Cultivation of Navicula sp. on rice straw hydrolysate for the production of biogenic silica

Rice straw hydrolysate (RSH) prepared at room temperature was found to be rich in silica (140 +/- 4.1 mg L-1) and other nutrients (nitrate-N: 160 +/- 4.3 mg L-1, total dissolve phosphate: 164 +/- 6.7 mg L-1, ammoniacal-N: 439.8 +/- 17 mg L-1). The aim of this work was to study four RSH dilutions (10, 30, 50, 70% v/v) to cultivate Navicula sp. with modified ASN-III as a control. The best result was achieved in 30% RSH in terms of doubling time (d = 1.49 days) and growth rate (mu max = 0.46 day(-1)). Compared to control, specific growth rate and biomass pro-ductivity were increased by 2.93 folds and 1.85 folds, respectively. Cultivation in 5 L reactor with optimized 30% RSH yielded frustule (54.2 +/- 1.9%), carbohydrate (12.4 +/- 1.2%), lipid (18.9 +/- 1.4%), and protein (8.2 +/- 0.6%). The residual solid fraction showed 18.99% increased theoretical methane yield than raw rice straw. Overall, the present process offers a sustainable solution to manage rice straw residue and recover nanoporous silica.

Automated summary

Rice straw hydrolysate (RSH) prepared at room temperature was found to contain high levels of silica and other nutrients. Cultivating Navicula sp. in a 30% dilution of RSH resulted in the best growth performance. The optimized cultivation process yielded frustule, carbohydrates, lipids, and proteins, and increased the theoretical methane yield compared to raw rice straw. This study provides a sustainable solution for managing rice straw residue and recovering nanoporous silica.