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Contenu archivé le 2022-12-23

Towards zero effluent in paper making

Objectif

A. BACKGROUND

Water is an essential resource of the paper manufacturing process. To make each tonne of paper, a typical paper machine uses 200 tonnes of water, most of which is not discharged but is recycled within the paper mill. In recent years the paper industry has substantially reduced the quantity of water discharged from its operations. The average discharge from Western European paper mills has been reduced from approximately 100 cubic metres of water per tonne of paper produced in the 1970s, to less than 20 cubic metres per tonne at present.

Some mills have even been able to close up their water systems completely, so that they discharge no liquid effluent. Total closure of the mill water system means that all process waters are treated and returned to the mill process. Such a mill is said to operate a Zero Liquid Effluent (ZLE) system. As well as having zero impact on receiving waters, a ZLE mill makes minimal demands on increasingly scarce water resources. A further benefit accruing to a ZLE mill is that it minimises its vulnerability to contamination of its water supplies.

Increasingly strong pressure to adopt ZLE technology is being felt by the European paper industry, because of the density of population and the strength of public concern about the environment. This concern is reflected in legislation at both the national and the European level.

The paper industry is extraordinarily diverse. As a consequence, technologies that work well and are cost-effective in one part of the industry may be ineffectual or financially disastrous if forced on other parts. If the doctrine of BATNEEC (Best Available Technology Not Entailing Excessive Costs) were to be applied in an uninformed manner, economic prosperity would suffer.

This diversity also means that the best technology for achieving ZLE at any given mill is determined to a considerable extent by the mill's technology, raw materials, and products. For example, an Italian fine paper mill may well have more in common with fine paper mills in Scotland or Germany than with neighbouring mills making packaging papers or board.

For these reasons, it is proposed to address, at the European level, the important issue of ZLE technologies by forming a COST Action under the name "Towards Zero Liquid Effluent in Papermaking". The COST Action will comprise a series of pre-competitive activities, with particular emphasis on sharing knowledge, scrutinising ideas, and forming networks.

The COST Action will be complementary to a number of other specific activities, funded variously by industry and by national and European funding agencies. While these specific activities will create and apply new science and technology, the COST Action will provide a valuable additional mechanism for forming consortia, for coordinating research, and for disseminating ideas and outcomes.

A caveat: The aim of ZLE papermaking, stated simply, is to eliminate discharges of liquid water from paper mills. Such a goal is not necessarily optimal for the environment. For example, a given paper mill might perhaps achieve ZLE only by using large amounts of capital equipment and electrical energy. The overall impact of the paper mill plus the power station on the environment might be greater than if the mill discharged some effluent. e.g. to a municipal treatment station. The term "ZLE papermaking" should therefore be taken to mean "papermaking operations in which discharges of liquid aqueous effluents are reduced to a level at which the overall environmental impact is minimised".

B. OBJECTIVES AND BENEFITS

The main objective of the Action is to provide industry with means to reduce substantially the cost of water conservation in papermaking. A principal method of achieving the objective will be to stimulate discussion between experts from member countries. A further objective of the COST Action will be to encourage universities, research institutes, and other research providers to apply their resources to the identified needs. Among the mechanisms to be used are the promotion of consortia of interested industrial sponsors for pre-competitive research. The expected benefits and outcomes include:

- Exchange of knowledge about successful and unsuccessful approaches to ZLE.

- Critical reviews of the underlying science, leading to further research.

- Formation of consortia to carry out research and development in specific areas.

- Transfer of relevant knowledge from other sectors of industry.

- Dissemination of information about the management of ZLE paper mills.

C. SCIENTIFIC PROGRAMME

C.1. Scientific approaches Zero Liquid Effluent technologies currently include:

- Conventional filtration.

- Extreme filtration, e.g. by membranes.

- Flotation.

- Biological treatment.

- Precipitation.

- Freeze crystallisation.

- Evaporation.

Before deciding on the mix of these and other technologies that are best suited to the needs of a given paper mill, a thorough understanding of the processes occurring within the mill systems must be developed. In particular, consideration must be given to:

- identifying the streams to be treated;

- characterising the contaminants in each stream of the system;

- assessing the mass load arising per tonne of production;

- identifying and evaluating other factors that could affect the ZLE systems.

The water chemistry of the mill must also be fully understood. This understanding will permit the identification of the problems which are most likely to occur in the mill as water discharge is reduced. Laboratory tests and pilot trials will be able to provide solutions to many of these potential problems.

New and improved process water treatment techniques are continually being developed, for a variety of industries. It is important to understand the principles or mechanisms of each technique, with particular reference to process waters of the paper industry, so that the most cost-effective set of ZLE processes can be identified for a specific paper mill.

C.2. Actual research techniques

The proposed COST Actions consist of two interrelated approaches:

Fundamental research

Fundamental research will focus on the performance of unit operations involved in ZLE processes. A wide variety of research needs are currently known to exist, and it will be an objective of the COST Action to prioritise these. They include:

- developing the science of colloid chemistry to deal with complex colloids such as paper machine process waters;

- developing better means for dynamic modelling of the water circulation in various classes of paper mills;

- adapting existing chemical and physical sensors, and developing new sensing techniques, for use in commercial papermaking operations;

- simulating ZLE unit operations on the laboratory scale, and modelling them to highlight gaps in the sciences pertaining to them;

- applying modern control science to ZLE processes;

- providing reliable data for use in developing improved commercial ZLE processes.

Applied research, demonstration, and management

In aiming for the goal of ZLE operation the European paper industry must remain financially competitive with its global competitors, i.e. it must maintain or improve product quality, and it must restrain costs. The industry caters for a wide variety of human needs, and it relies on renewable natural resources and on recycled paper. For these reasons, many aspects of the paper industry rely heavily, and will continue to rely, on factors that are difficult, if not impossible, to quantify.

Applied research and demonstration projects are therefore essential to adapting science and technology to the needs of each class of paper mill. The proposed COST Action will provide a forum in which prospective partners in applied research and demonstration projects can meet and agree on mutually satisfactory programmes.

Management plays a key role in attaining ZLE. The COST Action will include seminars, accessible also to non-technical managers, on the managerial aspects of running a ZLE paper mill successfully.

C.3. Types of activities

It is envisaged that the main activities under the proposed COST Action will be:

- organising workshops, seminars and conferences etc.;

- exchange of information including reports, publications, and modelling software;

- exchange of experts, engineers, scientists, and post-graduate students for training;

- collaborating projects between universities, institutes, and paper companies.

D. ORGANISATION AND TIMETABLE

The action will be led by a Management Committee responsible for overall planning, and for ensuring that each individual activity is properly executed and documented. Under the supervision of the Management Committee, the COST Activity is planned to be carried out by working groups:

Working group(s) F, having charge of fundamental research; and

Working group(s) A, having charge of applied research, demonstrations, and management projects.

The COST activity will be carried out in collaboration with existing research programmes within the area. Participants will include R&D centres in pulp and paper companies, research institutes, university departments, and suppliers to the paper industry of chemicals and of equipment for process water treatment. Experts from other sectors will also be encouraged to join in the Action, to stimulate cross-sectoral transfer of technologies.

Working group division

The Action is divided into fundamental researches and application studies. Correspondingly, the proposed division is:

Group(s) F: Fundamental studies, e.g. on chemical or physical models of unit operations in ZLE systems as well as dynamic models for process control.

Group(s) A: Application of ZLE systems to paper mills to identify potential problems and optimise combinations of ZLE systems.

It is anticipated that the Action will have two to four parallel working groups. Some working groups may have a shorter mandate, and new working groups may be formed during the course of the Action.

Action structure

The proposed duration of the Action is 4 years. Each working group will meet at least twice each year. Working group meetings will be organised in such a way as to support cross-fertilisation within the Action.

E. ECONOMIC DIMENSION

The following COST countries have indicated their interest in participating in the Action:

Austria Norway
Finland Portugal
France Romania
Germany Slovenia
Hungary Spain
Italy Sweden
Netherlands United Kingdom

The current rate of expenditure on activities covered by the proposed Action in the countries listed above is estimated to be approximately ECU 30 million at the 1997 price level.

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