Production of zeolitic concentrates from water treatment plant sludge

Author(s)

Thais Beatriz Miqueleti de Sena

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2025-02-25

Examining board members

Cauê Ribeiro de Oliveira; Hudson Wallace Pereira de Carvalho; Ana Rita de Araujo Nogueira

• Advisor: Cauê Ribeiro de Oliveira

Abstract

The growing environmental concerns and the need for sustainable solutions to manage waste generated by water treatment plants (WTPs) motivated this work, which aimed to synthesize zeolitic concentrates from selected WTP sludges, characterize these materials, and evaluate their behavior in soil incubation experiments. Representative sludge samples were collected from WTPs at different times of the year, sourced from model stations managed by SABESP, which provided the residues. These samples were selected at the initial stage of zeolitic concentrate production. To ensure appropriate stoichiometry for zeolite precipitation, the Si/Al ratio was adjusted to maintain a 1:1 molar ratio of Si. The zeolitic concentrates were synthesized using the hydrothermal method, followed by processing in an autoclave for pre-pilot scale production in an alkaline medium containing 4 mol·L-1 NaOH. The process was conducted at 120°C for a 5-hour aging period. The final product consisted of a mixture of zeolite and other mineral phases, characterized using standard techniques, including mineralogical analysis by X-ray diffraction, chemical analysis by X-ray fluorescence, morphological evaluation by scanning electron microscopy, surface area and pore volume analysis by N2 physisorption, and thermogravimetric analysis to study yield. A crucial aspect of the study was evaluating the effective immobilization of aluminum in the zeolitic structure. This was conducted by chemically analyzing aliquots collected from different media (organic acids, inorganic acids, neutral, and alkaline), in which the material was agitated for up to 312 hours. Additionally, soil and sand incubation tests were performed, incorporating the synthesized material along with a soluble phosphate fertilizer, such as triple superphosphate (TSP). The incubation lasted up to 42 days under controlled temperature and humidity conditions. Exchangeable phosphorus in soil and sand was analyzed using Mehlich-3 extraction to determine the conditions under which the zeolitic concentrate influences phosphorus availability. These experiments highlighted that treated WTP sludge does not significantly immobilize phosphorus. The findings of this study have the potential to contribute substantially to the development of effective and sustainable methods for disposing of and managing WTP waste. (AU)

• FAPESP's process: 23/02665-1 - Production of zeolitic concentrates from WTP sludge
• Grantee: Thais Beatriz Miqueleti de Sena
• Support Opportunities: Scholarships in Brazil - Master