Utilization of sisal waste for biotechnological applications: biogas, organic fertilizer, mushrooms and enzymes production

Sisal fibre processing generates large proportions of both wastewater and solid residues, which are not adequately utilized and disposed off untreated, leading to environmental pollution. Through waste audit at a sisal processing factory in Kenya, it was estimated that 611,875tonnes of sisalsolidwasteand3,511,900 m3ofsisal processing wastewater are produced annually. Anaerobic co-digestionofsolidsisalwastewithcowmanure generated a normalised methane yield of 0.329 m3/kg VS (added). Pre-treatment of the sisal residues reduces the salinity of the substrate for cultivation of Pleurotus species of mushrooms with high nutritional and antioxidant profiles. The results from this study indicate a diametrical cyclic pattern of Pleurotus enzymatic activities; laccase, manganese peroxidase and lignin peroxidase activities were high in vegetative growth phases and dropped upon initiation of fruiting body formation (18.1 U/ml, 7.9 U/ml and 0.32 U/ml, respectively). The nutritive and antioxidant potential of Pleurotus indicated the mainbioactivecomponents as phenoliccompounds,ascorbicacid,β-caroteneand lycopene (350.82-830.97 mg of GAEs/g, 5.07-5.29 mg/100g, 4.24-5.07 mg/100g, 4.44-5.05 mg/100g), respectively, as well as macro elements (Ca, Mg, Na, K, and P). These results indicate a possibility of harvesting enzymes for biotechnological applications as an extra benefit from mushroom cultivation on sisal waste. The results indicate that, the liquid biogas manure increased the available N, P and K contents in soils in addition to having a significantly higher effect (P≤ 0.05) on agronomic properties than that obtained with NPK fertilization. The physicochemical and nutritive properties of leafy vegetables investigated indicated crude proteins (0.81-11.37%) and high mineral elements contents. These results indicate that consumption of the leafy vegetables under investigation would contribute greatly to reduction of nutrition-related disorders for human health and to the food security.