Abstract
In this study, FeSO4 supplementation ranging from 0 to 4.5 mM, and MgSO4 supplementation ranging from 0 to 5.1 mM were investigated to observe the effect on the population dynamics, biochemical composition and fatty acid content of mixed microalgae grown in Anaerobic Liquid Digestate (ALD). Overall, 3.1 mM FeSO4 addition into ALD increased the total protein content 60% and led to highest biomass (1.56 g L−1) and chlorophyll-a amount (18.7 mg L−1) produced. Meanwhile, 0.4 mM MgSO4 addition increased the total carotenoid amount 2.2 folds and slightly increased the biomass amount. According to the microbial community analysis, Diphylleia rotans, Synechocystis PCC-6803 and Chlorella sorokiniana were identified as mostly detected species after confirmation with 4 different markers. The abundance of Chlorella sorokiniana and Synechocystis PCC-6803 increased almost 2 folds both in iron and magnesium addition. On the other hand, the dominancy of Diphylleia rotans was not affected by iron addition while drastically decreased (95%) with magnesium addition. This study helps to understand how the dynamics of symbiotic life changes if macro elements are added to the ALD and reveal that microalgae can adapt to adverse environmental conditions by fostering the diversity with a positive effect on high value product.
Highlights
Microalgae, having no need for arable land, is an attractive source of high value products by their rapid growth
The microbial community profiles and dynamics were first identified via metabarcoding of 16S rRNA, 18 S rRNA, 23S chloroplast rRNA an tufA regions
The community profiles changed drastically due to the macro element addition where the differences in the mixed algal community can be helpful for the adaptation to different environmental and growth conditions. 3.1 mM FeSO4 and 0.4 mM MgSO4 addition was found to be the optimum concentration with a positive effect on growth and biochemical composition
Summary
Microalgae, having no need for arable land, is an attractive source of high value products by their rapid growth. Even though direct land application is considered as the most cost-effective solution due to high soil remediation properties in agriculture and reducing the cost of the logistics[4], characteristics of the digestion effluent can cause phytotoxic effects in plants and/or contaminate the groundwater[5] In this aspect, microalgae can be efficiently grown in liquid digestate and stabilize the effluent without any further treatment. The aim of this study was to elucidate how population dynamics changed, and which species were favored by Fe and Mg supplementation The effect of these elements on biochemical composition of mixed culture and nutrient removal efficiency was investigated. The results of this study will contribute to the efforts to combine digestate treatment with microalgae cultivation for an effective conversion of high strength dark wastewater into high value byproducts
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