Effect of light intensity on the capability of different microalgae species for simultaneous biogas upgrading and biogas slurry nutrient reduction

In this study, we investigated the ability of microalgae to remove biogas slurry nutrients and upgrade biogas simultaneously under various light-emitting diode light intensities. Three green algae, namely, Scenedesmus obliquus, Chlorella sp., and Selenastrum bibraianum, were selected and cultivated in photobioreactor bags. The capacity of each microalga to reduce the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (M) of wastes was investigated. The growth rate and CO2 uptake of each microalga were also examined. Compared with S. bibraianum, S. obliquus and Chlorella sp. showed better combined results and were more suitable for simultaneous biogas upgrading and biogas effluent nutrient reduction. Results showed that the best results for biogas slurry nutrient reduction, CO2 removal, and upgrade effects were obtained from the treatment under moderate light intensity (150-170 mu mol m(-2) s(-1)) for S. obliquus. The highest reduction values of COD, TN, TI', dry weight, and CH4 concentration obtained were 93.08% +/- 4.62%, 84.12% +/- 437%, 86.76% +/- 4.58%, 465.31 +/- 19.44 mg L-1, and 94.41 +/- 3.16 (v/v), respectively. (c) 2015 Elsevier Ltd. All rights reserved.