systèmes de recyclage des eaux grises : en profondeur...

Introduction

Water scarcity, rising utility costs, and environmental pressure are compelling us to rethink how we use and reuse water in our built environment. One compelling solution is systèmes de recyclage des eaux grises, which capture, treat, and reuse wastewater from showers, baths, basins, and laundry (excluding toilets). By harnessing what is often wasted, these systems can deliver real savings, resilience, and a more circular approach to water management.

In many European cities, per capita water consumption remains 100–150 liters/day, and wastewater discharge is a major burden on treatment infrastructure. A well-designed gray water recycling system can reduce fresh water use by 25 % to 45 % (depending on design and behavior). In this article, we will explore the state of the art in these systems, how they work, their advantages and ROI, real examples, how they integrate into smart buildings, leading brands with European relevance, and cost estimates. Let’s journey into a future where every drop counts. Let’s Inspire…

1. High Performance Technologies & How They Work

What is “gray water” and why treat it?

Gray water is domestic wastewater excluding toilet and kitchen wastewater (i.e. excluding blackwater). It comes from showers, baths, hand-wash basins, laundry machines, and sometimes sinks (if plumbing is separated). Because it’s “lighter” in contamination than blackwater, it is more amenable to onsite treatment and reuse.

However, untreated, gray water can carry soap residues, hair, lint, oils, detergents, and microbes. Without proper treatment, storage or reuse can lead to odor, biological growth, or health risks.

Key system architectures & treatment steps

Modern systèmes de recyclage des eaux grises combine mechanical, biological, and membrane techniques. The typical process chain includes:

1. Pre-filtration / coarse screening
   Removal of hair, fibers, large particulates using screens, filters, or sedimentation.
2. Biological / biofilter/bioreactor stage
   A bacterial degradation stage (similar to activated sludge, moving-bed biofilm reactor, or constructed wetlands) to break down organic loads (BOD “Biochemical Oxygen Demand”, COD”Chemical Oxygen Demand”).
3. Membrane / ultrafiltration / microfiltration
   A membrane barrier to remove fine suspended solids, bacteria, and pathogens.
4. Disinfection / UV / chlorine / ozone
   A final disinfection step ensures microbial safety for reuse.
5. Storage & distribution / pump & control
   Treated water is stored in a (non-potable) buffer tank, and pumped to reuse points (toilet flushing, laundry, irrigation). Intelligent control valves ensure safety (e.g. fallback to fresh water if quality degrades).

Some systems also incorporate heat recovery—i.e., recapturing thermal energy from the treated water and using it to pre-heat incoming cold water or feed to the hot water circuit (a “WRG” option in DEHOUST’s GWtec system).

Membrane bioreactor (MBR) systems are among the highest performance options—they combine the bioreactor stage with a membrane in one compact unit, offering reliable effluent quality, small footprint, and modular scalability.

Certain vendors supply pre-assembled or plug-and-play modules that house all elements in a compact footprint. For instance, INTEWA offers preassembled graywater recycling systems with minimal spatial requirement, enabling reuse near source.

2. Advantages, Savings & Return on Investment

Water and wastewater cost savings

By recycling gray water, a household can reduce its demand for fresh (potable) water by 25 % to 45 %, depending on reuse design and user habits. In urban areas where water tariffs and sewage fees are high, this yields tangible cost reductions.

For example, in a household consuming 150 m³/year of fresh water (≈ €1.50/m³ costs), that’s €225/yr. A 35 % reduction yields ~ 52.5 m³ saved, i.e. ~ €78 savings in water. But also, savings in sewage charge (which is often tied to water use) double the impact.

In larger buildings or multi-unit developments, per-apartment savings scale significantly.

Value addition & regulatory incentives

• Increased property value / market appeal: Buildings already equipped for water reuse are more attractive to buyers and investors.
• Regulatory incentives: Some jurisdictions offer rebates, subsidies, or lower rates for buildings with water reuse infrastructure.
• Future-proofing: As water scarcity becomes more acute and regulations tighten, being ahead of the curve helps avoid retrofitting costs. Hydraloop’s white paper estimates that a “Recycle-Ready” building adds ~€1,190 extra cost over a baseline semi-detached home, but yields higher building value and long-term savings info.hydraloop.com.
• Reduced load on municipal systems: Less inflow and infiltration, lower stress on treatment plants, and reduced carbon emissions associated with treating fresh water and wastewater.

Payback estimates & ROI

Let’s consider rough cost / payback ranges for different classes of systems:

In a larger apartment building context, Hydraloop’s study shows that preparing a building as “Recycle Ready” costs roughly €1,190 extra in a semi-detached scenario, but yields ~45 % water saving, and increased building value.

Thus, ROI is context-dependent: local water/sewage tariffs, scale, user behavior, and system integration all matter.

3. Concrete Examples & Use Cases

Example 1: Single-family home with Hydraloop

Hydraloop, based in the Netherlands, offers decentralized gray water recycling units (H300, H600, Cascade) that collect, treat, and re-use gray water from showers, baths, washing machines, and HVAC condensation. Users may reuse water for toilet flushing, laundry, garden irrigation, and more. Hydraloop claims savings of 25 % to 45 % on total water usage.

Because these units are compact and often IoT-connected with self-cleaning features and remote monitoring, they are feasible retrofits in existing homes.

Example 2: INTEWA / AQUALOOP system in Europe

INTEWA supplies modules such as AQUALOOP for households, including preassembled graywater systems that require modest footprint (e.g. 1 m² for 1 m³ capacity). Their system treats approx. 300 liters/day (for a typical family) and integrates pretreatment, bioreactor, membrane, pump, control, sludge management.

Systems are operable in many European homes and already in use. INTEWA also certifies performance by international standards (e.g. NSF-350 Class C, BS).

Example 3: DEHOUST GWtec with heat recovery

Germany’s DEHOUST offers GWtec® greywater treatment systems using ultrafiltration and mechanical-biological filtration to produce high-quality non-potable water. Importantly, they offer an optional heat recovery (WRG) variant, which captures thermal energy from treated water and feeds it back to the hot water system, reducing heating demand (and thus energy costs).

Example 4: IDROCELL for hotel / building scale

IDROCELL (Italy) offers gray water reuse systems for larger-scale buildings (hotels, guesthouses, complexes). Their systems purify water from showers/lavabos into non-potable quality usable for flushing, cleaning, irrigation. Because of scale, per-unit cost is lower, and water and sewer savings become substantial.

Example 5: GREM membrane station

Remosa’s GREM station is a modular membrane-based gray water recycling station treating showers, baths, basins to a quality suitable for non-potable reus. These kinds of modular systems are suitable for multi-dwelling units or clusters of homes.

These examples illustrate that gray water recycling systems are viable at household, multi-home, and building scale, with modularity and flexibility.

4. Integration in Smart Homes & Smart Buildings

Integrating a gray water recycling system into a smart home or building unlocks synergies, improves control, and helps optimize resource flows.

Smart Integration Layers & Control Logic

1. Real-time monitoring & sensors
   Flow sensors, quality sensors (turbidity, ORP, residual disinfectant), tank level sensors feed data to the building management system (BMS) or home automation hub.
2. Rule-based logic & automation
   • Switch between fresh water and recycled water if quality degrades.
   • Prioritize reuse to toilets, laundry, or irrigation based on demand.
   • Pump scheduling to match pressure demands, off-peak energy usage.
3. Predictive & adaptive scheduling
   Use machine learning or heuristics to anticipate water demand (morning, evening showers) and maintain buffer levels.
4. Fault detection & remote alerts
   Identify membrane fouling, sensor drift, pump failure, and proactively alert maintenance staff.
5. Heat recovery coordination
   In systems with thermal recapture, coordinate with heating / hot water system to maximize energy reuse.
6. User interface & transparency
   Show consumption, reuse rates, savings, trend graphs in an app or dashboard to engage occupants, increasing awareness and proper behavior.

Architectural design & plumbing considerations

• Separate plumbing (dual pipe systems): From design stage, separate gray water drainage routes (from showers, basins) from blackwater.
• Recycle-ready fitout: Pre-install infrastructure (extra piping or conduit) to facilitate future installation of a full system (lower retrofitting cost). As Hydraloop notes, the additional cost to make a building recycle-ready is modest (~€1,190 for semi-detached)
• Modular and scalable plant rooms: Central recycling modules can be located in basements or core spaces, serving multiple units.
• Space reservation: Allow room for tanks, treatment modules, control panels, and maintenance access.
• Redundancy and fallback: Always include a fallback to fresh water supply if reuse fails or during maintenance.
• Standards & regulation compliance: In Europe, systems must meet local water reuse regulations and health standards (e.g. France’s ANSES warns reuse must be limited and controlled).

In smart buildings, the gray water recycling system becomes one more node in a holistic resource-management ecosystem: energy, water, ventilation, solar, and user behaviour all interacting intelligently.

5. Leading Brands, European Players & Price Benchmarks

Below is a selection of reputable manufacturers and brands active (or relevant) in Europe (or globally) for systèmes de recyclage des eaux grises, with approximate cost pointers.

Key European / regional players

• Hydraloop (Netherlands)
  A leading vendor of decentralized, smart gray water recycling units. Known for compact design, IoT monitoring, self-cleaning, and modular scaling.
  Prix: Their white paper suggests unit + associated “Recycle Ready” infrastructure in a building costs in total tens of thousands (for multi-unit) but for single-home units typically cost ranges of several thousand €. (Exact retail price varies by model & locale.)
• INTEWA / AQUALOOP (Germany / EU)
  Supplies preassembled modules intended for household or small building use.
  Prix: Because modules are prefabricated, marginal cost is lower; system cost depends strongly on scale and plumbing integration. (Manufacturer quotes needed.)
• DEHOUST (Germany, Europe)
  Offers GWtec® systems combining ultrafiltration, biological treatment and optional heat recovery (WRG)
  Prix: Typically for building-scale systems; manufacturer quote needed depending on capacity.
• IDROCELL (Italy)
  Vendor specializing in gray water reuse for hotels and large buildings.
  Prix: Pricings scale with capacity; likely in the tens of thousands EUR for building-level plants.
• Remosa (GREM systems, Europe)
  Modular membrane-based stations for treating shower/bath gray water
  Prix: Vendor-dependent, modular scaling typical.
• Ecodepur (Spain / Europe)
  Produces gray water treatment plants (e.g. BIOX DOMUS) for domestic reuse
• Graytec (Europe)
  Offers “Blue Circle” advanced recycling system for multi-residential and hospitality markets.
• Other global / engineering players
  Companies like Organica Water, Arvia Technology, Aquaco (UK), etc., may provide specialized solutions or large-scale systems in water treatment.
• Local / regional integrators
  In many countries, plumbing, HVAC, or environmental systems integrators partner with these manufacturers for installation, commissioning, and maintenance.

Sample cost points and benchmarks

• A simple 200-litre gray water recycling unit (for garden irrigation) — e.g. Manhattan 200-litre model — costs ~ £449 (~€520) in UK markets..
• For full residential reuse systems, UK estimates put membrane-biased systems in the £3,000–£5,000 bracket (excluding heavy plumbing).
• The additional cost to make a building “Recycle Ready” is estimated ~€1,190 in a semi-detached scenario, before the cost of the actual treatment unit.
• For custom or large building systems (e.g. Hydraloop in an apartment block) the capital investment can run tens of thousands of euros (depending on scale and units).

Because these systems are relatively specialized, a precise cost estimate always depends on local plumbing complexity, labor rates, regulatory compliance, and economies of scale.

Conclusion

Gray water recycling systems offer a powerful, sustainable tool in the transition toward resilient and circular water use in our homes and buildings. With mature modular technologies (biological + membrane + disinfection), these systems can deliver freshwater use reductions of 25 % to 45 %, cost savings, energy integration (when heat recovery is included), and greater appeal in the market. When smartly integrated into a home automation or building management ecosystem, they become dynamic resource systems rather than static add-ons.

European vendors such as Hydraloop, INTEWA, DEHOUST, IDROCELL, Remosa, and Graytec are leading in this space, with embedded designs, IoT capabilities, and growing deployment. Costs today place payback in the 5–15 year range depending on scale and tariffs, but as water becomes more expensive and regulation shifts, these systems will likely become standard in new builds.

For those who think ahead, adopting gray water recycling systems is not just a technical choice—it’s a values-driven decision to reduce waste, enhance resilience, and Inspire Energy in every drop. May your next home embrace water intelligence and circular thinking.