Appendix 75-B.2 - Activated carbon treatment systems

Section 75-B.2 Activated carbon treatment systems. These systems consist of filtration equipment which use activated carbon to remove organic chemicals from individual water supplies. They also may be used to improve the aesthetic quality of drinking water. These systems are normally installed between the water source and the first point of use in the water distribution system.

(a) When an activated carbon filter unit is installed to treat an individual water supply containing organic chemcials, it must meet all of the following conditions:

(1) The units are installed in-line and serve the whole household. Faucet or undersink units shall not be used for the removal of organic chemicals.

(2) The treatment unit must be capable of processing water at a flow rate of at least five gallons per minute (gpm). Flow rates may be reduced if additional pressurized storage is provided after the treatment unit to insure the system will provide at least five gpm of treated water to the household continuously for a minimum of 20 minutes.

(3) The maximum application rate shall be 10 gpm per square foot of activated carbon surface area. Flow rates shall be controlled by a flow limiting device.

(4) The minimum empty bed contact time shall be three minutes. This should be accomplished with at least two filter units of equal size placed in series.

(5) Only virgin carbon shall be used. The cylinder should be recharged at a point outside the residence and the spent activated carbon properly disposed of by the vendor.

(6) Disinfection must be provided after the activated carbon unit. The preferred method of disinfection is an ultraviolet unit with a minimum rating of five gpm. The unit shall have a fail-safe device that detects the intensity of the ultraviolet light and automatically shuts down the system when the intensity decreases to below the minimum effective level specified for the unit. A manual or automatic wipe must be provided. An alternate method of disinfection would be sodium hypochlorite. If sodium hypochlorite is used, contact time adequate to eliminate pathological organisms must be provided after the point of injection and prior to consumption. The local health unit having jurisdiction may allow the use of activated carbon units without disinfection upon the adoption of a formal procedure for the approval of treatment systems installations, and notification to homeowners of the need for disinfection.

(7) Treatment units capable of backwashing shall only use treated water for that purpose. Backwashing should be at a minimum flow rate of 10 gpm for at least two minutes. The backwashing must be accomplished in a manner that does not create a cross-connection. The wastewater shall not be discharged to the ground surface but may be discharged to a septic system.

(8) All components of treatment units must safely withstand the highest water pressure in the system.

(9) The following must be provided:

(i) A flow meter to record total flow.

(ii) Sampling taps for raw, partially treated and treated water.

(iii) Adequate valving to isolate the various components, and for backwashing of filters.

(iv) Only nontoxic materials and coatings.

(v) Ease of access to all components.

(vi) Prefiltration where appropriate to remove turbidity and bacteria.

(vii) Pressure gauges before and after the activated carbon unit.

(b) Other than whole-house units. Because organic chemicals can be inhaled and absorbed through the skin during baths and showers, the following types of point-of-use activated carbon units are not suitable for use where the water contains organics:

(1) Pour-through units - a stand-alone device, not attached to the water supply system, and normally manually operated.

(2) Faucet-mount units - a unit mounted directly at the outlet of an individual tap or faucet.

(3) In-line, one-tap units - a unit mounted in a supply line that serves only one tap or faucet.

(4) Line-bypass units - an in-line unit that serves a separate tap or faucet intended for drinking water use only.

Effective Date: 
Saturday, December 1, 1990
Doc Status: 
Complete