Reducing nitrogen losses during composting of poultry manure using the natural zeolite clinoptilolite

• Main Author: Kithome, Mussolini
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8430

Loss of N via NH₃ volatilization during composting of poultry manure reduces the agronomic value of the end-product and contributes to environmental pollution. The objectives of this study were to evaluate N losses via NH₃ volatilization during aerobic composting of poultry layer manure, examine the potential of natural zeolites to adsorb the volatilized NH₃ during composting, and evaluate the poultry manure-zeolite compost as a controlled-release N fertilizer. Eleven mineral samples were characterized for their physical properties, chemical composition, and NH₄⁺ adsorption capacity. The effectiveness of a clinoptilolite zeolite ZI as an NH₄⁺ adsorbent at pH range 4 to 7 was tested. The kinetics of NH₄⁺ exchange on the zeolite was evaluated at the pH range 4 to 7, initial NH₄⁺ concentrations ranging from 70.1 to 1401 mgN L⁻¹, and a temperature range of 25 to 55 °C. Ammonia emissions were measured during composting of poultry manure with zeolites and other amendments in a laboratory composting simulator. The resulting composts were applied to a sand based medium planted with ryegrass (Lolium multiflorum) where growth, N uptake, and NH₄⁺ and N0₃⁻ leaching were evaluated. The cation exchange capacity (CEC) and purity of the zeolites, with respect to mineralogy and constituent ions, influenced their affinity and adsorptive capacity for NH₄⁺. The amount of NH₄ ⁺ adsorbed increased with increasing pH and NH₄⁺ concentration. The estimated NH₄⁺ adsorption capacity increased linearly with pH (r2 = 0.994), ranging from 9660 mg N L⁻¹ at pH 4 to 13830 mg N L⁻¹ at pH 7. Studies on thermodynamics of NH₄⁺exchange on the zeolite ZI indicated a higher activation energy for desorption (5.65 kJ mol1) than for adsorption (2.32 kJ mol⁻¹). Composting poultry manure with 60% zeolite ZI (weight basis) reduced NH₃ losses by 44.3%. The compost had total N concentration of 17.04 g N kg⁻¹ and a high NH₄ ⁺ concentration (52.8% of the total N). The 60% zeolite Zl-amended compost treatment produced the highest ryegrass dry matter, N accumulation and N use efficiency compared to the other composts evaluated. Nitrogen leaching losses were low. Although composting poultry manure amended with the natural zeolite clinoptilolite can reduce N losses to the atmosphere, recycling it for crop utilization, the cost of the high amount of zeolite required may be prohibitive.