Methanization Test of Water Hyacinth and Azolla in Co-digestion and Fertilizing Value of Digestates in Benin (West Africa)

Abstract

Faced with the need for an alternative energy source following the extreme pressure exerted on woody resources accompanied by the increase of aquatic pests which invade water resources, the construction of mini reactors producing clean energy, biogas based on these invasive plants becomes a challenge. This investigation aims to assess the methane production potential of water hyacinth and Azolla in co-digestion and the fertilizing quality of the digestates obtained. A bio methanization test based on various combinations of organic substrates composed of water hyacinth and Azolla alone or in co-digestion under laboratory conditions at mesophilic temperature and neutral pH after 27 days was carried out. The source of enrichment in anaerobic microorganisms for fermentation processes in micro bioreactors consists of fresh pig manure. It appears that the combination of organic substrates including 75% of water hyacinth generated the maximum quantity of methane which is 1234 liters for one ton of organic substrates. This methane production is 1.93 times greater than that of the bioreactor containing water hyacinth alone, 1.90 times that containing azolla, 1.5 times that containing 25% water hyacinth +75% azolla then 3.04 times that containing the bioreactor composed of a high proportion of crushed Azolla filiculoides. The digestates are rich in N, P, K, Ca and Mg and had an amending power according to the NFU 44051 standard. For the construction of bioreactors with aquatic pests for the benefit of communities, co-digestion with a combination of substrates with a high proportion of water hyacinth is suggested.