1. U.P.V.
Esc. Univ. Ing. Téc. Industrial
Universität Essen
Nitrate removal for
drinking water conditioning
by fixing in storage crystals
Final work
Supervisors: Prof. J. García Garrido
Prof. Dr.-Ing. R. Widmann
Dr. M. Denecke
Dr. Alfons Grooterhorst
Author: cand.-Ing. Miguel García Hernández
Essen, Valencia, September 2002

2. i
Abstract
The increasing nitrate content in ground water of the Mediterranean Spanish coast is becom-
ing a serious problem. The reason for this nitrate increase is the excessive use of fertilisers
in intensive cultivation of orange trees.
In the last years, different physique-chemical, biological and catalytic methods for nitrate re-
moval had been developed. But there is still not a definitive method to treat the polluted wa-
ters containing nitrates. The proposal of the present work is due to the idea of CONZEPT
Gesellschaft für Unternehmerberatung mbH, Duisburg (Germany) to develop of a new
method which allows to reduce the nitrate concentration in water by the inclusion of these
anions in a crystal net. After the crystal formation process the crystals are removed from the
solution with the pollutant inside. The main reactants are sources of calcium and aluminium
ions required for the storage crystal formation process. The storage crystals are able to re-
place OH-
groups of the interlayer positions by mono, bi and trivalent ions in water. This fact
makes this technique very suitable to remove contaminants from water, obtaining a solid and
inert residue. Nevertheless, nitrates are not the first ions to get into the crystal-net. A hierar-
chy is established for the inclusion of anions in the crystals. First carbonates, sulphates, chlo-
rides, and then nitrates are included in the crystal net. So that better conditions must be
achieved to include in the crystal net as much nitrates as possible.
All experiments has been carried out with drinking water from a well placed in Alginet (Valèn-
cia - Spain) and with drinking water from the city of Essen. An important reduction of the ni-
trate concentration was observed. A 41% nitrate reduction was achieved in a single treat-
ment step experiment with a initial nitrate concentration of 164 mg/L. In multi-steps experi-
ments, the best result was a 67% nitrate reduction in a water with an initial concentration of
230 mg/L NO3
-
.

3. I
Contents
Page
Index I
Abbreviations III
List of figures V
List of tables VII
List of annexes VIII
1 Introduction 1
1.1 The nitrate problem 2
1.2 Objectives 3
2 Theoretical bases 4
3 Material and methods 7
3.1 Standard analytical methods 7
3.2 Chemicals 8
3.3 Laboratory equipment 9
3.4 Experimental procedure 11
3.4.1 Introduction 11
3.4.2 Preliminary tests 17
3.4.3 Experiments 19
3.4.3.1 Atmospheric batch experiments 19
3.4.3.1.1 Group 1: Nitrate group 20
3.4.3.1.2 Group 2: MgCl2 group 21
3.4.3.1.3 Group 3: pH group 22
3.4.3.1.4 Group 4: Multi-step-MgCl2-pH group 22
3.4.3.2 CO2-free batch experiments 23
3.4.3.2.1 Boiled water group 24
3.4.3.2.2 Mixture group 25
3.4.3.2.3 Standard procedure group 26
3.4.3.2.4 Calcium measurement group 26
3.4.3.3 Scaling-up. 28
3.4.3.4 Experimental tests 29
4 Results and Discussion 32
4.1 Preliminary test 32
4.2 Basic Experimental Data 35
4.3 Experiments 37

4. II
4.3.1 Batch 1: Atmospheric batch experiments 37
4.3.1.1 Nitrate group. 37
4.3.1.2 MgCl2 group 41
4.3.1.3 pH group 44
4.3.1.4 Multi-step, MgCl2, pH group 46
4.3.2 Batch 2: CO2-free atmospheric batch experiments 51
4.3.2.1 Carbonates polluted experiments 52
4.3.2.2 Carbonate-free experiments 54
4.3.2.2.1 Calcium measurement group 56
4.3.2.3 Scaling-up 59
5 Model explanation 63
5.1 Static model 64
5.2 Constant decreasing model 65
5.3 Dynamic decreasing model 66
5.4 Models comparison 67
5.5 Crystal formation model 70
5.5.1 Calcium solubility and nitrate reduction 72
6 Industrial scale 76
Summary and advises 80
7 References 82
8 Annexes 84

5. III
Abreviations
A Al2O3
Al3+
aluminium ion
Al2O3 aluminium oxide
C3 3 CaO
Ca2+
calcium ion
CaCO3 calcium carbonate
Ca(NO)3 calcium nitrate
CaO calcium oxide
Ca(OH)2 calcium hydroxide
CaSO4 calcium sulphate
CaCl2 calcium chloride
Cl-
chloride ion
CO2 carbon dioxide
CO3
2-
carbonate ion
°dH German hardness degrees
exp. experiment
FCO2 CO2 transfer rate across the solution interface
Fe2O3 iron oxide (III)
HCl hydrochloric acid
HCO3
-
bicarbonate ion
H2CO3 carbonic acid
K+
potassium ion
KH Henry’s law constant for CO2
Mg2+
magnesium ion
MgCl2 magnesium chloride
MgO magnesium oxide
min minute
M.M.A. Ministerio de Medio Ambiente
N2O nitrogen oxide (I)
Na+
sodium ion
NaNO3 sodium nitrate
Na2O sodium oxide
NaOH sodium hydroxide
NO2
-
nitrite
NO3
-
nitrate
NOx nitrogen oxides
OH-
hydroxide ion
pCO2 partial pressure of CO2
Pa Pascal
pp precipitate
rpm rounds per minute
SiO2 silicon oxide
SO3 sulphur oxide (VI)

6. IV
SO4
2-
sulphate ion
unctrl uncontrolled
Vw
CO2 piston velocity of CO2 in the water boundary layer
WHO world Health Organisation
λ wave length (nm)
µ micro

7. V
List of figures
Page
Figure 1-1 Location of wells in Spain which nitrate concentration overcomes
50 mg/L (M.M.A., 1998)
1
Figure 2-1 Structure of a-monochloride (Auer, 1992) 5
Figure 2-2 Theoretical calcium solubility according to the pH (Schröter et al.
1986) 6
Figure 3.4.1-1. General experimental procedure 13
Figure 3.4.2-1 Equilibrium system carbonic acid-carbonate (Schröter et al. 1986) 18
Figure 3.4.3.1-1 Water pre-treatment in atmospheric batch of experiments 20
Figure 3.4.3.2.1-1 CO2-free atmosphere water pre-treatment 25
Figure 3.4.3.2.4-1 Procedure in calcium measurement group 27
Figure 3.4.3.4-1 Water pre-treatment in test 5 to 10 30
Figure 4.1-1 Air filter interference 32
Figure 4.1-2 A
A and B
pH decrease in time in two solutions: without/with aluminium
source 34
Figure 4.3.1.1-1 Reduction of the nitrate concentration at different initial concentra-
tions in group 1 37
Figure 4.3.1.1-2 Dependence of the initial nitrate concentration with the relative
nitrate reduction 38
Figure 4.3.1.1-3 Different tendencies of the relative nitrate reduction according to
the theoretical reactants ratios 39
Figure 4.3.1.2-1 Effect of the MgCl2 addition to A water on the nitrate reduction 41
Figure 4.3.1.2-2 Effect of the MgCl2 addition to A water in the relative nitrate reduc-
tion 42
Figure 4.3.1.3-1 Effect of pH in the nitrate reduction 44
Figure 4.3.1.3-2 Effect of pH in the relative nitrate reduction 44
Figure 4.3.1.4-1 Nitrate reduction in multi-step, MgCl2, pH group 46