T.6 Constructed Wetland

Constructed Wetlands are engineered wetlands designed to filter and treat different types of wastewater mimicking processes found in natural environments.Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Constructed Wetlands can effectively treat raw, primary or secondary treated sewage, as well as greywater. The main types of Constructed Wetlands are horizontal flow (HF) wetlands and vertical flow (VF) wetlands, including the French VF wetland, which is a double-stage VF Constructed Wetland. In Constructed Wetlands a gravel media acts as a filter for removing solids, as a fixed surface to which bacteria can attach, and as a base for vegetation. The important difference between a vertical and horizontal wetland beyond the direction of the flow path, is the aeration regime. Compared to other wastewater treatment technologies, Constructed Wetlands are robust in that performance is less susceptible to input variations.

Total volume of water generated from washing food, clothes and dishware, as well as from bathing, but not from toilets (see blackwater). It may also contain traces of excreta (e.g. from washing diapers) and, therefore, some pathogens. Greywater accounts for approximately 65 % of the wastewater produced in households with flush toilets.Simple, single cell organisms that are found everywhere on earth. They are essential for maintaining life and performing essential “services”, such as composting, aerobic degradation
of waste, and digesting food in our intestines. Some types, however, can be pathogenic and cause mild to severe illnesses. Bacteria obtain nutrients from their environment by excreting enzymes that dissolve complex molecules into more simple ones which can then pass through the cell membrane.

The process by which biodegradable components are biologically decomposed by microorganisms (mainly bacteria and fungi) under controlled aerobic conditions.
Any cellular or non-cellular microbiological entity capable of replication or of transferring genetic material (e.g. bacteria, viruses, protozoa, algae or fungi).
Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
An organism or other agent that causes disease.A diverse group of unicellular eukaryotic organisms, including amoeba, ciliates, and flagellates. Some can be pathogenic and cause mild to severe illnesses.
Waste matter that is transported through the sewer.
An open channel or closed pipe used to convey sewage. See C.3 and C.4
User interface used for urination and defecation. An infectious agent consisting of a nucleic acid (DNA or RNA) and a protein coat. Viruses can only replicate in the cells of a living host. Some pathogenic viruses are known to be waterborne (e.g., the rotavirus that can cause diarrheal disease).
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.
Waste matter that is transported through the sewer.
Agent infectieux constitué d’une substance nucléique (ADN ou ARN) et d’une couche de protéines. Les virus ne peuvent se répliquer que dans les cellules d’un hôte vivant. Certains virus pathogènes sont connus pour être d’origine hydrique (par exemple le rotavirus qui peut provoquer des maladies diarrhéiques).

Design Considerations

For HF and VF wetlands efficient primary treatment is essential to prevent clogging. French VF wetlands can receive raw wastewater and require no pre-treatment. VF and French VF wetlands require intermittent loading (several times a day) to ensure aerobic conditions in the filter whereas HF wetlands and free-water surface (FWS) wetlands are loaded continuously. The specification (grain size, etc.) of sand and gravel used for the main layer defines the treatment efficiency in VF and French VF wetlands. In HF wetlands mainly an aerobic processes occur, whereas in VF and French VF wetlands with intermittent loading, aerobic processes are dominant. If topography allows intermittent loading it can be done with siphons thus avoiding external energy and pumps. Sizing of the surface mainly depends on the organic load (chemical oxygen demand per m² per day) and minimum yearly temperature. French VF wetlands consist of two stages, with at least two treatment lines to be used alternatively. The wetland plants must have deep roots and should be able to adapt to humid environments with slightly saline and nutrient-rich soil conditions. Phragmites australis or communis (reeds) are often chosen because they form a matrix of rhizomes efficient at maintaining the permeability necessary for large filtration and also decrease the risk of clogging.

Describes biological processes that occur in the presence of oxygen.
A mechanical separation process using a porous medium (e.g., cloth, paper, sand bed, or mixed media bed) that captures particulate material and permits the liquid or gaseous fraction to pass through. The size of the pores of the medium determines what is captured and what passes through.Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
The first major stage in wastewater treatment that removes solids and organic matter mostly by the process of sedimentation or flotation.
Gravity settling of particles in a liquid such that they accumulate. Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Materials

In principle, Constructed Wetlands can be built using locally available material, however, availability of sand and gravel (with required grain size distribution and cleanliness) is often a problem. Additional materials include a liner or clay, wetland plants, and a syphon or pump for intermittent loading. They are typically not suitable for pre-fabrication.

Applicability

Constructed Wetlands require wastewater to function and therefore are applicable only for waterborne sanitation systems. They are a viable solution where land is available and a wastewater treatment solution is required for a longer period of time. Wetland plants take time to become established, therefore the start-up time for Constructed Wetlands is quite long. Thus this technology is not suitable for the acute response phase but for the stabilisation and recovery periods and as a longer-term solution.

A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

The degradation of organic matter with the goal of reducing readily biodegradable compounds to lessen environmental impacts (e.g., oxygen depletion, nutrient leaching).
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Operation and Maintenance

In general, operation and maintenance (O & M) requirements are low. For VF and HF wetlands, the regular removal of primary sludge from mechanical pre-treatment is the most critical routine O & M activity. In French VF wetlands, the loading has to be alternated between the VF beds of the first stage on a weekly basis. Distribution pipes should be cleaned once a year to remove the sludge and biofilm that might cause blockage. During the first growing season, it is important to remove weeds that can compete with the planted wetland vegetation.

Mixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies, i.e. it has not been transported through a sewer. It can be raw or partially digested, a slurry or semisolid, and results from the collection and storage/treatment of excreta or blackwater, with or without greywater. Wastewater sludge (also referred to as sewage sludge) originates from sewer-based wastewater collection and (semi-)centralised treatment processes. The sludge composition will determine the type of treatment that is required and the end-use possibilities.Describes technologies for on-site collection, storage, and sometimes (pre-) treatment of the products generated at the user interface. The treatment provided by these technologies is often a function of storage and is usually passive (i.e. requires no energy input), except a few emerging technologies where additives are needed. Thus, products that are ‘treated’ by these technologies often require subsequent treatment before use and/or disposal. In the technology overview graphic, this functional group is subdivided into the two subgroups: “Collection/Storage” and “(Pre-)Treatment”. This allows a further classification for each of the listed technologies with regard to their function: collection and storage, (pre-) treatment only or both.Refers to the methods through which products are returned to the environment, either as useful resources or reduced-risk materials. Some products can also be cycled back into a system (e.g. by using treated greywater for flushing).A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The utilisation of products derived from a sanitation system.
A sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated.
The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

Waste matter that is transported through the sewer.
An open channel or closed pipe used to convey sewage. See C.3 and C.4
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.
Waste matter that is transported through the sewer.

Health and Safety

Under normal operating conditions, users do not come in contact with the influent or effluent. Influent and primary sludge must be handled with care as they contain high levels of pathogenic organisms. Removal of primary sludge can be a health hazard and appropriate safety precautions have to be taken. The facility should be designed and located such that odours (mainly from primary treatment) and mosquitos (mainly relevant for FWS wetlands) do not bother community members.

General term for a liquid that leaves a technology, typically after blackwater or sludge has undergone solids separation or some other type of treatment. Effluent originates at either a collection and storage or a (semi-) centralised treatment technology. Depending on the type of treatment, the effluent may be completely sanitised or may require further treatment before it can be used or disposed of.Mixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies, i.e. it has not been transported through a sewer. It can be raw or partially digested, a slurry or semisolid, and results from the collection and storage/treatment of excreta or blackwater, with or without greywater. Wastewater sludge (also referred to as sewage sludge) originates from sewer-based wastewater collection and (semi-)centralised treatment processes. The sludge composition will determine the type of treatment that is required and the end-use possibilities.Describes technologies for on-site collection, storage, and sometimes (pre-) treatment of the products generated at the user interface. The treatment provided by these technologies is often a function of storage and is usually passive (i.e. requires no energy input), except a few emerging technologies where additives are needed. Thus, products that are ‘treated’ by these technologies often require subsequent treatment before use and/or disposal. In the technology overview graphic, this functional group is subdivided into the two subgroups: “Collection/Storage” and “(Pre-)Treatment”. This allows a further classification for each of the listed technologies with regard to their function: collection and storage, (pre-) treatment only or both.Refers to the methods through which products are returned to the environment, either as useful resources or reduced-risk materials. Some products can also be cycled back into a system (e.g. by using treated greywater for flushing).A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The utilisation of products derived from a sanitation system.
The general name for the liquid that enters into a sanitation system or process (e.g., wastewater).
A sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated.
An organism or other agent that causes disease.The first major stage in wastewater treatment that removes solids and organic matter mostly by the process of sedimentation or flotation.
The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

Gravity settling of particles in a liquid such that they accumulate. Waste matter that is transported through the sewer.
An open channel or closed pipe used to convey sewage. See C.3 and C.4
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.
Le terme général employé pour un liquide sortant d’une infrastructure, habituellement après que les eaux noires ou les boues ont subi une séparation de la fraction solide ou un autre type de traitement. L’effluent provient soit d’un processus de collecte et de stockage, soit d’une technologie de traitement. En fonction du type de traitement, l’effluent peut être complètement assaini ou nécessiter un autre traitement avant d’être utilisé ou rejeté.Nom générique du liquide qui entre dans un système ou un processus (par exemple les eaux usées).Waste matter that is transported through the sewer.

Costs

As Constructed Wetlands are self-sustaining their lifetime costs are significantly lower than those of conventional treatment systems. Sewer lines might be the highest costs when implementing a water-borne sanitation system using Constructed Wetlands. The main O & M costs are related to the removal of primary sludge from the primary treatment (for VF and HF wetlands) and cost of electricity if pumps are used for intermittent loading. The cost of changing the filter material (approximatively every 10 years) should be factored in. The systems require significant space, and are therefore not preferred where land costs are high.

Mixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies, i.e. it has not been transported through a sewer. It can be raw or partially digested, a slurry or semisolid, and results from the collection and storage/treatment of excreta or blackwater, with or without greywater. Wastewater sludge (also referred to as sewage sludge) originates from sewer-based wastewater collection and (semi-)centralised treatment processes. The sludge composition will determine the type of treatment that is required and the end-use possibilities.Describes technologies for on-site collection, storage, and sometimes (pre-) treatment of the products generated at the user interface. The treatment provided by these technologies is often a function of storage and is usually passive (i.e. requires no energy input), except a few emerging technologies where additives are needed. Thus, products that are ‘treated’ by these technologies often require subsequent treatment before use and/or disposal. In the technology overview graphic, this functional group is subdivided into the two subgroups: “Collection/Storage” and “(Pre-)Treatment”. This allows a further classification for each of the listed technologies with regard to their function: collection and storage, (pre-) treatment only or both.Refers to the methods through which products are returned to the environment, either as useful resources or reduced-risk materials. Some products can also be cycled back into a system (e.g. by using treated greywater for flushing).A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The utilisation of products derived from a sanitation system.
A sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated.
The first major stage in wastewater treatment that removes solids and organic matter mostly by the process of sedimentation or flotation.
The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

Gravity settling of particles in a liquid such that they accumulate. Waste matter that is transported through the sewer.
An open channel or closed pipe used to convey sewage. See C.3 and C.4
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.
Waste matter that is transported through the sewer.

Social Considerations

Usually, treatment wetlands are easily accepted by locals and only minimal technical Capacity is required for O & M.

Fact Sheet Overview

Inputs

Blackwater
Effluent
Greywater

Outputs

Biomass
Effluent

Response Phase

Stabilisation +
Recovery + +

Challenging Ground Conditions

Suitable

Application Level

Household +
Neighbourhood + +
City + +

Water-based or Dry Technology

Water-Based

Management Level

Household +
Shared + +
Public + +

Technical Complexity

Medium

Functional Group

(Semi-) Centralised Treatment

Required Space

High

Objectives & Key Features

• TSS and TDS reduction
• Nitrification

Strength & Weakness

  • Low O & M requirements
  • Robust treatment performance and resistant to sudden loads of organic material or flow increases
  • Adaptable to local conditions
  • Long service life and possible use of the harvest material
  • Land requirement
  • Risk of clogging, depending on pre- and primary treatment
  • Electric pumps required for intermittent loading of
  • VF and French VF wetlands (if landscape does not allow gravity-driven systems)
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