Zeta potential distributions of model waters containing silica, humic acid, and differing ionic composition were evaluated. These distributions showed that under high ionic strength and in the presence of divalent cations, positive colloids exist in suspension with neutral and negative colloids.Positive colloids do not form at lower ionic strength or when polyvalent cations are absent. The existence of the positive colloids in suspension with the negative colloids suggests that, while electrodynamically unstable, some stabilizing factor is preventing coagulation. This stabilizing factor is likely adsorbed humic acid causing steric hindrance. Further tests indicated that under the conditions that lead to the existence of positive colloids, removal of humic acid by ferric chloride coagulation is diminished as compared to coagulation in lower ionic strength water or water containing just sodium chloride as the ionic matrix. As positively calcium-humic complexes can increase fouling of desalting membranes through the formation of densely packed fouling layers, understanding the mechanisms of coagulation in high ionic strength waters is crucial to improving performance of desalination operations.
INTRODUCCIÓNEl corazón de un sistema de potabilización de agua para consumo humano es el proceso de coagulación. En él se acondiciona el agua de tal forma que los procesos posteriores de limpieza, en donde, propiamente dicho, se remueven las impurezas, puedan realizar su función adecuadamente. Si la coagualación no funciona adecuadamente, tampoco funcionan adecuadamente los procesos posteriores de limpieza. Así de sencillo, si la coagulación no se optimiza tampoco se puede tratar el agua óptimamente. Pardójicamente, un proceso de tal importancia está lejos de ser operado de una manera óptima en las plantas de tratamiento de agua potable actualmente. Tradicionalmente la coagulación de las aguas que entran a las plantas de potabilización se realiza de una manera manual, y con controles fuera de linea que no permiten ajustar adecuadamente las dosis de las sustancias coagulantes a los cambios que tiene la planta tanto en cantidad como en calidad del agua que llega.La dosificación automática de coagulantes no es de niguna manera un proceso fácilmente automatizable debi-
Cultured bacteria addition is one of the technologies used for odor control and FOG (fat, oil, and grease) removal in wastewater collection systems. A set of full scale trials for odor control using bacterial addition in a 16 MGD system were conducted over a period of two years. The objectives of this study were to identify areas that could impact wastewater treatment plant operations due to the effect of bacterial addition in the collection system, to identify the level of those impacts, and to present some interesting findings from the recently completed case study. The plant operation data before and during the bacterial addition were reviewed. The application of the cultured bacteria presented in the study was found to have significant impacts on the operation of the WWTP in terms of influent BOD/TSS loading, primary settling, sludge production, energy use, dissolved sulfides concentration, and methane production.
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