Project Brief
A residential developer in the Middle East needed a containerised sewage treatment plant for a new development of 1,800–2,000 houses, approximately 5,000 population equivalent (PE). The enquiry arrived without a nominated flow rate — the developer asked us to derive the design capacity, container count, footprint, power demand and membrane replacement schedule from the population figure alone. This case documents that derivation, because the step most often skipped on PE-based enquiries is exactly the one that determines whether the plant fits on the plot.
| Parameter | Value |
|---|---|
| Development size | 1,800–2,000 dwellings |
| Design population | ~5,000 PE |
| Delivery format | Containerised (site had no civil works programme) |
| Preferred process | MBR or equivalent advanced biological treatment |
| Region | Middle East |
Source: client-supplied design basis.
Step 1 — From Population Equivalent to Design Flow
PE is a load unit, not a flow unit. Converting it requires a per-capita wastewater figure, and that figure is region-specific: arid-climate residential developments typically generate less wastewater per person than temperate ones, because outdoor water use does not reach the sewer.
At a design basis of 150 L/PE·day of sewage, 5,000 PE produces 750 m³/day — an average of 31.3 m³/h. Small residential catchments do not deliver that flow evenly: a peaking factor of 2.5–3.0 is normal at this population, which puts the hydraulic peak at roughly 78–94 m³/h.
This is the number that sizes the pipework, the pumps and the membrane tank — not the daily average. A plant designed only to the 31.3 m³/h average will surcharge every morning.
Source: HydroPure design calculation. The 150 L/PE·day basis and the 2.5–3.0 peaking factor are standard engineering values for residential catchments of this size and must be confirmed against local water-consumption records before contract.
Step 2 — Organic Load and Biological Volume
The organic load follows directly from PE. At the conventional 60 g BOD₅ per PE per day, 5,000 PE generates 300 kg BOD₅/day.
An MBR carries this at an elevated mixed-liquor concentration. At 8,000 mg/L MLSS and a food-to-microorganism ratio of 0.08 kg BOD/kg MLSS·day:
| Step | Calculation | Result |
|---|---|---|
| Daily BOD load | 5,000 PE × 60 g/PE·d | 300 kg BOD₅/d |
| Required MLSS mass | 300 ÷ 0.08 | 3,750 kg |
| Aerobic volume | 3,750 kg ÷ 8 kg/m³ | ≈ 470 m³ |
| Anoxic volume (denitrification) | ≈ 30% of aerobic | ≈ 140 m³ |
| Total biological volume | — | ≈ 610 m³ |
Source: HydroPure design calculation using standard MBR design parameters.
Step 3 — Membrane Area
Membrane area is set by continuous throughput, not by peak flow, provided a balancing tank absorbs the diurnal swing. At 750 m³/day treated over 24 hours — 31.3 m³/h — and a conservative design flux of 18 LMH:
31,300 L/h ÷ 18 L/m²·h ≈ 1,740 m² of membrane area.
Design flux is the single most consequential number in an MBR quotation. A supplier quoting 25–30 LMH will show a smaller, cheaper membrane package — and will spend the plant's operating life fighting fouling and chemical cleaning frequency. We size at 18 LMH deliberately.
Source: HydroPure design calculation.
Step 4 — Container Count and Footprint
A 40 ft high-cube container offers roughly 67 m³ of gross internal volume, of which about 80% is usable as process volume once walkways, pipework and freeboard are deducted — call it 54 m³ per container.
| Function | Volume / duty | 40 ft HC containers |
|---|---|---|
| Anoxic + aerobic biology | ≈ 610 m³ | 11–12 |
| Membrane tanks | ≈ 1,740 m² membrane | 2–3 |
| Blowers, panel, CIP, dosing | Equipment room | 1 |
| Screening + balancing | Peak absorption | 2 |
| Indicative total | — | 16–18 |
This is the point at which a containerised MBR needs an honest conversation. At 5,000 PE the container count is high enough that a hybrid arrangement — containerised equipment and membranes, site-built concrete tanks for the biology — is usually cheaper per m³ and easier to maintain. Containerisation earns its premium at small and mid scale, or where a construction programme genuinely cannot be run.
Source: HydroPure design calculation. Final container count depends on the selected membrane module and tank geometry.
Step 5 — Power Demand
MBR plants consume 0.8–1.5 kWh per m³ treated, with aeration — process air plus membrane scouring — accounting for the majority. At 1.0 kWh/m³, a 750 m³/day plant draws roughly 750 kWh/day, about 31 kW average, with installed capacity higher to cover peak scouring and standby duty.
For a development in a region with an unreliable grid, this figure drives the generator sizing conversation, and it is worth having before the plant is ordered rather than after.
Source: HydroPure design calculation using published MBR specific-energy ranges.
Membrane Life and Replacement Planning
Membrane life on municipal-strength sewage is typically 5–8 years when the plant runs at design flux and the cleaning regime is maintained. Two habits shorten it more than anything else: sustained operation above design flux, and deferred chemical cleaning. Both are invisible in year one and expensive in year four.
A replacement budget should be provisioned from commissioning, not raised as a surprise capital request when the first modules reach end of life.
Equipment Delivered
- MBR Integrated Wastewater Treatment System — biological and membrane process core.
- MBR Membrane Module (DF Series) — membrane modules and racks.
- GX Rotary Mechanical Bar Screen — inlet screening, without which membrane life is not defensible.
The technology trade-off behind this selection is set out in our MBR vs MBBR comparison. For the packaged-plant format in general, see our packaged wastewater treatment plant engineering guide.
Frequently Asked Questions
How many m³/day is 5,000 PE?
It depends on the per-capita wastewater basis, which is why no supplier should quote from PE alone. At 150 L/PE·day the answer is 750 m³/day; at 200 L/PE·day it is 1,000 m³/day — a third more plant. Always confirm the local figure against actual water-consumption records before fixing capacity.
How many containers does a 5,000 PE MBR need?
Indicatively 16–18 forty-foot high-cube containers once biology, membranes, equipment room and balancing are counted. At that number, hybrid delivery — containerised equipment with site-built concrete biological tanks — is usually more economical than full containerisation.
What design flux should an MBR be sized at?
We size at 18 LMH for municipal-strength sewage. Quotations built on 25–30 LMH look cheaper because they carry less membrane area, but they buy that saving with higher fouling rates, more frequent chemical cleaning and shorter membrane life. When comparing MBR bids, compare the flux before comparing the price.
How long do MBR membranes last?
Typically 5–8 years on municipal sewage at design flux with a maintained cleaning regime. Running above design flux and deferring chemical cleans are the two habits that shorten it most.
What effluent standard can a containerised MBR meet?
An MBR reliably produces effluent suitable for discharge and, in many cases, for non-potable reuse such as landscape irrigation. The binding standard is whichever the local authority applies, so the effluent specification must be fixed against the actual discharge permit or reuse regulation before the process is finalised — not assumed from a technology datasheet.
