A sodium percarbonate/ultraviolet system generated free radicals for degrading capsaicin to alleviate inhibition of methane production during anaerobic digestion of lipids and food waste.

Abstract To alleviate inhibition of anaerobic digestion caused by capsaicin, which is easily soluble in the lipid components of food waste (FW), an advanced oxidation process with sodium percarbonate/ultraviolet (SPC/UV) was used to generate free radicals for degrading capsaicin and recovering methane production. Free radical sweeping showed that the free radicals •OH, O2•— and CO3•— worked together to degrade capsaicin. Gas chromatography-mass spectrometry showed that capsaicin likely had four degradation pathways via conversion into benzoquinone, and finally into carbon dioxide and water. The degradation rate of capsaicin in lipids increased from 62.2% to 96.0% when the SPC concentration increased from 2 mmol/L to 32 mmol/L (UV intensity = 20.66 mW/cm2). The degradation rate increased from 70.9% to 94.6% when the UV intensity increased from 20.66 mW/cm2 to 46.86 mW/cm2 (SPC concentration = 4 mmol/L). The subsequent products after capsaicin degradation were subjected to anaerobic digestion either directly or by adding FW. The reduced intracellular oxidative kinases of anaerobic digestion microorganisms recovered the CH4 yield from 27.2 mL/g-total volatile solids (TVS) with capsaicin to 311.2 mL/g-TVS with degraded capsaicin, which was 40.7% that of the control group (765.3 mL/g-TVS without capsaicin). After adding FW, the CH 4 yield of SPC/UV degradation effluent was 504.1 mL/g-TVS, which was 82.6% that of the control group (610.4 mL/g-TVS).