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There has been considerable interest in cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. However, almost all mass cultures of algae are carbon-limited. Therefore, to reach a high biomass and oil productivities, the ideal selected microalgae will most likely need a source of inorganic carbon. Here, growth and lipid productivities of Tetraselmis suecica CS-187 and Chlorella sp were tested under various ranges of pH and different sources of inorganic carbon (untreated flue gas from coal-fired power plant, pure industrial CO₂, pH-adjusted using HCl and sodium bicarbonate). Biomass and lipid productivities were highest at pH 7.5 (320 ± 29.9 mg biomass L⁻¹ day⁻¹and 92 ± 13.1 mg lipid L⁻¹ day⁻¹) and pH 7 (407 ± 5.5 mg biomass L⁻¹ day⁻¹ and 99 ± 17.2 mg lipid L⁻¹ day⁻¹) for T. suecica CS-187 and Chlorella sp, respectively. In general, biomass and lipid productivities were pH 7.5 > pH 7 > pH 8 > pH 6.5 and pH 7 > pH 7.5 = pH 8 > pH 6.5 > pH 6 > pH 5.5 for T. suecica CS-187 and Chlorella sp, respectively. The effect of various inorganic carbon on growth and productivities of T. suecica (regulated at pH = 7.5) and Chlorella sp (regulated at pH = 7) grown in bag photobioreactors was also examined outdoor at the International Power Hazelwood, Gippsland, Victoria, Australia. The highest biomass and lipid productivities of T. suecica (51.45 ± 2.67 mg biomass L⁻¹ day⁻¹ and 14.8 ± 2.46 mg lipid L⁻¹ day⁻¹) and Chlorella sp (60.00 ± 2.4 mg biomass L⁻¹ day⁻¹ and 13.70 ± 1.35 mg lipid L⁻¹ day⁻¹) were achieved when grown using CO₂ as inorganic carbon source. No significant differences were found between CO₂ and flue gas biomass and lipid productivities. While grown using CO₂ and flue gas, biomass productivities were 10, 13 and 18 %, and 7, 14 and 19 % higher than NaHCO₃, HCl and unregulated pH for T. suecica and Chlorella sp, respectively. Addition of inorganic carbon increased specific growth rate and lipid content but reduced biomass yield and cell weight of T. suecica. Addition of inorganic carbon increased yield but did not change specific growth rate, cell weight or content of the cell weight of Chlorella sp. Both strains showed significantly higher maximum quantum yield (Fᵥ/Fₘ) when grown under optimum pH.

There has been considerable interest on cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. The ideal microalga characteristics are that it must grow well even under high cell density and under varying outdoor environmental conditions and be able to have a high biomass productivity and contain a high oil content (~25–30 %). The main advantage of Chlorophyta is that their fatty acid profile is suitable for biodiesel conversion. Tetraselmis suecica CS-187 and Chlorella sp. were grown semi-continuously in bag photobioreactors (120 L, W × L = 40 × 380 cm) over a period of 11 months in Melbourne, Victoria, Australia. Monthly biomass productivity of T. suecica CS-187 and Chlorella sp. was strongly correlated to available solar irradiance. The total dry weight productivity of T. suecica and Chlorella sp. was 110 and 140 mg L⁻¹ d⁻¹, respectively, with minimum 25 % lipid content for both strains. Both strains were able to tolerate a wide range of shear produced by mixing. Operating cultures at lower cell density resulted in increasing specific growth rates of T. suecica and Chlorella sp. but did not affect their overall biomass productivity. On the other hand, self shading sets the upper limit of operational maximum cell density. Several attempts in cultivating Dunaliella tertiolecta CS-175 under the same climatic conditions were unsuccessful.

The cultivation of Arthrospira platensis (Spirulina) is well-established in applied phycology, but the high cost of conventional media limits large-scale production. Anaerobically digested food effluent (ADFE), rich in nitrogen and phosphorus, offers a cost-effective alternative while mitigating environmental impacts. This study evaluated ADFE as a partial replacement for Zarrouk’s medium, with 37.5%, 50%, and 70% substitutions, the latter two added incrementally. Cultivation was conducted in paddlewheel-driven raceway ponds under outdoor conditions for 22 days during the Australian autumn. The highest biomass productivity (8.83 g m−2 d−1) was achieved with 70% ADFE, significantly outperforming Zarrouk’s medium (p < 0.05). Chlorophyll a content remained unaffected (p > 0.05), and ammonium (N-NH4+) declined to near zero by day 9, indicating efficient nutrient uptake. These findings demonstrate that staged ADFE addition can successfully replace up to 70% of Zarrouk’s medium while maintaining robust A. platensis growth, highlighting its potential as a sustainable alternative for large-scale microalgal cultivation.

Alexandrium spp. blooms and paralytic shellfish poisoning pose serious economic threats to coastal communities and aquaculture. This study evaluated the removal efficiency of two Alexandrium minutum strains using natural kaolinite clay (KNAC) and kaolinite with polyaluminum chloride (KPAC) at three concentrations (0.1, 0.25, and 0.3 g L−1), two pH levels (7 and 8), and two cell densities (1.0 and 2.0 × 107 cells L−1) in seawater. PAC significantly enhanced removal, achieving up to 100% efficiency within two hours. Zeta potential analysis showed that PAC imparted positive surface charges to the clay, promoting electrostatic interactions with negatively charged algal cells and enhancing flocculation through Van der Waals attractions. In addition, the study conducted a cost estimate analysis and found that treating one hectare at 0.1 g L−1 would cost approximately USD 31.75. The low KPAC application rate also suggests minimal environmental impact on benthic habitats.

Alexandrium spp. blooms produce a range of toxins, including spirolides, goniodomins, and paralytic shellfish toxins (PSTs). Of these, PSTs are the most impactful due to their high affinity for voltage-gated sodium ion channels in nerve cell membranes. This interaction can cause neurological effects such as paralysis and, in severe cases, may lead to death. Given the implications of Alexandrium blooms on public health, all mitigation, prevention, and treatment strategies aim to reduce their socioeconomic impacts. However, monitoring harmful algal blooms remains difficult due to confounding influences such as pollution, climate change, and the inherent variability of environmental conditions. These factors can complicate early detection and management efforts, especially as the intensity and frequency of blooms continue to rise, further exacerbating their socioeconomic consequences. This review offers insights into several management approaches to prevent and control Alexandrium blooms, focusing on modified nano-clays as a promising emergency mitigation measure for low-density toxic algal blooms, especially in areas predominantly used for recreational fishing. However, it is recommended that treatment be coupled with monitoring to alleviate reliance on treatment alone.

There is currently great interest in microalgae as sources of renewable energy and biofuels. Many algae species have a high lipid content and can be grown on non-arable land using alternate water sources such as seawater. This paper discusses in detail the issue of sustainability of commercial-scale microalgae production of biofuels with particular focus on land, water, nutrients (N and P) and CO 2 requirements and highlights some of the key issues in the very large scale culture of microalgae which is required for biofuels. The use of genetically modified algae is also considered.

Increasing microalgal biomass productivity and enhancing nutrient removal rates are critical when growing microalgae in wastewater. In most cases, the effluents such as anaerobically digested food effluent (ADFE) are very turbid. Using such effluents as a medium for an algal culture would leave the culture with high turbidity resulting in photo-limitation of the algal culture. Light-diffusing systems can be used to overcome the light limitation in microalgal cultures. In this study, red luminescent solar concentrators were used to shift the sunlight into the desired wavelength and deliver it into the depth of cultures of an outdoor microalgal consortium cultivated in ADFE in paddlewheel-driven raceway ponds. Biomass productivity and specific growth rate of cultures grown using red luminescent solar concentrators (LSCs) were 61% and 59% higher than those in control cultures. The nitrogen assimilation rate of biomass under red LSCs was 1.8-fold higher than that in the control. Further, the lipid content of the cultures under red LSCs (490 mg lipid g−1 biomass) was 30% higher than that of the control. The results of this study showed that using red LSCs can improve microalga growth on ADFE when paddlewheel raceway ponds are used.

The successful cultivation of microalgae on anaerobically treated wastewaters would not only allow for the bioremediation of the waste stream but also the cost effective production of algal biomass. In this study, the growth and bioremediation ability of a microalgal consortium of Chlorella sp. and Scenedesmus sp. for treating anaerobically digested piggery effluent (ADPE) was assessed and compared using a thin layer reactor (TLR) (0.5-cm depth, 350 L) and a conventional raceway pond (15-cm depth, 1500 L) with an initial ammonium concentration of 110 ± 10 mg N-NH4+ L−1. The ammonium removal rate of microalgae grown in the TLR (19.23 mg N-NH4+ L−1 d−1) was 1.4 times higher than that grown in the raceway pond. The ash-free biomass yield (0.84 g L−1) and the average volumetric biomass productivity (60 mg L−1 d−1) of the algal consortium in the TLR were 2.5 and 2 times higher than that achieved in the raceway pond, respectively. However, considering four times higher culture volume in the raceway pond, the average areal biomass productivity in the raceway pond (4.2 g m−2 d−1) was more than two times higher than the productivity achieved in the TLR (1.9 g m−2 d−1). As a result of this, the areal lipid productivity of the microalgae grown in the raceway pond was also 2.7 times higher than that grown in the TLR. Our results indicated that under the operational conditions evaluated in this study and based on areal biomass productivity, raceway pond performed better than the thin layer reactor for treating ADPE.

Abstract Botryococcus braunii CCAP 807/2 has been studied intensively for biofuel production due to its high hydrocarbon content. This strain is also capable of producing high value carotenoids. The aim of the study was to analyse the carotenoid production of B.braunii 807/2 under different growing conditions, first, by using different media and light intensities in indoors, and next, to examine the carotenoid composition between green, intermediately pigmented and red B. braunii grown in indoors and outdoors. The alga was cultured indoors under two different light intensities (100 and 500 μmol photons m−2 s−1) using three different media: a control with complete modified CHU 13 medium, modified CHU 13 without N and modified CHU13 without N + 2Fe. All cultures were grown at 25 °C with 12:12 h light:dark cycle and were mixed with magnetic stirrers. For the determination of carotenoid composition at different stages, the green, intermediately pigmented and red cells were collected from indoor and outdoor cultures and analysed for their carotenoid composition using HPLC. The cultures grown at high light intensity reached the highest biomass yield at 0.6 g L−1 on day 16, whereas their counterparts at low light intensity took 30 days to reach the same biomass yield. The carotenoid production of B. braunii 807/2 at high light intensity increased up to twofold in 2 days compared to the ones grown at low light. Botryococcus braunii 807/2 accumulates lutein, canthaxanthin and astaxanthin and β,β-carotene as the main carotenoids. Whilst lutein was the major carotenoids of the green/intermediate cells, canthaxanthin and astaxanthin were the predominant carotenoids of the red cells under indoor and outdoor culture, respectively. This study suggests that Botryococcus braunii 807/2 is a potential candidate for the production of lutein and/or astaxanthin. It accumulates a high amount of lutein when grown under optimum conditions and a high amount of astaxanthin when grown under sub-optimum conditions outdoors.

The Earth receives around 1000 W.m⁻² of power from the Sun and only a fraction of this light energy is able to be converted to biomass (chemical energy) via the process of photosynthesis. Out of all photosynthetic organisms, microalgae, due to their fast growth rates and their ability to grow on non-arable land using saline water, have been identified as potential source of raw material for chemical energy production. Electrical energy can also be produced from this same solar resource via the use of photovoltaic modules. In this work we propose a novel method of combining both of these energy production processes to make full utilisation of the solar spectrum and increase the productivity of light-limited microalgae systems. These two methods of energy production would appear to compete for use of the same energy resource (sunlight) to produce either chemical or electrical energy. However, some groups of microalgae (i.e. Chlorophyta) only require the blue and red portions of the spectrum whereas photovoltaic devices can absorb strongly over the full range of visible light. This suggests that a combination of the two energy production systems would allow for a full utilization of the solar spectrum allowing both the production of chemical and electrical energy from the one facility making efficient use of available land and solar energy. In this work we propose to introduce a filter above the algae culture to modify the spectrum of light received by the algae and redirect parts of the spectrum to generate electricity. The electrical energy generated by this approach can then be directed to running ancillary systems or producing extra illumination for the growth of microalgae. We have modelled an approach whereby the productivity of light-limited microalgae systems can be improved by at least 4% through using an LED array to increase the total amount of illumination on the microalgae culture.