Estudo da colmatação biológica através da atividade enzimática em colunas de simulação de sistema de filtração em margem

Abstract

Bank filtration (BF) is established as a simple and viable method for water treatment, however, it presents operating conditions that are related to the quality and quantity of water produced, such as biological clogging. The study sought to evaluate and relate the biological clogging of the filter media to the microbiological activity in BF simulation columns. Nine filters filled with 30 cm of sand as filter media were used. These were divided into triplicates and filled with fine sand (d10 = 0,16 mm), medium sand (d10 = 0,44 mm) and coarse sand (d10 = 1,33 mm). The filtration system was operated for 34 days at an initial filtration rate of 1.94E-4 m.s-1, with daily analysis of turbidity, apparent color, true color, pH, electrical conductivity, temperature and dissolved oxygen from inlet and filtered water, in addition to flow and pressure loss reading. After the end of the operation, columns were drained and opened to filter media collection at different depths. Enzymatic analysis of the filter media was performed through hydrolysis of Fluorescein Diacetate (FDA) and degradation of Triphenyltetrazolium Chloride (TTC), in addition to organic matter content analysis. There was a reduction of K10 in the order of 6% and 7% in the first 5 cm of filter bed in all columns, as well as higher content of organic matter and enzymatic activity, reflecting the biological clogging process and greater interception of solids in the first layer of the bed filter. Coarse sand (d10 = 1.33 mm) showed greater internal clogging compared to medium (d10 = 0.44 mm) and fine sand (d10 = 0.16 mm), which presented greater external clogging. Fine sand (d10 = 0.16 mm) showed an accumulated organic matter content of 0.37%, a fluorescein accumulated concentration of 12.19 μg.g-1 and 2.37 μg.g-1.h-1 dehydrogenase concentration. Medium sand (d10 = 0.44 mm) corresponded to an accumulated organic matter content of 0.15%, concentration fluorescein of 33.77 μg.g-1 and 3.50 μg.g-1.h-1 dehydrogenase concentration. Coarse sand (d10 = 1.33 mm) showed an accumulated organic matter content of 0.29%, an accumulated fluorescein concentration of 38.37 μg.g-1 and 8.60 μg.g-1.h-1 dehydrogenase concentration. The organic matter content was not proportional to the enzymatic activity. Homogeneous filter media with higher specific porosity seem to favor the presence and distribution of organic fractions and enzymatic activity. The filtration process provided removal of turbidity (≤84%), apparent color (≤50%) and true color (≤27%) in the filtered water. Other physical and chemical parameters of the filtered water proved to be favorable for the biological clogging formation observed. It is concluded that the methods of enzymatic and organic analysis were useful in the evaluation of biological clogging and its influence on hydraulic parameters. However, there is still the need to determine conditions for enzyme activity such as the presence of dissolved oxygen and nutrients throughout the filter media. The determination of this and other issues allows the expansion of relevant concepts related to biological clogging in bank filtration systems.