Contribuição para a melhoria do processo de espessamento de lamas primárias em ETAR Municipal

Abstract

TThe present study was integrated in a traineeship carried out at the Ílhavo wastewater treatment plant and the main objective is the analysis of the thickening process of primary sludge in the gravimetric thickener in order to improve its performance.Initially, some parameters of the liquid effluent and the sludge along the process were analysed, namely total solids (TS), total suspended solids (TSS), pH, volatile solids (VS) and volatile suspended solids (VSS). The analysis of these parameters allowed to conclude that in general, all parameters analysed are close to the values reported in the literature.Considering the main objective of this study, eight commercial flocculants (S4, S6, S7, S8, A3, A5, A6 and A8), all of them organic cationic polymers, were tested. The concentrations tested using the jar-test procedure were 10, 12.5, 15 and 17.5 ppm, and the parameters measured in each case were the sedimentation height as a function of time, the percentage of TS in the sedimented fraction, TSS in the clarified fraction, pH and total alkalinity. The laboratory results allowed us to conclude that the kinetics of flocculant performance were similar, and in general after 75 min the steady state was obtained. Nevertheless, the S7 and S8 polymers were selected as the ones with the best performance.Finally, a preliminary industrial scale test was performed using the S7 flocculant at a concentration of 25 ppm. The results obtained were not conclusive, since an increase in ST concentration in the thickener outlet stream was not observed. Therefore, these studies should be further developed in the future.In summary, it can be concluded that it is important to re-evaluate the WWTP sludge circuits in order to obtain a better efficiency of the thickener, thus facilitating the anaerobic digestion, which use this sludge as raw material.

O presente estudo foi integrado num estágio curricular efetuado na ETAR de Ílhavo e tem como principal objetivo e análise do processo de espessamento de lamas primárias no espessador gravítico, de modo a melhorar o seu desempenho. Numa fase inicial, foram analisados alguns parâmetros do efluente e das lamas ao longo do processo, designadamente os sólidos totais (ST), suspensos totais (SST), pH, sólidos voláteis (SV) e sólidos suspensos voláteis (SSV). A análise destes parâmetros permitiu concluir que de um modo geral, todos os parâmetros analisados se encontram próximos dos valores reportados na literatura.Tendo em conta o objetivo principal deste estudo, foram testados laboratorialmente oito floculantes comerciais (S4, S6, S7, S8, A3, A5, A6 e A8), todos polímeros catiónicos orgânicos. As concentrações testadas em jar-test foram 10, 12,5, 15 e 17,5 ppm, tendo sido medido em cada caso a altura de sedimentação em função do tempo, a percentagem de ST na fração sedimentada, SST na fração clarificada, pH e alcalinidade total. Os resultados laboratoriais permitiram concluir que as cinéticas de atuação dos floculantes eram análogas, e em geral ao fim de 75 min obtinha-se estado estacionário. Ainda assim, globalmente foram selecionados os polímeros S7 e S8 como aqueles que apresentavam melhor desempenho. Finalmente, foi realizado um ensaio preliminar à escala industrial utilizando o floculante S7, com uma concentração de 25 ppm. Os resultados obtidos mostraram que a concentração de ST na corrente de saída do espessador teve uma variação pouco significante face ao valor de referência. Assim, estes estudos devem ser aprofundados no futuro. Em suma, pode concluir-se que é importante reavaliar os circuitos de lamas na ETAR de modo a obter um melhor aproveitamento do espessador, facilitando assim a digestão anaeróbia, que usa estas lamas como matéria prima.The present study was integrated in a traineeship carried out at the Ílhavo wastewater treatment plant and the main objective is the analysis of the thickening process of primary sludge in the gravimetric thickener in order to improve its performance.Initially, some parameters of the liquid effluent and the sludge along the process were analysed, namely total solids (TS), total suspended solids (TSS), pH, volatile solids (VS) and volatile suspended solids (VSS). The analysis of these parameters allowed to conclude that in general, all parameters analysed are close to the values reported in the literature.Considering the main objective of this study, eight commercial flocculants (S4, S6, S7, S8, A3, A5, A6 and A8), all of them organic cationic polymers, were tested. The concentrations tested using the jar-test procedure were 10, 12.5, 15 and 17.5 ppm, and the parameters measured in each case were the sedimentation height as a function of time, the percentage of TS in the sedimented fraction, TSS in the clarified fraction, pH and total alkalinity. The laboratory results allowed us to conclude that the kinetics of flocculant performance were similar, and in general after 75 min the steady state was obtained. Nevertheless, the S7 and S8 polymers were selected as the ones with the best performance.Finally, a preliminary industrial scale test was performed using the S7 flocculant at a concentration of 25 ppm. The results obtained were not conclusive, since an increase in ST concentration in the thickener outlet stream was not observed. Therefore, these studies should be further developed in the future.In summary, it can be concluded that it is important to re-evaluate the WWTP sludge circuits in order to obtain a better efficiency of the thickener, thus facilitating the anaerobic digestion, which use this sludge as raw material.