Dual nutrient heterogeneity modes in a continuous flow photobioreactor for optimum nitrogen assimilation to produce microalgal biodiesel

The impact of different nitrogen sources on the microalga, Chlorella vulgaris, was studied in a newly developed microalgal-bacterial photobioreactor via a dual nutrient heterogeneity mode. The mechanisms of nitrogen transformation and valorisation were unveiled, and subsequently, optimized via dual nutrient heterogeneity feeding modes comprising of various NH4+-N and NO3--N concentrations. The nitrogen-assimilation mechanism from the microalgal-bacterial consortium was found to reduce microalgal growth inhibition, stemming at high NH4+-N concentrations. Accordingly, the total nitrogen removal efficiency was enhanced from 40.91% to 96.38% accompanied with maximum microalgal biomass production of up to 792 mg/L at a balanced or higher NH4 thorn -N loading from mixed nitrogen environment. The harvested microalgal biomass contained high lipid accumulation of approximately 30% when fed with optimum NH4 thorn -N and NO3--N loadings at 60 and 58 mg/d, respectively. At this mixed nitrogen species loadings, high unsaturated fatty acid methyl esters (FAME) were attained. Indeed, the major FAME species (97%-10 0%) fell within the C16-18 range, signifying biodiesel characteristics conformity to the requirements for quality biodiesel application. Therefore, the dual heterogeneity modes of balanced NH4+-N and NO3--N loadings into photobioreactor could offer effective microalgal nitrogen assimilation for sustainable wastewater treatment and microalgae-based biodiesel production simultaneously. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The impact of different nitrogen sources on the microalga, Chlorella vulgaris, was studied, and the mechanisms of nitrogen transformation and valorization were unveiled. Balanced NH4+-N and NO3--N loadings could simultaneously achieve high nitrogen removal efficiency and microalgal biomass production, as well as suitable high lipid accumulation for biodiesel application.