Treatment of food waste digestate using microalgae-based systems with low-intensity light-emitting diodes

Abstract

Anaerobic digestion of food wastes coupled with digestate post-treatment using microalgae-based systems could recover large amounts of energy and nutrients worldwide. However microalgae inhibition by high ammonia concentrations and low light transmittances affecting photosynthesis should be overcome to develop full scale implementations. This study evaluated the potential of microalgae-based reactors supplied with red LEDs at low intensity (660 nm and 15 μmol·m-2·s-1) to treat food waste digestate. LED reactors were compared with control reactors exposed to natural solar radiation. From a range of species in the inoculum, Chlorella vulgaris showed high adaptation to both lighting regimes and digestate environmental conditions, characterized by a C:N:P ratio of 74:74:1. Removal efficiencies for control and LED reactors were 84.0% and 95.8 % for soluble COD and 89.4% and 53.0 % for ammonia, respectively. Approximately 50% of ammonia in control reactor and 15% in LED reactor was lost mainly through volatilization, whereas 17% and 36% of ammonia was transformed in organic nitrogen in control and LED reactors, respectively. Low-intensity LEDs maintained microalgae growth in levels similar to solar radiation and supported efficient digestate treatment, showing a potential for further application in optimization of full scale reactors at a relatively low energy cost.