Tratamento de água contaminada com cobre (cu2+) utilizando filtração lenta e adsorção.

Abstract

Around the world, billions of people have no access to potable water and directly consume surface or underground water with no treatment and different degrees of microbiological and inorganic contamination. As a result, there are numerous annual cases of diseases and deaths related to consumption of contaminated water, particularly in isolated communities. Considering the exposed, the present study evaluated the treatment of water contaminated with Cu2+ in a system composed of slow filtration and adsorption in a pilot scale. In the first phase of the study, two slow filter models using as filter medium a kaolin residue from mining activities were evaluated, one with a double-layer filter bed (FL-D) and the other with a triple-layer filter bed (FL-T). The filters were fed with water from Piranhas River in an intermittent regime during 92 days. The performance of FL-D and FL-T was evaluated considering several physicochemical and biological indicators of water quality, and the load loss and schmutzdeckes of each filter were also monitored. In the second phase, the adsorption of Cu2+ in red rice husk was analyzed using Fourier-transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and scanning electron microscopy. Kinetics and adsorption isotherms tests were conducted using 2 g of red rice husk and 50 mL of Cu2+ synthetic solution, with concentrations of 1 to 128 mg L-1. A fixed-bed adsorption column in laboratory scale was set to evaluate the dynamic adsorption of Cu2+ in a 5-cm thick adsorbent bed made of red rice husk, employing a synthetic solution and a real solution (river water previously treated using FL-T), in a concentration of 8 mg L-1 and flow of 13 mL min-1. Moreover, a fixed-bed adsorption column in a pilot scale was installed in the experimental system as a post-treatment unit after FL-T and employed to treat Piranhas River water with 8 mg L-1 of Cu2+. The results of the first phase indicated that slow filters using kaolin residue as a filter medium exhibited average removal above 68% for turbidity, 74% for total Fe, 75% for ammoniacal nitrogen, 97% for total coliforms, and 96% for E. coli, being FL-T more efficient for the removal of turbidity and total coliforms. The results of the second phase revealed the presence of several hydroxyl, carbonyl, and carboxyl functional groups and the distribution of grooves and rugosities on the red rice husk surface. The adsorption kinetics data indicated that the balance was reached after 20 min and the data exhibited the best fit with the pseudo-second order model (R² = 0.98). The maximum adsorption capacity of Cu2+ by red rice husk experimentally obtained was 2.30 mg g-1 and the experimental data adjusted better to the Langmuir model, with qmax estimated as 7.19 mg g-1. The adsorption column in laboratory scale exhibited an exhausting time of 310 min, adsorption capacity of 1.12 mg g-1 , and saturation percentage of 79% for the real solution; the data were better adjusted to the Thomas model (R² = 0.95–0.99). The adsorption column in pilot scale adequately treated 104 L of water, in accordance with the maximum value allowed for Cu2+ in potable water, before reaching the rupture point. Therefore, based on the results, the proposed system is a promising alternative for the treatment of water contaminated with Cu2+, efficiently reducing several indicators of water quality to acceptable levels as per national regulations (Ordinance GM/MS nº 888/2021) and international regulations of the World Health Organization.