Natural pigments and biogas recovery from cyanobacteria grown in treated wastewater. Fate of organic microcontaminants

Cyanobacterial wastewater-based biorefineries are a sustainable alternative to obtain high-value products with reduced costs. This study aimed to obtain phycobiliproteins and carotenoids, along with biogas from a wastewater-borne cyanobacterium grown in secondary effluent from an urban wastewater treatment plant, namely treated wastewater. For the first time, the presence of contaminants of emerging concern in concentrated pigment extracts was assessed. Tertiary wastewater treatment was conducted in a 3 L photobioreactor inoculated with Synechococcus sp., and operated in semi-continuous regime with a hydraulic retention time of 6 days. The carotenoid content was stable (reaching up to 4 mg g DW^-1) regardless of the wastewater composition, while the phycobiliprotein content (up to 214 mg g DW^-1) varied according to nitrogen availability. In concentrated pigment extracts, only 3 (out of 20) organic microcontaminants were detected. The biochemical methane potential of pigment-extracted biomass (222 NL CH₄ kg VS^-1) was still 72 % of raw biomass. In conclusion, a cyanobacteria culture rich in Synechococcus sp. appears as a promising source of bio-based products in a circular economy approach.