| In the last 20 years, the water treatment industry has constantly been challenged to meet stringent drinking water standards aimed at accomplishing two primary objectives: microbial disinfection and reduction of dissolved organic compounds. Low-pressure membrane filtration processes, such as ultrafiltration, have been shown to meet existing and anticipated regulations on disinfection requirements. However, this filtration process is not effective at removing dissolved organic compounds, such as natural organic matter and organic micropollutants.; Application of powdered activated carbon to ultrafiltration systems is an attractive process alternative capable of meeting both disinfection and organic removal requirements. This hybrid process combines the adsorption capabilities of activated carbon with the particle separation provided by the membranes.; Identification of the optimum process design and the limitations of these systems can be facilitated by the use of adsorption models. The objective of this research was to develop a series of mathematical models to predict the removal of organic compounds when powdered activated carbon is dosed in membrane filtration systems. The models were based in a single set of equilibrium and kinetic parameters that can be evaluated in bench scale experiments. The models were verified experimentally with laboratory-scale membrane filtration pilot units for the removal of 4-nitrophenol in organic-free water, and dissolved organic matter in groundwater.; The models were used to evaluate various dosing procedures (step versus pulse input) and to assess the benefit of dosing the powdered activated carbon in continuous-flow reactors installed upstream of the membranes to increase the carbon retention time in the system. Also, the effect of recirculating the activated carbon from the membrane backwash to a floc blanket reactor installed upstream of the membranes was evaluated as a means to increase the overall adsorption efficiency of the process.; The results of this study showed that, for a given carbon dose, the application of carbon as a pulse input always yields lower adsorbate concentrations in the membrane permeate. Furthermore, application of the activated carbon to continuous-flow reactors installed upstream of the membranes, and the recirculation to a floc blanket reactor after backwash results in significantly lower carbon dose for a given adsorbate removal. |
