Improving astaxanthin production of Haematococcus pluvialis on the outdoor large scale cultivation by optimizing the disinfection strategy of photobioreactor

Astaxanthin production is often plagued by biological contaminants during the outdoor culture of Haematococcus pluvialis. The contaminants may even lead to the failure of the whole cultivation. To reduce the contaminants during outdoor culture and ensure the stability of large-scale astaxanthin production, the disinfection strategies using sodium hypochlorite in outdoor closed horizontal tube photobioreactor (HTPBR) were studied. The effective concentration of sodium hypochlorite for disinfection was 80 mg.L-1 by comparing the tolerances of various kinds of biological contaminants to sodium hypochlorite. Moreover, a degradation model of sodium hypochlorite was established to quantify the concentration of residual sodium hypochlorite in HTPBR. The predicted value of this model was close to the measured value, the maximum deviation was 4.88 mg.L-1, and the average deviation was 1.97 mg.L-1. In order to avoid adverse effects on astaxanthin accumulation, the residual sodium hypochlorite or sodium thiosulfate after disinfection should be controlled below 0.1 mg.L-1 and 10 mg.L-1, respectively. By comparing the multiple disinfection effects on outdoor HTPBRs, a low level of the total bacterial count was observed in HTPBR with double disinfection. By optimizing the disinfection strategy, the biological contaminants were reduced, and the volume content of astaxanthin was 2.37 times that of the unoptimized disinfection strategy. This study indicated that the astaxanthin yield can be improved by reducing the biological contaminants during the culture of H. pluvialis. The information will be a foundation for the disinfection strategy of other microalgae cultivation reactors.

Automated summary

This study investigated the disinfection strategies using sodium hypochlorite in outdoor closed horizontal tube photobioreactor, focusing on reducing biological contaminants, quantifying residual sodium hypochlorite concentration, and optimizing disinfection strategies to improve astaxanthin yield.