Sustained release properties of cement-bonded composites with organic waste based anaerobic digestate as nutrient carriers for marine microalgae.

Anaerobic digestate is an organic effluent from biogas plants that generate renewable energy from organic waste under anaerobic conditions. Cement-bonded digestate composites with digestates based on animal manure and food waste based were subjected to sustained release property tests to investigate their utility as nutrient carriers for phytoplankton grown in oligotrophic coastal seas. Batch experiments showed that inorganic phosphate, ammonium nitrogen, and dissolved organic nitrogen species were released from the cement-bonded digestate composite. The inorganic phosphate and ammonium nitrogen were used directly by phytoplankton. The amount of inorganic phosphate and ammonium nitrogen released from the cement-bonded digestate composite was strongly correlated with the inorganic phosphate or nitrogen levels in the composite. This correlation allowed us to estimate the amount of these compounds released from the cement-bonded digestate composite from their concentration of in the anaerobic digestate reactants. The nutrients released from the cement-bonded digestate composite were taken up by marine microalgae, making these composites an effective terrigenous nutrient carrier for the growth of marine microalgae. The cement-bonded digestate composite developed in this study connects terrigenous anaerobic digestate from biogas plants to oligotrophic coastal seas and thus creates a novel nutrient pathway.