Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE)

Abstract

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m−2) than Scenedesmus sp. biofilm (9.39 g m−2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L−1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L−1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L−1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L−1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L−1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68–81 % of removed nitrogen in biomass, while in suspension, only 55–71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.