1. Dual-Pipe Utility Infrastructure & Purple Pipe Mandate
To eliminate cross-contamination between drinking water and recycled industrial water, Dholera enforces strict physical separation of utility mains:
- Purple Conduit Identification (RAL 4001): All subterranean pipes, valves, hydrants, and indoor plumbing conveying tertiary recycled water must be color-coded Pantone Purple / RAL 4001 Red Violet with continuous warning stencil text reading “RECYCLED WATER – DO NOT DRINK”.
- Dual-Pipe Building Plumbing: All industrial plants and commercial complexes must install separate dual-plumbing systems. Potable water lines operate at 3.0 bar, while tertiary recycled lines operate at 3.5 bar to prevent back-siphonage into drinking water mains.
- No Physical Cross-Connections: No physical interconnection, bypass valve, or removable spool piece is permitted between potable water and recycled water piping under any circumstances.
2. Tertiary Water Quality & RO Permeate Benchmarks
Municipal Wastewater Treatment Plants (STP/CETP) utilize advanced membrane filtration (Ultrafiltration + Reverse Osmosis) to achieve high-purity recycled water:
- Ultrafiltration (UF) + RO Filtration: Sewage and industrial wastewater undergo secondary biological treatment (MBBR/MBR), followed by 0.02-micron Ultrafiltration and High-Rejection Reverse Osmosis (RO).
- Total Dissolved Solids ($\text{TDS} < 100\text{ mg/L}$): Tertiary RO permeate supplied to factories must meet stringent quality standards: $\text{TDS} < 100\text{ mg/L}$, Turbidity $< 0.5\text{ NTU}$, $\text{BOD}_5 < 5.0\text{ mg/L}$, and zero detectable E. coli bacteria.
- Cooling Tower Makeup Reuse Mandate: Heavy manufacturing plants must utilize tertiary recycled water for 100% of their cooling tower makeup water requirements, conserving freshwater for domestic human consumption.
The table below outlines DICDL tertiary recycled water quality standards:
| Water Parameter Benchmark | Raw Sewage Inlet Level | Secondary Treated Level | Tertiary Recycled Water (DICDL Grid) | RO Permeate Industrial Grade | Mandatory Industrial Application |
|---|---|---|---|---|---|
| **Total Dissolved Solids (TDS)** | $1,200 – 2,500\text{ mg/L}$ | $1,000\text{ mg/L}$ | $\le 400\text{ mg/L}$ | $\le 100\text{ mg/L}$ | Boiler Feed & Semiconductor |
| **Biochemical Oxygen Demand** | $250 – 450\text{ mg/L}$ | $\le 20.0\text{ mg/L}$ | $\le 5.0\text{ mg/L}$ | $\le 2.0\text{ mg/L}$ | Cooling Tower Makeup Water |
| **Total Suspended Solids (TSS)** | $300 – 600\text{ mg/L}$ | $\le 30.0\text{ mg/L}$ | $\le 2.0\text{ mg/L}$ | $\le 0.5\text{ mg/L}$ | Industrial Washing & Flushing |
| **Turbidity (NTU)** | $100 – 250\text{ NTU}$ | $\le 10.0\text{ NTU}$ | $\le 1.0\text{ NTU}$ | $\le 0.2\text{ NTU}$ | Process Water Makeup |
| **E. coli / Coliforms** | $> 10^6\text{ MPN/100ml}$ | $< 1,000\text{ MPN}$ | Zero Detectable | Zero Detectable | Landscape Irrigation & Toilets |
3. Zero Liquid Discharge (ZLD) Compliance for Fabs
- On-Site ZLD Systems for Fabs: Semiconductor wafer fabs and chemical manufacturing plants generating toxic process trade waste must install on-site Mechanical Vapor Recompression (MVR) evaporators and crystallizers to recover 95% to 98% of process water, solidifying hazardous salts for secure landfill disposal.
- Ultrasonic Flow Recorders: Factories must install SCADA-linked ultrasonic flow meters on both potable inlet lines and tertiary recycled water lines, streaming daily water balance ratios to DICDL environment servers.
Frequently Asked Questions (FAQ)
#### What is the color-coding standard for recycled water pipes in Dholera?
All pipes, valves, and conduits conveying tertiary recycled water in Dholera must be color-coded Purple (RAL 4001) with clear warning labels reading “RECYCLED WATER – DO NOT DRINK”.
#### Can tertiary recycled water be used in industrial cooling towers in Dholera?
Yes. DSIRDA GDCR Section 10.9 mandates that industrial plants must use tertiary recycled RO water for 100% of their cooling tower makeup water requirements.
#### What is the TDS benchmark for DICDL tertiary recycled water?
DICDL tertiary treated RO water delivered to industrial customers features a Total Dissolved Solids ($\text{TDS}$) level below 100 mg/L, making it ideal for industrial boilers and processing.
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