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Graphic element Research > Growth > Research projects > Cross-disciplinary projects > Bio-cleaning aids paper-mill water conservation
Graphic element Bio-cleaning aids paper-mill water conservation
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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 Papiertechnische 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.

Innovative anaerobic kidney approach

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.

Alternative aerobic processing approach

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.

   Offering strategic advantages

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 stability.

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 5%.

See also
Growth programme shows new ways to sustainable development
Innovative anaerobic kidney approach
Alternative aerobic processing approach
Offering strategic advantages

Key data

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.


PAPER KIDNEY Advanced water treatment technologies for kidney operating of zero effluent water systems for paper and board production (BRPR988002)

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