03 Junio 2019
Alternative versions to

"Aerated Pond"

Aerated Pond

Autor
Eawag (Swiss Federal Institute of Aquatic Science and Technology)
Dorothee Spuhler (seecon international gmbh)

Resumen ejecutivo

An aerated pond is a large, mixed aerobic reactor similar to facultative ponds in waste stabilization pond systems, with the difference that natural oxygenation is enhanced . Mechanical aerators provide oxygen and keep the aerobic organisms suspended and mixed with water to achieve a high rate of organic degradation. As natural oxygenation is  enhanced, ponds can be deeper (thus smaller in surface) and are suited also for colder climates compared. There are two types of aerated ponds: common aerated lagoons (enhanced facultative ponds) and completely mixed aerated ponds are in essence activated sludge systems without sludge. The effluent of aerated ponds may be reused or used for recharge, but settled sludge requires a further treatment or correct disposal.

Ventajas
Resistant to organic and hydraulic shock loads
High reduction of BOD and pathogens
No real problems with insects or odours if designed and maintained correctly
Can treat high loads
Less land required than for simple pond systems (e.g. WSP)
The treated water can be reused or discharged if a secondary maturation/settling pond follows the aerated lagoon/completely mixed aerated pond
Desventajas
Requires a large land area
High energy consumption, a constant source of electricity is required
High capital and operating costs depending on the price of land and of electricity
Requires operation and maintenance by skilled personnel
Not all parts and materials may be locally available
Requires expert design and construction [no-ecompendium] supervision [/no-ecompendium]
Sludge and possibly effluent require further treatment and/or appropriate discharge
Entradas Salidas

Blackwater, Faecal Sludge, Greywater, Brownwater, Faeces, Excreta

Sludge, Fertigation Water, Biogas (if anaerobic pond is covered)

Introduction

Factsheet Block Body

Increased mixing and aeration from the mechanical units means that the ponds can be deeper and tolerate much higher organic loads than a maturation or a facultative pond (see waste stabilisation ponds). The increased aeration allows for increased degradation and increased pathogen removal. As well, because oxygen is introduced by the mechanical units and not by light-driven photosynthesis, the ponds can function in more northern climates. Mechanical aeration enhances the treatment efficiency and reduces the required hydraulic retention time (HRT) for aerobic degradation of organics (ROSE 1999). It also increases pathogen removal because of the favourable effect of oxygen on solar water disinfection (CURTIS et al. 1992). The smaller area requirement means that it is appropriate for both rural, and peri-urban environments (TILLEY et al. 2008). However, the use of aerators also increases the complexity of the systems and technical material and energy is needed (ARTHUR 1983).

Schematic view of an artificially aerated facultative lagoon (partially mixed). Source: TILLEY et al. (2014)
Schematic view of an artificially aerated facultative lagoon (partially mixed). Source: TILLEY et al. (2014)

 

There are two types of aerated ponds:

  • Aerated facultative ponds or lagoons (see also waste stabilisation pond systems), when it is desired to have a more aerobic system, compacter than normal facultative ponds, or when loads for conventional facultative ponds are too high.
  • Completely mixed aerated ponds or lagoons.

 

Schematic view and picture of a surface complete mix aerator. Source: UNKNOWN (n.y.(
Schematic view and picture of a surface complete mix aerator. Source: UNKNOWN (n.y.)

 

Aerators used in partially mixed lagoons are generally placed on the lagoon surface and provide enough turbulence to satisfy the oxygen demand for aerobic oxidation, but they allow a sludge layer to form at the bottom of the pond. When energy is readily available, the water may be pumped through flow form cascades before entering the ponds for aeration. Aerators used in a completely mixed lagoon can be surface mechanical mixers or subsurface diffusers. They should provide enough energy to maintain the solids in suspension.

Completely mixed aerated lagoons are in essence activated sludge units without sludge return (ARTHUR 1983). As the sludge remains in suspension, effluents of completely mixed ponds require a post-treatment in a sedimentation pond. Just like for WSPs, the effluent of ponds can be reused in agriculture (e.g. irrigation)  or aquaculture (e.g. macrophyte or fish ponds) even though it has generally lower nutrient loads. However, the sludge which forms at the bottom of the aerated facultative lagoon or the sedimentation ponds (in the case of a completely mixed pond) needs to be dug out regularly. And before it can be reused in agriculture it requires a further treatment (e.g. through composting (compost chamber or large scale composting, anaerobic digestion or a constructed wetland).  

Design Considerations

Factsheet Block Body

Influent should be screened and pre-treated to remove garbage and coarse particles that could interfere with the aerators. Because the aeration units mix the pond, a subsequent settling tank is required to separate the effluent from the solids.

The pond should be built to a depth of 2 to 5 m and should have a detention time of 3 to 20 days, depending on the treatment target.

To prevent leaching, the pond should have a liner. This can be made from clay, asphalt, compacted earth, or any other impervious material. A protective berm should be built around the pond, using the fill that is excavated, to protect it from runoff and erosion.

Aerated facultative pond/lagoon

The design of an aerated facultative pond is very similar to that of a facultative pond, with an aerobic zone close to the surface and a deeper, anaerobic zone. But there are no requirements in term of surface area as the process is independent of photosynthesis. The two main design criteria are HRT and depth. The HRT should be adopted in order to allow a satisfactory removal of BOD (biological oxygen demand) and is usually 4 to 10 days (VON SPRELING 2005) for organic loads of 20 to 30 g BOD/m3.day (SASSE & BORDA 1998). The depth of the pond should be planned keeping in mind the compatibility with the aeration system and the need of an aerobic layer of approximately 2 meters to oxidise the gases from the anaerobic decomposition of the bottom sludge. The amount of oxygen to be supplied by the aerators for the aerobic degradation/stabilisation of the organic matter should normally be equal to the total ultimate influent BOD (VON SPRELING 2005). However, such lagoons are generally designed using empirical methods: a HRT of 4 to 5 days results in 70 to 90% BOD5 removal in a partially mixed aerated lagoon by power requirements of 4 W/m3 (ARTHUR 1983).

 

Completely mixed aerated pond

Completely mixed aerated lagoons are essentially aerobic. The aerators serve not only to guarantee the oxygenation of the medium, but also to maintain the suspended solids (biomass) dispersed in the liquid medium. These systems are also called flow-through lagoons or CSTR (completely-stirred tank reactor) lagoons. Aerated ponds act similarly to aeration tanks in activated sludge processes. The main difference is that solids are not recirculated. Biomass and solids from the raw sewage are maintained together in suspension. This enhances the contact between bacteria contained in the biomass (responsible for the degradation) and the raw sludge to be degraded. Hence, the efficiency of completely aerobic ponds increases in comparison to partially mixed ponds and allows a reduction in volume.

Land requirements for this system are the smallest within ponds systems. The typical HRT of a completely mixed aerated lagoon is in the order of 2 to 4 days. This time is enough for an efficient removal of the suspended solids (VON SPRELING 2005). A HRT of 4 days, resulting in 70 to 90% BOD5 removal, requires about 20 W/m3 of energy (ARTHUR 1983). Aerated ponds have removal capabilities similar to facultative lagoons, except that nitrification of ammonia-nitrogen can be nearly completed in warm seasons, while cold weather will halt that process (U.S.EPA 2002). As the quality of effluent from these ponds is not satisfactory for direct discharge into the environment, completely mixed aerated lagoons should be followed by settling ponds. These may be either several short HRT ponds (i.e. 2 day), requiring frequent de-sludging (VON SPRELING 2005); or a single 10-day facultative pond with sufficient depth to allow long-term sludge storage. Aerators should be positioned carefully to avoid dead areas where solids are able to settle out already in the aerated pond. Small aerators rather than fewer large ones provide more evenly spread mixing, and rounded pond corners also help in avoiding dead areas (ARTHUR 1983).

Health Aspects/Acceptance

Factsheet Block Body

The pond is a large expanse of pathogenic wastewater; health hazards can be caused by the aerosol effect releasing pathogens into the air (ARTHUR 1983); care must be taken to ensure that no one comes in contact with or goes into the water. The aeration units can be dangerous to humans and animals. Fences, signage, or other measures should be taken to prevent entry into the area.

A mechanically aerated pond can efficiently handle effluents with a  high concentration and can reduce pathogen levels significantly. But electricity service must be uninterrupted and replacement parts available to prevent extended downtimes that may cause the pond to turn anaerobic (TILLEY et al. 2008).

Costs Considerations

Factsheet Block Body

Investment costs are moderate to high, but expert design is required. Due to the large energy consumption for mixing and aeration, operation and maintenance is expensive. The aeration devices also increase the complexity of the unit and thus the vulnerability for technical failure (due to lack of replacement/spare parts or engineering skills). In consequence, the costs are generally higher than for WSP systems, depending on the local context and the availability of electricity. In some cases, solar-power driven aeration systems may be worth considering.

Operation and Maintenance

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Permanent, skilled staff is required to maintain and repair aeration machinery and the pond must be desludged every 2 to 5 years. and the sludge needs to be either post-treated (e.g. [1182]-anaerobically digested], composted, [1868compos-incinerated]) or correctly disposed (TILLEY et al. 2008). The influents need also to be screened or settled as any large object could damage the aeration system. The pond itself must also be fenced off so no coarse objects can be thrown in.

Care should be taken to ensure that the pond is not used as a garbage dump, especially considering the damage that could result to the aeration equipment.

At a Glance

Factsheet Block Body

Working Principle

Aerated ponds or lagoons are similar to facultative ponds, with the difference that natural oxygenation is enhanced by mechanical air injection. As the oxygenation does not depend on algae activity and photosynthesis, ponds can be deeper (thus smaller in surface) and are also suited for colder climates. Mechanical aeration enhances the treatment efficiency due to more intense bacterial aerobic degradation and increases pathogen removal.

Capacity/Adequacy

Adapted for almost all wastewater (also industrial) in rural or urban areas. However, electricity supply needs to be continuous and a foul odour might be a problem in urban areas.

Performance

Aerated facultative ponds: 70 to 90 % BOD; HRT: 4 to 10 day
Completely mixed aerated ponds: 70 to 90 % BOD; HRT: 2 to 4 day; high phosphorus, nitrogen and ammonia removal.

Costs

Investment costs depend on the availability of mechanical aerator systems. However, operation and maintenance costs are high due to the large energy consumption of aeration and the need for skilled staff for operation and maintenance.

Self-help Compatibility

Planning and construction supervision carried out by technical experts; community labour contribution during construction possible; permanent skilled staff required for operation.

O&M

Permanent skilled staffs are required to repair and maintain aeration machinery; Sludge needs to be dug out every 2 to 5 years and either further treated (e.g. anaerobic digestion, composting) or correctly disposed.

Reliability

High reliability regarding treatment efficiency and shock loadings; however, the system does not work at all in case of power failure.

Main strength

High treatment efficiency for relatively small area requirement and (compared to activated sludge) lower technology requirements.

Main weakness

Requires permanent energy and skilled staff.

Aplicabilidad

A mechanically aerated pond can efficiently handle concentrated influent and significantly reduce pathogen levels. It is especially important that electricity service is uninterrupted and that replacement parts are available to prevent extended downtimes that may cause the pond to turn anaerobic.

Aerated ponds can be used in both rural and peri-urban environments. They are most appropriate for regions with large areas of inexpensive land located away from homes and businesses. Aerated lagoons can function in a larger range of climates than Waste Stabilization Ponds and the area requirement is smaller compared to a maturation pond. But they are also more complex from a technical and operational point of view.

Referencias

Notes in the Design and Operation of Waste Stabilization Ponds in Warm Climates of Developing Countries

Anaerobic, facultative and maturation ponds as wells as aerated lagoon systems are presented as an appropriate solution in developing countries where sewerage systems are present. The technical content was reviewed by Prof. Duncan Mara (University of Leeds, England). Detailed design, operation and maintenance guidance is given. Hence, this paper can be useful as a technical manual.

ARTHUR, J.P. (1983): Notes in the Design and Operation of Waste Stabilization Ponds in Warm Climates of Developing Countries . (= World Bank Technical Paper , 7 ). Washington: The World Bank URL [Visita: 08.05.2018] PDF

Small and Decentralized Wastewater Management Systems

Decentralised wastewater management presents a comprehensive approach to the design of both conventional and innovative systems for the treatment and disposal of wastewater or the reuse of treaded effluent. Smaller treatment plants, which are the concern of most new engineers, are the primary focus of this book.

CRITES, R. TCHOBANOGLOUS, G. (1998): Small and Decentralized Wastewater Management Systems. New York: The McGraw-Hill Companies Inc

Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight to Damage Faecal Coliforms in Waste Stabilization Pond Water

This scientific article describes how solar light and oxygen lead to damage of faecal coliforms in waste stabilization ponds. Humic substances absorb the energy of the sunlight and react with surrounding oxygen, leading to the formation of toxic reactive oxygen species (ROS).

CURTIS, T.P. ; MARA, D.D. ; SILVA, S.A. (1992): Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight to Damage Faecal Coliforms in Waste Stabilization Pond Water. Entradas: Applied and Environmental Microbiology : Volume 58 , 1335-1343. URL [Visita: 02.04.2010]

DEWATS

Exhaustive report on technological, operational and economic aspects of decentralised waste water treatment systems. Spreadsheet examples support the reader in designing and planning waste water treatment systems components.

SASSE, L. BORDA (1998): DEWATS. Decentralised Wastewater Treatment in Developing Countries. Bremen: Bremen Overseas Research and Development Association (BORDA) URL [Visita: 03.06.2019]

Part Three: Stabilization Ponds

Almost 200 pages on the treatment process and design parameters of waste stabilisation ponds. Very exhaustive.

SPERLING, M. von (2005): Part Three: Stabilization Ponds. Entradas: SPERLING, M. von ; LEMOS CHERNICHARO, C.A. de ; (2005): Biological Wastewater Treatment in Warm Climate Regions Volume 1. London: 495-646. URL [Visita: 16.02.2011]

Compendium of Sanitation Systems and Technologies. 2nd Revised Edition

This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

TILLEY, E. ULRICH, L. LUETHI, C. REYMOND, P. ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies. 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag) URL [Visita: 28.07.2014] PDF

Compendium of Sanitation Systems and Technologies

This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

TILLEY, E. LUETHI, C. MOREL, A. ZURBRUEGG, C. SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and Technologies. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (EAWAG) and Water Supply and Sanitation Collaborative Council (WSSCC) URL [Visita: 15.02.2010] PDF

Onsite Wastewater Treatment Systems Manual

Rather old design manual for onsite wastewater treatment options. However, valuable information on established systems such as septic tanks, sand filters, aerobic treatment units (suspended growth and fixed film), disinfection, nutrient removal as well as wastewater segregation and recycling are given. Additional information is given on disposal methods and appurtenances.

U.S.EPA (1980): Onsite Wastewater Treatment Systems Manual. (= EPA 625/1-80 , 12 ). United States Environmental Protection Agency, Office of Water Office of Research and Development

Onsite Wastewater Treatment Systems Manual Technology Fact Sheet 5. Fixed-Film Processes

Technical factsheet on aerobic fixed-film processes (trickling filters and rotating biological contactors). Applications, main design assumptions, performance and maintenance are discussed.

U.S.EPA (2002): Onsite Wastewater Treatment Systems Manual Technology Fact Sheet 5. Fixed-Film Processes. Entradas: U.S.EPA (1980): Onsite Wastewater Treatment Systems Manual. 008.
Lecturas complementarias

Compendium of Sanitation Systems and Technologies (Arabic)

This is the Arabic version of the Compendium of Sanitation Systems and Technologies. The Compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

TILLEY, E. ULRICH, L. LUETHI, C. REYMOND, P. SCHERTENLEIB, R. ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies (Arabic). 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag) PDF

Notes in the Design and Operation of Waste Stabilization Ponds in Warm Climates of Developing Countries

Anaerobic, facultative and maturation ponds as wells as aerated lagoon systems are presented as an appropriate solution in developing countries where sewerage systems are present. The technical content was reviewed by Prof. Duncan Mara (University of Leeds, England). Detailed design, operation and maintenance guidance is given. Hence, this paper can be useful as a technical manual.

ARTHUR, J.P. (1983): Notes in the Design and Operation of Waste Stabilization Ponds in Warm Climates of Developing Countries . (= World Bank Technical Paper , 7 ). Washington: The World Bank URL [Visita: 08.05.2018] PDF

Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight to Damage Faecal Coliforms in Waste Stabilization Pond Water

This scientific article describes how solar light and oxygen lead to damage of faecal coliforms in waste stabilization ponds. Humic substances absorb the energy of the sunlight and react with surrounding oxygen, leading to the formation of toxic reactive oxygen species (ROS).

CURTIS, T.P. ; MARA, D.D. ; SILVA, S.A. (1992): Influence of pH, Oxygen, and Humic Substances on Ability of Sunlight to Damage Faecal Coliforms in Waste Stabilization Pond Water. Entradas: Applied and Environmental Microbiology : Volume 58 , 1335-1343. URL [Visita: 02.04.2010]

Small and Decentralized Wastewater Management Systems

Decentralised wastewater management presents a comprehensive approach to the design of both conventional and innovative systems for the treatment and disposal of wastewater or the reuse of treaded effluent. Smaller treatment plants, which are the concern of most new engineers, are the primary focus of this book.

CRITES, R. TCHOBANOGLOUS, G. (1998): Small and Decentralized Wastewater Management Systems. New York: The McGraw-Hill Companies Inc

Onsite Wastewater Treatment Systems Manual

Rather old design manual for onsite wastewater treatment options. However, valuable information on established systems such as septic tanks, sand filters, aerobic treatment units (suspended growth and fixed film), disinfection, nutrient removal as well as wastewater segregation and recycling are given. Additional information is given on disposal methods and appurtenances.

U.S.EPA (1980): Onsite Wastewater Treatment Systems Manual. (= EPA 625/1-80 , 12 ). United States Environmental Protection Agency, Office of Water Office of Research and Development

Epuration des eaux usées par Lagunage a Microphytes et a Macrophytes en Afrique de l'Ouest et du Centre- Etat des lieux, performances épuratoires et critères de dimensionnement

Stabilization ponds are a very promising sustainable centralized wastewater treatment option for West Africa due to the favourable climate. Pilot studies could demonstrate their performance in the local context; however none of the full-scale applications works. Besides the poor economic situation and little political support, it is also the lack of training and research that contributes to this situation. This work presents the establishment of an international research collaboration network and main technical recommendations based on an exhaustive assessment on the state-of-the-art of stabilization ponds in the West-African context.

KONE, D. (2002): Epuration des eaux usées par Lagunage a Microphytes et a Macrophytes en Afrique de l'Ouest et du Centre- Etat des lieux, performances épuratoires et critères de dimensionnement. (= Doctoral Thesis ). Lausanne: Swiss Federal Institute of Technology (EPFL).

Language: French

Part Three: Stabilization Ponds

Almost 200 pages on the treatment process and design parameters of waste stabilisation ponds. Very exhaustive.

SPERLING, M. von (2005): Part Three: Stabilization Ponds. Entradas: SPERLING, M. von ; LEMOS CHERNICHARO, C.A. de ; (2005): Biological Wastewater Treatment in Warm Climate Regions Volume 1. London: 495-646. URL [Visita: 16.02.2011]

Waste Stabilisation Ponds

This document provides information and instructions on waste stabilisation ponds. Various case studies are mentioned, e.g. the wastewater-fed fishponds in Calcutta in India.

VARON, M. P. MARA, D. D. (2004): Waste Stabilisation Ponds. Delft: International Water and Sanitation Centre URL [Visita: 17.05.2012]

Compendium of Sanitation Systems and Technologies. 2nd Revised Edition

This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

TILLEY, E. ULRICH, L. LUETHI, C. REYMOND, P. ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies. 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag) URL [Visita: 28.07.2014] PDF
Estudios de caso

Water for Urban Agriculture

Various case studies on the reuse of pond and lagoon treated water in urban agriculture.

RUAF (2008): Water for Urban Agriculture. (= Urban Agriculture Magazine , 20 ). Leusden: Resource Center on Urban Agriculture and Food security (RUAF) Foundation
Material de capacitación

Aerated, Partial Mix Lagoons

Short factsheet on the design, operation, maintenance and costs of aerated lagoons (partially mixed ponds) form the United States Environment Protection Agency.

EPA (2002): Aerated, Partial Mix Lagoons. (= Wastewater Technology Fact Sheet ). Washington, D.C.: United States Environment Protection Agency (US EPA) URL [Visita: 26.03.2010]

Part Three: Stabilization Ponds

Almost 200 pages on the treatment process and design parameters of waste stabilisation ponds. Very exhaustive.

SPERLING, M. von (2005): Part Three: Stabilization Ponds. Entradas: SPERLING, M. von ; LEMOS CHERNICHARO, C.A. de ; (2005): Biological Wastewater Treatment in Warm Climate Regions Volume 1. London: 495-646. URL [Visita: 16.02.2011]

Wastewater stabilization ponds: Principles of planning and practice.

The book has been divided in two parts. Part A provides a comprehensive summary concerning the various aspects of constructing, operating and maintaining pond systems. It also considers aspects such as management and safety. Part B is intended for persons making the preliminary designs on which cost estimates and, hence, choices can be made. In particular, the appendix and annex provide a working example and a simple methodology to help the designer in preparing adequately detailed designs.

WHO (1987): Wastewater stabilization ponds: Principles of planning and practice.. (= WHO EMRO Technical Publication , 10 ). Alexandria: World Health Organization Regional Office for the Eastern Mediterranean

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