Section 840. Chemical treatment

A. Usage. Chemicals shall be compatible with the treatment works unit operation and have no detrimental effect upon receiving waters. Pilot plant studies or data from unit operations treating design flows of sewage or domestic wastewaters of similar characteristics (organic levels, metal concentrations, etc., within 25% of proposed design) shall be required to determine appropriate chemicals and feed ranges.

1. Space shall be provided where at least 30 days of chemical supply can be stored in dry storage conditions at a location that is convenient for efficient handling, unless local suppliers and conditions indicate that such storage can be reduced without limiting the supply.

2. Liquid chemical storage tanks must:

a. Have a liquid level indicator.

b. Have an overflow and a receiving basin or drain capable of receiving accidental spills or overflows.

3. Powdered activated carbon shall be stored in an isolated fireproof area, and explosion proof electrical outlets, lights and motors shall be used in all storage and handling areas in accordance with local, state and federal requirements.

4. Chemicals shall be stored in covered or unopened shipping containers, unless the chemical is transferred into an approved covered storage unit.

5. Solution storage or day tanks feeding directly should have sufficient capacity for 24-hour operation at design flow.

6. Acid storage tanks shall be vented to the outside atmosphere, but not through vents in common with day tanks.

B. Features. Provisions shall be made for measuring quantities of chemicals used to prepare feed solutions. Storage tanks, pipelines, and equipment for liquid chemicals shall be specific to the chemicals and not for alternates.

1. Chemicals that are incompatible (i.e., strong oxidants and reductants) shall not be fed, stored or handled in such a manner that intermixing of such compounds could occur during routine treatment operations.

2. Provisions shall be made for the proper transfer of dry chemicals from shipping containers to storage bins or hoppers in such a way as to minimize the quantity of dust that may enter the room in which the equipment is installed. Control shall be provided by use of:

a. Vacuum pneumatic equipment or closed conveyor systems;

b. Facilities for emptying shipping containers in special enclosures; or

c. Exhaust fans and dust filters that put the hoppers or bins under negative pressure in accordance with federal and state requirements.

3. Concentrated acid solutions or dry powder shall be kept in closed, acid-resistant shipping containers or storage units. Concentrated liquid acids shall not be handled in open vessels, but should be pumped in undiluted form from original containers to the point of treatment or to a covered day or storage tank.

4. For the handling of toxic chemicals, suitable carts, lifting devices, and other appropriate means shall be provided in accordance with the material safety data sheets and applicable state and federal requirements.

a. Provisions shall be made for disposing of empty containers by an approved procedure that will minimize exposure to the chemical.

b. The transfer of toxic materials shall be controlled by positive actuating devices.

5. Structures, rooms, and areas accommodating chemical feed equipment shall provide convenient access for servicing, repair, and observation of operation.

a. Floor surfaces shall be smooth but slip resistant, impervious, and well drained with a slope of 1/8-inch per foot minimum.

b. Open basins, tanks and conduits shall be protected from chemical spills or accidental drainage.

6. A minimum of two chemical feeders shall be provided for continuous operability. A standby unit or combination of units of sufficient capacity shall be available to replace the largest unit during shutdowns. The entire feeder system shall be protected against freezing and shall be readily accessible for cleaning.

7. Chemical feeders shall be of such design and capacity to meet the following requirements:

a. Feeders shall be able to supply, at all times, the necessary amounts of chemicals at an accurate rate throughout the range of feed.

b. Proportioning of chemical feed to the rate of flow shall be provided where the flow rate is not constant.

c. Diaphragm or piston type positive displacement type solution feed pumps should not be used to feed chemical slurries.

d. The treatment works service potable water supply shall be protected from contamination by chemical solutions or sewage by providing either an air gap between the portable water supply line and solution tank, or a suitable reduced pressure zone, backflow prevention device.

e. Chemical-contact materials and surfaces must be resistant to the aggressiveness of the chemical solutions.

8. Dry chemical feeder systems shall:

a. Measure the chemical volumetrically or gravimetrically.

b. Provide effective mixing and solution of the chemical in the solution pot.

c. Preferably provide gravity feed from solution pots.

d. Completely enclose chemicals and prevent emission of dust to the operation room.

9. Chemical feeders should be reasonably adjacent to points of application to minimize length of feed lines. Chemical feeders shall be readily accessible for servicing, repair and observation. Chemical feeding equipment should be provided with containment barriers or protective curbing so that chemicals from equipment failure, spillage or accidental drainage will be contained. Chemical feed control systems shall provide for both automatic and manual operation including:

a. Feeders that are automatically controlled should provide for reverting to manual control as necessary.

b. The feeders shall be capable or being manually started.

c. Automatic chemical dose or residual analyzers should be considered and, where provided, should include alarms for critical values and recording charts.

10. Solution tank dosing shall provide for uniform strength of solution, consistent with the nature of the chemical solution. Continuous agitation shall be provided to maintain slurries in suspension. Two solution tanks shall be required for a chemical to assure continuity of chemical application during servicing. Tank capacity should provide storage for 24 hours of operation and:

a. Each tank shall be provided with a drain.

b. Means shall be provided to indicate the solution level in the tank.

c. Make-up potable water shall enter the tank through an air gap.

d. Chemical solutions shall be kept covered, with access openings curbed and fitted with tight covers.

11. Subsurface locations for solution tanks shall:

a. Be free from sources of possible contamination.

b. Assure positive drainage for groundwater, accumulated water, chemical spills, and overflows.

c. Be protected from aggressiveness.

12. Solution tank overflow pipes shall:

a. Be turned downward.

b. Have free discharge.

c. Be located where noticeable.

d. Be directed so as not to contaminate the wastewater or receiving stream or be a hazard to operating personnel, in accordance with VOSH requirements.

13. Service water used in the feeder system shall be:

a. From sources acceptable to the department.

b. Protected from contamination by appropriate means.

c. Ample in supply and adequate in pressure.

d. Provided with means for measurement when preparing specific solution concentrations. Where a booster pump is required, duplicate equipment shall be provided.

14. Scales shall be provided as follows:

a. For volumetric dry chemical feeders.

b. Accurate to measure increments of 0.5% of load.

c. For weighing of carboys that are not calibrated volumetrically.

d. For large treatment works, indicating and recording type scales are desirable.

15. Chemical application equipment should:

a. Assure maximum efficiency of treatment.

b. Provide maximum protection of the receiving waters.

c. Provide maximum safety to operators.

d. Assure satisfactory mixing of the chemicals with the wastewater.

e. Provide maximum flexibility of operation through various points of application, when appropriate.

f. Prevent backflow or back-siphonage between multiple points of feed through common manifolds.

g. Provide for the application of pH affecting chemicals to the wastewater prior to the addition of coagulants.

C. Safety. Gases from feeders, storage, and equipment exhaust shall be conveyed to the outside atmosphere, above grade and remote from air intakes in accordance with applicable state and federal requirements.

1. Special provisions should be made as necessary for ventilation of feed and storage rooms in accordance with VOSH and applicable fire code requirements.

2. For each operator who will handle dry chemicals, protective equipment should be provided, including personal protective equipment for eyes, face, head, and extremities, and protective shields and barriers, in accordance with VOSH requirements.

3. Facilities should be provided for eye washing and showering, in accordance with VOSH requirements. Protective equipment and neutralizers shall be stored in the operating area.

Historical Notes

Former 12VAC5-581-900 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-840, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.