Evaluation of the Physical–Chemical and Microbiological Characteristics of the Phospho-Compost Produced Under Forced Aeration System at the Industrial Scale

Abstract

The objective of this work was to evaluate the composting process of agro-industrial waste (coffee husk, plantain peel, bovine manure, and food waste) with rock phosphate supplementation using static piles with forced aeration. Three 5-tonne piles of waste were composted in each treatment; supplementation treatment contained 15% (dry basis) rock phosphate and the control did not. Carbon/nitrogen ratio, total and soluble phosphorus, oxygen concentration, pH, and temperature were measured throughout composting. Both treatments reached final C/N ratios about 9.0. Total and soluble phosphorus was higher for supplemented piles (6.4% and 154 ppm, respectively) compared to control (3.1% and 106 ppm, respectively). The lowest oxygen concentrations (below 40% oxygen saturation) was observed in the first 15 weeks. Based on their Solubilization Index (SI), 203 isolations of phosphate-solubilizing bacteria were obtained and characterized. For supplemented piles, molecular identification was made to the two isolates with the highest SI in the mesophilic phase and to one isolate in the thermophilic phase. Mesophilic isolates were identified as Pseudomonas aeruginosa and the thermophilic one as Nocardiopsis spp. (99% probability). Rock phosphate addition did not affect the final product quality, since both treatments comply with the parameters of mature compost. Compost supplementation with rock phosphate is a viable strategy not only to supply phosphorus to the soil, but also to increase its content of phosphate-solubilizing bacteria.