Why Frankfurt Projects Use Containerized MBR STPs
A containerized package MBR is a pre-engineered, compact wastewater treatment system built inside standard 20 ft or 40 ft shipping containers, combining biological treatment and membrane filtration within a single modular unit (wateracademia.com). The unit arrives fully equipped and requires only water and power connections to start operating, which removes most of the civil works that would otherwise sit on a Frankfurt site (wateracademia.com). The deployment case for a Frankfurt residential block, worker camp or refugee/construction camp includes six recurring benefits: fast deployment, compact design, high effluent quality, scalability by connecting multiple containers, mobility for relocation, and reduced construction cost compared with a poured-in-place plant (wateracademia.com).
The practical question is not whether a containerized MBR can meet Frankfurt or Hessen discharge expectations, because it can. The system produces permeate with biochemical oxygen demand (BOD), total suspended solids (TSS), TKN and ammonia well below typical discharge limits, so the sizing target is hydraulic and organic load, not effluent polishing margin (dynatecsystems.com). What changes between a permanent residential block and a temporary camp is the design population and the load profile, not the underlying architecture. This guide provides a calculation chain: population → flow → loads → reactor and membrane dimensions → 20/40 ft container count. The same chain underpins containerized MBR sizing in Central Europe and is portable to any Rhein-Main site brief.
Step 1 — Convert Occupancy Into a Design Population
Design population N is the maximum number of equivalent persons the STP must serve at peak demand, and it is the single number that drives every step downstream. For a permanent Frankfurt residential development, N is the number of dwellings multiplied by an assumed persons-per-dwelling factor confirmed with the client or against local data. For a worker, refugee or construction camp, N is the nominal bed count at full occupancy, plus an allowance defined for visitors, site staff and shift overlap.
German and EU sizing practice is sensitive to the assumed per-capita water use: a small change in N or in per-capita flow q produces a proportional change in design average daily flow Q_avg, and the rest of the sizing chain amplifies that error. Population drives both hydraulic load in m³/day and organic load in kg BOD/day, so a defensible N acts as the primary control lever for the design. Step 2 carries N into the hydraulic calculation.
Step 2 — Translate Population Into Average Daily Flow in m³/day
Design average daily flow Q_avg in m³/day is the working hydraulic unit for a containerized MBR sizing memo. The IDA Water Security Handbook 2019 and 2020–2021 edition state the working conversion explicitly: the primary unit is the cubic metre on a per-day basis, where one cubic metre is 1,000 litres, and one cubic metre of water weighs one metric ton. This conversion allows the engineer to align results with the Handbook's reuse and desalination inventories (IDA Water Security Handbook 2019; IDA Water Security Handbook 2020–2021).
Q_avg is calculated as N multiplied by the per-capita flow q in L/person/day, then divided by 1,000. The per-capita flow q is a Frankfurt-specific input the engineer must confirm from local data or the client brief. A single residential block or camp almost always lands well below the 500 m³/d inventory threshold in the 2019 IDA inventory, which is why a containerized MBR system is the appropriate reference class for these projects. Step 3 turns Q_avg into the peak loads the system must accommodate.
Step 3 — Apply a Peak Factor and Estimate Organic Load
A containerized MBR must ride through the worst-case morning and evening peaks. The peak factor K is a multiplier on Q_avg taken from local German practice or the project brief. Daily peak flow is Q_peak = K × Q_avg in m³/day, and hourly peak flow is Q_peak_hour = K_h × Q_avg / 24 in m³/h, where K_h is the hourly peak factor. The project brief typically supplies the peak factors, the per-capita flow q, and the design population N together as part of the load model.
Organic load L_BOD in kg BOD/day is computed from N and a per-capita BOD contribution in g BOD/person/day. L_BOD is then divided by the mixed-liquor volatile suspended solids (MLVSS) mass to set the food-to-microorganism (F/M) target, a sizing parameter used in Step 4. Both hydraulic and organic loads are now quantified in m³/day and kg BOD/day. Step 4 uses these loads to size the actual reactor volume and membrane area.
Step 4 — Size the Bioreactor Volume and Membrane Area
Bioreactor volume V_bioreactor is sized from hydraulic retention time (HRT) using HRT = V_bioreactor / Q_avg, where HRT is a project input in the typical MBR range. Sludge retention time (SRT) is set independently of HRT, and a longer SRT provides the nitrification capacity needed to meet low ammonia targets in MBR permeate (dynatecsystems.com). V_bioreactor then sets the reactor tank dimensions that must physically fit inside the container envelope.
Membrane area A_m is calculated as A_m = Q_peak / J, where J is the design flux of the specific module. The HydropureWater DF-series flat-sheet MBR module provides 80–225 m² of membrane area per module, producing 32–135 m³/day per module. The broader containerized MBR system envelope of 10–2,000 m³/day defines the upper bound for a single line. The table below summarises the parameters for Step 5; per-project values (HRT, J, F/M, K) must be confirmed with the manufacturer and the client brief.
| Parameter | Symbol | Source of value | Envelope in research |
|---|---|---|---|
| Average daily flow | Q_avg | Engineer (N × q / 1,000) | Well below 500 m³/d inventory threshold (IDA Handbook 2019) |
| Peak flow | Q_peak | Engineer (K × Q_avg) | K is a project input |
| Organic load | L_BOD | Engineer (N × per-capita BOD) | Per-capita BOD is a project input |
| F/M ratio | F/M | Manufacturer / brief | Sizing parameter |
| Hydraulic retention time | HRT | Manufacturer / brief | Sizing parameter |
| Sludge retention time | SRT | Manufacturer / brief | Longer SRT supports nitrification (dynatecsystems.com) |
| Membrane flux | J | Module datasheet | Depends on module |
| DF-series module area | A_module | DF-series datasheet | 80–225 m² per module |
| DF-series module flow | Q_module | DF-series datasheet | 32–135 m³/day per module |
| Single-line MBR envelope | Q_line | Manufacturer | 10–2,000 m³/day |
The module count is Q_peak divided by Q_module, and the total membrane area is the module count multiplied by A_module. These figures are checked against the DF-series flat-sheet MBR module envelope before proceeding to Step 5.
Step 5 — Select Container Count and ISO 20/40 ft Layout
The physical boundary for a containerized MBR is the 20 ft or 40 ft standard shipping container. A typical three-container layout assigns one container to the bioreactor, a second to the membrane skid and clean-in-place gear, and a third to blowers, controls and disinfection. A single-container package is feasible for the smaller end of the duty envelope, and a two-container package is the common middle ground for residential blocks and small camps. Multiple containers can be connected for higher flows (wateracademia.com).
Expansion is straightforward because out-of-basin membrane configurations allow simple addition of more membrane skids without replacing the bioreactor (dynatecsystems.com). The table below translates the Step 4 envelopes into a container count; per-project values must be confirmed with the manufacturer and the client brief.
| Daily flow band | Likely container count | Typical role split | Notes |
|---|---|---|---|
| Up to ~30 m³/day | 1 × 20 ft | Bioreactor + membrane skid in one unit | Compact residential block or small camp |
| ~30–135 m³/day | 1–2 × 20 ft or 1 × 40 ft | Reactor in one unit, membrane + CIP in the second | Mid-size residential block or worker camp |
| ~135–500 m³/day | 2–3 × 40 ft | Reactor, membrane skid, blowers/controls | Larger camp or multi-block residential |
| ~500–2,000 m³/day | Multiple 40 ft units in parallel | Parallel lines, each within 10–2,000 m³/d envelope | Expansion by adding membrane skids (dynatecsystems.com) |
The engineer reconciles the container count against Q_avg, Q_peak and the single-line envelope of the chosen containerized MBR system.
Frankfurt Compliance Hooks and Pre-Order Checklist
The Urban Waste Water Directive 91/271/EEC serves as the compliance anchor for discharges from small agglomerations in the EU. Any containerized MBR specification for a Frankfurt site should reference this directive, with specific numeric limits confirmed against current Hessen implementing rules before issue. The plug-and-play positioning reduces civil works, but electrical connection, inlet and outlet piping, and sludge handling remain site responsibilities (wateracademia.com).
The pre-order inputs the engineer must collect from the client are: confirmed design population N, per-capita flow q, peak factor K, influent BOD/COD/TSS range, required effluent limits, footprint and container access envelope, and power availability. Supply questions to confirm with the manufacturer include: single-unit m³/day envelope, membrane area per module, membrane type, control system architecture, and lead time. For sites pushing towards stricter nutrient targets, this chain is the starting point for advanced nutrient removal for stricter effluent targets.
Frequently Asked Questions
How many containers do I need for a Frankfurt residential block of, say, 200 people?
The container count is set by Q_peak and the per-module flow. With a design population of 200 persons, an engineer-confirmed per-capita flow q, and the chosen DF-series module envelope of 32–135 m³/day, the engineer works backwards from Q_peak to a module count and then checks whether the resulting bioreactor volume, membrane skid and blowers fit into one 40 ft container or require two. The DF-series flat-sheet MBR module datasheet and the chosen membrane flux J determine the final container count.
What drives the cost of a containerized MBR STP for a Frankfurt project?
Cost drivers include the single-line m³/day envelope, the number of containers, the membrane area and module count, the membrane type, the control system architecture, and the effluent polish scope. Request a written quote that itemises these line items against the Q_avg and Q_peak in the design memo, and confirm whether commissioning, freight to Frankfurt and the first membrane replacement are included.
How do I select a supplier for a containerized MBR in the Rhein-Main region?
Ask the manufacturer to confirm the single-unit m³/day envelope, the membrane area per module, the membrane type, the control system architecture, and the lead time against a Q_avg and Q_peak derived from the calculation chain. A supplier that can show an operating