Section 890. High rate treatment processes

A. General.

High rate treatment processes are characterized by:

1. Precise coagulation control;

2. Turbidity monitoring throughout the process;

3. pH monitoring throughout the process;

4. Reduced flocculation time;

5. Reduced sedimentation time;

6. Use of multimedia filters incorporating anthracite and silica or other types of filter materials; and

7. Filter rates greater than two gallons per minute per square foot of filter area and not exceeding four gallons per minute per square foot of filter area.

B. Instrumentation.

1. The coagulation process shall be controlled by:

a. Zeta potential shall be measured by microelectrophoresis;

b. Dual pilot filters shall be required. The pilot filter shall consist of a small filter (about six inches in diameter) containing the same type and depth of media as the plant filters, and which is operated in the same manner as the larger plant units except that the plant raw water after the treatment chemicals have been added rather than the coagulated and settled water is applied to the pilot filter. The pilot filter shall be equipped with recording turbidimeters on the effluent to measure the filterability of the water as reflected by turbidity monitoring. Departures from these standards using proprietary pilot filters may be considered;

c. Streaming current monitor--a continuous sampling instrument which measures the electric current generated when water flows past suspended particles contained in the water; and

d. In addition to one of the above devices, a multiple six-gang stirring machine for performing jar tests shall be provided.

2. Indicating and recording turbidity monitoring shall be provided for monitoring the turbidity of:

a. The raw water;

b. Settled water from each sedimentation basin;

c. Filter effluent from each filter; and

d. Finished water leaving the treatment plant.

3. Indicating and recording pH monitoring equipment shall be provided for monitoring:

a. The raw water;

b. The flash mix effluent; and

c. The finished water leaving the treatment plant.

C. Unit processes.

1. Flash mix facilities shall conform with 12VAC5-590-870 C.

2. Flocculation design shall comply with 12VAC5-590-870 D, except the minimum detention time shall be 20 minutes.

3. Sedimentation design shall comply with 12VAC5-590-870 E, except the minimum effective detention time shall be three hours.

4. Filtration.

a. The maximum rate of filtration shall not exceed four gallons per minute per square foot of filter area.

b. Number of filter units. At least two units shall be provided at plants having a rated capacity less than two million gallons per day. The total number of filters necessary at plants having a rated capacity equal to or greater than two million gallons per day may be estimated using the following formula:

N = 1.35 (Q)^0.5

(Based upon the formula as per Morrell and Wallace from Hardenbergh and Rodie's "WATER SUPPLY AND WASTE DISPOSAL 1960" and modified for the high rate process).

Where N equals the number of filter units, Q equals the plant capacity in million gallons per day.

c. Filters incorporated in the high rate treatment process shall be of the dual media or multimedia type. The media shall consist of anthracite, silica sand, or other suitable filter materials. Both dual media and mixed media filters will be considered. Since filters media designs utilized in the high rate treatment process are generally proprietary in nature, no attempt will be made to set standards for the minimum filter media depth, the effective size and uniformity coefficient of the filter media, or the specific gravity. However, beds having a minimum total depth of 27 inches of filter media with a minimum of 10 inches of fine sand will be considered. Other proposals for high rate processes shall be considered individually by the division.

d. Structural details and hydraulics - see 12VAC5-590-880 A 4.

e. Washwater trough - see 12VAC5- 590-880 A 5.

f. Filter bottoms and strainers - see 12VAC5-590-880 A 7.

g. Surface wash - see 12VAC5-590-880 A 8.

h. Appurtenances - see 12VAC5-590-880 A 9.

i. Backwash - see 12VAC5-590-880 A 10.

j. Miscellaneous - see 12VAC5-590-880 A 11.

5. Chemical application.

a. Suitable equipment for application of filter aids (polymers) to the influent of the filters shall be provided.

b. See 12VAC5-590-860.

Historical Notes

Derived from VR355-18-009.05 § 3.26, eff. August 1, 1991; amended, Volume 09, Issue 17, eff. June 23, 1993.

Statutory Authority

§§ 32.1-12 and 32.1-170 of the Code of Virginia.