Uso de coagulantes químico e orgânico no tratamento de águas provenientes de sistema lêntico: estudo de caso: Lago Igapó II

Abstract

The purpose of this study was to evaluate, through physical and chemical parameters, the efficiency in the process of coagulation/flocculation/sedimentation of two chemical coagulants ( aluminum sulfate and ferric chloride ) and one natural (Moringa oleifera), treating water from a lentic system (Lago Igapó II ), located in the city of Londrina – PR. Two water collections with different characteristics were made: the first collection was made after a period of drought and showed low levels of suspended and dissolved solids; and the second collection was made after a rainy period and had relatively high levels of suspended and dissolved solids. The coagulant solution obtained from the seeds of Moringa oleifera was prepared according to the methodology of Bergamasco (2008). The chemical coagulant solutions were made as the methodology of Trevisan (2014) . Three levels of variation in the pH of the water were tested, there levels of dosing of each of coagulating solutions and three times of sedimentation were tested. Was simulated with the jar- test the same conditions of rapid mixing and flocculation used in ETAs. After the test of coagulation/floculation/sedimentation was made, a comparative study to remove turbidity, color apparent and pH change after 3, 13 and 23 minutes of settling was made. For the first battery of tests on the jar- test, it was used the water samples with low dissolved solids conditions for all three coagulants, and was seen that this fact hindered the formation of flakes and hence the sedimentation process, leading to removing results of the physical parameters apparent color and turbidity often negative. For the second round of tests, it was used the water samples with high presence of dissolved solids, and it has shown most representative results. The chemical coagulants has shown higher removal at higher dosages (25 ml and 35 ml), however the pH has been standing out as the dominant variable in the success of the apparent color and turbidity removal process, presenting removal of these parameters peaks around 95 % for ferric chloride and 99% for aluminum sulfate, being the closest pH of neutrality (8.0) which obtained those best removal results and that also met the potability limits of Ordinance 2914/2011 of the Ministry of Health. The coagulant solution based on Moringa oleifera’s seeds showed lower rates of removal (about 85% for both physical parameters evaluated) and also did not meet the potability limits for drinking water set by the aforementioned Ordinance, but showed a wider range of pH to work with.