Digestate as Sustainable Nutrient Source for Microalgae—Challenges and Prospects

Abstract

The interest in microalgae products has been increasing, and therefore the cultivation industry is growing steadily. To reduce the environmental impact and production costs arising from nutrients, research needs to find alternatives to the currently used artificial nutrients. Microalgae cultivation in anaerobic effluents (more specifically, digestate) represents a promising strategy for increasing sustainability and obtaining valuable products. However, digestate must be processed prior to its use as nutrient source. Depending on its composition, different methods are suitable for removing solids (e.g., centrifugation) and adjusting nutrient concentrations and ratios (e.g., dilution, ammonia stripping). Moreover, the resulting cultivation medium must be light-permeable. Various studies show that growth rates comparable to those in artificial media can be achieved when proper digestate treatment is used. The necessary steps for obtaining a suitable cultivation medium also depend on the microalgae species to be cultivated. Concerning the application of the biomass, legal aspects and impurities originating from digestate must be considered. Furthermore, microalgae species and their application fields are essential criteria when selecting downstream processing methods (harvest, disintegration, dehydration, product purification). Microalgae grown on digestate can be used to produce various products (e.g., bioenergy, animal feed, bioplastics, and biofertilizers). This review gives insight into the origin and composition of digestate, processing options to meet requirements for microalgae cultivation and challenges regarding downstream processing and products.

Microalgae Cultivation on Nutrient Rich Digestate: The Importance of Strain and Digestate Tailoring under PH Control

“…Microalgae have been widely studied to remediate wastewater from water treatment processes, aquaculture facilities, and other industries [3][4][5], and there has been a growing interest in utilising their bioremediation properties to tackle the growing digestate issue in Northwest Europe [6][7][8]. Indeed, digestate composition shows a vast potential to support microalgal growth, especially in terms of macronutrients such as phosphorus and nitrogen [9,10], and also other microelements, which, at the right concentrations, can provide essential nutrition to microalgae [11].…”

Integrated Approach for Carbon Sequestration and Wastewater Treatment Using Algal–Bacterial Consortia: Opportunities and Challenges

“…In an open pond system, this leads to the escape of CO 2 into the atmosphere [110,111]. With varying temperatures, the insoluble solids and other components can contribute to dark coloration, especially in the waste streams, leading to absorbance of light of certain wavelength, reducing the available light energy impacting photosynthesis of algae [112]. Temperature also affects all the metabolic activities of algal cell by highly influencing the cell composition, nutrient and CO 2 uptake, and ultimately, the growth rate.…”

“…A recent estimate shows that the average cost for cultivation of algae is EUR 10 kg −1 , of which a considerable part accounts to nutrient inputs. Given such huge requirements of water and chemical nutrients, wastewaters with abundant organic (C, N, and P) and inorganic nutrients serve as best substitutes [81,112,131], and the costs can be reduced to less than EUR 5 kg −1 [112,132,133]; a few reports on microalgae-based wastewater treatments are summarized in Table 2. Due to the nutrient removal efficiency, microalgal cultivation in wastewater reduces the requirement of chemicals for their growth, thereby providing the additional advantage of eco-friendly wastewater treatment.…”

Characterization of an aerated submerged hollow fiber ultrafiltration device for efficient microalgae harvesting

“…Frequently occurring suspended macromolecules make employment of alternative approaches with active filter cake or clogging removal necessary. These could be crossflow filtration, for example, in the construction form of dynamic crossflow filtration [4, 12]. The use of filter aids like in yeast filtration is not applicable.…”