Journal of Water Resource and Protection, 2012, 4, 460-463 Published Online July 2012 (
Super critical Water Technology Applied to the
Purification of Waters Contaminated by Toxic
Micro-Polluting Organic Compounds
Gabriele Di Giacomo, Luca Taglieri
Department of Chemistry, Chemical Engineering and Materials, University of L’Aquila, L’Aquila, Italy
Received April 12, 2012; revised May 15, 2012; accepted June 3, 2012
Purification of water contaminated by toxic organic compounds at low and very low concentration is a quite in teresting
challenge from both the technical and the economical point of view. In fact, the direct destruction of organic com-
pounds dissolved in very diluted aqueous solution is very costly and hardly achievable. To overcome this problems it
was studied and developed a new water purification process which is made of three step s: 1) removal of the diluted and
toxic polluting compounds by adsorption on activated carbon beds operating at ambient P ant T; 2) regeneration of the
exhausted carbon bed with supercritical water in order to obtain a mixture of water and polluting compounds signifi-
cantly more concentrated than the contaminated liquid water; 3) destruction of the toxic compounds in a continuous
Supercritical Water Oxidation Reactor. Step 1) was studied at laboratory scale in order to obtain all the required infor-
mation for modeling the adsorption operation; step 2) was modeled by using literature experimental data and, step 3)
was validated at pilot plant scale. In all the above mentioned steps, phenol was used as representative o f polluting com-
Keywords: Supercritical Water Oxidation; Water Purification Pr ocess; S ol i d-Liquid Adsorpt i o n; Gas- Sol i d
1. Introduction
Millions of tons of organic compounds are manufactured
each year. Most of these compounds are toxic, poorly
biodegradable, and persistent, sometimes give biological
magnification. An important class among these chemi-
cals is aromatic chlorinated hydrocarbons such as chlo-
robenzene, chloronitrobenzene, poly-chlorinated biphen-
yls (PCB), polycyclic aromatic hydrocarbons (PAH) and
dioxins. These chemicals contaminate very large amount
of wastewater (often originated from chemical process
industry both using and producing organic compounds)
and drinking water (when spills or soil pollutants reach
the groundwater lev el). A process co mmonly us ed for the
purification of waste waters contaminated by low con-
centrations of organic compounds is the adsorption on
activated carbon beds [1,2]. Two main problems arise
from this process: the regeneration of activated carbon
and the ultimate disposal of polluting organic compounds.
It has been demonstrated [3,4] that the Supercritical Wa-
ter (SCW) can be efficiently used for regenerating the
spent activated carbon bed; coherently with the fact that
SCW behaves as an organic liquid solvent. In addition,
many researchers have shown the effectiveness and the
wide range of applicability o f Supercritical Water Oxida-
tion (SCWO) in destroying toxic organic compounds
[5-9]. The purpose of this paper is to develop and to de-
scribe a new process (obtained by properly combining an
adsorption section with a SCWO section) characterized
by high efficiency in both water purification and destruc-
tion of polluting materials without producing any haz-
ardous by-product.
2. Materials and Methods
Activated carbon and phenol, as representative polluting
compound, were purchased from SICAV (Chieti, Italy)
and Aldrich, respectively. All the thermodynamic and
kinetic details related to the adsorption section were
studied at laboratory scale and reported in previous pa-
pers [1,2], while all the details related to the regeneration
of the spent activated carbon bed with SCW were re-
ported by [3] and [4].
The SCWO of the gaseous stream containing the pol-
lutants removed from the activated carbon bed was vali-
dated by using a pilot plant which can operate at pressure
up to 80 MPa and at temperature up to 1000 K. The con-
tinuous SCWO plant was made by a 0.9 m, 9/16” OD,
opyright © 2012 SciRes. JWARP
3/16” ID AISI 316 tube. Pre-heaters and SCWO reactor
are equipped with 3 PID controllers in order to maintain
the reaction temperature at a fixed value. The gaseous
stream obtained by cooling to room temperature the su-
percritical solution coming out from the SCWO reactor is
measured with an accuracy of ±0.1% by a mass flow
meter which also acts as totalizer (MICRO MOTION
3. Results and Discussion
By using the results on both equilibrium and kinetics ad-
sorption of compounds polluting liquid aqueous solutions
[1,2], alo ng with the results of [3] and [4], on th e regene-
ration of activated carbon with SCW, it was developed a
new process which enables one to remove almost com-
pletely the polluting compounds from the liquid water
which, in turn, are completely destroyed in the SCWO
section of the process shown in Figure 1.
For this process, the material balance along with the
values of P and T of each stream are reported in Table 1.
As can be seen the SCW required to regenerate the
spent activated carbon bed is about 20% of the treated
contaminated water. As a consequence the quantity of th e
water processed in the SCWO section is 5 times lower,
while the concentration of the polluting compound is 5
times higher. Since the SCWO section is characterized
Figure 1. Flow sheet of the proposed process.
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Table 1. Material balance of the process shown on Figure 1, based on 100 m3/h of micro-polluted water.
Stream n. Description Temperature (˚C) Pressure (bar)
Mass flow rate
1 Air 25 1 522
2 Demineralized water 25 1 171,422
3 Contaminated water 25 1 100,000
4 Air - 350 522
5 Air 440 350 522
6 Contaminated water 25 1.75 100,000
7 Contaminated water 25 1.75 100,000
8 SCW 25 1 19,828
9 Purified water 25 1 80,070
10 SCW 25 350 19,828
11 SCW 78 350 19,828
12 SCW 450 350 19,828
13 SCW and desorbed contaminants 450 350 19,854
14 Gaseous mixtures from SCWO reactor 450 350 20,374
15 Gaseous mixtures from SCWO reactor 470 350 20,374
16 Gaseous mixtures from SCWO reactor 374 350 20,374
17 Water and gas 300 350 20,374
18 Water and gas 300 1.2 20,374
19 Steam 120 1.2 171,422
20 Water and gas 40 1.2 20,374
21 Recovered steam 120 1.2 1807
22 Gas 40 1.2 532
23 Purified water 40 1.2 19,843
24 Steam 120 1.2 169,615
25 Condensed water 99 1.2 1807
26 SCW 179 350 19,828
27 Purified water 25 1 80,070
28 Flue gas 800 2
29 Flue gas 460 2 7118
30 Flue gas 426 2 7118
31 Purified water 40 1.2 99,913
by high investment and operating costs in comparison
with the adsorption section, the proposed process allows
one to purify the water and to destroy the toxic comput-
ing compounds in an optimal way from both the techni-
cal and economical point of view.
In Table 2 are reported the list of symbols used in the
process flow sheet along with the corresponding signifi-
4. Conclusion
It has been found that by properly combining an adsorp-
tion section with SCWO section it is possible to effi-
ciently purify polluted and micro-polluted water and to
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Table 2. Description of the symbols used in Figure 1.
Symbol Description
W01 Overheater
W02 Preheater
W03 Overheater
W04 Condenser
W05 Vaporizer
W06 Overheater
C01 Compressor
B01 Feed tank
B02 Gas-liquid separetor
B03 Tank
P01/06 Pumps
R01 SCWO reactor
K1 Fixed bed adsorber
K2 Fixed bed adsorber
V01/27 Valves
VR01/03 Ropture disk
M01/02 Mixer
efficiently destroy the toxic polluting organic compounds
in an optimal way. In fact, the process developed in this
study allows one to take advantage of the best characteri-
stics of the combined techn ologies. In addition, since the
regeneration of the spent activated carbon bed in done by
using SCW, it is possible to avoid the production of any
kind of polluting stream and the consumption of any kind
of chemicals.
5. Acknowledgements
This work has been financially supported by the Italian
Ministry of the Research, RIA Program.
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