Abstract
Photoautotrophic microalgae offer high promise for a tertiary treatment of livestock wastewater owing to their rapid growth and nutrient uptake. To screen better microalga for the tertiary treatment, batch photobioreactor tests were conducted using Chlorella emersonii, Chlorella sorokiniana, and Botryococcus braunii. This study evaluated their specific growth rates, CO2 utilization rates, and nutrient removal rates to provide appropriate selection guidelines. Based on statistical comparisons, results indicate that selecting the right microalgae was the key to success in the tertiary treatment since each microalga responded differently, even under the same light, temperature, and nutrient conditions. Among the tested species, Chlorella emersonii was found to present the fastest photoautotrophic growth, total inorganic carbon (TIC) utilization, and nutrient removal for livestock wastewater treatment. Regression results identified that its specific growth and total nitrogen removal rates were as high as 0.51 day−1 and 0.18 day−1, respectively. Estimated TIC utilization over the supplied TIC was much higher (~34%) than those of others (11%–18%). This systemic evaluation of rate-limiting factors provides a quantitative understanding of the kinetic-based selection strategy of microalgae to polish livestock wastewater with better effluent quality.
Highlights
Livestock wastewater contains a large amount of nitrogen and phosphorus; the efficiencies of primary and secondary treatment are relatively low [1]
This significant difference reconfirms that biomass productivity could be different between genus and species under the same growth conditions; the selection of optimal microalgae is crucial from a treatment engineering standpoint
At 75 mg·N/L (Figure 2b), even though Chlorella emersonii demonstrated the fastest exponential growth, the biomass concentration of Chlorella emersonii at Day 4 was reduced by about 21% (1029 mg dry weight (DW)/L), while little differences were noticed in the cases of Chlorella sorokiniana (3.3%) and Botryococcus braunii (1.4%)
Summary
Livestock wastewater contains a large amount of nitrogen and phosphorus; the efficiencies of primary and secondary treatment are relatively low [1]. Reducing the use of fossil fuels would considerably reduce CO2 and other pollutant production; developing alternative, renewable, and carbon neutral sources that can replace fossil fuels will form the future technical trend [4]. One of the potential alternatives is renewable biodiesel production via microalgae cultivation under controlled conditions [5]. Various studies have been demonstrated how to increase biofuel productivity despite the fact that its current status is yet in the research scale [6,7]. These days, Water 2017, 9, 192; doi:10.3390/w9030192 www.mdpi.com/journal/water
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