Integration of dairy manure wastewater treatment and biofuel production by microalgae-bacteria consortia in a biofilm reactor

Abstract

Microalgae can efficiently remove nutrients and pollutants from wastewater while converting these substances into reusable biomass. This study explores the potential of microalgae for dairy manure wastewater (DMW) treatment via optimizing process conditions, and employing an algal-bacterial biofilm for continuous wastewater treatment coupling with bioproducts production. A pollutant-tolerant microalga Desmodesmus sp. and a bacterium Bacillus megaterium (Ds-Bm), when co-cultured in suspension, demonstrated efficacy in removing COD and ammonia nitrogen of 50 % raw DMW wastewater under an adjusted nitrogen: phosphorous ratio of 16:1. The total lipid content increased by 45.9 % compared to pure algae culture. A continuous algae-bacterial biofilm photobioreactor was then constructed for raw DMW wastewater treatment without dilution, achieving a COD removal efficiency of 85–92.2 % and meeting the emission standards for livestock wastewater. The ammonium nitrogen removal load reached 4.6 g N/m³/d, with a maximum removal efficiency of 46.5 %. Following a 21-day operation, algae biomass notably increased (the yield and productivity were 122.5 g/m² and 3.7 g/m²/d), with a 15.8 % lipid content. Cultivation in DMW led to a significant reduction in the C18:3 polyunsaturated fatty acid content (<12 %), ensuring compliance with biodiesel feedstock standards. Hence, this Ds-Bm biofilm photobioreactor offers promise for effective wastewater treatment and cost-efficient biodiesel production.