Water Recycling in Textile Wet Processing Edited By J Kenneth Skelly

Contents

Preface
‘The small old-fashioned book, for which you need only pay sixpence at a bookstall, works miracles to this day, turning bitter waters into sweetness …’ George Eliot, 1819–1880. The real world of water recycling is not quite so simple as this quotation could be construed to suggest! The complex subject of water recycling presents a global challenge to all industries which require large volumes of water. Environmental factors necessitate that effluent is treated either on-site or in municipal sewage works to remove contaminants to an acceptable level before discharge, for example, to a watercourse. The logical question then arises whether the treated effluent can be reused or what type of further treatment is necessary to raise the water quality to a level suitable for reuse, thereby removing or reducing the volume which is discharged.

The concept for this book developed from a paper entitled ‘Water recycling’ prepared for the year 2000 issue of the Society’s Review of Progress in Coloration (vol. 30, page 21). It became apparent that each example of water recycling developed in practice was specific to the conditions at a particular site. While many different techniques and combinations had been used to treat effluent, the selection of the preferred configuration of effluent treatments to produce treated water suitable for recycling for a given works was a difficult technical, economic and regulatory matter. However, over the last decade a considerable amount of practical experience and confidence in water recycling has been built up. One of the objectives of the book has been to present particular case studies of water recycling illustrating practical application of the techniques being discussed.

However, one recommendation mentioned by several authors in different chapters concerns the advisability of introducing a key project on cost saving and best practice before water recycling at an already established dyehouse is considered. This first essential, economic, step concerns implementing waste reduction measures for water and other utilities through introduction of best practice for all wet processes carried out at a given site. The total volume of effluent and the total effluent load can be significantly reduced by such measures, which can include reuse of water within a process. Indeed, the result may be more cost-effective in the short-term than ambitious recycling plans for the combined effluent which may have to be considered in the longer term.

In 1995, the Society published the book Colour in Dyehouse Effluent edited by Peter Cooper which described the state of the art of various treatments available to reduce or remove colour from dyehouse effluent, which had become an environmental issue. The present publication takes the subject further now that techniques for colour removal from effluent are well established. Furthermore, the imperative of economic factors has focussed attention at attempting to off-set the costs of colour removal by recycling.

The subject of water recycling in wet processing is covered in four parts:

Part I Reuse of process water in selected processes Chapters 1–3
Part II Recycling combined effluent Chapters 4–10
Part III Recycling of municipally treated wastewaters containing dyehouse effluent Chapters 11,12
Part IV The future for recycling Chapters 13–15

The objective has been to obtain contributions from authors and organisations for each subject who have national and international experience. Each chapter is an individual approach by an authority from a particular country and diversity of discussion has been encouraged to give interest to the subject. The comparison of views and yet the many common conclusions drawn in the chapters to different aspects of the subject is revealing. One comment made in several case studies concerns the quality of water produced being suitable for washing-off operations, while in practice this step had not been implemented. This suggests that the cost of storage and distribution of the treated effluent together with the need to implement monitoring and control measures to ensure consistency of the water quality are key factors in the practical introduction of recycling under current conditions.

Part I describes the reuse of process water from sizing, scouring and bleaching, and dyeing with authors from the USA, Germany and the UK. The value of modern membrane separation and process controllers in these processes is highlighted.

Attention is drawn to Part II, Chapter 4, ‘Options available and operational considerations’ by Peter Cooper. This chapter forms a link with the 1995 Society book on colour in dyehouse effluent and reviews options available for on-site recycling of combined effluent. Chapters 5–9 cover recycling systems using membrane, adsorption, chemical oxidation and electrochemical, biological oxidation and reduction, coagulation and flocculation techniques with introductory sections on the mechanisms for the removal of contaminants. The authors come from the USA and UK with a contribution from Australia and a range of case studies including examples from The Netherlands and Sri Lanka. Chapter 10 reviews developments in recycling in continental Europe and the author is based in Germany.

Part III is concerned with recycling of municipally treated wastewater. Chapter 11 describes Italian experience in recycling combined effluent from several works by municipal authorities in special advanced treatment facilities and recycling back to industry via aqueducts with authors from Politechnico di Milano. Chapter 12 consists of an introduction and reprints of two papers on relevant topics included with the help and cooperation of John Churchley of Severn Trent Water plc. The reprints review the operations of sewage treatment works in the English Midlands where various tertiary treatments have been used to remove colour before discharge to river, together with a description of a new advanced treatment plant to raise the quality of river water to drinking water standard.

Part IV includes three chapters under the heading ‘The future of recycling’ which covers challenges facing recycling. Chapter 13 discusses on-site biological-based treatments, which together with tertiary colour removal processes, produce treated effluent suitable for discharge to river and with possibilities for reuse. However, the economic barriers to recycling on an existing site with established infrastructure are considerable. The final two chapters discuss, in general terms, water quality requirements of treated effluent and the economics of recycling – subjects of key importance to all recycling systems in the future.

A glossary of abbreviations used in the text has been added for ease of reference. In conclusion, the managing editor would like to thank all the authors who have contributed to this publication. Through the availability of good email communications, close collaboration with authors all over the world has been established, which made preparation of the book a pleasant and good-humoured task.

Especial thanks are due to the internationally known chapter authors from the USA, Germany and Italy who share with me an interest in this subject and I regard as my colleagues and friends.

Finally personal thanks are due to all my friends in the UK who have supported the project and given advice and help. In this respect John Easton, Peter Cooper and Malcolm Lockerbie, together with Paul Dinsdale and Carmel McNamara of the SDC, must be specially thanked. In addition Barry Hazel and Dick Horrocks, who both read the complete script, made valuable suggestions to improve the text which was an important contribution to the final form of the book. Their interest and assistance is much appreciated.