This document presents a case study of ammonia and hydrogen emissions from an industrial waste landfill in Barcelona, Spain. The landfill contained melting salts from recycled aluminum production, which reacted with water to produce ammonia, hydrogen, and hydrogen sulfide gases. The author monitored gas emissions over time and found ammonia and hydrogen concentrations followed parallel trends. Emissions abruptly increased after heavy rainfall, indicating water infiltration enhanced gas production. Mathematical models using first-order decay equations accurately described gas concentration trends before and after this secondary peak, supporting the hypothesis that water influenced gas generation rates.

1. AMMONIA AND HYDROGEN EMISSIONS
FROM AN INDUSTRIAL WASTE
LANDFILL: A CASE STUDY
J. FELIUBADALÓ
Entitat Metropolitana de Serveis Hidràulics i Tractament de Residus, C/ 62,
nº 16 - 18, Ed. B, 08040 Barcelona, Spain.
SUMMARY: Emissions from IW of gases other than methane an carbon dioxide are until now not
studied as in MSW landfills are. This paper deals with the origin, monitoring, temporal evolution and
mathematical modelization of ammonia and hydrogen emissions from a IW landfill. Melting salts from a
recycled aluminium metallurgical process, among some other kinds of waste, compose the landfilled
mass.
1. INTRODUCTION
Emissions of MSW landfills are currently a well-known subject, in terms of quality (range of major:
methane and carbon dioxide, and minor compounds) and in terms of quantity, rate and temporal
evolution of these parameters.
Related to mono-industrial waste landfills, a lack of data is found, perhaps due to the relative
scarceness of this kind of facilities and also to the extreme diversity of industrial substances disposed in
them.
Because of a number of reasons (Relea et al., 1995), the Authorities in waste management of the
Metropolitan Area of Barcelona have been applying historically an splitting strategy between wastes of
diverse origins. This strategy is currently being incorporated into Spanish and European regulations on
waste landfilling.
Moreover, these Authorities have played a role of substitution of private initiative when the industrial
waste management was not technically and economically attractive for it. In this context, at the last
1980's, the EMSHTR established and operated for about seven years an industrial waste landfill in a
ancient clay quarry at Cerdanyola (a village about 15 Km at the North-West from Barcelona). The
extremely low values of hydraulic conductivity of the clay (even below 10-11 m.s-1) made it specially
suitable for that purpose. This landfill was located about 2 Km at the East from that referred by the
same authors (op. cit.).
In principle, the landfill was established for a single industrial waste: the melting salts from recycled
aluminium metallurgical process. Further, some other kinds of waste were also disposed there, namely
non-special general industrial waste, industrial sewage sludge from the treatment of

2. brine destined to electrolytic production of chlorine and caustic soda, and polluted soils from an ancient
chemicals plant at a nearly Barcelona borough.
The approximate amounts and percentages of every kind of waste are summarized in Table 1.
Table 1 - Amounts and kinds of landfilled waste
Kind of waste Amount, t Percentage
Melting salts 118.000 18,4
Industrial sewage sludge 77.000 12,0
Polluted soils 7.000 1,2
Non-special general industrial waste 440.000 68,5
Total 642.000 100,0
2. ORIGIN AND CHEMICAL FEATURES OF MELTING SALTS
The metallurgical process mentioned above lies basically in the melting, in a chemically reducing
atmosphere, of a mixture of aluminium recycled goods and melting salts (almost all sodium and
potassium natural chlorides). Molten salts float over the molten aluminiun, protecting it from oxydation
and absorbing in its mass most of the aluminium impurities.
As a result of this process, and specially due to the reducing character of the atmosphere in which it
takes place, in the residual salts is present a certain amount (2 - 3%) of metallic aluminium, besides with
some other by-products: aluminium nitrides, hydrides and sulphides, formed by the reaction of this
element with nitrogen and hydrogen, both present at the reducing atmosphere, and by the reaction of it
and of salts alkaline metals with the sulphur compounds usually present at the fuel used for the melting
process.
The overall chemical reactions describing these processes can be summarized, respectively, as
follows:
2 Al + N2 ???> 2 AlN
2 Al + 3 H2 ???> 2 AlH3
+
3 S + 2 Al ???> S3Al2 and S + 2 Na ???> SNa2
If waste salts are put in contact with water, these componds react with it, giving aluminium and sodium
hydroxides and, respectively, ammonia, hydrogen and hydrogen sulphide, probably according to the
following reactions:
AlN + 3 H2O ???> NH3 + Al(OH)3
AlH3 + 3 H2O ???> 3 H2 + Al(OH)3
S3Al2 + 6 H2O <???> 3SH2 + 2Al(OH)3, and SNa2 + 2 H2O<???> SH2 + 2 NaOH

3. As it can be seen, in all cases these processes give some alkaline or amphoteric solid compounds
besides with three kinds of gases, all of them with a negative environmental impact due to various
reasons: toxicity and corrosivity in the case of ammonia, explosiveness in that of hydrogen, and
toxicity in that of hydrogen sulphide. By the way, it is worth to point up that the alkalinity of sewage
sludge disposed together with the casting salts contributes to the stabilization of the alkaline compunds
formed.
In the other hand, levels of hydrogen sulphide were found neglectable when compared with those of
ammonia and hydrogen. Therefore, it was decided to monitorize only the last two, whose levels were in
the range of percentages, whereas that of hydrogen sulphide was in the range of mg/m3.
3. SAMPLING AND ANALYSIS METHODS AND PERIODICITY OF SAMPLING
3.1. Sampling and analysis methods
Ammonia, because of its chemical properties, which made impossible its instrumental analysis, was
collected and analyzed by a “classical” method: chemical absorption in sulphuric acid and colorimetric
dosing by Nessler method. Sampling was performed by means a "train" of three maxi-impigers, the first
two filled with H2SO4 0,1N and the third, empty, acting as a trap. Gas to be sampled was forced trough
the train by a peristaltic air pump.
Hydrogen was analyzed at a laboratory by an instrumental method (gas cromatograpy). So, its
sampling lay just in the collection in an hermetic poliethylene bag by means of an air pump.
3.3. Periodicity of samplings and unit of time
It has been performed a total of 22 samplings and subsequent analysis, distributed about evenly in time,
between February 1995 (just after the cessation of landfilling), and March 1998, when concentrations
of both gases dropped below worrying levels. Although intervals between samplings are not exactly
equal, in the following they will be considered as constant, in order to simplify calculations and graphics.
Consequently, the time unit used will be that interval, and calculations will be done on that basis. An
elemental calculation gives that the equivalence factor with year is 6,6316 samplings per year.
4. RESULTS
Results of the entire series of ammonia and hydrogen analysis are presented together at Figure 1, in
order to highlight the appoximately parallel temporal evolution of concentrations of both gases (note that
those of hydrogen have been reduced by a factor of 10).
The most appealing feature of both evolutions is, undoubtedly, the abrupt rising they show at the 11th
sampling. As it will be discussed further, both evolutions could be approached quite accurately by a first
order decay mathematical model, but that describing the evolution until that point fails to be valid from it.
However, the remaining part of both evolutions can be described with about the same accuracy as well
by another first-order decay equation or, more precisely, by an equation of the same kind that the first
but with other parameters.

4. As it can be seen in Figure 1, the degree of parallelism of the evolutions of ammonia and hydrogen
allows the description of both phenomena by the same kind of mathematical model, as explained at
Chapter 6.
0,8
Concentrations, % v/v
0,7
0,6
0,5 Ammonia conc.
0,4 Hydrogen conc./10
0,3
0,2
0,1
0
0
2
4
6
8
10
12
14
16
18
20
Sampling nº
Figure 1. Evolution of ammonia and hydrogen concentrations by volume.
5. DISCUSSION OF RESULTS
Looking for an explanation for the abrupt rising of concentrations described above, and having
considered that the rising is not attributable to any landfilling of materials (since it had completely ceased
before the beginning of sampling) nor to ambient temperature (since the rising has not a seasonal -
depending pattern), the sole one that appeared to be reasonable was the dependence of water
infiltration. In spite of the quality of landfill capping performed (1 m. of clay, 0,20 m. of draining inert
material and 0,80 m. of topsoil), it appears obvious that any amount of rainfall and runoff water can
reach the melting salts and re-enhance the production of ammonia and hydrogen accordingly to
processes described at Chapter 2.
This assumption about water intrusion into landfill body s corroborated by the fact that even at
i
present, that is, four years after the closure, there is still a certain production of leachate.
Moreover, the parallelism of evolutions of ammonia and hydrogen pointed at Chapter 4, strongly
suggests a common cause for the rising of both concentrations.
So, in order to investigate the influence of water intrusion, it has being plotted (see Figure 2) the
evolution of rainfall (directly measured in place) during the sampling period. The comparison of its
profile with that of concentrations shows that:
• It occurs a first strong peak of rainfall between samplings 6 and 10, with a total of 368 l/m2, whereas
the rising of concentrations occurs at sampling 11, that is, a few months later.
• A second important peak of rainfall occurs between samplings 17 and 20, with a total of 382 l/m2.
In opposition to the precedent, this peak has no correspondence with any one of concentration
evolution.
These facts would be consistent with the explanation of, whereas at the time af first rainfall peak there
was still any amount of aluminium hydrides and nitrides to react with water and so produce enough

5. ammonia and hydrogen to give a noticeable peak in its evolution, by the time of second rainfall peak,
these substances were already exhausted, and thus, it does not occur a second evolution peak.
140
120
Rainfall, l/m2
100
80
60
40
20
0
0
2
4
6
8
10
12
14
16
18
20
Sampling nº
Figure 2. Evolution of rainfall.
6. MATHEMATICAL MODELS
6.1. General
Like in municipal organic solid waste (Coops et al, 1995), the kinetics of the reaction of aluminium
nitrides and hydrides with water to give aluminium hydroxide and, respectively, ammonia and hydrogen
can be described, whit more or less accuracy, by mathematical models based on equations depending
on the kinetic order of reactions taking place.
Since in the case in study reactions are at least bimolecular, the models should be of second or even
further orders (Babor and Ibarz, 1962).
Nevertheless, second and further orders models are very difficult to apply in practice, and so its
practical usefulness is limited; so, in this case it was taken a first order model, that is, one giving a
negative exponential profile for the reaction rate or, correspondingly, for concentrations of both gases.
First order models are, as it is well-known, based on the following general equation:
-kt
Ct = C0* e (1)
where Ct is the concentration at the instant t, C0 that of the initial instant and k is the velocity constant of
the process.
The last is related with Ct and C0 by the equation
k = (1/t) * ln (C 0/Ct ) (2)
Thus, to know C0 and Ct gives the value of k or, in other words, completely determines the equation or
equations ruling the mathematical model. Therefore, for the complete determination of a first order

6. equation, it is sufficient to have the initial value of concentration (C0) and its value after a known time t
(C t ). It is easy to demonstrate that equation (2) can be generalized to any pair of values of t:
k = 1/(t2-t1) * ln (C1/C2) (3)
If, as in this case, one looks for the modelization of a set of empirical data, these values of C might be
chosen so as to positive and negative errors of model were approximately compensated, in order to
maximize the accuracy of it. This can require a number of trials.
Moreover, in this case, the special feature of the set of values reported in Chapter 5 leads to the
need of two equations, the first describing the evolution before the secondary peak reported there and
the second accounting for the remainder of the obtained values. It is worth to point here that this
procedure has an evident physical interpretation. In effect, the overall phenomenon can be described in
terms of the succession of two approximately exponential decay processes, the second of them starting
from a secondary concentration peak due to an external incidental cause.
6.2 Calculation of coefficients
The coefficients of equations constituting the mathematical model [(2) and (3) respectively for the left
and right part of it, as it has been explained above] have been derived, both for the cases of ammonia
and hydrogen, from empirical data plotted at Figure 1.
The values used for calculation of parameters for ammonia and hydrogen models are those listed in
Table 2:
Table 2 - Values of t and C used for calculation of ammonia model parameters
Ammonia Hydrogen
Instant Concentration, % Instant Concentration, %
t0 = 0 C0 = 0,8 t0 = 0 C0 = 7,8
t1 = 6,8 C1 = 0,2 t1 = 10 C1 = 0,5
t2 = 11 C2 = 0,45 t2 = 11 C2 = 4,5
t3 = 15,5 C3 = 0,07 t3 = 15,5 C3 = 0,7
The application of the corresponding values to expressions (2), (3) and (1) gives for the whole
mathematical model for ammonia the following equations:
Cat1 = 0,80 * e -0,2038 t (4) and C
a
t2 = 0,45 * e -0,4134 t (5)
Being (4) valid between instants 0 and 10, and (5) for the remaining period.
And the equations fot hydrogen model are
Cht1 = 7,8 * e -0,2747 t (6) and C
h
t2 = 4,5 * e -0,4134 t (7)

7. Being as well (6) valid until instant 10, and (7) between 11 and 21ones.
It is to be noted that, accordingly with the last statement of paragraph 4.1, the exponent of equation (7)
is the exactly the same of (5) one, and that its coefficient is that of (5) multiplied by a
factor of 10. Note as well that the unit of all exponents is the (sampling intervall)-1. To express them in
year—1they must be divided by the factor 6.6316, as stated at 4.3.
6.3. Comparison between observed and model-derived values of concentration.
In order to show graphically this comparison, observed and model - derived values have been plotted
together, respectively for ammonia and hydrogen, at Figures 3 and 4.
7. CONCLUSIONS
• As it could be expected, the decay of concentrations for the two studied gases (both of them coming
from inorganic substances) is much faster (by a factor of about 10) than that of methane and carbon
dioxide in biogas, due, instead, to the decomposition of organic products.
• The rate of generation for ammonia and hydrogen appears to be strongly related to water intrusion
into waste mass. This statement is supported by the observational evidence and by its explanation in
chemical theoretical terms. No other external factors appear to have a comparable influence on
generation rate.
• In spite of deviations due to external causes other than water intrusion, first order mathematical
model appears to be a quite good approach to observational results. In the other hand, the
enhancements of generation rate due to water intrusions can also be approached just re-adjusting the
parameters of model to observational data.
• If these enhancements do not occur, the simplicity of the first order model allows to derive its
parameters (that is, to define completely the model equation) from just two values of concentration at
two known instants of time.
ACKNOWLEGEMENTS

8. Author gratefully acknowledges Adoración Pascual, Maria Gràcia Rosell, Xavier Guardino and Emili
Castejón, from the Instituto Nacional de Seguridad e Higiene en el Trabajo, at
Ammonia concentrations, % v/v
0,8
0,7
0,6
0,5 Observed conc.
0,4
Math. model conc.
0,3
0,2
0,1
0
0
2
4
6
8
10
12
14
16
18
20
Sampling nº
Figure 3. Ammonia observed versus mathematical model derived concentrations.
Hydrogen concentrations, % v/v
8
7
6
5 Observed conc.
4
Math. model conc.
3
2
1
0
0
2
4
6
8
10
12
14
16
18
20
Sampling nº
Figure 4. Hydrogen observed versus mathematical model derived concentrations.
whose laboratory in Barcelona has been performed all the analytical work, and Miquel Gelabert, Juan
Leyva and Josep Mª Biescas, from the EMSHTR, who have shared with Mrs. Pascual and himself the
sampling works.
REFERENCES
Relea F., Feliubadaló J. and Montells R. MSW and NSIW landfilling: an emission comparison.
Proceedings Sardinia 95, Fifth International Landfill Symposium, CISA publisher, Cagliari, vol.
III, 223-234.
Babor J.A. and Ibarz J. Química General Moderna, Editorial Marín, Barcelona 1962, 294-295.

9. Coops O., Lunning L., Oonk H. and Weenk A. Validation of gas formation models. Proceedings
Sardinia 95, Fifth International Landfill Symposium, CISA publisher, Cagliari, vol. I, 634-646.