compared to photobioreactors without Se, with biomass productivity highest under red light. Furthermore, Se boosted maximum Chl α concentration, improving photosynthetic efficiency. These findings suggest that optimizing light conditions can significantly enhance the nutritional value of Spirulina, offering a potential solution to global hunger by providing a sustainable, selenium-enriched food source.

Unveiling underlying factors for optimizing light spectrum to enhance microalgae growth

Emerging research highlights the potential of specific light spectral regions to significantly enhance microalgae biomass production compared to conventional white light illumination. However, conflicting results of existing studies on the most optimal wavelengths reveal a knowledge gap regarding the underlying factors for optimal spectrum. The present paper aims to address this gap by critically analyzing existing studies on light spectral quality and its impact on microalgae growth. The analysis focuses on identifying the key factors determining an optimal light spectrum for microalgae cultivation. The study critically evaluates the effects of narrow wavelengths, assessing whether monochromatic light may be effective in maximizing biomass yield. While wavelength manipulation has a high potential, a deeper investigation into combining narrow wavelengths at varying ratios to determine the most effective spectral composition for maximizing growth is required. The study aims to provide insights into designing an optimal light spectrum for sustainable and efficient microalgae cultivation.

Factorial experiment to identify two-way interactions between temperature, harvesting period, hydraulic retention time, and light intensity that influence the biomass productivity and phosphorus removal efficiency of a microalgae-bacteria biofilm

Rotating algae biofilm reactors (RABRs) can reduce energy requirements for wastewater reclamation but require further optimization for implementation at water resource recovery facilities (WRRF). Optimizing RABR operation is challenging because conditions at WRRF change frequently, and disregarding interaction terms related to these changes can produce incorrect conclusions about RABR behavior. This study evaluated the two-way interaction and main effects of four factors on the biomass productivity and phosphorus removal efficiency of a microalgae-bacteria biofilm grown in municipal anaerobic digester centrate, with factor levels and operating conditions selected to mimic a pilot RABR at a WRRF in Utah. Two-way interactions harvesting period*light intensity (LI), harvesting period*temperature, and LI*hydraulic retention time (HRT) had significant effects on biomass productivity: at high temperature and low LI, highest biomass productivity was achieved with a 14-day harvesting period, but at medium temperature and high LI, highest biomass productivity was achieved with a 7-day harvesting period. At high HRT, highest biomass productivity occurred at low LI, but at low HRT, highest biomass productivity occurred at high LI. Phosphorus removal was strongly influenced by LI and occurred most rapidly during the first 2 days HRT, which suggests precipitation contributed significantly to phosphorus removal. These observations provide insight for further RABR optimization.

Municipal and industrial wastewater blending: Effect of the carbon/nitrogen ratio on microalgae productivity and biocompound accumulation

Municipal wastewater (MW) and industrial wastewater from juice processing (IWJ) were blended in different proportions to assess the effect of the carbon/nitrogen (C/N) ratio on pollutant removal, microalgal biomass (MB) cultivation, and the accumulation of carotenoids and biocompounds. MB development was not observed in treatments with higher C/N ratios (>30.67). The wastewater mixture favored the removal of dissolved organic carbon (75.61 and 81.90%) and soluble chemical oxygen demand (66.78-88.85%), compared to the treatment composed exclusively of MW (T7). Treatments T3 and T6 (C/N ratio equal to 30.67 and 7.52, respectively) showed higher Chlorophyll-a concentrations, 1.47 and 1.54 times higher than T7 (C/N ratio 1.75). It was also observed that the C/N ratio of 30.67 favored the accumulation of carbohydrates and lipids (30.07% and 26.39%, respectively), while the C/N ratio of 7.52 improved protein accumulation (33.00%). The fatty acids C16:0, C18:1, C18:2, and C18:3 had the highest concentrations. Additionally, increasing the C/N ratio can be an efficient strategy to improve the production of fatty acids for biofuels, mainly due to the increased concentration of shorter-chain fatty acids (C16:0). These findings suggest that blending wastewater not only enhances treatment performance but also increases the accumulation of valuable carbohydrates and lipids in MB, and optimizes fatty acid production for biofuel applications. This research represents significant progress towards feasibility of using MB produced from wastewater.

Insights into the removal of antibiotics from livestock and aquaculture wastewater by algae-bacteria symbiosis systems

With the burgeoning growth of the livestock and aquaculture industries, antibiotic residues in treated wastewater have become a serious ecological threat. Traditional biological wastewater treatment technologies-while effective for removing conventional pollutants, such as organic carbon, ammonia and phosphate-struggle to eliminate emerging contaminants, notably antibiotics. Recently, the use of microalgae has emerged as a sustainable and promising approach for the removal of antibiotics due to their non-target status, rapid growth and carbon recovery capabilities. This review aims to analyse the current state of antibiotic removal from wastewater using algae-bacteria symbiosis systems and provide valuable recommendations for the development of livestock/aquaculture wastewater treatment technologies. It (1) summarises the biological removal mechanisms of typical antibiotics, including bioadsorption, bioaccumulation, biodegradation and co-metabolism; (2) discusses the roles of intracellular regulation, involving extracellular polymeric substances, pigments, antioxidant enzyme systems, signalling molecules and metabolic pathways; (3) analyses the role of treatment facilities in facilitating algae-bacteria symbiosis, such as sequencing batch reactors, stabilisation ponds, membrane bioreactors and bioelectrochemical systems; and (4) provides insights into bottlenecks and potential solutions. This review offers valuable information on the mechanisms and strategies involved in the removal of antibiotics from livestock/aquaculture wastewater through the symbiosis of microalgae and bacteria.

A modified cultivation strategy to enhance biomass production and lipid accumulation of Tetradesmus obliquus FACHB-14 with copper stress and light quality induction

In this study, a two-stage culture strategy was refined to concurrently enhance the growth and lipid accumulation of Tetradesmus obliquus. The results unveiled that, during the initial stage, the optimal conditions for biomass accumulation were achieved with 0.02 mg·L-1 Cu2+ concentration and red light. Under these conditions, biomass accumulation reached 0.628 g·L-1, marking a substantial 23.62 % increase compared to the control group. In the second stage, the optimal conditions for lipid accumulation were identified as 0.5 mg·L-1 Cu2+ concentration and red light, achieving 64.25 mg·g-1·d-1 and marking a 128.38 % increase over the control. Furthermore, the fatty acid analysis results revealed an 18.85 % increase in the saturated fatty acid content, indicating enhanced combustion performance of microalgae cultivated under the dual stress of red light and 0.5 mg·L-1 Cu2+. This study offers insights into the potential application of Tetradesmus obliquus in biofuel production.

Co-culturing microalgae with endophytic bacteria from bamboo for efficient nutrient and heavy metal removal coupling with biogas upgrading

The construction of dominant algal species and bacterial strains in algal treatment technology was crucial for pollutant removal. In order to enhance the purification capability of microalgae toward heavy metals in water as well as biogas slurry and biogas, symbiotic systems were respectively constructed using Chlorella vulgaris and two different endogenous bacteria (microalgal endophytic bacteria S395-2 and plant endophytic bacteria BEB7). The results demonstrated that the endogenous bacteria (S395-2 and BEB7) effectively promote the growth, biomass yield, photosynthetic activity, and carbonic anhydrase activity of microalgae. Additionally, BEB7 exhibited superior promotion effects on microalgae compared to S395-2. Moreover, the BEB7-microalgae co-cultivation system not only efficiently removed heavy metals from water but also effectively purified the nutrients and CO2 in biogas slurry. The optimal effect was observed when the ratio of BEB7 to microalgae was 10:1. This study has established a solid theoretical foundation for the application of microalgae in pollutant purification. PRACTITIONER POINTS: Endogenous bacteria effectively promoted microalgal performance. The optimal ratio of BEB7 to microalgae was 10:1. Chlorella vulgaris-BEB7 showed the best removal performance.