What 'sizing' a containerized MBR STP really means in London
Sizing a containerized membrane bioreactor (MBR) for a London residential or camp project is a two-axis calculation: hydraulic load (m³/day) that sets the container and pipework, and organic/BOD load (kg BOD/day) that sets the aeration tank volume and membrane area. A containerized MBR is a biological treatment process combined with ultrafiltration (UF) membrane filtration, replacing the secondary clarifier used in conventional activated sludge (HUBER, Mena-Water). The UF stage is what makes the MBR footprint small enough to fit inside a 20' or 40' ISO container, and what lets a London consultant specify a single pre-assembled unit instead of a civil-built plant.
Two linked numbers must be balanced: peak instantaneous flow, which the membrane tank and feed pumps must accept without surge damage, and the daily organic load, which the aeration tank and membrane flux rating must process without loss of treatment efficiency. A larger population does not automatically mean more containers — it means a longer or wider membrane tank within the same ISO footprint, or a second biological container in a multi-unit train. What changes the container count in London is rarely the population on its own; it is the combination of peak factor, trade waste, and whether the effluent must reach irrigation-reuse quality or only consent-to-discharge quality.
Three London-specific drivers shift the answer away from a textbook sizing. Phased handovers on residential developments mean the plant must turn down and ramp up without losing biological activity. Construction and seasonal worker camps generate synchronous shower and canteen peaks that push peak factors above the residential norm. Event and scout camps run near-empty for long stretches and full for short bursts, which is the worst case for biomass stability. The UK compliance frame then decides whether a containerized MBR is even viable: the Environment Agency's small-sewage discharge rules, Thames Water's Section 102/106 requirements for new connections, and Building Regulations Part H for drainage layout each impose constraints on discharge quality, access, and tank sizing that a generic export-market data sheet will not address.
The inputs to collect before you do any sizing calculation
Before any London consultant can brief a supplier, they need a defensible intake pack. Population is the first figure, but it has to be split between stable residential occupancy and camp-style peak occupancy — a 200-bed construction camp that is 90% full on weekday nights and 10% full on weekends is not the same hydraulic load as 200 residents. Per-capita flow must be confirmed against UK Water Industry Act and Water UK guidance; the 50 gpd (US gallons per day) per capita baseline that Pure Aqua publishes is an order-of-magnitude check only and should not be used as the design figure on a UK project.
Peak factor is the variable that most often turns a single-container design into a two-container train. UK-typical residential peak factors sit in the 2.0–2.5× average dry weather flow range, while camps with synchronous shower blocks, shift-change laundries, or event-driven spikes sit higher. A camp sizing that ignores the peak factor will pass the average daily m³ test and fail the membrane tank's surge capacity on a Monday morning.
Organic load is the parallel calculation: BOD per person per day multiplied by population gives kg BOD/day, and that number — not the flow — sets the aeration tank volume and verifies the membrane flux remains within the UF module's rating. Trade waste is the next adjustment. Camps add canteen grease and laundry surfactant; residential schemes with ground-floor commercial units add FOG (fats, oils and grease) and food waste. Both shift the FOG and surfactant load and may require a preceding rotary bar screen or grease trap ahead of the MBR container. The reuse target closes the intake: does the client need irrigation-quality effluent (Mena-Water cites this as a standard MBR output) or just consent-to-discharge quality? Reuse adds a polishing or disinfection stage and often a second container.
Step-by-step: turning population and load into m³/day and container count
The sizing method is a six-step sequence that a London consultant can run on a spreadsheet before issuing an enquiry.
Step 1 — Average dry weather flow. Multiply the design population by the per-capita flow. Use Pure Aqua's 50 gpd per capita (≈190 L/h/d) figure only as an order-of-magnitude check, then replace it with a UK-specific figure derived from Water UK or the local water company's charging rules. The result is the average m³/day that the MBR must process on a typical day.
Step 2 — Peak flow. Multiply the average dry weather flow by the peak factor. For UK residential, 2.0–2.5× covers most cases; for camps, work the peak from the occupancy profile (highest bed-night plus canteen plus laundry in the same hour). This peak figure sets the membrane tank and feed pump capacity, not the container count.
Step 3 — Organic load. Multiply BOD per capita (typically 60 g BOD/person/day for domestic sewage) by the population to get kg BOD/day. Cross-check this against the MBR's MLSS (mixed liquor suspended solids) and membrane flux rating — if the flux is exceeded, the membrane area or the number of modules has to grow, even if the hydraulic side looks comfortable.
Step 4 — Map to container format. Pure Aqua ships 20' and 40' high-cube (HC) containers; the biological train of a single 40' HC container covers the bulk of small-to-medium London projects. Mena-Water's benchmark is more than 1,200 m³/day in a single 40' ISO container, which is the upper bound of what one container can handle on the hydraulic side. A 200-home residential scheme typically fits the biological train inside one 40' HC container, with the membrane module area sized off the organic load rather than the flow.
Step 5 — Add a second container when the train outgrows a single unit. Blowers, sludge buffer, drum-screen pre-treatment (Pure Aqua specifies 1.5 mm perforation), and any reuse-polishing stage usually sit in a separate container to keep the membrane container maintenance-friendly. A pre-engineered containerized MBR membrane bioreactor system from a UK supplier will typically price a two-container train (process + blower/sludge) as the standard offer for residential schemes above ~100 homes, with a third container added only when reuse polishing is in scope.
Step 6 — London-specific site checks. Confirm headroom for Building Regulations Part H access requirements, and for tanker desludging access on buried or semi-buried installations. Confirm the electrical supply is UK 400V/3-phase/50Hz rather than the 460V/3-phase/60Hz that Pure Aqua's standard container ships with. A PVDF flat-sheet MBR membrane module retrofit or supply should be specified against UK voltage from the enquiry stage.
Containerized MBR parameter reference: what the supplier should quote you
The table below sets out the membrane, container, and operating parameters a serious UK supplier should quote on a containerized MBR offer. A generic package-plant data sheet that does not address these items is not a usable London specification.
| Parameter | Typical value or range | Source |
|---|---|---|
| Membrane type | Hollow-fibre UF, nominal pore size 0.04 µm | Pure Aqua |
| Membrane material | PVDF (polyvinylidene difluoride), TIPS process | Pure Aqua |
| UF pore-size range (general) | 2–100 nm; rejects bacteria and viruses | HUBER |
| Container format | 20' and 40' high-cube ISO containers | Pure Aqua |
| Pre-treatment | 1.5 mm perforation drum screen | Pure Aqua |
| Operating temperature range | 20–30°C (68–86°F) | Pure Aqua |
| Design temperature | 20°C (68°F) | Pure Aqua |
| Capacity benchmark | More than 1,200 m³/day in a single 40' ISO container | Mena-Water |
| Cleaning regime | Continuous coarse-bubble air scour on the membrane surface; one or two chemical maintenance clearings per year | Mena-Water, HUBER |
| Biomass benefit vs. conventional activated sludge | Higher biomass concentration; secondary clarifier replaced by membrane filtration | HUBER, Mena-Water |
The cleaning regime is the line item that makes the MBR genuinely low-touch in a London camp or residential setting. Continuous air-scour on the membrane surface (HUBER) and one or two chemical maintenance clearings per year (Mena-Water) is the envelope to specify in writing, including confirmation that the cleaning chemicals are UK-stock items. The capacity benchmark of more than 1,200 m³/day in a single 40' ISO container is a useful upper bound for the biological train, but the membrane area within that container must still be sized off the organic load, not the headline flow figure.
Residential versus camp projects: where the sizing math diverges
A camp is not a residential block with fewer people, and treating it as one is the most common London sizing error. The occupancy profile drives the divergence: residential gives a stable daily flow with predictable morning and evening peaks, while a construction camp gives a weekday-high, weekend-low pattern and an event or scout camp gives a near-empty baseline interrupted by short full-occupancy bursts. Both camp types push the peak factor above the residential norm and therefore demand a larger hydraulic buffer within the membrane tank or an upstream flow-equalisation container.
Pre-treatment load diverges as well. Camp canteens and shower blocks add FOG and lint; a 1.5 mm drum screen (Pure Aqua) is the minimum pre-treatment, and many London consultants add a preceding rotary bar screen at the head of the train to protect the drum screen and the membranes from heavy lint and food waste. Residential schemes with ground-floor commercial units face the same FOG and surfactant risk from food and drink tenants and benefit from the same upstream screen arrangement. The 1.5 mm drum screen is rated for the standard domestic load, not for a 200-bed camp's canteen peak.
Reuse targets are where camps diverge most clearly. Campsites — particularly seasonal workers' camps, scout camps, and event camps — often want irrigation-grade reuse for grounds, and Mena-Water highlights irrigation reuse as a built-in MBR capability. The container train should therefore include a polishing or disinfection stage, which usually means a third container for the reuse equipment rather than fitting it into the biological container. Mobility is a second camp-specific driver: Mena-Water's I-version (fully integrated) is designed to be shifted between sites, which is a useful specification for phased London construction camps where the plant moves as the development completes in phases.
Sludge handling is the final divergence. Camps with intermittent operation benefit from a dedicated sludge buffer container so that biological activity is not lost during quiet periods. The MBR's higher biomass concentration compared with conventional activated sludge (HUBER) makes it more tolerant of these pauses, but only if the sludge buffer is sized to keep the biomass aerated and fed during the low-occupancy window. A separate sludge handling container is also where a plate-frame filter press for cake production can be added if the site has limited tanker access.
UK compliance, commissioning and what to put in the supplier spec
The technical sizing only becomes a London-procurable specification when the compliance hooks are written into the enquiry. The first item is the effluent requirement: Environment Agency discharge consent limits, or Water UK and Building Regulations Part H for very small flows, set the BOD, TSS, and ammonia targets the MBR must hit. Specifying these up front prevents a supplier from offering a generic export-market data sheet that does not meet UK consent limits.
Electrical and control specification is the second item and the one most often missed. Pure Aqua's standard container ships at 460V/3-phase/60Hz, which is not the UK supply. The enquiry must specify UK 400V/3-phase/50Hz, and the supplier must confirm a UK-rated panel. PLC control with remote monitoring is the next item: Mena-Water and HUBER both offer remote support, and for an unattended London site this is essential, not optional. The PLC should log flow, membrane transmembrane pressure, and aeration status to a UK-hosted or client-hosted dashboard.
Factory acceptance testing (FAT) and plug-and-play delivery are the procurement hooks that make a containerized MBR genuinely faster to commission than a civil-built plant. Mena-Water highlights ISO-container standardization specifically because it enables factory QA before the container leaves the yard. The enquiry should require a FAT report and a witnessed FAT for any unit above the 1,200 m³/day benchmark, plus a pre-commissioning checklist that includes membrane integrity test, air-scour verification, and control-loop simulation. The membrane cleaning regime must be specified in writing: continuous air-scour on the membrane surface (HUBER) plus one or two annual maintenance clearings (Mena-Water), with the cleaning chemicals confirmed as UK-stock items and the membrane replacement interval quoted as a parts-and-labour figure. The MBR versus underground package STP trade-off is worth raising with the supplier at this stage if site constraints push the design below ground. Finally, access for desludging and for lifting the container into place is the forgotten item on tight London sites — the enquiry should include a site layout drawing that confirms crane reach, tanker access, and the Part H access shaft geometry before the container is built.
Frequently Asked Questions
How many containers do I need for a 200-home residential scheme in London?
A 200-home residential scheme with a standard 2.3-person-per-household assumption and a UK per-capita flow in the 150–180 L/h/d range lands in the 70–80 m³/day average flow band, which fits the biological train inside a single 40' HC container on the hydraulic side. A two-container train (process container plus a separate container for blowers, sludge buffer, and the 1.5 mm drum screen) is the typical UK supplier offer at this scale. Confirm the membrane area is sized off the organic load, not the headline flow, and request a written single-line diagram of the proposed train before order.
What does a containerized MBR cost in the UK, and what should I budget for?
The research data does not quote a UK list price for a containerized MBR, and any figure circulated without a site-specific enquiry is unreliable. What a London consultant should request from a UK supplier is a budget estimate broken into: container and membrane module, blower and control panel (UK 400V/3-phase/50Hz), pre-treatment screen, commissioning and FAT, and a separate annual membrane-cleaning and consumables line. The membrane replacement interval should be quoted as a parts-and-labour figure at the enquiry stage, since this is typically the largest lifecycle cost on a containerized MBR.
How do I choose a UK supplier for a containerized MBR rather than an import-only manufacturer?
Confirm the supplier will deliver a UK-rated electrical panel (400V/3-phase/50Hz) and not a 460V/3-phase/60Hz export unit, will provide a UK-hosted remote-monitoring service, and will commit to a UK-based commissioning engineer. Ask for a written membrane replacement interval, a confirmed UK stock-holding for the cleaning chemicals, and a reference list of UK containerized MBR installations of similar m³/day. A supplier that cannot answer these five items is not yet set up for the London market.
What does a containerized MBR actually remove from the sewage, and how often do the membranes need replacing?
An MBR combines biological treatment with ultrafiltration membranes. Pure Aqua's hollow-fibre UF operates at a nominal pore size of 0.04 µm, and Mena-Water and HUBER describe UF in the 2–100 nm range; both reject bacteria and viruses and retain suspended solids that a conventional activated-sludge clarifier would let pass. The membranes do not need regular chemical cleaning — Mena-Water cites one or two maintenance clearings per year — and replacement is driven by fouling, mechanical damage, or loss of permeability rather than a fixed calendar. A written membrane-replacement interval and a cleaning-chemicals schedule are the two items to pin down at enquiry stage.
Related Equipment
- containerized MBR membrane bioreactor system — specifications, capacity range, and technical data
- PVDF flat-sheet MBR membrane module — specifications, capacity range, and technical data
Further Reading
- Birmingham containerized MBR sizing guide
- MBR versus underground package STP trade-off
- UV polishing for MBR reuse projects
