Exploring technological strategies for valorization of solid sisal waste: A research review

Abstract

The sisal industry in Tanzania generates large amounts of waste which is an un-tapped bioresource. Research was undertaken to establish appropriate technologies  for its valorisation to mushrooms, biogas and biogas manure (BGM).Physical and biological pre-treatments achieved methane yield increments of 23-30% whereas co-digestion with fish waste achieved methane yield increments of 59-94%. Sisal fibre waste was demonstrated to be a novel biofilm-carrier for treating sisal pulp leachate. With a loading rate of 9.0 kgVS/m³/day, the packed-bed bioreactor was operated without process stress. Sisal decortication waste (SLDW) and sisal boles (SBW) were found to be suitable for oyster mushroom cultivation. With water-pretreated SBW and saline-SLDW, biological efficiencies of  26-86% were obtained. SBW was utilized for commercial-scale mushroom cultivation and yielded 250kg/ton of wet substrate. Residues of mushroom cultivation (SMS) were anaerobically co-digested with cow dung manure and yielded 230-300L CH₄/kg VS_added which indicated  the potential of SMS for AD.Co-digestion of SLDW with cow dung manure in a 10m³ continuous stirred tank reactor gave about 400 litres CH₄/ m³/day, and 260 L/day of BGM  which was superior to NPK fertilizer. In conclusion, sisal waste has potential for valorisation, and integrating mushroom and biogas production for better economics  is feasible.

Key words: sisal waste, anaerobic digestion, mushrooms, valorisation