Valorization of food waste digestate to ash and biochar composites for high performance adsorption of methylene blue

The valorization and appropriate treatment of food waste digestate (FWD) is a critical issue for facilitating the sustainable development of anaerobic digestion and actualizing a circular economic. The FWD contains high ash contents and is conventionally considered as an inappropriate feedstock for producing high-value products such as biochar. However, this ash content may also have a chance to enhance the application performance of biochar as an adsorbent if positive synergic effect is identified. This study used industrial FWD as a widely obtainable feedstock for producing ash-biochar composites (ABCs) for methylene blue (MB) contaminated wastewater abatement. The obtained ABCs performed a maximum MB adsorption capacity of 1123.5 mg/g. Mechanism and modeling assessments demonstrated that the ash components on the surface of ABC adsorbent enhanced MB removal by providing alkaline adsorption environment and more oxygen-based n-t interaction sites. In addition, increasing pyrolysis temperature enlarged the biochar surface area and homogenously rearranged the carbon structure to strength the t-t interaction between MB and ABC adsorbent. This research suggests that FWD is principally an ideal feedstock that can be directly used for making high-performance absorbents for wastewater treatment.

Automated summary

The valorization and appropriate treatment of food waste digestate (FWD) is crucial for sustainable anaerobic digestion and circular economy. This study demonstrates that industrial FWD, a widely available feedstock, can be used to produce ash-biochar composites (ABCs) for efficient wastewater treatment. The obtained ABCs show a high adsorption capacity for methylene blue (MB), and the mechanisms behind this adsorption involve the ash components providing an alkaline adsorption environment and the rearrangement of carbon structure strengthening the interaction between MB and ABC.