Water resource recovery coupling microalgae wastewater treatment and sludge co-digestion for bio-wastes valorisation at industrial pilot-scale.

Abstract This case study is part of a circular bioeconomy project for a winery company aiming to integrate a microalgae-based system within the existing facilities of the winery WWTP, promoting nutrient recovery and transformation into valuable products and bioenergy. Microalgae were used for wastewater treatment, removing N-NH 4 + (97%) and P-PO 4 -3 (93%). A pilot anaerobic reactor was used for batch anaerobic mono-digestion of secondary sludge (WAS) and for co-digestion of WAS and algal biomass. The methane yield using WAS from two different wine production seasons was 155.4 and 132.9 NL CH4 kg VS-1. Co-digestion led to the highest methane yield (225.8 NL CH4 kg VS-1). The application of the bio-wastes for fertilization was assessed through plant growth bioassays: mono- and co-digestion digestates and dry algal biomass enhanced plant biomass accumulation (growth indexes of 163%, 155% and 121% relative to those of the control - commercial amendment, respectively), demonstrating a lack of phytotoxicity.