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Statistical model to infer potassium concentrations in compost produced by organic waste

Abstract:

Among the problems that must be satisfactorily faced and solved by the Universidad Central de Venezuela concerns the handling of solid waste produced by the University itself. The University Dining Hall, to take one extreme example, produces as much as 0.8 tons of solid waste a day. The inadequate handling of solid waste can give rise to unacceptable sanitary conditions that entail the deterioration of the temporary storage site. Among the options universally accepted to avoid this is the separation of organic solid waste to prepare compost. The general objective of this work was to set up a model that would allow us estimate conditions in the production of compost whose potassium contribution is reproducible. The solid waste generated in the kitchen of the University Dining Hall of the Universidad Central de Venezuela was used to make compost. The experiment consisted of the Box-Behnken fractionated factorial design using the factors identified and ranks of variation obtained in preliminary tests which were: solid waste (D), sawdust (C) and added humidity (A), as well as the period of aireation (B). The selected answer as an indicator of nutrient contribution was potassium. We thus prepared 29 different mixes of solid waste, where the factors considered according to the mentioned design were combined. The surface model consisted of obtaining a mathematical function of the form: y = β 0 + β iX ij + β ij X iX j + β 1X 1i + ε ij, ∀ i = 1,2,3,4 J = 1,2,3 where y corresponds to the analyzed answer, X ij is the factor i level j, finally ε ij the random error corresponding to these variables. The equation corresponding to the model of surface for the analyzed answer (amount of potassium, y 4) was obtained, grouped as follows: y 4 = 27,16 + 1,40A - 1,43B - 12,80C + 12,56D - 0,51AB - 3,36AC - 4,92AD + 3,63BC-1,70BD - 5,47CD. This equation is optimized until obtaining the maximum point. This is obtained using an interactive method with specific software. Finally, a model was designed that allows us to establish the conditions of initial mixture to prepare compost whose potassium contribution is repeated.