Evaluation of chlorophyll and anti-oxidative components harvested from the anaerobic digestion of fruit and vegetable waste

• Two-phase anaerobic sludge blanket filter system is built with packed concentric column for increasing sludge retention time (SRT) during treatment of fruit and vegetable waste (FVW).
• A suitable SRT is manifested crucial for feeding homogenate of FVW in batch operation without circulation of sludge.
• Pigments and related antioxidants were present in the suspension solid gradually accumulated in the digester.
• Recycle of fruit and vegetable resources concerning pigments and anti-oxidative compounds is proposed.

Two-phase up-flow sludge blanket filter (TUBF) digestion process of fruit and vegetable waste homogenate generated anaerobic sludge with concentrated pigments and reducing compounds. In the 5–50 L scale-up daily batch and semi-batch operations, the organic loading rate attained was over 6 kg COD/m3.day. A comparative study indicated that Minox polyethylene ring packing was critical for optimization of anaerobic digestion. The biogas production in terms of the volatile fatty acid pattern with a C2–C6 level of 600 mg/L through liquefaction and acidification (LA) maintained the alkalinity over 3500 mg/L and stabilized the pH of the LA phase at 5.2–6.8 according to the loading status. In the semi-batch operation of 50 L, pigments gradually condensed in the sludge layer were concentrated by a factor of at least ten fold, and a high level of reducing activity was retained by the chlorophyll and anti-oxidative components.