Nutrient removal and microalgal biomass production from different anaerobic digestion effluents with Chlorella species

Hyeonjung Yu,Jaai Kim,Changsoo Lee

doi:10.1038/s41598-019-42521-2

Hyeonjung Yu, Jaai Kim + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-42521-2

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Abstract

Potential of microalgal cultivation as an alternative approach to the treatment of anaerobic digestion (AD) effluents was examined using two representative Chlorella species, Chlorella vulgaris (CV) and Chlorella protothecoides (CP). Both species effectively removed NH4+-N from the AD effluents from four digesters treating different wastes under different operating conditions. In all experimental cultures on the AD effluents, NH4+-N (initial concentration, 40 mg/L) was completely removed within 10 days without residual NO3−-N or NO2−-N in batch mode. Compared to CP, CV showed greater biomass and lipid yields (advantageous for biodiesel production), regardless of the media used. Prolonged nitrogen starvation significantly increased the lipid accumulation in all cultures on the AD effluents, and the effect was more pronounced in the CV than in the CP cultures. On the other hand, compared to CV, CP showed significantly faster settling (advantageous for biomass harvesting) in all media. Our results suggest that the Chlorella cultivation on AD effluents under non-sterile, mixed-culture conditions may provide a viable way to manage and valorize the problematic effluents. Diverse bacteria derived from the AD effluents co-existed and presumably interacted with the Chlorella species in the cultures.

Highlights

With growing concerns about energy crisis and global warming, the need for sustainable energy sources is steadily increasing
When cultivated on UL, Rm was 8.5 mg/L·d for Chlorella vulgaris (CV) and 10.4 mg/L·d for Chlorella protothecoides (CP), whereas qm was 9.0 d−1 for CV and 6.3 d−1 for CP. These results indicate that, chlorophyll is a rough measure of microalgal biomass, CV might have performed superior to CP in terms of the specific activity to remove NH4+-N from the anaerobic digestion (AD) effluents
CV and CP were tested for their potential to grow on and treat different AD effluents, i.e., HF, LF, UL, and WH, in comparison to a synthetic medium Bristol medium (BT), in batch mode

Summary

Introduction

With growing concerns about energy crisis and global warming, the need for sustainable energy sources is steadily increasing. It has been demonstrated as effective, conventional BNR has two major drawbacks that weaken the economic application of the process: the high consumption of oxygen and the need for an external carbon source These limitations are of even greater concern when treating wastewater with high ammonia nitrogen concentration and low available organic content, such as AD effluents[2]. C. vulgaris and C. protothecoides both have promising potential in commercial applications for food, nutrition, and energy purposes, and their ability to grow both autotrophically and heterotrophically could contribute to further degradation of organic residues in AD effluents[16] Both species have shown greater biomass production and higher lipid productivity or content in the presence of organic carbon sources than in autotrophic cultures[17,18], which indicates another potential benefit of using AD effluent as a culture medium. This is a unique study in that it involves a set of physicochemical and biochemical approaches that allow for a holistic view of microalgal cultivation, from growth monitoring to kinetic modeling, lipid production, and microbial community structure, for complex AD effluents of different characteristics

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