pH treatments in continuous cultivation to maximize microalgal production and nutrient removal from anaerobic digestion
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pH treatments in continuous cultivation to maximize microalgal production and nutrient removal from anaerobic digestion effluent of aquatic macrophytes Jun Qian 1 & Xin Liu 1 & Syuhei Ban 1
&
Masaaki Fujiwara 2 & Toshimitsu Kodera 2 & Shinichi Akizuki 2,3 & Tatsuki Toda 2
Received: 13 March 2020 / Revised and accepted: 29 June 2020 # Springer Nature B.V. 2020
Abstract Green algae have great potential for removing inorganic nutrients from anaerobic digestion effluent (ADE), but there is insufficient available magnesium (Mg) in the ADE from aquatic macrophytes for effective algal growth. In this study, we determined suitable pH and hydraulic retention time (HRT) for maximizing growth of the alga Chlorella sorokiniana and nutrient removal efficiency with a flow-through continuous cultivation system. This used ADE from aquatic macrophytes, adjusted to pH 5.0, 6.0, 6.5 and 7.0 at two HRTs of 6 and 8 days. The highest C. sorokiniana biomass concentration was obtained in the pH 6.5 treatment, being 0.50 and 0.67 g L−1 at 6 and 8 days of HRT, respectively, without Mg enrichment. Both were equivalent to 83.6 mg L−1 day−1 of biomass productivity. Removal rates of both ammonium nitrogen and phosphate phosphorus were almost 100% in pH 6.5 and 7.0 treatments and declined to below 60% in pH 5.0 and 6.0 treatments during the study period. The results demonstrated that a source medium pH of 6.5 using a continuous cultivation system (irrespective of the two HRTs), and increasing available Mg, was suitable for maximizing C. sorokiniana biomass productivity and nutrient removal from the ADE. Keywords Biomass recovery . Flow-through cultivation . Nutrient removal . pH control . Mg availability . Bio-digester effluent
Introduction In recent decades, the excessive growth of aquatic macrophytes has led to global ecological and social problems such as water stagnation, deterioration in drinking water supplies, interference with fishing activities, obstruction to boat navigation, and a negative influence on tourism (Abbasi et al. 1990; Charudattan 2010; Hussner et al. 2017). Periodical harvesting and effective utilization are a good strategy for keeping their growth under control because it is difficult to control or Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10811-020-02196-z) contains supplementary material, which is available to authorized users. * Syuhei Ban [email protected] 1
Department of Ecosystem Studies, The University of Shiga Prefecture, Hikone, Shiga 522-8533, Japan
2
Faculty of Science and Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan
3
Division of Engineering, University of Guanajuato, Juarez Avenue, Center Zone, 36000 Guanajuato, Mexico
eliminate these macrophytes with chemical or biological agents owing to high costs (Abbasi and Nipaney 1986). Anaerobic digestion (AD) is a low-cost and effective method to treat the harvested macrophytes because it can stabilize organic waste (including macrophytes) and generate methane-rich biogas as an energy s
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