Periurban sanitation: what's the problem?

To meet the WHO/UNICEF target of ‘Water & Sanitation for All by 2025’ some 4.4 billion people will have to be provided with improved sanitation during 2001−2025, and around half of these are/will be in ‘urban’ areas – but in reality we are talking about periurban areas. Given that most population growth over the next few decades will occur in ‘urban’ (again, really periurban) areas of developing countries, periurban sanitation will have to become much more important than it already is. Our current focus is on achieving the sanitation target of the Millennium Development Goals, but these efforts will have to be doubled if we are to meet the WHO/UNICEF 2025 sanitation target in periurban areas, and then maintained for the next quarter century as we seek to meet the sanitation needs of the additional two billion or so people expected in periurban areas by 2050. So the Big Question is: How can we provide affordable sanitation to these very large numbers of poor people in periurban areas in developing countries? The answer to this question depends in part on the population density: at low population densities on-site sanitation systems are normally feasible, but (and as we have known since the early 1980s), even if there is sufficient space for them, they may not necessarily be the cheapest option (and, because we are attempting to serve poor and very poor people, we have to consider cost); and, of course, at high population densities on-site systems become infeasible as there is no space for them. In addition to being affordable, the chosen sanitation system has to be both socially acceptable and institutionally feasible. Consider the typical periurban situation: a high population density, one too high to permit on-site sanitation systems. What are the ‘best’ solutions for sanitation? If affordable, the system of choice would normally be simplified sewerage (also known as ‘condominial’ sewerage). With this sanitation system we should remember that in Natal in northeast Brazil, where it was developed in the early 1980s, it became cheaper than on-site sanitation at the relatively low population density of ~160 persons per ha, there were no connection charges and the monthly charge for the service was only USD 1.50; and that in Chisty Nagar in Orangi, Karachi, Pakistan, where Brazilian-style simplified sewerage was first installed in Asia in the mid-1980s, the residents obtained their water (only ~27 litres per person per day) from public standpipes, thus demonstrating that a plentiful on-plot water supply is not a sine qua non for the system. Simplified/condominial sewerage is one of the components of the very successful ‘Slum networking’ programme in India, and it has also been used in small villages in northeast Brazil. It is socioculturally very acceptable as it appears to its users to be similar to conventional sewerage, so their sanitation system is the ‘same’ as that enjoyed by the rich. It is also institutionally acceptable simply because it is a sewerage system and, as such, it can be readily understood and appreciated even by very conservative sewerage design engineers, especially when they realise that its hydraulic design is actually more rigorous than that used for conventional sewerage

Sanitation Now: What is Good Practice and What is Poor Practice?

To meet the 2015 Millennium Development Goals sanitation target or the 2025 universal sanitation coverage target it is essential that it is properly understood where the available sanitation options are applicable. In high-density low-income urban areas conventional sewerage and ecological sanitation systems are inapplicable solely on grounds of cost. In these areas the options are simplified sewerage, low-cost combined sewerage and community-managed sanitation blocks. In medium-density urban areas on-site systems are also applicable (alternating twin-pit VIP latrines and pour-flush toilets, urine-diverting alternating twin-vault ventilated improved vault latrines, biogas toilets and ecological sanitation systems, all with greywater disposal or use). In medium- to low-density rural areas the options are the same as those in medium-density urban areas, with single-pit VIP latrines and pour-flush toilets, rather than alternating twin-pit systems. The level of water supply service (public or community-managed standpipes, yard taps, multiple-tap in-house supplies) also influences the choice of sanitation option

Application of existing knowledge: the only way to meet the MDG sanitation target in developing countries

The MDG sanitation target is, at current progress, unlikely to be met. The most important reasons for this are (1) that at local level, and in some countries at national level, engineers and planners simply do not know what sanitation systems are available, nor how to design them; and (2) a lack of political commitment, commonly at local level but again in some countries at national level. Local lobbying by the media and demonstrations (in urban areas) by the poor might change political attitudes, but without the appropriate knowledge local engineers and planners will remain unable to design sanitation systems for the urban and rural poor. The ‘sanitation challenge’ from today to 2015 is how to get this knowledge to local professionals in their own language

Quantifying health risks in wastewater irrigation

The guidelines developed by the World Health Organization for the safe use of wastewater in agriculture are based on a tolerable additional disease burden of 10-6 disability-adjusted life year loss per person per year, equivalent to rotavirus disease and infection risks of approximately 10-4 and 10-3 per person per year, respectively. The combination of standard quantitative microbial risk analysis techniques and 10,000-trial Monte Carlo risk simulations, using ranges of parameter values that reflect real life, are then used to determine the minimum required pathogen reductions for restricted and unrestricted irrigation which ensure that the risks are not exceeded. For unrestricted irrigation the required pathogen reduction is 6- 7 log10 units and for restricted irrigation 3- 4 log10 units. For both restricted and unrestricted irrigation wastewater treatment has to achieve a 3-4-log10 unit pathogen reduction, and in the case of unrestricted irrigation this has to be supplemented by a further 3-4-log10 unit pathogen reduction provided by post-treatment, but pre-ingestion, health protection control measures, such as pathogen die-off between the last irrigation and consumption (0.5- 2 log10 unit reduction per day, depending on ambient temperature) and produce washing in clean water (1 log10 unit reduction). Wastewaters used for both restricted and unrestricted irrigation also have to contain no more than 1 human intestinal nematode egg per liter; if children under the age of 15 are exposed then additional measures are required such as regular deworming at home or at school

A Numerical Guide to Volume 2 of the Guidelines and Practical Advice on how to Transpose them into National Standards

[INTRODUCTION] In 2006, the World Health Organization published the third edition of the Guidelines, in collaboration with FAO and UNEP. The third edition consist of four volumes; volume 2, explained in this guidance note, addresses methods, procedures and guideline values for the safe use of wastewater in agriculture. In essence, the Guidelines are a code of good management practice. Volume 2 aims to ensure that health risks associated with the use of wastewater for irrigating crops (including food crops that are or may be eaten uncooked) are assessed and managed. Other than the 1989 second edition, this new edition therefore offers much more than a set of guideline values. The new approach will challenge programme managers and engineers responsible for wastewater treatment and use who need to know how to use the recommended methods and procedures to design wastewater use systems that do not adversely affect public health. They will have to learn about and understand in detail the ‘numerical’ recommendations in the Guidelines so that the wastewater use systems they design are safe. However, it is not straightforward for these professionals to comprehend these numerical recommendations simply by reading the Guidelines − it requires a considerable amount of study and there are several concepts (for example, disability-adjusted life years) and topics (quantitative microbial risk analysis) with which few are familiar. They need a ‘Guide to the Guidelines’. The purpose of this Guidance Note is to provide programme managers and engineers with a succinct overview of new concepts and topics

Periurban sanitation: what's the problem?

To meet the WHO/UNICEF target of ‘Water & Sanitation for All by 2025’ some 4.4 billion people will have to be provided with improved sanitation during 2001−2025, and around half of these are/will be in ‘urban’ areas – but in reality we are talking about periurban areas. Given that most population growth over the next few decades will occur in ‘urban’ (again, really periurban) areas of developing countries, periurban sanitation will have to become much more important than it already is. Our current focus is on achieving the sanitation target of the Millennium Development Goals, but these efforts will have to be doubled if we are to meet the WHO/UNICEF 2025 sanitation target in periurban areas, and then maintained for the next quarter century as we seek to meet the sanitation needs of the additional two billion or so people expected in periurban areas by 2050. So the Big Question is: How can we provide affordable sanitation to these very large numbers of poor people in periurban areas in developing countries? The answer to this question depends in part on the population density: at low population densities on-site sanitation systems are normally feasible, but (and as we have known since the early 1980s), even if there is sufficient space for them, they may not necessarily be the cheapest option (and, because we are attempting to serve poor and very poor people, we have to consider cost); and, of course, at high population densities on-site systems become infeasible as there is no space for them. In addition to being affordable, the chosen sanitation system has to be both socially acceptable and institutionally feasible. Consider the typical periurban situation: a high population density, one too high to permit on-site sanitation systems. What are the ‘best’ solutions for sanitation? If affordable, the system of choice would normally be simplified sewerage (also known as ‘condominial’ sewerage). With this sanitation system we should remember that in Natal in northeast Brazil, where it was developed in the early 1980s, it became cheaper than on-site sanitation at the relatively low population density of ~160 persons per ha, there were no connection charges and the monthly charge for the service was only USD 1.50; and that in Chisty Nagar in Orangi, Karachi, Pakistan, where Brazilian-style simplified sewerage was first installed in Asia in the mid-1980s, the residents obtained their water (only ~27 litres per person per day) from public standpipes, thus demonstrating that a plentiful on-plot water supply is not a sine qua non for the system. Simplified/condominial sewerage is one of the components of the very successful ‘Slum networking’ programme in India, and it has also been used in small villages in northeast Brazil. It is socioculturally very acceptable as it appears to its users to be similar to conventional sewerage, so their sanitation system is the ‘same’ as that enjoyed by the rich. It is also institutionally acceptable simply because it is a sewerage system and, as such, it can be readily understood and appreciated even by very conservative sewerage design engineers, especially when they realise that its hydraulic design is actually more rigorous than that used for conventional sewerage

Sanitation options in rural and urban areas: best practices

Suitable low-cost sanitation systems for use in poor rural and urban areas are described. For dispersed rural areas Arborloos generally represent the ‘best’ choice. As the density increases other options may be used, including alternating twin-pit or twin-vault systems providing they can be desludged by the users. In poor urban areas the choice is normally between simplified sewerage, low-cost combined sewerage and community-managed sanitation blocks

Sewerage: a return to basics to benefit the poor

Around 2.8 billion people, mostly in developing countries, currently lack adequate sanitation. Approximately half live in urban areas, where the most appropriate sanitation solution is commonly simplified sewerage. This paper presents the rigorous hydraulic design basis of simplified sewerage and compares this design approach with that used in the UK for conventional sewerage. It reviews simplified sewerage construction and how this achieves major cost savings and also avoids the problems commonly experienced with manholes

Estimation of Ascaris infection risks in children under 15 from the consumption of wastewater-irrigated carrots

Ascaris lumbricoides, the large human roundworm, infects ,1,200 million people, with children under the age of 15 being particularly at risk. Monte Carlo quantitative microbial risk analyses were undertaken to estimate median Ascaris infection risks in children under 15 from eating raw carrots irrigated with wastewater. For a tolerable additional disease burden of 1025 DALY (disability-adjusted life year) loss per person per year (pppy), the tolerable Ascaris infection risk is ,1023 pppy, which can be achieved in hyperendemic areas by a 4-log unit Ascaris reduction. This reduction can be easily achieved by wastewater treatment in a 1-day anaerobic pond and 5-day facultative pond (2 log units) and peeling prior to consumption (2 log units)