Transformation of alum sludge into biodegradable composite fertilizers: insights into nutrient release and availability.
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Tons of alum sludge (AS) are produced worldwide during the water treatment process, and the reuse of this waste could contribute to the circular economy of water treatment companies. The chemical composition of AS makes it a promising raw material for the development of zeolitic materials with potential agricultural applications.1 Biodegradable matrices have been used as a strategy to increase fertilization efficiency and reduce nutrient losses in fertilizers. A commonly used polysaccharide biopolymer is thermoplastic starch (TPS), widely employed in the development of such materials due to its low cost, high biodegradability, and flexibility, which allows the material to be molded into various shapes and facilitates granule production. In this work, we developed a composite fertilizer using TPS, urea (as both a plasticizer and nitrogen source), and zeolite synthesized from AS and evaluated its nutrient availability in greenhouse experiments. The zeolitic material was prepared from AS using an alkaline medium and autoclave treatment, resulting in sodalite zeolite (SOD-Na), which was later converted into SOD-K through a cation exchange process. Dry mass, chlorophyll content (SPAD index), and nutrient availability in the aerial parts of ryegrass (Lolium multiflorum) were evaluated across eight greenhouse treatments, containing: 1-AS; 2-AS+urea; 3-SOD-K; 4-SOD-K+urea; 5-Composite fertilizer; 6-Composite fertilizer+Trichoderma asperelloides; 7-Control; and 8-Control+urea. Results from the material incubation experiments clearly showed differences in plant growth and nutritional quality, with notable improvements in the treatments when the composite fertilizer was applied. Additionally, aluminum from AS was found to be strongly retained within the crystalline structure in the form of aluminosilicate, which ensures low availability of this element. The composite fertilizer developed using biodegradable matrices and AS shows potential as a controlled-release fertilizer.
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Alumínio, Fertilizante, Lodo Residual, Material Biodegradável, Aluminum, Sludge