Construction of an efficient microalgal-fungal co-cultivation system for swine wastewater treatment: Nutrients removal and extracellular polymeric substances (EPS)-mediated aggregated structure formation

Microalgal-fungal co-cultivation technology has demonstrated outstanding efficacy in wastewater treatment and valuable resources recovery. However, it is still unclear how extracellular polymeric substances (EPS) could potentially affect the formation and development of co-cultivation aggregates. In this work, efficient microalgal-fungal co-cultivation systems (MFCS) were developed for swine wastewater treatment. Different co-cultivation systems were established using various microalgae (Chlorella sorokiniana and Scenedesmus dimorphus) with fungi (Aspergillus oryzae or Aspergillus niger). The results showed that the introduction of fungi improved nutrient removal, and C. sorokiniana-A. oryzae co-cultivation system demonstrated the highest removal efficiency for chemical oxygen demand (COD) (85.9 %), ammonium (NH4+-N) (76.5 %), and total phosphorus (TP) (60.3 %). Biomass production in co-cultivation system was higher, and S. dimorphus-A. oryzae co-cultivation system achieved the highest biomass production of 0.74 g/L. In addition, the lipid content in co-cultivation system was up to 33.3 %, which was 1.8 times higher than that in the mono-cultivation group. Besides biomass production, A. oryzae also promoted the photosynthetic activity of C. sorokiniana, showing higher pigments content and electron transport efficiency. The morphology of co-cultivation systems displayed complex interactions between fungi and microalgae, forming aggregated structures. The analysis of EPS demonstrated their importance in the formation and stabilization of microalgae-fungal aggregates. Moreover, proteins and polysaccharides, along with chemical bonds (N-H, C = O and C-O-C), played a crucial role in the formation and development of aggregates. This study provides insights into the potential of MFCS for swine wastewater treatment, highlighting the importance of species selection and EPS-mediated interactions in enhancing system performance.