Waste-to-BioEnergy pathway for waste activated sludge from food processing industries: An experiment on the valorization potential under CO2 and N2 atmospheres through microwave-induced pyrolysis

Pyrolysis is a green and effective method for converting various waste streams into products with bio-energy potential. Waste activated sludge (WAS) from industries requires post-treatment before disposal and will cause serious pollution if not managed properly. Pyrolysis is a viable method for converting WAS into higher-value bio-products. This is the first study to use a lab-scaled microwave reactor to analyse WAS from a food processing and manufacturing company's wastewater treatment plant. The goal is to compare bioproduct formation under various N-2 and CO2 atmospheres in order to analyse the WAS waste-to-bioproduct transformation pathway. Result revealed that CO2 pyrolysis on WAS tends to: 1) increase water formation (similar to 19 wt%), 2) produce biochar with higher energy density profit (similar to 14%) and 3) generate gaseous products with a higher CO proportion (similar to 50 vol%). WAS pyrolysis under N-2 atmosphere showed 1) an overall better energy profit (<83.2 %), while producing 2) a higher gaseous yield (similar to 32 wt%) with 3) higher H-2 proportion (similar to 29 vol%) and 4) biochar of larger surface area (22 m(2)/g). Integrating CO2 as the pyrolysis medium utilises the excess CO2, potentially relieving the carbon burden on the environment.

Automated summary

Pyrolysis is an effective method for converting waste activated sludge (WAS) into higher-value bio-products, with CO2 pyrolysis tending to increase water formation, produce biochar with higher energy density and generate gaseous products with a higher CO proportion. WAS pyrolysis under N-2 atmosphere showed overall better energy profit, higher gaseous yield with higher H-2 proportion, and biochar of larger surface area. Integrating CO2 as the pyrolysis medium could potentially relieve the carbon burden on the environment.