Adequation of operating conditions of a Direct Filtration Water Treatment Plant
Water treatment; coagulation; direct filtration; two-stage filtration; coastal lagoon with low turbidity.
Changes in the quality of surface water sources have been recurrent in developing countries due to their accelerated urbanization processes. In this sense, it is essential that water treatment technologies in these regions are able to adapt to variations in water quality to produce safe effluent and in compliance with legislation. Direct filtration is a treatment technology that, when optimized, is effective and easy to operate, however, for this technology to work properly, low values of color and turbidity of the influent raw water are required. One way to get around this limitation in springs with seasonal variations in water quality is the use of a two-stage filtration system, which allows the treatment of raw water of worse quality, with less susceptibility to sudden variations in quality, and the application of rates of greater filtration. Thus, the objective of this work is to optimize operational conditions of coagulation in a Water Treatment Plant, designed and operated with direct filtration technology for the treatment of coastal lagoon water with low turbidity and moderate color, in addition to comparing the performance of the direct filtration system with double filtration under normal conditions and after heavy rains. For this, static tests were carried out in a jar test apparatus + Laboratory Sand Filter (LSF) and simulations in a pilot installation of direct filtration/ two-stage filtration. The quality of treated water was monitored through the parameter’s turbidity, apparent color, true color, residual chlorine, zeta potential, pH and temperature. The jar test + LSF tests showed that PAC and Aluminum Sulphate coagulants are effective for removing color and turbidity from raw water in the range of 8 to 15 mg/L of chemical, in addition to flocculation and pre-oxidation steps increase the efficiency of the system. Tests in a pilot installation showed that the direct filtration and double filtration systems presented stable final effluent with turbidity less than 0.5 NTU and apparent color less than 15 uC, however, the filtration run of the direct filtration system was very short due to the rapid evolution of pressure drop due to retention of particulate material. The double filtration system presented long filtration lines, slow pressure loss evolution and adequate removal of color and turbidity, including for tests with raw water of worse quality, being a promising alternative for the treatment of water from fountains with low turbidity and moderate color.