Advanced microalgal cultivation in biomethanation digestate to maximize resource utilization of food waste leachate

The pressed-off leachate obtained from the organic fraction of the municipal solid waste (i.e. OFMSW or food waste) dewatering, is an acidic wastewater with high concentrations of organic matter, turbidity, and color that is difficult to treat but has a significant resource utilization potential. Anaerobic digestion is a well-known and efficient treatment method of the OFMSW leachate, yielding a biofuel (biogas) and a liquid digestate, rich in nutrients and organic compounds, which is more suitable than the OFMSW leachate for biomass conversion. Advanced microalgae cultivation has been identified as a promising technology that could maximize resource utilization of digestate of pressed-off leachate from food waste (FWPD), however the specific microalgae growth parameters on FWPD (e.g. nutrient concentrations, light, temperature, pH, etc.), are still unclear. Thus, an orthogonal experimental design was used to assess the impacts of different parameters on Chlorella vulgaris growth and nutrients utilization from FWPD. Three major factors were investigated at three levels: organic loading (52.55, 31.53, and 10.51 g VS·L^-1), light intensity (1000, 2000 and 3000 Lux) and photoperiod (8, 12 and 16 h). Range analysis results indicated that organic loading at 52.55 g VS·L^-1 was the most influential factor on microalgal biomass yield, total chlorophyll content, total nitrogen and total phosphorus recovery. Additionally, organic loading was also the driving factor for protein and carbohydrate accumulation in microalgal biomass, contrary to lipid accumulation where photoperiod was the predominant factor. The results of this study are providing novel information for the optimization of microalgae cultivation in FWPD and shed light on understanding the mechanisms dictating the process.