Virginia Law

Ion exchange may be utilized as a unit operation in which ions are exchanged between two different materials, usually a solid-liquid, but may involve a liquid-liquid exchange. In wastewaters, the exchange usually involves a solid resin material consisting of readily ionized compounds. Treated effluent (secondary or advanced treatment) passes at a controlled rate through a certain volume of resin within a contactor. The removal of 90-95% of the ammonia nitrogen can be achieved by such treatment. Ion exchange may also be utilized for removing heavy metals, nitrates, phosphates, sulfides, phenol, and chlorophenols from wastewaters.

1. The process specifically designed for ammonia nitrogen removal uses a clinoptilolite resin. Many of the design considerations are applicable to other types of ion exchange treatment, including:

a. Flow, total dissolved solids, suspended solids, ion specific concentrations, alkalinity, pH, and resin structure.

b. The rate of exchange based upon selectivity of the resin, the exchange capacity of the resin, waste strength, and the effluent requirements.

c. The exchange capacity and break through point.

d. Certain contaminants which create treatment problems in the operation of ion exchange. Where these contaminants exist, their removal shall be provided for if necessary through the methods of pretreatment listed in Table 10.

2. Clinoptilolite mineral should be crushed and screened resulting in particle sizes in the range of 20 X 50 mesh. Ion exchange capacities and selectivity shall be determined in pilot plant studies for the particular wastewater in question. The pH of the influent to the exchange resin contactor should be in the range of 4-8.

3. The following parameters shall be considered for design of the ion-exchange contactor:

a. Flow rates in the range of five to 15 resin volumes per hour are normal but the specific design loading shall be confirmed by pilot studies or performance data.

b. The contactors may be gravity or pressure type units.

c. A minimum of two units is required. The number of contactors required is governed by the length of cycle which can be achieved while still meeting effluent quality goals. This shall be determined by pilot tests on the specific wastewater involved.

d. The number of contactors shall be adequate to treat the maximum flow rate in compliance with appropriate permit or certificate requirements, with one contactor out of service for maintenance and an appropriate number out of service for regeneration.

e. Means must be provided to uniformly distribute the influent flow and regenerant flow over the entire area of the contactor.

f. Make-up clinoptilolite storage shall be provided, as well as a water slurry transfer system to move the clinoptilolite from storage to the contactor.

g. Facilities to wash the clinoptilolite prior to transfer to the contactor shall be provided. Means to transfer clinoptilolite from a contactor to the storage system for washing should also be provided.

h. The process shall be controlled by a control system which will automatically initiate and program the regeneration cycle and return the contactor to normal service.

i. Each contactor shall have a flow totalizer. Also, each contactor shall have a flow rate controller to maintain equal flows to all contactors.

j. Each contactor shall be equipped with an efficient surface wash device.

4. With a neutral regenerant, provisions shall be made for a contactor backwash supply with minimum capacity equivalent to 10 gpm/sq ft of contactor area. If wastewater temperatures exceed 25°C (72°F) for prolonged periods, a greater capacity may be required. If a high pH regenerant is used, a minimum backwash capacity of 15 gpm/sq ft should be provided.

5. Regeneration facilities shall be provided for the ion exchange resin. Regeneration may be by high pH regenerant or neutral pH regenerant. Supportive data from fully operational units or from a pilot plant shall be provided to demonstrate acceptability of the proposed regeneration method.

6. Treatment or recovery of regenerant shall be provided. The design should provide for removal of ammonia with recovery of the regenerant through either (i) electrolytic treatment at neutral pH, or (ii) air stripping, or (iii) steam stripping, at elevated pH. Supportive data from a fully operational unit or pilot plant shall be provided to demonstrate acceptability of electrolytic treatment at neutral pH and steam stripping at elevated pH.