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close this bookGATE - 1/95 - Waste Water: Resource Management and Environmental Hygiene (GTZ GATE, 1995, 56 p.)
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View the documentSetting new priorities
View the documentKey technology of the future
View the documentAssessing and promoting anaerobic technology: A GTZ project
View the documentHealth projects when Cholera Rages
View the documentUsing of root-zone wastewater treatment plants
View the documentLocal sewage disposal in Germany: the pros and cons of privatisation
View the documentCan we learn from the past?

Setting new priorities

Unsatisfactory wastewater disposal endangers health and is jeopardising the vital resources of water and soil

Developing countries must invest more funds in the disposal of liquid and solid waste. The return of epidemics which we thought belonged to the past can also be attributed to the fact that this part of public infrastructure has been neglected particularly in urban agglomerations. Dr. Klaus Erbel, Head of GTZ's Division "Water, Waste-Management and Protection of Natural Resources" explains to gate how this must be a key activity of development cooperation.

gate: Even the United Nations Water Decade did not trigger off a decisive improvement in wastewater disposal in many developing countries. 90 to 95 % of all communal wastewater is discharged unpurified into rivers and lakes. The pollution load has been overstepped in many instances. Has the construction of sanitation facilities been underrated in infrastructural investments by the affected countries and in bilateral and multilateral cooperation for development?

Erbel: We repeatedly observe that governments and local authorities in many countries only place a low priority in investments in sanitation infrastructure. This applies both to wastewater purification and to solid waste disposal. Whether minister or mayor, it is always better for his/her image to inaugurate a new road or new waterworks rather than to celebrate the completion of a certain number of kilometers of sewerage canals or latrines.

Development cooperation is usually a response to applications for projects, and so it is difficult to instigate action, even though we are of the opinion that the cleaning up of waters and the reduction of health risks should have highest priority. Some newly industrialising countries are beginning to rethink matters.

Too expensive

gate: What is the role of appropriate technology in wastewater disposal? Centralised plants like those in urban agglomerations in industrialised countries can hardly be a model for countries of the South.

Erbel: Centralised systems which collect flushed sewage are not always appropriate, simply because they have become far too expensive in most towns. This is particularly the case in regard to the so-called flushing or mixed sewage system containing both rain water and polluted water, rather than to the sewage treatment plants themselves. Houses usually have to be connected to the drinking-water supply in order to have enough water to flush away the pollutant substances. In many (arid) countries such water connections don't exist. Appropriate technology in this instance consists of multi-chamber cesspits which are regularly emptied and in which a large amount of the wastewater (e.g. washing water) can seep into the underground without causing any extensive environmental pollution.

"Polluter pays"

gate: Enormous amounts of money are necessary for sewage disposal. How can this money be raised? How can the "polluter pays" principle be applied in countries of the South when it is often difficult to apply in industrialised nations?

Erbel: In view of the limited funds available from development aid donors on the one hand and the countries' own governments and authorities on the other, there is no medium- or long-term alternative to the principle that whoever discharges wastewater into the system also has to pay for the treatment of this water.

We recommend that, first of all, the "polluter pays" principle should apply to large and small-scale industries and that information and sensitisation campaigns should raise the individual citizen's awareness that they also will have to contribute to the protection of their own environment via charges coupled to the water supply tariffs.

Successful project

gate: Can you state any examples of successful projects in which GTZ has cooperated with developing countries on wastewater treatment? What was the reason for the success? What conditions were right?

Erbel: An example of a successful project in TC Advisory Services on wastewater is the support for the "Office national de l'assainissement" (ONAS) in Tunis. The framework conditions were indeed very favourable:

Both the government and also the public were aware of the problem of protecting the environment, above all the water resources, because Tunisia earns much of its foreign exchange from tourism and tourism demands clean beaches and safe water.

Steady economic growth and substantial financial support from numerous multilateral and bilateral donors made it possible to invest in environmental protection.

The ONAS' personnel is very motivated. The low staff fluctuation rate means that the transfer of knowledge through our project and the contents of this transfer could be well-accepted and continuously applied.

Project success is also due to the fact that the partner organisation was an active and constructive partner in drawing up solutions. Training of expert personnel was supported by cooperation with the local engineering college (EcNational des Ingeurs Tunesiens ENIT). The long-term assignment of highly qualified experts from Germany and the development policy sensitivity led to the development of a situation of trust and confidence right up to ministerial level. The resulting political support meant in turn that the project received all the necessary manpower administrative and financial support it required.

gate: Faced with the global shortage of water, wastewater has become a valuable raw material which must be recycled. What action is necessary to this end?

Erbel: I feel it is particularly necessary to recycle purified or at least partly purified wastewater for use in irrigation and for re-use in industry. Irrigated farming systems using recycled water must, however, continuously monitor the quality of water, and this is not always possible in many countries.

Focus on urban regions

gate: Industrial expansion is causing additional sewage disposal problems in urban conglomerations. Should development cooperation set a new priority here?

Erbel: In my opinion, environmental problems in many urban conglomerations are taking on such proportions that development aid organizations will soon receive a flood of applications for support. Just a few cases of epidemics due to inadequate waste disposal are enough for this to take place. Cooperation for development has two choices: either to capitulate in the face of the dimension and frequency of such problems and the funding they demand, or, indeed, making it one of its key activities. Rural development has been a high priority area to date. But it is now becoming clear that these approaches have not led to any serious reduction in the rural exodus or halted urban growth. For this reason alone, cooperation for development must begin to address the issue of the quality of life in large conglomerations, an approach which will probably be more effective in reducing the poverty of wide sections of the underprivileged population. Numerous third world countries will have to assure better living conditions for the urban population, which bears the main brunt of national productivity, with or without external assistance.

Rm

Les investissements dans le domaine de l'cuation des eaux us figurent aux tous derniers rangs sur la liste des prioritde nombreux pays en dloppement. Dans l'interview donnau GATE par Klaus Erbel, Chef de division a GTZ, celui-ci pronostique un accroissement des probls environnementaux dulant de systs d'assainissement dcients dans les agglomtions urbaines des pays en dloppement. C'est pourquoi, ce secteur devrait devenir un domaine d'action prioritaire de la cooption au dloppement.

Extracto

En muchos paises en des arrollo, las inversiones en eliminacie aguas residuales ocupan uno de los os lugares en la lista de prioridades. Klaus Erbel, jefe de divisie la GTZ, pronostico en una entrevista con gate que los problemas ambientales derivados de deficiencias en materia de eliminacie aguas negras aumentarian en los grandes centros urbanos de los paises en desarrollo. Por lo tanto, deberia darse mayor prioridad a este sector en el marco de la politica de desarrollo.

Key technology of the future

Recent trends of anaerobic technology for the disposal of solid and liquid waste by Hartlieb Euler and Andreas Krieg

For many years the rationale behind using biogas technology (or anaerobic technology) in developing countries was the search for renewable sources of energy. Nowadays environmental protection aspects are the significant factor. A technology which previously just filled a "niche" is now becoming a key technology for integrated, solid and liquid waste-treatments concepts both in industrialised and developing countries.

The dominating motive behind using biagas technology was to produce energy and fertiliser on a decentralised basis for small farms. The initial dissemination programmes assisted by German development cooperation therefore centred on adapting the technology on site for agricultural biogas plants.

Environmental and disposal aspects were only exceptional priorities. Projects for domestic and industrial wastewater treatment rarely applied the anaerobic option.

Over the course of the years additional side effects of farm-based facilities have become significant advantages of anaerobic technology in a rural environment: improved hygienic situation; reduced work load for women and children who are traditionally responsible for fetching firewood; smoke-free kitchens reducing respiratory and eye diseases; orderly disposal of human faeces via latrines in households, community buildings and institutions, lowering the incidence of worm and parasitic diseases which are a common cause of death in many countries.

Experiences from German development cooperation have shown, however, that small farms do not possess sufficient capital to invest in biogas plants to replace firewood without bringing any increase in farm income. Since the mid-1980s, therefore, successful dissemination concepts for small scale plants have been coupled with loan programmes and/or subsidy programmes (see "Lessons from the Thai-German Biogas Programme", gate 3/94).

Planning, construction, maintenance and repair work nowadays is done by specialised, trained private contractors who guarantee the longterm success of the technology

Since the 1980s, constructing biogas plants is no longer a leisure time activity for amateurs. Quality certificates, training certificates and operation licences, detailed building plans and long-term guarantees by experienced engineers and private sector companies have upgraded the image of anaerobic technology even in the small-scale agricultural sector.

Biogas plants for agroindustries

The original priority goal of biogas technology - to improve the living conditions of small farmers - has been replaced by a more pragmatic orientation to environmental and infrastructure-policy goals.

At the same time, integrated rural programs now combine composting, water supply, other renewable energies, agricultural production and processing with anaerobic technology, into a mix which fits the specific location.

For the past five years biogas plants are also becoming a regular feature on larger farms (with 50 to 5000 heads of cattle equivalents) and agroindustries (of all sizes) in industrialised countries, particularly in the food processing industry.

In Europe this trend has been largely influenced by environmental legislation, in many other countries by protests and actions by people living in the neighbourhood of these operations.

Series production

Higher electricity prices for feeding electricity from highly efficient co-generation plants into the public grid have become attractive economic incentives for these industries. In the meantime, high returns on investment have become the decisive factor for investment in many countries. The technical reliability and productivity of the anaerobic plant can be guaranteed now.

The technology and marketing of agroindustrial plants and large-scale biogas plants has greatly changed worldwide within the last few years. At the end of the 70ies traditional manufacturers of industrial machinery had only limited success in trying to introduce the technology. The market rarely operated up to anything beyond highly subsidised or often questionable prototypes.

In the meantime, an agriculture based plant technology, often derived from silos or gully container technology, combined with efficient power and heat aggregates have conquered the markets. The main building elements are now made in series production. In particular technical accessories such as gully pumps, mixers, heating and insulation, and equipment for sulphur purification and power-and-heat combination (i. e. co-generation) are almost completely standardised, allowing modular construction with prefabricated elements. This is essential for the success of anaerobic technology which can be adapted individually to the needs of each farm, region or country, using standardised modules which are far more advantageous from both the cost and technical viewpoints.

Co-fermentation system

In Germany in particular, anaerobic technology has opened up new prospects for disposing of agricultural and domestic waste thanks to the co-fermentation system. Co-fermentation means that agricultural waste substances, gully and solid manure is fermented together with organic waste and wastewater from private households (garden waste and grass from lawns, market waste, sewage) and with liquid and solid waste from abattoirs, the beverage and vegetable preserving industry, breweries, dairies, sugar starch and alcohol production, kitchens and canteens, etc.

The successes achieved are founded both on the disposal fees which the agroindustry and local authorities have to pay to the operator for dumping organic solid waste or treating organically polluted liquid waste. On the other hand, the operators of the plant can use the biogas production to generate electricity which is then fed into the public grid.

Because of the different sources of the material being fermented and their possible pollutant contents, some ecological misgivings can be raised against this disposal method. To avoid soil contamination, the substrate must first undergo a detailed analysis before it is used as fertiliser. Furthermore, the transport of materials to be fermented should not require more energy than that which will be generated by fermenting it.

Wastewater technology

The co-fermentation system reactivates links between agricultural and domestic disposal of liquid and solid waste. Indeed, the anaerobic technology for agriculture was developed in the 1940s in Europe at local authority wastewater treatment level. If only for cost reasons local authorities and agroindustries often copy parts of the processes that agriculture develops and uses to treat solid and liquid waste.

On the other hand, factory farming operations which produce large quantities of organically polluted wastewater each day benefit from using the efficient technology systems operated in municipal wastewater treatment: The "Upflow-Sludge-Blanket" known as USB is one example, now broadly applied. This system feeds the wastewater to be treated into the bottom of the reactor and when flowing up through a bacterial zone the organic parts are rapidly fermented. The purified water can than be discharged into lagoons or rivers .

Municipal water treatment technology

Shortage of public funds has impacted on municipal sewage treatment plants worldwide which traditionally use high-cost and energy intensive (aerobic) water treatment technologies. Centralised wastewater collection and treatment solutions with large-scale sewage networks and centralised sewage treatment plants can only be an economically viable option when a sufficient volume of wastewater is collected.

Numerous promising examples of small and medium sized anaerobic purification plants for domestic, institutional and village waste are now on the market. Smaller urban centres with 5,000 to 100,000 inhabitants however still require more effective, locally-appropriate technology standards - also for anaerobic purification systems which are economically viable and guarantee long-term operating safety.

Municipal solid waste

In warmer climates in particular, centralised sewage systems can cause considerable hygienic problems.

The local ecological water balance also can benefit from decentralised nature based approaches in rural areas. More than 50 % of sewage treatment plants for human excrements in industrialised countries are nowadays equipped with anaerobic purification stages for sludge treatment.

In developing countries anaerobic wastewater treatment processes are installed because they require less equipment and less costs - and consequently save foreign exchange.

Problems arising from the lack of skills and training are met on the management side, however, particularly in remote areas.

In industrialised countries with overflowing waste dumps and emission problems, anaerobic technology is frequently used to supplement or replace aerobic solutions.

This applies both to dumps with mixed waste which collect, purify and use the small parts of the gas obtained, and also to centralised composting concepts for organic waste.

Many towns collect organic waste in so-called "bio bins" from households, markets, gardens and start to treat it in anaerobic reactors as well. The process products are gas and water which is recirculated and often retreated, and a stabilised and valuable residue which can also be used as fertiliser or for soil structuring.

Modern lower-cost fermentation plants for solid communal wastes are basically advanced models of the an aerobic plants used in agriculture. They require only limited industrial processing and control technology. Depending on the amount of disposal fees involved, anaerobic and combined aerobic/anaerobic solid-waste treatment plants are considered a fundable and quite viable investment particularly in European countries - the bioComp system of the T.B.W. Company in Frankfurt is one example (see photo).

Municipal waste treatment using the biocomp procedure developed by T. B. W. is based on combined anaerobic/aerobic composting. 13,000 tons of organic municipal waste are processed in this plant each year. The course material is forwarded to the (aerobic) composting plant The fine material is mixed with the liquid separated from the digested sludge and forwarded to the first fermentation stage. It takes approx. two weeks for the slurry to pass from the top to the bottom of the first-stage fermentation reactor. The active sludge then proceeds to the second reactor via bottom drain. When it passed out of this reactor at least 60 percent of the substrate's original organic content has bean converted into biogas. The digested sludge is press-dewatered and sent for composting. Two thirds of the press liquid returns to the process. The rest undergoes partial mechanical-biological purification. Figure: Awater/T.B.W.


Biocomp - combined anaerobic/aerobic composting

Integrated approaches

The interested public, waste experts and also political decision-makers in industrialised and developing countries all have limited knowledge of the potentials of anaerobic technology for waste treatment and how it can be combined into integrated environmentally friendly solutions.

Inadequate legislation, lacking control capacities and the arguments of industry against what they call excessively high investments in environmental protection are further constraints.

Growing interest

The high-energy and often high-cost methods traditionally used especially in warmer climates are often preferred by disposal plant builders from industrialised countries because they are more experienced in this area. Considerable efforts are needed in order to obtain inter-ministerial and inter-sectoral approaches in the future.

The anaerobic process is still often considered as a second choice for the treatment of liquid and solid waste. For economic and ecological reasons, however, it will only be a question of time before it is a must to select the economically and ecologically optimal technology mix.

The growing interest by developing countries, by sectoral departments in technical cooperation organisations and at national and international conferences proves this trend.

· The initial costs when introducing the process are still the chief investment constraint to anaerobic wastewater and solid waste treatment in agroindustry. Unless legislative standards are established on the basis of the "polluter pays" principle and unless public pressure increases in particular the industry will continue to delay its treatment effort.

· To treat human faeces it is important to disseminate those standardised systems which are easy to maintain.

Personnel training and sensitisation of the population are equally important.

· Awareness must change. «Waste is rubbish" must be replaced by "Waste is a valuable material". Savings in raw material resources will then take on an economic value.

· Operator and cooperation models of financing are in sight: Plants are prefinanced from the expected operational benefits to the companies, the energy saved and produced and other process products which are being retrieved.

Rm

La technologie du biogaz pourrait devenir une technologie clans les strates d'assainissement intCeci s'applique de la m mani aux pays industriels et aux pays en dloppement. L'auteur prnte des exemples et applications provenant de l'agro-industrie et des communes. Les possibilitoffertes par la technologie du biogaz sont toutefois encore trop peu connues a fois des ingeurs et des politiciens.

Extracto

La produccie bogas podria convertirse en una technologia clave para las concepciones integradas de eliminacie aguas residuales, tanto en los paises industrializados como en el Tercer Mundo. El autor presenta ejemplos de aplicacin la agroindustria y las comunas. Sin embargo, existe un dcit de informaciobre el biogas, tanto entre los ingenieros como entre los
politicos.

Assessing and promoting anaerobic technology: A GTZ project

The highly complex wastewater purification processes used in industrial nations are often not feasible in countries of the South. Systems are needed which are easy to operate and maintain, financially viable and compatible with the environment.

Depending on the local situation anaerobic technology could be - often in combination with other treatment systems - an alternative option to meet these requirements.

In industrialised nations too, this technology is be coming increasingly significant in treating wastewater with a high degree of organic pollution.

First experiences have shown that decentralized anaerobic treatment of liquid and solid waste from households and industry is a low-cost, energy-friendly method particularly suitable for warm climatic zones. No systematic basic criteria are on hand, however, to assist decision-making by planners, investors, operators or supervising bodies. The GTZ project operating from April 1995 to August 1997 aims to work out such criteria.

The goal of the supra-regional project is to compile the potential applications of anaerobic technology used to purify and treat domestic and industrial solid and liquid waste. Together with technical components priority is given to economic factors and regulative policy issues.

The project is comparing the performance parameters of anaerobic technology with those of other technologies and in combination with other wastewater treatment procedures, and critically analysing the process and operating problems encountered in existing plants.

The findings are to be useful decision-making aids in order to improve the treatment of liquid and solid waste in future waste water projects.

Anticipated results:

1. An overview of practical experiences so far available which will be assessed in relation to the given framework conditions.

2. Initial criteria for the use of anaerobic technology, including the necessary technical adjustments on the basis of practical operations.

3. Investigations into the problems met and optimal operation of existing plants in two countries.

4. Institutions to implement measures at national level will be identified and assisted.

National and supraregional organisations in selected project regions (focusing on Latin America) are cooperating the project. Initial findings and publications are scheduled as from 1996.

Contact person at GTZ:
Dr. Dieter Mutz
Division 4140
P.O. Box 5180
65726 Eschborn
Tel +49-6196-79-1277
Fax +49-6196-79-6105

Health projects when Cholera Rages

Hygiene must have higher priority by Peter Weis

The outbreak of the cholera epidemic in Peru in January 1991, the first such epidemic on the American continent in the 20th century, drew public interest again to this classical pest which has plagued poor underprivileged people the world over for centuries. Such a cholera epidemic which attracts great attention by the media obstructs our view for the fact that even when there is no cholera, diarrhoeal diseases join acute respiratory diseases, measles, malaria and tuberculosis in being the major causes of sickness and death in developing countries.

World-wide, one infant in four of those dying under 5 years of age dies from a diarrhoeal disease. The vibrio cholerae pathogen only plays a minor role. Viruses, particularly rotavirus, are the main cause of diarrhoeal diseases, followed by bacterial pathogens and parasites (Table 1).

Table 1

Causes of diarrhoeal diseases

· viruses: rota virus, adeno virus, enterovirus (polio, coxsackie, etc.)
· bacteria: salmonella, shigella, yersinia, campylobacter, vibrio cholerae, pathogenic, E.coli
· parasites: entamoeba histolytica, giardia lamblia, cryptosporidium

Experience from history

Long-term monitoring of diarrhoeal diseases on a global scale shows that despite world-wide efforts, the estimated number of new cases per year remained constant at 1 billion cases annually between 1980 and 1990, although the annual diarrhoeal specific mortality in the same period fell from 4.6 million to 3.2 million (Bern et al. 1992). It can be concluded that c. 0.3 % of all patients with diarrhoeal diseases die from the disease. Morbidity and mortality rates are not evenly spread.

They cluster quite characteristically in children in their first years of life, reaching a maximum in infants aged 6 to 12 months (Table 2) who average 5 diarrhoeal episodes per year and in conditions of poverty and particularly susceptible groups such as pregnant women, malnourished and undernourished people and individuals with a compromised immune system (e.g. AIDS patients) .


Table 2: Estimated median diarrhoeal morbidity. For under-5-years old, based on the results from 18 studies in developing countries.

Since the 19th century, the public health sector and also water engineers around the world assumed that improving the quality of drinking water could make a significant contribution to reducing diarrhoeal discases and consequently raising the health status of the population (Kolsky, 1993). From the historical viewpoint this opinion was underlined by the work of John Snow on the cholera epidemic in London in 1854 (Hennekens, 1987).

Thirty years before Pasteur and Koch brought out their germ theories, Snow, a practising physician and epidemiologist, claimed that cholera was transmitted by contaminated water. He put forward impressive epidemiological data to prove this: People whose water came from the Southwark and Vauxhall Company, which pumped non-filtered river water from the Thames into the water supply system, were subject to eightfold the risk of dying from cholera than people whose water was pumped by the Lambeth Company, which took water upstream from London and passed it through sand filters.

Experience from the cholera epidemic in the German city of Hamburg in 1892 strikingly confirmed John Snow's findings: while Hamburg was hit by a cholera epidemic causing high mortality, the then neighbouring town of Altona which was already using sand filters was largely spared from the epidemic.

Indeed, improved drinking water supplies in London and Hamburg could have avoided many cholera-induced deaths; but this should not distract from the fact that most diarrhoeal diseases including cholera are not transmitted solely by drinking water. This was proven most impressively 140 years after John Snow in 1991 in Trujillo/Peru (Swerdlow et al., 1992). The public water supply system was indeed contaminated with cholera germs - not least because the water was not chlorinated - but the highest risk for the individual to be hit by the cholera disease was inadequate personal hygiene (for example dipping hands into the drinking water container) and from eating unhygienically prepared food at fiestas (Table 3).


Table 3: Univariate analysis of risk factors for Cholera among patients and controls, Trujillo, Peru (1991)

The observations made by Snow right through to Swerdlow allow the conclusion that the factor "water" and the problem of diarrhoeal diseases link up via two different mechanisms (which also require different intervention strategies): The infection can be transmitted by a direct water supply (water-borne) or the infection can be transmitted because of the lack of water for personal hygiene (water-washed).

The problem is that the water-borne and water-washed categories are not mutually exclusive, and all faecal-orally transmitted diseases can be passed on both by waterborne and water-washed means and the percentage of each type of transmission depends not only on the etiology but also epidemiological and socio-economic factors and can greatly vary from case to case. Faecal-disease-bearing germs can directly reach the host by water (waterborne) or via the hands, food, flies or from the fields (Table 4). The problem of controlling diarrhoeal diseases is one of assessing the extent to which the frequency of diarrhoeal diseases could be reduced through an improved quality of drinking water vs. greater quantities of water of unimproved quality parallel to hygiene education measures (e.g. water and soap!).


Table 4: Multiple Transmission Routes

Routes of possible transmissions of disease from faeces. PB, primary barrier; SB, secondary barrier. Source: Transactions of the Royal Society of Tropical Medicine and Hygiene, Vol 87, p S3/44, 1993. Figure: M. Sehring

Water quantity and hygiene education

An analysis of 53 intervention programs (Esrey et al., 1985) found that better quality water brought about a 16 % average reduction in the frequency of diarrhoeal diseases, whereas improving the availability of water leads to an average reduction of diarrhoeal diseases of 25 %. Even if more strict selection criteria were applied (see Table 5) the results remain the same Increasing the quantity of water has a greater influence on preventing diarrhoeal diseases than improving the quality. Hygiene measures and hygiene education which should be accompanied by a greater availability of water in conditions of poverty experienced in many developing countries, should concentrate on the following four measures (Cairn-cross, 1990):


Table 5: Median reductions in diarrhoeal disease morbidity from improvements in one or more components of water and sanitation

- washing of hands
- washing of food
- washing of cooking utensils and crockery
- disposal of children's stools.

In an outbreak of bacterial dysentery, a 69 % reduction in secondary infection was possible thanks solely to a massive effort to promote washing hands with soap (Khan, 1982).Thesamemeasure, but not using soap, in a control group led to a far lower reduction in the incidence of diarrhoeal diseases. To control diarrhoeal diseases, two basic strategies can be taken:

· Reduction of diarrhoea-induced mortality by improved case management, particularly oral rehydration therapy (ORT), promotion of breast-feeding, antibiotics (in strictly indicated cases, particularly in cases of bloody diarrhoea) and specific care of disease episodes for people suffering from malnutrition and undernutrition. Efforts to promote the care-seeking behaviour and improved access to primary health care services are also of substantial importance if mortality rates are to be reduced.

· Reduction of diarrhoea-induced morbidity by improving the quality and quantity of water, the sanitation conditions, promoting health and hygiene conditions, empowerment of women and, finally, promoting family planning, because fewer children, born at greater intervals suffer from far less episodes of disease and diarrhoea.

Conclusions

1. To control diarrhoeal diseases a sufficient quantity of water is often far more important (or at least equally important) as improved quality of water. Where diarrhoea is endemic and overall faecal contamination is high, it is reasonable to focus on quantity rather than quality of water.

2. The significance of water and wastewater measures to control diarrhoeal diseases differs greatly from region to region and in line with the corresponding etiology and epidemiologic situation.

3. Hygiene behaviour is often a decisive determinant for achieving a sustained Improvement in the control of diarrhoeal diseases and should receive far more intensive pro motion (health and hygiene education in the scope of primary health care).

4. The established programmes to control diarrhoeal diseases operated both by the WHO (Division of Control of Diarrhoeal Diseases) and also by the GTZ in the framework of district health projects still focus too exclusively on case management particularly using oral rehydration. It is however acknowledged that these measures were of paramount importance in reducing the global diarrhoeal-specific mortality over the last decade.

References:

Bern C. et al.: The magnitude of the global problem of diarrhoeal disease: a ten-year update. Bulletin of the World Health Organization, 70 (6): 705-714 (1992)

Cairncross, A.M.: Health impacts in developing countries: new evidence and new prospects. Journal of the Institution of Water and Environmental Management, 4,571-577

Esrey, S.A. et al.: Intervention for the control of diarrhoeal diseases among young children; Improving water supplies and excreta disposal facilities: Bulletin of the World Health Organization, 63,757-772 (1985)

Hennekens, Charles H.: Epidemiology in medicine, p. 5-8 (1987)

Kawata, K.: Water and other environmental interventions the minimum investment concept. American Journal of Clinical Nutrition, 31, 2114-2123 (1978)

Khan, M.U.: Interruption of shigellosis by hand washing. Transactions of the Royal Society of Tropical Medicine and Hygiene, 76,164-168 (1982)

Kolsky, P.J.: Diarrhoeal disease: current concepts and future challenges: Water, sanitation and diarrhoea: the limits of understanding. Transactions of the Royal Society of Tropical Medicine and Hygiene (1993) 87 Supplement 3,43-46

Swerdlow, David S. et al.: Waterborne transmission of epidemic cholera in Trujillo, Peru: lessons for a continent at risk; The Lancet, Vol 340: 28-33 (1992)

Rm

Pour prnir les des de maladies diarrhues comme le chol, de nombreux programmes de dloppement rise jour ont exerceur effort en direction d'une amoration de la qualite l'eau. Des des scientifiques auxquelles l'auteur fait rrence montrent toutefois que l'accroissement des disponibiliten eau,liescampagnes d'cation en mati d'hygi, semble reprnter une strate plus porteuse. L'auteur est d'avis que les programmes de santevraient e modifin consence.

Extracto

Hasta la fecha, uno de los instrumentos mas importantes que han utilizado los programas de desarrollo para prevenir epidemias de enfermedades diarreicas tales como el colera ha sido mejorar la calidad del agua potable. Sin embargo, los analisis cientcos presentados por el autor indican que podria ser mas efectivo aumentar la oferta de agua y realizar simultanemente programas de educacion higico-sanitaria. Seg autor, convendradaptar los programas de salud a estos nuevos conocimientos.

Using of root-zone wastewater treatment plants

Successes achieved with a pilot plant in Berlin by Harald Kraft

Decentralised wastewater treatment systems have been tested in Germany for some years now. They are feasible solutions for the treatment of domestic wastewater. Our author describes a plant in Berlin and how a root-zone wastewater treatment plant can be used in urban conglomerations.

Five systems

Using plants for wastewater treatment has been further developed and tested since the mid 60ies. There are five major systems: (see figure 1).


Wastewater treatment using plants

· A flooded basin fully covered with helophytes (i.e. plants which grow on swampy soils) with a horizontal percolation (or flow).

· Rhizomes (shoots) of helophytes attached to swimming grids and hanging freely in water.

· Root-zones of soil filters covered with helophyte growth, and vertical percolation (or flow).

· Root-zones covered with soil filters with helophytes with a vertical percolation.

· Layer of fine gravel with helophytes on the soil and horizontal percolation.

The systems can be combined in numerous ways. There are hardly any limits using plants to purify wastewater either before discharging it into a watercourse, or purifying it in the body of water itself.

Nowadays plant-based sewage treatment facilities are used to purify groundwater, rainwater, surface water, domestic and industrial wastewater, seepage (from solid waste and sludge dumps) and to dehydrate and process sewage sludge.

Purifying wastewater

The wastewater pollutants are degraded in three stages:

1. by the metabolism of micro-organisms;
2. the metabolism of the plants (helophytes);
3. by solidification in the soil and filter material.

Oxygen and other root discharges flow via the plant roots into the soil saturated with wastewater. The inflow of oxygen allows the existence of both aerobic and anaerobic organisers. The remaining root discharges are assumed to bring about a chemical change in the soil in turn which changes the quantity and quality of soil flora.

It is assumed that pathogenic germs existing in the root-zone can be very effectively eliminated, root discharges with an antibiotic effect (reed) being involved in this.

The capacity to take up organic materials and heavy metals and to transform organic substances are other qualities of the plant. The root growth considerably changes the permeability of the soil water.

Hygiene risks reduced

The operation of a root-zone sewage treatment plant generally requires that the wastewater is well pre-purified, including a sludge treatment stage. This is possible in an Imhoff-tank or a septic tank. The root-zone sewage treatment facility requires a large surface area, estimated at a minimum of 5 m² per inhabitant (in Germany). To stop mosquitos from breeding, care must be taken to ensure that no sewage can come to the surface.

The advantages of the root-zone sewage treatment plant are its simple construction, low energy consuption, lack of any machinery, and the minimum maintenance required, which together keep running costs low. The purification capacity is comparable to that of conventional biological treatment plants. No other treatment system, however, can ensure such extensive elimination of pathogenic germs without applying additional chemical or physical processes.

Pilot project in Berlin

Another great advantage is that the treated sewage can be recycled in agriculture and reduces hygiene risks in the groundwater and surface water.

In 1987 the International Building Exhibition (IBA) in Berlin/Germany, planned and constructed an environmentally compatible housing and urban development project. The project aimed to demonstrate how drinking water consumption, as well as the ecological damage caused by wastewater could be reduced by the conscious management of the resource water.

The newly-built housing complex in Block 6, Berlin-Kreuzberg, which consists of 106 residential units and a 10,000 m² inner courtyard were planned and built to demonstrate the following: reduced water consumption; reduced energy consumption; utilization of rainwater; treatment and reuse of domestic wastewater; groundwater recharge through percolation of treated wastewater and excess rainwater overflow; integration of the root-zone sewage treatment facility into a recreational area; reduction in the amount of solid waste.

Design of the sewage treatment facility:

- an Imhoff (septic) tank for preliminary treatment,
- a root-zone treatment plant for biological treatment,
- a polishing pond for the final treatment.

The domestic sewage of 73 apartments of the pilot project in Berlin is pumped from a collector pit outside the building into the Imhoff tank. The remaining apartments are directly connected to the public sewerage.

Preliminary Treatment

The Imhoff tank was constructed with two pre-fabricated round basins with a filling volume of 34 m³ each and one channel-type aluminium settling tank with a settling area of 5 m³. The basins are covered and the digestion tank is aerated over the roofs of the new buildings.

The root-zone sewage treatment plant consists of 4 modules, operated in parallel, each with a design load of 50 PE (population equivalents). The modules are constructed with waterproof reinforced concrete and divided into 4 sub-basins. Each module inlet is provided with an inlet channel through which treated wastewater is passed through a dentate sill into a feeder channel, which in turn distributes the wastewater over the entire surface of the next filter.

Clumps of Phragmites australis (reed) is planted in filters of the first two sub-basins. The filter of the third sub-basin is planted with Schoenoplectus lacustris (bulrush) in clumps. At the filter of the fourth sub-basin, Phragmites australis (reed) is used as the plant-cover. The difference between inflow and outflow levels yields a medium flow gradient of 2.2 %.

The polishing pond is a waterproof reinforced concrete tank with a volume of 105 m³ and a mean depth of 1.0 m. The clarified effluent is channelled to two pumps. The first pumps into the domestic water tank of the residential block, and the second is used for groundwater recharge.

Satisfied local population

The treatment facility is also a place of interest to many visitors. The bridges, the pond, and the paths within the treatment plant are attractions for the children who come to play here. The hill of the Imhoff tank is used as a lawn or as a playground. The benches next to the rainwater pond are used very frequently. The growth of the trees around the treatment plant is very satisfactory. The children rarely walk inside the zone which is charged with wastewater.

It is remarkable that there have been almost no cases of vandalism and that the amount of litter found in the whole area is negligible.

According to surveys by a research project of the Technical University of Berlin, 97 % of the inhabitants feel comfortable in their apartments (57 % feel comfortable' 40 % feel very comfortable). Thus the wastewater treatment plant in their leisure area does not disturb them.

In March 1988, the treatment plant was fed with the wastewater of 250 inhabitants (2.4 m²/cap.). However, since March 1989, having been overloaded during the preceding winter, the wastewater was reduced to that of approximately 200 inhabitants (3 m²/cap).

The concentration of pollution load is very high. During the first year of operation it was 40 % higher than the concentration of inflows of public treatment plants. During the growing season in spring, the minimum requirements were surpassed. In winter months, however, the minimum requirements could not be met during times of high load by a specific area of 3 m²/cap.

The high percentage of denitrification, the approx. 60 % retention of phosphorus, and the widespread elimination of germs are worthy of note. Despite the high charge by faecal bacteria, the effluent of the polishing pond is almost within the limits set by the guide-lines of the European Community for bathing water.

The emission of faccal odours is negligible throughout the year and is perceptible ouly in the region of the inflow duct. Altogether, the emission of wastewater odours is lower than expected by the enginecrs.

After 1990, the load was reduced such that the effluent is within the limits set by the guide-lines of the EC for bathing water. Since 1992 the waterclosets of approximately35 apartments have been supplied with treated wastewater. In 1993, the distribution of purified wastewater was extended to 72 apartments.

Economising Drinking Water

The concept of the Berlin plant-based water treatment facility, which recycles purified water from bathtubs and showers and uses it to flush toilets has proven to be a success. Erwin Nolde, scientist at the University of Berlin, provided back-up assistance to the pilot project and can put forward the following calculation:

"The maintenance and operation of a grey-water treatment plant to take the wastewater for 60 people requires an input of approximately DM 3,500 per year. Compared with the price of "only" 7 Marks per m³ for drinking and wastewater this constitutes cost savings of about DM 7,500. Assuming an average of 2.5 persons per housing unit, investment costs of about DM 1,700/ housing unit (or 700 DM/ person) should be calculated - hardly more than is needed to connect to cable-TV, which society is well-prepared to do. The ecological benefits of such a facility are enormous. Within one year, we calculated that more than 1,000 cubic metres of drinking water were economised and the load on waterworks and sewage-works was lowered accordingly."

Source: Politische Okologie, Special Issue No. 5, Munich 1994

Rm

Les installations d'assainissement onctionnement dntraliseprntent une option ide pour les rons rurales mais conviennent lement pour les agglomtions urbaines. Ceci est mis endence 'exemple d'une installation d'ration biologique mise en place dans la capitale allemande Berlin. L'eau rest utiliscomme eau de che.

Extracto

Las instalaciones descentralizadas no solo son ideales para eliminar aguas residuales en zonas rurales. Tambipueden utilizarse en grandes zonas urbanas, como lo demuestra una instalacie fitopurificaciue opera en la capital alemana de Berlin. El agua depurada se usa para evacuar excrementos de los inodoros.

Local sewage disposal in Germany: the pros and cons of privatisation

by Erich Englmann

Structural adjustment programs in the countries of the South recommend that private companies should deliver infrastructure services instead of public enterprises. Industrial countries such as Germany, faced with ever tighter public budgets, are also considering this path. Sewage disposal in Germany falls under the mandate of local authorities in the interest of public welfare. The numerous organisational set ups used are now being reconsidered.

Mandate of the local authorities

In Germany sewage disposal is a public-sector task, transferred to local authorities under the constitutions of the individual states and their pertinent legislation. It is a mandatory task which the local authorities carry out in their own area of purview. They have the right to carry out those measures necessary for public welfare in their area. How they do this is their own affair.

Being a mandatory public task, sewage disposal is not subject to any taxation at the present time as long as it is carried out by public authorities. The cost of investments, operation and other expenditures of local sewage treatment plants are passed on to the users according to the "polluter-pays principle", i.e. producers of wastewater, in the form of charges and contributions. These contributions may cover the investment costs in full or in part; the local authority of the company is responsible for decision-making. Charges are based on operating costs, the calculated costs and the sewage fees. The calculated costs depend on which part of the investment costs are not covered by the contributions, and also on the depreciation and interest payments.

Different forms of organisation

In Germany the sewage charges are calculated in direct relation to the amount of drinking water taken from the public system.

Municipalities can choose from optional types of organizational forms in order to carry out their sewage disposal mandate. These basic forms are:

· municipality - oriented enterprises.
· municipal public utility undertakings,
· the BOT (build, operate, transfer) model
· the cooperation model.

The decision for one of these models chiefly depends on the local conditions, the size of the local authority, the type of services offered and the State legislation. The following criteria play a role:

· the characteristics of the services to be offered
· the costs of services delivered
· the financing potentials
· the procedure for calculating fees.

Municipality operated enterprises

Municipality-operated enterprises are operated by the municipal administration in the scope of its overall budgets and the municipality sets the legal and organisational framework. The enterprise does not have its own specific operating assets but is administered as part of the municipal budget which is run on cameralistic principles. The municipal council takes all major decisions. Being a dependent part of the local authority administration, the municipality-operate d enterprise is subject unrestrictedly to municipal budgetary law. The full cost cover principle is applied to all expenditures. This means that all or part of the appropriations are used as a general receipts in the administrative budget, or allocated for other purposes in the assets budget.

Consequently, large quantities of outside capital are used to finance sewage investments, and reserves cannot be formed.

Municipal public utility undertaking

The municipal public utility undertaking is also a dependent of the local administration. Contrary to the municipality-operated enterprise, however, it is separated from the general budget operated as a special accounting entity from the financing viewpoint. The municipality retains full ownership and liability vis-is third parties. The utility is nevertheless organised independently and manages its own income and expenditures.

In contrast to the municipality-operated enterprise, a commercial accounting system is used, characterised by an economic plan to which the strict coverage principles of budgetary law do not apply. Municipality-operated enterprises are easier to manage on business principles and accounting is more transparent.

Build' operate and transfer model - BOT

In this BOT model the sewage disposal services are delivered by a private company against payment by the municipality. The private company either buys municipal property or builds new plants on leasehold real estate. Contracts are awarded after public tendering. The operator plans, finances, builds and runs the plant over a longer time period (20 - 30 years) at its own risk and on the basis of an operating contract entered to with the municipality. The owner and operator of the facility is therefore no longer the municipality but the private enterprise. This operator calculates a set sewage treatment tariff (DM/m³ sewage) which can only be adjusted on the basis of defined indexed clauses. The municipality retains responsibility for the public disposal of sewage. It is also still responsible for charges.

The cooperation model

The cooperation model, similar to the BOT model, is based on the maximum transfer of tasks. Instead of the purely privately-run company this model is a mixed private company (limited company) in which the municipality has a majority holding. The company can place orders with third parties for the construction and also for the maintenance of sewage plants. At least part of these operations are usually placed with the municipality's co-shareholder company. Similar to the BOT model, the aim is that a private company, the co-shareholder - builds and operates the sewage plant. The chief difference to the BOT-model is that the municipality, through its majority stockholding in the joint company, can directly influence how services are rendered, and has better access to the sewage plants, which remain the property of the joint company. The cooperation model therefore combines private capital, know-how and greater flexibility with an adequate influence-taking by the municipality.

Pat recipes don't exist

Some 70 % of Germany's 16,000 municipalities perform their sewage disposal mandate through municipality-operated enterprises. Some 150 local authorities have contracted private operators to carry out these tasks, although mainly in Germany's new states in Eastern Germany.

No pat recipes are on hand to help a municipality decide what is the most suitable model. The decision on the best form of organisation for municipal sewage disposal must be taken on the basis of objective criteria for each individual case. A detailed analysis has to be made on the basis of financial and operating figures and in the light of local conditions.

To assess which model is most suitable, priorities must be given to

- flexibility of operations
- transparency of costs for the citizen (fees, appropriations)
- optimisation of business management.

Municipality-operate d enterprises are not easy to organise in day-to-day management, and have proven to have some disadvantages. They may indeed even generate higher costs for the consumer.

The municipal public utility undertaking is more flexible than municipality-operat e d- enterprises and its accounts are more transparently organised. However, the earmarking of receipts from sewage charges limits the general scope of action of the local authority.

The advantage of the BOT model rather than a completely non-privatised solution is that services are rendered in the light of market-oriented incentives for more efficient technical solutions. Another advantage of this model is that a functioning sewage disposal system can be set up relatively quickly even in an administration that only disposes of limited capacity. The disadvantage are the very complex contracting necessary, the municipality's loss of control potential and the long-term binding to one operator

All the abovementioned situations also apply to developing economies, particularly the fact that a decision on which specific form of organisation is most suitable can only be taken in each individual case, to fit in with local conditions and on the basis of a business analysis of costs. If limited or even no capacity is available in the administration to carry out sewage disposal operations, it could be more advantageous to incorporate private companies in order to establish a functioning sewage disposal system more quickly, perhaps based on the BOT model. This demands, however, that a functioning water management authority is set up.

Rm

Les travaux d'ipement en infrastructures, dans le secteur de l'assainissement notamment, doivent-ils e pris en charge par des entreprises priv? Compte tenu de contraintes budgires grandissantes, cette question est discutm en Allemagne. Cette approche est proposaux pays en dloppement dans le cadre des programmes d'ajustement structurel. L'auteur parvient a conclusion que la solution optimale pour le secteur de l'assainissement en Allemagne rdait dans une rrtition des tes entre l'Etat et le secteur privIl est d'avis qu'une privatisation de ce secteur art enti doit e exclue.

Extracto

Conviene dejar servicios pos tales como la eliminacie aguas residuales en manos de empresas privadas? Este es un tema muy debatido en Alemania actualmente, debido a la creciente escasez de fondos pos. Ademas, es una solucion que se recomienda a los paises en desarrollo querealizan programas de reajuste estructural. El autor llega a la conclusie que, en Alemania, la mejor solucion para la eliminacie aguas residuales es repartir las responsabilidades entre entidades publicas y privadas. Asimismo, rechaza la idea de una privatizacion absoluta.

Can we learn from the past?

The decision to install a flush-sewer system in German towns and its consequences by Engelbert Schramm

The introduction of the water closet and a disposal system using water to flush faeces to rivers by passing through a technical network of sewers and a sewage treatment plant was a controversial issue in 19th century Germany. This method which was widely practised in Europe's industrial cities clearly did nothing but shift the wastewater disposal problem. Engelbert Schramm feels that this system has reached its economic and social limits in highly industrialised countries such as Germany.

Before industrialisation, when Germany's towns were still quite small, human excrements were collected in cesspits usually located under the latrine. When the cesspit was full it was emptied and people either spread the contents over their own fields outside the town, or this manure was collected by farmers.

Complaints that towns were becoming "mucked up" mostly related to the excrements of riding horses, cart horses and draft oxen which littered the streets. The disposal of human faeces, in contrast, functioned quite smoothly up until the 19th century. Problems only set in when industrialisation attracted more and more people to the towns, which began to spread over larger areas. The average distance to fields to be manured also increased.

The flush sewer system

The emptying of the cesspits, and the fact that domestic servants emptied the night-pails made it impossible for the rich citizens to preserve their own «private sphere». The aristocracy developed a sensitivity to the smell caused by transporting faecal matter and welcomed the news that a water closet had been invented. This toilet was emptied by a siphon outlet and had an air-trap drain to prevent any odours escaping.

With the water closet, a seemingly fascinating solution had been developed: the flushing sewerage system which used water to transport faecal matter into the rivers via artificial channels underneath the towns. In 1842 the first flushing sewerage system on the European continent was built in Hamburg. Other urban planners soon began to copy this example.

Most physicians, engineers and local politicians in Germany felt that this technology was the decisive step towards establishing a new system to transport faecal matter. Faeces were to be transported through the sewerage system, if possible within an hour, from the houses into the river. This rapid transport of faeces would - it was thought - have a positive impact on the health conditions in urban centres. It would relieve the contamination of the soil which hygienists thought to be the cause of numerous diseases.

Large quantities of water, unthinkable up to then, were flushed through the closets in the houses. A centralised water supply system and a quite irrational use of clean water were preconditions for transporting faecal matter. The flushing sewer system transported domestic wastewater, waste fluids from industrial production and, in Germany, also rain water from paved surfaces. 270 m³ of water per inhabitant were transported each year through the urban sewerage network. This enormous water throughput was necessary to channel the wastewater through the underground without stagnation.

The debate on the flush sewer system

Constructing centralised sewage systems and excessive water supply systems was an expensive affair for urban dwellers, and consequently, setting up a flush sewerage system to remove faeces was usually a very controversial is sue. Alternatives were developed, some of which even reached technical maturity:

· The Dutch engineer Liernur developed a vacuum toilet which sucked faecal matter into containers situated in the vicinity which were regularly emptied.

· Other towns operated so-called barrel systems. The containers were regularly emptied and the faecal matter which was not directly distributed to farmers in the region was processed to fertiliser in special factories.

In light of these options many local politicians, physicians and engineers no longer saw the need to build a sewerage system. Finally the specialists split into two factions. The German Association for Public Health Care (Deutscher Verein fentliche Gesundheitspflege) spoke in favour of building a sewerage system on 26.9.1877. Its members did not see any justification in prohibiting the discharge of sewage effluent bearing the faecal matter from closets into surface waters because "the scientific impact and cost of a tolerable degree of river pollution is not sufficiently clarified to permit generally valid regulations at the present time".

As reaction to this the International Association for the Conservation of Clean Rivers, Soil and Atmosphere (Internationaler Verein fur die Reinhaltung der Flusse, des Bodens und der Luft) was established just four days later. Its members demanded that the faecal matter should not be discharged into the sewerage network and subsequently into the river waters. They repeatedly called attention to the fact that the flush sewerage system transformed rivers into cloacas which prohibited swimming and made the water undrinkable. Opponents of the sewerage system put forward the British example to assess such impacts: in 1865 the Thames, loaded with the faecal matter from London, lost its ecological balance; the resulting "Great Stink" even made it impossible for the British Parliament to carry on working.

Such conditions in Germany where the rivers are far longer, would affect wide areas of land. Although they did not adopt the preventive arguments of the International Association, local authorities did take action that municipalities could not discharge faeces-containing effluent from the sewerage system completely untreated into the rivers. But the first sewerage works only separated off the solid matter from the water using mechanical screens and sedimentation basins. This sewage sludge was then distributed to farmers as manure. Nowadays, farmers are very sceptical about this fertiliser because of the heavy metals, organic chlorine compounds and tensides contained in wastewater. Only one third of the total volume of sewage sludge is presently used in agriculture, the remainder is burned and dumped.

Rm

L'introduction des toilettes au et, en m temps, du tout-'ut, syst dans lequel les matis fles sont transport dans un rau de canalisations et sont rejet dans les fleuves apravoir trait dans des stations d'ration, a fait l'objet de plus d'une controverse dans l'Allemagne du 19. sie. Il s'est av trrapidement que cette mode, aujourd'hui couramment pratiqudans les villes europnes, n'a fait que transposer les probls d'assainissement n autre niveau. De l'avis de l'auteur, ce syst se heurte es limites d'ordre nomique et social, m dans un pays hautement industrialis

Extracto

En la Alemania del siglo XIX fue muy debatida la introducciel inodoro o water y del correspondiente sistema de alcantarillado hidrico en el que las heces eran transportadas por conductos artificiales a las plantas depuradoras y de alli a los rios. Pronto se hizo patente que este mdo - de uso generalizado en las ciudades europeas de hoy- solo trasladaba los problemas derivados de la eliminacie aguas residuales a otros puntos. El autor opina que incluso en Alemania, un pais altamente industrializado, el sistema amenaza con superar los limites de viabilidad econa y social.

Step by step retrofitting

In the second half of this century it became clear that sewerage plants which only treated the water in a settlement basin would have to add a further treatment stage. More and more urban dwellers (and also households in rural regions) connected to the sewerage system with the consequence that water pollution intensified further. Domestic households also began to use more chemicals, which changed the composition of domestic wastewater. Fish death in Germany's large rivers was an experience repeated almost every summer.

The second purification stage in Germany's sewerage works is usually a biological purification system: In a reaction tank, to which aerobic bacteria have generally been added, organic pollutants are coagulated into sludge flocs by means of dioxygenising bacterial metabolism. The purification is all the more intensive if the oxygen supply is raised by artificial aeration (requiring a high energy input).
But even optimally operating sewerage plants with both primary and secondary purification stages are unable to adequately retain the nutrients in the water. The algae plague and seal deaths in the North Sea in 1988 resulted in European Union's demands for greater elimination of nitrogen and phosphorus compounds (initially for sewerage plants in larger cities) in order to protect the rivers and the sea. This third purification stage usually consists of a chemical process in which some anaerobic biological processes are integrated.

Cost intensive re-equipping of existing sewerage plants is essential. Many towns, individual citizens and also local authorities are resisting the costs this entails; resistance is chiefly directed at the demands of the European Union. Local politicians forget that we are really just paying for decisions made in the 1 9th century.


Task Analysis Sheet: Introducing Latrines

Is it really a sanitation technology?

As early as the end of the last century - when only few towns possessed a sewage treatment plant - it was al ready clear that flush sewerage technology did not lead to an improvement in the health situation: A cholera epidemic in 1892 in Hamburg originated from the fact that wastewater polluted with cholera pathagens had infiltrated into the water-works. The typhus epidermic in the Ruhr Valley region in the early 20th century had the same cause. However, 20 years following the conflict on whether or not to introduce the flush sewerage system no one drew attention to the fact that the sewerage system constantly polluted river water with pathogens. The roots of the problem were thought to be the fact that urban or private water works did not sufficiently purify river water before feeding it into the supply system. Slow sand filtration, chlorination and other end-of-pipe technologies were stipulated for river-side water publication.

Only now are policymakers beginning to realise that the flush sewerage system just means a changed distribution of pathogens in the environment. They are transported out of town into downstream waters. Sewerage from Germany's cities pollutes downstream lakes and rivers with pathogens to such an extent that bathing had to be prohibited (pursuant to EU legislation). Therefore Berlin is discussing the further extension its sewerage plants. Micro-filters in a fourth purification stage are to retain viruses and bacteria. Will this make the flush sewerage system an ecologically sound method at long last?

Learning from the past

In retrospect the arguments put forward by the International Association which had disappeared after such a few years, were the right ones. The successful strategy of the German Association for Public Health Care to promote the flush sewage system did not link the status of centralised sewage treatment to public health care aspects but rather to the scientific knowledge at that time. This approach makes its mark in the purses of city dwellers: In Germany today a family of four has to pay c. DM 140 per month for water and sewerage. The 1 9th century water in*astructure based exclusively on a centralised system is now confronting its economic and social limits! It is high time to change the paradigm: Perhaps decentralised water treatment systems, compost toilet systems etc. can be further developed to make them not only feasible for urban fringes.

The question put forward by the "International Association" is still pointing in the right direction: "What means have we to ensure that latrines are sufficiently cleaned and human waste is safely removed without endangering the rivers?" The vision of a sustainable city which does not live at the expense of its environment could probably become reality if we draw the consequences from the past.

IRC International Water and Sanitation Centre

IRC is an independent, non-profit organization. It is supported by and linked with the Netherlands Government, UNDP, UNICEF, the World Bank and WHO. For the latter it acts as a Collaborating Centre for Community Water Supply and Sanitation.

The centre aims to ensure the availability and use of appropriate knowledge and information in the water, sanitation and environment sector in developing countries.

· Activities include capacity development for information management, exchange of available knowledge and information, and development and transfer of new knowledge on priority issues.

· Emphasis in programme activities is on community-based approaches including rural and low-income urban water supply and sanitation systems, community participation and hygiene education, the roles of women, maintenance systems, rehabilitation and environmental management.

Highlights is published as part of the IRC Documentation Unit's Current Awareness Services. It contains a selection of news items and contents page from 250 journals, newsletters and other sources related to the water and sanitation sector. Each issue deals with a two month period.

For further information:
IRC
P.O. Box 93190
2509 AD The Hague
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Telephone: +31-(0)70-3314133
Telefax: +31-(0)70-3814034