Abstract
The microalgae-based technology has been developed to reduce biogas slurry nutrients and upgrade biogas simultaneously. In this work, five microalgal strains named Chlorella vulgaris, Scenedesmus obliquus, Selenastrum capricornutum, Nitzschia palea, and Anabaena spiroides under mono- and co-cultivation were used for biogas upgrading. Optimum biogas slurry nutrient reduction could be achieved by co-cultivating microalgae (Chlorella vulgaris, Scenedesmus obliquus, and Nitzschia palea) with fungi using the pelletization technology. In addition, the effects of different ratio of mixed LED light wavelengths applying mixed light-emitting diode during algae strains and fungi co-cultivation on CO2 and biogas slurry nutrient removal efficiency were also investigated. The results showed that the COD (chemical oxygen demand), TN (total nitrogen), and TP (total phosphorus) removal efficiency were 85.82 ± 5.37%, 83.31 ± 4.72%, and 84.26 ± 5.58%, respectively at red: blue = 5:5 under the co-cultivation of S. obliquus and fungi. In terms of biogas upgrading, CH4 contents were higher than 90% (v/v) for all strains, except the co-cultivation with S. obliquus and fungi at red: blue = 3:7. The results indicated that co-cultivation of microalgae with fungi under mixed light wavelengths treatments was most successful in nutrient removal from wastewater and biogas upgrading.
Highlights
Increasing energy demands and declining supplies of fossil energy resources have attracted significant attention worldwide[1]
The present study focuses on microalgal strain growth, biogas upgrade, and biogas slurry nutrient reduction using five selected microalgae strains in three cultivation treatments
Cultures 2 has higher growth rates, which was in agreement with the findings of Zhou et al.[15] and Wrede D.16, who observed that cultures 2 is highly effective in terms of bioflocculation of microalgal cells and did not require additional chemicals and low energy inputs
Summary
Increasing energy demands and declining supplies of fossil energy resources have attracted significant attention worldwide[1]. The present study focuses on microalgal strain growth, biogas upgrade, and biogas slurry nutrient reduction using five selected microalgae strains in three cultivation treatments. These five strains used in this work were selected on account of their high growth rates (in the range of 0.327–0.451 d−1) and strong nutrient removal ability (more than 60% removal of COD) in wastewater on the basis of our previous research[11]. We evaluate CO2 removal and slurry nutrient reduction under different mixed LED light wavelengths, red light and blue light treatments, based on the studied biogas upgrading and biogas slurry purification methods. The optimal parameters are determined by analyzing growth rates and mean daily productivity as well as nutrient removal efficiency and biogas purification
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