Direct PHA production from sewage sludge: a scalable strategy for wastewater resource recovery

Polyhydroxyalkanoates (PHA) are biodegradable polymers with wide-ranging industrial applications. Producing PHAs from sewage sludge offers a sustainable waste valorization and biopolymer synthesis strategy. Sewage sludge, a byproduct of wastewater treatment, is rich in organic carbon and thus serves as a suitable substrate for microbial PHA production. This process reduces the environmental burden of sludge disposal and enhances the economic feasibility of biopolymer production by using low-cost feedstock. Despite promising advances, large-scale implementation remains limited due to insufficient economic and ecological validation, as most studies focus on laboratory-scale optimization. This study presents encouraging preliminary results from batch experiments using three types of sludge: conventional activated sludge, integrated fixed-film activated sludge and mixed microalgae-activated sludge. The direct accumulation strategy was employed through controlled pulse-feeding and PHA was extracted using the green solvent 2-methyltetrahydrofuran. Preliminary results show consistent PHA production for activated sludge, achieving 23.1 ± 4.5 gPHA g-1 VSS. The extraction process yielded high purity (85 ± 6%) and recovery efficiency (87 ± 2%). Ongoing experimental activities will test the efficiency of different sludge samples, validating the integration of the direct accumulation approach into future water resource recovery facilities paving the way for environmentally sustainable and economically viable biopolymer production.