Growth and photo-physiology of microalgal biofilms grown in food and piggery waste digestates

Abstract

Conventional suspension-based microalgae cultivation for treating anaerobically digested effluents (ADEs) suffers several setbacks such as inadequate light access, and expensive biomass harvesting. Biofilm cultivation is a promising alternative due to its simplicity, efficiency, and cost-effectiveness, but its applicability to a wide range of ADEs from diverse sources needs to be understood. Here, perfused biofilm approach was used to grow Chlorella sp. to treat anaerobically digested food (ADFE) and piggery (ADPE) effluents. To monitor the vitality and photosynthesis performance throughout the biofilm growth, chlorophyll-a fluorescence of the biofilm was studied in situ. Chlorella sp. grew successfully in ADPE with approximately 15 % and 12 % higher biomass yield and productivity than in ADFE. Approximately 10 % higher total ammonia nitrogen (TAN) removal efficiency was achieved in ADPE compared with ADFE. There was no difference in phosphate (up to 85 %) and COD (between 14 and 16 %) removal efficiencies in both effluents. The Chlorella species exhibited divergent photochemical mechanisms in both effluents. While it showed efficient transfer of electrons along the electron transport system in ADPE till day 10, inhibition of electron transport on day 4 was seen in ADFE, which improved later on day 10. Conversely, the efficiency of primary photochemistry (Fv/Fm) and the efficiency of water-splitting in PS II (Fv/Fo) reveal that the algae experience stress in the early stage of the culture in both effluents probably due to overcrowding or early acclimatization. The overall assessment of the Chlorophyll-a fluorescence parameters reveals more efficient photosystem activities in ADPE than in ADFE.