Cooling coil led to the collapse of N-replete Haematococcus pluvialis cultures by releasing lethal levels of Cu2+

Abstract

Photobioreactors for outdoor microalgal cultivation should be equipped with temperature control devices to avoid overheating. However, it is still not clear whether the cooling devices would release poisonous levels of Cu2+ that could affect the growth of microalga. In this study, the half maximal inhibitory concentration (IC50) of Cu2+ was determined by studying the effects of Cu2+ concentrations on the growth and photosynthesis of Haematococcus. Then, the Cu2+ release dynamics were studied by soaking copper cooling coils in water for different times. The results indicated that the IC50 of Cu2+ for Haematococcus was approximately 20 μM (16.9 μM) and, above this level, the growth and photosynthesis were obviously inhibited before astaxanthin production. Meanwhile, after being soaked in water for only 10 h, the copper cooling coil released 40 μM Cu2+, which was 100% higher than the IC50 and high enough to impose severe heavy metal stress on cells. These results indicated that Haematococcus was sensitive to Cu2+. Devices made with copper or copper-containing materials could release lethal levels of Cu2+ if exposed to a liquid environment and brought into direct contact with microalgal cells. This research sheds some light on the design and operation of cooling systems for outdoor large-scale microalgal cultivations.