The research aimed to evaluate the physical aspects of the liquid phase and the
solid phase, as well as to evaluate the performance of the decanters of an ETEI,
located in Barcarena, through the mass balance and comparison of the TAH and
the solids application rate (TAS). with project references and standards. Two of
the four lines of ETEI decanters under study were monitored, on two consecutive
days samples were collected from the liquid phase at the inlet and outlet, and
from the solid phase, the ETEI sludge. The analyzes were carried out at the
Laboratory of the Federal University of Pará (LAESA), together with the solids
analyses, flow data was consulted using online monitoring instruments, as well
as project data in technical files and a survey of normative and bibliographical
references. With the results obtained, it was possible to conclude that the
concentration of total solids is higher in Decanter 82E when compared to
Decanter 82C. The result of the solids analysis also made it possible to evaluate
the higher percentage in the portion of fixed suspended solids, that is, indicating
a higher inorganic load characteristic. Regarding the mass balance, a generation
of solids inside the decanters is observed due to the fact inherent to the process
which refers to the presence of caustic soda in the raw effluent, aligned with the
neutralization reaction that occurs in the medium through the use of sulfuric acid,
forming sodium sulfate as a by-product of the treatment process, therefore this
increase in solids is expressed in terms of dissolved solids. Regarding the
assessment of the TAH observed in the monitored data, it was higher than the
minimum indicated by Metcalf & Eddy (1991), but it remained in line with the
design reference, compatible with the behavior of flows at low load. And in this
same comparative logic, the TAS evaluation remained in both decanter 82C and
82E at a rate lower than the minimum indicated by Metcalf & Eddy (1991)
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