Integrated production of edible mushrooms (pleurotus hk-37 and coprinus cinereus) and biogas from mixed solid sisal wastes.

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University of Dar es Salaam
Sisal fibre production in Tanzania uses only 2% of the plant and the remaining 98% of the biomass is waste. Although a threat to the environment, sisal wastes represent unexploited bio-resource that can be transformed into valuable bio-products. However, due to scantiness of innovative technologies and their adoption for production of valuable products, the waste remains underutilized and is disposed of improperly leading to environmental pollution. This study was therefore undertaken to establish suitable technological strategies for utilization of mixed solid sisal waste fractions namely sisal boles/stems (SB) and sisal leaf decortication residues (SL) for production of edible mushrooms and biogas. Although rich in organic matter, their fibrous nature and low nitrogen content limit the anaerobic digestion (AD) process. Mushroom cultivation prior to AD was included as an innovative way of alleviating these limitations. The suitability of mixed sisal wastes for mushroom cultivation was assessed with white rot basidiomycetous fungi namely; Coprinus cinereus and Pleurotus HK-37 on cow dung manure supplemented formulations. Biological efficiencies (BE) in the range of 7-64% were obtained for various formulations with the two mushrooms. Examination of lignocellulolytic enzymes profiles during mushroom growth revealed laccase to be predominant and highly expressed during full mycelia colonization compared to fruiting phase, whereas lignin peroxidase exhibited characteristic wave-like patterns with the highest peaks observed during full mycelia colonization and soon after first flush harvests. Carboxy-methyl cellulase activities were low in the vegetative phase, increased sharply after the first flush when pinheads appeared to initiate fruit body formation and declined during mushroom harvesting. Contrarily, xylanase activities were high during mycelia colonization phase and declined during the first primordia and fruiting body formation phases. For pectinase, activities increased during full mycelia colonization, followed by a characteristic wave-like pattern. The spent mushroom substrates (SMS) after mushroom cultivation were subsequently used for biogas production using batch bioreactors. AD of SMS gave higher biogas production compared to the controls in most cases up to the second flush harvest. Methane yields obtained (286-300 L/KgVSadded) indicated that SMS after the second mushroom flush still contained considerable organic matter to support AD. For microbial biomass immobilization, fish scales were used as methanogenic biofilm carriers during AD of SMS leachate in semi-batch bioreactor. For C. cinereus SMS leachate, highest chemical oxygen demand (COD) removal of around 62.1% was obtained with an OLR of less than 12.0 g COD/L/d where the highest mean methane yield of 30 ±8L/kgCODdegraded was achieved. For P. HK-37 SMS leachate, the highest COD removal of 71.48% was observed at OLR of 6.28 gCOD/L/d and a methane yield of 23L/kgCODdegraded obtained. This study has established an integrated process for the production of mushrooms and biogas from mixed solid sisal waste fractions. Sisal boles/stems were proven to be potential novel substrates for both mushroom cultivation and biogas production. The most suitable substrate formulations for both C. cinereus and P. HK-37cultivation were SL:SB (25:75) and SL:SB (50:50) supplemented with 20% and 30% cow dung manure, respectively. Essential baseline data for use in future research at pilot scale for AD of SMS to biogas is presented.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF QK617.T34R39)
Edible mushrooms, Biogas, Solid sisal waste, Sisal fibre production, Tanzania
Raymond, P. (2018). Integrated production of edible mushrooms (pleurotus hk-37 and coprinus cinereus) and biogas from mixed solid sisal wastes. Doctoral dissertation, University of Dar es Salaam.