New concept of biodiesel production using food waste digestate powder: Co-culturing algae-activated sludge symbiotic system in low N and P paper mill wastewater

This paper aims to demonstrate an innovative process for the conversion of food waste digestate (FWD) powder into biofuel. The effects of different doses of FWD are investigated on microalgae-activated sludge (MAS) in treating pulp and paper mill wastewater (PPW) which generally contains insufficient nitrogen and phosphorus. FWD was added to adjust the initial N:P molar ratio in MAS at various levels (8:1 to 15:1). The highest Auxenochlorella protothecoides biomass achieved was 1.67 gL(-1) at a 13.45:1 N/P molar ratio of PPW. After 10 days of cultivation, Auxenochlorella protothecoides-activated sludge system removed 91.7%, 74.6%, and 91.5 % of total nitrogen, phospho-rus, and sCOD respectively at D0.836 gL-1 DD. The highest lipid productivity was reported as 41.27 +/- 2.43 mg L-1 day(-1). Fatty acid methyl ester (FAME) analysis showed the presence of an appreciable percentage of balanced satu-rated and unsaturated fatty acids i.e. palmitic, oleic, and linoleic acid, rendering its potential as a feedstock for biodie-sel production. Activated sludge induced flocculation of Auxenochlorella protothecoides was measured. The whole process establishes an effective means of circular economy, where the secondary source of recyclable nutrients i.e. FWD will be used as a source of N and P in PPW to obtain algal biodiesel from a negative value industrial wastewater.

Automated summary

This paper presents an innovative process for converting food waste digestate into biofuel and investigates the effects of different doses of digestate on microalgae-activated sludge in treating pulp and paper mill wastewater. The study shows that adjusting the N:P molar ratio in the sludge by adding digestate can enhance biomass production and remove nitrogen, phosphorus, and COD from the wastewater. The process demonstrates the potential for a circular economy and biodiesel production.