Simplified sewerage
Encyclopedia
Simplified sewerage is a low-cost sewer
system that collects all household wastewater
(WC
wastes and sullage) in small-diameter pipes laid at fairly flat gradient
s. Simplified sewers are laid in the front yard or under the pavement (sidewalk) or - if feasible - inside the back yard, rather than in the centre of the road as with conventional sewerage. It is suitable for existing unplanned low-income areas, as well as new housing estates with a regular layout. With simplified sewerage it is crucial to have management arrangements in place to remove blockages, which are more frequent than with conventional sewers.
Simplified sewerage is sometimes also referred to as conventional sewerage with appropriate standards, implying that most conventional sewers are overdesigned.
Currently more than two billion people in developing countries do not have access to adequate sanitation
. The United Nations
have set the target to halve the share of those without access to adequate sanitation by 2015 as part of the Millennium Development Goals. The annual cost of reaching this target has been estimated at US$ 14 billion per year, including both conventional sewers and latrines in rural areas. It is estimated that simplified sewerage reduces investment costs by up to 50% compared to conventional sewerage. Assuming that US$ 10 billion would have to be spent on conventional sewers, the use of simplified sewerage could potentially save US$ 5 billion annually.
The concept of simplified sewerage emerged in parallel in Natal
, Brazil
and Karachi
, Pakistan in the early 1980s without any interaction or communication.
In both cases particular emphasis was given to community mobilization, an essential element for the success of simplified sewerage. In Latin America, and particularly in Brazil, simplified sewerage is also known as condominial sewerage
, a term that undercores the importance of community participation in planning and maintenance at the level of a housing block (known as condominio in the Spanish and Portuguese use of the term).
. It is estimated that in Brazil some 5 million people in over 200 towns and cities are served with simplified sewerage - or condominial sewerage. This corresponds to about 3% of the population of Brazil and about 6% of the population connected to sewers. They serve poor and rich alike.
Simplified sewerage has also been used in
In Pakistan, beginning with the Orangi Pilot Project
in Karachi, a variation of simplified sewerage using larger diameter pipes has been used.
Typically, in the planning process for a simplified sewerage system, meetings are carried out at the housing block (condominio) level for information, discussions and clarifications required for a joint group decision on network design, community contributions during construction and maintenance responsibilities. Users might finance and implement in-house sanitary installations and household connections and would agree on a suitable type of condominial branch. They are asked to comply with agreements established for construction and operation of the condominial branch, as well as payment of tariffs. In turn, the service provider agrees to fulfill his responsibilities as established in the “Terms of Connection ” between the parties.
The community participation process also provides a good opportunity for complementary actions like hygiene
promotion, which can have a significant impact on public health at a relatively limited cost.
In Latin America typical simplified sewer diameters are 100 mm, laid at a gradient of 1 in 200 (0.5 percent). Such a sewer will serve around 200 households of 5 people with a wastewater flow of 80 litres per person per day. In Pakistan, however, there are no rigorous standards for sewer diameters. In a small pilot as part of the Orangi Pilot Project
pipes with a diameter of 150mm were used.
Laying small diameter pipes at fairly flat gradients requires careful construction techniques. Plastic pipes are best used as they are more easily jointed correctly. This reduces wastewater leakage from the sewer and groundwater infiltration into it. With simplified sewerage there is no need to have the large expensive manholes of the type used for conventional sewerage — simple brick or plastic junction chambers are used instead.
Construction can be carried out by contractors or by trained and properly supervised community members. Training and proper supervision are actually needed in both cases, since contractors in many cities are not familiar with simplified sewerage.
Construction costs of simplified sewerage are up to half the costs of conventional sewerage. Investment cost savings come from various design features that may or may not be present in a particular simplified sewerage system.
Cost-saving features of any simplified sewerage system are a smaller diameter of pipes, smaller and shallower trenches and simplified manholes. The two latter features are estimated to account for most of the cost savings.
Other features that could further reduce costs may only be present in some systems, such as:
An element that may slightly increase costs compared to conventional sewerage is the introduction of grease traps or of interceptor chambers for the settlement of sludge. The latter are more common in South Asia and are not used in the condominial model.
A recent study of four countries shows cost savings of 31-57% from the use of simplified sewerage compared to conventional sewerage with unit costs varying from US$ 119 per connection in a neighborhood in Bolivia and to US$ 759 per connection in a small town in Paraguay. A detailed estimate gives the costs of simplified sewerage in Lima as at least US$ 700 per household (US$120–140 per person), including in-house sanitary facilities (US$ 100 per household) and including design, supervision and social intermediation costs (US$ 126 per household, which are common costs shared with water infrastructure), but excluding taxes.
In general, at higher population densities sewer systems are cheaper than on-site sanitation (such as septic tank
s). The switching value at which sewerage becomes less costly is largely determined by the type of sewerage, conventional or simplified. A 1983 study in Natal
showed that the investment costs for simplified sewerage were lower than for on-site systems at the quite low population density of about 160 people per hectare
. Conventional sewerage, however, was cheaper only at densities above 400 people per hectare.
The original concept of householders being responsible for O&M of in-block condominial sewers has not worked well in the long term. A study of simplified sewerage systems in Brazil has shown that effective maintenance of sewers by utilities has often been the result of community pressure by neighborhood associations. Without such pressure maintenance by utilities has often been inadequate, and community maintenance has not come about either.
Therefore, alternative management systems had to be developed and a few examples are provided below:
Concerning maintenance costs, available information indicates similar costs and requirements for the simplified and the conventional system under the same conditions. Simplified systems typically require more interventions, but the cost per intervention is lower. Comparative analytical studies are not yet available, however.
Over the last years, countries like Bolivia and Peru reviewed and modernized technical standards according to methods and criteria established and accepted in Brazil in the 1980s, thus overcoming the latter constraint.
Case Studies and Pilot Projects
Sanitary sewer
A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
system that collects all household wastewater
Wastewater
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...
(WC
Flush toilet
A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing...
wastes and sullage) in small-diameter pipes laid at fairly flat gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
s. Simplified sewers are laid in the front yard or under the pavement (sidewalk) or - if feasible - inside the back yard, rather than in the centre of the road as with conventional sewerage. It is suitable for existing unplanned low-income areas, as well as new housing estates with a regular layout. With simplified sewerage it is crucial to have management arrangements in place to remove blockages, which are more frequent than with conventional sewers.
Simplified sewerage is sometimes also referred to as conventional sewerage with appropriate standards, implying that most conventional sewers are overdesigned.
Currently more than two billion people in developing countries do not have access to adequate sanitation
Sanitation
Sanitation is the hygienic means of promoting health through prevention of human contact with the hazards of wastes. Hazards can be either physical, microbiological, biological or chemical agents of disease. Wastes that can cause health problems are human and animal feces, solid wastes, domestic...
. The United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...
have set the target to halve the share of those without access to adequate sanitation by 2015 as part of the Millennium Development Goals. The annual cost of reaching this target has been estimated at US$ 14 billion per year, including both conventional sewers and latrines in rural areas. It is estimated that simplified sewerage reduces investment costs by up to 50% compared to conventional sewerage. Assuming that US$ 10 billion would have to be spent on conventional sewers, the use of simplified sewerage could potentially save US$ 5 billion annually.
The concept of simplified sewerage emerged in parallel in Natal
Natal, Rio Grande do Norte
-History:The northeastern tip of South America, Cabo São Roque, to the north of Natal and the closest point to Europe from Latin America, was first visited by European navigators in 1501, in the 1501–1502 Portuguese expedition led by Amerigo Vespucci, who named the spot after the saint of the day...
, Brazil
Water supply and sanitation in Brazil
Water supply and sanitation in Brazil is characterized by both achievements and challenges. Among the achievements is an increase in access to piped water supply from 66% to 77% between 1990 and 2006; an increase in access to improved sanitation from 71% to 77% in the same period; a functioning...
and Karachi
Karachi
Karachi is the largest city, main seaport and the main financial centre of Pakistan, as well as the capital of the province of Sindh. The city has an estimated population of 13 to 15 million, while the total metropolitan area has a population of over 18 million...
, Pakistan in the early 1980s without any interaction or communication.
In both cases particular emphasis was given to community mobilization, an essential element for the success of simplified sewerage. In Latin America, and particularly in Brazil, simplified sewerage is also known as condominial sewerage
Condominial sewerage
Condominial sewerage is the application of simplified sewerage coupled with consultations and ongoing interactions between users and agencies during planning and implementation. The term is used primarily in Latin America, particularly in Brazil, and is derived from the term condominio ....
, a term that undercores the importance of community participation in planning and maintenance at the level of a housing block (known as condominio in the Spanish and Portuguese use of the term).
Background
In developing countries, connection to sewer systems is often costly for poor households, despite typically low monthly sewer tariffs. This apparent paradox is explained by the high costs of in-plot and in-house sanitary installations that have to be paid entirely by the user, by sometimes high sewer connection fees levied by utilities, and by a lack of community consultation. As a result, in many cities in developing countries conventional sewers are laid at high costs under a street, while many users on that street do not connect to them. In Brazil, in some cities connection rates in the early 1990s were less than 40% of the intended beneficiary population.Application
Simplified sewerage is most widely used in BrazilWater supply and sanitation in Brazil
Water supply and sanitation in Brazil is characterized by both achievements and challenges. Among the achievements is an increase in access to piped water supply from 66% to 77% between 1990 and 2006; an increase in access to improved sanitation from 71% to 77% in the same period; a functioning...
. It is estimated that in Brazil some 5 million people in over 200 towns and cities are served with simplified sewerage - or condominial sewerage. This corresponds to about 3% of the population of Brazil and about 6% of the population connected to sewers. They serve poor and rich alike.
Simplified sewerage has also been used in
- BoliviaWater supply and sanitation in BoliviaBolivia’s water and sanitation coverage has greatly improved since 1990 due to a considerable increase in sectoral investment. However, the country continues to suffer from what happens to be the continent’s lowest coverage levels as well as from low quality of services...
, beginning with a pilot project in El AltoEl AltoAt one time merely a suburb of adjacent La Paz, Bolivia, on the Altiplano highlands, the city of El Alto is today one of Bolivia's largest and fastest-growing urban centers. As of the 2001 census, the population was 649,958. In 2010, the population may be nearly 900,000, or more. The city contains...
; - HondurasWater supply and sanitation in HondurasWater supply and sanitation coverage in Honduras has increased significantly in the last decades. However, the sector is still characterized by poor service quality and poor efficiency in many places. Coverage gaps still remain, particularly in rural areas....
, primarily in marginal areas of Tegucigalpa where simplified sewerage has been introduced in 20 communities with 24,000 inhabitants; - PeruWater supply and sanitation in PeruThe water and sanitation sector in Peru has made important advances in the last two decades, including the increase of water access from 30% to 62% between 1980 and 2004. Sanitation access has also increased from 9% to 30% from 1985 to 2004 in rural areas. Advances have also been achieved...
, primarily in marginal areas of Lima; - in South AfricaWater supply and sanitation in South AfricaWater supply and sanitation in South Africa is characterized by both achievements and challenges. After the end of Apartheid South Africa's newly elected government inherited huge services backlogs with respect to access to water supply and sanitation. About 15 million people were without safe...
, where pilot projects were carried out in JohannesburgJohannesburgJohannesburg also known as Jozi, Jo'burg or Egoli, is the largest city in South Africa, by population. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, having the largest economy of any metropolitan region in Sub-Saharan Africa...
and Durban; - in Sri Lanka, where the National Housing Development Authority implemented over 20 schemes in the 1980s and 90s.
In Pakistan, beginning with the Orangi Pilot Project
Orangi Pilot Project
The Orangi Pilot Project refers to a socially innovative project carried out in 1980s in the squatter areas of Orangi Town, Karachi, Sindh, Pakistan. It was initiated by Akhtar Hameed Khan, and involved the local residents solving their own sanitation problems...
in Karachi, a variation of simplified sewerage using larger diameter pipes has been used.
Community participation
Community participation in the planning of any sewer system is a fundamental requirement to achieve higher household connection rates and to increase the likelihood of proper maintenance of in-block sewers. In addition, it can motivate users to assume parts of the costs of the sewer system that they are able to assume, such as contribution of labor for construction and/or maintenance.Typically, in the planning process for a simplified sewerage system, meetings are carried out at the housing block (condominio) level for information, discussions and clarifications required for a joint group decision on network design, community contributions during construction and maintenance responsibilities. Users might finance and implement in-house sanitary installations and household connections and would agree on a suitable type of condominial branch. They are asked to comply with agreements established for construction and operation of the condominial branch, as well as payment of tariffs. In turn, the service provider agrees to fulfill his responsibilities as established in the “Terms of Connection ” between the parties.
The community participation process also provides a good opportunity for complementary actions like hygiene
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
promotion, which can have a significant impact on public health at a relatively limited cost.
Design and construction
Simplified sewers are usually laid in the front yard or under the pavement (sidewalk). In some rare cases it is possible to lay them in the back yard. Sidewalk branches are usually preferred in regular urbanizations, while the front and back yard branches are particularly suited to neighborhoods with challenging topography or urbanization patterns. However, in some cases neither of these options is possible. For example, in South Asia, in many cities there is no sidewalk or front yard, so pipes have to be laid in the middle of the street as with conventional sewers.In Latin America typical simplified sewer diameters are 100 mm, laid at a gradient of 1 in 200 (0.5 percent). Such a sewer will serve around 200 households of 5 people with a wastewater flow of 80 litres per person per day. In Pakistan, however, there are no rigorous standards for sewer diameters. In a small pilot as part of the Orangi Pilot Project
Orangi Pilot Project
The Orangi Pilot Project refers to a socially innovative project carried out in 1980s in the squatter areas of Orangi Town, Karachi, Sindh, Pakistan. It was initiated by Akhtar Hameed Khan, and involved the local residents solving their own sanitation problems...
pipes with a diameter of 150mm were used.
Laying small diameter pipes at fairly flat gradients requires careful construction techniques. Plastic pipes are best used as they are more easily jointed correctly. This reduces wastewater leakage from the sewer and groundwater infiltration into it. With simplified sewerage there is no need to have the large expensive manholes of the type used for conventional sewerage — simple brick or plastic junction chambers are used instead.
Construction can be carried out by contractors or by trained and properly supervised community members. Training and proper supervision are actually needed in both cases, since contractors in many cities are not familiar with simplified sewerage.
Investment cost comparison
The cost of sewerage - conventional or simplified - are always site-specific, and estimates are subject to controversies.Construction costs of simplified sewerage are up to half the costs of conventional sewerage. Investment cost savings come from various design features that may or may not be present in a particular simplified sewerage system.
Cost-saving features of any simplified sewerage system are a smaller diameter of pipes, smaller and shallower trenches and simplified manholes. The two latter features are estimated to account for most of the cost savings.
Other features that could further reduce costs may only be present in some systems, such as:
- shorter networks;
- avoidance of the need to damage pavements and sidewalks (if they already exist and if pipes are laid in front or back yards);
- decentralized, small-scale wastewater treatment, and consequently elimination of main collectors and sewage pumping stations.
An element that may slightly increase costs compared to conventional sewerage is the introduction of grease traps or of interceptor chambers for the settlement of sludge. The latter are more common in South Asia and are not used in the condominial model.
A recent study of four countries shows cost savings of 31-57% from the use of simplified sewerage compared to conventional sewerage with unit costs varying from US$ 119 per connection in a neighborhood in Bolivia and to US$ 759 per connection in a small town in Paraguay. A detailed estimate gives the costs of simplified sewerage in Lima as at least US$ 700 per household (US$120–140 per person), including in-house sanitary facilities (US$ 100 per household) and including design, supervision and social intermediation costs (US$ 126 per household, which are common costs shared with water infrastructure), but excluding taxes.
In general, at higher population densities sewer systems are cheaper than on-site sanitation (such as septic tank
Septic tank
A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations...
s). The switching value at which sewerage becomes less costly is largely determined by the type of sewerage, conventional or simplified. A 1983 study in Natal
Natal, Rio Grande do Norte
-History:The northeastern tip of South America, Cabo São Roque, to the north of Natal and the closest point to Europe from Latin America, was first visited by European navigators in 1501, in the 1501–1502 Portuguese expedition led by Amerigo Vespucci, who named the spot after the saint of the day...
showed that the investment costs for simplified sewerage were lower than for on-site systems at the quite low population density of about 160 people per hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
. Conventional sewerage, however, was cheaper only at densities above 400 people per hectare.
Operation and maintenance
Good operation and maintenance (O&M) is essential for the long-term sustainability of any sewerage system, but particularly for simplified sewerage, since the low diameter of pipes and low gradients make the system more vulnerable to clogging.The original concept of householders being responsible for O&M of in-block condominial sewers has not worked well in the long term. A study of simplified sewerage systems in Brazil has shown that effective maintenance of sewers by utilities has often been the result of community pressure by neighborhood associations. Without such pressure maintenance by utilities has often been inadequate, and community maintenance has not come about either.
Therefore, alternative management systems had to be developed and a few examples are provided below:
- In rural CearáCearáCeará is one of the 27 states of Brazil, located in the northeastern part of the country, on the Atlantic coast. It is currently the 8th largest Brazilian State by population and the 17th by area. It is also one of the main touristic destinations in Brazil. The state capital is the city of...
a villager is employed by the Residents’ Association to maintain the sewers and the wastewater treatment plantSewage treatmentSewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
(typically, a single facultative waste stabilization pond). He is also responsible for the water supply. - In parts of RecifeRecifeRecife is the fifth-largest metropolitan area in Brazil with 4,136,506 inhabitants, the largest metropolitan area of the North/Northeast Regions, the 5th-largest metropolitan influence area in Brazil, and the capital and largest city of the state of Pernambuco. The population of the city proper...
in northeast Brazil the state water and sewerage company employs local contracting firms for O&M. Usually this is done by a small team comprising a technician engineer and two laborers who work in a low-income area served by simplified sewerage and to whom residents report any problems. - In BrasíliaBrasíliaBrasília is the capital city of Brazil. The name is commonly spelled Brasilia in English. The city and its District are located in the Central-West region of the country, along a plateau known as Planalto Central. It has a population of about 2,557,000 as of the 2008 IBGE estimate, making it the...
the water and sewerage company, which has over 1,200 km of condominial sewers, uses van-mounted water jet units to clear any blockages.
Concerning maintenance costs, available information indicates similar costs and requirements for the simplified and the conventional system under the same conditions. Simplified systems typically require more interventions, but the cost per intervention is lower. Comparative analytical studies are not yet available, however.
Constraints for the application of simplified sewerage
According to Jose Carlos Melo, who is considered to be the "father" of condominial sewers in Brazil, some important constraints for the application of simplified sewerage are:- Lack of information on fundamentals and techniques of the approach or lack of experience in its application,
- Resistance to change: Institutional, technical and operational changes required by the service provider for implementing the condominial approach usually provoke resistance and can hinder the application.
- Normative and legal restrictions: Existing conservative design and construction standards linked to conventional systems can be an essential constraint in the introduction and dissemination of the systems.
Over the last years, countries like Bolivia and Peru reviewed and modernized technical standards according to methods and criteria established and accepted in Brazil in the 1980s, thus overcoming the latter constraint.
Sources
General- Simplified Sewerage, Sanitation Connection, Duncan Mara, Leeds University
- CONDOMINIAL SYSTEMS - BRAZILIAN PANORAMA AND CONCEPTUAL ELEMENTS, Leeds University
- Jose Carlos Melo: La ciudad y el saneamiento, 2007
- Roszler, MIT: Reasons for the failure of community participation in the maintenance of Brazilian condominial sewers
- Water and Sanitation Program: Expanding the condominial water and sanitation model in Latin America
- Jose Carlos Melo, 1996: What is a condominial system?
- Gabrielle Watson: Good Sewers Cheap? Agency-Customer Interactions in Low-Cost Urban Sanitation in Brazil, The World Bank, 1995.
- Miguel Vargas-Ramírez and Teresa Cristina Lampoglia: Scaling-up using condominial technology, waterlines, Vol. 25, No. 2, October 2006, p. 11-13
Case Studies and Pilot Projects
- Neder and Nazareth, 1983: Condominial sewer systems for the Federal District of Brazil
- IRC/WSP 2004: The El Alto Condominial Sewer Pilot Project in Bolivia
- Building Partnerships for Development in Water and Sanitation, 2000: The El Alto Condominial Sewer Pilot Project in Bolivia
- Condominial Sewer Pilot Project in Johannesburg, South Africa
- UNICEF 1997: The construction of low-cost sewerage systems in Tegucigalpa: A feasible solution for the urban poor?