Section 1090. Lime stabilization of septage

A. General. Lime stabilization of septage is a process consisting of the addition of hydrated lime in sufficient quantity usually 50 pounds per 1000 gallons, to raise the pH and hold it at 12 or higher for at least 30 minutes before dewatering or land spreading. The process normally requires mixing during the lime addition process as well as a mixing tank to facilitate the holding and mixing requirement.

B. Mixing equipment.

1. Mixing may be accomplished by recirculation through the pump truck. Mixing through the pump truck is limited to operations where no more than one load at a time is processed. In this case a mixing tank is not required.

2. When a mixing tank is required a minimum capacity of 2000 gallons shall be provided. Mixing tank volume in excess of 2000 gallons may be required on a case-by-case basis. When separate mixing capability is necessary it may be accomplished by either mechanical mixing or air diffusion.

a. Mechanical mixers shall be capable of maintaining the bulk fluid velocity above 26 ft/minute and an impeller Reynolds number greater than 1000.

b. Diffused air requirements range from 150 to 250 CFM/1000 Ft of tank volume for course bubble diffusers. The diffusers shall be mounted such that a spiral roll is established in the mixing tank away from the point of lime addition.

C. pH. Suitable methods of measuring pH values in excess of 12 shall be provided and maintained to measure the pH of the septage-lime mixture.

D. Dewatering. Dewatering is required prior to landfilling lime stabilized septage and may be desirable before land spreading. Criteria for dewatering facilities may be found in 12VAC5-580-700 of the Sewerage Regulations. In addition all filtrate from the dewatering facilities must be:

1. Disposed of in a subsurface soil absorption system; or

2. Collected in an impervious container or earthen basin for ultimate disposal in an approved sewerage system or treatment works or by land spreading.

E. Storage facilities. Regardless of the equipment used to land spread the lime stabilized septage, there will be extended time periods, particularly during winter, when the septage cannot be land applied. Therefore, storage facilities shall be provided. The design and construction of the storage facilities shall adhere to the following criteria:

1. General site requirements. If the storage facilities are to be constructed of manufactured materials, i.e., steel or concrete, the site requirements shall conform to 12VAC5-610-1080 B 2. Where an earthen storage facility is to be provided site requirements shall conform with 12VAC5-610-1080 B 1 and 2.

2. Design requirements.

a. Transfer facilities. When the storage facilities are located adjacent to the mixing facilities described in subsection B of this section the piping shall be arranged in such a manner to eliminate spillage, reduce splashing and facilitate distribution of the septage through the storage unit.

b. Receiving facilities. When the storage facilities are remote from the mixing facilities and require vehicular transport of the lime stabilized septage the receiving facilities shall conform to 12VAC5-610-1080 C 1.

c. Capacity. The storage volume shall be based upon a mass balance which considers as a minimum monthly pumping rates (number of loads pumped per month), number, location and nature of land spreading sites including soil type, crop cover and topography and seasonal application to cropped or pastured land. In no case shall the storage capacity be less than 60 days.

d. Storage facilities. When the storage facility is of a manufactured material (steel, concrete, etc.) it shall be watertight and fitted with appropriate piping and appurtenances to facilitate removal of the stored material. When the storage facility is of earthen construction it shall adhere to the design requirements contained in 12VAC5-610-1080 C 2 a (2), (3), (4), (5), and (6) above. See Appendix P.

Historical Notes

Derived from VR355-34-02 § 4.44, eff. February 5, 1986; amended, eff. May 11, 1988.

Statutory Authority

§§ 32.1-12 and 32.1-164 of the Code of Virginia.