Dechlorination of Highly Chlorinated Water - Disinfection of Pipelines and Storage Facilities Field Guide - page 99

The primary advantages of Venturi injection systems are
￿ efficient operation over a wide range of pressures;

￿ available in a wide range of sizes, flows, and injection

capacities;

￿ no external energy requirements; and

￿ instantaneous mixing in the injection chamber.

The primary disadvantages of Venturi injection systems are
￿ more sophisticated equipment requirements than gravity

feed systems;

￿ slightly more labor intensive set-up;

￿ higher unit equipment cost than gravity feed systems;

and

￿ require constant monitoring.

Spray feed systems. The dechlorinating solution can be
sprayed into the flow (on pipe walls, surfaces, or pipeline appur-
tenances) via a backpack sprayer similar to those used for pesti-
cide and herbicide application or a chemical fire extinguisher.
The advantage of this technique is that the chemical feed rate is
fairly constant (given a steady pressure within the solution
chamber). Therefore, dosages can be approximated fairly accu-
rately, and a piped or channelized flow is not required to effec-
tively feed the chemical. This method is typically more effective
in adding dechlorinating chemicals to sheet flows than the other
alternatives previously described.
A significant disadvantage of a spray feed system is that it
requires the equipment to be set up at a stationary point and
monitored for adequate chemical and pressure. If a stationary
point is not available, a person will have to don the sprayer and
continuously apply the dechlorinating agent to the flow.

Flow-through systems. Flow-through systems (Figure 7-2)
include any method where the solid chemical is held stationary
and the flow is allowed to run over, around, or through it. Exam-
ples include pumping chlorinated water through a container
filled with dechlorinating agent, or laying permeable bags of the