Evaluation of Lateritic Soil and (Fungal) Agaricus Impudicus Biomass for Adsorption–Desorption of Nitrogen and Phosphorus from Human Urine

Abstract

Human urine contains high concentrations of nitrogen and phosphorus, whose uncontrolled discharge contributes to eutrophication and nutrient losses in agricultural systems. Recovering these nutrients using low-cost natural materials offers a sustainable alternative to synthetic fertilizers. This study evaluated the performance of lateritic soil (LS) and fungal biomass (Agaricus impudicus) as potential adsorbents and desorbents for the recovery of ammonium nitrogen (NH₄⁺–N) and phosphorus (P) from human urine. The physicochemical properties of the adsorbents were characterized using Fourier Transform Infrared Spectroscopy, scanning electron microscope, X-ray Fluorescence (XRF), and elemental analysis. Batch adsorption experiments were conducted under varying operational conditions to evaluate nutrient recovery performance. Physicochemical properties of human urine were evaluated using atomic absorption spectrometry (AAS), nesslerization method, Molybdenum antimony colorimetric, pH meter and electrical conductivity meter. Time-dependent data were fitted using Pseudo first order (PFO), Pseudo second order (PSO), Elovich and Intra-Particle diffusion kinetic models. Equilibrium data were analyzed using Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm models to elucidate adsorption mechanisms and capacities. Batch and column desorption experiments were conducted to evaluate the desorption behavior of lateritic soils and fungal adsorbent. Elemental and XRF analysis revealed that lateritic soils possess aluminium and iron oxides that facilitate ligand exchange and inner sphere complexation during adsorption. Fungal biomass on the other hand, contains carboxyl and hydroxyl that enable adsorption of 〖NH〗_4^+-N and P via electrostatic bonding. PFO best described the time-dependent data for 〖NH〗_4^+-N and P adsorption for the two adsorbents indicating physisorption was the dominating adsorption mechanism. For 〖NH〗_4^+-N adsorption, the D–R model best described lateritic soil (R² = 0.968), indicating physical adsorption, whereas the Freundlich model best fitted A. impudicus biomass (R² = 0.813). Lateritic soil exhibited higher adsorption capacity (16.3 mg/g) than fungal biomass (12.0 mg/g). For phosphorus, the Langmuir model provided the best fit for both materials (R² = 0.939–0.946), with lateritic soil demonstrating a substantially higher capacity (24.6 mg/g) than fungi (6.2 mg/g), likely due to iron and aluminum oxides. Desorption tests showed that fungal biomass achieved the highest nutrient release (43.93% 〖NH〗_4^+-N and 44.83% P). Overall, lateritic soil and A. impudicus biomass exhibited promising adsorption–desorption performance, demonstrating their potential as low-cost, environmentally sustainable materials for nutrient recovery and circular fertilizer production. Thus, these results provide comparative evaluation of lateritic soil and fungal biomass for simultaneous nitrogen and phosphorus recovery from human urine. These findings also demonstrate the potential integration of locally available natural materials into decentralized sanitation and nutrient recycling systems for sustainable agriculture.