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ACTIVATED CARBON PROCESSES 14.33

• Provide a vacuum cleaning system for picking up loose carbon.
• Provide a method for automatically and accurately measuring carbon levels in storage
bins and vessels. A backup manual system should be provided to track bed and bin lev-
els. Depths can be monitored by placing a permanent reference mark such as a stain-
less steel plate, laminated plastic staff gauge, or painted gauge marks directly on the
inside wall of each bed and bin.

Materials of Construction. Materials of construction for carbon adsorption plants vary.
Epoxy-coated steel, type 316 stainless steel, concrete, and fiberglass are all used for ves-
sels; stainless steel, lined carbon steel, fiberglass, and plastic have been used for piping.
Problems have been reported with plastic due to abrasion and scouting from the transport
of carbon slurries.
Dry carbon and carbon in water slurries are not corrosive. Damp or wet carbon, how-
ever, is extremely corrosive. Precautions must be taken to ensure that only proper materi-
als are used in contact with damp carbon. All metal in contact with damp carbon must be
corrosion-resistant (type 316 stainless steel) or noncorrosive (fiberglass). Tanks, vessels,
and fittings may be fabricated of epoxy or rubber-coated steel, stainless steel (type 316),
glass-reinforced polyester (fiberglass), or concrete. At existing plants, embedded metals
can be field-lined with rubber, glass-reinforced polyester, vinyl ester, or epoxy. Valves and
instruments such as flowmeters and eductors must be protected from corrosion.

REGENERATION OF GRANULAR
ACTIVATED CARBON

Facilities for on-site regeneration of GAC are expensive, making it generally impractical
for smaller water systems which are generally designed to waste spent carbon and replace
it with new. Larger systems must carefully look at the economics of installing regenera-
tion equipment.

Regeneration Facilities
GAC is expensive when compared with sand and anthracite filter media. As a result, it is
often cost-effective to regenerate and reuse GAC. Two basic approaches to regenerating
GAC are off-site regeneration and on-site regeneration.
The rate at which contaminants break through the carbon bed determines the size of
the regeneration system. The primary design criterion for a reactivation system is the rate
of carbon regeneration (mass per unit time, e.g., kg/h). A complete regeneration or reac-
tivation process typically consists of a furnace system, including a feed system, a drying
or dewatering scheme, and a reactivation process. A simple regeneration system sche-
matic is presented as Figure 14.14.
Typical carbons used in water treatment require regeneration from every 6 months to
5 years, depending on the application. On-site regeneration is generally not cost-effective
unless the carbon exhaustion rate is over 910 kg per day. Current U.S. applications fall
in the range of off-site regeneration (225 to 700 kg per day). For facilities using less than
225 kg per day, off-site disposal should be considered.
For off-site disposal applications, virgin carbon is first purchased from a carbon sup-
plier. Once carbon becomes exhausted, it is transported in slurry form by gravity to a
drainage collection tank where the supernatant is routed to the plant headworks for treat-