Controlled fermentation of food industrial wastes to develop a bioorganic fertilizer by using experimental design methodology

Abstract

A controlled fermentation was conducted to develop and design a bioorganic fertilizer based on three wastes generated by the food industry: olive mill wastewater (OMW), molasses and rice hulls by inoculation with selected strains of lactic acid bacteria (LAB), of the species “ Lactiplantibacillus plantarum” and “ Levilactobacillus brevis ” and of the yeast of the species “ candida famata ”. The fermentation with commercial yeasts and particularly the species of “ saccharomyces ” produced an unstable fertilizer with a high pH value (6.14).Whereas, the fermentation test with an inoculum composed of 20% yeast and 80% lactic acid bacteria showed a decrease in pH at 4.66 and a maximum enzymatic activity of 43.900 IU/l after 30 h. This combination allowed an appropriate morphological and microbiological quality of the bioorganic fertilizer. To determine with precision, the optimum conditions of this fermentation an optimization design was applied. As a result of experiments and statistical validation of the fitted model, the bioorganic fertilizer with the lowest pH value was achieved after fermentation of 53.2% OMW, 19.1% molasses, 21.3% rice hulls and 6.4% inoculum content. The final pH was able to reach a value of 4.07 with desirability of the order of 99.7%. A fertilizer with the lowest possible pH allowed farmers longer storage periods and required no special storage conditions.