Parameter Untreated Treated

Two large municipal waste water installations in California and in Virginia utilize a regenerant with a pH near neutral. The active portion of the regenerant is a 2 percent sodium chloride solution. A typical elution curve for ammonium with this type of regenerant is shown Fig. 9.8. It is seen that approximately 25-30 bed volumes are required before the ammonium concentration reaches equilibrium, while 10-20 bed volumes are sufficient at high pH regeneration. If the régénérant is recovered, see below, the volume is not very critical. Variations in régénérant flow rates of 4-20 bed volumes I hr do not affect régénérant performance. Typical design values are 10 bed volumes / hr.

Figure 9.8. Ammonium elution with 2% sodium chloride. The concentration of ammonium-N, mg/l in regenerant is plotted versus the number of bed volumes used.

Bed volumes

Figure 9.8. Ammonium elution with 2% sodium chloride. The concentration of ammonium-N, mg/l in regenerant is plotted versus the number of bed volumes used.

The regeneration cycle is usually followed by back washing with 2-4 bed volumes. The back wash water is mixed with the influent to remove the minor ammonium present. The regenerant may be recovered by either air or steam stripping. When the ammonia is removed by this process, the clinoptilolite is ready to be used again for next regeneration cycle.

Cellulose ion exchangers are selective to proteins and offer a possibility for

protein recovery. The capacity is about 1 meqv / g , but with a low bulk weight, the capacity will only be roughly 0.2 eqv /1 . As 50% of this capacity is selective for proteins and proteins have a high equivalent weight, the capacity on a weight to weight basis is still attractive, although it is strongly dependent on the source of protein, including how much time the proteins have had to decompose before the treatment. Due to the slow diffusion rate of proteins, the retention time of waste water in the cellulose ion exchanger is required to exceed 12-15 minutes. Regeneration can be carried out by sodium hydroxide, which expand the cellulose fibers, whereby the proteins are released. To ensure the presence of a sufficiently high sodfum concentration and thereby obtain the sodium-form of the ion exchange material, elution by a mixture of sodium hydroxide and sodium chloride is recommended. Proteins dissolved in the elution liquid may be recovered for instance by precipitation; see also Section 11.1.

Figure 9.6 is also valid for this ion exchange process, for which a column height of about 1.5 m is recommended.

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