T.7 Trickling Filter

A Trickling Filter is a fixed-bed, biological reactor that operates under (mostly) aerobic conditions. Pre-settled wastewater is continuously ‘trickled’ or sprayed over the filter. As the water percolates through the pores of the filter, organics are degraded by the biofilm covering the filter material.Describes biological processes that occur in the presence of oxygen.
Refer to biodegradable plant material (organic waste) that must be added to some technologies in order for them to function properly. Organic degradable material can include, but is not limited to, leaves, grass and food market waste. Although other products in this compendium contain organic matter, the term organics is used to refer to undigested plant material.Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

The Trickling Filter is filled with a high specific surface area material, such as rocks, gravel, shredded PVC bottles, or special pre-formed plastic filter media. The high specific surface provides a large area for biofilm formation. Organisms that grow in the thin biofilm over the surface of the media oxidise the organic load in the wastewater into carbon dioxide and water, while generating new biomass. The incoming pre-treated wastewater is trickled over the filter, e.g. with the use of a rotating sprinkler. In this way, the filter media goes through cycles of being dosed and exposed to air. However, oxygen is depleted within the biomass and the inner layers may be anoxic or an aerobic.

Describes biological processes that occur in the presence of oxygen.
Refers to plants or animals grown using the water and/or nutrients flowing through a sanitation system. The term biomass may include fish, insects, vegetables, fruit, forage or other beneficial crops that can be utilised for food, feed, fibre and fuel production.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. An oxygen depleted environment with partially aerobic and anaerobic conditions fluctuating in time and space
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 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 ratio of the surface area to the volume of a solid material (e.g., filter
media).
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Design Considerations

The filter is usually 1 to 2.5 m deep, but filters packed with lighter plastic filling can be up to 12 m deep. Primary treatment is essential to prevent clogging and to ensure efficient treatment. Adequate air flow is important to ensure sufficient treatment performance and prevent odours. The underdrains should provide a passageway for air at the maximum filling rate. A perforated slab supports the bottom of the filter, allowing the effluent and excess sludge to be collected. With time, the biomass will grow thick and the attached layer will be deprived of oxygen; it will enter an endogenous state, will lose its ability to stay attached and will slough off. High-rate loading conditions will also cause sloughing. The collected effluent should be clarified in a settling tank to remove any biomass that may have dislodged from the filter. The hydraulic and nutrient loading rate (i.e. how much wastewater can be applied to the filter) is determined based on wastewater characteristics, type of filter media, ambient temperature, and discharge requirements.

Refers to plants or animals grown using the water and/or nutrients flowing through a sanitation system. The term biomass may include fish, insects, vegetables, fruit, forage or other beneficial crops that can be utilised for food, feed, fibre and fuel production.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.
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.
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.
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.Waste matter that is transported through the sewer.

Materials

Not all parts and materials may be locally available. The ideal filter material is low-cost and durable, has a high surface to volume ratio, is light, and allows air to circulate. If available, crushed rock or gravel is usually the cheapest option. The particles should be uniform and 95 % of them should have a diameter between 7 and 10 cm. A material with a specific surface area between 45 and 60 m2/m3 for rocks and 90 to 150 m2/m3 for plastic packing is normally used. Larger pores (as in recycled plastic packing) are less prone to clogging and provide for good air circulation.

The ratio of the surface area to the volume of a solid material (e.g., filter
media).

Applicability

A Trickling Filter is usually part of a wastewater treatment plant as a secondary or tertiary treatment step and is applicable only in water-borne systems. It is a viable solution during the stabilisation and recovery phase of an emergency when a longer-term solution is required. This technology can only be used following primary clarification since high solids loading will cause the filter to clog. A low-energy (working with gravity) trickling system can be designed, but in general, a continuous supply of power and wastewater is required. Trickling Filters are compact, they are best suited for peri-urban or large, rural settlements. Trickling Filters can be built in almost all environments, but special adaptations for cold climates are required.

The degradation of organic matter with the goal of reducing readily biodegradable compounds to lessen environmental impacts (e.g., oxygen depletion, nutrient leaching).
Follows secondary treatment to achieve enhanced removal of pollutants from effluent. Nutrient removal (e.g., phosphorus) and disinfection can be included in the definition of secondary treatment or tertiary treatment, depending on the configuration. See POST
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Operation and Maintenance

A skilled operator is required full-time to monitor the filter and repair the pump in case of problems. Sludge that accumulates on the filter must be periodically washed away to prevent clogging and keep the biofilm thin and aerobic. High hydraulic loading rates (flushing doses) can be used to flush the filter. Optimum dosing rates and flushing frequency should be determined from the field operation. The packing must be kept moist. This may be problematic at night when water flow is reduced or when there are power failures. Snails grazing on the biofilm and filter flies are well known problems associated with Trickling Filters and must be handled by backwashing and periodic flooding.

Describes biological processes that occur in the presence of oxygen.

Costs

Capital costs are moderate to high depending on the filter material and feeder pumps used. Costs for energy have to be considered. Energy is required to operate the pumps feeding the Trickling Filter.

Social Considerations

Odour and fly problems require that the filter be built away from homes and businesses. Appropriate measures must be taken for pre- and primary treatment, effluent discharge and solids treatment, all of which can still pose health risks.

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.
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.
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.Waste matter that is transported through the sewer.

Fact Sheet Overview

Inputs

Blackwater
Effluent
Greywater

Outputs

Effluent
Sludge

Response Phase

Stabilisation +
Recovery + +

Challenging Ground Conditions

Suitable

Application Level

Neighbourhood +
City + +

Water-based or Dry Technology

Water-Based

Management Level

Public + +

Technical Complexity

High

Functional Group

(Semi-) Centralised Treatment

Required Space

Medium

Objectives & Key Features

• TSS and TDS reduction, nitrification

Strength & Weakness

  • Can be operated at a range of organic and hydraulic loading rates
  • Efficient nitrification (ammonium oxidation)
  • High treatment efficiency with lower land area requirements compared to wetlands
  • High capital costs
  • Requires expert design and construction, particularly the dosing system
  • Requires operation and maintenance by skilled personnel
  • Requires a constant source of electricity and constant wastewater flow
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