Articles
COMPOSTING OF THE SOLID FRACTION OF OLIVE MILL WASTEWATER
Article number
549_1
Pages
19 – 28
Language
English
Abstract
Two by-products from the olive mill industry, olive leaves (OL) and the solid fraction of the olive mill wastewater (SOMW), were transformed by composting with the aim of obtaining a stable material which could be used as an organic fertiliser.
The initial composting mixture consisted of 65% SOMW and 35% OL on a dry weight basis which is equivalent to 83% SOMW and 17% OL on a fresh weight basis.
The waste mixture was composted by the Rutgers static pile system, which maintains a temperature ceiling in the pile, through the on-demand removal of heat by ventilation.
Due to the high total organic carbon (CTO) to total nitrogen (NT) ratio of both wastes, the initial mixture had a CTO/NT ratio higher than that recommended for composting, which caused the required composting time to be longer than usual.
It should be noted that at the end of the biooxidative phase the mixture was very stable with little change in the values of pH (8.5), OM (44%), CTO (30%), and NT (1.8%) occurring during the maturation phase.
The value of the humification degree (CEC/CTO) was already higher than 1.7 at the end of the thermophilic phase, which would indicate that the material was mature according to the limit established for manure.
Therefore, this ratio cannot be used as a maturation index in this type of compost.
However, at the end of the biooxidative phase the compost had a humification index (CHA/CTO x 100) higher than 13%, a percentage of humic acids (CHA/CEXT x 100) higher than 62%, a humification ratio (CEXT/CTO x 100) higher than 22, a value of the CHA/CFA ratio higher than 1.6 and a value of the water soluble carbon (Cw) to organic nitrogen (NORG) ratio lower than 0.70. All these values indicated that the mixture had attained a high maturation degree.
The initial composting mixture consisted of 65% SOMW and 35% OL on a dry weight basis which is equivalent to 83% SOMW and 17% OL on a fresh weight basis.
The waste mixture was composted by the Rutgers static pile system, which maintains a temperature ceiling in the pile, through the on-demand removal of heat by ventilation.
Due to the high total organic carbon (CTO) to total nitrogen (NT) ratio of both wastes, the initial mixture had a CTO/NT ratio higher than that recommended for composting, which caused the required composting time to be longer than usual.
It should be noted that at the end of the biooxidative phase the mixture was very stable with little change in the values of pH (8.5), OM (44%), CTO (30%), and NT (1.8%) occurring during the maturation phase.
The value of the humification degree (CEC/CTO) was already higher than 1.7 at the end of the thermophilic phase, which would indicate that the material was mature according to the limit established for manure.
Therefore, this ratio cannot be used as a maturation index in this type of compost.
However, at the end of the biooxidative phase the compost had a humification index (CHA/CTO x 100) higher than 13%, a percentage of humic acids (CHA/CEXT x 100) higher than 62%, a humification ratio (CEXT/CTO x 100) higher than 22, a value of the CHA/CFA ratio higher than 1.6 and a value of the water soluble carbon (Cw) to organic nitrogen (NORG) ratio lower than 0.70. All these values indicated that the mixture had attained a high maturation degree.
Authors
A. Roig, A. García-Gómez, M.P. Bernal, J. Cegarra
Keywords
olive mill wastewater, olive leaf, composting, organic fertiliser
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