Preparation of sludge-based recycled fertilizer

Abstract Phosphorus and nitrogen are the main nutrients in agricultural and municipal sludges. They runoff easily to waterways especially when sludges are used as fertilizers. The main goal of this study was to create a slow-release sludge-based recycled fertilizer that is stable and easy to handle and spread. The production of recycled fertilizer contained four steps: 1) adjusting and decreasing the pH of the sludge to prevent ammonium evaporating as ammonia, 2) drying the sludge to a suitable moisture content to enable granulation and pelleting, 3) granulating or pelleting the sludge with some additives to improve the quality of the fertilizer, 4) drying the produced fertilizers at room temperature. Additives in the granulation or pelleting process were biocarbon, calcium hydroxide or ammoniumsulfate. Elemental analysis and leaching tests of mixed recycled fertilizer product provided information about the mechanical strength and the total and soluble nutrient contents