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Effects of pure and mixed substrates of sisal waste, grass (Panicum coloratum) and a combination of the two substrates at 50:50 (w/w) on nutritional composition, minerals and antioxidant potential of sun-dried Pleurotus sapidus 969 were investigated in the present study. To determine the proximate chemical composition and antioxidant properties of the samples, standard analytical procedures were employed. Moisture content, crude protein and crude fibre ranged between 11.09-12.80%, 6.4-6.6% and 18.3-30.5%, respectively. Macro elements Ca, Mg, Na, K, and P were also found in substantial amounts with K being present in an exceedingly higher amount (541.3-657.1 mg/100g) than the other macro minerals. The samples from the three substrates contained antioxidant β-carotene (4.6-6.0 mg/100g), lycopene (4.9-5.1mg/100g), Vitamin C (5.2-5.6 mg/100g), phenols (361.0-859.0 mg of GA/g) and flavanoids (33.5-64.0 mg RE/g).Mushroom harvested from mixed substrates contained better nutritional qualities than the pure substrate, although the phenolic content in mushrooms cultivated on sisal substrate was higher. The results further showed that, all the extracts exhibited scavenging ability and metal chelating activity. The findings showed that Pleurotus sapidus 969 is rich in nutrients, macro minerals as well as natural antioxidant which could be explored for pharmaceutical applications.

Sisal leaf decortications residue (SLDR) is amongst the most abundant agro-industrial residues in Tanzania and is a good feedstock for biogas production. Pre-treatment of the residue prior to its anaerobic digestion (AD) was investigated using a two-stage pre-treatment approach with two fungal strains, CCHT-1 and Trichoderma reesei in succession in anaerobic batch bioreactors. AD of the pre-treated residue with CCTH-1 at 10% (wet weight inoculum/SLDR) inoculum concentration incubated for four days followed by incubation for eight days with 25% (wet weight inoculum/SLDR) of T. reesei gave a methane yield of 0.292 +/- 0.04 m(3) CH(4)/kg volatile solids (VS)(added). On reversing the pre-treatment succession of the fungal inocula using the same parameters followed by AD, methane yield decreased by about 55%. Generally, an increment in the range of 30-101% in methane yield in comparison to the un-treated SLDR was obtained. The results confirmed the potential of CCHT-1 followed by Trichoderma reesei fungi pre-treatment prior to AD to achieve significant improvement in biogas production from SLDR.

The degradation and biogas production potential of sisal fibre waste could be significantly increased by pre-treatment for reduction of particle size. Batch-wise anaerobic digestion of sisal fibre waste was carried out in 1-l digesters with fibre sizes ranging from 2 to 100 mm, at an ambient temperature of 33 °C. Sediment from a stabilisation pond at a sisal production plant was used as starter seed. Total fibre degradation increased from 31% to 70% for the 2 mm fibres, compared to untreated sisal fibres. Furthermore, the results confirmed that methane yield was inversely proportional to particle size. Methane yield increased by 23% when the fibres were cut to 2 mm size and was 0.22 m3 CH4/kg volatile solids, compared to 0.18 m3 CH4/kg volatile solids for untreated fibres. By anaerobic digestion and biogas production, the 148,000 tonne of waste sisal fibres generated annually in Tanzania could yield 22 million m3 of methane, and an additional 5 million m3 of methane if pre-treatment by size reduction to 2 mm was applied.

Pre-treatment of sisal pulp prior to its anaerobic digestion was investigated using an activated sludge mixed culture under aerobic conditions in batch bioreactors at 37 degrees C. The progression of aerobic pre-treatment of the residue in relation to the activities of some extracellular hydrolytic enzymes in the slurry was monitored. The highest activity of hydrolytic enzymes was obtained at 9 h of pre-treatment. Filter paper cellulase had a maximum activity of 0.90 IU/ml, while carboxymethyl cellulase, amylase and xylanase were produced to a maximum of about 0.40 IU/ml. The methane yield obtained after anaerobic digestion of the pre-treated pulp ranged between 0.12 and 0.24 m3 CH4/kg VS added. The highest and lowest values were obtained for 9 and 72 h of pre-treatment, respectively. Nine hours of pre-treatment of sisal pulp prior to anaerobic digestion demonstrated a 26% higher methane yield when compared to the sisal pulp without pre-treatment. The consortia of microorganisms in activated sludge demonstrated a useful potential in the production of hydrolases acting on major macromolecules of sisal pulp. The fact that a correlation was observed between high enzyme activity and high methane yield at 9 h of aerobic pre-treatment suggests that such a short pre-treatment period could be an alternative option for increasing solubilization of sisal pulp and promoting methane productivity.

Solid sisal waste fractions which included composted sisal boles and sisal leaves decortication residues supplemented with cow dung manure at various rates used singly and/or in combination as substrates were investigated for cultivation of oyster mushroom (Pleurotus HK-37). The effect of the test sisal waste substrates and cow dung manure of various supplementation rates were evaluated by mushroom yield, biological efficiency and mushroom size. Pinheads occurred in all substrates within 3 to 5 weeks of transfer of bags to the cropping room. The overall best results of mushroom production were obtained in a substrate combination of 50 % sisal leaves + 50 % sisal boles (based on 450 g wet weight substrate) supplemented by 30 % cow dung manure with the mushroom yield of 184.64 g fresh mushrooms/kg moist substrate weight and percentage biological efficiency (B.E) of about 63 %. Mushroom size of 6.10 was obtained in sisal boles substrate supplemented by 20 % cow dung manure. Least yield of 26.73 g fresh mushrooms/kg moist substrate weight and lowest B.E of 8.95 % were obtained from non-supplemented substrate of sisal leaves alone. The study concluded that, supplementation using cow dung manure may play an important role on increasing the yield and productivity of Pleurotus HK-37 on solid sisal waste fractions under the conditions investigated.

A single stage anaerobic digester employing a sisal fibre waste fixed bed was studied for biogas production from sisal pulp waste. The fibre was colonized by microorganisms involved in biogas production. The sisal pulp waste to be digested was fed from the top and was sprinkled intermittently with recirculating leachate from the material. Organic loading rates of 0.1-10 kg volatile solids (VS) m-3d-1 could be applied and methane yields in the range of 0.13-0.48 m3 CH4 kg-1 VS added were obtained. The average methane content in the biogas produced from sisal pulp waste was 55%, and the biogas production rate was 0.15-0.54 m3m-3d-1. The methane yield obtained and the highest organic loading rate that could be sustained by this simple, fixed-bed digester are indications of an attractive system in terms of performance and reliability. It is concluded that the sisal fibre waste fixed bed is a promising carrier for microbes and can be employed for long-term operation without changing the bed. Tanzania Journal of Science Vol. 31 (2) 2005: pp. 41-52

Three methanogenic biofilm bioreactors were studied to evaluate the performance of three types of carriers. The carrier material were consisted of sisal fibre waste, pumice stone and porous glass beads, and the bioprocess evaluated was the methanogenesis anaerobic digestion of sisal leaf waste leachate. Process performance was investigated by increasing the organic loading rate (OLR) step-wise. The best results were obtained from the bioreactor packed with sisal fibre waste. It had the highest chemical oxygen demand (COD) removal efficiencies in the range of 80-93% at OLRs in the range of 2.4-25 g COD L -1 d -1 . The degradation pattern of volatile fatty acids (VFAs) showed that the degradation of propionate was limiting at higher OLRs. The stable pH and higher partial alkalinity (PA) of the outflow illustrated that packed-bed bioreactors have a good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in a two-stage anaerobic process. In conclusion, sisal fibre waste was shown to be a novel promising biofilm carrier and would work very well in methanogenic biofilm bioreactors treating sisal leaf tissue waste leachate. Furthermore both sisal wastes are available in the neighbourhood of sisal industries, which makes anaerobic digestion scale up at sisal factory level feasible and cost-effective.

Co-digestion of various wastes has been shown to improve the digestibility of the materials and biogas yield. Batchwise digestion of sisal pulp and fish waste was studied both with the wastes separately and with mixtures in various proportions. While the highest methane yields from sisal pulp and fish waste alone were 0.32 and 0.39 m(3) CH4/kg volatile solids (VS), respectively, at total solid (TS) of 5%. co-digestion with 33% of fish waste and 67% of sisal pulp representing 16.6% of TS gave a methane yield of 0.62 m(3) CH4/kg VS added. This is an increase of 59-94% in the methane yield as compared to that obtained from the digestion of pure fractions at 5% TS. (C) 2004 Elsevier Ltd. All rights reserved.

The utilization of agro-industrial residues to cultivate edible mushrooms is of great environmental importance. However, the use of lignocellulose as carbon source depends on the capacity of the mushroom to produce lignocellulolytic enzymes and to secrete them to the extracellular substrate. Thus, the profile of lignocellulolytic enzymes produced during different phases of cultivation of Pleurotus HK-37 on sisal waste fractions supplemented with cow dung manure was determined. Mushroom cultivation was performed in plastic bags using substrates formulated by mixing various proportions of sisal leaf residues and sisal boles and supplementing with cow dung manure on dry weight basis. A total of three hydrolytic (carboxymethyl cellulase, pectinase and xylanase) and two oxidative (laccase and lignin peroxidase) enzymes produced by Pleurotus HK-37 were analyzed. Among these enzymes assayed, laccase was found to be predominant and highly expressed. After 30 days of incubation, its activity was 158.75 ± 7.66 Ug-1wet spent mushroom substrate (SMS) on 30% supplemented sisal leaf decortication residues: sisal boles (25:75) substrate formulation. The highest lignin peroxidase activity observed was 4.01 ± 1.12 Ug-1wet SMS during full mycelia colonization on unsupplemented sisal leaf decortication residues: sisal boles (25:75) substrate formulation. Meanwhile, for the hydrolytic enzymes; the highest carboxymethyl cellulase activity (5.45 Ug-1wet SMS) was observed on unsupplemeted sisal leaf decortication residues: sisal boles (75:25) substrate formulation 50 days after of substrate inoculation, that of xylanase (3.73 ± 0.98 Ug-1wet SMS) was found on 10% supplemented sisal leaf decortication residues: sisal boles (0:100) substrate formulation after 20 days and that of pectinase (8.28 ± 2.14 Ug-1wet SMS) was observed 20 days after substrate inoculation on 30% supplemented sisal leaf decortication residues: sisal boles (100:0) substrate formulation. The present investigation indicates the utilization of solid sisal wastes as support-substrate for production of both edible mushrooms and extracellular enzymes during solid state fermentation; it also provides an alternative approach and value-addition to these agrowaste residues.