Evaluation of physicochemical, microbiological, and energetic characteristics of four agricultural wastes for use in the production of green energy in Moroccan farms

BACKGROUND: Animal husbandry is one of the agricultural activities that generates economic benefits for agriculture. We detected significant development of these activities in Morocco. Currently, it is stuck between the increase of organic waste polluting the farm environment and the energy needed to ensure the activities. Faced with this challenge, we determined all physical, chemical, and microbiological characteristics for livestock wastes most spread in Morocco. We evaluated also their ability to be used as bioresources for the anaerobic digestion and incineration ways for energy production to agricultural units. METHODS: We worked on four organic wastes (cow dung, horse manure, broiler droppings, and the excrement of laboratory mouse). The physical, chemical, and microbiological characteristics: moisture, total solids, volatile solids, organic carbon, nitrogen, ions and heavy metals, staphylococci, coliforms, yeasts and fungi and total aerobic mesophilic bacteria are determined by standard methods. The determination of lower heating value is performed with calorimetric bomb. The biogas production is determined by four batch types of digesters. All digesters are incubated at 35 ± 1 ℃ for 40 days. The volumes of biogas produced are corrected under standard pressure and temperature conditions. RESULTS: We noticed that the four agricultural wastes have a lower heating value closer to each other. When comparing the physicochemical composition of our wastes with that of Tanner’s theoretical waste, we have found that the valorization of these organic wastes by incineration is without energy and economic benefits. The microbiological content reflects the presence of a reservoir of pathogenic bacteria. On the other hand, the biogas potential shows that cow waste produces the largest amount of biogas. The co-digestion is necessary for horse manure, chicken manure, and excrement of laboratory mouse in order to increase their biogas potential. The mineral composition shows the possibility of using digestate of these wastes as an organic amendment to plants. CONCLUSIONS: The comparison of the physicochemical and microbiological characteristics of the four organic wastes in Morocco reflects some important points. Firstly, there is an urgency to intervene to treat and valorize these wastes before putting them in the open air. Secondly, the incineration of this waste is inadequate from an energy point of view. In the third position, these wastes present a great ability to be used as feed substrates of farm digesters. Finally, the biogas potential and the mineral composition of these wastes demonstrates the ability to use them as bioresources capable of producing green energy and an organic amendment to Moroccan farms.