Most of the work was financially supported by STOWA (Stichting Toegepast Onderzoek Water), the umbrella organisation co-ordinating and funding almost all applied water research in The Netherlands.
Parts of this work were also financially supported by two Dutch water boards: Hoogheem-raadschap Delfland (Delft) and HoogheemHoogheem-raadschap Rijnland (Leiden).
Keywords: Anammox, biological, chemical, energy, nutrients, sanitation, SHARON, source separation, struvite, sustainable, treatment, urine, wastewater.
Printed and bound by Ponsen & Looijen bv ISBN-10: 90-6464-016-5
ISBN-13: 978-90-6464-016-2
c
J.A. Wilsenach, 2006
Cover design - J.A. Wilsenach: Manneken peace on earth, floating through a space defined
by finite elements of Anammox organisms.
Image of earth: NASA. Image of Storm Troopers: public domain.
Treatment of source separated urine
and its effects on wastewater systems
Proefschrift
ter verkrijging van de graad van doctor
aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof.dr.ir. J.T. Fokkema,
voorzitter van het College voor Promoties,
in het openbaar te verdedigen op maandag 26 juni 2006 om 17:30 uur
door
Jacobus Albertus WILSENACH
Bachelor of Engineering (Honours)(Water Resources Engineering) Universiteit van Pretoria, Zuid-Afrika,
Samenstelling promotiecommissie: Rector Magnificus, voorzitter
Prof.dr.ir. M.C.M. van Loosdrecht, Technische Universiteit Delft, promotor Prof.dr.ir. P.A. Wilderer, Technische Universität München
Prof.dr.ir. J.H.J.M. van der Graaf, Technische Universiteit Delft Prof.dr.ir. J.B. van Lier, Wageningen Universiteit
Prof.dr.ir. S.M. Lemkowitz, Technische Universiteit Delft Dr.ir. P.J. Roelveld, Grontmij De Bilt
“And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every moving thing that move upon the earth”
Genesis 1, 28
King James Version of the Bible
“I do not know whether there will come a time when we can no longer afford our waste-fulness - chemical wastes in the rivers, metal wastes everywhere, and atomic wastes buried deep in the earth or sunk in the sea. When an Indian Village became too deep in its own filth, the inhabitants moved. And we have no place to which to move.”
Contents
I Introductory review, thesis structure, conclusions and outlook
1
I.1 Development of sanitation and urban water drainage from 1850 until today . . 3
I.2 Origin and evolution of the concepts ‘sustainability’ and ‘sustainable devel-opment’ . . . 6
I.2.1 Background to the growing attention for ‘sustainable development’ . 6 I.2.2 ‘Sustainable development’ is a political definition . . . 7
I.2.3 Various interpretations of ‘sustainable development’ . . . 8
I.2.4 The more sceptical views on aspects of ‘sustainability’ . . . 10
I.2.5 A more pragmatic understanding of ‘sustainability’ . . . 11
I.3 New developments in conventional and alternative sanitation and urban water systems - arguments for and against . . . 13
I.3.1 Improvements and new developments in conventional sanitation and urban water systems . . . 13
I.3.2 Arguments for a complete systems change in urban water effluent and sanitation . . . 18
I.3.3 Technological systems mirror value systems . . . 22
I.4 Criteria and tools for the evaluation of sanitation and urban water systems . . 29
I.4.1 Basis for criteria . . . 29
I.4.2 The social environment and cultural criteria . . . 30
I.4.3 The economical environment and cost criteria . . . 31
I.4.4 The biological environment and emission criteria . . . 31
I.4.5 The geophysical environment and criteria of resource depletion . . . 33
I.4.6 The technological environment and functional criteria . . . 34
I.4.7 Source separation of rainwater and urine have the best prospects of improving urban water management . . . 34
I.4.8 Tools for further analysis and comparison of systems . . . 38
I.5 Thesis structure and content, with summaries of main results . . . 42
I.6 Conclusions . . . 51
I.6.1 General approach and methodology . . . 51
I.6.2 Effects of separate urine treatment on earth systems . . . 52
I.6.3 Biological nitrogen removal from urine and sludge rejection water . . 53
I.6.4 Phosphate and potassium recovery from urine and sludge rejection
water . . . 54
I.6.5 Process integration . . . 54
I.7 Outlook and future work . . . 55
I.7.1 Preliminary cost evaluation of urine separation technology . . . 55
I.7.2 New concept for local-central treatment for peri-urban areas . . . 58
I.7.3 Aspects of sanitation and public health . . . 60
I.7.4 Future work on biological nitrogen removal . . . 60
I.7.5 Future work on struvite (MAP and KMP) recovery . . . 61
I.7.6 Definition of a reference system . . . 61
I.7.7 Sustainable technological systems and sustainable societies . . . 62
II Publications
63
1 The limited role of municipal wastewater treatment in the nutrient cycles (N, P, K) in the Netherlands. 65 1.1 Introduction . . . 671.2 Global and local nitrogen cycle; ammonia synthesis and waste treatment . . . 69
1.2.1 Industrial ammonia synthesis . . . 69
1.2.2 Nitrogen recovery/removal techniques . . . 70
1.3 Global phosphate cycle, recovery and recycle . . . 73
1.4 Nitrogen and phosphate flux through the Netherlands . . . 74
1.5 The fate of potassium in wastewater . . . 77
1.6 Economic considerations of nutrient recycle . . . 77
1.7 Conclusions . . . 78
2 Effects of separate urine collection on advanced nutrient removal processes 81 2.1 Introduction . . . 83
2.2 Method . . . 85
2.2.1 The BCFS c process . . . 85
2.2.2 Important model parameters . . . 86
2.2.3 Reference simulation . . . 86
2.2.4 Urine separation . . . 87
2.2.5 Primary sedimentation . . . 89
2.2.6 Chemical phosphate removal . . . 89
2.2.7 Increased treatment capacity . . . 89
2.3 Results . . . 90
2.3.1 Raw wastewater . . . 90
2.3.2 Pre-settled wastewater . . . 91
2.3.3 Pre-precipitated wastewater . . . 93
2.3.4 Improved effluent quality with primary sedimentation . . . 94
2.3.6 Increased treatment capacity . . . 95
2.4 Discussion . . . 96
2.4.1 Effluent quality . . . 97
2.4.2 Capacity increase . . . 97
2.4.3 Technology transition . . . 98
3 Integration of processes to treat wastewater and source separated urine. 99 3.1 Introduction . . . 101
3.2 Reference and Integrated Wastewater and Urine Treatment (IntWUT) processes102 3.3 Method . . . 105
3.3.1 Influent characteristics . . . 105
3.3.2 Modelling of the BCFS reference process . . . 106
3.3.3 Modelling of the IntWUT-BCFS process . . . 107
3.3.4 Modelling of the InWUT-A process and sensitivity analysis . . . 107
3.3.5 Integration of different process units and assumptions . . . 108
3.3.6 Assessment of energy demand for different scenarios . . . 109
3.4 Results and discussion . . . 111
3.4.1 Effluent concentrations of the reference and the IntWUT-BCFS process111 3.4.2 Effects of solids retention time and temperature on effluent concen-trations: IntWUT-A process . . . 111
3.4.3 Effects of different nutrient contents on the effluent concentration: IntWUT-A process . . . 113
3.4.4 Mass balances . . . 114
3.4.5 Energy balance . . . 117
3.4.6 Area requirement and land use . . . 120
3.4.7 Implementation of new technology . . . 121
3.5 Conclusion . . . 121
4 Evaluation of separate urine collection and treatment to augment existing waste-water treatment works 125 4.1 Introduction . . . 127
4.2 Case study: Wastewater treatment plant De Groote Lucht . . . 128
4.3 Materials and method . . . 129
4.3.1 Data and analysis . . . 129
4.3.2 Mass balances . . . 130
4.3.3 Modelling . . . 131
4.4 Results and Discussion . . . 135
4.4.1 Effect of separate urine treatment on nitrogen removal within current flow scheme . . . 135
4.4.2 Effect of separate urine treatment on nitrogen removal within pro-posed flow scheme . . . 136
4.4.3 Effect of separate urine treatment on ammonium oxidation . . . 137
4.5 Conclusion . . . 138
5 Biological nitrogen removal from urine. 139 5.1 Introduction . . . 141
5.2 Materials and method . . . 142
5.2.1 Synthetic urine mixture used for substrate . . . 142
5.2.2 Sequencing batch reactor (SBR): nitritation . . . 143
5.2.3 Continuous stirred tanks reactors (CSTR) with recycle: nitritation-denitrification . . . 144
5.2.4 Fixed bed reactor (FixBR): anaerobic ammonium oxidation (Anam-mox) . . . 145
5.2.5 Fixed bed reactor (FixBR): complete autotrophic nitrogen removal (CANON) . . . 145
5.2.6 Fluorescence in situ hybridization and microscopy . . . 146
5.2.7 Analytical methods . . . 146
5.3 Results and discussion . . . 146
5.3.1 Nitritation process . . . 146
5.3.2 Anammox process . . . 152
5.3.3 CANON process . . . 154
5.3.4 General discussion: Efficient biological nitrogen removal . . . 156
5.3.5 Process integration . . . 161
6 Phosphate and potassium recovery from source separated urine through struvite precipitation 163 6.1 Introduction . . . 165
6.2 Precipitation theory and process description . . . 166
6.3 Materials and method . . . 167
6.3.1 Synthetic urine mixture . . . 167
6.3.2 Batch tests . . . 168
6.3.3 Continuous stirred tank reactor (CSTR) for struvite precipitation and settling . . . 169
6.3.4 X-ray diffraction (XRD) and analysis . . . 170
6.4 Results . . . 170
6.4.1 Batch tests . . . 170
6.4.2 Precipitation efficiency in continuous operation: MAP and KMP . . . 171
6.4.3 Liquid/solid separation in continuous operation . . . 172
6.5 Discussion . . . 176
6.5.1 Precipitation efficiency . . . 176
6.5.2 Crystallisation and recovery efficiency . . . 177
Part I
Introductory review, thesis
structure, conclusions and outlook
from 1850 until today
We drink only a minute amount of all drinking water. Virtually all of the drinking water that enters households is used to transport wastes. Dirt, detergents, food-rests and human excreta are all dissolved or suspended in water, which then flows away from urban environments through a network of sloping conduits, called sewers. The quality of drinking water is drastically changed during this transportation process. At the same time, the quality of the wastes is also changed from being concentrated to being diluted. This mixture of water and wastes is called wastewater.
The modern practice of transporting wastewater through sewers originated during the mid 19thcentury industrial revolution in Europe. The growth of cities in this period is generally
associated with increasing population densities and a general degradation of urban hygiene. The classic case of John Snow, the Londoner who removed the handle from the Broad Street pump in 1854, illustrates the first causal link between diseases and their transmission through water. The need to clean up cities led to a drastic improvement in urban design, including disposal of excreta through sewers. In many cases, sewers already existed for rainwater drainage, but these systems were also much expanded and resulted in so-called combined
sewers1. Although the improvement in community health was enormously successful on the
short term, some long-term problems were inherent in this practice. Discharging untreated wastewater into fresh water bodies did not only spoil aquatic environments, but actually distributed the original problem of sanitation. As cities became larger and populations grew - in comparison to the constant volume of receiving water bodies - water borne diseases 1Sewers existed in ancient civilizations, as for example revealed by the well-preserved public toilets at Ostia (the port of ancient Rome), but the modern engineered system is a recent development.
were reintroduced with flushing toilets. The problem had thus only been replaced from groundwater to surface waters. Only after Pasteur’s discovery of bacteria in the 1880’s did epidemiology gradually replace superstitious explanations for diseases. The public under-standing of pathogens (organisms causing disease) is therefore relatively new compared to the sanitary use of sewers.
Throughout the course of the 20th century, wastewater transport and discharge have
gradually advanced towards wastewater transport and treatment. Nearly a century ago, for example, Rothuizen (1917) dedicated 167 pages on an elaborate explanation of the relatively new development of wastewater transport and sewerage, but a mere 22 pages on the purifica-tion of wastewater. The treatment processes described as part of the ‘purificapurifica-tion’ included rather crude techniques, such as sedimentation, septic tanks and rudimentary trickling filters. Much was relied upon the “self-purification of water” and the general advice was to collect drinking water as far upstream as possible. Today, nearly all of Europe’s cities have advanced wastewater treatment works, where the mixing of water and wastes is largely reversed. This reversal process, i.e. wastewater treatment, requires the input of resources to a series of physical, chemical, and biological unit processes.
Organic matter in wastewater (proteins, carbohydrates and fats) has to be removed to prevent the depletion of oxygen in receiving waters. Organic matter is mostly measured as chemical oxygen demand (COD) and removed through biological oxidation. Nutrients - nitrogen and phosphorus - have to be removed for various reasons. Ammonium (NH+
4)
is the main constituent of the total nitrogen in wastewater and has to be removed, because free ammonia (NH3) is toxic to most aquatic animals. Ammonium will also be oxidised to
nitrate (NO−
3)in receiving waters, which further depletes the oxygen concentration. Although
ammonium is biologically converted to nitrate in most wastewater treatment plants
(nitrifi-cation), nitrate also has to be removed (denitrification) since it jeopardizes drinking water
abstraction from water bodies. Since atmospheric nitrogen is always available, phosphate (P) is the limiting nutrient for the growth of blue-green algae (eutrophication) and denitrification alone will not prevent eutrophication. Phosphate therefore has to be removed chemically or biologically to prevent algal blooms in receiving waters. Blue-green algae are not only toxic, but once algae start to decompose, the oxygen concentration will be depleted further.
State-of-the-art activated sludge systems (e.g. the Modified UCT process) produce ef-fluent water in which COD < 50 mg/l, Ntot <10 mg/l, NH+4 <1 mg/l and Ptot <0.5
mg/l, constituting an overall removal efficiency of 80-90%. In fact, the quality can be improved almost at will, through various post-treatment options and with an increasing input of resources. In spite of all this, the most important function of the urban wastewater system remains sanitation. Wastewater treatment plants often have special disinfection units - such as UV-light, ozonation or chlorination - to destroy pathogens. Most harmful bacteria are already removed in the activated sludge process and disinfection therefore doesn’t form part of the treatment process in the Netherlands. Wherever this technology is well maintained, water borne diseases are practically non-existent today. From this point of view, conventional urban wastewater systems have been very successful.
of wastewater discharge, the distinction between upstream and downstream has now become problematic. Due to the enormous population increase over the past 50 years, urbanisation and large water transfer schemes (e.g. Lesotho Highlands in Southern Africa) hardly any wa-ter can be found ‘upstream’ and everyone lives ‘downstream’ of the Global village2. The aim
of wastewater treatment therefore needs to be expanded from sanitation and environmental protection to include water quality control, with the ultimate aim of water recycle. At the same time, the ideal of more sustainable systems has been gaining attention during the past 15 years. A general critique against classical civil engineering projects is that they have not dealt with transport, drinking water, energy and wastewater in an integrated way. These were all designed as linear systems, without consideration of the cyclic character of most natural systems.
Harmful non-domestic substances in modern cities are neither decomposed nor accu-mulated, but simply removed (similar to domestic waste 150 years ago). The wastewater system therefore perfectly mirrors all human activity. One such example is the relatively high concentration of zinc in activated sludge, signifying our use of galvanised steel. Another example is the increasing number of synthetic hydrocarbons, which eventually find their way into the wastewater system. Since even the most advanced wastewater treatment plants are only designed to remove nutrients (measured in mg/l), removal of micro-pollutants (measured in ng/l) will necessitate ad-hoc additions with ever-increasing costs and energy demand.
The current technology is mostly a solution that lags behind the problem, rather than a pro-active approach. Many researchers are therefore questioning the sustainability of conven-tional systems, asking whether alternative solutions for sanitation and water drainage won’t improve the overall water cycle. However, if unambiguous criteria and reference cases are not clearly defined, and if sustainability is not understood properly, there is no reason to think that alternative systems will improve the state of the natural or urban environment.
In the following sections, the origins and consequent use of the concept ‘sustainable development’ and the more loosely used term ‘sustainability’ are discussed. It is argued that wherever ‘sustainability’ is not translated from its ideological context to a more prag-matic understanding of technical systems, opposing technologies could all be presented as ‘sustainable’. The term ‘sustainability’ has to be negated in favour of better design criteria, or indicators. These indicators will help to identify bottlenecks holding back real technical breakthroughs. Separate collection and management of both rainwater and urine are the two most obvious and promising new approaches. The separation of rainwater will improve the hydraulic performance of the urban water system, provided local treatment of rainwater is possible. The possible implementation of such techniques is not discussed in any depth. The separate treatment of urine, which contains the majority of nutrients, could improve the process performance. The potential impacts of separate urine collection on wastewater pro-cesses are discussed at length. The practical implementation of specific treatment propro-cesses for urine is also discussed in some detail. The conclusions have technical as well as social implications.
I.2 Origin and evolution of the concepts ‘sustainability’ and
‘sustainable development’
I.2.1 Background to the growing attention for ‘sustainable development’
For many people, life on earth could be described by poverty, malnutrition, diseases, pol-lution, living in squalor, lack of basic services, etc. This picture is broadcast daily by most television channels. For many people, on the other hand, life could be described by wealth, obesity, longevity, increasing consumption, living in the urban sprawl, a wide range of services, etc. It is generally believed that the world’s population will grow from 6 billion today to 8.5 billion3 by the year 2025. Furthermore, the spread between rural and urbanpopulations is now equal, but nearly all the future population growth is expected to be in the urban environments of developing countries. This is equivalent to building 8 new cities - of 10 million people each - every year. Consequently, resources will be exploited further and pollution will increase accordingly. This will add to the destruction of natural habitat and damage to ecosystems. Environmentalist movements4proclaim the dire consequences of the
seemingly unlimited human and economic growth to nature and mankind alike. According to the widespread media coverage, these and related problems seem to persist, or worsen.
In our era, these and other similar issues were discussed on the international podium for the first time in 1972 at the United Nations (UN) Conference on the Human Environment held in Stockholm. In the same year, the ‘Club of Rome’ created a computer programme to model future scenarios, based on extrapolations of quantities of natural resources, food production, population, etc., from the years 1900 and 1970. The resulting report - ‘Limits to growth’ - forecasts a collapse by the year 2100, due to three simultaneous crises, i.e. 1) overuse of farmland, 2) resources depletion and 3) intolerable pollution increases. The recommendations were for a drastic change in our production and consumption patterns, as well as for a campaign of active birth control.
The Brundtland commission introduced the concept of ‘sustainable development’ into the public arena. In ‘Our common future’, the report written by this commission for the UN in 1987, sustainable development was defined as: “...development that meets the needs of
the present without compromising the ability of future generations to meet their own needs.”
The UN conference on Environment and Development (‘Earth Summit’) in 1992 in Rio de Janeiro attracted more attention than its predecessor in 1972. Messages from the ‘Earth Sum-mit’ highlighted damage to the natural environment that undermines earth’s life supporting systems as a result of both poverty and excessive wealth. The resulting policy document - Agenda 21 - included general programme areas, such as changing consumption patterns, an integrated approach to development, promoting alternative energy sources, cutting down
31 billion = 1x109
on emissions linked to climate change, protecting and promoting human health conditions, etc. Special emphasis was also placed on the global scarcity of fresh water resources and preventing the pollution thereof.
The UN World Summit on Sustainable Development (‘World Summit’) in 2002 in Jo-hannesburg was a mega-conference, held under the all-inclusive banner of
People-Planet-Prosperity. The WEHAB initiative contributed to the ‘World Summit’ by focussing on
key areas (water, energy, health and environment, agriculture, biodiversity and ecosystems management). Most of these issues were subsequently incorporated in the Plan of Imple-mentation, in which financial and technical assistance are pledged to achieve Millennium Development Goals. One such goal (for example on water and sanitation) is “to halve by
2015 the proportion of the population without access to safe drinking water and sanitation”.
This means that almost 2 billion people will have to get access to some form of safe and functional toilets during the next ten years. This has to be achieved primarily through mobi-lization of international and domestic finance and capacity building for water and sanitation infrastructure. However, many interpretations of the Plan of Implementation are possible, as discussed further in the following paragraphs.
I.2.2 ‘Sustainable development’ is a political definition
Current literature and the Internet provide numerous definitions of ‘sustainable development’ (and the more general term ‘sustainability’). The definition as formulated by the Brundtland commission (encountered in many versions) is probably the most widely held view of what ‘sustainable development’ entails and has become canonical as such. This is problematic, because Brundtland’s definition is formulated in the tradition of modern environmentalism, which relies on essentially European cultural constructs of ‘nature’ and ‘wilderness’ (Allenby, 2002). Moreover, this definition implies that the needs of the present are known -in an era dur-ing which Europe lacks very little, for example -in terms of Maslow’s classical hierarchy of needs. By further implication, the global future should then be modelled on the current European consumption patterns, or needs, which are infinite, ranging from the most basic needs (e.g. “I need a toilet”) to any presumed need (e.g. “I think I need a Lear jet”5).
The problem regarding needs in connection with ‘sustainable development’ is worked out in more detail by Levit et al. (1998).
Another example is the World Conservation Union’s 1991 formulation of ‘sustainable development’ as “Improving the quality of life while living within the carrying capacity
of supporting ecosystems.” This definition runs into similar philosophical problems as the
Brundtland definition, because quality of life depends on a subjective personal and cultural experience, which cannot be quantified, or even standardised. These two definitions (there are others too) with their strong emphasis on needs and quality of life have placed the spotlight on human rights. The connection between the environmental lobby and a mostly humanist interpretation of ‘sustainable development’ shouldn’t be too surprising, since people like Hinchman (2004) argues convincingly that environmentalism is fundamentally a humanist
project. Both these definitions suggest an ethical element, including notions of fairness, rights, responsibility, etc. Although the UN policy documents go some way to identify a few of the most pressing needs that have to be satisfied to improve the quality of life of many people, no action in accordance with this mission will in itself guarantee sustainable development.
Whereas environmentalism used to be a counter-culture, it has now become part of the mainstream global politics and, ironically, lost most its former power of criticism. ‘Sustain-able development’ has therefore become the prime goal of environmentalism (Allenby, 2002). The elevation of ‘sustainable development’ from a contingent definition to an absolute end, allows it to go unchecked, because there is no politically correct antithesis. This involves the pitfalls normally associated with any ideology6. A parallel can be drawn between ‘sustainable
development’ and what Chalmers (1982) calls the “ideology of science as it functions in our society”. In much the same way that the slogan ‘scientifically improved formula’ is used to advertise anything from washing powder to motor oil, the term ‘sustainable’ is supposed to be associated with goodness and purity. However, the more practical meaning of ‘sustainable’ remains vague.
I.2.3 Various interpretations of ‘sustainable development’
The UN policy frameworks aim at directing a complex and ill-understood endeavour - ‘sus-tainable development’ - thus leaving room for many possible interpretations. For example, the ‘World Summit Plan of Implementation’ is mostly constructed with key phrases such as:
• “promote sustainable water use”
• “enhance the use of sustainable materials” • “intensify water pollution prevention” • “improve access to services”, etc.
development’ - almost everyone will agree that issues concerning People-Planet-Prosperity are somehow at stake in one way or another. However, where any one of the these ‘pillars of sustainable development’ is overshadowed by the importance of other issues, or simply neglected, one is likely to encounter yet a different image of what still goes under the term ‘sustainable development’. Table I.1 shows how different accents within different politico-socio-economic contexts may change the meaning of ‘sustainable development’.
In various interpretations of ‘sustainable development’ the less pressing aspects receive less attention. For example, prosperity isn’t a problem in Europe with good income parity, leading to a more enlightened view of ‘sustainability’ where quality of life has to be preserved alongside (or even through) the preservation of ecosystems. In contrast to this view, Africa, parts of Asia and South-America house the world’s largest wilderness areas, and don’t see preservation of eco-systems (other than for pure economic reasons) as important in compar-ison to the dire needs of the poor, leading to a stronger focus on development and poverty alleviation. The strong nationalist character of superpowers (e.g. USA and China) require that the wealth (power) of the nation, as more abstract entity, has to be increased within limits of available resources. The reader could surely provide other examples to further demonstrate the meandering meaning of ‘sustainable development’. Moreover, since the politicisation of ‘sustainable development’ most politically sensitive issues have disappeared from the agenda. A good example is active birth control, which was explicitly identified by most environmentalists (e.g. the ‘Club of Rome’), but which is absent from the UN policy documents on ‘sustainable development’.
Table I.1: Interpretations of ‘sustainable development’ according to cultural context7
People - Planet Planet - Prosperity Prosperity - People
Improve quality of life (through) preservation of eco-systems, to be
achieved mostly via
cultural and political routes (strong in Europe)
Expand wealth while
ensuring a sufficient resource base for future generations, to be achieved
via super-efficient
technologies (strong
in the USA and China)
Poverty eradication and better service delivery, to be achieved via capacity building and mobilisation of international capital (strong in Africa)
et al. (1998) illustrate the ulterior motives of stakeholders in the energy sector:
• Oil companies claim a lack of conclusive evidence for man-made climate change. • Meteorologists insist that more research is crucial to establish whether (and how much)
climate change is man-made.
• Advocates of nuclear power emphasise that their processes are free of CO2emissions.
• Manufacturers streamline the energy use and emissions related to their products in pursuit of ‘eco-labels’.
Engineers working in any part of the world, at large companies, or at research institutions, are likely to adopt the prevailing culture either through habit or through direct policy implemen-tation. Translating the rhetoric into ‘independent’ or ‘objective’ metrics is easier said than done.
I.2.4 The more sceptical views on aspects of ‘sustainability’
In contrast to the underlying motivation that inform the ideal of ‘sustainable development’, some hold the world (and the state it’s in) in a much more positive light, arguing that the problems of pollution and resource depletion are not only over-exaggerated, but also that the situation is in fact improving.
The ultimate resource, according to Julian Simon (1981) is human ingenuity. Perceived problems of ‘sustainability’ are accordingly best addressed by political and economic free-dom and not by restrictive conservation programmes, because “necessity is the mother of all invention”. Interestingly, the second edition of ‘The ultimate resource’ in 1997 shows that many of Simon’s 1981 predictions held true. This general outlook is found in different manifestations. One example is that resources are not brute facts of nature, but products of our imaginative use of the elements in nature. In this sense, resources are not; they become, as put by de Gregori (1987).
environmentalists discredited Lomborg’s questioning of their consensus (Lomborg not being an authoritative environmentalist), without going into much factual detail.
‘Dissidents’ are not readily accepted on public podia, because as Allenby (2002) points out, ‘sustainable development’ has become a forbidding ideology tolerating no criticism. One therefore feels some sympathy with Lomborg and others who argue that this polarisation and lack of open dialogue only strengthens their arguments. On the other hand, we need to acknowledge the reality of physical limits (e.g. thermodynamics, mass balances). Equally important are impacts on earth’s life support systems. Some groups (e.g. Giorgi et al., 2001) have extensively modelled regional climate on a global scale and see patterns emerging correlating with data, suggesting that earth’s climate is indeed changing due to greenhouse gas emissions. The significance of such predictions is normally highly controversial: “A system can only be known to be sustainable [or not] after there has been time to observe if the prediction holds true. Usually there is so much uncertainty in estimating natural rates of renewal that a simple prediction is always highly suspect” (Costanza and Patten, 1995).
This is especially important regarding potential triggers in complex natural systems, which - once pulled - could lead to irreversible and potentially catastrophic damage. Scientific knowledge is relatively scarce here, and the behaviour of many such systems, for example the earth’s climate and delicate eco-systems, cannot be predicted deterministically. These uncertainties make it seem reasonable (even wise) to err on the safe side of doubt, and clean up economical and technological systems.
I.2.5 A more pragmatic understanding of ‘sustainability’
It is widely believed that engineers are instrumental in creating solutions to the problem of ‘un-sustainability’, but this belief is rarely translated from its political context. Furthermore, neither the axioms of the environmental pessimists nor that of the optimists are of much use to the (research) engineer. In a sense, engineers should not choose in favour of either. This battle is fought on an ideological level where the truth content of opposing arguments becomes suspect. A more important issue is at stake here, namely: technical prowess alone will be insufficient - even futile - in solving the complex problems of an increasingly humanized world.
or natural science. What engineers need to do is to identify and separate the more implicit cultural/normative aspects in order to focus on the more technical/quantitative aspects. This is not at all to say that any of the cultural/normative aspects regarding issues of ‘sustainable development’ are less important, but that these aspects are far too important to be blindly co-opted as part of technological schemes. This means that the underlying motivation has to be made explicit8. At the same time, it has to be accepted that human and economic interaction
forms part of technological systems, and do not operate parallel to it. Engineers need to realise that cities, for example, are neither made up of static things, nor processes at steady state, but dynamic and complex systems in which engineering (material and energy flux) as well as human culture (flow of information, population profile, etc.) are equally important (Allenby, 2002).
Ayres (1998) and Ayres et al. (1998) argue from first principles that growth is limited, because exergy is used up in the production process (i.e. the ability to do work is not conserved). ‘Sustainability’ therefore involves “a radical dematerialization of goods and recycle of non-renewable material, driven by solar energy”. Ayres (1999) developed this idea further in terms of the ‘spaceship’ economy. Given enough exergy flux from an outside system (the sun) and a variety of sufficiently large waste stockpiles relative to the fraction active in the economy and the efficiency of waste recovery, a system can be maintained indefinitely. The role of the ‘spaceship’ to provide a living environment (mother Earth as
Gaia9) should not be smothered by technology, because technology might not be able to
replace these systems again. The size of the steady state economy is therefore limited. Within this context, sustainability can be achieved only where resources are not used faster than they can be regenerated, and pollutants are released to no greater extent than natural resources can assimilate them (Merkel, 1998). In section I.3, new developments and the growing attention for ‘sustainability’ in the field of sanitation and urban water systems are discussed. The tools available for the analysis and comparison of different systems - with specific reference to sanitation and wastewater systems - are subsequently discussed in section I.4.
8Whether one recognizes the value of the ‘natural’ environment as merely a life-support system, or whether eco-systems have intrinsic value (as seen from within a religious framework) could influence the choice and character of technological systems.
I.3 New developments in conventional and alternative
san-itation and urban water systems - arguments for and
against
I.3.1 Improvements and new developments in conventional sanitation
and urban water systems
Improvement in effluent quality from advanced wastewater treatment processes The basis for operating enhanced biological nutrient removal systems has changed consid-erably during the last 20 years. Whereas operation was previously based on empirical skills (black box art), operation can now be based on a much better understanding of complicated biological interactions (science).
The improvement of personal computers’ data processing capacity has enabled dynamic simulation of mathematical models, such as the family of Activated Sludge Models10. This
has provided a new basis for studying biological nutrient removal processes and to optimise processes. For example, Hao (2001) exclusively used model simulations in his study to optimise ‘sustainable biological nutrient removal processes’. The upshot of this advance, combined with improved sensors, is that biological nutrient removal processes can now be controlled almost fully automatically (e.g. Ingildsen and Wendelboe, 2003; Meijer, 2004). Model calibration and verification can now be used to streamline the operation of complicated activated sludge processes, such as the BCFS process11in which many recycle flows need to
be optimised, in terms of energy demand, utilisation of organic matter and, ultimately, effluent quality.
Even though not all wastewater is treated in state-of-the-art systems, a great improvement in general effluent quality has been achieved through the incremental improvement of treat-ment processes. Figure I.1 shows the improvetreat-ment in nutrient (N and P) removal of waste-water treatment plants in The Netherlands over the past two decades. The drop in influent phosphate load during the late 1980’s is due to discontinuing phosphate in washing powders. The increase in N in the first ten years represents the larger number of people connected to wastewater treatment plants, whose wastewater was previously untreated. During the same period, the number of wastewater treatment installations has decreased from 505 in 1981 to 384 in 2001, underlining the trend towards larger and more centralized wastewater treatment works.
Further improvement of the effluent quality of wastewater treatment (i.e. tertiary treat-ment or effluent polishing) has to be questioned in the light of other sources of pollution, such as diffuse pollution from agriculture.
10The family of IAWQ Activated Sludge Models now includes ASM1 (Henze et al., 1987), ASM2 (Gujer et al., 1995), ASM2d (Henze et al., 1999) and ASM3 (Gujer et al., 1999).
0 20000 40000 60000 80000 100000 1980 1985 1990 1995 2000 2005 0 4000 8000 12000 16000 20000 Year
Ntot influent Ptot influent
Ptot effluent
Ntot effluent
Figure I.1: Influent/effluent loads for total nitrogen (N) and phosphate (P) to/from wastewater treatment works in The Netherlands, 1981 - 2001, (CBS, 2005).
Minimising resource requirements: COD, energy, area
Although effluent quality has long been the prime focus of wastewater treatment, the growing attention for sustainability has triggered efforts to minimize the resources required in the treatment process. Most organic matter in wastewater has traditionally been oxidised, thereby reducing the potential of biogas production.
A better understanding of the cultures present in biological wastewater treatment and discovery of denitrifying phosphorus removal bacteria in many Modified UCT processes enabled further optimisation (Kuba et al., 996a,b). A lower COD/N ratio is required, because nitrate is reduced while phosphate is taken up, which means that more COD can be removed through primary sedimentation (depending on the required effluent quality). The efficiency of primary sedimentation can be improved through flocculation with addition of organic polymers, whereby 80% of the particulate COD is directly available for anaerobic diges-tion and therefore biogas producdiges-tion (Mels et al., 2001; van Nieuwenhuijzen, 2002). Apart from these incremental improvements in wastewater treatment, other innovations suggest that novel processes could play a major role within the existing infrastructure.
et al., 1998). This has the double advantage of a lower oxygen demand in nitrification (i.e. less energy) and a lower organic carbon requirement (e.g. methanol) in denitrification. The resulting SHARON12process has been implemented successfully on full-scale (Mulder et al.,
2001; van Kempen et al., 2001).
The discovery of bacteria capable of anaerobic ammonium oxidation put nitrogen removal in yet a new light. This process - Anammox - was described by van de Graaf et al. (1996), who showed that nitrite acts as electron acceptor for the biological oxidation of ammonium. This means that roughly half of the ammonium needs to be converted to nitrite, after which no organic carbon is required for nitrogen removal. Jetten et al. (1997) proposed the integration of SHARON and Anammox processes in municipal wastewater treatment within the existing infrastructure: Through high sludge production in the first stage of an A/B process, more bio-gas could be produced, while the amount of concentrated nitrogen in reject water is increased for subsequent treatment in a combined SHARON-Anammox process. The feasibility of the combined SHARON-Anammox process was demonstrated by van Dongen et al. (2001b,a). The prerequisites of high ammonium concentrations and a high temperature (> 30◦C) are less
crucial in a single CANON13 process, incorporating nitrifyers as well as anammox bacteria
(Hao et al., 2002; Sliekers et al., 2002). A good overview of the above and some related processes is given by Verstraete and Philips (1998).
Yet another innovation in dealing with ammonium nitrogen is that of the enhanced bio-logical augmentation of nitrifying organisms in side stream reactors. The overall nitrification process can be improved at high loading or low temperatures, or both through installation of the ‘BABE’ process in the sludge return line (Salem et al., 2002, 2003).
Secondary settling tanks contribute much to the physical footprint of plants, but is only one technique for sludge/water separation amongst others. Membrane bioreactors (MBR) retain all sludge without additional separation process units, and therefore enable compact processes irrespective of sludge age. This also allows for a superior effluent quality, especially in terms of suspended solids. The pore diameters of membranes typically vary between 0,1 and 1 mm for micro-filtration and between 0,01 and 0,1 mm for ultra-filtration, which does not allow pathogens through. Research at the first full scale wastewater treatment plant in the Netherlands, Beverwijk, has shown that proper pre-treatment of wastewater is vital and that additional expenses related to a MBR can be justified only when very strict effluent standards apply. A serious drawback of MBR is the power required for the trans membrane pressure. Early cross-flow membranes (also called inside-out filtration) had a typical energy requirement of 5 kWh/m3(van Houten, 2004), which is equivalent to a power
demand of around 60 W/person14. This power demand can be reduced by a factor of ten
in a configuration with internal or submerged membranes (outside-in), making better use of gravity and requiring a lower trans-membrane pressure. However, this set-up does not allow for as high a flux as with inside-out filtration and is more prone to fouling. Future MBR research should therefore also focus on preventing the bio-fouling of membranes. A
12Single reactor High activity Ammonium Removal Over Nitrite
13Complete Autotrophic Nitrogen removal Over Nitrite
comprehensive overview of MBR in The Netherlands is given in Bielars et al. (2005). Another different approach for end-of-pipe treatment is a sequencing batch reactor instead of a continuous reactor with external sludge retention. Granular sludge, which has much better sludge settling characteristics than normal activated sludge, can be used in sequencing batch reactors with short idle periods for settling. Further development of this technique could eventually make secondary settling tanks redundant, thereby reducing the physical footprint of wastewater treatment plants by 75% (de Bruin et al., 2004), without increasing the energy input.
Biological phosphate removal enables phosphate recovery
Rock phosphate is a finite resource, with proven resources sufficient for another 100 years of economic use (Driver et al., 1999), which means it has to be recycled. Since phosphate rock without trace heavy metals is becoming scarce, the phosphate industry in the Nether-lands (producing elemental phosphorus) pro-actively encourages the recovery of phosphate as secondary raw product (Schipper et al., 2001). Chemical phosphate removal in wastewater results in an insoluble and practically useless product (FePO4), but phosphate can be
recov-ered through biological phosphate removal. An overview of phosphate recovery techniques is given in Brett et al. (1997). Brandse and van Loosdrecht (2001) discuss the possibility of direct recovery from the BCFS process. Furthermore, the reject water from sludge treatment allows for recovery in side stream reactors, such as struvite (e.g von Münch and Barr, 2001). Calcium phosphate - Ca3(PO4)2- can also be recovered in the Crystalactor process (Piekema
and Giesen, 2001) that is perfectly suited for the thermal phosphorus production process. However, this is a relatively complex and expensive process and the current low price of rock phosphate doesn’t make it economically feasible. In a completely different approach, Jozuka (2001) suggests that it is possible to recover phosphate from sludge incineration ash in much the same way as conventional phosphate fertilizer production.
Sewer networks are still the most efficient transport system
Even though disconnection of wastewater and rainwater in separate sewers will increase the cost, the average costs in cities is still low in comparison to individual wastewater treat-ment systems (IBAs15) in remote locations where sewer connections are not feasible. The
purchase and installation cost of IBAs vary from €4,300 to €8,600 depending on the class (emission criteria), while the operation and maintenance cost vary from €65 to €450 per year. 100 94 75 55 31 14 5 0 20 40 60 80 100 1940 1950 1960 1970 1980 1990 2000 2010 Y ear C um m ul at ive pe rc en ta ge
Figure I.2: Cumulative percentage of the total length of existing gravity sewers (80,000 km) according to the decade of construction.
Overflows from existing and remaining combined sewers can also be prevented. Tcho-banoglous (1991) illustrate a range of mechanisms for controlling combined sewer overflows, such as flow regulators and outlets. However, they also suggest reducing overflows through source controls, separate stormwater and wastewater systems and temporary storage (in-system, surface and off-line).
ab Razak and Christensen (2001) demonstrate the improvement in a river through con-struction of a deep tunnel to intercept CSO’s for temporary storage. After implementation of the tunnel, faecal coliforms and other pollutants have drastically decreased in the receiving water. Many novel methods of emptying temporary storage basins are being developed, for example the use of a vacuum system (Dziopak and Niemczynowicz, 1999). The policy in the Netherlands, in accordance with the EU Water Framework Directive (see for example Zabel et al., 2001) has been to prevent all combined sewer overflows through construction of temporary storage basins.
Per capita investments and costs in conventional wastewater systems are reasonably low Although conventional wastewater treatment works are imposing, with a seemingly large area and energy demand, the picture is put in perspective when the total connected population
is considered. Advanced biological nutrient removal plants require a minute amount of external electricity (or mechanical power): 1-2 W/person (Nowak, 2003), which is roughly equal to the smallest LED standby lamp. The per capita area of treatment plants is also quite small: The new Harnaschpolder treatment plant, being built between Delft and The Hague, is located on 20 ha and will treat wastewater of roughly 1.3 million people, which is equivalent to 0.15 m2/person (van den Bor and van Bragt, 2005). In the period 2000
-2004, the approximate cost of wastewater treatment in The Netherlands was a very moderate €50/person.a. Nowak (2002) calculated the treatment cost in Austria between 1993 and 1998 to be roughly €35/person.a. Around 60% of the total cost was for the down payment of the civil and mechanical construction. Of this construction cost, the bulk is related to the mechanical and electrical installations, and only 10% of this cost is related to structural work and the value of the land. The other 40% of total costs was spent on operation and maintenance. Half of this cost was for personnel and administration. An earlier report from Balmer and Mattsson (1994) suggests that roughly the same order of magnitude and pattern of costs distribution apply in Sweden. The quantities quoted above suggest that there is, in general, little room for improvement. These quantities also set the boundary for novel treatment schemes.
I.3.2 Arguments for a complete systems change in urban water effluent
and sanitation
New approaches to old problems
In contrast to researchers and engineers improving the conventional wastewater system, a new school of thinking has emerged. A short overview is presented here to introduce the basic philosophy suggesting a complete change in the way we think about sanitation and urban water management. In order to focus only on the general trends, some ideas are excluded, and some perhaps overemphasised. For brevity, the following synopsis16is offered:
services of sanitation and urban water drainage, thereby avoiding water pollution rather than treating it. Household wastes should be collected separately according to their origin and composition: Toilet water contains almost all the N, P, K and pathogens and most of the COD (black water). Furthermore, most of the N, P and K (and a small amount of COD) in the toilet water originate from urine (yellow water), which contributes less than 1% to the total wastewater volume. Water from showers, baths, washbasins, etc. (grey water) contain little nutrients and only some organic material. Food rests and washing machine effluent contain a relatively large COD load. These different wastes should rather be treated at the source with more specific and efficient technologies. Source control will also allow for the treatment of micro-pollutants, such as artificial hormones and pharmaceutical end-products, which are not removed in conventional systems. Ultimately, sewer systems - which are capital intensive and difficult to maintain - will become redundant with successful source control technology. Alternative and decentralized systems can therefore reduce the cost of sanitation and urban water management and will be more sustainable overall.
Some of the more specific criticisms aimed at the alternative wastewater system and some proposed alternative technologies are briefly discussed below.
Sewers are expensive, unreliable and lags urban design
Many argue that the dilution of excreta with pure drinking water (and relatively clean water from showers or baths) endangers receiving waters. Even if complete purification were achieved at wastewater treatment plants (which is normally not the case), some untreated wastewater will still reach the receiving waters. Sewers usually leak, which means they pollute the groundwater of arid areas (exfiltration), while groundwater infiltration (in high rainfall areas) dilutes the wastewater even further. Combined sewers also fail to transport all wastewater during heavy rains, resulting in overflows. Sewers are also capital intensive (when built) and are responsible for a large part of the total cost of urban water management. Repair and maintenance of sewer systems are always disruptive.
Figure I.3: The dense cityscape of Sao Paolo, Brazil (left) and urban sprawl on the outskirts of Las Vegas, USA (right). The difference in the use of space is crucial in the planning and design of sewer networks and sanitation.
Black water collection and biogas production
Practically all pathogens in wastewater originate from faeces. An annual global death toll of 5 million people due to waterborne diseases is directly related to poor sanitation, i.e. untreated faeces (e.g. Otterpohl et al., 2003). Apart from this problem, the loss of organic matter and nutrients (through flush toilets) leads to the degrading of soil quality. Separate treatment and recycle of black water will also return some important micro-nutrients, such as Mg and Ca, together with N, P, K and S to soils where it originated, in this way closing the nutrient cycle. This can be done without introducing heavy metals into the food cycle, which is becoming problematic with industrial fertilizer. At the same time water pollution is prevented, rather than cured.
Otterpohl et al. (1999) highlights ten variations on the basic idea of separating toilet water from other household effluent water. A range of collection and treatment mechanisms ranging from high-tech to low-tech solutions are discussed. At the one end of the scale, vacuum toilets and pipelines can be used to transport waste with minimal water to a de-central treatment installation. Here, an anaerobic digester can convert organic material into biogas. After hygienisation the effluent can be used as a liquid fertiliser with a relatively high nutrient content. This concept has been installed at a housing complex in Lübeck, Germany (Otterpohl, 2002). On the other end of the scale are many low-tech options, such as waterless composting toilets, or desiccation toilets that are solar heated (in warm regions). The faecal matter from a urine separation toilet (i.e. ‘brown water’) can be treated in a ‘Rottebehaelter’ consisting of a faecal composting filter bag (Gajurel et al., 2003).
et al. (2003). The most efficient anaerobic biodegradability was about 60% of the influent COD, while 70% of the produced biogas was methane.
Yellow water to natural fertiliser: separate urine collection and treatment
It was said that toilet water contains most nutrients. Yet, within toilet water urine contributes the lion’s share of nutrients. With little variation in literature, it’s generally accepted that human urine contains approximately 80% of the ammonium, 50% of the phosphate and 70% of the potassium in municipal wastewater, but contributes less than 1% to the total wastewater volume (Larsen and Gujer, 1996; Fittschen and Hahn, 1998; Otterpohl, 2002; STOWA, 2002). Nutrients in urine can be used as a fertiliser, which will supplement and partly replace industrial fertilizer production (with some environmental benefits). Applying source separated urine to farmland to replace industrial fertilizer has been done mostly in Sweden (e.g Johansson, 2000), but also more recently in Germany (Simons and Clemens, 2003).
Liquid fertilizer can be produced in a moving bed biofilm reactor where half the ammo-nium is oxidised to nitrate, without pH control (Udert et al., 2003a). All organic matter is removed in this process, and the low pH in the final product prevents ammonium volatilisa-tion, which has to be kept in mind when urine is spread onto fields.
Lind et al. (2000) was able to recover phosphate in urine as struvite, while 65 - 80% of the ammonia could be recovered through adsorption on natural zeolites (especially clinoptilolite). Some potassium was also removed as struvite. This mixture is believed to be a good slow release fertiliser. A different management and transport technique is freezing of urine at -14◦C, followed by melting, whereby 80% of all nutrients can be concentrated in 25% of the
original volume (Lind et al., 2001). In contrast to freezing-melting, evaporation is another possible process in development for concentrating nutrients from urine, after stabilisation of ammonium with acid (Niederste-Hollenberg et al., 2003). The re-use of treated urine for flushing toilets have also been investigated (Guljas et al., 2004).
Grey water treatment
Rainwater management
Whereas classical urban hydrology sought to remove rainwater as quickly as possible, a new trend is to remove rainwater as slowly as possible. Local retention, open rain water drainage and retention ponds all form part of this rainwater management strategy.
Villarreal et al. (2004) reported on measures to reduce rainwater runoff from an in-ner city area. Accordingly, green-roofs can be effective at lowering the peak flow rate as well as the total runoff after storms, as implemented for example at a housing complex in Lübeck, Germany (Otterpohl, 2002). Retention ponds could reduce peak flows up to the 10-year rainfall event. Yet, many urban surfaces must remain impervious in order to function (e.g. roads). Different hardened surfaces have different pollutants and different runoff characteristics (Boller, 2004). Roads and parking cover 60 - 75% of hardened urban areas. Source control of rainwater runoff from these surfaces should include some form of treatment, such as barrier systems, adsorber systems to concentrate pollutants instead of contaminating natural soil, etc. Ideally, rainwater retention and infiltration should also be coupled to local water use.
I.3.3 Technological systems mirror value systems
We can loosely define two increasingly divergent schools of thinking, both portraying their ideas within the framework of ‘sustainable’ technology. On the one hand, established groups continue mostly with the incremental improvement of conventional urban water management systems. This includes two distinctly separate fields, one concerned with transport (sewer infrastructure) and one concerned with the end-of-pipe treatment process. On the other hand, new schools have developed, mostly in Western Europe, stimulating thought on alternatives for sanitation and urban water management. This group proposes a complete systems change, away from the centralised end-of-pipe techniques towards source control systems.
The motivation for implementing new techniques, and for further research, often contains a strong normative element relative to its factual content. A few examples of normative aspects encountered in various arguments are discussed below:
• “... one may consider the invention of flushing sewers as one of the greatest sins of engineers.” (Wilderer, 2004) and “The mixing of faeces with the big amount of wastewater is the crime that has so often been committed and has and does result in the death of so many million people.” (Otterpohl, 2003). There can be no doubt here about the ideological basis, or the ethical stance, underlying these statements. Regardless of whether one agrees or not, when these statements are encountered alongside factual and technical information, it becomes impossible to say where norms stop and facts start. To someone with a different sense of ‘sin’ or ‘crime’, these arguments are irrelevant. Convictions of this kind can therefore neither justify nor rebuke any technological system.
of ‘service water’ in a second network. Nolde (1999) described the success of de-central systems to treat relatively clean water (bathtubs, showers and wash basins) in order to recycle the water for flushing toilets in Berlin, a city relying on a rather scarce amount of surface water for drinking water. However, the large-scale supply of service water to a new neighbourhood in Utrecht via a second network attracted much attention in the Dutch press when the two networks were - by accident - interconnected and led to stomach disorders. Apart from this mistake, the dual network did not generate any of the promised savings with which it should have paid back the investment. Ironically, the required quality of service water is always still relatively high. The idea of dual water networks was shot down in other (potentially interested) Dutch cities as ‘just another hobby horse of the environmentalists’. Service water in The Netherlands -where water isn’t scarce - was quite simply not a good idea.
• The use of water to transport waste is often blamed for chronic water shortages. Yet, water is practically never lost unless through evaporation, which is not relevant in most wastewater systems. The quality of water deteriorates in sewers, but it can also be improved again (in the extreme to distilled water). After conventional treatment, the quality of water can also improve in natural systems, e.g. marshlands, engineered wetlands or in rivers. Wastewater is already being re-used in some industries. Wa-ter scarcity is therefore not only a question of availability, but also of applicability (Harremoës, 2002). Other and simpler solutions for reducing chronic water shortages include, for example, arresting the unaccounted for losses in drinking water supplies. • “Large scale centralised wastewater treatment plants require high investment, energy,
operating and maintenance cost” (Werner et al., 2003). As shown in section I.3.1, the energy demand of conventional wastewater treatment is almost insignificant. In contrast, a small electrical extraction fan - fitted with a composting toilet - easily requires more energy (per person) than the complete centralized biological treatment. The cost of conventional treatment was also shown to be very moderate (if compared to other infrastructure services). Furthermore, the main cost components of conventional treatment are personnel and the mechanical/electrical installation (Nowak, 2002). Both these cost components decrease with larger and more centralized treatment works. • “Current systems are going against the laws of nature, while ecosan [ecological
• Alternative sanitation (and ecosan) generally fit within the vision of ‘decentralized communitarianism’. As part of this philosophy, mankind should be more in contact with nature, because environmental problems originate from large-scale technological installations and urbanized capitalism. Accordingly, environmental problems have to be solved where people live within self-reliant communes (Allenby, 2002). The reality, however, is that people tend to specialise (they do not build their own houses, nor stitch their own clothes, nor grow their own vegetables, etc.) and wish for neither more contact with nature, nor for more contact with their own waste. The impact of ‘decentralized communitarianism’ will remain marginal while its appeal is limited to fringe communities. Improving the sustainability of wastewater systems for the environmentally unconscious is a more immediate and important challenge.
• In order to lower the total nitrogen effluent concentrations, many treatment plants have been expanded with post-denitrification units. These are normally (sand)filters where methanol is dosed as carbon source. Apart from the direct cost of methanol, as well as the indirect costs of resource depletion, other difficulties are associated with methanol dosing, including safety hazards. However, the overall effect of better effluent qualities from municipal wastewater treatment is rather small, when compared to diffuse pollution from agriculture, etc. One has to ask whether it’s still possible to see the trees through the forest of laws and regulations.
• Legislation in the Netherlands, for example, now prohibits any overflow of combined sewers. In order to comply with this, many retention basins have been built at great cost. The norm here is that a centralised sewer system is the only (affordable) techno-logical solution. In fact, other solutions exist, as has been shown. One has to admit that some inertia exists amongst engineers by reverting to conventional thinking as the only basis for problem solution.
The arguments and actions discussed above are weakened by ideological blind spots and are therefore unconvincing, or at best limited in their appeal. This in itself is not too much of a problem. However, these arguments are used at the peril of creating caricatures of any effort to improve the sustainability of the urban water system.
While the conventional sanitation and urban water system is by definition the most ob-vious choice for new developments, advocates of an alternative approach have to offer very good arguments to motivate a complete systems change. These arguments should consistently apply to alternatives as well. Some of the good arguments against the conventional system cut both ways, for example:
to the conventional system. However, no attempt is made to explain why these high-tech systems won’t be “out of order after a few years” when constructed in the ‘Third World’. In a similar tone, Larsen and Gujer (2001) refer to “the difficulties of exporting concepts of western urban water management technologies to the rest of the world.” Subsequently, they describe a conceptually complex design for a washing machine, with no effluent other than clean water and solid waste, but do not explain how this concept will be exported to the ‘rest of the world’. In comparison to these fantastic concepts, conventional wastewater systems are still relatively simple. Admittedly, neither of the two articles cited here explicitly states that the proposed alternatives will solve sanitation and wastewater problems in the ‘Third World’. Yet, in criticizing the conventional system on these grounds, an expectation is created for a proposal of viable alternatives. Having said this, it is rather ironic that biological excess phosphate removal was discovered in India (Shrinath et al., 1959) and that advanced biological nutrient removal (i.e. the Modified UCT process) was also developed in the ‘rest of the world’ before the concept was exported to the ‘West’.
• It is widely believed that about 5 million people die annually due to water borne diseases. Sewers are mostly blamed for this death toll. “In Africa virtually all sewage is discharged without treatment into receiving water bodies. The figures for Latin Amer-ica, the Caribbean and Asia are not much better.” (Esrey, 2002). This quotation, like those in the previous paragraph, carries the implicit message that alternative systems will somehow perform better. This belief is unfounded. For example, the lack of ownership and commitment was blamed for the “embarrassing” failure of an ecosan project at a school in South Africa (Austin, 2003). On the other hand, several activated sludge plants in Zimbabwe - being a poorer country still - were operated with a total nitrogen effluent concentration below 10 mg/l and total phosphate below 1 mg/l (Marks et al., 1987). Unless alternative forms of sanitation and urban water drainage become maintenance free and almost free of charge, i.e. available to the poorest of the poor without subsidy or assistance, such alternatives cannot be guaranteed against failure. If this could be realised, such systems would obviously be very popular in the rich countries too! Nevertheless, what is most important, is to realise that the criticism addressed towards the technology is misplaced: “Most analyses indicate that the ‘water crisis’ is primarily an institutional problem reflecting lack of capacity, finance and political will... rather than a water crisis as such.” (Brende, 2004). The fact that sanitation is inadequate in many parts of the world is not disputed. However, in keeping with the philosophy of controlling problems at their source, efforts to improve the world’s sanitation - and ultimately the fresh water quality - should be aimed directly at poverty alleviation and human resource development. This is obviously a daunting task, but other approaches are mostly symptomatic cures that will eventually prove unsustainable.
inflexible and leads to a natural monopoly, in which privatisation is only possible with much regulation.” (Larsen and Gujer, 2001). However, privatisation is only one model amongst others for service delivery and not necessarily the best. Private companies are ultimately concerned with making a profit and it could be argued that delivery of basic services should not be profit driven. For example, drinking water supply to some of the poorest communities in Southern Africa was privatised. A logical consequence was to turn off the water supply for non-payment. Subsequently, people unable to pay were forced to collect drinking water directly from (polluted) surface waters. The privatisation of water supply, supposed to improve service delivery, ironically led to sporadic outbreaks of cholera.
When European researchers introduce problems of the ‘rest of the world’ into the dis-cussion, media images and supposed cultural contexts of the ‘rest of the world’ are conflated with the understanding of technological systems. This is not surprising, since the same is done when the discussion is directed towards European problems, i.e. technology is always embedded in culture. However, the difference is that while the European context is well understood, problems in the ‘the rest of the world’ (and their origins!) are often not.
The views highlighted above show how the boundaries between environmentalism, envi-ronmental science and envienvi-ronmental technology are rather vague. Although the decision to study wastewater science and technology already implicates some belief that societal impacts on water should be mitigated through technological solutions, the underlying environmen-talism, with its implicit motivating influences, gives substance to such a decision. This leads Allenby (2002) to remark that: “Environmental science displays a highly normative penumbra...” There could be no doubt about this in the case of environmental technology, because if science were more concerned with the world as it is, technology is by definition more concerned with the world as we would like to create it.
On the one hand, one could ask whether good, objective and unbiased research results could be achieved when a research programme is already founded in some ideology of world-improvement, i.e. aimed at replacing certain existing and outdated systems with new and improved technology? On the other hand, is it wise - or more, is it justified - within the limited budgets of universities, and within the broader inequality between the rich and the poor, to investigate new techniques with only a mild interest in whether something interesting or useful will emerge? These questions are further complicated by issues regarding the rights of individuals to water and sanitation versus the common good, or issues of regional inequality, and whose responsibility it should be to put the wrongs right. This is treacherous terrain, not easily traversed. No attempt is made to address these questions in full. Harremoës (1998) has the following to offer:
“The role of the [environmental] engineer is to make available to society as many techni-cal options as possible and to put these options into the proper perspective in relation to the objectives of society. This includes making clear when technology alone does not provide solutions to the problems created by the development of society.”
