Recuperação ácida de íons Al3+ de lodo residual de estação de tratamento de água: avaliação do potencial de reuso do coagulante

Abstract

Water treatment is crucial for preserving public health. During this process, waste known as residual sludge arises, the management and disposal of which represent challenges that require effective solutions. In this context, the aim of this work was to recover Al3+ ions from the residual sludge coming from the decantation of a Water Treatment Plant (WTP) by means of the acidification process. The aim is to explore the viability of these recovered ions as a coagulant in raw water. The material was characterized using granulometric analysis (ABNT NBR 7181/1984, 6502/95, 6508/1984 and 5734/1980) and chemical analysis using X-ray fluorescence spectrometry (XRF). Extractions were prepared with 100 g sludge/L distilled water and then the efficiency of metal recovery in the supernatant of the dried sludge solution was tested by performing jartest analysis with the recovered coagulant in raw water. The specific mass was then determined in the granulometric analysis, which showed a result of 2.445 g.cm³ in accordance with the resolutions of NBR 6508/1984. Regarding the classification of the residual sludge according to NBR 6502/1995, after analysis it was classified as a soil with 9% clay, 46% silt, 46% sand and 0% pebble, which can be classified as not very uniform, in addition to identifying that the sample is poorly graded because it has many empty states in its particles. During the characterization analyses using the X-ray Florescence (XRF) methodology, it was possible to obtain the following results for the raw sewage sludge: 6.77% Aluminium, 31.78% Aluminium Oxide, 3.50% Iron and 16.44% Iron Oxide, in addition to various other elements, oxides and organic matter. Next, jartest tests were carried out to create coagulation diagrams, where kaolinite and humic acid were used to make artificial raw water, after which the recovered coagulant was applied (pH 7, variable dosages from 5 to 25 mg.L-1) to the raw water in natura, where 99.5% of the turbidity and 100% of the color was removed. We therefore concluded that the residual sludge has the granulometric characteristics of a silt-sandy-clay soil, according to the results obtained during the analysis. In addition to identifying through XRF analysis that the sludge under study has considerable percentages of aluminum and iron, which we were able to extract through acidification and constitute a new coagulant which showed an efficiency of over 99% for removing color and turbidity.