, l
The conventional approach in urban areas of industrialized countries is to dispose of excreta and greywater by means of large sewer systems, with the disposal of the final effluent into surface waters occuring after centralized treatment. The common user attitude towards this conventional approach is based on the wish to flush wastewater and faeces away without any further thought to its . Alternative solutions which are also able to provide sanitation for low-income settlements require the increased involvement of users in the planning, implementation and operation of environmental sanitation services.
The case for change
The large number of people around the world who still do not have access to adequate water, sanitation, drainage and waste disposal services provides sufficient evidence that the conventional approach to environmental sanitation is unable to make a significant dent in the existing service backlog. The approach is generally too expensive in less developed countries, except for the core of major cities and other well-to-do areas; even in these areas it has generally been found not to be sustainable (due to lack of competent institutions and manpower), and treatment deficiencies have led to serious environmental problems and deterioration of drinking water resources. It is becoming more and more doubtful if conventional systems are sustainable in the long run. In addition to the high costs, these systems consume large amounts of energy which are mostly produced using non-renewable resources and contributing to the global greenhouse effect. In addition, valuable nutrients such as nitrogen and phosphorus are wasted. Recent studies have also shown that increasing amounts of chemical trace elements and hormones are discharged from centralised treatment plants with unknown long-term effects on the environment.
Poor planning at the heart of the problems
Although there are many reasons for the failure to achieve satisfactory sanitation coverage poor planning lies at the heart of current. Services are not conceived in an integrated way that takes into account all their potential impacts. For example, provision of water supply without allowing for the removal of wastewater may create standing water, thereby producing health hazards and poor living conditions which may outweigh its positive benefits. Nor is sufficient attention paid to the fact that the reduction of waste and the more efficient use and reuse of water and materials is the most effective way to reduce demand for waste treatment and disposal. The need for holistic and integrated planning has been insufficiently recognized.
There has also been a tendency to develop systems that respond to problems of environmental waste management as perceived by policy makers and professionals, rather than by households and communities. Decisions regarding interventions - especially those requiring sophisticated technology, - are commonly taken at a remote administrative level. This frequently results in the refusal of the supposed users of services to accept operational or financial responsibility, thereby jeopardizing its sustainability. To promote user ownership of services, decisions should be taken at a level as close as possible to the source of the problem, in consultation with the people most directly affected.
The Strategic Sanitation Approach (SSA)
The introduction of the Strategic Sanitation Approach [1] as a planning tool to match users' priorities and preferences with affordability is a major innovation in environmental sanitation. However, initial efforts at applying this new approach have illustrated a number of difficulties [2]. Although it is based on user participation, it tends in fact to be "top down", in the sense that the required skills are rarely found at local level and requires support from external agencies. It also requires a "planning culture" which is often missing in sanitation agencies in developing countries, and can be time-consuming and expensive.
The "Household-Centred Environmental Sanitation" Model (HCES)
The HCES model builds on the SSA concept and has been suggested recently by working group of the Water Supply and Sanitation Collaborative Council [3]. Its fundamental premise is the need to put people and their quality of life at the centre of any environmental sanitation system. It is based on two principles (recognising that they should be applied in such a way as to balance economic and environmental good):
* The minimisation of waste-generating inputs (water, goods and materials), and the reduction of waste outputs (wastewater, solid waste and stormwater);
* The solution of environmental sanitation problems as close as possible to where they occur.
In order to apply these principles, the model proposes an administrative structure for environmental sanitation services composed of concentric circles with the household at the hub, matched to human settlement/administrative/ political structures, and to the water resource and waste disposal base. (Figure 1)
The process begins at the household level, so that consumers decide what level of service(s) they want and can afford, on the basis of available information about costs, benefits and operational responsibilities. The household is the core, the first circle in the management of environmental services. The next circle of activity is the community, to which the household relinquishes areas that it is not itself able to assume. The community, in turn, passes on those responsibilities it is unable to meet to the next circle. Five tiers of circle are envisaged -- household, community, local, district, national -- but the area and size of population encompassed by any circle is flexible. They can reflect any convenient administrative or political structure or topographical area. In passing responsibilities from one circle to another, the principle is that only tasks beyond the capacity of one circle are handed on to the next.
At the household level, most of the responsibilities related to service provision will be operational. In the intermediate levels, operational responsibilities will decrease while policy responsibilities grow in proportion to the position of the circle. At the level of the outermost circle -- national or river basin -- most will concern the development of environmental sanitation policies, strategic planning and regulations.
Among the advantages of the HCES model are the following:
* The approach balances human and environmental needs and is likely to be more sustainable than any model currently in use.
* It can be applied regardless of political system, but in order to be sustainable implies a commitment to decentralised, participatory structures.
* The basic concept and approach of the model is applicable in and developing settings. It can be used anywhere, independently of economic level, size of population, and environmental characteristics, at either the micro or macro level. Of course this does not imply that the specific solutions and services should and will look the same everywhere. Different conditions will lead to different solutions even if the same principles are applied.
The implications of adopting the household-centred model are profound, and require that the environmental sanitation community radically rethink its policies and practices. In particular, placing the household at the centre of the model demands an adaptation of technology to match people's needs, rather than a change of people's behaviour to accommodate technology.
Alternatives to conventional excreta and wastewater management
The search for alternatives to the conventional approach has been intense, and occasionally controversial. Alternatives fall basically into three categories or a combination of them:
* on-site systems: excreta are disposed of on the site of generation;
* off-site systems with centralized treatment but using simpler and cheaper sewer systems;
* decentralized systems: wastewater is treated in small non-centralized plants close to the place of generation and the effluent is then reused locally or discharged into surface waters, or the storm drainage system not requiring large sewer systems.
On-Site Systems
Conventional wisdom holds that on-site systems can only be used in low-density areas, thus the ready acceptance for their use in rural areas, and sometimes in urban fringe areas. This opinion probably reflects experience with the early dry on-site systems, which consisted of single-pit latrines which required the owner to move the superstructure over to a newly-dug pit whenever the first one was full. As part of the development of the ventilated improved pit latrine (VIP), designed to avoid odour and insect problems, dual-pit units have been introduced. This design allows the use of one pit until full; the second pit is then used while the contents of the first mature until they can be safely removed two years later. The latrine remains permanently at one location and can be used at much higher densities, as long as access to the pits for emptying is assured. There is a big range of different on-site sanitation systems described in the literature [4,5,6].
On-site systems using small amounts of water are usually also constructed with two pits, for the same reasons that dual pits are used for dry latrines: to allow decomposition of waste and pathogen inactivation in one pit while the other pit is used. The small amount of water used for flushing percolates into the soil from the pit. Apart from the manual pour flush (only very rarely are cistern-flush systems used), the latrine functions as does a modern toilet, with a water trap sealing out odours and insects.
Both dry and wet systems are especially useful where water supply is limited (e.g., standpost or yard hydrant supplies). With limited water supply greywater disposal is not a major problem and can be used for garden watering or simply infiltrated into the ground.
A familiar and reliable on-site system is the septic tank and drain field, widely used in both industrialized and less developed countries. It is a good system provided that two operating conditions can be met: the tank itself must be fully desludged at regular intervals (and proper provision made for treatment of the sludge prior to final disposal) and the soil conditions must be satisfactory for proper treatment of the liquid effluent. Unfortunately, these conditions often do not apply in less developed countries. Emptying is only partial, and over time the tank fills with compacted sludge, and stops providing treatment.
Off-site Systems
High costs and the need for in-house water supply have been the main problems with conventional sewer systems. Intensive efforts have been made to find alternative solutions and several approaches have been introduced in developing as well as industrialized countries. The ones considered appropriate for application in less developed countries are settled sewerage and simplified sewerage . (Pressure and vacuum sewer systems have also been developed, but they require technical competence for sustainable operation that is often not available in developing countries). Both systems use small-diameter sewers laid at shallow depths in which the flow is, ideally due to gravity.
In settled sewerage systems, wastewater from one or more households is discharged into a single-compartment solids interceptor tank. The settled (solids free) effluent is then discharged into shallow, small-bore gravity sewers. Since the sewers receive only settled sewage, they are designed very differently from conventional sewers. The most obvious differences are that they are not designed for self-cleansing velocities and that the flow in the sewers can change along their length, from normal gravity open-channel flow to full-bore pressure flow and then back to open-channel flow.
The simplified sewerage system is essentially conventional sewerage stripped down to its hydraulic basics with design standards updated to reflecting technical progress made since sewers became the preferred solution to wastewater disposal problems in the last century. Small-diameter sewers laid at shallow gradients are used to convey the sewage. The sewers are often laid inside housing blocks, when the system is known as condominial sewerage.
These alternative sewer systems are less expensive to construct, and also can be to operate, than conventional sewers. Capital cost savings, under favourable conditions, can amount to as much as 50% of the cost of conventional sewers [7].
Decentralized Systems
A non-centralised wastewater management system consists of several smaller units serving individual houses, clusters of houses or small communities. The wastewater treatment facilities are correspondingly smaller, e.g. for 20 - 10,000 population equivalent. Black and greywater can be treated or reused separately from the hygienically much more dangerous excreta. Installations with urine separation devices can also be integrated.
It is generally assumed that centralised systems are more economical in the urban and suburban context, benefiting from the economies of scale. Often it is also argued that the operation of small treatment plants is less reliable and that large systems are more cost-effective. Considering the fact, that such non-centralised systems do not require long and usually very capital intensive sewer lines, it is very possible that under certain circumstances the overall costs of the entire system are considerably smaller than for a centralised system, especially in economies where the costs for capital are high compared to labour costs. Also from an ecological point of view, a non-centralized system might be more suitable. It is, for instance, less detrimental to the aquatic system if the discharge of only partially treated wastewater is distributed along the length of the receiving water. If large amounts of wastewater are discharged at one central point, it is much more important that full treatment is achieved all the time. It is well known that this requirement is difficult to fulfil under the circumstances prevailing in developing countries (e.g. lack of financial resources, lack of proper O&M, lack of skilled labour, etc.) In addition, under certain circumstances a non-centralized system might require less stringent discharge standards because the self-purifying capacity of a river can better be utilized when the wastewater discharges are distributed.
Non-centralized systems are also more flexible and can better be adapted to the local conditions of the urban area concerned. This is especially important for the fast growing agglomerations in developing countries with highly heterogeneous conditions and requirements.
Conclusions
For both human needs and better environmental management, radical re-thinking is needed. Alternatives to conventional solutions are needed which can provide water and sanitation for all within a framework that balances the needs of people with those of the environment. Technical and institutional alternatives are required which can make services less expensive and thus more affordable to low-income customers. This can only be achieved by systematically involving all stakeholders in the planning, implementation and operation stages. The Household-Centred Environmental Sanitation model has been suggested as a strategic planning tool for a comprehensive analysis of urban environmental sanitation needs and the systematic planning of service improvements. It has been developed in the context of environmental sanitation, but could equally be applied to water demand management, and indeed to integrated water resources management.
The conventional approach in urban areas of industrialized countries is to dispose of excreta and greywater by means of large sewer systems, with the disposal of the final effluent into surface waters occuring after centralized treatment. The common user attitude towards this conventional approach is based on the wish to flush wastewater and faeces away without any further thought to its . Alternative solutions which are also able to provide sanitation for low-income settlements require the increased involvement of users in the planning, implementation and operation of environmental sanitation services.
The case for change
The large number of people around the world who still do not have access to adequate water, sanitation, drainage and waste disposal services provides sufficient evidence that the conventional approach to environmental sanitation is unable to make a significant dent in the existing service backlog. The approach is generally too expensive in less developed countries, except for the core of major cities and other well-to-do areas; even in these areas it has generally been found not to be sustainable (due to lack of competent institutions and manpower), and treatment deficiencies have led to serious environmental problems and deterioration of drinking water resources. It is becoming more and more doubtful if conventional systems are sustainable in the long run. In addition to the high costs, these systems consume large amounts of energy which are mostly produced using non-renewable resources and contributing to the global greenhouse effect. In addition, valuable nutrients such as nitrogen and phosphorus are wasted. Recent studies have also shown that increasing amounts of chemical trace elements and hormones are discharged from centralised treatment plants with unknown long-term effects on the environment.
Poor planning at the heart of the problems
Although there are many reasons for the failure to achieve satisfactory sanitation coverage poor planning lies at the heart of current. Services are not conceived in an integrated way that takes into account all their potential impacts. For example, provision of water supply without allowing for the removal of wastewater may create standing water, thereby producing health hazards and poor living conditions which may outweigh its positive benefits. Nor is sufficient attention paid to the fact that the reduction of waste and the more efficient use and reuse of water and materials is the most effective way to reduce demand for waste treatment and disposal. The need for holistic and integrated planning has been insufficiently recognized.
There has also been a tendency to develop systems that respond to problems of environmental waste management as perceived by policy makers and professionals, rather than by households and communities. Decisions regarding interventions - especially those requiring sophisticated technology, - are commonly taken at a remote administrative level. This frequently results in the refusal of the supposed users of services to accept operational or financial responsibility, thereby jeopardizing its sustainability. To promote user ownership of services, decisions should be taken at a level as close as possible to the source of the problem, in consultation with the people most directly affected.
The Strategic Sanitation Approach (SSA)
The introduction of the Strategic Sanitation Approach [1] as a planning tool to match users' priorities and preferences with affordability is a major innovation in environmental sanitation. However, initial efforts at applying this new approach have illustrated a number of difficulties [2]. Although it is based on user participation, it tends in fact to be "top down", in the sense that the required skills are rarely found at local level and requires support from external agencies. It also requires a "planning culture" which is often missing in sanitation agencies in developing countries, and can be time-consuming and expensive.
The "Household-Centred Environmental Sanitation" Model (HCES)
The HCES model builds on the SSA concept and has been suggested recently by working group of the Water Supply and Sanitation Collaborative Council [3]. Its fundamental premise is the need to put people and their quality of life at the centre of any environmental sanitation system. It is based on two principles (recognising that they should be applied in such a way as to balance economic and environmental good):
* The minimisation of waste-generating inputs (water, goods and materials), and the reduction of waste outputs (wastewater, solid waste and stormwater);
* The solution of environmental sanitation problems as close as possible to where they occur.
In order to apply these principles, the model proposes an administrative structure for environmental sanitation services composed of concentric circles with the household at the hub, matched to human settlement/administrative/ political structures, and to the water resource and waste disposal base. (Figure 1)
The process begins at the household level, so that consumers decide what level of service(s) they want and can afford, on the basis of available information about costs, benefits and operational responsibilities. The household is the core, the first circle in the management of environmental services. The next circle of activity is the community, to which the household relinquishes areas that it is not itself able to assume. The community, in turn, passes on those responsibilities it is unable to meet to the next circle. Five tiers of circle are envisaged -- household, community, local, district, national -- but the area and size of population encompassed by any circle is flexible. They can reflect any convenient administrative or political structure or topographical area. In passing responsibilities from one circle to another, the principle is that only tasks beyond the capacity of one circle are handed on to the next.
At the household level, most of the responsibilities related to service provision will be operational. In the intermediate levels, operational responsibilities will decrease while policy responsibilities grow in proportion to the position of the circle. At the level of the outermost circle -- national or river basin -- most will concern the development of environmental sanitation policies, strategic planning and regulations.
Among the advantages of the HCES model are the following:
* The approach balances human and environmental needs and is likely to be more sustainable than any model currently in use.
* It can be applied regardless of political system, but in order to be sustainable implies a commitment to decentralised, participatory structures.
* The basic concept and approach of the model is applicable in and developing settings. It can be used anywhere, independently of economic level, size of population, and environmental characteristics, at either the micro or macro level. Of course this does not imply that the specific solutions and services should and will look the same everywhere. Different conditions will lead to different solutions even if the same principles are applied.
The implications of adopting the household-centred model are profound, and require that the environmental sanitation community radically rethink its policies and practices. In particular, placing the household at the centre of the model demands an adaptation of technology to match people's needs, rather than a change of people's behaviour to accommodate technology.
Alternatives to conventional excreta and wastewater management
The search for alternatives to the conventional approach has been intense, and occasionally controversial. Alternatives fall basically into three categories or a combination of them:
* on-site systems: excreta are disposed of on the site of generation;
* off-site systems with centralized treatment but using simpler and cheaper sewer systems;
* decentralized systems: wastewater is treated in small non-centralized plants close to the place of generation and the effluent is then reused locally or discharged into surface waters, or the storm drainage system not requiring large sewer systems.
On-Site Systems
Conventional wisdom holds that on-site systems can only be used in low-density areas, thus the ready acceptance for their use in rural areas, and sometimes in urban fringe areas. This opinion probably reflects experience with the early dry on-site systems, which consisted of single-pit latrines which required the owner to move the superstructure over to a newly-dug pit whenever the first one was full. As part of the development of the ventilated improved pit latrine (VIP), designed to avoid odour and insect problems, dual-pit units have been introduced. This design allows the use of one pit until full; the second pit is then used while the contents of the first mature until they can be safely removed two years later. The latrine remains permanently at one location and can be used at much higher densities, as long as access to the pits for emptying is assured. There is a big range of different on-site sanitation systems described in the literature [4,5,6].
On-site systems using small amounts of water are usually also constructed with two pits, for the same reasons that dual pits are used for dry latrines: to allow decomposition of waste and pathogen inactivation in one pit while the other pit is used. The small amount of water used for flushing percolates into the soil from the pit. Apart from the manual pour flush (only very rarely are cistern-flush systems used), the latrine functions as does a modern toilet, with a water trap sealing out odours and insects.
Both dry and wet systems are especially useful where water supply is limited (e.g., standpost or yard hydrant supplies). With limited water supply greywater disposal is not a major problem and can be used for garden watering or simply infiltrated into the ground.
A familiar and reliable on-site system is the septic tank and drain field, widely used in both industrialized and less developed countries. It is a good system provided that two operating conditions can be met: the tank itself must be fully desludged at regular intervals (and proper provision made for treatment of the sludge prior to final disposal) and the soil conditions must be satisfactory for proper treatment of the liquid effluent. Unfortunately, these conditions often do not apply in less developed countries. Emptying is only partial, and over time the tank fills with compacted sludge, and stops providing treatment.
Off-site Systems
High costs and the need for in-house water supply have been the main problems with conventional sewer systems. Intensive efforts have been made to find alternative solutions and several approaches have been introduced in developing as well as industrialized countries. The ones considered appropriate for application in less developed countries are settled sewerage and simplified sewerage . (Pressure and vacuum sewer systems have also been developed, but they require technical competence for sustainable operation that is often not available in developing countries). Both systems use small-diameter sewers laid at shallow depths in which the flow is, ideally due to gravity.
In settled sewerage systems, wastewater from one or more households is discharged into a single-compartment solids interceptor tank. The settled (solids free) effluent is then discharged into shallow, small-bore gravity sewers. Since the sewers receive only settled sewage, they are designed very differently from conventional sewers. The most obvious differences are that they are not designed for self-cleansing velocities and that the flow in the sewers can change along their length, from normal gravity open-channel flow to full-bore pressure flow and then back to open-channel flow.
The simplified sewerage system is essentially conventional sewerage stripped down to its hydraulic basics with design standards updated to reflecting technical progress made since sewers became the preferred solution to wastewater disposal problems in the last century. Small-diameter sewers laid at shallow gradients are used to convey the sewage. The sewers are often laid inside housing blocks, when the system is known as condominial sewerage.
These alternative sewer systems are less expensive to construct, and also can be to operate, than conventional sewers. Capital cost savings, under favourable conditions, can amount to as much as 50% of the cost of conventional sewers [7].
Decentralized Systems
A non-centralised wastewater management system consists of several smaller units serving individual houses, clusters of houses or small communities. The wastewater treatment facilities are correspondingly smaller, e.g. for 20 - 10,000 population equivalent. Black and greywater can be treated or reused separately from the hygienically much more dangerous excreta. Installations with urine separation devices can also be integrated.
It is generally assumed that centralised systems are more economical in the urban and suburban context, benefiting from the economies of scale. Often it is also argued that the operation of small treatment plants is less reliable and that large systems are more cost-effective. Considering the fact, that such non-centralised systems do not require long and usually very capital intensive sewer lines, it is very possible that under certain circumstances the overall costs of the entire system are considerably smaller than for a centralised system, especially in economies where the costs for capital are high compared to labour costs. Also from an ecological point of view, a non-centralized system might be more suitable. It is, for instance, less detrimental to the aquatic system if the discharge of only partially treated wastewater is distributed along the length of the receiving water. If large amounts of wastewater are discharged at one central point, it is much more important that full treatment is achieved all the time. It is well known that this requirement is difficult to fulfil under the circumstances prevailing in developing countries (e.g. lack of financial resources, lack of proper O&M, lack of skilled labour, etc.) In addition, under certain circumstances a non-centralized system might require less stringent discharge standards because the self-purifying capacity of a river can better be utilized when the wastewater discharges are distributed.
Non-centralized systems are also more flexible and can better be adapted to the local conditions of the urban area concerned. This is especially important for the fast growing agglomerations in developing countries with highly heterogeneous conditions and requirements.
Conclusions
For both human needs and better environmental management, radical re-thinking is needed. Alternatives to conventional solutions are needed which can provide water and sanitation for all within a framework that balances the needs of people with those of the environment. Technical and institutional alternatives are required which can make services less expensive and thus more affordable to low-income customers. This can only be achieved by systematically involving all stakeholders in the planning, implementation and operation stages. The Household-Centred Environmental Sanitation model has been suggested as a strategic planning tool for a comprehensive analysis of urban environmental sanitation needs and the systematic planning of service improvements. It has been developed in the context of environmental sanitation, but could equally be applied to water demand management, and indeed to integrated water resources management.
टिप्पणियाँ
Vivek K Rai
Bhopal