Paradigms in Sewerage Engineering

Citation: This article was publislhed in Sharon Beder,'Technological Paradigms: The Case of Sewerage Engineering', Technology Studies, 4(2), 1997, pp. 167-188.

This is a final version submitted for publication. Minor editorial changes may have subsequently been made.

Abstract

Sewerage engineering practice operates within a paradigm in the sense that the engineering community reached a consensus earlier this century that a narrow range of treatment options would form the basis of its subsequent practice. This consensus prevents serious consideration of alternative technologies and constrains innovative research at a time when the paradigm is no longer adequate in a changing environment where sustainability is crucial. A technological revolution is required but is unlikely to emerge from within the sewerage engineering community unless that community recognises that their existing paradigm is inadequate to the needs of the community and the broader environment .

For many decades now engineers have chosen sewage treatment solutions from a small range of technologies that are consistent with the water-carriage of the sewage (in pipes) to a waterway for disposal. Conventional treatment methods are classified into stages. The preliminary stages involve grit removal and the screening of gross solids from the sewage. Primary treatment removes some suspended solids from the sewage by sedimentation in tanks. Secondary treatment utilises micro-organisms to break down organic matter, mainly with biological filters or activated sludge treatment. All of these processes had been invented and were in use by 1920.[1]

Alternative sewage treatment technologies which proved effective in the past have largely been dropped from the engineer's repertoire despite their public appeal. Chinese aquaculture was successfully practiced for centuries. Sewage irrigation and other forms of sewage farming[2] were successfully used in the nineteenth century and remnants of those early farms still operate today such as the Werribee sewage farm in Melbourne. For the most part though, these technologies have been abandoned as victims of the current sewerage engineering paradigm.

In recent times the sewerage engineering paradigm has been challenged as debates rage over which technologies are most appropriate. For example, in the United States municipal engineers are arguing that advanced primary treatment should be allowed to be substituted for secondary treatment (Sun, 1989). In Wellington, New Zealand a new city council was elected on the promise to install secondary treatment but were convinced by sewerage engineers that innovative treatments could be installed for less cost (Beder, 1989b; pp. 147-52). In Sydney, Australia the public demands for better sewage treatment have given rise to a whole range of new treatments. And in coastal towns throughout Australia communties are pushing for a return to sewage farming and an end to ocean outfalls. (Beder, 1989b; pp.140-3). We are seeing an emerging revolution in sewerage treatment technologies.

Technological paradigms (Wojick, 1979) define the range of technologies which an engineer draws upon in 'normal' practice. The sewage engineering paradigm is wider than just sewage treatment and includes the use of water-carriage for collection of sewage (Beder, 1993a; Beder, 1990). However for this paper is confined to sewage treatment.

The recognition that technological paradigms exist has important implications for other areas of technological development, particularly with respect to sustainable development. Sustainable development has succeeded in gaining widespread support amongst the world's decision makers and power brokers and was endorsed by the governments of 100 nations in the UN General Assembly in 1987 (Beder, 1993b). In 1992 at the United Nations Conference on Environment and Development the governments of the world endorsed Agenda 21, an action plan for achieving sustainable development. In its chapter 31 on the scientific and technological community Agenda 21 specifically recognises the need for a better understanding of the role of technology in achieving sustainable development.

This paper is intended to demonstrate some of the factors that constrain and impede attempts to redesign our technological systems (Freeman, 1974) to be sustainable in the long term. It is suggested that the concept of technological paradigms is a way of understanding why engineers are often resistant to the adoption of radically different technologies, even those that are potentially superior in terms of costs and technical accomplishment. The usefulness of the concept of a paradigm is demonstrated using the development of sewage treatment as a case study.

The paper shows how a paradigm is formed, the role it plays and the factors which constrain or encourage the emergence of a new paradigm. The concept of technological paradigms, the commitment of engineering communities to them, and a knowledge of why those communities promote some technologies and inhibit others will enable governments and managers to facilitate shifts towards new "clean" and energy efficient technologies. The sewerage engineering case study will also further the literature on technological paradigms through the illustration of a paradigm in action since few such case studies exist.

Literature Review: Theory of Paradigms

The term paradigm is borrowed from Thomas Kuhn (1970) who postulated in 1962 that science progresses through periods of "normal science," which operates within a scientific paradigm, interspersed with periods of "scientific revolutions". Kuhn said the scientific achievements on which 'normal science' are based serve to define the problems and methods for research and "to attract an enduring group of adherents". These scientific achievements, together with the "law, theory, application and instrumentation" that they incorporate, form the basis of a scientific paradigm. It is this paradigm which is studied in universities as preparation for students to join the scientific community.

The work of engineers exhibits many of the qualities of "normal" science in that research is generally of a gradual cumulative nature, making improvements on past achievements and that solutions are sought from within a restricted range of possible solutions. Similarly practice is based on applying the appropriate technological methods from an arsenal of "tried and true" methods.

Several writers have applied the concept of a paradigm to technological development. Edward Constant (1984) argued that the routine work of engineers and technologists, which he called 'normal' technology, involves the "extension, articulation or incremental development" of existing technologies. A technological paradigm or "tradition", Constant said, is subscribed to by engineers and technicians who share common educational and work experience backgrounds. The "tradition" relates to a field of practical endeavour rather than to any academic discipline. Rachel Laudan (1984) argued that the function of "traditions" is to allow technologists to focus on potentially solvable problems and to provide the methods with which to solve those problems.

Giovanni Dosi (1982) described a technological paradigm as "an "outlook", a set of procedures, a definition of the "relevant" problems and of the specific knowledge related to their solution" (p.148). Such a paradigm, Dosi said, embodies strong prescriptions on which technological directions to follow and ensures that engineers and the organisations for which they work are "blind" to certain technological possibilities.

Richard Nelson and Sidney Winter (1977) also observed that there is sometimes a technological paradigm or "regime" operating which relates to the technicians beliefs about what is feasible or at least worth attempting.

The sense of potential, of constraints, and of not yet exploited opportunities, implicit in a regime focuses the attention of engineers on certain directions in which progress is possible, and provides strong guidance as to the tactics likely to be fruitful for probing in that direction. In other words, a regime not only defines boundaries, but also trajectories to those boundaries. (p. 57)

In many cases, Nelson and Winter argued, those directions involve improvements to major components of a system. Similarly Laudan said that problems tackled within a "tradition" tend to be those of cumulative improvement.

The idea of a technological paradigm is particularly appropriate to the practice of engineering where the practitioner seeks to apply a selected technology in a specific location and situation. Sewerage engineering practice seems to take place within a paradigm in the sense that the engineering community reached a consensus earlier this century that a narrow range of treatment options would form the basis of their subsequent practice. This consensus inhibits serious consideration of alternatives like sewage farming and ensures that engineering decisions are reaffirmed when subject to review by 'independent experts'.

A Sewerage Engineering Paradigm

Kuhn argues that the acquisition of a paradigm "is a sign of maturity in the development of any given scientific field" (1970; p.11). Before such a paradigm is formed there is a continual competition between various views of nature that are all more or less "scientific" but represent incommensurable ways of seeing the world (1970, p.4). This is also true of the early developmental stage of sewerage treatment engineering. The competition between treatment technologies could not be resolved whilst there was no engineering consensus. Proponents of different technologies had differing objectives (to utilise the sewage, to minimise land usage or cost, to treat the sewage) and consequently differing measures of efficacy were used in 19th Century sewerage engineering.

During the second half of the nineteenth century sewage treatment methods developed rapidly with most of the research going on in Britain, Europe and the United States and the merits of these methods were vigorously debated. It was a time when articles on sewage treatment appeared not only in engineering journals but also in scientific journals and books on the topic were written by lawyers and medical men as well as by engineers. Sewage treatment was a subject that the general public had a strrong interest in and it was debated in the letters pages of newspapers (Beder, 1989a; chapter 3).

Most developments were based on empirical research and the theoretical understanding of how they worked came later. The impetus for this research came mainly from Britain where there was a perceived need to clean up the rivers and streams. Many local authorities were forced to experiment with different methods and variations on methods so as to conform with legal and government requirements. Several companies saw this as an opportunity to make a profit and various processes and materials were patented and marketed.

Some major parameters for the paradigm were worked out during these years. The triumph of water carriage over dry conservancy methods of sewage collection was a significant development (Beder, 1989a; chapter 2). The competing technologies of the late nineteenth century were therefore developed to deal with a diluted waste stream carried by gravity to a centralised location. Sewage farms and chemical precipitation methods were the early contenders.

The debate amongst the experts over the merits of sewage farming, was fierce. Burke, an English barrister, wrote in 1873 that

a well-known sanitary reformer once said to us that he knew only one topic besides polemics upon which men's party spirit got the better of their good sense, and even of their regard for truth and justice, and that was the treatment of sewage.(1873; p.ix)

This led to the most confusing discrepancies in the statistics, Burke observed, so that manure was valued at over [[sterling]]5 per ton by one writer and at less than the cost of carriage by the next. A high authority claimed that a sewage farm was unhealthy to neighbouring residents whilst the statistics showed the death-rate in the area had decreased markedly since the establishment of the farm (Burke, 1873, p.x). As for the chemical analysis of the effluent, Burke complained, "One would think that when we had reached the region of pure science a calm voice would speak from the laboratory in the unprejudiced tones of perfect accuracy" (p. xi) But no, each scientist found differing amounts of nitrogen and reached different conclusions from what they did find.

The inability to resolve these controversies over scientific points would later be typical of controversies over chemical precipitation, artificial filters, septic tanks and other treatment methods. It was symptomatic of an immature field of study which had not been fully colonised by a professional group with its own paradigm.

In the face of mounting disputes, a Royal Commission was appointed in 1898 to "inquire and report what methods of treating and disposing of sewage may properly be adopted." It sat for seventeen years and took evidence from many engineers, scientists, doctors and other experts. It also conducted various experiments and site visits to treatment works. The Commission influenced the development of sewage treatment engineering and marked the transition between two distinct phases of that development. One engineering writer, commented, "in a sense the Royal Commission marked the transition from folklore to a scientific approach to sewage treatment practices and requirements and heralded the opening of an era of rapidly developing and increasingly sophisticated technology" (Sidwick, April 1976; p. 199).

Although earlier sewage treatment methods were usually based in science and engineering rather than folklore, it is the perception of scientific maturity in the field that is significant here and this can be compared with Kuhn's description of the transition from a developing science to one that is governed by a paradigm. The incommensurable goals of sewerage experts were swept aside by the Royal Commission.

The Development of Stages and Standards - The Death of an Ideal

The origins of the modern concept of primary and secondary treatment arose from the Royal Commission. A number of the witnesses at the Commission hearings proposed two stage treatment for the sewage. The first stage would be to remove some of the sewage solids and the second, oxidation of the remaining organic matter. The Commissioners considered detritus tanks, plain sedimentation tanks, septic tanks and chemical precipitation as preliminary processes. The second stage of treatment consisted of biological filters, contact bed systems or land treatment and was the "real" treatment. The Commission did not consider these two stages as separable but rather as two stages, both necessary for the treatment of sewage.

The Commission's real achievement was in paving the way for some form of consensus amongst the engineering community. They did not do this by imposing their judgement of the competing technologies on the engineering community. What they did was to recommend standards of effluent that should be achieved by whatever process was chosen. These standards, commonly referred to as the 20:30 standard (Biological Oxygen Demand not more than 20mg/l and suspended solids not more than 30 mg/l), were not only accepted in Britain at the time but they are still used all over the world.[3]

The significance of these standards was that they paved the way for a philosophy that treatment should not be optimal but rather 'good enough'.Previously it had been thought possible that an ideal treatment solution could be found that achieved a high purity of effluent, left no awkward by-products and had no smell and this was what many researchers aspired to. The Royal Commission made the competition between processes on this basis irrelevant. What use was it to achieve a higher degree of purity than was necessary?

The usage of the term 'sewage purification' was gradually replaced partly because it was said to be misleading to "laymen" who supposed that once purified the sewage became pure "whereas the sanitary engineer may mean only that it is purer than it was before" (Metcalf and Eddy, 1915; p. 197). The skill of the engineer now lay, not in achieving the highest quality effluent but rather in achieving an adequate quality of effluent for as little money as possible and letting nature do as much of the work as possible (Metcalf and Eddy, 1915; p. 197).

Of the three main processes considered by the Royal Commission as a preliminary treatment, it was plain sedimentation that came to be the standard treatment used. Sedimentation tanks were simply tanks in which the sewage was left for a period of time during which some of the solids settled out. Plain sedimentation was seldom seriously considered before the Royal Commission. It was considered to be "a process midway between chemical precipitation and septic tank treatment, but having the advantages of neither" (Sidwick, 1976; p. 195).

Chemical treatment , although it was more efficient at removing suspended solids, fell into disfavour except in temporary or exceptional circumstances, for example when there was a high proportion of industrial waste in the sewage (Stanbridge, 1976, p.20). Likewise septic tanks were abandoned for centralised sewage treatment works although they continued to be used for individual and small groups of houses that were too isolated to be connected to a public sewerage system.

Plain sedimentation was simple and cheap as a single stage treatment. Although the Royal Commission had set standards that could be met using sedimentation in conjunction with a second stage of treatment, in many places, particularly at ocean outfalls, sedimentation was installed without a second stage treatment. Sedimentation became part of the paradigm because it was considered to be good enough by municipal engineers, not because it was technically superior or achieved a better effluent.

The Paradigm - Consensus and Narrowed Options

The narrowing of sewerage treatment research to ways of improving existing methods rather than innovative new treatments is characteristic of practice within a technological paradigm. Constant, Laudan, Nelson and Winter all describe 'normal' technology, as involving the "extension, articulation or incremental development" of existing technologies in certain directions.

Progress in sewerage treatment research since the Royal Commission has been largely of this type. Rather than radical innovations, improvements have been incremental. Screens have been mechanised, the grit removal process improved and mechanical scraping devices developed for removing the sludge from sedimentation tanks and for removing the scum from those tanks. A large part of the effort has concentrated on automating the process which is not only unpleasant for workers but also expensive because of the labour intensity (Sidwick, Oct 1976, pp. 515-6).

A comparison of engineering texts at the turn of the century and today shows that little new has been developed in the way of new treatment methods. In fact the options have considerably narrowed for primary treatment. Engineers today are sometimes quite defensive about the lack of original ideas that have emerged since 1915. An engineer writing for an American engineering journal.

it is indeed distressing to find "instant experts", many in the public arena, who believe the field is static because modern methods resemble those of past years. This belief demonstrates their ignorance, for the current methods of treatment are based on sound physical, chemical, and biological principles which do not change with time... The fact that the application of these basic principles has changed so little is a monumental tribute to our forebears in the field (Fuhrman, 1984, p. 312).

John Sidwick, a sewerage engineer, in an article on the history of sewage treatment wrote that he was surprised how much "the earlier impetus of development" was reduced;

improvements have largely been refinements of existing practices rather than the creation of new practices. It may, of course, be that there are no new techniques to be discovered, but this seems unlikely. A more probable explanation is that until recently effluent standards are capable of consistent achievement by conventional processes and that since research investment is always limited, those directing research preferred, quite rightly, to devote effort to improving processes of known worth rather than to investigating the unknown ( 1976; p.520).

David Wojick (1979; p.241) in his description of technological paradigms says that 'normal' technology involves the "artful application of well-understood and well-recognised decision-making procedures". In this way there is no ambiguity or doubt about what counts as a good solution within the engineering community. The skill of the modern sewerage engineer lies in the ability to choose, from within the paradigm, the cheapest treatment process for a given situation that will perform the minimum treatment necessary to conform with local regulations and standards.

Professional Control and Autonomy

The formation of a paradigm permitted the development of educational courses devoted to this field and united sanitary engineers against outsiders and other members of the engineering profession. But does the paradigm define the engineering community or does the engineering community form the paradigm? Henk Van den Belt and Arie Rip (1987) argue that the development of a technology along a trajectory requires a 'cultural matrix', that is, a subculture of technical practitioners. Whilst a cultural matrix may be necessary for a paradigm to exist, it may also be that a technological community cannot exist in any coherent form without some form of paradigm. Michael Callon (1980) has argued that social group formation is simultaneous with the definition of research problems and he links the struggle between social protagonists to define what is problematic and what is not with the formation of the groups which will take charge of those research problems which are defined in the struggle.

Whilst sewage disposal methods were a matter of debate amongst engineers last century, the general public were able to take part in the debate and be taken seriously by decision-makers. Doctors, lawyers and non-professionals felt competent to comment on the theory of treatment methods and criticise proposed schemes. The formation of a paradigm has enabled sewerage engineers to consolidate their position as the 'experts' and to restrict the role of outsiders to that of an 'uninformed public' which can acquiesce with a particular proposal or protest against it but which is in no position to question the range of treatment methods available. Other professionals are particularly likely to respect the boundaries of expertise set up by the paradigm.

And although various treatments for sewage were debated in the meetings and proceedings of engineering and scientific societies in the nineteenth century, until recently twentieth century engineering magazines dealt with the details of particular applications of an acceptable technology or improvements and refinements to existing technologies. Such discussions contain assumptions and jargon which make them uninteresting to the uninitiated and they are seldom read by those outside the field. (It is only now that the merits of conventional secondary treatment have come into question that more general debates are appearing in these journals.)

The sewerage engineering community perpetuates its paradigm through education and practice, which are largely determined by the engineering community. The acceptable treatment methods, classified into stages, have been taught for several decades to students training to be sewerage, sanitary or public health engineers and as a result it is taken for granted by most engineers that such methods are satisfactory and appropriate to most situations.

Although earlier engineers could design and build effective sedimentation tanks, the engineering science of sedimentation has progressed to a stage where students are taught how to calculate the submerged weight of a particle of sewage, the velocity it will settle at, what drag forces it will be subject to as it settles and so on so that sedimentation tank shape and size can be optimised and detention times fine-tuned. Modern sewerage engineering students are taught exactly why and how a sedimentation tank works.

The advantage of such sophisticated knowledge is debatable, especially given that sewerage treatment works are seldom operated at optimum conditions, and flows are extremely variable. The acquisition of this knowledge does however serve another purpose. The increased scientisation and mathematisation of these sewage treatment methods has given them an aura of precision, efficiency and certainty and conveys the impression that only engineers can understand the field of sewage treatment.

A specialised knowledge base was sought keenly by engineers as a basis for the claim for professional status during the nineteenth century. Although most engineers were employees, they believed in a social hierarchy which awarded power and influence to those with knowledge and skill and they sought to be recognised as professionals rather than workers. In particular, civil and mechanical engineers required science as part of their specialised knowledge base so that they would be differentiated from the technicians, mechanics and skilled craftsmen in the occupational hierarchy (Layton, 1971).

Although engineers could mark out their professional territory their autonomy was still limited. Gary Gutting (1984; p. 57) has criticised the concept of a technological paradigm because of the difficulty of defining a technological community and attributing to it the autonomy necessary to make the term of paradigm significant. If evaluation is up to outsiders then engineers cannot be autonomous. This view neglects the ability of engineers to influence the evaluation that outsiders make or impose. Moreover the ability of engineers to set their own objectives and constraints may be less than that of scientists but it is difficult to argue that scientists have a free choice about their goals and constraints either.

The formation of the sewerage paradigm did rely to a large extent on the official sanction of the British Royal Commission but the Commission based its conclusions on evidence given by the engineering community and results of experiments and projects undertaken by engineers. Moreover the Commission did not determine the paradigm but only set the standards that it should meet. The formation of the paradigm resulted from choices made by engineers working for local government authorities.

The autonomy of the engineering community lay in its ability to dictate the range of technologies which would be taken seriously. Outside authorities might set standards and regulate the available money but the engineers decided how to meet the standards and if they could be met with the finances available. A community might demand a higher stage of treatment from within the paradigm but would not be able to ensure that alternative treatments, such as sewage farming, from outside the paradigm were seriously considered.

The infringement on engineering autonomy posed by employers is limited by the shared interest in the same technological system and the correlation between the engineers paradigm and the interests of the firm or authority for whom they work. Constant (1984; p.29) observed that practitioners are usually located within a few organisations that are readily identifiable with a particular technology.

The sewage engineering paradigm incorporates a philosophy of staged treatment, whereby treatment is installed stage by stage so that at any one time only a minimum amount of treatment needs to be installed. As public complaints and political pressure increases, then a bit more treatment is installed. This delays the agony of public spending. In its own way the philosophy of staged treatment was a recognition by engineers that the "efficacy" of treatment methods is socially negotiated and therefore variable and they were making provision for changing public perceptions of what was "good enough". The skill of the engineer lay in being able to choose a minimum form of treatment from the paradigm and convincing the public that this was all they required.

Because of staged treatment, sewerage technology exhibits what has been referred to by some writers (Dosi, 1982; Nelson & Winter, 1977) as a 'trajectory' which is particularly persistent. The trajectory projects into the future the socially constructed characteristics of the system acquired in the past when the physical components were designed (Hughes, 1983; p.140). The authority and control of engineers as experts in the field of sewerage management was assured through closure by consensus following the British Royal Commission into Sewage Disposal. Tom Beauchamp observes of consensus closure,

Here it does not matter whether a correct or fair position has been reached. It does not matter whether, as a matter of justification and method, some point of view is well defended. Nor need principals believe that a permanent solution has been found, or even a definitive one. It only matters that there is consensus agreement that the force of one position has overwhelmed others. . . the weight of evidence might play no role at all in bringing about the consensus (1987; p.30).

The technologies which formed the basis of the sewerage paradigm were not technically superior to those discarded but were agreed by sewerage engineers to be satisfactory and appropriate. The paradigm was necessary for the profession of sanitary/sewerage engineering to maintain a certain degree of autonomy and to help guard the boundaries of their profession against outsiders.

Paradigm Inadequacies

Kuhn (1970) argued that scientists become aware of anomalies in the paradigms they are working within when there is a recognition by scientists that "nature has somehow violated the paradigm-induced expectations". However, contradictions between theory and reality are not sufficient to dislodge an engineering paradigm which is not based on a best fit with nature but is socially negotiated. The interested parties must agree about its disutility.

Some writers have tried to make analogies with Kuhn's concept of anomalies. Constant (1984) identified "presumptive anomalies" which are presumed to exist when it is predicted by the engineer that a conventional technology will fail under certain future conditions or it is predicted that an alternative technology will do a better job. The second type of anomaly which Constant identified is the "functional-failure" when the technology does not work very well because conditions have changed, allied technologies have changed or other parts of the system have advanced more quickly.

The identification of "functional-failure" or even "presumptive anomalies" depends on how the technology is evaluated. Constant (1983) has recognised this in his article on "technological testability" and Wojick (1979) has similarly pointed out the central part that "evaluation policy" plays in a technological paradigm. Evaluation policies enable engineers and managers to judge their designs and plans and are based on scientific theory, engineering principles, rules of thumb, legislation, professional standards or moral precepts. They determine decision-making procedures within which "normal technology" can take place. Such evaluation policies, because they are part of the paradigm are unlikely to force paradigm change or even to highlight paradigm inadequacies.

Many things have changed in the past seventy years since the sewerage treatment paradigm was formed, many of which might have highlighted anomalies and caused engineers to look for radically different technologies but didn't. The actual composition of city sewage has changed substantially with the growth of industry and the increased use of inorganic and artificial materials in industrial processes. Sewage treatment methods were developed at a time when sewage contained mainly natural organic matter. These methods do not treat toxic chemicals, heavy metals, organochlorines that are contained in the sewage. In fact some of these substances actually interfere with the microorganisms necessary for secondary and tertiary treatment, killing them off and turning whole batches of sewage 'off'.

Engineers have coped with this problem partly by restricting what can be put into the sewers but this is usually not successfully policed and enforced because it would require a large and expensive force of inspectors. Political pressures can also mean that the sewers continue to be used for disposal of industrial waste with toxic contaminants. Moreover, the effects of these substances in waterways is uncertain and it is only when a disaster occurs such as happened in Minamata, Japan, where hundreds of fish-eating people got mercury poisoning, that the adverse health effects can be proven.

The paradigm was set before much was known about the transmission of disease via swimming in sewage polluted waters and at a time when viruses were unknown. There is still much controversy over what health threats might be posed by such recreational use of waters into which sewage is discharged. Treatment methods were not designed to eliminate pathogens from the sewage, but rather to prevent waterways becoming a nuisance after the treated effluent was discharged into them. As a result, although sewage may contain as many as 110 different types of virus, conventional sewage treatment processes cannot be counted on to remove them (Goyal et al, 1984; p.758). Primary sedimentation does not remove viruses at all. A representative of the World Health Organisation remarked in 1976 that, "The sanitary engineers who built the early community sewage and water systems did not know about viruses, which is understandable, but many modern sanitary engineers still do not know about viruses, which is neither understandable nor excusable" (Melnick, 1976; p.4)

The paradigm has become universal but was in fact developed in a particular socio-physical context of relatively affluent northern nations. It was transferred from Europe to Africa and Asia whether or not the treatment and collection methods were appropriate to their different social, religious and climatic context. Sewage collection and treatment methods proved too costly and slow to cope with the rapid growth of mega-cities with their slum areas, such as Addis Abbeba and Calcutta. In other countries, such as Thailand and Burma, people living by rivers and dependent on them for food, found that their food source was degraded by the use of those rivers for sewage treatment and disposal.

In affluent western nations changing community expectations arising from the greater environmental awareness that has been manifest since the 1960's and 70's have meant that the public is now concerned to preserve river and marine ecosystems and it is far less tolerant of the degradation of recreational facilities and the possibility of getting even mildly sick after swimming. There is a growing discrepancy between community desires and goals and the objectives of the technologies employed by engineeers to deal with sewage. This is partly because of the change in societal goals and the widening sphere of community concern both in terms of their surroundings and also in terms of future generations. But it is also because research within the paradigm has been cumulative and this has meant that "errors" have also been cumulative.

Yet the dual problems of environmental degradation and water-borne disease have not been enough for most engineers to admit to "functional-failure" of the paradigm or any other sort of anomaly or to convince sewerage engineers that a new paradigm is needed. And the legislation and standards for sewage effluent that are a central part of the "evaluation policy" have tended to conform with the capabilities of the paradigm. Bathing criteria have usually been in terms of concentrations of faecal coliform rather than viruses; and toxic chemicals going into the ocean have often been limited in terms of concentrations rather than total quantities despite the likelihood that they would bioaccumulate.

The paradigm also fails to address the problem of scarcity of water and nutrients. Although there has always been a significant segment of most communities concerned about the need to recycle the resources contained in human waste, the engineering community and the government authorities tended to treat such concerns as sentimental rather than practical and this is reflected in the development of a paradigm which is extremely wasteful of these resources. Now that the need to conserve water and nutrients has become a much more central concern in the context of todays emphasis on sustainability, the old paradigm with its infrastructure (pipes leading to the sea/rivers) and adherents, has become an obstacle to the achievement of these new objectives. Technologies which aim to recycle these resources tend to be developed by groups outside of the paradigm and are therefore not taken seriously.

Wojick (1979) argued that anomalies occur in technological paradigms when standard procedures repeatedly "fail to eliminate known ills" or when knowledge shows up the importance of factors which have previously been incorrectly evaluated. Those contesting the evaluation policy may be outside the paradigm community and their view may be disputed. They can then, Wojick says, turn to the government for a ruling. Those contesting the sewerage paradigm are indeed outsiders but this means that they are almost powerless to change it and their appeals to government have been ineffectual.

The government regulatory authorities are unlikely to force changes on the engineering community because they are well aware of the costs that would be involved in changing the system and the problems created by toxic chemicals and viruses are hard to prove, invisible, and their effects longterm. Most regulatory authorities employ and are advised by engineers who inform them of what is possible to achieve and what is not. It seems unreasonable to the engineers and scientists in regulatory authorities and expert advisors to government, schooled in the paradigm, to set standards that cannot be met using available technology.

Discussion and Conclusion

Most sewerage engineers today operate within an outdated technological paradigm. The paradigm was based on a consensus about appropriate technologies reached by the engineering community earlier this century. This consensus, which has shaped engineering education and practice for most of the century, hinders serious consideration of alternatives that may be better suited to modern conditions.

However, the potential for a new paradigm is growing. Engineers within the paradigm are also becoming increasingly dissatisfied with conventional primary and secondary treatment methods. Secondary treatment plants are expensive to build, operate and maintain. They are land intensive which is a growing problem for coastal cities forced to install secondary treatment on prime real estate near ocean outfalls. They also create a large amount of sludge[4] which is difficult and costly to deal with. The problem is exacerbated by the tendency for viruses and heavy metals to concentrate in the sludge making incineration, ocean dumping, burial and reuse as fertiliser potentially hazardous.

One other reason for a reluctance to go to secondary treatment is that it would force sewerage authorities to be more restrictive on what wastes are allowed to be put into the sewers by industry in order to protect the micro-organisms required in biological sewage treatment.

Various substitutes for secondary treatment have arisen that are cheaper, produce less sludge and allow the continued extensive use of the sewers for industrial waste disposal. Submarine ocean outfalls are one such option that has been pushed. However the replacement of secondary treatment by submarine outfalls has created its own problems. Grease, which is broken down in the secondary treatment process, is now perceived to be a major problem when sewage outfalls discharge near swimming beaches. Only some of the grease is removed from the sewage during sedimentation treatment (by skimming the floating grease from the surface of the sewage in the tank). The remaining grease forms a floating slick on the surface of the sea making the sewage field highly visible and leaving obvious traces in the form of grease balls on the sand. This has caused engineers to note the inappropriateness of primary treatment: "most primary treatment plants do a much better job of removing settleables than removing floatables. It would be much better if this were the other way around (Ryan, undated; p.11).

In the United States engineers have been trying to replace secondary treatment with new forms of primary treatment. The US Environmental Protection Agency (EPA) requires that all major cities install secondary treatment but engineers and scientists in various States have been arguing that cities should be allowed to install chemical precipitation using polymers. (Sun, 1989). So far the EPA have refused to allow any city a waiver from the secondary treatment requirement because no city has been able to prove that an alternative treatment will not adversely affect marine life.

A similar battle has been waged in Sydney, Australia. Highly publicised community dissatisfaction with existing treatment methods has led to funds being invested in new technologies to solve the problem. One, invented by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), is a form of precipitation using magnetite and a magnetic field to separate out the suspended solids. Another uses membranes to filter out suspended solids. These methods would be much more robust in handling toxic chemicals than secondary treatment, would produce less sludge, are claimed to be much cheaper and are being touted as substitutes for secondary treatment.

Public pressure and the cost (both economic and environmental) of new dams are also forcing governments, such as the NSW government in Australia, to require engineers to at least explore the potential of treatment options which reuse and recycle wastewater as much as possible. Most recently, after years of dismissing the recycling of Sydney sewage as not feasible, the Sydney water authority has announced that it will be beginning trials of water recycling facilities in a move to eliminate the need to build more dams and it has declared an "ultimate aim of stopping all dry-weather sewage discharges, either into inland waterways or the ocean through the city's coastal deepwater outfalls" (Beale, 1995; p.2). In Israel, reuse of waste water has become the rule rather than the exception and this is likely to be the trend as clean water becomes scarce in various parts of the world.

Outside the engineering community, ecologists are working on various forms of ecological engineering which focus on the utilization and recycling of sewage. Niemczynowicz (1992; p.140) gives examples of Free Water Surface Systems, mainly consisting of oxidation ponds, and Subsurface Flow Systems, mainly consisting of wetland systems, both natural and artificial. He points out that such wastewater treatment systems are currently being researched in thousands of facilities around the world. Indeed ecological engineering is a growing field of study in itself with its own journal and text books.

What this paper demonstrates is that for these new developments to be incorporated into normal engineering practice there needs to be a change in the sewerage engineering paradigm; in particular the emphasis on `good enough' solutions at a minimum cost. "Good enough" solutions have been defined by legislation which is shaped by the technological paradigm in place. In the past engineers have taken a certain pride in achieving minimum designs that comply with legislation. The philosophy of `good enough' solutions at a minimum cost, needs to be replaced by one where engineers take pride in producing environmentally beneficial solutions that go beyond the legal standards that define `good enough'.

Recommendations for Managers and Other Decision-Makers

In the private sector the mechanisms behind technological change can be more readily understood in terms of market forces. The need to reduce costs, increase profits and maintain or open up new markets provides the motivation to remove bottle necks from the manufacturing process, redress system imbalances and remove uncertainty by decreasing dependence on labour and resources whose supply is not guaranteed. Such incentives are not the primary movers within the public sphere where technologies associated with the housekeeping role of the state are slow to change.

Environmental costs are treated as externalities, unaccounted for in national accounts, or even in the account books of water authorities. Yet those environmental costs have very real economic impacts. The once only use of fresh water to transport and dispose of wastes must be paid for through the provision of dams and other means of water provision and the depletion of high quality water resources that results is having increasing social and developmental consequences, particularly in arid parts of the world. The pollution which results from the use of waterways for waste disposal also has costs in terms of aquatic and marine environments. Any comparison of traditional treatment technologies with alternatives that are being developed would need to consider the economic costs of water depletion and pollution as well as the less quantifiable "quality of life" costs of environmental degradation.

Engineers play a key role in advising government agencies about which technologies are available, which are preferable and which are most cost effective. This advise tends to be shaped by the existing sewerage engineering paradigm.

If managers and decision-makers want to open up the range of feasible technological solutions that are to be considered and developed then

The existing paradigm and the reasons for it need to be understood by managers and decision-makers so that the parameters which constrain and shape it can be altered. For example, effluent standards played a key role in the formation of the sewerage paradigm. Radical innovation in sewage treatment technology came to a halt after the British Royal Commission recommended standards which were adopted by most government authorities in the Western world. These standards affirmed existing technologies as adequate.
Legal standards continue to be central to the continued viability of an engineering paradigm and the technological system it is embedded in. Whilst waste treatment methods are able to meet legal regulations and standards there is little reason to ditch the paradigm or consider radical innovation. Standards should therefore not be based on what technologies within the paradigm can achieve but rather on what decision-makers want to be achieved in the longer term. This in turn will force technological innovation.
Decision-makers need to be prepared to consult with people who are not committed to the existing paradigm. This may mean going outside the engineering community for expert advice but it will also mean considering the views of a wide range of people, including environmentalists and the general public.
Engineers themselves need to recognise the constraints that the paradigm imposed on them in order to free themselves of them and be more open to alternatives that come from outside their field or which are preferred by the public.
Ensuring that engineering graduates address environmental issues in their work requires more than just teaching them to assess the impact of their activities on the environment and how to install pollution control devices. Engineering graduates will need to come to terms with the social and political factors which shape and direct technological change and to understand their own role with respect to technological change.

Recommendations for Researchers

A technological revolution in sewerage engineering is possible but it requires the recognition by all parties that the existing paradigm is inadequate. This can be promoted in a number of ways by researchers:

There is a need for a more precautionary approach to environmental impacts of engineering practice. The traditional approach of requiring proof of significant environmental impacts of sewage treatment methods before changing those methods needs to be replaced by one that seeks treatment methods that minimise impacts.
The development by researchers of new technologies that convincingly and economically solve the problems posed by existing technologies and minimise environmental impacts is obviously necessary to convince policy makers to abandon outdated and inadequate technologies.
Alternatives to technologies within the paradigm will by definition be less developed because they have been neglected, ignored or are recent inventions. A straight comparison of performance and costs between highly developed existing technologies within the paradigm and emerging technologies needs to take this into account and to consider the potential of these alternative technologies in the short and long term future.
There is a need to research other technological paradigms that might require revising in the light of recent environmental concerns. Energy generation, supply and usage is an obvious area. Agricultural technology is another. In each case there are preferred technologies and methods that are most often implemented and alternatives, promoted by environmentalists and others, that are neglected or not fully developed. There is the opportunity for technologies to be radically altered so that they are much more attuned to the biophysical world and this, in turn, would have a dramatic effect on the interface between human and natural systems.

Issues for the 21st Century

The circumstances, motivation and reasoning that encouraged agreement when the sewerage paradigm was formed early this century is no longer appropriate for the coming century. Whilst the paradigm has enabled engineers to deal with the public health problems associated with unsewered settlements in a quick and efficient manner, the ability of the paradigm to ensure clean and healthy ecosystems into the future at an affordable price is limited. It is estimated that the cost of provision of water supply and sanitation to urban areas in the developing world by the end of this century could cost US$357 billion (Niemczynowicz, 1992; p.135).

Consider the following: 37 billion m3 of sewage water per year is released in China without treatment. It means that more than 2000 medium/large treatment plants would be needed. It is, of course, unrealistic to believe that this can be accomplished in the near future. Thus, European sewage treatment technology becomes irrelevant for China as well as for many other countries. On the other hand, China has a long tradition of ecologically sound wastewater recycling in mulit-level biological systems based on aquaculture. ...Unfortunately, during the development process, these practices have been considered old fashioned and have tended to be abandoned.(Niemczynowicz 1992; p.135)

A real technological revolution will require a recognition that environmental problems cannot be dealt with adequately through adjustments to the existing paradigm. What is required for the 21st century is a new approach to sewage treatment that does not merely seek to dispose of a city's waste products in the cheapest manner but rather seeks to

(i) minimise the production of industrial wastes through clean technologies

(ii) minimise the use of water; and

(iii) reincorporate remaining domestic wastes into the cycles of life in new and innovative ways.

This is already beginning to happen because of the pressure of environmentalists and communities anxious to protect their waterways and because of real environmental problems.

Some engineers are resisting this move because they fear the loss of the paradigm within which their skills and experience are based. In countries like Australia, a relatively dry continent where water is supplied at increasing environmental costs and where coastal beaches are central to the beach culture that Australians identify so strongly with, too many sewerage engineers still prefer ocean disposal to all other options. It is these views that need to change.

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Notes

[1] Since that time a third stage, tertiary treatment has been added.

[2] Sewage farming methods used in 19th Century Britain consisted of downward intermittent filtration or broad irrigation.

[3] It was known that sewage used up oxygen dissolved in waterways when it decomposed and so it was decided that the amount of dissolved oxygen absorbed by a particular effluent in 5 days at 65 degrees Fahrenheit gave the best single test index of the polluting potential of that effluent. This BOD[5] test is still used as an indicator today.

[4] Sludge is a by-product of sewage treatment and consists of the solids which have been removed from the sewage together with a certain amount of liquid.