Decentralized wastewater system

Last updated
Constructed wetland for decentralized wastewater treatment at a school in Lusaka, Zambia Constructed wetland (5268650754).jpg
Constructed wetland for decentralized wastewater treatment at a school in Lusaka, Zambia

Decentralized wastewater systems (also referred to as decentralized wastewater treatment systems) convey, treat and dispose or reuse wastewater from small and low-density communities, buildings and dwellings in remote areas, individual public or private properties. [1] Wastewater flow is generated when appropriate water supply is available within the buildings or close to them.

Contents

Decentralized wastewater systems treat, reuse or dispose the effluent in relatively close vicinity to its source of generation. They have the purpose to protect public health and the natural environment by reducing substantially health and environmental hazards.

They are also referred as "decentralized wastewater treatment systems" because the main technical challenge is the adequate choice of a treatment and/or disposal facility. [2] [3] A commonly used acronym for decentralized wastewater treatment system, is DEWATS. [3]

Background

Comparison to centralized systems

Centralized wastewater systems are the most widely applied in well-developed urban environments and the oldest approach to the solution of the problems associated with wastewater. [4] They collect wastewater in large and bulk pipeline networks, also referred as sewerage, which transport it at long distances to one or several treatment plants. Storm water can be collected in either combined sewers or in a separate storm water drains. The latter consists of two separate pipeline systems, one for the wastewater and one for the storm water. The treated effluent is disposed in different ways, most often discharged into natural water bodies. The treated effluent may also be used for beneficial purposes and in this case it is referred as reclaimed water.[ citation needed ]

The main difference between decentralized and centralized systems is in the conveyance structure. In decentralized systems the treatment and disposal or reuse of the effluent is close to the source of generation. This results in a small conveyance network, in some cases limited only to one pipeline. The size of the network allows for applications of different conveyance methods, in addition to the well-known gravity sewers, such as pressurized sewers and vacuum sewers. The quantity of the effluent is low and is characterized by significant fluctuations.[ citation needed ]

Applications

In locations with developed infrastructure, decentralized wastewater systems could be a viable alternative of the conventional centralized system, especially in cases of upgrading or retrofitting existing systems. [5] This can be easier to accomplish with decentralized systems, as centralized infrastructures have long lifetimes and are locked into their location and condition. [6] Many different combinations and variations of hybrid systems are possible.

Decentralized applications are a necessity in cases of new urban developments, where the construction of the infrastructure is not ready or will be executed in future. In many regions, the infrastructure development (roads, water supply and especially wastewater/drainage systems) is executed years after the housing development. In such cases decentralized wastewater facilities are considered as a temporary solution, but they are mandatory, in order to prevent public health and ecological problems. In this context, decentralized solutions are favorable in their ability to be locally applied as needed, while still carrying the potential to cover large areas at lower costs. [6]

Decentralized systems allow for flow separation or source separation, which segregates different types of wastewater, based on their origin, such as: black water, greywater and urine. [5] This approach requires separate parallel pipeline/plumbing systems to convey the segregated flows and the purpose is to apply different level of treatment and handling of each flow and to enhance the safe reuse and disposal of the end products. [7]

In the specific case of developing countries, where localities with poor infrastructure are common, decentralized wastewater treatment has been promoted extensively because of the possibility to apply technologies with low operation and maintenance requirements. [8] In addition, decentralized approaches require smaller scale investments, compared to centralized solutions. [6]

Types

Decentralized wastewater system in Torvetua eco-village in Norway. Wastewater is collected by a vacuum sewer. Greywater is treated locally. Torvetua eco-village (3254898889).jpg
Decentralized wastewater system in Torvetua eco-village in Norway. Wastewater is collected by a vacuum sewer. Greywater is treated locally.

Based on the size of the served area, different scales of decentralization could be found:[ citation needed ]

Wastewater treatment options

Biogas digester for decentralized wastewater treatment at Meru Prison, Kenya Biogas digester at Meru prison (3504698658).jpg
Biogas digester for decentralized wastewater treatment at Meru Prison, Kenya

Treatment/disposal facilities requiring effluent infiltration

Usually they are applied at on-site level and are adequate because of the very low wastewater quantity generated. However, they require suitable soil conditions, permitting infiltration of the excess water, and low ground water table. If not applied properly, they may be a serious source of ground water pollution. [9]

Treatment facilities resembling natural purification processes

Their application requires significant surface area, because of the slow pace of the biological processes applied. For the same reason they are more suitable for warmer climates, because the rate of the purification process is temperature dependent. These technologies are more resilient to fluctuating loads and do not require complex maintenance and operation. [10] Constructed wetlands are more suitable for applications at on-site or at neighbourhood level, while stabilization ponds could be a viable alternative for decentralized systems at the level of small towns or rural communities.[ citation needed ]

Engineered wastewater treatment technologies

There is a large variety of wastewater treatment plants where different treatment processes and technologies are applied. [11] Small-scale treatment facilities in decentralized systems, apply similar technologies as medium or large plants. [12] For on-site applications package plants are developed, which are compact and have different compartments for the different processes. However, the design and operation of small treatment plants, especially at neighbourhood or on-site level, present significant challenges to wastewater engineers, related to flow fluctuations, necessity of competent and specialized operation and maintenance, required to deal with a large number of small plants, and relatively high per capita cost. [13]

Regulations and management

Water pollution regulations in the form of legislation documents, guidelines or ordinances prescribe the necessary level of treatment, so that the treated effluent meets the requirements for safe disposal or reuse. Effluent may be disposed by discharging into a natural water body or infiltrated in the ground. In addition, regulations mention requirements regarding the design and operation of wastewater systems, as well as the penalties and other measures for their enforcement. Centralized systems are designed, built and operated in order to fulfil the existing regulations. Their management usually is executed by local authorities. In hybrid systems and small centralized systems in towns or rural communities management can be executed in the same way. [12] [ citation needed ]

In the case of decentralization at on-site level and clusters of buildings, the whole wastewater system is located within private premises. The costs and responsibility for the design, construction, operation and maintenance is the responsibility of the owner. In many cases specialized companies might execute the operation and maintenance procedures. The local authorities issue permits and may provide support for the operation and management in the form of collecting wastes, issuing certificates/licenses for standardized treatment equipment, or for selected qualified private companies. From regulatory point of view, the control of the quality of treated effluent for reuse, discharge or disposal is entirely the responsibility of local or national government authorities. This might be a challenge if a large number of systems must be controlled and inspected. It is in the owner's interest to operate and maintain the system properly, especially in the case of reuse of the treated effluent. Most often the operational problems are associated with clogging of the treatment facilities as result of irregular removal of the sludge or hydraulic overloading due to increased number of population served or increased water consumption. [9] [ citation needed ]

Urban planning and infrastructure issues

Wastewater systems are part of the infrastructure of urban or rural communities and the urban planning process. Urban planning data and information, such as plots of individual dwellings, roads/streets, stormwater drainage, water supply, and electricity systems are essential for the design and implementation of a sustainable wastewater system. In decentralized wastewater systems, which collect and treat wastewater only, stormwater might be overlooked and cause flooding problems. If planned decentralized solutions are applied, stormwater drainage should be executed together with the roads system.[ citation needed ]

In under-developed population centres where no infrastructure is available, is difficult to provide sustainable sanitation measures; e.g. pit latrines/septic tanks need periodic cleansing, usually executed by vacuum trucks, which have to access the latrine and need a basic road for this purpose. [14] Fecal sludge management deals with the organization and implementation of this practice in a sustainable way, including collection, transport, treatment and disposal/reuse of faecal sludge from pit latrines and septic tanks. [15]

In the cases of new urban/rural developments, or the retrofitting of existing ones, it is advisable to consider different alternatives regarding the design of the wastewater system, including decentralized solutions. A sustainable approach would require optimal technical solutions in terms of reliability and cost effectiveness. [16] [17] From this perspective, centralized solutions might be more appropriate in many cases, depending on existing sizes of plots, topography, geology, groundwater tables and climatic conditions. But when applied adequately, decentralized systems allow for the application of environmentally friendly solutions and reuse of the treated effluent, including resource recovery. In this way, alternative water resources are provided and the environment is protected. Public awareness, perceptions and support play an important part in the urban planning process for choosing adequate wastewater systems which fit the specific context. [16] [18]

Examples

BORDA

One example of decentralized treatment is the "DEWATS technology" which has been promoted under this name by the German NGO BORDA. [3] [8] It has been applied in many countries in South East Asia and in South Africa. [19] [20] It applies anaerobic treatment processes, including anaerobic baffled reactors (ABRs) and anaerobic filters, followed by aerobic treatment in ponds or in constructed wetlands. This technology was researched and tested in South Africa where it was shown that the treatment efficiency was lower than expected. [21]

Botswana Technology Centre

A case study of a decentralized wastewater system at on-site level with treated effluent reuse was performed at the Botswana Technology Centre in Gaborone, Botswana. [22] It is an example of a decentralized wastewater system, which serves one institutional building, located in an area served by municipal sewerage. Wastewater from the building is treated in a plant consisting of: septic tank, followed by planted rock filter, bio-filter and a surface flow wetland. The treated effluent is reused for irrigation of the surrounding green areas, but the study registered outflow from the wetland only during periods of heavy rains. This example shows the need for careful estimation of the expected quantity, quality and fluctuations of the generated wastewater when designing decentralized wastewater systems.[ citation needed ]

EcoSwell

Founded in 2013, the Peru-based NGO EcoSwell works on rural development projects, including water supply and sanitation in Peru; they are based in the northwestern Lobitos district of the Talara region, an arid coastal area that faces water stress. [23] EcoSwell establishes decentralized wastewater systems with the help of local residents and interns, including communal biodigesters, dry toilets, and greywater reuse projects. [24] They also work on reforestation and constructed wetlands as avenues to naturally treat waste effluent and deactivate pathogens. [24]

See also

Related Research Articles

<span class="mw-page-title-main">Sanitation</span> Public health conditions related to clean water and proper excreta and sewage disposal

Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems aim to protect human health by providing a clean environment that will stop the transmission of disease, especially through the fecal–oral route. For example, diarrhea, a main cause of malnutrition and stunted growth in children, can be reduced through adequate sanitation. There are many other diseases which are easily transmitted in communities that have low levels of sanitation, such as ascariasis, cholera, hepatitis, polio, schistosomiasis, and trachoma, to name just a few.

<span class="mw-page-title-main">Greywater</span> Type of wastewater generated in households without toilet wastewater

Greywater refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater from toilets. Sources of greywater include sinks, showers, baths, washing machines or dishwashers. As greywater contains fewer pathogens than blackwater, it is generally safer to handle and easier to treat and reuse onsite for toilet flushing, landscape or crop irrigation, and other non-potable uses. Greywater may still have some pathogen content from laundering soiled clothing or cleaning the anal area in the shower or bath.

<span class="mw-page-title-main">Sanitary sewer</span> Underground pipe for transporting sewage

A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to a sewage treatment plant or disposal.

<span class="mw-page-title-main">Wastewater treatment</span> Converting wastewater into an effluent for return to the water cycle

Wastewater treatment is a process which removes and eliminates contaminants from wastewater and converts this into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes. The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater, the treatment plant is called a Sewage Treatment. For industrial wastewater, treatment either takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant. Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.

<span class="mw-page-title-main">Industrial wastewater treatment</span> Processes used for treating wastewater that is produced by industries as an undesirable by-product

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.

Onsite sewage facilities (OSSF), also called septic systems, are wastewater systems designed to treat and dispose of effluent on the same property that produces the wastewater, in areas not served by public sewage infrastructure.

Water supply and sanitation in the United States involves a number of issues including water scarcity, pollution, a backlog of investment, concerns about the affordability of water for the poorest, and a rapidly retiring workforce. Increased variability and intensity of rainfall as a result of climate change is expected to produce both more severe droughts and flooding, with potentially serious consequences for water supply and for pollution from combined sewer overflows. Droughts are likely to particularly affect the 66 percent of Americans whose communities depend on surface water. As for drinking water quality, there are concerns about disinfection by-products, lead, perchlorates, PFAS and pharmaceutical substances, but generally drinking water quality in the U.S. is good.

<span class="mw-page-title-main">Sustainable sanitation</span> Sanitation system designed to meet certain criteria and to work well over the long-term

Sustainable sanitation is a sanitation system designed to meet certain criteria and to work well over the long-term. Sustainable sanitation systems consider the entire "sanitation value chain", from the experience of the user, excreta and wastewater collection methods, transportation or conveyance of waste, treatment, and reuse or disposal. The Sustainable Sanitation Alliance (SuSanA) includes five features in its definition of "sustainable sanitation": Systems need to be economically and socially acceptable, technically and institutionally appropriate and protect the environment and natural resources.

The Bremen Overseas Research and Development Association (BORDA) is a non-profit international development organization headquartered in Bremen, Germany.It has regional offices in Afghanistan, India, Indonesia, Mexico, and Tanzania as well as several project offices within each region. BORDA began its work in 1977, starting with its first project, “Technology Transfer of Biogas India-Ethiopia.” Since then, it has been active in the delivery of basic needs services across the developing world.BORDA is a partner organization of the Sustainable Sanitation Alliance. BORDA participates in the promotion and implementation of DEWATS systems in many countries in Asia and Africa.

<span class="mw-page-title-main">Sewage treatment</span> Process of removing contaminants from municipal wastewater

Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage,  using aerobic or anaerobic biological processes. A so-called quarternary treatment step can also be added for the removal of organic micropollutants, such as pharmaceuticals. This has been implemented in full-scale for example in Sweden.

Syria is a semi-arid country with scarce water resources. The largest water-consuming sector in Syria is agriculture. Domestic water use is only about 9% of total water use. A big challenge for Syria is its high population growth, with a rapidly increasing demand for urban and industrial water. In 2006, the population of Syria was 19.4 million with a growth rate of 2.7%.

<span class="mw-page-title-main">Effluent sewer</span>

Effluent sewer systems, also called septic tank effluent gravity (STEG), solids-free sewer (SFS), or septic tank effluent drainage (STED) systems, have septic tanks that collect sewage from residences and businesses, and the liquid fraction of sewage that comes out of the tank is conveyed to a downstream receiving body such as either a centralized sewage treatment plant or a distributed treatment system for further treatment or disposal away from the community generating the sewage. Most of the solids are removed by the interceptor tanks, so the treatment plant can be much smaller than a typical plant and any pumping for the supernatant can be simpler without grinders.

Water supply and sanitation in Japan is characterized by numerous achievements and some challenges. The country has achieved universal access to water supply and sanitation, has one of the lowest levels of water distribution losses in the world, regularly exceeds its own strict standards for the quality of drinking water and treated waste water, uses an effective national system of performance benchmarking for water and sanitation utilities, makes extensive use of both advanced and appropriate technologies such as the jōkasō on-site sanitation system, and has pioneered the payment for ecosystem services before the term was even coined internationally. Some of the challenges are a decreasing population, declining investment, fiscal constraints, ageing facilities, an ageing workforce, a fragmentation of service provision among thousands of municipal utilities, and the vulnerability of parts of the country to droughts that are expected to become more frequent due to climate change.

Sustainable implant is an urban typology that acts as a decentralized infrastructure provision hub on the neighborhood or district scale. Sustainable implants provide integrated infrastructure services that maintain cycles of energy, water and material, as well as provides social and economic returns. The concept originates from Arjan van Timmeren's research, Autonomy & Heteronomy (2006), as an answer to the problem of scale versus innovation in infrastructure; wherein infrastructure benefits from increasing returns to scale but suffer from extremely slow rate of change and turnover. To answer this problem, the sustainable implant is an instrument for mid-scale facilitation of alternative system innovation. The sustainable implant is a synthesis of techniques for sustainable processing of urban flows within an ecological processing device. The objective of a sustainable implant is to generate qualitative and quantitative improvements for utility service provision.

<span class="mw-page-title-main">Urine-diverting dry toilet</span> Dry toilet with separate collection of feces and urine without any flush water

A urine-diverting dry toilet (UDDT) is a type of dry toilet with urine diversion that can be used to provide safe, affordable sanitation in a variety of contexts worldwide. The separate collection of feces and urine without any flush water has many advantages, such as odor-free operation and pathogen reduction by drying. While dried feces and urine harvested from UDDTs can be and routinely are used in agriculture, many UDDT installations do not apply any sort of recovery scheme. The UDDT is an example of a technology that can be used to achieve a sustainable sanitation system. This dry excreta management system is an alternative to pit latrines and flush toilets, especially where water is scarce, a connection to a sewer system and centralized wastewater treatment plant is not feasible or desired, fertilizer and soil conditioner are needed for agriculture, or groundwater pollution should be minimized.

<span class="mw-page-title-main">Fecal sludge management</span> Collection, transport, and treatment of fecal sludge from onsite sanitation systems

Fecal sludge management (FSM) is the storage, collection, transport, treatment and safe end use or disposal of fecal sludge. Together, the collection, transport, treatment and end use of fecal sludge constitute the "value chain" or "service chain" of fecal sludge management. Fecal sludge is defined very broadly as what accumulates in onsite sanitation systems and specifically is not transported through a sewer. It is composed of human excreta, but also anything else that may go into an onsite containment technology, such as flushwater, cleansing materials, menstrual hygiene products, grey water, and solid waste. Fecal sludge that is removed from septic tanks is called septage.

<span class="mw-page-title-main">Vermifilter</span> Aerobic treatment system, consisting of a biological reactor containing media

A vermifilter is an aerobic treatment system, consisting of a biological reactor containing media that filters organic material from wastewater. The media also provides a habitat for aerobic bacteria and composting earthworms that purify the wastewater by removing pathogens and oxygen demand. The "trickling action" of the wastewater through the media dissolves oxygen into the wastewater, ensuring the treatment environment is aerobic for rapid decomposition of organic substances.

<span class="mw-page-title-main">Water reuse in California</span>

Water reuse in California is the use of reclaimed water for beneficial use. As a heavily populated state in the drought-prone arid west, water reuse is developing as an integral part of water in California enabling both the economy and population to grow.

<span class="mw-page-title-main">Container-based sanitation</span> Sanitation system which uses removable containers

Container-based sanitation refers to a sanitation system where toilets collect human excreta in sealable, removable containers that are transported to treatment facilities. This type of sanitation involves a commercial service which provides certain types of portable toilets, and delivers empty containers when picking up full ones. The service transports and safely disposes of or reuses collected excreta. The cost of collection of excreta is usually borne by the users. With suitable development, support and functioning partnerships, CBS can be used to provide low-income urban populations with safe collection, transport and treatment of excrement at a lower cost than installing and maintaining sewers. In most cases, CBS is based on the use of urine-diverting dry toilets.

Sewer mining is a concept where municipal wastewater (sewage) is pumped from a trunk sewer and treated on-site to accommodate a range of local, nonpotable water needs. It is a strategy for combating water scarcity. It combines decentralized wastewater management and water reclamation. Since 2012, it is used as a tool for improving water management and promoting reuse of water in Australia.

References

  1. "Learn about Small Wastewater Systems". United States Environmental Protection Agency . 7 January 2015. Retrieved October 15, 2020.
  2. 1 2 "Decentralized wastewater systems: a program strategy, EPA, Washington DC, USA" (PDF). Retrieved 20 March 2017.
  3. 1 2 3 "DEWATS/Decentralized wastewater treatment, BORDA, South-east Asia" . Retrieved 20 March 2017.
  4. Karman D. (2007) The 'Cloaka Maxima' and the monumental manipulation of water in archaic Rome, On-line journal  The Water of Rome, retrieved on the 18 March 2017
  5. 1 2 3 4 Tchobanoglous G., Leverenz H. (2013) The rationale for decentralization of wastewater infrastructure, in: Source separation and decentralization for wastewater management, ed: Larsen T.A., Udert K.M., Lienert J., IWA publishing, London, UK
  6. 1 2 3 Birkenholtz, Trevor (2023-07-05). "Geographies of big water infrastructure: Contemporary insights and future research opportunities". Geography Compass. 17 (8). doi:10.1111/gec3.12718. ISSN   1749-8198.
  7. WHO (2006). WHO Guidelines for the Safe Use of Wastewater, Excreta and Grey water . World Health Organization (WHO), Geneva, Switzerland
  8. 1 2 Sasse, L. (1998). DEWATS Decentralised Wastewater Treatment in Developing Countries. Bremen Overseas Research and Development Association (BORDA), Germany
  9. 1 2 Onsite wastewater treatment systems manual (2002), EPA 625/R-00/008, Washington DC, USA
  10. Scholzel & Bowel (1999) Small scale treatment plant project – report on project criteria, guidelines and technologies, SOPAC TR288, retrieved on the 18 March 2017
  11. Wastewater engineering : treatment and reuse (4th ed.). Metcalf & Eddy, Inc., McGraw Hill, USA. 2003.   ISBN   0-07-112250-8.
  12. 1 2 Crites R., Tchobanoglous G. (1998) Small and decentralized wastewater management, WCB/McGraw-Hill, ISBN   0-07-289087-8
  13. Boller. M. (1997) Small wastewater plants- a challenge to wastewater engineers, Water Science and Technology, Vol 35, issue 6, p.1-12
  14. Eggimann S., Truffer, B., Maurer, M. (2016). "Economies of density for on-site waste water treatment". Water Research. 101: 476–489. doi:10.1016/j.watres.2016.06.011. PMID   27295622.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. WSTF (2015). Design and Technologies of Decentralised Treatment Facilities - Manuals and further documents developed in the context of GIZ’s Water Sector Reform Programme. Water Services Trust Fund (WSTF), Nairobi, Kenya
  16. 1 2 Andersson, Kim; Dickin, Sarah; Rosemarin, Arno (2016-12-08). "Towards "Sustainable" Sanitation: Challenges and Opportunities in Urban Areas". Sustainability. 8 (12): 1289. doi: 10.3390/su8121289 . ISSN   2071-1050.
  17. Eggimann, S. The optimal degree of centralisation for wastewater infrastructures. A model-based geospatial economic analysis Doctoral Thesis. ETH Zurich., 30. November 2016.
  18. Wastewater - the untapped resource, The UN world water development report 2017, UNESCO
  19. ESCAP, UN-Habitat, AIT (2015). Policy guidance manual on wastewater management with a special emphasis on decentralized wastewater treatment systems. United Nations Economic and Social Commission for Asia and the Pacific (ESCAP), United Nations Human Settlements Programme (UN-Habitat) and Asian Institute of Technology (AIT), Bangkok, Thailand
  20. WRC (2014). DEWATS process for decentralised wastewater treatment - Technical lessons from eThekwini Municipality. Water Research Commission (WRC), Gezina ZA, South Africa
  21. Reynaud, N. (2015). Operation of Decentralised Wastewater Treatment Systems (DEWATS) under tropical field conditions. PhD thesis, Faculty of Environmental Sciences, Technical University, Dresden
  22. Hranova R (2005) The Wastewater Reuse Practice in Botswana – a Challenge for the Development of the Water Sector, Proceedings of the BIE annual conference – 19–21 October 2005, Gaborone, Botswana. (Proceedings in CD format)
  23. "Our Story". EcoSwell. Retrieved 2024-04-22.
  24. 1 2 "Water and Sanitation". EcoSwell. Retrieved 2024-04-22.