A train of four 55-gallon cannisters of activated carbon is to be used to reduce the nitroglycerine (NG) content of 400 gph of wastewater from 2,000 ppm by weight to less than 1 ppm. Each cannister has a diameter of 2 ft and holds 200 lb activated carbon (ρb = 32 lb/ft3). Each cannister is equipped with a liquid-flow distributor to promote plug flow through the bed of carbon. The effluent from the first cannister is monitored so that when a 1 ppm threshold of NG is reached, that cannister is removed from the train and a fresh cannister is added to the end of the train. The spent carbon is mixed with coal for use as a fuel in a coal-fired power plant at the process site. Using the following pilot-plant data, estimate how many cannisters are needed each month and the monthly canister cost at $700 per cannister.

Pilot-plant data:

Tests with the same 55-gallon cannister to be used in the commercial process; water flow rate = 10gpm; NG content in feed = 1,020 ppm by weight.

Breakthrough correlation:

tB = 3.90 L – 2.05, where tB = time, h, at breakthrough of the 1 ppm threshold and L = bed depth of carbon in feet.