How Tehran's Domestic Wastewater Actually Behaves
Domestic sewage treatment in Tehran is sized for a per-capita wastewater flow of 186.06 ± 7.85 L/d and per-capita loadings of 32.96 g BOD₅, 49.25 g COD, and 37.31 g TSS (PMC study, April 2007 – November 2013, nine WWTPs). Operating plants deliver 92.11–93.41% BOD₅, 89.65–90.97% COD, and 91.48–93.18% TSS removal, yet about 13% of collected wastewater is still discharged without adequate treatment. MBR, SBR, and packaged A/O (WSZ) plants all meet typical ABFA reuse targets when correctly sized for these loadings.
The 186 L/d figure is the defensible design basis; the ABFA-published 378 L/d.cap water-consumption rate should be used as the upper-bound supply-side check, not as the hydraulic load to the biological train. A plant sized on 378 L/d will over-spec aeration tanks and diffusers by roughly 2× and waste blower energy for the next 20 years. The table below summarises the GPCD (generation per capita per day) numbers every Tehran STP design should anchor to (PMC 2014 dataset, standard deviation in parentheses).
| Parameter | GPCD (g/d.cap) | ± SD | Design comment |
|---|---|---|---|
| BOD₅ | 32.96 | 1.91 | 27% below DOE 1990s default — reduce aeration volume |
| COD | 49.25 | 2.49 | Use for carbon-balance and coagulant dose |
| TSS | 37.31 | 2.44 | 32% below DOE default — recheck clarifier sizing |
| TKN | 6.77 | 0.53 | Drives nitrification oxygen demand |
| Total P | 1.96 | 0.11 | Biological P removal borderline; check chemically |
| TDS | 92.23 | 5.68 | Relevant for irrigation reuse salinity check |
| Organic N | 2.07 | 0.39 | Track through the A/O train |
| TS | 128.96 | 6.69 | Drives sludge mass balance |
Two long-term shifts matter more than the absolute numbers. First, average influent TSS in Tehran fell from 353.33 mg/L in 1984 to 198.65 mg/L in 2013 — a 56% decline. Aeration basins sized on 1990s defaults are now over-designed for carbon but often under-designed for nitrification, because the N/COD ratio has shifted upward as carbon load fell. Second, the Biodegradability Index (BOD₅/COD) has eroded by roughly 15% over recent decades, which raises aeration energy per kg BOD removed and pushes tertiary coagulant demand upward for any TSS-polish step.
Out of an estimated 22.78 MCM/year of collected wastewater (2007–2013 average), only 19.75 MCM/year — about 87% — actually reached a treatment plant; the remaining 13% is the political pressure that funds new STPs and the headline number that ABFA reports to the press. Any new design must demonstrate, in the feasibility stage, that the proposed collection intercept will close that 13% gap before the biological train is over-specified for phantom flow.
What Treatment Must Achieve: Removal Efficiencies and ABFA Effluent Targets
Tehran's operating WWTPs deliver a defined removal band that any new process must match or beat, otherwise the bid will be rejected at the compliance review. The bands below are drawn from the same PMC dataset (2007–2013, nine plants).
| Parameter | Removal band (%) | Typical effluent at design influent* | Common ABFA reuse/discharge target |
|---|---|---|---|
| BOD₅ | 92.11 – 93.41 | ~12 mg/L | ≤ 25 mg/L (irrigation), ≤ 30 mg/L (discharge) |
| COD | 89.65 – 90.97 | ~26 mg/L | ≤ 60–100 mg/L (irrigation) |
| TSS | 91.48 – 93.18 | ~16 mg/L | ≤ 30–40 mg/L (irrigation) |
| TKN | 84.62 – 88.26 | ~7 mg/L | ≤ 10–15 mg/L (reuse) |
| Total P | 58.52 – 61.24 | ~7 mg/L | Site-specific; chemical polish if < 2 mg/L required |
| TS | 28.65 – 31.72 | ~700 mg/L | Driven by TDS; manage through source control |
* Design influents used for the back-calculation: BOD₅ ≈ 177 mg/L, COD ≈ 265 mg/L, TSS ≈ 200 mg/L, TKN ≈ 45 mg/L, P ≈ 17 mg/L — derived from the GPCD table divided by 186 L/d.
Biological treatment alone clears BOD₅ and COD comfortably against typical ABFA reuse targets, but TSS polishing is the consistent bottleneck. Conventional activated sludge with a well-operated secondary clarifier will land TSS at 15–25 mg/L, which is at the edge of the 30–40 mg/L irrigation band but not safely under it during peak flow. For projects targeting cooling-tower makeup or unrestricted green-space irrigation, the upgrade path is to add UF or to step up to a submerged MBR — a HydropureWater MBR membrane bioreactor will drop TSS to < 5 mg/L and turbidity to < 1 NTU without a separate tertiary filter, which is the standard configuration for any reuse project with a 24-hour distribution line.
Choosing the Right Process: MBR, SBR, or Packaged A/O (WSZ) for Tehran
Process selection for domestic sewage treatment in Tehran collapses to four drivers: design flow, reuse target, available footprint, and operator skill. The three topologies below cover roughly 90% of the domestic STPs being built or retrofitted in Iran in 2026.
| Criterion | MBR (submerged PVDF) | SBR (batch activated sludge) | WSZ packaged A/O (buried) |
|---|---|---|---|
| Flow range (m³/d) | 10 – 2,000 | 200 – 2,000 | 24 – 1,920 (1 – 80 m³/h) |
| Footprint vs CAS | ~40% (60% smaller) | ~70% (no separate clarifier) | Smallest — fully buried, landscaped over |
| Effluent BOD₅ | < 5 mg/L | 10 – 20 mg/L | 15 – 25 mg/L (with built-in clarifier) |
| Effluent TSS | < 1 mg/L | 10 – 20 mg/L | 15 – 30 mg/L |
| CAPEX band (Tehran, 2026) | High (membrane modules + screens) | Medium (basin + decanters) | Low–medium (factory-built, fast install) |
| OPEX band | High (membrane aeration, CIP chemicals) | Medium (less aeration than MBR) | Low (no operator, low energy) |
| Reuse-ready | Yes — direct to irrigation/cooling | Only with tertiary polish | Only with tertiary polish |
| Typical Tehran use case | Reuse projects, water-scarce districts, hotels, hospitals | Standard district plants, EPC discharge-only projects | Compounds, rural clusters, schools, < 80 m³/h sites |
For reuse projects — which is the direction ABFA is pushing in 2026 — MBR is the default. The HydropureWater MBR membrane bioreactor in the 10–2,000 m³/d range pairs with the DF series PVDF flat-sheet MBR module for plants that need to retrofit an existing aeration tank. MBR also tolerates the falling-BI loadings in Tehran better than CAS, because the high MLSS (8,000–12,000 mg/L) buffers the lower BOD₅/COD ratio.
For standard discharge-only projects in the 200–2,000 m³/d range, SBR is the workhorse: no separate clarifier, well understood by Iranian operators, and lower CAPEX than MBR. The trade-off is a larger basin volume and effluent TSS in the 10–20 mg/L band, which is fine for discharge but needs a sand filter or disc filter if the client later wants to reuse the flow.
For compounds, hotels, hospitals, and rural clusters below 80 m³/h, the WSZ underground package sewage treatment plant is the default. It is fully buried (landscaping or a car park goes on top), fully automated with no operator, and installs in weeks rather than months. The honest limitations are limited hydraulic shock tolerance and a lower upgrade ceiling than MBR — if the client later wants reuse, you will be retrofitting a polish train, not just swapping a module.
Sludge: The Hidden Half of Every Tehran STP
Sludge handling is consistently the most under-scoped part of a Tehran STP bid, and the data shows why. The PMC study estimates 504 m³/d of sludge is generated from the 3.15 M population served by Tehran WWTPs, of which 346 m³/d exits as raw excrement; less than 40% of Iran's total domestic sludge is fully treated (Tajrishi, cited in PMC 2014). A design that handles the water side but leaves sludge to a "Phase 2" will fail the ABFA review.
The default thickening step is a gravity thickener or DAF pre-thickener to push sludge from ~1% DS to 3–5% DS, followed by mechanical dewatering. For plants up to roughly 500 m³/d of sludge volume, a HydropureWater plate and frame filter press is the standard — it reaches 20–30% DS cake in a single step, handles the variable sludge that comes off a Tehran biological train, and runs on intermittent duty without an operator. Upstream of the press, a high-efficiency sedimentation tank (lamella clarifier) handles sludge recirculation and clarifies the press filtrate before it is returned to the head of the plant.
Design targets for the cake: ≥ 20% DS for landfill disposal; ≥ 25–30% DS if the cake is transported off-site or sent to co-composting. If the cake is running below 18% DS, the bottleneck is usually polymer dose or feed solids — for a practical tuning guide see the engineering note on polymer optimisation in sludge dewatering.
Disinfection and Reuse: Closing the Loop on Treated Effluent
Once the biological train delivers BOD₅ < 15 mg/L and TSS < 20 mg/L, the disinfection choice is driven by the reuse destination, not by what is cheapest. Three configurations cover almost every Tehran project.
For irrigation reuse off a short distribution line (most compounds, parks, roadside landscaping), UV is the right primary disinfectant. It has no chlorine by-products, no chemical storage on site, and a UV sterilizer for tertiary disinfection in flange, open-channel, or self-cleaning form slots into the existing tertiary channel without civil changes. UV is genuinely cost-effective only when the upstream effluent is already low-turbidity — which is why MBR + UV is the standard pairing for Tehran reuse projects.
For > 90% reuse targets where the water travels a long distribution line (industrial parks, large green-space networks), the residual matters and chlorine dioxide is the right call. A chlorine dioxide generator (ZS series) sized 50–20,000 g/h provides a stable residual that survives the pipe network without the trihalomethane formation of chlorine. For hospital, school, or food-processing reuse streams where biofilm and taste/odour control matter, add a redundant ozone step — an ozone generator for water-tank sterilization handles both disinfection and oxidation of trace organics in a single pass.
2026 Compliance and Procurement Checklist for Tehran
- Lock the influent design basis at 186 L/d.cap with the GPCD table above; use the ABFA 378 L/d.cap figure only as the supply-side upper bound, not as the hydraulic load.
- Pick the process by reuse target: MBR for direct reuse, SBR for standard discharge, WSZ for buried sites ≤ 80 m³/h.
- Specify a rotary mechanical bar screen upstream of any MBR tank or fine-bubble aeration grid — screenings are the single biggest cause of MBR membrane fouling in Tehran retrofits.
- Budget the plate and frame filter press and sludge-thickening step in the same procurement lot as the biological train; do not leave sludge to Phase 2.
- Match disinfection to the reuse destination: UV for short-line irrigation, ClO₂ for long distribution, ozone for sensitive reuse (hospital, food).
- Confirm ABFA reuse/discharge limits in writing before bid submission — limits vary by receiving body (municipality, DOE, regional water authority).
- Include a 12-month operating consumables line (membrane CIP chemicals, polymer, UV lamps) in the OPEX, not just the CAPEX — Tehran's falling-BI influent pushes both membrane cleaning and polymer dose above Western defaults.
For a cross-check on SBR and MBR design in a different climate and regulatory frame, the domestic sewage treatment in Bristol and domestic sewage treatment in Sheffield 2026 guides run the same MBR-vs-SBR comparison against UK consent limits.
Frequently Asked Questions
What per-capita wastewater flow should a new Tehran STP be sized to?
Design to 186 ± 7.85 L/d.cap based on the PMC 2007–2013 average across nine Tehran WWTPs. The ABFA-published 378 L/d.cap water-consumption figure is the supply-side upper bound, not the hydraulic design load — sizing on 378 L/d will oversize aeration tanks by roughly 2×.
What removal efficiencies do Tehran's operating WWTPs actually achieve?
Operating plants deliver 92.11–93.41% BOD₅, 89.65–90.97% COD, and 91.48–93.18% TSS removal (PMC, 2007–2013). Against the GPCD loadings, that puts typical effluent at BOD₅ ~12 mg/L, COD ~26 mg/L, and TSS ~16 mg/L — comfortably inside ABFA's agricultural irrigation reuse band.
How much sludge does a Tehran STP actually produce, and how dry should the cake be?
For a population of 3.15 M, Tehran generates roughly 504 m³/d of sludge, of which 346 m³/d exits as raw excrement. The dewatering target is ≥ 20% DS for landfill and ≥ 25–30% DS if the cake is transported off-site or co-composted; a plate-and-frame filter press is the default for plants up to ~500 m³/d of sludge volume.
MBR, SBR, or WSZ — which is the right pick for a Tehran domestic STP?
Pick by reuse target: MBR for any project that needs direct reuse (BOD₅ < 5 mg/L, TSS < 1 mg/L); SBR for standard district plants in the 200–2,000 m³/d range with discharge-only consent; WSZ buried package for compounds, hotels, and rural sites at ≤ 80 m³/h where landscaping above the tank is required.
Related equipment and engineering reading
- Underground Package Sewage Treatment Plant (WSZ Series)
- Domestic Sewage Treatment in San Diego: 2026 Engineering Guide
- Domestic Sewage Treatment in Binh Duong: 2026 Engineering Guide
- Anaerobic Digester for Domestic Sewage: 2026 Engineering Guide
- Belt Filter Press for Domestic Sewage Wastewater: 2026 Engineering Guide
