Objectif Sciences International

Ecological Wastewater Treatment

Thomas EGLI — 2011-03-04T13:32:06Z

The NGO includes various members skilled in lagooning, reed bed filtration, and ecological wastewater treatment. The Architecture Service offers you the opportunity to implement these particularly effective techniques.

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While, for example, French regulations (Order of May 6, 1996) set the limit values for treated effluent at 40 mg/l for BOD5 [1] and 30 mg/l for TSS [2], experimental monitoring conducted over 12 consecutive months on an ecological filtration system showed results of 14 mg/l BOD5 (min = 5 mg/l; max = 33 mg/l) and 4.6 mg/l TSS (min = 2 mg/l; max 10 mg/l) at the system's output.

Also in France, several municipalities have implemented this type of wastewater treatment and achieved better results than those required by European standards, which are stricter than French standards; to name just two, Honfleur in Calvados with a capacity of 26,000 population equivalent, and Corcoué/Logne in Loire Atlantique with a capacity of 1,600 population equivalent.

General Explanations

Several similar terms refer to this type of treatment: “phyto-purification,” “filter gardens,” “phytoremediation,” “macrophyte beds,” “planted filters.”

To achieve the ecological treatment of wastewater from a greenhouse or household (showers, toilets, kitchens...), wastewater is collected and then transferred, after screening or through a grease trap, to sealed basins using natural clay layers, compacted bottoms, or specific waterproofing installations. These basins, which are embanked and connected, also contain gravel for drainage, as well as bacterial microorganisms and plants. The water sequentially passes through each basin and is completely purified by the end. Note that the purified water must often be discharged via overflow, but discharge into a surface environment (streams, rivers...) requires official authorization from the municipality or landowner where the treated water is released. Analyses must also confirm the treatment's effectiveness. Maintenance of these installations is essential (regular dredging), but these systems are consistently more effective than traditional systems, including in terms of logistics.

Overall, there is limited documentation, though competent specialists and professionals are becoming increasingly available. The Architecture Service of the NGO Objectif Sciences International provides you with this expertise.

Detailed System Components

The following components describe the implementation developed by the Architecture Service of the NGO Objectif Sciences International. Various alternatives exist, but this version combines all key advantages, though it requires a bit more space than each alternative when used alone. This setup produces the highest possible water quality at system output, resulting in pure water.

Pre-Filtration

While wastewater from toilets is pre-filtered through a screen (either a pit filled with medium-sized rocks or a vertical-flow PVC screen, each with a volume of 0.1 m3 to 0.2 m3 per user and an outlet at the bottom), wastewater from showers, sinks, and kitchens is pre-filtered within a grease trap (0.05 m3 to 0.1 m3 per user—if the grease trap volume is reduced, maintenance cleaning frequency increases and insufficient temperature drop results in improper function. The larger the trap, the less frequent emptying is needed).

These two parallel devices prevent clogging materials from reaching the vegetative filter bed and separately recover 80% of the dry matter in the wastewater.

The emptying of these two pre-filters follows a standard schedule (per the manufacturer's documentation). The collected dry matter and grease are to be reused conventionally (for fertilizer spreading or compost for soil creation). The volume determines the time between each emptying.

Organic and Phosphate Filtration

A first basin of 5 m2 per user, 1 m deep, is filled with porous gravel, preferably basaltic, where water arrives at the surface, and reeds (Phragmites) are planted. The reeds' rhizomes (root networks) harbor bacterial colonies. These are aerobic bacteria, meaning they consume oxygen and organic matter.

In this first filtration basin, phosphates in the water are absorbed by the porous gravel, while complex organic matter, which reed roots cannot absorb, is digested by the bacteria, which release simpler organic molecules that the reeds can absorb.

To ensure ongoing phosphate absorption, the gravel should be replaced every 30 years if the basin has a volume of 5 m2 per user at a depth of 1 m. However, we recommend testing the phosphate levels before replacing the gravel, as the period could be longer, which is advantageous for logistics and finances.

Other rhizome plants could replace reeds (essential for hosting bacterial colonies), but the reeds' natural resistance to wind prevents surface clogging, adding further benefit to this model.

Nitrate Filtration

After the water flows through the first basin's surface, it is directed into a second basin of half the size and with an elongated surface to increase flow time. Water is injected at the bottom of this second basin, which also contains porous gravel but no reeds. It is covered with sand and topped with clay-rich soil to create an airtight seal. The anaerobic bacteria here don't consume oxygen (since none is available) but instead consume the nitrates present in the water.

In this second filtration basin, residual phosphates are stored by the gravel, remaining complex organic matter is consumed by the bacteria, as well as all remaining nitrates. The bacteria also consume simpler organic matter.

This second basin's gravel only needs to be changed every 30 to 40 years or less (based on tests of water composition at the output).

Lagooning

Water exiting the second basin is phosphate- and nitrate-free, nearly devoid of organic matter, and clear. However, it is not drinkable because it still contains harmless bacteria that could cause intestinal issues.

This water can be released into the soil, which completes its natural purification, or collected as a pond or fire water reserve. In a warm country with mosquitoes, this lagoon should be avoided; soil filtration is preferable. In this case, verify that the water percolates deeply into the soil or create a controlled flow, avoiding standing water to prevent mosquito larvae.

Public Access Buildings

Public buildings (ERP) experience variable occupation, leading to fluctuating effluent flow. Conventional basins could dry out and harm the reeds. The NGO Objectif Sciences International's Architecture Service designed a model for ERP with a riverbed shape to support low, medium, and high flow, allowing reeds and bacteria to thrive even during low-occupancy periods.

Under Snow?

The filtration basins operate well under snow and at sub-zero temperatures. Simply trim and lay reeds flat before snowfall to form an insulating layer, keeping the basin functional with minimal efficiency loss. Once snow melts, remove last year's reed stalks to prevent unnecessary organic buildup, which can be composted.

Flow Control

Water is not visible in the first basin; it flows horizontally below the gravel surface, then downward. Overflow near the top prevents surface water from becoming exposed. The second basin also keeps water below the surface, avoiding mosquito access.

Reeds

The reeds perform four functions:

The plants absorb nutrients (nitrates and phosphates), contributing actively to purification.
The root zone (rhizosphere) supports purifying microorganisms. Oxygen produced in the leaves is returned through roots for aerobic bacteria, which are highly effective in organic matter treatment.
Roots stabilize the filter structure, preventing clogging and ensuring maximum diffusion.
During sunny summers, evapotranspiration can reach 10 liters per m² of the bed, reducing discharge when streams are low.

If you are interested in ecological wastewater treatment, please contact us.

[1] biochemical oxygen demand over 5 days

[2] total suspended solids

Description of the Architecture Service Offer

2010-01-29T15:20:26Z

The Architecture Service team at the NGO Objectif Sciences International is made up of architects, project engineers, geologists, biologists, ecology specialists, and physicists, allowing for a comprehensive approach to your projects or studies.

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Our work is organized along three complementary axes:

Analyzing your needs, using quality standards, and adhering to your guidelines and specifications.
Architectural production (sketches, plans, project management...) and technical work (expert reports, studies...).
Securing full funding for your project.

The Architecture Service Director of the NGO serves as your primary point of contact as the project engineer. Our development team secures full funding to cover 100% of your project. Finally, construction oversight is managed by a joint team of project engineers and architects to ensure flawless execution.

For each project, we create a dedicated section with restricted access, where each step has a collaborative online space to enhance face-to-face interactions held at your location, on-site, or in our offices.

Method

In fulfilling our mission, we support you in interactions with all stakeholders (funders, regulatory bodies, on-site contractors...) and can also represent you if you have limited time.

You will always have a single contact person within our team who manages your project from conception to completion. This contact also acts as an advisor, providing invaluable support in decision-making.

To ensure your project's success, your ongoing collaboration is essential. Each project stage requires your approval: study, sketch, preliminary design...

We place particular importance on meeting the needs of projects that benefit from our services, adhering to the announced deadlines, and honoring all our commitments.

The Architecture Service of the NGO Objectif Sciences International invests fully in financing your project only under strict conditions: the project must belong to education, sustainable development, ecology, fundamental scientific research, scientific research on urgent ecological, energy, or social issues, or educational or humanitarian projects. Commercial projects are not eligible for our financing services. However, project leaders wishing to leverage our expertise in bioclimatic design, structural renovation, aesthetic touches, or materials are welcome to use our architecture and construction management services.

Project Stages

Initial Order and Specifications: Your entire project is described and collected in an initiating document, which is finalized after an initial exchange period. A Specifications Document is then drafted and shared internally. You may share it with partners, and its content remains adaptable. The initial fixed document allows us to revisit the original vision as the project evolves, while the specifications provide coherence for subsequent proposals (your specifications may adapt to new proposals).

Sketch: Proposal of one or more comprehensive solutions, verification of project feasibility, potential program adjustments or additional information, followed by beneficiary approval.

Preliminary Project Design (PPS): Defines the general layout in plan and volume, proposes technical arrangements, and provides a preliminary cost estimate. The building permit application follows the PPS phase.

Final Project Design (FPD): Based on the PPS and approved by the beneficiary, the FPD aims to ensure compliance with regulations, determining dimensions and the appearance of the structure through plans, sections, and facades.

Project Study: Defines the general design. Plans are created at a 1:50 scale, with key architectural details at 1:20 scale.

Building Permit: Preparation of the required document for the building permit application, including work declarations for projects not requiring a permit.

Tender Documentation: Preparation and distribution of the tender documentation for obtaining bids.

Contract Assistance: Support for the project owner in contract setup and managing the market, including call for tenders and analysis of applications.

Approval: Verification of contractors' execution studies for compliance.

Construction Management: Oversight of construction to ensure conformity and issuing work orders.

Completion: Support for the project owner during handover and the warranty period.

International...

Our multicultural team seamlessly adapts to cross-border and international projects. Cultural differences imply legal variations in project management and the architectural process steps.

Below are the steps our Architecture Service will follow based on your project's country.

France:


Processus Architectural sur la France: Français

Latin America:


Processus Architectural sur l'Amérique Latine: Espagnol / Français

Québec:
http://www.oaq.com/fr/architecte/services_architecte.jsp

Switzerland:


Processus Architectural sur la Suisse: Français

Japan: ...coming soon...