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Mangroves are threatened with extinction worldwide. Many mangrove reforestation projects have been developed, but very few have achieved their restoration objectives. With the ambitions to contribute for rehabilitation of mangrove ecosystems, the aim of this study was to assess the effects of substrate composition and level of insertion on the growth and development of Rhizophora seedlings in nurseries. The experiment was conducted in a semi-lighted nursery set up in situ. Rhizophora propagules were reared on three types of mangrove substrates (type 1:75% of mud and 25% of sand; type 2: 50% of mud and 50% of sand, and type 3: 25% of mud and 75% of sand) with different levels of insertion (at ¼; ½ and ¾). Seedling heights and diameters were recorded, as well as the time of appearance of the first leaves and the variation of number of leaves. The greatest average height (40.2 ± 7.48 cm) and the highest mean diameter (1.2 ± 0.01 cm) were obtained for the substrate composed of 75% mud and 25% sand. The best growth and development of seedlings were recorded on the substrate type 1 with an insertion at ¼. Seedling production at ¼ insertion of substrate type 1 appeared the most effective combination. The production of Rhizophora seedlings on the substrate combining 25% Sand and 75% Mud with an insertion level at 1/4 seems to be the best method for the complete restoration and rehabilitation of the mangrove ecosystem of the Wouri estuary.

Waste management is a major concern in large cities under heavy demographic pressure. Landfill, the oldest form of solid waste management is gradually being replaced by new technics such as biomethanisation. With the purpose of contributing to the achievement of one of the Sustainable Development Goals, particularly SDG7 (affordable and clean energy), the aim of this study is to assess the fermentable fraction of organic wastes into biogas. This survey was carried out in and around Douala city. Biological material consisted of water hyacinth (WH), household wastes (HW), oil palm wastes (OPW) and a mixture of these three substrates (MS) was collected and introduced with cow dung used as inoculum in a biodigester. Some physico-chemical parameters of substrates were determined. Results have shown that substrates used have a pH around neutral. The C/N ratio has shown an excess of nitrogen in the WH, but a deficit in the OPW and MS. The household wastes have presented an ideal ratio for the biological stability of the anaerobic digestion system (21.153 ± 0.695). At the end of the experimentation, a large degradation of organic matter has been observed with COD decrease rates of 37.55 ± 0.12 % (WH), 45.46 ± 0.60% (HW), 48.27 ± 0.34% (OPW) and 46.71 ± 0.26% (MS). All air chambers were inflated and the combustion has shown a blue flame, proof of very high proportions of methane in the flammable biogas. A sanitation process has led to clean energy production. [ABSTRACT FROM AUTHOR]