Caracterização dos resíduos da estação de tratamento de água da UFLA e aproveitamento na confecção de tijolos de solo-cimento

Abstract

With the increase in population, more water has been collected for due treatment processes, given that, during these processes, residue, the so called Drinking Water Treatment Plant (DWTP) sludge, is generated. This residue is, generally, destined back to the watercourse, without any treatment. Therefore, the present work had the objective of characterizing the crude water that arrives at the DWTP/UFLA, quantifying the residue generated during treatment and confectioning soil-cement bricks with different amounts of the dehydrated residue. In order to estimate the amount of sludge the DWTP/UFLA generates, water processing and treatment was monitored for five months (May to September of 2014). We also characterized physical and chemical variables of crude water and effluents of filter and decanter cleaning. From the obtained variables, we used empirical equations to estimate residue generation at the DWTP/UFLA and to compare these to the values observed in loco. Residue samples were collected, thickened by gravity and dehydrated in drying beds. Different mass fractions (0%, 3%, 5%, 8% and 10%) were inserted into the soilcement brick matrix, forming treatments T0, T1, T2, T3 and T4. The bricks were trialed at days 14 and 28 of drying, regarding water absorption and resistance to compression, according to the Brazilian Technical Norms. The results of the filter and decanter effluent characterizations, as well as of the thickened residue, indicated that these present high polluting potential, and must not be released into the environment with no previous treatment. The dewatering system comprised of the gravity thickener and drying beds presented satisfactory performance, reducing the volume of sludge, which propitiated an increase in the content of solids in the same. Regarding the bricks, the stabilization of the soil-cement mixture occurred, decreasing brick porosity from day 14 to day 28 of drying, also decreasing water absorption. Only treatments T0, T1 and T2 adapted to NBR 8491, regarding water absorption. The resistance to compression trials showed increase in resistance from day 14 to day 28. However, no treatment met the demands of norm NBR 8491. Therefore, we conclude that the incorporation of DWTP sludge caused changes to the physical and mechanic properties of the bricks. We were unable to conclude that DWTP residue cannot be used as material for the confection of bricks, given that even T0 did not reach the minimum compression resistance demanded by the norm, indicating that other factors also interfere on the physical and mechanic properties of bricks.