IN-PLANT AND IN-LINE BOD/SUSPENDED SOLIDS REDUCTION
WITH HYDROGEN PEROXIDE
John A. Shepherd, Research Engineer
FMC Corporation
Industrial Chemicals Division
Princeton, New Jersey 08540
INTRODUCTION
Hydrogen peroxide is attaining increasing use in sewage treatment.   Collection system
and treatment plant odor and corrosion problems resulting from the presence of sewage
sulfides are controlled by hydrogen peroxide.   Filamentous bulking of sludge may be
eliminated by peroxide treatment.
Additional treatment and operational benefits directly resulting from hydrogen peroxide use have been observed and measured.   Improved solids settling and plant dissolved
oxygen maintenance are obtained.   A major benefit from peroxide treatment which has
been measured is a substantial increase in BOD and suspended solids (SS) reduction.
Long-term operating data at several waste treatment plants using the FMC hydrogen
peroxide sewage odor/corrosion control system confirm that both in-line and in-plant
increased BOD and SS reduction may occur as a result of peroxide use.   These data show
that the amount of BOD and SS removal or reduction may be far in excess of what could
occur only as a result of the addition of active oxygen from hydrogen peroxide.   However, increased BOD and SS reductions have not occurred in all plants using the peroxide
treatment system.
There are many definitions for BOD.   One is "the amount of oxygen required for the
aerobic biological oxidation of the organic solids in a sewage or waste is the biochemical
oxidation demand (BOD)" [1].   Consider that the BOD of a waste is an assessment of
the amount of oxygen used for the respiratory activities of the microorganisms in a biological process [2].   One must accept the fact, however, that the concept of BOD as a
measure of the pollution potential of an aqueous waste stream is empirical, as is the BOD
analytical test procedure itself [2,3].
Chemical reduction of BOD has been known for many years.   "Application of chlorine to sewage effects a reduction of BOD which is generally considered to be real as well
as apparent.   Whether it is employed for the prevention of sulfide production in long
sewer outfalls, for the avoidance of septicity, for the deodorization of foul sewage, or
for the disinfection of sewage effluents, introduction of chlorine effects a reduction of
BOD concurrent with the accomplishment of these purposes" [4].
This reduction is, at least in part, a permanent reduction involving elimination or alteration of substances capable of exerting BOD.   Research has indicated that the application
to sewage of enough chlorine to produce a trace of residual after 15 min reduces the 5-
day BOD by 15 to 35%.  This reduction amounts to about 2 mg/l of BOD per mg/l of
chlorine taken up.   It has been concluded that three kinds of reactions are involved;
1. Direct oxidation, resulting in destruction of BOD-exerting compounds.
2. Substitution of chlorine for hydrogen.  When this substitution takes place on nitrogen
atoms, chloramine compounds having more or less bactericidal power are formed.
When the substitution is on carbon atoms, the compounds are not bactericidal but
are no longer available as food.
3. Addition to unsaturated compounds   This again produces compounds that are not
bactericidal but are not available as food [5].
As to whether the 5-day BOD reduction observed results from a reduction of the total
amount of decomposable material or a reduction of the rate at which BOD is exerted, or
both, the evidence has not been decisive.   Studies have indicated that both the total
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