Robert P. Carnahan

Permeability of electrolytes through a flat RO membrane in a direct osmosis study

Abstract A direct osmosis study was carried out using several 1:1 and 2:1 electrolytes, which diffused in a RO TFC membrane. The solute permeability DSMKS/δ has been calculated using the preferential sorption capillary flow model. It was found that to some extent the ions maintain their hydration in the membrane and the permeation is a function of the hydrated radii rather than crystal ionic radii. Moreover, a linear dependence was found between electrolyte permeability through the membrane and their average diffusivity in infinite dilute solution. The relatively low permeation of 2:1 chloride salts was attributed to the interaction with the membrane surface charge.

FOULING PREDICTION IN REVERSE OSMOSIS PROCESSES

In recent years, membrane separation processes have successfully established footholds in all areas of chemical separations. Semipermeable membranes are now enhancing and even replacing long-time standard techniques such as distillation and solvent extraction (1). They are also being used in the preparation of purified chemical and biological products as well as the treatment and recovery of many industrial waste streams (2, 3). Many of these recent technological advances follow from successful research begun in the 1950s to desalinate seawater using synthetic membranes in reverse osmosis processes. While other methods to desalinate seawater have proven too unreliable or too expensive, the use of reverse osmosis in the production of potable water has steadily increased (4). Despite its growing popularity and improved technology, reverse osmosis, RO, along with all membrane separation processes continues to be plagued with one persistent problem. The problem is membrane fouling (5). Eyecamp has defined this broad term as the following:

Biofouling of PVD-1 reverse osmosis elements in the water treatment plant of the City of Dunedin, Florida

Abstract Camp, Dresser and McKee Consulting Engineers, in May of 1993, requested the University of South Floridas Civil Engineering Department to assist them in solving the biofouling problems at the City of Dunedins Water Treatment Plant. The City had identified the biological foulants to be Pseudomonos a and a variety of yeasts. A biofilm was forming on the lead elements in the first stage of all their reverse osmosis skids. A program consisting of a series of laboratory and field studies was developed to find a method for cleaning the fouled elements. A solution for preventing further contamination of the system was also to be developed in the second phase of the study.

Mass transfer in RO TFC membranes: dependence on the salt physical and thermodynamic parameters

Abstract The objectives ofthis research were to determine the importance ofparameters such as ionic size, ionic hydrated size, diffusivity in solution, enthalpy of hydration ΔH and relative Gibbs (free) energy ΔΔG on the salt permeation coefficient DK/δ in a RO TFC membrane. The experimental apparatus consisted of a commercial RO water maker and an in-line sensors system, which allows data acquisition on a continuous base for temperature, pH, conductivity, flow rates, and operating pressure. The solutions investigated were monovalent and divalent chlorides. Each feed solution was tested at 0.1 M. A preferential-sorption capillary-flow model PSCF was used in data evaluation. It was found that salt diffusivity, hydrated radii, enthalpy and entropy of hydration exert the controlling effect on the membrane selective transport, and any of them can be used in a comparative estimation of DK/δ. The relative Gibbs energy emerged as a parameter which can fully characterize the membrane selectivity and permits the prediction of DM for a certain salt in a certain membrane.

Recycling of Municipal Solid Waste Ash Through an Innovative Technology to Produce Commercial Zeolite Material of High Cation Exchange Capacity

Municipal solid waste ash (MSW ash) samples, obtained from a local incinerator in Florida, were converted via a chemical process into zeolite material. The conversion process was performed by applying a two step treatment. The ash samples were fused at 550C under alkaline conditions and then the fused ash samples were treated hydro-thermally at 60 C and 100C for different periods. This innovative technology involves adjusting the SiO2/Al2O3 ratio of the ash from 13.9 to 2.5 by adding sodium aluminates and by using a solid to liquid ratio of 10. The fusion step formed sodium silicate and sodium aluminum silicate phases. These phases acted as precursors to the formation of zeolite A. Zeolite A was successfully formed within the ash matrix when samples were fused and SiO2/Al2O3 was adjusted. The maximum cation exchange capacity, CEC, was measured by using ammonium acetate solution. The CEC of the produced zeolitic ash material has increased significantly from 17 meq/100g for non-treated ash up to 212 meq/100g for the treated ash. The cation exchange capacity of the produced zeolite ash material is close to that available from commercial zeolite materials which have a CEC of 245meq/100g. Zeolite A formation within the ash matrix increased the potential of using the ash as an adsorbent for industrial and environmental applications including ammonia removal from waste water or any other similar application that involves cation exchange.