Tertiary Treatment Plants (TTP)

A tertiary treatment plant (TTP) is a membrane-based polishing system that takes biologically treated effluent — from an ETP, STP or CETP — and removes residual dissolved salts, suspended solids, colour and pathogens to produce reuse-grade water. The standard architecture is UF followed by single- or two-pass RO, with pre-treatment selected against the specific feed chemistry. TTP is the third stage of wastewater treatment, applied after primary (physical) and secondary (biological) treatment.

TTP is required when the end-use demands water quality beyond what a biological treatment plant produces. The most common triggers are: cooling-tower makeup for thermal power or industrial plants (CEA norms on fresh-water intake reduction), boiler-feed demineralisation, process-water recycling to displace fresh-water purchase, ZLD pre-conditioning where TTP produces the membrane-ready feed for downstream evaporation, and compliance with tightened discharge norms (CPCB 2017 standards for select industries require treated effluent below 100 mg/L TDS).

In common usage the terms overlap, but they are not identical. Tertiary treatment refers to the third stage of wastewater treatment — after primary and secondary — and typically involves membrane-based processes (UF + RO) that significantly reduce TDS. Polishing treatment is a broader term that can refer to any final clean-up step, including sand filtration, activated carbon, UV disinfection or softening, without necessarily involving membranes or TDS reduction. A TTP that includes UF + RO is always a polishing step, but not every polishing step qualifies as tertiary treatment.

A standard SRPEPL TTP train follows four stages: pre-treatment (lime-soda HRSCC softening, activated carbon, cartridge filtration or antiscalant dosing — selected per feed chemistry), ultrafiltration (UF) to remove suspended solids and achieve SDI <3, reverse osmosis (RO) in single- or two-pass configuration depending on target product quality, and optional post-treatment (degassing, mixed-bed polishing, UV disinfection) for specific end-uses. Pre-treatment selection is critical — it determines UF and RO membrane life and cleaning frequency.

RO recovery in a TTP typically ranges from 70% to 80% on the first pass, depending on feed TDS, silica concentration, temperature and scaling indices (LSI, S&DSI). For feeds below 2,000 mg/L TDS with moderate hardness, 75–80% is achievable with standard antiscalant dosing. For higher-TDS or high-silica feeds (common in thermal power cooling-tower blowdown), recovery may be limited to 65–70% unless a high-recovery second stage or UHP system is added. The concentrate stream — typically 20–30% of the feed volume — is routed to ZLD, recycled or discharged per consent conditions.

Specific energy consumption for a UF + RO TTP is typically 0.8–2.5 kWh per cubic metre of permeate produced. The lower end applies to low-TDS municipal sewage feeds (<1,000 mg/L) with single-pass RO; the upper end applies to higher-TDS industrial or blowdown feeds requiring two-pass RO and higher operating pressures. Pre-treatment energy (HRSCC mixers, ACF backwash pumps) adds 0.1–0.3 kWh/m³. These figures exclude raw-water intake pumping and treated-water distribution, which are site-specific.

Yes — and in most Indian ZLD trains, the TTP is the critical front-end stage. The UF + RO permeate from the TTP is the recovered reuse water (70–80% of feed volume), while the RO concentrate is the feed to the evaporation stage (MEE, MVR or forced-circulation evaporator). TTP design directly determines ZLD economics: higher RO recovery means less concentrate to evaporate, which reduces MEE steam consumption and crystalliser sizing. SRPEPL delivers integrated TTP + ZLD systems under single EPC contracts — the SAIL Bokaro ZLD (₹35.69 Cr, commissioned) and the 660 MW × 2 supercritical TTP + ZLD (₹50 Cr, under execution) are both examples of this integrated delivery.

Yes. SRP Membranes — SRPEPL's manufacturing arm — produces spiral-wound brackish-water RO elements (SRP BW series), high-pressure RO elements (SRP HP series) and ultrafiltration modules at two facilities in Panchkula (Haryana) and Baddi (Himachal Pradesh). These elements are used in SRPEPL's own EPC projects, including TTP systems. In-house membrane supply gives SRPEPL control over membrane specification, replacement lead times and post-commissioning technical support — all under one engineering team. For full product specifications, visit srpmembranes.com.

SRPEPL delivers TTPs under multiple contract structures: turnkey EPC (lump-sum, item-rate or hybrid), Design-Build-Operate (DBO) with 5–10-year O&M terms, BOOT/annuity where SRPEPL retains ownership and charges per kilolitre, and retrofit/upgradation of existing TTPs for capacity enhancement or technology upgrade. The contract model is selected based on the buyer's procurement framework — PSU tenders typically specify EPC or DBO; private industrial buyers may prefer BOOT for off-balance-sheet treatment.