Água de abastecimento com elevada turbidez: eletrocoagulação/flotação como pré-tratamento em estações de tratamento de água

Abstract

Freshwater sources, surface (rivers, lakes) or groundwater, are generally used as resources for water supply. In order to the water to be distributed, treatments that aim at its ―safety‖ regarding aesthetic qualities, physical and chemical standards, as well as controlling diseases (biological standards), are necessary. Raw water, as a consequence of certain periods of the year, or even because of the presence of sediment or suspended solids in the source, may cause a significant increase in turbidity levels. Therefore, conventional treatment processes, such as coagulation and filtration, may be impeded, requiring pretreatment. Electrocoagulation/flotation is an electrochemical process, in which electrical energy is provided to the electrodes – making an electrolytical cell – with an anode (oxidation reactions) and cathode (reduction reactions), and these promote coagulation and flotation of particles, thus treating water. The main goal of this work was to evaluate the use of electrocoagulation/flotation as pretreatment of drinking water with different levels of turbidity, offering a pretreatment method for Water Treatment Plants. The electrocoagulation/flotation reactor was used in bench scale with aluminum electrodes in monopolar connection, operating in batch. Synthetic raw water with different turbidity ranges was simulated using different concentrations of sodium bentonite. Firstly, experimental design with DCCR 2³ effects test was performed and better operating conditions were defined for a DCCR 2², in which the best treatment condition (electric current 1.85 A, electrolysis time of 20 min and pH 9) was used for applicability in different turbidity.Turbidity removals were found to be satisfactory (about 99.00%) for high turbidity ranges (550 uT at 3500 uT) and the flotation removal mechanism was higher up to approximately 2600 uT, after which sedimentation prevailed. Trials after treatment could be fit as a class 1 freshwater, according to the CONAMA Resolution no. 357/05, because of its turbidity, TDS and chloride, requiring only the simple treatment for water supply, but taking into consideration the parameters evaluated in the potable water legislation. Thus, pretreatment by electrocoagulation/flotation may be indicated for water treatment plants, on account of its proved high efficiency in turbidity reduction.