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Polyunsaturated fatty acids (PUFAs) are highly appreciated on their nutritive value for human health and aquaculture. P. purpureum, one of the red microalgae acknowledged as a promising accumulator of ARA, was chosen as the target algae in the present research. Effects of sodium bicarbonate (0.04-1.2 g/L), temperature (25, 30 and 33 °C) and phosphate (0.00-0.14 g/L) on biomass yield, total fatty acids (TFA) and arachidonic acid (ARA) accumulation were investigated systemically. NaHCO3 dose of 0.8 g/L and moderate temperature of 30 °C were preferred. In addition, TFA and ARA production were significantly enhanced by an appropriate concentration of phosphate, and the highest TFA yield of 666.38 mg/L and ARA yield of 159.74 mg/L were obtained at a phosphate concentration of 0.035 g/L. Interestingly, with phosphate concentration continuing to fall, UFA/TFA and ARA/EPA ratios were increased accordingly, suggesting that phosphate limitation promoted unsaturated fatty acids and arachidonic acid biosynthesis. Low concentration of phosphate may be favored to increase the enzymatic activities of ∆6-desaturase, which played a key role in catalyzing the conversion of C16:0 to C18:2, and thus the selectivity of UFA increased. Meanwhile, the increase of ARA selectivity could be attributed to ω6 pathway promotion and ∆17-desaturase activity inhibition with phosphate limitation. Phosphate limitation strategy enhanced unsaturated fatty acids and ARA biosynthesis in P. purpureum, and can be applied in commercial scale manufacturing and commercialization of ARA.

Objectives: This study investigated the effect of aeration rate and light intensity on biomass production and total fatty acids (TFA) accumulation by Porphyridium purpureum. The red microalgae is also known to accumulate considerable amount of arachidonic acid (ARA). Results:In artificial seawater medium, the highest yield of TFA (473.44 mg/L) was obtained with the aeration rate of 3 L/min and light intensity of 165 µmol/m 2 s, whilst the highest yield of ARA (115.47 mg/L) was achieved with the aeration rate of 3 L/min and light intensity of 110 µmol/m 2 s. It was found that higher aeration rate led to more biomass and TFA/ARA production. However, higher light intensity could contribute to biomass accumulation, but it was adverse for TFA and ARA biosynthesis. Conclusion:By optimizing two operating factors (i.e., light intensity and aeration rate), TFA and ARA production by P. purpureum was significantly improved. This research provides a potential alternative means for producing ARA.

The production of copious quantities of waste palm oil mill effluent (POME) is an unavoidable consequence of palm oil industries, and requires effective treatment before discharge into the environment. Microalgae possess a significant nutrient bio‐sorption capacity in addition to high photosynthetic and carbon bio‐sequestration rates, and hence can be exploited for sustainable POME treatment operations. Bioprocess research on the use of microalgal cells to remove specific chemical species from POME is limited. This work investigated the application of the microalgae Chlorella vulgaris and Nannochloropsis sp. for nitrogen and phosphorus removal from POME with simultaneous biomass production. Both microalgae species displayed maximum total nitrogen and phosphorus removal efficiencies at 50 % POME concentration within 8 days. Studies on nitrogen and phosphorous addition demonstrated that a N/P molar ratio of 10:1 improved biomass accumulation with 90.0 % nitrogen and 82.1 % phosphorus removals. These results showed that high treatment efficiencies can be obtained using C. vulgaris and Nannochloropsis sp. for applications in industrial POME treatment.

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