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This work examines the biorefining potential of mixed fruit and vegetable waste generated in star-category hotels in the National Capital Region (NCR) in India, targeting recovery of high value bioactive phytochemicals, biogas (energy) and digestate (soil amender). Grab sample of fruit and vegetable waste collected from a selected star-category hotel was analyzed for its composition and antioxidant characteristics. Through a primary survey of 15 such hotels, fruit and vegetable consumption and the corresponding waste generation was estimated and the organic waste management practices examined. Based on the survey data, a model waste (consisting of peels of pineapple, papaya, potato, pomegranate, apple, onion and citrus) was prepared. Phytochemicals recovery procedure was optimized for both real and the model mixed waste. Trolox equivalent antioxidant capacity (TEAC) was determined by both 2,2 diphenyl-1-picrylhydrazyl (DPPH) and 2-2 azinobis (3-ethyl-benzothiazoline-6-sulphonic acid) (ABTS) assays followed by preliminary identification of the phytochemicals. The efficacy of the anaerobic digestion (AD) of the model waste was tested before phytochemicals recovery (NT sample) and in the solid residue left after phytochemicals recovery (T-1 and T-2 samples). A preliminary estimate of annual resource recovery and resource productivity was performed and a circular bioeconomy framework proposed.
Star-category hotels in NCR generate fruit and vegetable waste mostly as peels that forms a major component (~ 47%) of the total fruits and vegetables consumed. Waste management practices are variable ranging from complete in-house handling (through composting, vermicomposting or utilization as livestock feed) to complete disposal to the urban local bodies (ULBs) that either landfill, utilize in waste-to-energy plants or use the organic fraction for composting or biomethanation (with biogas production).
The optimal experimental conditions for maximum phytochemicals recovery and antioxidant activity was ultrasonic assisted extraction of vacuum dried, dichloromethane (DCM) treated samples in 70% acetone (real hotel waste) and ultrasonic assisted extraction of vacuum dried, non DCM treated samples in ~ 63% acetone (model waste, T-1 sample). For model waste, this resulted in total extractable polyphenols, TEP (30,494.30 ± 2,865.25 mg gallic acid equivalent, GAE / 100 g), total extractable flavonoids, TEF (303.77 ± 9.31 mg rutin equivalent, RE / g), total extractable flavones, TEFn (483.58 ± 16.28 mg RE / 100 g) and total extractable flavanols, TEFl (69.39 ± 4.53 mg catechin equivalent, CE / 100 g); TEAC with DPPH and ABTS assays was 641.05 ± 26.5 and 639.55 ± 10.88 μM TE respectively. These phytochemicals included various high-value compounds viz. gallic acid (158.6 ± 11.6 μg / g), ferulic acid (1,950.95 ± 97.94 μg / g), rutin (1,041.22 ± 52.56 μg / g) and catechin (269.92 ± 19.29 μg / g). Recovery and reuse of the extraction solvent (acetone, water and DCM) was possible.
Recovery of bioactive phytochemicals from mixed fruit and vegetable waste enhanced the AD process with shorter time lag in gas generation and increased production of biogas with higher methane (CH4) content. The biomethanation potential (BMP) (L / g VS) and CH4 content (%) was respectively, 0.198 ± 0.06 and 41 ± 3 (NT sample), 0.275 ± 0.36 and 57 ± 3 (T-1 sample) and 0.303 ± 0.39 and 62 ± 3 (T-2 sample).
From 126 star-category hotels of NCR generating ~ 13,013 MT of mixed fruit and vegetable waste, a preliminary estimate of annual recovery of resources viz. phytochemicals, biogas and digestate are respectively 799 MT, 1,06,973 m3, and 10,502 MT (T-1 sample) and 759 MT, 1,18,035 m3, and 9,096 MT (T-2 sample). For NT sample, the biogas and digestate production are 38,261 m3 and 10,762 MT respectively. A combination of phytochemicals recovery followed by AD is thus an alternative, biorefinery based concept for valorization of mixed fruit and vegetable waste from hotels. Sample T-1 is recommended in view of its highest resource productivity of 1.27, compared to 1.00 (T-2 sample) and 0.03 (NT sample). Overall, this study indicates the potential for capturing the maximum value from hotel fruit and vegetable waste with possibility of transitioning towards sustainable urban environment using a circular bioeconomy framework approach.
Keywords: hotel waste, fruit and vegetable waste, resource recovery, phytochemicals, bioactive compounds, trolox equivalent antioxidant capacity (TEAC), anaerobic digestion, biogas production, circular bioeconomy.
