RESUMO
Wastewater reuse has been widely discussed as an essential strategy to minimize the consumption of drinking water for less noble purposes. During biological wastewater treatment, organic matter is converted into a complex matrix containing a variety of soluble organic compounds. The objective of the present study was to evaluate the removal efficiency of the residual organic load in the final effluent from wastewater treatment plant with a conventional activated sludge process by different coagulants and parameters of coagulation-flocculation process, using dissolved organic carbon (DOC) concentration, molecular weight (MW) size distribution by size exclusion chromatography (SEC) coupled to mass spectrometry (MS), and zeta potential (ZP) analyses. The results showed a DOC removal efficiency up to 45% with iron chloride, and of 38% for aluminum sulfate and 31% for PAC coagulants. ZP was also measured during the procedures and authors conclude that the ZP also does not have a determining role in these removals. SEC and MS assessment was able to detect changes on secondary effluent molecular weight distribution profile after effluent coagulation-flocculation, this technique might be a promising tool to understand the composition of effluent organic matter and be helpful to estimate and optimize the performance of wastewater effluents treatment processes.
Assuntos
Floculação , Compostos Orgânicos/análise , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Purificação da Água/métodos , Compostos de Alúmen/química , Análise da Demanda Biológica de Oxigênio , SolubilidadeRESUMO
The main objective of this study was to propose an improvement to the flocculation kinetics model presented by Argaman and Kaufman, by including a new term that accounts for the irreversible floc breakup process. Both models were fitted to the experimental results obtained with flocculation kinetics assays of low turbidity raw water containing Microcystis aeruginosa cells. Aluminum sulfate and ferric chloride were used as coagulants, and three distinct average velocity gradient (G) values were applied in the flocculation stage (20, 40 and 60â s-1). Experimental results suggest that the equilibrium between the aggregation and breakup process, as depicted by Argaman and Kaufman's original model, might not be constant over time, since the residual turbidity increased in various assays (phenomenon that was attributed to the irreversible floc breakup process). In the aluminum sulfate assays, the residual turbidity increase was visible when G = 20â s-1 (dosages of 60 and 80â mgâ L-1). For the ferric chloride assays, the phenomenon was noticed when G = 60â s-1 (dosages of 60 and 80â mgâ L-1). The proposed model presented a better fit to the experimental results, especially at higher coagulant dosages and/or higher values of average velocity gradient (G).