Valorization of trout skins for a circular bioeconomy: Ecological leather production and anaerobic co-digestion of tanning effluents with trout byproducts (Morocco)

Abstract

• Vegetable tanning of fish skins is an alternative for the leather industry. • Pinus halpensis tree bark contains high levels of tannin. • Co-digestion of RTBP with effluent produced a methane yield between 217 and 318 Nml/gVS. • Toxicity of tannin oxidation byproducts causes low biodegradability in S2 and S3. With growing environmental concerns, sustainable alternatives in the leather industry are crucial. This study explores the potential of trout skins as a raw material to produce ecological leather and evaluates the biodegradability of the co-digestion of its effluents with the byproducts of the same fish. The biodegradability of the three substrates S1, S2 and S3 was 67.54%, 41.95% and 37.69% respectively, while the experimental methanogenic potential was 318 Nml/g VS, 249 Nml/g VS and 217 Nml/gVS respectively. Four kinetic models were used to calculate the theoretical methanogenic potential of the three substrates: Logistic function, Modified Gompertz, Transference function and First order. The methane yield nearest to the experimental findings is that predicted by Logistic function, for S1 the yield was 314.92 Nml/g VS with a percentage error equal to 1.03%, for S2 the yield was 249.38 Nml/g VS (% error = 0.16%), and for S3 the yield was 218.57 Nml/g VS (% error = 0.75%). Also, the results predicted by the Modified Gompertz model were close to experimental results. This confirms that the best models for estimating the methane yield from the co-digestion of trout byproducts and tannery effluent are the Modified Gompertz and Logistic function models. These findings give managers and green economy stakeholders the information they need to create suitable plans for handling organic waste.