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Oxidation Ditches in Wastewater Treatment
ttar:,r Res. Vol. 17. No. $. pp. 955-956. 19•3 Pergamon Press Ltd. Printed in Great Britain
BOOK REVIEWS Oxidation Ditches in Wastewater Treatment, by D. BARNT,S, C. F. FORSTERand D. W. M. JOHNSTONE. Pitman Books. London, 1983. pp. 278, £31.50 The importance of the oxidation ditch process as the simplest and perhaps the most dependable method of treating wastewater with activated sludge is shown by its adoption in countries with different climates and its application to numerous types of wastewater. It is essentially a process that began life in the field, rather than in the laboratory, and there it has continued to develop largely in order to meet more and more exacting needs. Since such development has been the result of trial and error, rather than prediction based on theoretical considerations, practical experience has been the spur to progress. But in spite of the very considerable amount of operating experience upon which progress has been based, text books coordinating practical operational experience with design data are almost non-existent. One important reason for this situation may have been that oxidation ditches were originally designed for small communities where facilities for systematic scientific observation and recording were less important than satisfactory performance. However, the practical demonstration of the success of the process in the 1950s soon ensured its adoption, especially on the Continent, and this has continued with ever widening uses. In this book the editors have succeeded in bringing together a group of experts with experience in design and operation in oxidation ditch technology; in addition excellent accounts are given of the transformations of organic and inorganic substances that are brought about by the microorganisms active in the sludge. If the true forerunner of the oxidation ditch was the Sheffield paddle system in 1920, as the book suggests, this reached its limit because of the low oxygenation capacity of the paddles and their inability to provide sufficient surface turbulence to make good the oxygen deficiency by oxygen absorption from the atmosphere. Pasveer, the inventor of the ditch system, clearly recognised the need to ensure an adequate input of oxygen, admitting that this was double the requirement of a conventional activated sludge system but pointing to the compensating advantages that were more costly to obtain by other means; in addition he stated that "'no one" . . . "'should be satisfied if the BOD removal is not 98% or more", compared with 85-90% for trickling filters and 92-94% for activated sludge (Low Cost Waste Treatment, Symposium, Nagpur, 27-29 October 1969. CPHERI, Nagpur, India 1972, p. 186). In the general aspects of treatment in oxidation ditches the importance of dissolved oxygen control in order to save energy is emphasized and the effectiveness of the process in obtaining substantial denitrification at no cost is described. In an excellent chapter on the various types of ditches and aerators that have been used, the realistic performance data given should help designers to curb over-optimistic expectations of suspended-solids free effluents. In this connection an outstanding chapter on the evaluation of the Carrousel system at works of the Thames Water Authority provides a detailed account of the performance of several plants and an interpretation of their results; particularly useful are the observations on settling tank performance when considered in relation to mass flux theory. The methods of providing oxygen, the performance and testing of aerators and the factors influencing aerator efficiency are described. The chapter on oxidation ditch construction 955
deals with practical problems arising from site conditions, w,atertightness and methods of lining ditches, types of aerators and their mounting, sludge settlement and sludge surplusing, and advice on the provision of a power supply. The original concept of Pasveer was to decant settled effluent from an aeration tank when aeration ceased. This principle has been adopted in New South Wales, Australia where about 200 plants operate with continuous inflow of sewage, with part of the plant taken out of use for quiescent settlement of the sludge and decanting of the settled effluent. This book fulfills the editors' objectives in providing a concise, comprehensive and well documented account of the theoretical aspects and essential practical factors in the design and construction of oxidation ditches for the treatment of sewage and industrial wastewater. The subjects of the various chapters are treated in a way that should allow the information to be generally applicable to conditions that exist in most parts of the world. S. H. JENKINS~
Aquatic Toxicology and Hazard Assessment, edited by J. G. PEARSON,R. B. FOSTERand W. E. BISHOP.American Society of Testing and Materials, American Technical Publishers, Herts., 1982, £32 This book contains the Proceedings of the Fifth Annual Symposium on Aquatic Toxicology, sponsored by the ASTM, held in Philadelphia in October 1980. The four main topics covered are Research Needs in Aquatic Toxicology and Hazard Assessment, New Concepts in Aquatic Toxicology, Biological Availability and Sediment Toxicity and Hazard Assessment and Water Quality Critera. These topics are dealt with in 27 papers, more than half of them devoted to subjects failing within the second topic. The book commences almost on a note of despair, with the statement that in spite of "incredible activity in the field" "there has been no significant growth and development in the science of aquatic toxicology in the last five years". The reason for this outlook is that the editors recognise an increase in what they term quantitative growth, i.e. greater knowledge of the effects of chemicals and their potential hazards but see no comparable growth in scientific breakthrough, new hypotheses, new scientific principles to help in making more rapid and accurate assessments of environmental hazards. In this respect the science of aquatic toxicology may be following the well trodden path of many other branches of science--plateaus of exploration in order to establish facts, followed by the rare surmounting of new peaks from which new ranges of facts can be established. But the book gives a reason for the absence of qualitative growth which is worth examining; it attributes quantitative growth to the demands of regulatory agencies which always ask the same questions and discourage innovative ways of looking into existing problems. Because regulatory agencies try to avoid having to make scientific judgements in the science of aquatic toxicology in which so few fundamental concepts exist, it is argued, they mechanise the process of obtaining toxicological data suitable for use for regulatory purposes. If this is put forward as one of several arguments in support of obtaining more fundamental knowledge on the physiology and biochemistry of toxicology it perhaps might be supported but only if it is recognised that the first duty of a regulatory agency concerned with water quality is to
BOOK REVIEWS Oxidation Ditches in Wastewater Treatment, by D. BARNT,S, C. F. FORSTERand D. W. M. JOHNSTONE. Pitman Books. London, 1983. pp. 278, £31.50 The importance of the oxidation ditch process as the simplest and perhaps the most dependable method of treating wastewater with activated sludge is shown by its adoption in countries with different climates and its application to numerous types of wastewater. It is essentially a process that began life in the field, rather than in the laboratory, and there it has continued to develop largely in order to meet more and more exacting needs. Since such development has been the result of trial and error, rather than prediction based on theoretical considerations, practical experience has been the spur to progress. But in spite of the very considerable amount of operating experience upon which progress has been based, text books coordinating practical operational experience with design data are almost non-existent. One important reason for this situation may have been that oxidation ditches were originally designed for small communities where facilities for systematic scientific observation and recording were less important than satisfactory performance. However, the practical demonstration of the success of the process in the 1950s soon ensured its adoption, especially on the Continent, and this has continued with ever widening uses. In this book the editors have succeeded in bringing together a group of experts with experience in design and operation in oxidation ditch technology; in addition excellent accounts are given of the transformations of organic and inorganic substances that are brought about by the microorganisms active in the sludge. If the true forerunner of the oxidation ditch was the Sheffield paddle system in 1920, as the book suggests, this reached its limit because of the low oxygenation capacity of the paddles and their inability to provide sufficient surface turbulence to make good the oxygen deficiency by oxygen absorption from the atmosphere. Pasveer, the inventor of the ditch system, clearly recognised the need to ensure an adequate input of oxygen, admitting that this was double the requirement of a conventional activated sludge system but pointing to the compensating advantages that were more costly to obtain by other means; in addition he stated that "'no one" . . . "'should be satisfied if the BOD removal is not 98% or more", compared with 85-90% for trickling filters and 92-94% for activated sludge (Low Cost Waste Treatment, Symposium, Nagpur, 27-29 October 1969. CPHERI, Nagpur, India 1972, p. 186). In the general aspects of treatment in oxidation ditches the importance of dissolved oxygen control in order to save energy is emphasized and the effectiveness of the process in obtaining substantial denitrification at no cost is described. In an excellent chapter on the various types of ditches and aerators that have been used, the realistic performance data given should help designers to curb over-optimistic expectations of suspended-solids free effluents. In this connection an outstanding chapter on the evaluation of the Carrousel system at works of the Thames Water Authority provides a detailed account of the performance of several plants and an interpretation of their results; particularly useful are the observations on settling tank performance when considered in relation to mass flux theory. The methods of providing oxygen, the performance and testing of aerators and the factors influencing aerator efficiency are described. The chapter on oxidation ditch construction 955
deals with practical problems arising from site conditions, w,atertightness and methods of lining ditches, types of aerators and their mounting, sludge settlement and sludge surplusing, and advice on the provision of a power supply. The original concept of Pasveer was to decant settled effluent from an aeration tank when aeration ceased. This principle has been adopted in New South Wales, Australia where about 200 plants operate with continuous inflow of sewage, with part of the plant taken out of use for quiescent settlement of the sludge and decanting of the settled effluent. This book fulfills the editors' objectives in providing a concise, comprehensive and well documented account of the theoretical aspects and essential practical factors in the design and construction of oxidation ditches for the treatment of sewage and industrial wastewater. The subjects of the various chapters are treated in a way that should allow the information to be generally applicable to conditions that exist in most parts of the world. S. H. JENKINS~
Aquatic Toxicology and Hazard Assessment, edited by J. G. PEARSON,R. B. FOSTERand W. E. BISHOP.American Society of Testing and Materials, American Technical Publishers, Herts., 1982, £32 This book contains the Proceedings of the Fifth Annual Symposium on Aquatic Toxicology, sponsored by the ASTM, held in Philadelphia in October 1980. The four main topics covered are Research Needs in Aquatic Toxicology and Hazard Assessment, New Concepts in Aquatic Toxicology, Biological Availability and Sediment Toxicity and Hazard Assessment and Water Quality Critera. These topics are dealt with in 27 papers, more than half of them devoted to subjects failing within the second topic. The book commences almost on a note of despair, with the statement that in spite of "incredible activity in the field" "there has been no significant growth and development in the science of aquatic toxicology in the last five years". The reason for this outlook is that the editors recognise an increase in what they term quantitative growth, i.e. greater knowledge of the effects of chemicals and their potential hazards but see no comparable growth in scientific breakthrough, new hypotheses, new scientific principles to help in making more rapid and accurate assessments of environmental hazards. In this respect the science of aquatic toxicology may be following the well trodden path of many other branches of science--plateaus of exploration in order to establish facts, followed by the rare surmounting of new peaks from which new ranges of facts can be established. But the book gives a reason for the absence of qualitative growth which is worth examining; it attributes quantitative growth to the demands of regulatory agencies which always ask the same questions and discourage innovative ways of looking into existing problems. Because regulatory agencies try to avoid having to make scientific judgements in the science of aquatic toxicology in which so few fundamental concepts exist, it is argued, they mechanise the process of obtaining toxicological data suitable for use for regulatory purposes. If this is put forward as one of several arguments in support of obtaining more fundamental knowledge on the physiology and biochemistry of toxicology it perhaps might be supported but only if it is recognised that the first duty of a regulatory agency concerned with water quality is to