vol 77 n° 5 2011 - Office International de l'Eau

STUDII SI CERCETARI
socio-political reception of sewage sludge recycling
Phosphorus is recovered chemically
from ash remaining after
mono-incineration of sludge. This
yields plant nutrients after removal
of heavy metals.[11 and 12] The
question remains, however, as to
how economic this operation is.
Due to the increasing phosphorus
shortages, this will not be a question
in 20 years’ time, and it
would do no harm to prepare in
advance.
The process certainly has the
advantage that the resulting phosphorus
fertiliser has neither a chemical
nor a psychological connection
with sludge, and all barriers
to agricultural use are removed.
Could this be a potential solution?
From a purely engineering standpoint,
it is a safe and final means
of using sludge, but its costs must
be carefully assessed.
All of these factors have combined
to greatly increase the cost
of wastewater treatment. Sludge
management costs have by now
risen to the extent that, depending
mainly on the size of the works,
they account for nearly half the
total costs of wastewater treatment.
This statement is confirmed in the
literature: “Sludge amounts to only
a few percent by volume of processed
sewage or wastewater, but
its handling accounts to up to 50%
of total operating costs.” [13].
Climate change is a new factor
which could radically change the
socio-political reception of sewage
sludge use. Recycling of treated
wastewater on agricultural land
was widespread in Hungary in
the 1970s and 80s, but for the reasons
we have discussed it practically
came to an end by the turn
of the millennium. Climate change
could give new momentum to this
form of recycling.[14]
Using treated wastewater for
irrigation dispenses with need to
remove nutrients, which are used
directly in the soil before the water
reaches the wider environment,
and greatly reduces the quantity
of sewage sludge. [15]
An interesting example is irrigation
in Murcia in Spain, for
which wastewater is transported
140 km. Irrigation for energy crops
can reduce wastewater treatment
costs, partly through revenue from
the crops. It also contributes to
CO2 emission reductions. The procedure
could usefully be subjected
to lifecycle analysis (LCA).[12]
4.
social and
political changes
Figure 2 shows the political environmental
factors affecting use
of sewage sludge and how these
factors interact.
The top row of the figure lists
the spheres of activity where the
factors take effect. Factors are grouped
into those working in favour
of recycling and those working
against it. The diagram largely
draws on experiences in Hungary,
although it also incorporates wider
European information in the area.
These factors are constantly varying
in space and time. One side
occasionally gains strength at the
expense of the other, and in a way
deforms the system. The conditions
for finding the most appropriate
solutions are when all of the factors
are brought into balance.
This balance has not been achieved
in the case of the new Budapest
Central Wastewater Treatment
Plant. Central Europe’s largest
wastewater treatment facility (350
000 m3/d) was opened in 2010,
but because of the many arguments
and protests, there is still no a
final and satisfying solution to dealing
with wastewater sludge in
2011.
One of the most striking phenomena
arising from the political
transition in Hungary is the disintegration
of water utilities. The
33 town, county and regional utilities
were split up into 400 very
small entities, with an adverse effect
on service quality. At the same
time, foreign multinational companies
have acquired various holdings
in utilities serving Budapest
and larger towns. These businesses
have brought a new market-oriented
outlook to the sector.
Concentration has now begun,
and large utilities have in many
places taken over smaller ones.
There is an ongoing argument as
to how far the water utility sector
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