VALORIZATION OF SEWAGE SLUDGE THROUGH THE INCORPORATION OF DATE PALM PETIOLES PRIOR TO COMPOSTING

Abstract

The agricultural reuse of sewage sludge is often limited by its relatively low carbon-to-nitrogen ratio and the presence of potentially toxic elements. This study investigated the use of date palm (Phoenix dactylifera L.) petioles as a carbon-rich co-substrate to modify the initial characteristics of sewage sludge before composting. Five mixtures with different sludge-to- petiole mass ratios (100:0, 80:20, 60:40, 40:60, and 20:80, w/w) were prepared and characterized. Physicochemical properties (pH, electrical conductivity, nitrate concentration, and chemical oxygen demand), CHNS elemental composition, energy-dispersive X-ray fluorescence (ED-XRF), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS) were used to assess the characteristics and potential suitability of the mixtures as composting substrates. Increasing the proportion of date palm petioles progressively raised the carbon-to-nitrogen ratio from 6.51 in raw sewage sludge to 31.86 in the mixture containing 80% petioles, while nitrogen content and the relative concentrations of potentially toxic elements decreased through dilution. ED-XRF analysis showed that the mixtures retained the major mineral elements, while the relative concentrations of several trace elements decreased with increasing petiole proportion. FTIR spectra showed the coexistence of functional groups characteristic of sewage sludge and lignocellulosic biomass, while SEM–EDS observations revealed heterogeneous and porous structures. Overall, the results indicate that date palm petioles have good potential as a carbon- rich co-substrate for adjusting the initial characteristics of sewage sludge before composting. This approach also offers an opportunity to valorize two abundant organic residues and may contribute to more sustainable sludge management within a circular economy framework. Further composting experiments are required to determine the effects of these formulations on organic matter stabilization, compost maturity, nutrient evolution, and the agronomic quality of the final product.