DEVELOPMENT AND OPTIMIZATION OF MICROBIAL COMPOST POWDER FOR CLAY PELLETS: TOWARD A FUNCTIONAL AND MARKETABLE GROWING MEDIA

Abstract

This study presents the development and optimization of a microbial-enriched compost powder applied as a bioactive coating on porous fired-clay pellets, designed as a functional growing-media carrier derived from agricultural residues. The clay pellets were fabricated from locally sourced clay incorporating 15 wt% corn cob as a pore-forming additive and fired at 900°C to generate a lightweight porous ceramic matrix suitable for microbial attachment. Key physical and mechanical properties of the pellets, including firing shrinkage, water absorption, apparent porosity, bulk density, and compressive strength, were quantitatively evaluated to verify structural integrity and carrier performance. The compost powder was enriched with three functionally distinct microbial groups—phosphate-solubilizing, antagonistic, and nitrogen-fixing microorganisms—and their proportions were optimized using Response Surface Methodology based on a Box–Behnken Design. Butterhead lettuce was employed as a model plant to validate the functional response of the integrated carrier–coating system. The optimized formulation (0.7% phosphate solubilizers, 0.235% antagonists, and 2.7% nitrogen fixers, w/w) produced a shoot dry weight of 2.83 g, in close agreement with the model-predicted value of 2.84 g (R² = 0.9938). The results demonstrate that biomass-modified fired-clay pellets can provide a mechanically stable and porous carrier platform for microbial compost coatings, while statistical optimization supports effective tuning of biological inputs within a fixed engineered matrix. The integrated system shows potential as a waste-derived functional material relevant to sustainable growing media and environmental engineering applications.