Citation: Sharon Beder, Pipelines and Paradigms: The Development of Sewerage Engineering, Australian Civil Engineering Transactions, Vol. CE35, No 1 March 1993, pp79-85.

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

Sharon Beder's Other Publications


SUMMARY This paper puts forward the idea that the practice of sewerage engineering involves adherence to a paradigm. It will be argued that the circumstances, motivation and reasoning that encouraged agreement when the paradigm was formed early this century may not be appropriate today. Furthermore the mechanisms for reappraisal of the prevailing paradigm do not exist within the engineering community nor within the regulatory bodies which often employ or are advised by engineers.


In the private sector the mechanisms behind technological change can be 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 do not exist within the public sphere where technologies associated with the housekeeping role of the state are slow to change. Sewerage treatment technology, in particular, has changed very little in the last seventy years despite a period of innovation and rapid change prior to that. Yet there is some public dissatisfaction, particularly amongst environmentalists, with the existing treatment methods.

Sewerage engineering practice seems to be operating 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 prevents serious consideration of alternatives and ensures that engineering decisions are reaffirmed when subject to review by `independent experts'.


For 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 where the sewage will be discharged. Dry conservancy methods of sewage collection and land treatment of sewage have long since been discarded as possibilities for areas being sewered or requiring new sewage treatment plants.[#] The push to discard them came from the medical profession and government officials as well as from engineers.

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 of the suspended solids from the sewage and almost always consists of sedimentation of those solids in tanks. Secondary treatment utilises aerobic micro-organisms to break down some of the organic matter in the sewage and the two main methods of doing this are biological filters or activated sludge treatment.

Tertiary treatment is an additional stage that has been added since this time. It involves additional filtering or oxidation of the effluent. A nutrient removal stage may also be added. However the basic primary and secondary treatment processes that are most often used had been invented and were in use by 1920. They have since been improved upon and refined, and the underlying principles are better understood, but there have been no breakthroughs or revolutions in conventional sewage treatment since then.(Stanbridge, 1976; Sidwick, 1976b, p520)

Previous attempts to apply Kuhn's theory of paradigms to technology have been criticised because there was no obvious equivalent to the scientific community amongst technologists. It was argued that engineers are not autonomous in that they are not the sole arbiters of the merits of a technology (Gutting, 1984, p57). In the case of sewerage engineering it is true that standards are set by people outside of the engineering community. These standards have an important bearing on the paradigm in that they define the goals to be achieved.

The British Royal Commission into Sewage Disposal (1898-1915) was a key event for sewerage engineering because it set effluent standards to be achieved by sewage treatment processes. The importance of the Commission to the maturity of sewerage engineering has been noted by engineers in the field,

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, 1976a, p199)

However, the Royal Commission (1908) considered only those technologies which had been implemented by engineers in various parts of Britain and relied to a large extent on the evidence of practicing engineers. Nor did the Commission choose which of those technologies would afterwards form the basis of the paradigm.

The autonomy of the engineering community lies in its ability to dictate the range of technologies which will be taken seriously. Outside authorities may set standards and regulate the available money but the engineers decide how to meet the standards and if they can be met with the finances available. The public may demand a higher level of treatment but can seldom successfully demand alternative treatments from outside of the paradigm.

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 without offending the sensibilities of a large portion of the public. An early American engineering text argued that "Changing the character of the sewage merely for the sake of making it less offensive or dangerous is a waste of money unless it is necessary."(Metcalf and Eddy, 1935)

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 to students training to be sewerage or public health engineers for several decades and as a result it is taken for granted by most engineers that such methods are satisfactory and appropriate to most situations. This professional agreement contrasts markedly with the controversy amongst engineers of the nineteenth century over the relative merits of the various competing sewage treatment methods that were available. The author of one text on `sewage utilization' wrote in 1873:

a well-known sanitary reformer once said to us that he only knew of one topic besides polemics upon which men's party spirit go the better of their good sense, and even of their regard for truth and justice, and that was the treatment of sewage. An out-and-out irrigationist would go to the stake in support of his views, and would hardly even use an A B C dispatch box, while the advocates of the various "systems" are equally bigoted in their own way, and consider all those who differ from them as quite outside the pale of sanitary or scientific consideration.(Burke, 1873, p.ix)

Whilst various treatments for sewage were debated in the meetings and proceedings of engineering and scientific societies in the nineteenth century, today's engineering magazines deal with the details of particular applications of an acceptable technology or improvements and refinements to existing technologies (to produce a better quality effluent from existing plants). Such discussions contain assumptions and jargon which make them uninteresting to the uninitiated and they are seldom read by those outside the field.

Moreover 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. 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 who are in no position to question the range of treatment methods available.

The creative innovation which characterised the nineteenth century is markedly absent in the twentieth century and this is sometimes a cause of defensiveness amongst engineers. An article in an American engineering journal provides a good example,

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, p312)

Another engineer who wrote a series of articles in the 1970s outlining the history of sewage treatment was surprised at discovering how little had changed in the last seventy years and noted that

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.(Sidwick, 1976b, p520)

He suggests that since the existing techniques are able to satisfy existing effluent standards consistently there is no reason to direct research into new methods. In fact, effluent standards have not changed appreciably since the British Royal Commission made its recommendations early this century and this goes a long way towards explaining the lack of basic research into new treatment methods. However two other factors are also important. The first is the presence of existing treatment plants of past design and the second is the philosophy of staged treatment.

Because engineering practice incorporates cost minimisation, engineers are always keen to make use of whatever is available to them in terms of natural and `man-made' resources in their efforts to minimise costs. There is a great reluctance to tear down existing treatment plants and start again. An old treatment plant will have involved a large capital input when it was first built and will probably be achieving some results, even if those results are unsatisfactory. Even if new methods were developed engineers would in most cases prefer to improve or upgrade or augment the existing facility.

The philosophy of staged treatment not only allows for engineers to apply only the level of treatment necessary for a particular situation but also facilitates the upgrading of an existing facility when circumstances change. Primary treatment can be augmented with secondary treatment if standards change or the effluent quality needs to be upgraded for other reasons. Staged treatment also ensures that engineers can install a lesser degree of treatment without too much risk, since they can install further stages of treatment if the first plant proves to be inadequate without the completed work being wasted.


The sewerage engineering paradigm is firstly based on water-carriage technology. The struggle between water-carriage technology and dry conservancy methods of dealing with sewage took place in the nineteenth century. Water-carriage technology triumphed on the basis of theories, beliefs and values which were held at that time (Tarr, 1984; Beder, 1989).

The advocates of both water carriage and dry conservancy methods relied on scientific theories that are largely discredited today. The water-carriage lobby argued that organic wastes had to be removed from places of habitation as soon as possible because if they were given time to putrefy or decompose they would give rise to `miasmas' or disease producing gases which were responsible for the spread of diseases such as typhoid. Water-carriage enabled these wastes to be whisked away immediately whereas dry conservancy methods required that the wastes be stored about the premises (Sewage and Health Board, 1875, p6; Tarr, 1984).

The dry conservancy enthusiasts believed that it was the solid portion of human wastes which caused the pollution of waterways and which contained the major part of the nutrients. They were concerned that these nutrients be utilised to fertilise the land rather than pollute the waterways. This could be done more effectively if the wastes were not diluted in water and taken to a centralised point, but rather retained in their pure or in an improved form that could be taken to where manure was most needed (Burke, 1873, p21; Waring, 1889, p365).

Water-carriage technology, which was favoured by many, although not all engineers, involved large scale excavation and construction of sewers as well as the centralisation of sewage for disposal and brought sewage disposal within the engineering domain. It was attractive to the authorities since it made waste disposal a more automatic procedure and a public rather than an individual responsibility. It was felt that the individual could not be trusted. As one text put it,

the lower classes of people cannot be allowed to have anything to do with their own sanitary arrangements: everything must be managed for them.(Corfield, 1871, p118)

The automatic nature of water carriage as opposed to the labour intensive nature of most dry conservancy methods which required the wastes to be regularly collected and carted away was also attractive. Florence Nightingale observed in an 1870 report

The true key to sanitary progress in cities is, water supply and sewerage. No city can be purified sufficiently by mere hand-labour in fetching and carrying. As civilisation has advanced, people have always enlisted natural forces or machinery to supplant hand- labour, as being much less costly and greatly more efficient. (Sewage and Health Board, 1875, p6)

The engineering profession, the medical profession and the authorities made the removal of health-threatening wastes from the cities and towns their first or at least their most public priority and considerations of utilising those wastes as fertiliser or preventing the pollution of waterways were quite secondary, if they were considered at all.

Dry conservancy methods did not reach their peak of popularity till after many sewerage systems were constructed. Their popularity was a result, in fact, of the pollution of waterways that was perceived to accompany water-carriage methods. This lateness on the scene was an immediate drawback since sewers had been installed and had proven to achieve immediate results in decreasing the mortality rate in areas where they were installed. Moreover, the existence of a physical infrastructure of pipes encouraged the continued use of pipes rather than the scrapping of an expensive and proven system in favour of a relatively unproven one.

The staging of treatment into primary, secondary and tertiary treatment arose out of the perceived inadequacy of single stages of treatment. It was recognised by the 1870s that removing some of the suspended solids, or clarifying the effluent did not prevent the effluent from putrefying and causing a nuisance when discharged (Sewage and Health Board, 1877, p9; Stanbridge, 1976, p19). Chemical treatment, sedimentation and septic tank treatment were almost always followed by a second stage of treatment; usually some form of filtration.

When the British Royal Commission sat at the turn of the century they considered sewage treatment (other than land treatment) in terms of `preliminary' treatment followed by some form of filtration. The use of the term `preliminary' was intended to indicate that `preliminary' treatment was not a full treatment on its own and was not considered as such during the Commission's sitting (Royal Commission, 1908, p18).

The Royal Commission considered chemical precipitation, plain sedimentation and septic tanks as the main forms of preliminary treatment and found all performed satisfactorily when used in conjunction with filters, and that the operating cost difference between them was minimal when the filters used were appropriate to them. For example, sedimentation treatment was cheaper than chemical treatment but because it removed less of the suspended solids required more expensive filtration (1908, pp18-46).

Following the Commission, sewerage engineers gradually came to favour sedimentation as a primary treatment method for municipal plants. It had not been a preferred method before the Commission but after it was officially found to be as good as chemical precipitation and septic tank treatment it gained favour. The use of primary treatment on its own, gave sedimentation a cost advantage over chemical precipitation and the tendency to implement treatment in stages as money came available or as the need arose ensured that the cheapest first stage was chosen. Moreover the cost of chemicals for precipitation was an increasing one over time (Sidwick, 1976a, p195).

Septic tank treatment went out of favour for plants of any size, partly because of the smell which accompanied them. They had a very bad reputation with the public and it was found difficult to site them (Parliamentary Standing Committee, 1906). Although engineers had vehemently denied that septic tanks caused odour nuisances in the vicinity, the Commissioners found that all sewage treatment works were liable to smell at times and that septic tank treatment was likely to be more offensive than the others.(Royal Commission, 1908, pp44-5)

The use of `artificial' filters came to prevail over the use of the land as a filtration medium in which the aerobic microorganism could oxidise and nitrify the sewage effluent. The pressure to replace land treatment had come from towns and cities where suitable land for this purpose was scarce or expensive and the Royal Commission on sewage disposal had in fact been established to settle a dispute between local authorities who wanted to use artificial filters and the Local Government Board which believed that only land treatment was satisfactory (Sidwick, 1976c, p71). The declaration by the Commission that artificial filters were adequate was enough to spell the end for land treatment even though the Commissioners tended to prefer land treatment.


What is important in the setting of the sewerage engineering paradigm at this time is that firstly, the choice of methods was not based on technical superiority in terms of performance in achieving effluent purification. Nor was the choice made by the British Royal Commission which nevertheless played an important role in dismissing exaggerated claims for some treatment methods and setting standards.

The choice was made by engineers on the basis of their search for `good enough' solutions at a minimum cost; solutions that the public would accept at the turn of the century. The economics of the various solutions depended only on capital and operating costs for the particular stage of treatment being considered. They did not include possible environmental costs. The economics of utilising the sewage was calculated on early twentieth century price structures which reflected the cheapness and attractiveness of artificial fertilisers, resource availability (including water), pumping costs and the abundance of water supplies at that time.

It is not only economic values which have changed in the past seventy years. The actual composition of city sewage has also changed substantially with the growth of industry and the increased use of inorganic and artificial materials in industrial processes. Sewage treatment methods within the paradigm are aimed at removing suspended solids which will settle out of the effluent and decreasing the oxygen demand of the sewage by breaking down organic material with the use of naturally occurring microorganisms contained within the sewage and in the environment. (Oxygen demand is a particular problem in rivers because oxygen is required by other living organisms in the river and oxygen may not be replaced or regenerated quickly enough to ensure these organisms survive.) These methods do not remove or treat toxic chemicals, heavy metals, organochlorines or most of the grease and oil that is 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 cannot be successfully policed and enforced without a large and expensive force of inspectors. 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. It is notable in this regard that mercury is one of the few substances that is completely banned from Sydney's sewer systems (MWS&DB, undated). Other substances are restricted by concentration and an `over-careful' approach is rejected by industries who have an economic bonus in the use of the sewers for waste disposal.

Grease is seen, by engineers as a major problem for swimming beaches near sewage outfalls because the grease, which forms a floating slick on the surface of the sea, makes the sewage field highly visible and leaves obvious traces in the form of grease balls on the sand. Some grease is removed from the sewage during sedimentation treatment by skimming the floating grease from the surface of the sewage in the tank. This has caused engineers to note the inappropriateness of the treatment paradigm,

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, p11)

There has been much controversy, which has yet to be settled, as to the danger that swimming in sewage polluted water poses to people (Gameson, 1975). Treatment methods were not designed to eliminate pathogenic bacteria from sewage, but rather to prevent the waterways becoming a nuisance after the treated effluent was discharged into them. The paradigm was set before viruses were known. 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, 1984 p758). Primary sedimentation does not remove viruses or pathogenic bacteria at all. A representative of the World Health Organisation has said:

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, p4)

Because the paradigm does not specifically deal with viruses or pathogenic bacteria, their presence is not monitored. Monitoring of sewage effluent is confined to measuring levels of faecal coliform which are not dangerous in themselves but merely indicate the presence of sewage. Authorities, who will not set standards that cannot be met by the available technology, set standards for bathing waters in terms of concentrations of these faecal coliforms which are generally agreed not to correlate statistically with viral counts because faecal coliforms have a more rapid die-off rate than many viruses and pathogens (Goyal, 1984, p.758).

There are two other major problems which arise from sewage treatment within the paradigm and which are subject to much research and experimental work. The first is the disposal of the sludge which is a by-product of sewage treatment and consists of the solids which have been settled out of the sewage together with a certain amount of liquid. This problem has been present since the nineteenth century but has been exacerbated by the tendency for viruses and heavy metals to concentrate in the sludge making incineration, burial and sea dumping of the sludge, even after treatment, environmentally hazardous procedures (Goyal, 1984; Browne and Hazell, 1981, p23).

The second problem is the fact that conventional sewage treatment does not remove the nutrients from the sewage and this has caused the choking up of many waterways with excessive plant growth. Research into solving this problem has been tackled in terms of a search for a further stage of treatment, which can be added to the paradigm, and will remove the nutrients from the effluent before discharge (SPCC, 1986).

Changing community expectations have also created problems for the paradigm on two levels. The public is far less tolerant of the degradation of recreational facilities and more willing to pay for higher degrees of treatment but many treatment plants built when sewage flows were smaller and public expectations lower do not have the space available nearby to expand and incorporate, for example, secondary treatment. This has lead to a solution for ocean outfalls of extending the outfalls under the sea for a few kilometres. Such an ad hoc solution aims at keeping the sewage from view by discharging it at greater depths where it will be more dispersed and may be kept beneath the surface when the temperature difference between the top and lower levels of water is great enough to produce a thermoclyne (Caldwell Connell, 1976).

The other change in community expectations arises from the greater environmental awareness that has been manifest since the 1960s and 70s. This awareness has meant that the public is not only concerned with their own health but also with the preservation of river and marine environments and the species that live in them. Very little research has been done into the effects of sewage, especially industrial wastes, on such ecosystems and the phenomenon of bioaccumulation of certain substances up the food chain has only been discovered fairly recently.


A scientific paradigm, Kuhn (1970) has observed, eventually throws up anomalies which scientists can no longer ignore and they are forced to acknowledge that the existing paradigm is not adequate. This cannot happen in the same way in engineering where contradictions between theory and reality are not being constantly tested and where a "good enough" result is all that is required.

Several writers have suggested ways in which paradigms change in other fields of technology. Edward Constant (1984) identifies two types of anomaly that occur. One type are "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. It is not, however, in the sewerage engineer's interests to recognise such a failure in advance since they are not in a competitive situation where not predicting it would disadvantage their firm. Moreover the historical evidence suggests that sewerage engineers are more likely to wait to see if such a failure happens and then deny that it has while they work on a way of fixing it (Beder, 1989).

The second type of failure which Constant identifies 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 trouble with sewerage engineering is that such a failure is not clear-cut and many environmentalists would argue that it has already happened, but that the engineers are ignoring it.

This difficulty in identifying when a technology is satisfactory was recognised by David Wojick (1979) who defines technological paradigms in terms of an "evaluation policy" which enables engineers and managers to judge their designs and plans. Anomalies occur in such paradigms, Wojick argues, 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 turn to the government for a ruling.

In the case of the sewerage question, there are certainly a number of people who would argue that conventional sewage treatment has failed to eliminate the problems associated with industrial waste and that the new fields of virology and ecology have pointed to important factors that have previously been ignored by sewerage engineers. Many engineers dispute this. They cope with changed situations as best they can by upgrading existing treatment plants, moving points of discharge and adding further stages of treatment to the paradigm. The weight of huge capital intensive technological infrastructures makes this the most economically feasible thing to do.

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. They act within those bounds. Governments themselves can do no more than legislate that "the best practicable technology" is installed; they will not set standards that cannot be met by the available technology.

Environmentalists have a difficult job convincing the public that problems, which are not visually obvious, do exist. Even if they achieve this the public, like the authorities, tends to readily accept the bounds of technological possibility that the `experts' put forward. The experts believe these bounds themselves. It is clear that it would take a major disaster or crisis, perhaps similar to that which is occurring in the area of hazardous waste disposal at the moment, to cause the limitations of the paradigm to become vexatious to the engineering community and to encourage a renewed spate of research and innovation which might lead to a new paradigm which would be more suited to modern conditions.


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Browne, J.H. and Hazell, W.R., "Report on I.A.W.P.R. London Conference on Disposal of Sewage Sludge to Sea and Study Tour of U.K. and U.S.A", Metropolitan Water Sewerage and Drainage Board, Sydney, (1981).

Burke, U.R., "A Handbook of Sewage Utilization", 2nd ed., E & F.N.Spon, London, (1873).

Caldwell Connell, "Sydney Submarine Outfall Studies", Metropolitan Water Sewerage and Drainage Board, Sydney, (1976).

Constant, E., "Communities and Hierarchies: Structure in the Practice of Science and Technology", in Laudan, R., ed, "The Nature of Technological Knowledge", D.Reidel, (1984) pp. 27-46.

Corfield, W.H., "A Digest of Facts Relating to the Treatment and Utilisation of Sewage", MacMillan & Co, (1871), p.118.

Fuhrman, R., "History of Water Pollution Control", Journal WPCF 56, no 4, April 1984, p.312.

Gameson, A.L.H., ed, "Discharge of Sewage From Sea Outfalls", Pergamon, Oxford, (1975).

Goyal, S. et al, "Human Pathogenic Viruses at Sewage Sludge Disposal Sites in the Middle Atlantic Region", Applied and Environmental Microbiology, Vol 48, no 4, Oct 1984.

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Kuhn, T.S., "The Structure of Scientific Revolution", 2nd ed, University of Chicago Press, (1970).

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Metcalf & Eddy, "American Sewerage Practice", Volume III, McGraw-Hill, (1935).

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Parliamentary Standing Committee on Public Works, "Scheme of Sewerage for the Municipality of Drummoyne", NSW Legislative Assembly Votes & Proceedings, (1906).

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* This is analogous to Thomas Kuhn's concept of scientific paradigms which are "based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice."(1970, p10)

# Various alternatives to water carriage were put forward in the second half of the nineteenth century (Beder, 1989). These alternatives were often subsumed under the heading of `dry conservancy' methods and they included dry closets in which excrement was covered by earth or some other material and which were cleaned out periodically, pan systems in which excrement was kept in small closed containers that were regularly collected, and pneumatic systems which were pipe systems relying on vacuums for pushing or sucking the excrement to its destination. Variations on each of these themes were patented by the dozen in several countries. Land treatment involves the use of sewage to irrigate fields which were used for growing crops or grasses and the use of the land as a filtration medium.

^ for example, Ralph Burke, a lawyer, and W.H.Corfield, M.A., M.B. (Royal College of Physicians) were both prominent and much quoted sewage authorities. Moreover the letters to the editors columns and the proceedings of the various professional and scientific societies give plenty of other examples.

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