Paper and board production are among the most
water-intensive of industrial processes, consuming an average of 20 m3/tonne.
Waste reduction methods and closed loop recirculation have already cut
consumption in Europe by more than 90%, but are frequently accompanied
by losses in quality and productivity. In the European Commission-funded
PAPER KIDNEY project, a team co-ordinated by German research institute
Stiftung (PTS) explored two innovative purification processes, with
the aim of achieving efficient effluent-free manufacture.
Closed-loop water circuits in a papermaking plant
can be compared to the flow of blood in the human body, which requires
regular cleansing by the kidneys to prevent the build up of toxins and
contraries. In a paper mill, the recycling of recovered paper leads to
an accumulation of contaminants arising from paper additives and foreign
matter such as food particles entering the water flow. These can give
rise to severe deterioration in end-product quality, as well as to productivity
problems caused by slime formation, odour and machine failure. Consequently,
manufacturers are often obliged to reopen their closed systems.
In the three-year BRITE-EURAM
PAPER KIDNEY project, a consortium comprising research institutes, water
treatment companies and paper mills representing five countries co-operated
to investigate thermophilic (elevated temperature) anaerobic and aerobic
biotechnological treatments, polishing steps and membrane technology with
the potential to permit trouble-free recycling.
The ultimate objective of this Commission-funded initiative
is to close water circuits in paper and board production as far as possible.
However, as well as causing contamination problems because of 'contraries',
closing the circuits leads to significant increases in process water temperature.
To avoid the energy consumption required for pre-cooling and post-heating,
the aim was to develop advanced process-integrated treatment systems that
would allow reliable purification at higher-than-usual temperatures.
In the first approach,
thermophilic anaerobic 'kidney' technology was combined with an
aeration step and membrane ultra-filtration. The anaerobic process
relies on the action of naturally occurring bacteria that feed upon
the pollutants in an oxygen-free environment. Preliminary pilot
trials carried out by PTS in collaboration with Dutch environmental
protection specialist Paques
demonstrated for the first time that a thermophilic version of this
treatment could provide effective purification over several months.
Excellent degradation rates were achieved at
temperatures around 55°C. After parameter optimisation, COD
(chemical oxygen demand - a measure of pollution) could be reduced
by 50 to 80%, and sulphate levels by 30 to 50%. This was despite
the fact that the volumetric and sludge loadings were much higher
than those typically encountered in the routine mill environment.
PTS also showed the advantage of a subsequent
aeration step as a means of removing calcium - concentrations of
which could be cut by more than 50%.
Anaerobic treatment not only gave excellent
purification results, but also proved to have a positive effect
on the downstream ultra-filtration unit by increasing the retention
capability of the membranes used.
These trials form the basis for pilot and full-scale
testing now underway at the VPK
Oudegem Papier paper mill in Belgium. Meanwhile, the exploration
of further process variations continues, with the aim of arriving
at an overall concept for closed-loop plant operation.
The second approach
- thermophilic aerobic processing of the effluent from anaerobic
degradation - was tested on a laboratory-scale by Centro
de Estudios e Investigaciones Técnicas de Guipúzcoa
(CEIT), Spain, over a six-month period.
COD reduction rates were found to be lower than
those for mesophilic (25° to 35°C) treatment under comparable
conditions. Filtration of the effluent produced water with good
characteristics for reuse - but at present, the approach was deemed
to be economically unfeasible for high flow rates.
First pilot-scale trials of a process comprising
thermophilic aerobic treatment, followed by sedimentation and biomass
separation by ultra-filtration, will nevertheless be conducted later
in the year at the SAICA
mill in Spain.
PAPER KIDNEY is due
to be completed in November 2001. Its results to date have been
extremely encouraging, particularly via the first approach. The
performance of the innovative thermophilic anaerobic system, together
with a downstream aeration step, proved to be significantly better
than could be achieved with the mesophilic anaerobic reactors previously
considered to be state of the art in the paper industry. Moreover,
a long-term trial lasting more than one year has validated its operational
Even if this system proves not be cheaper to
use in the long term, it offers strategic advantages. For example,
many mills are limited in their absolute effluent load by discharge
legislation - which can put a brake on production. The kidney approach
could make it possible to increase production while simultaneously
keeping effluent discharge at former levels, or even reducing them.
This method also has important benefits beyond
that of facilitating optimal water reuse. Bacterial decontamination
converts the carbon from any organic compounds present into methane,
which can be burned as a cost-saving fuel for the plant. The ability
to function at a constant higher temperature also shortens paper
and board drying times, potentially increasing productivity by around
Improving production sustainability is an
important element of the Innovative products,
processes and organisation key action. PAPER KIDNEY is determining
the feasibility of minimising paper mills' water consumption without
compromising product quality.
KIDNEY Advanced water treatment technologies for kidney operating
of zero effluent water systems for paper and board production