Cocoa beans are found inside an outer husk; 60% of the cocoa fruit is the outer husk, which is a waste biomass. The husk cannot be used directly as a soil amendment as it promotes the fungal black pod disease, which reduces crop yield. The pods are segregated from the trees, and their plant nutrient value is wasted. This is particularly true for the small acreage farmers in West Africa. Cocoa pod husk is well suited to be used as a biomass source for electricity production. The waste ash is rich in potassium, which can be converted in various chemical products, most notably, high-purity potassium carbonate. This study reviews the information known about cocoa and cocoa pod husk, and considers the socio-economic implications of creating a local economy based on collecting the cocoa pod husk for electricity production, coupled with the processing of the waste ash into various products. The study demonstrates that the concept is feasible, and also identifies the local conditions required to create this sustainable economic process.

Cashew apple bagasse is biomass rich in little-exploited lignocellulosic material. This study used this biomass as a support for cell immobilisation of Saccharomyces cerevisiae. For this purpose, the immobilisation technique by attachment to a surface was applied. The bagasse used in this study contained 32.6% lignin. After delignification, the lignin content of the bagasse was 3.33%. The cell density was 1.21 × 108 cells g-1 for the immobilised cells prepared for 24 h. For the immobilised cells prepared for 48 h, the cell density was 1.71 × 108 cells g-1. Microscopic observations showed that the adhesion of the yeast cells to the surface of the support occurred on all layers with the cells immobilised for 48 h. These results highlight the efficiency of cell immobilisation of S. cerevisiae on cashew apple bagasse.

The extraction of precious minerals leaves behind an important amount of tailings. When stored in nature, these tailings contribute to environmental degradation. To reduce this degradation, tailings are incorporated in construction as substitute to natural materials. The objective of this study was to use a design of experiments (DOE) to reveal how the substitution of natural river sand (NRS) by gold mine tailings (GMT) in concrete manufacturing can be optimally achieved. This DOE considered three constituents: the amounts of NRS/GMT, that of gravel and of cement. The experimental domain was defined within the concrete standards dosage of 350 kg/m3 and 400 kg/m3 as the lower and upper levels, respectively. The smallest compressive strength on standard cubic specimens on the 28th day varied between 11 N/mm2 and 37 N/mm2 following to the experimental domain. The values of the compressive strength of the experiments carried out allowed to acquire the model of the strength with the coefficients of each factor: Strength=23.25−5.86*A+4.56*B−1.96*C−0.56*A*B+1.41*A*C+1.08*B*C+0.71*A*B*C (with A: GMT+NRS; B: cement; C: gravel). The values of the cumulative weight of the coefficients of each factor were 36.7% (A), 64.5% (B) and 76.6% (C). The study also found that a larger dosage of gravel (40 kg) improves the concrete compressive strength when GMT substitutes NRS between 70% and 100% and when 15 kg of cement is used. For a sustainable and better reuse of GMT as construction materials, an economic and environmental study (the leaching of metals) of the concrete based on GMT would be ideal to consider a large scale production.