Greywater Recycling: Reusing Water from Sinks and Showers
We flush drinking-quality water down the toilet. Stop the waste. Greywater recycling treats water from showers and sinks to reuse it for flushing and gardening.
In an average home, 50-80% of wastewater is Greywater.
- Greywater: Water from showers, sinks, washing machines. (Contains soap, skin, dirt).
- Blackwater: Water from toilets and kitchen sinks (high food/oil). (Contains feces, pathogens, grease).
Treating blackwater requires a full Sewage Treatment Plant (STP). Treating greywater is much simpler and cheaper.
Types of Greywater Systems
1. Direct Diversion (The "Bucket" Method)
Simple systems for small homes.
- Mechanism: A valve diverts your washing machine/shower water directly to the garden hose.
- Rule: No Storage. The water must hit the soil immediately to prevent bacterial growth.
- Use: Irrigation of trees and bushes only.
2. Biological Treatment (Automated)
Advanced systems for apartments or office buildings.
- Step 1: Collection: Separate plumbing pipes collect only shower and bathroom sink water.
- Step 2: Aeration: Air is pumped into a tank. Bacteria eat the soap and skin cells (BOD).
- Step 3: Filtration: Passed through a sand filter or Ultrafiltration membrane to remove solids.
- Step 4: Disinfection: UV light or Chlorine kills pathogens.
- Result: Clear, odorless water that can be stored for days.
What Soaps are Safe? (The "Garden Rule")
If you put greywater on plants, you are feeding them whatever chemicals you use in the shower.
| Chemical | Effect on Plants | Verdict |
|---|---|---|
| Sodium (Salt) | Salts the soil, preventing roots from drinking. | ❌ Avoid |
| Boron (Borax) | Toxic to plants even in tiny amounts. | ❌ Avoid |
| Bleach (Chlorine) | Kills soil bacteria and burns roots. | ❌ Avoid |
| Phosphates | Acts as fertilizer (good), but causes algae in lakes. | ✅ Okay for Garden |
| "Biodegradable" | Means it breaks down, doesn't mean non-toxic. | ⚠️ Check Label |
Uses for Recycled Greywater
| Application | Required Treatment Level |
|---|---|
| Subsurface Irrigation (Drip lines under soil) | Coarse Filtration (Mesh Screen) |
| Surface Irrigation (Sprinklers) | Biological Treatment + Disinfection |
| In-Home Toilet Flushing | Advanced Filtration (Membrane) + Disinfection |
| Car Washing | High Quality (Ultrafiltration) |
The "24-Hour Rule"
Never store untreated greywater for more than 24 hours.
- Fresh Greywater: Has some bacteria but is safe to handle.
- Aged Greywater (>24h): The bacteria multiply millions of times. The oxygen runs out. It turns anaerobic (black) and smells like rotten eggs. It is now a biohazard.
FRP (Fiber-Reinforced Plastic) Sewage Treatment Plants
FRP (Fiber-Reinforced Plastic) sewage treatment plants are modern systems designed for efficient wastewater management. Using durable and corrosion-resistant materials, these plants offer long-lasting performance.
Importance of pH Control in Wastewater Treatment
Wastewater treatment plants play a critical role in safeguarding the environment and public health by treating sewage and industrial wastewater before it is discharged back into water bodies or reused. One of the fundamental aspects of wastewater treatment is pH control.