Page 185 - Industrial Wastewater Treatment, Recycling and Reuse

Advanced Oxidation Technologies for Wastewater Treatment: An Overview 159

in this process. Also the problem of higher total dissolved solids (TDSs;
because of the added iron salt) need to be handled. With some adjustments
to eliminate these drawbacks, Fenton chemistry can be successful in treating
some organic pollutants on an industrial scale.
3.3.1 Reactor Used for Fenton Oxidation

A batch Fenton reactor essentially consists of a non-pressurized stirred reactor
with metering pumps for the addition of acid, base, a ferrous sulfate catalyst
solution, and industrial strength (35–50%) H 2 O 2 . It is recommended that the
reactor vessel be coated with an acid-resistant material, because the Fenton
reagent is very aggressive, and corrosion can be a serious problem. The pH
of the solution must be adjusted for maintaining the stability of the catalyst.
For many chemicals, the ideal pH for the Fenton reaction is found to be
between 3 and 4, and the optimum catalyst to peroxide ratio is usually
1:5 wt/wt. Reactants are added in the following sequence: wastewater fol-
lowed by dilute sulfuric acid (for maintaining acidic conditions) and catalyst
in acidic solutions, followed by base or acid for the adjustment of pH at a con-
stant value, and lastly, H 2 O 2 (must be added slowly with proper maintenance
oftemperature).Becausethewastewatercompositionsarehighlychangeable,
the Fenton reactor needs some design considerations to give flexibility in
terms of the operating parameters. The discharge from the Fenton reactor
is fed into a neutralizing tank for adjusting the pH of the stream followed
by a flocculation tank and a solid-liquid separation tank for adjusting the
TDS content of the effluent stream. A schematic representation of the Fenton
oxidation treatment is shown in Figure 3.5.

Hydrogen peroxide Alkaline Polymer
agent coagulant
Iron chloride (II)

pH adjusting agent
Raw waste water

Treated water

Oxidation Neutralization Flocculation
reaction tank tank tank
Solid-liquid separation tank
Figure 3.5 Treatment flowsheet for Fenton oxidation.