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Highlights • CO2 alleviated the photodamage of H. lacustris under high irradiance. • CO2 injection contributes to a low ROS level under high light intensity. • H. lacustris achieved a promising growth rate under high light., Haematococcus lacustris (H. lacustris), a promising source for astaxanthin production, is a light-sensitive microalga that is prone to sluggish growth when subjected to high levels of irradiance. A challenge in H. lacustris culture is to find a way to efficiently use illumination to maintain vigorous growth and harvest dense biomass, which is essential for further exploiting the potential for astaxanthin production. Previous studies have shown that in addition to illumination, carbon supply in culture is a key limitation for algae growth. Here, we investigated a combined culture approach involving high light intensity (110 μmol m−2s-1) and injection of a 1% (v/v) CO2 air-gas mixture which provided an effective method for H. lacustris culture to achieve both a high growth rate and high cell density. The cell number in the group with high light exposure combined with CO2 enrichment was increased almost four-fold compared with a high light group (110 μmol m−2s-1 without CO2 injection). Additional experiments suggested a possible mechanism in which elevated CO2 increases the electron sink capacity, thus alleviating photoinhibition and oxidative damage. The scaled-up photobioreactor demonstrated much better performance, with growth rates improved by 50–350 %, providing further evidence that this new method can improve algal cell production. Overall, our work provides an efficient way for H. lacustris culture and manufacture, with potential industrial applications.

Summary: Haematococcus pluvialis, the richest bioresource for natural astaxanthin, encounters a challenge of achieving high growth rate when it comes to mass biomass production. Based on the substrate consumption model and Redfield ratio, rapid algae growth benefits from a proper carbon supply. However, the conventional cultivation schemes with limited carbon dioxide (CO2) supply and inefficient carbon mass transfer could have constrained the carbon capture and growing ability of H. pluvialis. We hypothesize that optimal H. pluvialis growth improvement may be achieved by efficient CO2 supply. Here, in this study, we first identified the carbon consumption of H. pluvialis during exponential growth. Then, a novel microbubble-driven photobioreactor (MDPBR) was designed to satisfy the carbon demand. The novel microbubble photobioreactor improves the CO2 supply by reducing bubble size, significantly elevating the CO2 mass transfer. With only 0.05 L min−1 of gas flow rate, higher cell growth rate (0.49 d−1) has been achieved in MDPBR.

Summary The mitigation of biofouling has received significant research attention, with particular focus on non‐toxic and sustainable strategies. Here, we investigated quorum sensing inhibitor (QSI) bacteria as a means of controlling biofouling in a laboratory‐scale system. Approximately, 200 strains were isolated from coral (Pocillopora damicornis) and screened for their ability to inhibit quorum sensing (QS). Approximately, 15% of the isolates exhibited QSI activity, and a typical coral symbiotic bacterium, H12‐Vibrio alginolyticus, was selected in order for us to investigate quorum sensing inhibitory activity further. Confocal microscopy revealed that V. alginolyticus extract inhibited biofilm formation from Pseudomonas aeruginosa PAO1. In addition, the secondary metabolites of V. alginolyticus inhibited PAO1 virulence phenotypes by downregulating motility ability, elastase activity and rhamnolipid production. NMR and MS spectrometry suggested that the potential bioactive compound involved was rhodamine isothiocyanate. Quantitative real‐time PCR indicated that the bacterial extract induced a significant downregulation of QS regulatory genes (lasB, lasI, lasR, rhlI, rhlR) and virulence‐related genes (pqsA, pqsR). The possible mechanism underlying the action of rhodamine isothiocyanate analogue involves the disruption of the las and/or rhl system of PAO1. Our results highlight coral microbes as a bioresource pool for developing QS inhibitors and identifying novel antifouling agents.

In this study, Chlorella vulgaris (C. vulgaris) were cultured in cell culture flask supplied with intermittent CO2 enriched gas. The impact of CO2 concentration (from 1% to 20% v/v) on the growth of C. vulgaris cultured in domestic wastewater was exploited in various perspectives which include biomass, specific growth rate, culture pH, carbon consumption, and the removal of nitrogen and phosphorus compounds. The results showed that the maximum microalgal biomass concentration, 1.12 g L−1, was achieved with 10% CO2 as a feed gas. At 20% CO2 the growth of C. vulgaris suffered from inhibition during initial 1.5 d, but acclimated to low pH (6.3 in average) with relatively higher specific growth rate (0.3–0.5 d−1) during subsequent culture period. After the rapid consumption of ammonium in the wastewater, an obvious decline in the nitrate concentration was observed, indicating that C. vulgaris prefer ammonium as a primary nitrogen source. The total nitrogen and phosphorus decreased from 44.0 mg L−1 to 2.1–5.4 mg L−1 and from 5.2 mg L−1 to 0–0.6 mg L−1 within 6.5 d under the aeration of 1–20% CO2, respectively, but no significant difference in consumed nitrogen versus phosphorus ratio was observed among different CO2 concentration. The kinetics of nutrients removal were also determined through the application of pseudo first order kinetic model. 5–10% CO2 aeration was optimal for the growth of C. vulgaris in the domestic wastewater, based on the coupling of carbon consumption, microalgal biomass, the nutrients removal and kinetics constants.

Background: Harvesting algal biomass is an important unit operation in the production of biofuel from algae. However, many of the known techniques available for harvesting and dewatering microalgal biomass are energy intensive and in some cases intrusive and inefficient. Here we show that microflotation mediated by fluidic oscillation is an approach that differs from dissolved air flotation by the nonintrusive laminar flow approach, as well as low energy consumptions, and is also different from dispersed air flotation by the method of bubble generation. Results and discussion: Using three metallic coagulant types, recovery efficiencies of 99.2, 98.1 and 95.2% were obtained for ferric chloride, ferric sulfate and aluminum sulfate, respectively. The benchmarks in the literature for dissolved air flotation are 40–98%. Conclusion: Biofuel production from microalgae can be facilitated by the improvement of a key unit operation such as harvesting and dewatering. The study outcome strongly recommends the techniq...

A periodic CO2 dosing strategy for D. salina 19/30 batch culture is proposed. A model of periodic CO2 dosing including dosing time calculation, dosing interval estimation and final chlorophyll yield prediction was established. In experiments, 5% CO2/95% N2 gas was periodically dosed into D. salina culture. Two different gas dosing flow rates were tested. The corresponding dosing time for each flow rate was estimated via the model (10 min·d−1 for 0.7 L·min−1 and 36 min·d−1 for 0.3 L·min−1). Daily pH measurements showed that the pH of these cultures dosed periodically was always kept between 7.5 and 9.5, which highlights that periodic gas supply can maintain a suitable range of pH for microalgal growth without expensive buffers. Notably the culture dosed for set daily intervals was seen to have similar growth to the culture supplied constantly, but with much higher CO2 capture efficiency (11%–18%) compared to continuous dosing (0.25%). It shows great potential for using periodic gas supply to reduce cost, wasted gas and energy use.