Phosphate Rejection Research Articles

Phosphate removal from water by red mud using crossflow microfiltration

Red mud (which is a waste material formed during the production of alumina and primarily contains ferric and aluminium oxides) was used as an adsorbent for the removal of phosphate ions from water using crossflow microfiltration. It is shown that phosphate ions act as a coagulant for red mud particles, forming a compressible cake with a compressibility index of unity. As shown also by dead-end filtration experiments, the cake resistance decreases with increasing phosphate concentration. The phosphate rejection is a strong function of feed dispersion pH, phosphate and red mud concentration ratio as well as the concentration of co-ions such as sulphate ions used to adjust the dispersion pH. Under certain conditions, especially when pH=5.2, steady state permeate flux and phosphate rejection reach a maximum with 100% rejection achievable. The permeate also contain metal ion impurities originating from red mud and their concentrations increase with increasing red mud concentration and decreasing pH. The effects of other process variables, crossflow velocity and membrane pore size on phosphate rejection and permeate flux are also studied.

Ultrafiltration of a polymer-electrolyte mixture

We present a mathematical model to describe the ultrafiltration behaviour of polymer-electrolyte mixtures. The model combines the proper thermodynamic forces (pressure, chemical potential and electrical potential differences) with multicomponent diffusion theory. The model is verified with experimental data on the ultrafiltration of aqueous solutions of PEG-4000 and potassium phosphate. The single solute rejection of PEG-4000 goes through a maximum as also found by others. The single solute rejection of potassium phosphate depends on the ionic strength of the solution. At low ionic strength rejections are found of 50%. Solutions containing a high concentration of PEG-4000 and potassium phosphate show a negative rejection for potassium phosphate. This is caused by the strongly non-ideal behaviour of these aqueous solutions. The model predicts the behaviour of single solute experiments quite well, but some deviations are found with the mixed solute experiments. However, negative rejections found in the mixed solute experiments are predicted by the model.

Waste water renovation by sewage ultrafiltration

The Sewage Ultrafiltration (SUF) process has been tested in a mobile pilot plant using tubular IDE Hybrid Ultrafiltration membranes (HUF). The plant was operated at 30% and 95% water recovery, at various circulation velocities on untreated oxidation pond effluent. Effects of circulation velocity, various cleaning procedures as well as frequency of cleaning, on product quality and flux were investigated. The SUF product typcially contained a BOD of less than 5 ppm (from a feed of 600 ppm), a COD of 40 ppm (from a feed of 3100 ppm) while the rejection of N kj (from a feed of 238 ppm) was 85%. Rejection of total phosphate (as P) was almost complete. Fluxes increased with increasing velocity reaching 37.2 gfd at 10ft/sec and 8 atm. Periodical mechanical cleanings performed by the passage of an oversized sponge ball through the membranes, combined with occassional chemical cleaning were found to be effective in membrane flux restoration. SUF is shown to be a membrane process eminently capable of treating municipal and industrial waste water containing suspended solids and undesirable organic compounds.