Tertiary Treatment — PSF, ACF & UF
The polishing stage that makes CPCB reuse limits consistently achievable
Secondary treatment alone will not hold BOD, TSS and turbidity within CPCB reuse limits under varying load. The tertiary stage is what converts a compliant-on-paper plant into a consistently compliant one, and it is included as standard on every plant we supply.
Process Flow
What Each Stage Does
Stage 1 — Pressure Sand Filter (PSF)
- FRP or MSEP pressure vessel with graded silica sand over a supporting gravel bed.
- Removes residual suspended solids and turbidity carried over from settling.
- Reduces TSS to below 10 mg/l, meeting the CPCB reuse requirement.
- Backwash and rinse initiated on differential pressure across the bed.
Stage 2 — Activated Carbon Filter (ACF)
- Granular activated carbon bed over graded gravel support media.
- Adsorbs residual colour, odour, dissolved organics and free chlorine.
- Protects downstream reuse, particularly cooling tower make-up.
- Delivers odour-free, visually clear water for domestic flushing.
Ultrafiltration (UF) System for Further Polishing
Where the end use demands a higher grade of water than PSF and ACF alone provide, a hollow-fibre Ultrafiltration system is installed downstream of the Activated Carbon Filter. UF membranes of approximately 0.02 micron pore size remove suspended solids, colloidal matter, bacteria and cysts almost completely, delivering turbidity consistently below 1 NTU. Recommended for cooling tower make-up, high-grade flushing, water features, and any application feeding a downstream RO plant.
What Each Stage Achieves
| Parameter | After Secondary | After PSF + ACF | After Optional UF |
|---|---|---|---|
| Total Suspended Solids | 20 – 30 mg/l | < 10 mg/l | < 2 mg/l |
| Turbidity | 5 – 10 NTU | < 2 NTU | < 1 NTU |
| BOD | 15 – 20 mg/l | < 10 mg/l | < 5 mg/l |
| Colour & Odour | Perceptible | Unobjectionable | Nil |
Need reuse-grade water?
Every plant we supply is engineered with tertiary treatment as standard — ask us about adding UF for higher-grade reuse.
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