How to Size a Containerized MBR STP in Tunis, Tunisia (2026 Guide)

Why Containerized MBR Is the Default Choice for Tunis Residential and Camp Projects

Containerized membrane bioreactors (MBR) arrive on a Tunisian site fully assembled and pre-tested inside an ISO frame, which collapses the civil-works window that a conventional concrete activated-sludge plant would require (SIGMADAF, 2025; MENA-Water via HUBER, 2025). For residential compounds and labour/work camps on the outskirts of Tunis — sites that often lack an existing sewer connection and have to be commissioned in a single construction season — that plug-and-play delivery is the practical reason MBRs are displacing concrete STPs.

Replacing the secondary clarifier with submerged ultrafiltration membranes also lets the aeration tank run at 6,000–12,000 mg/L mixed-liquor suspended solids (MLSS), roughly three times the 2,000–4,000 mg/L band of a conventional activated-sludge reactor, so the biological stage shrinks dramatically (SIGMADAF, 2025). MENA-Water documents that more than 1,200 m³/day can be filtered in a single 40-ft ISO container, giving Tunisian designers a defensible capacity anchor when they size a packaged HydropureWater containerized MBR system for anything from a 200-person staff block to a 1,000-person camp. Because the package is delivered with the membrane modules, blowers, control panel and chemical-cleaning skid already mounted, the only on-site work is hook-up of the inlet, outlet and power — a major advantage where civil contractors are on a tight programme.

Tunis-Specific Inputs That Change Your MBR Sizing

Before picking a 20' or 40' HC container, lock down the local variables that drive every downstream number. The design population should count residents plus staff and visitors, and for camps it must be the peak occupancy during construction or tourist season, not the annual average — a 500-pax camp that averages 350 pax year-round will size the membrane and equalization tank to the 500 figure, otherwise the membranes run above design flux on the busiest weekends. The per-capita wastewater flow for Middle East and North Africa residential projects is commonly 150–200 L/p/d; Pure Aqua's MBR-C is designed around 50 US gpd per capita (≈190 L/p/d), which is a useful US anchor but should be cross-checked against ONAS guidance for the specific Tunis district (Pure Aqua, 2025). The peak factor for Tunis residential is typically 1.5–2.5× average dry-weather flow, but camps with shift-change showers can exceed 3× — confirm with ONAS (urban) or ANGER/ANGED (rural and governorate sites) which value applies to the tender. Influent temperature matters because biology and membrane flux both move with it: Pure Aqua MBR-C is rated 20–30°C with a 20°C design point, and Tunis summer sewage of 25–30°C keeps biology active but may force a flux derating if winter influent drops. Finally, confirm the discharge and reuse target — sewer, irrigation or surface water — because each option sets a different effluent envelope and may require downstream UF, RO or advanced oxidation (SIGMADAF, 2025).

Step 1 — Convert Population Into Design Flow and Organic Load

The first arithmetic step on any Tunis MBR datasheet is the average daily flow:

Qavg (m³/d) = Population × per-capita flow (L/p/d) ÷ 1000

For a 500-pax residential block at 180 L/p/d, Qavg works out to 90 m³/d. That single number sets the container size, the equalization volume, the feed-pipe diameter and the membrane area — it must be defended with the population and per-capita assumptions written on the same line. The organic load is calculated in parallel, because the biological stage sizes off kilograms of BOD per day, not flow alone: residential sewage typically carries 50–60 g BOD/p/d and 100–120 g COD/p/d, which for 500 pax gives roughly 27.5 kg BOD/d and 55 kg COD/d. Sanitary sewage strength in Tunisia generally sits in the 250–500 mg/L BOD and 500–1,000 mg/L COD range for mixed residential, but a recent sewerage study for the district should always be used to override the textbook figure. For camps, add a food-service load (oils, fats, food solids) on top of the domestic BOD; these must be removed in pretreatment, not in the MBR, because SIGMADAF explicitly warns against sending fats, oils and hair into the membrane tank (SIGMADAF, 2025). Document Qavg, BOD load (kg/d) and COD load (kg/d) on a single line — these three numbers drive every downstream step in the sizing sequence.

Step 2 — Apply a Peak Factor and Size the Hydraulic Train

The peak hourly flow sets the size of the equalization tank, the feed pumps and the bar screen, even though the membranes themselves are sized off Qavg:

Qpeak = Qavg × peak factor

For Tunis residential, use 1.8–2.5 as an initial band; for labour/work camps with batch occupancy and shared shower blocks, use 2.5–3.0. The equalization volume is typically 4–8 hours of Qavg so the MBR sees a near-constant feed — critical when the upstream population is small and peak factors are high, because a 500-pax camp with a 3× peak will see momentary surges that the membranes cannot follow without buffer volume. Feed pumps and pipework are sized on Qpeak, not Qavg, and undersizing here is the most common cause of MBR hydraulic upsets on small Tunisian sites. MENA-Water offers its containerized MBRs in two configurations: the fully integrated I-Version where everything sits inside the ISO frame for mobile applications, and the U-Version where aeration and buffering take place in underground tanks (MENA-Water via HUBER, 2025); space-constrained Tunis sites with no room for buried civils typically select the I-Version. Pretreatment — drum screen, grit chamber and FOG removal — must be sized to Qpeak and is normally installed upstream of the ISO container, so a GX rotary mechanical bar screen with a 1.5 mm perforation drum matches the Pure Aqua MBR-C reference design (Pure Aqua, 2025).

Step 3 — Size the Biological Reactor and Membrane Area

Translating flow and load into reactor volume and membrane area is the step where a manufacturer's datasheet is read critically. The MBR aeration tank runs at 6,000–12,000 mg/L MLSS per SIGMADAF, well above the 2,000–4,000 mg/L of conventional activated sludge — that is why the aeration tank footprint collapses to a fraction of a concrete plant (SIGMADAF, 2025). Hydraulic retention time (HRT) is typically 4–8 hours at Qavg; lower HRT is possible at higher temperatures, but Tunis summer temperatures near 30°C reduce oxygen solubility and must be checked against the blower's actual airflow delivery, not its nameplate. Membrane flux — the litres of permeate produced per square metre of membrane per hour — is the next decision: design at 15–25 L/m²·h for flat-plate MBR, or 10–18 L/m²·h for hollow-fibre UF to limit fouling, and always confirm with the membrane maker's curve for the target MLSS. The three commercial membrane geometries documented in the research differ in pore size and polymer: SIGMADAF flat-plate membranes are 0.2 µm average / 0.4 µm nominal pore size in chlorinated polyethylene and are explicitly PFAS-free; Pure Aqua MBR-C uses 0.04 µm PVDF hollow fibre via thermally induced phase separation; HUBER describes UF membranes in the 2–100 nm range (SIGMADAF, 2025; Pure Aqua, 2025; HUBER, 2025). All three deliver near-reuse-quality permeate, but flux, cleaning interval and chlorine tolerance differ. Aeration sizing splits into fine-bubble diffusers for oxygen transfer and coarse-bubble air scour under the membranes to control biofouling; SIGMADAF stresses that diffuser efficiency drives overall MBR performance and must be specified on the bid (SIGMADAF, 2025).

Once the design flux and flow are set, required membrane area is calculated as Qavg ÷ (flux × 24) — for the 500-pax worked example at 20 L/m²·h this is approximately 188 m², well within the area that flat-plate modules such as the DF series flat sheet MBR module can pack into a single 40' HC frame.

Step 4 — Match the Membrane System to a 20' or 40' HC ISO Container

Standard containerized MBRs are built in 20' and 40' high-cube (HC) ISO containers; Pure Aqua MBR-C and MENA-Water both document this envelope explicitly, and MENA-Water confirms that more than 1,200 m³/day can be filtered in a single 40-ft ISO container at its packing density (Pure Aqua, 2025; MENA-Water via HUBER, 2025). For residential blocks up to approximately 200 m³/day and most labour/work camps, a single 20' HC unit typically suffices; above that, step to one 40' HC unit or two parallel 20' HC units for operational redundancy. MENA-Water builds the inside tanks from stainless steel sheets inside the ISO frame — a corrosion-relevant detail for Tunisian coastal or humid sites, where bidders offering coated carbon steel should be asked to justify the coating specification. Pure Aqua MBR-C documents a seaworthy, insulated container with zero water leakage and an enhanced structure, which on a hot Tunis site helps control condensation and protects the membrane modules from thermal cycling. For mobile or phased projects — a construction camp that relocates with the work front, for example — MENA-Water's I-Version is designed to be lifted off its foundations and moved, with quality-tested plug-and-play recommissioning at the new site. Footprint planning should include truck access for the low-loader, a 1 m clearance around the container for maintenance, and a screened inlet chamber upstream.

Worked Example — 500-Person Camp on the Outskirts of Tunis

To make the sizing sequence defensible on a Tunisian datasheet, walk it end-to-end on a concrete case. Take a 500-pax labour camp on the outskirts of Tunis with shared shower and kitchen blocks. Population 500 × 180 L/p/d = 90 m³/d Qavg. Apply a peak factor of 2.5 for camp shower peaks → Qpeak ≈ 225 m³/d (≈9.4 m³/h peak). Organic load at 55 g BOD/p/d = 27.5 kg BOD/d; influent BOD ~305 mg/L sits comfortably inside the typical residential range and is treatable in MBR at 6,000–12,000 mg/L MLSS (SIGMADAF, 2025). Required membrane area at 20 L/m²·h design flux and 90 m³/d average works out to approximately 188 m² — readily handled by flat-plate MBR modules in a single 40' HC ISO container at MENA-Water's documented packing density, with redundancy headroom for one cassette out of service. Pretreatment must include a 1.5 mm drum screen sized to Qpeak (Pure Aqua MBR-C reference) and a grit/FOG chamber ahead of the equalization tank; the article treats these as items to specify with the bidder rather than fabricating capacity figures. Container count: one 40' HC ISO MBR + one equalization/buffer tank + upstream screening/FOG removal, road-transportable on standard low-loaders and fitting a typical Tunis camp plot.

Pretreatment and Reuse Polishing Around the MBR Container

An MBR container is only as reliable as the equipment feeding it, and the polishing train downstream is what decides whether the effluent can be reused or only discharged. SIGMADAF is explicit: do not send fats, oils or hair into the MBR, so a coarse/fine screen plus a dedicated FOG removal stage must sit upstream of the equalization tank (SIGMADAF, 2025). For irrigation reuse targets in Tunis, MBR permeate is normally followed by UF and/or RO polishing; SIGMADAF also notes that MBR package plants can integrate ultrafiltration, reverse osmosis or advanced oxidation downstream of the biological reactor when reuse quality is required. Disinfection is the next decision: UV is chemical-free and effective against chlorine-resistant organisms, while ClO₂ generation provides a residual for long reuse loops — confirm with ONAS/ANGED which residual is acceptable for the specific discharge point. A DAF unit for FOG removal ahead of the MBR, a UV sterilizer for reuse polishing downstream, and a plate and frame filter press for waste-activated-sludge dewatering complete the minimum package for a decentralized camp, since SIGMADAF describes MBR waste sludge generation as minimal but still requiring occasional blowdown. For Tunis sites aiming at irrigation reuse, a MBR + UV + sludge thickener train is the realistic baseline; RO is added when salt or trace-contaminant targets apply.

Selection and Procurement Checklist for a Tunis Containerized MBR

Convert the sizing sequence into a bid-evaluation checklist so no critical question gets lost between the commercial and technical reviewers. Start with the scope in one line: influent characterization → pretreatment → equalization → MBR container → disinfection → sludge handling, each item on the same Qavg and Qpeak basis so bids are comparable. Ask every bidder for the same set of datasheet numbers — flux (L/m²·h), MLSS (mg/L), HRT (h), aeration airflow (Nm³/h), membrane area (m²) and container dimensions — so SIGMADAF-, MENA-Water- and Pure-Aqua-class plants can be compared on an apples-to-apples basis (SIGMADAF, 2025; MENA-Water via HUBER, 2025; Pure Aqua, 2025). Confirm the power supply carefully: Pure Aqua MBR-C ships 460 V / 3-phase / 60 Hz, and Tunis mains run 400 V / 3-phase / 50 Hz, so a transformer or a 50 Hz panel build must be requested up front to avoid a retrofit after delivery. Ask for PLC-controlled cleaning cycles and remote monitoring — MENA-Water advertises that it can "consult anytime via remote monitoring from back office" — because remote diagnostics reduce site-visit frequency on camps that are not permanently staffed. Finally, request membrane warranty terms, expected chemical-cleaning frequency (SIGMADAF and MENA-Water both note 1–2 maintenance cleanings per year for UF MBR) and reference installations in hot-climate or North African projects. For projects that may be re-tendered or relocated, also evaluate a packaged underground option such as the WSZ underground integrated sewage treatment against the containerized MBR. A useful cross-check is the wastewater treatment capacity calculation guide, and for a parallel European reference the Madrid containerized MBR sizing guide and the Colombo containerized MBR sizing guide both use the same population-to-container workflow adapted to local influent conditions.

Frequently Asked Questions

What is the realistic cost band for a containerized MBR STP in Tunis for a 500-person camp?

The research does not publish a current 2026 price for a 40' HC ISO containerized MBR delivered and commissioned in Tunis. Buyers should request a written quotation that itemises the container, membrane modules, blowers, control panel, pretreatment skids, equalization tank, disinfection unit and sludge dewatering, plus shipping, ONAS/ANGED approval fees and one year of spares. A meaningful cost comparison requires at least three bidders returning numbers on the same Qavg/Qpeak/flux basis before any band can be defended.

How do I shortlist containerized MBR suppliers for a Tunis residential or camp project?

Shortlist on three documented criteria: the bidder can quote flux, MLSS, HRT, aeration airflow and membrane area on the same datasheet (SIGMADAF, MENA-Water and Pure Aqua all publish these figures); the bidder can build a 50 Hz / 400 V panel for Tunis mains, since Pure Aqua MBR-C ships at 460 V / 60 Hz as standard and the transformer must be specified (Pure Aqua, 2025); and the bidder offers a remote-monitoring option with documented response time, which MENA-Water advertises explicitly (MENA-Water via HUBER, 2025). Ask each shortlisted bidder for at least one reference installation in a hot-climate or North African project.

How do I decide between a single 40' HC ISO container and two parallel 20' HC containers?

The research gives a direct capacity anchor: MENA-Water documents that more than 1,200 m³/day can be filtered in a single 40-ft ISO container (MENA-Water via HUBER, 2025). Below that envelope, choose a single 40' HC unit when site space allows and the camp population is stable; choose two parallel 20' HC units when redundancy matters more than footprint, or when the camp may be expanded later in phases. For a 500-pax camp at 90 m³/d average, a single 40' HC container leaves substantial headroom for peak loading and one cassette out of service.

What pretreatment is mandatory upstream of a containerized MBR in Tunis?

A coarse/fine screen and a grit/FOG removal stage are mandatory because SIGMADAF explicitly warns against sending fats, oils and hair into the MBR (SIGMADAF, 2025). Pure Aqua MBR-C documents a 1.5 mm perforation drum screen as the standard pretreatment reference (Pure Aqua, 2025). Both items must be sized to Qpeak, not Qavg, so they do not become the bottleneck during shift-change or meal-time surges.