Pyrolytic valorization of aquaculture wastewater-grown Mychonastes sp. biomass into renewable fuels and chemicals: Mechanistic insights into a circular bioenergy pathway

Aquaculture wastewater (AWW) represents an underutilized resource for sustainable energy production while posing environmental risks. This study presents a dual-function bioprocess using a newly isolated microalga, Mychonastes sp. ZUK01, to simultaneously remediate shrimp AWW and generate energy-rich biomass for pyrolytic conversion. Here, a circular bioenergy pathway referes to a closed-loop biological CO2 assimilation process during wastewater remediation, followed by pyrolytic conversion into renewable energy carriers. Cultivated under autotrophic conditions, ZUK01 achieved >95% removal of nitrogen, phosphate, and sulphate species within 15 days, alongside biomass productivity of 0.41 g/L and carbon capture (0.75 ± 0.051 g/L CO2). The biomass showed favorable characteristics for pyrolysis, including high volatile content (81.97 ± 0.27%), low ash (0.35 ± 0.09%), and a higher heating value of 18.80 MJ/kg. Thermogravimetric analysis (TGA/DSC) and iso-conversional kinetic modeling (Friedman, KAS, FWO) revealed a multi-stage degradation process with increasing activation energies (151.9–262.9 kJ/mol), indicating the progressive decomposition of complex biochemical fractions. Py-GCMS and TG-FTIR-MS analyses demonstrated temperature-dependent formation of carboxylic acids, hydrocarbons, nitrogenous volatiles, and aromatics, with 800 °C favoring hydrocarbon production. Collectively, these findings demonstrate a circular wastewater-microalgae-pyrolysis pathway that couples efficient nutrient remediation with biomass production and subsequently valorized into renewable fuels and chemicals via pyrolysis.