Transforming sludge-containing urban wastewater to clean energy and biochemicals via an algae-based carbon-neutral pyrolytic pathway

Traditional sludge management methods are energy and cost intensive. This study evaluated the filamentous cyanobacterium Pseudoscillatoria coralii BERC01 to remove sludge from wastewater while simultaneously producing biomass for clean energy. P. coralii BERC01 removed 99.99 % of the sludge and reduced other pollutants by 45–86 % within three days. The biomass was rich in carbon and hydrogen, with a high heating value of 21.60 MJ/kg, highlighting its potential as a feedstock for clean energy. The biomass was pyrolyzed at heating rates of 10–50 °C/min. The transformation demonstrated high energy efficiency, characterized by higher transformation efficiency (76–79 %), reduced activation energy (192–196 kJ/mol), and a lower energy barrier (∼4 kJ/mol) between activation energy and enthalpy values. The pyrolysis products primarily consisted of aliphatic compounds, ketones, esters, alkyl halides, and phenols. Additionally, an artificial neural network regression model was trained on MLP data to compute activation energy values, which closely aligned with pyrolysis data interpretations (R2 > 0.988). The M-DAEM model also accurately fitted the experimental data (R2 > 0.993), further validating the pyrolysis results. This research underscores the integration of cyanobacteria-based wastewater treatment with pyrolysis as a sustainable sludge management strategy, paving the way for carbon-neutral resource recovery and energy production.