value dramatically. The result is that
supercritical water becomes a very good
solvent for nonpolar materials.
The oxidation process occurring in
water under supercritical conditions,
the so called SCWO process, leads to
rapid destruction of a wide variety of
organic species, normally considered to
be refractory or diffcult to break down
under conventional treatments, to more
simple molecules (such as CO2 and
H2O) in quite short reaction times.
For this reason, this technology has
already been used for the treatment
of a wide variety of wastes, including
sludge. In fact, SCWO can achieve an
organic matter removal >99 percent
operating at reaction times of less than
a minute. Main products include water,
CO2 and inorganic salts. Although the
SCWO’s gas emissions mainly and
inherently contain CO2, no highly
harmful emissions (NOx, SOx) do occur,
unlike what happens with other thermal
treatments such as incineration.
CONSTRUCTING A PROTOTYPE
In order to perform a demonstration,
one of the key objectives for LIFE Lo2x
was to design and construct a prototype
for the supercritical water co-oxidation
of urban sludge and other wastes.
The developed prototype, localised
in Paterna-Fuente del Jarro WWTP
(Valencia, Spain), is able to treat up to 1
tonne of dry matter per day.
The following results were achieved
during the experimental campaign of
the LIFE Lo2x project:
• > 99% elimination of organic matter.
The COD of SCWcO effuent is in
average lower than 200 mgO2/L,
reaching values even lower than 25
• 100 percent elimination of pesticides.
Imazalil is degraded through
SCWcO up to 350 mg/kg, four
orders of magnitude higher than the
concentration removed by anaerobic
• 100 percent elimination of
pathogens. Escherichia coli,
Clostridum perfringens and
Salmonella are completely
eliminated. SCWcO leads to
• >85 percent heavy metals are
recaptured for safe handling.
Heavy metals are mainly detected
in inorganic solid fraction of the
• Recovery of nutrients.
Mineralization of nitrogen and
phosphorus facilitates the nutrient
recovery in order to be used as
building blocks of fertilizers.
Nitrogen occurs in the liquid phase
(NH4~ 2 g/L) while phosphorus
is present in the inorganic solid
fraction of the SCWcO effuent
(P2O5~ 25 percent)
• No highly harmful gases are
produced. CO2 is the main gas
generated by SCWcO. Typical
undesired gaseous products from the
combustion processes as NOx and
SOx are not produced.
• 98 percent reduction of sewage
sludge leaving WWTP. Total solid
reduction higher than 90 percent.
The inorganic solid fraction
from SCWcO is a resource for
phosphorous industry whereas
Percentage of incinerated sludge in Spain by region (2014)