effect of the addition of sodium nitrate to sewage on hydrogen sulfide production and b.o.d....

Effect of the Addition of Sodium Nitrate to Sewage on Hydrogen Sulfide Production andB.O.D. ReductionAuthor(s): H. HeukelekianSource: Sewage Works Journal, Vol. 15, No. 2 (Mar., 1943), pp. 255-261Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25029567 .

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EFFECT OF THE ADDITION OF SODIUM NITRATE TO SEWAGE ON HYDROGEN SULFIDE PRODUC

TION AND B.O.D. REDUCTION *

By H. Heukelekian

Associate, Dept. Water and Sewage Research, New Brunswick, N. J.

Nitrates are similar to sulfates in so far as they both can be reduced

under anaerobic conditions to supply oxygen for bacterial oxidations.

One important difference between these two oxygen-rich compounds is

to be noted. Whereas the end product of sulfate reduction is an

odorous compound, nitrate reduction results in inoffensive products:

nitrates, ammonia and nitrogen gas. What happens when both sul

fates and nitrates are present together under anaerobic conditions?

Are they reduced simultaneously, or does the reduction of one precede and prevent the reduction of the other? The practical aspects of this

question are whether, in the presence of nitrates, the reduction of

sulfates and the consequent production of hydrogen sulfide can be

prevented, and how much nitrate is required to bring about this de

sirable result.

There are several sources of information available on the use of

nitrate for the prevention of hydrogen sulfide production. An inter

esting use of sodium nitrate in Coney Island Creek to alleviate the

pressing problem of hydrogen sulfide production is reported by Car

penter (1). Chlorinated lime was strewn over the surface of the water

to neutralize as much of the hydrogen sulfide as possible and then

sodium nitrate was added to prevent the further development of the

gas. The hydrogen sulfide content of the water was reduced by this

treatment. Even the mud banks seemed to be deodorized. Fales (2)

reported the use of sodium nitrate in conjunction with the discharge of

treated paper mill and tannery effluents into a stream at extremely low

flow during the warm weather. The treatment was effective in pre

venting offensive odors. A report by Sanborn (3) deals with the use of sodium nitrate for retarding the offensive odors produced from

cannery wastes in lagoons. The source of odors in this case was from

the reduction of organic compounds and the nitrates were applied as

a source of oxygen to satisfy a part of the oxygen demand of the

organic matter and thus to prevent anaerobic decomposition. From

laboratory tests it was concluded that the addition of sodium nitrate

to furnish enough oxygen to satisfy 50 per cent of the five-day B.O.D.

gave complete protection against odors. Reduction of the nitrate

dosage to the 40 per cent level gave stale or musty odors. Lower dos

ages of nitrate gave increasing odors.

In addition to these various sources of information it is known that

oxidized effluents containing nitrates are stable and do not produce *

Journal Series Paper of the New Jersey Agricultural Experiment Station, Rutgers Uni

versity, Department of Water and Sewage Research.

255



256 SEWAGE WORKS JOURNAL March, 1943

odors. Furthermore, the discarded nitrate method for the determina

tion of the oxygen demand of sewage was based on the principle of the reduction of nitrate and the utilization of the oxygen liberated for the oxidation of putrescible organic matter. It would seem, from the

foregoing considerations, that of the various sources of oxygen for the

oxidation of organic matter, namely oxygen, nitrates and sulfates, the

order of utilization is as given. No nitrate reduction takes place until

all the dissolved oxygen disappears and sulfates are reduced after the

nitrates. M?thyl?ne blue is not reduced until all the nitrates disappear.

0 2 4 6 8 10 DAYS

Fig. 1.?The effect of the addition of sodium nitrate on sulfide production from sewage.

It was considered, therefore, of interest to determine the effect of the addition of sodium nitrate to sewage on the retardation of sulfide pro duction under anaerobic conditions. It would be expected that the

addition of nitrate under these conditions would also result in B.O.D.

reduction. The extent of this reduction was also investigated.

Methods

Municipal domestic sewage was divided into several portions. Various quantities of sodium nitrate were added, distributed into

tightly stoppered bottles and incubated at 20? C. At intervals total



Vol. 15, No. 2 EFFECT OF ADDITION OF SODIUM NITRATE 257

sulfides were determined by aspiration of the acidified sample with carbon dioxide gas and trapping the liberated hydrogen sulfide in neutral zinc acetate solution.

Results

Odor Control.?A comparison of the effect of the addition of 120

p.p.m. sodium nitrate to sewage is given in Fig. 1. When no nitrate was added, hydrogen sulfide production started on the fourth day and

increased regularly to 16 p.p.m. on the tenth day. There was no sulfide

for the first five days when nitrate was added. Thereafter, it in creased slowly up to eight days and more rapidly to a value of 10

p.p.m. in 10 days. The figure in the inset shows the difference in sulfide content of the sewage without and with nitrate addition. The

12

10

(A 9 ? u. -J D (O

O h

o.' ?

K

\

-M

K

-X

^

4

\

^

\

-3 DAY -4

-5

-6 "

.7 "

-9 "

v

-k

\

N:

\

1

\ 40 80 120

P.P.M. NaN03

P.P.M NaN0? 20 40 60 80 '

100

7oO* DEMAND SATISFIED 85 ,70 25 4 (20

33.9

140 ' 160 42.3

. Fig. 2.?The relationship between the quantities of sodium nitrate added and sulfide production.

differences became increasingly greater up to 8 days incubation.

Thereafter, the rate of sulfide production with the addition of nitrate was higher than without the addition and the difference decreased. It is of interest to note that the nitrate added had completely dis appeared at the end of 24 hours yet its residual effect was felt for a

long time thereafter.

In Fig. 2 are presented the results of a more detailed study of the effect of various amounts of sodium nitrate on sulfide production. The addition of sodium nitrate varied from 0 to 150 p.p.m. On the




basis of available oxygen in the nitrate the additions represented 0,

8.5, 17, 25.4, 33.9 and 42.3 per cent of the 5-day B.O.D. of the sewage. It will be seen that sodium nitrate had a definite retarding effect on sulfide production, the effect being greater with greater concentration.

In fact there is a direct relationship between the concentration of

nitrate added and the retardation as measured by the time required to

produce 1 p.p.m. of sulfide. This is shown graphically in the inset of

Fig. 2.

The results of these experiments indicate that nitrates are effec

tive in preventing sulfate reduction. The preferential reduction might,

however, be due to the fact that nitrate-reducing organisms in sewage are present in greater numbers than the sulfate-reducing organisms, and that in sewers where a sulfate-reducing flora is established the

effect of nitrates might not be so pronounced. In order to determine

the effect of this factor, sewage was enriched with sulfate-reducing

organisms by the addition of sludge from a previously septicized sew

age. Centrifuged residue from two liters of previously septicized sewage was added to 8 liters of fresh sewage, divided into two portions, to one of which 120 p.p.m. of sodium nitrate was added. The sulfates

produced from the seeded control and the portion which had received in addition sodium nitrate are given in Table I. Nitrates had com

Table I.?Effect of Addition of Sodium Nitrate to Sewage Seeded with Sulfate Reducing Organisms on Sulfide Production

Total Sulfides, Parts per Million

Days Without Nitrate With Nitrate

1 0.8 0.9

2 3.0 0.4

3 7.5 1.0

5 13.0 6.2

7 13.7 11.5

9 14.0 12.6

pletely disappeared in twenty-four hours. Seeding accelerated sulfide

production in comparison with the results obtained from the previously unseeded sewages. But even under these conditions the addition of

nitrate gave definite retardation of sulfide production for a period of

three days. B.O.D. Reduction.?Different quantities of sodium nitrate were

added to the sewage, which was kept under quiescent conditions in

open vessels and B.O.D. determined. The results are given in Table

II. The B.O.D. in the control decreased from 117 to 103 p.p.m. The

addition of sodium nitrate accelerated the reduction. With higher quantities of sodium nitrate, greater reductions were obtained. The

reduction of nitrate was not complete in one day with the largest dose

of sodium nitrate. The B.O.D. removed per unit of oxygen in the

sodium nitrate added varied by .57, .85 and .58 with the 25, 50 and 100

p.p.m. doses respectively.




Table II.?Effect of Sodium Nitrate Additions to Sewage on B.O.D. Reduction

NaNOs Added P.p.m.

Initial P.p.m.

After 1 Day

P.p.m.

Decrease Over Initial

P.p.m.

Decrease Due to NaNOs

P.p.m.

O2 Supplied by NaNOa

P.p.m.

P.p.m. B.O.D. Reduced

P.p.m. O2 Supplied by NaN03

0

25

50

100

117 117 117 117

103 95 79 70

14 22 38 47

24 33

0 14.1

28.2

56.5

.57

.85

.58

The experiment was repeated in closed bottles in order to prevent

atmospheric reaeration. The results are given in Table III. The

nitrates disappeared completely in one day except with the 200 p.p.m. addition of sodium nitrate. The B.O.D. in the control decreased by 20 p.p.m. in one day. The decrease in B.O.D. was greater with sodium

nitrate additions, the difference increasing with the higher concentra

tions. The ratio of B.O.D. reduced to 02 supplied, due to the addition

of sodium nitrate, increased from .42 with 25 p.p.m. addition to .65 with

100 p.p.m. addition. With 200 p.p.m. addition this ratio was 0.4, prob

ably due to the fact that nitrates were not completely reduced. The

ratios were generally lower than in the previous experiment.

Table III.?Effect of Sodium Nitrate Additions to Sewage on B.O.D. Reductions

NaNOa Added P.p.m.

Initial P.p.m.

After 1 Day

P.p.m.

Decrease Over Initial

P.p.m.

Decrease Due to NaNOa

P.p.m.

O2 Supplied by NaNOs

P.p.m.

P.p.m. B.O.D. Reduced

P.p.m. O2 Supplied by NaN03

0

25

50

100 200

143 143 143 143 143

123 117 107 86 78

20 26 36 57 65

6 16 37 45

0 14.1

28.2

56.5

113.0

0

.42

.56

.65

.40

There is an available source of nitrate nitrogen in most trickling filter effluents. The return of such effluents to sewage with adequate detention might result in higher B.O.D. removals due to (1) the ni

trates in the effluent and (2) the seeding with oxidizing organisms. In order to determine the value of returning trickling filter effluents on

the oxidation of sewage, and the relative role played by the nitrates

and the organisms in the effluent, two experiments were run. Steri

lized and non-sterilized trickling filter effluents from standard filters were obtained and mixed with sewage in equal volumes. The control

consisted of sewage diluted with an equal volume of water. Compari son was also made with diluted sewage to which sodium nitrate was

added in amounts equivalent to the quantity of nitrate in the trickling filter effluent. The results are given in Tables IV and V.

In the first experiment the sewage mixed with trickling filter effluent had a lower initial B.O.D. than the control, in the second experiment the reverse was true. But in both tests the B.O.D. reduction with the




Table IV.?Effect of Nitrate in Trickling Filter Effluent on B.O.D. Reduction of Sewage

Treatment NOj-N P.p.m.

5 Day B.O.D.

Initial P.p.m.

1 Dav P.p.m.

Decrease P.p.m.

Sewage.

Sewage + NaN03.

Sewage -f- trickling filter effl.

Sewage + trickling filter effl. sterilized.

102 102 66 66

76 69 34 33

26 33 32 33

Table V.?Effect of Nitrate in Trickling Filter Effluent on B.O.D. Reduction of Sewage

Treatment NO?-N P.p.m.

5 Day B.O.D.

Initial P.p.m.

1 Day P.p.m.

Decrease P.p.m.

Sewage.

Sewage + NaN03.

Sewage -f- trickling filter efli.

Sewage ~f- trickling filter effl. sterilized.

0

8.0

10.0

10.0

117 117 148 153

103 79

107 109

14 38 39 44

trickling filter effluent was equal to sewage to which an equivalent

quantity of sodium nitrate was added. Furthermore, no greater re

ductions were obtained with the non-sterile effluent than with the sterile

effluent. It appears that the beneficial value of trickling filter effluent resides in its nitrate content and not in the seeding with oxidizing

Discussion

The retarding influence of sodium nitrate on sulfide production from sewage which has been shown in this study cannot be attributed

to any direct inhibitive or toxic action of the nitrate. The proper

explanation should take into consideration the preferential reduction of nitrates, rather than sulfates, under anaerobic conditions. The re

duction of the added nitrate was complete during the first twenty-four hours and yet the residual effect on sulfide production was exerted for a longer period. Therefore, another indirect factor plays a role,

namely the oxidation of putrescible organic matter by the oxygen liberated from the reduction of nitrates. As the putrescible organic

matter becomes oxidized the need for the reduction of sulfates is

diminished. The direct relationship between the sodium nitrate dos age and retardation in sulfide production is to be attributed to the

increased oxidation of organic matter by the oxygen in the nitrate.

An additional value from the addition of sodium nitrate is the re

duction of B.O.D. Sodium nitrate, both from the standpoint of odor

control and B.O.D. reduction, would be uneconomical except under

unusual circumstances and could not compete with chlorine used for

the same purposes. However, the nitrates contained in the trickling




filter effluent should be of value in this respect. It is also of interest to note that the value derived from the contact of sewage with filter ef fluent does not arise from the seeding with oxidizing organisms but from the nitrates. Therefore, effluents containing little or no nitrates

should be of indifferent effect, except in so far that they may contain appreciable quantities of dissolved oxygen. Recycling of high rate

filter effluents into the sedimentation tanks have been claimed to result

in added advantage in removing B.O.D. If such is the case then other

factors such as dissolved oxygen or dilution might play a role rather

than the nitrates or the seeding.

Summary

Experiments with additions of sodium nitrate to sewage have shown

that the sodium nitrate reduces and delays sulfide production from

sewage. The effects were proportional to the quantity of nitrate

used. Nitrate further has the effect of reducing the B.O.D. by a value

equal to 0.5 to 0.8 for each unit of oxygen in the sodium nitrate added.

The mixing of sewage with trickling filter effluent results in removal

of B.O.D. equivalent to the nitrate content of the effluent. The or

ganisms in the effluent seem to play only a minor role in the higher removals of B.O.D.

References

W. T. Carpenter, ? '

Sodium Nitrate Used to Control Nuisances.y '

Water Works and Sewerage,

79, 175 (1932). A. L. Fales,

il Treatment of Industrial Wastes from Paper Mills and Tannery on Neponsit

River.'' Jour. Ind. Eng. Chem., 21, 216 (1929). W. T. Sanborn, liNitrate Treatment of Cannery Waste.'' Fruit Products Journal, 20, 207

(1941).



effect of the addition of sodium nitrate to sewage on hydrogen sulfide production and b.o.d....

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