Sizing a Containerized MBR STP for Austin, TX in 2026

Why Austin Projects Need a Specific Containerized MBR Sizing Approach

Containerized membrane bioreactors (MBRs) are sold with manufacturer sizing rules that were not written for Texas regulators. Pure Aqua's MBR-C platform, for example, is sized around an "approximate population (50 gpd per capita)" column on its product sheet — a useful equipment-side starting point, but not a TCEQ Chapter 305 design value (containerized MBR system reference). The project engineer of record must reconcile that number with the per-capita loading the regulator expects and document which one governs.

Three Austin-specific factors make that reconciliation non-trivial. First, City of Austin Water sits on top of TCEQ Chapter 305 with its own reuse criteria for landscape irrigation projects, so the post-MBR polishing step (UV, chlorine dioxide) is set by the city, not by the membrane supplier. Second, Hill Country camps and resorts run on a weekend-peak versus weekday-base occupancy curve, and a single per-capita number cannot capture the morning surge on a Saturday check-in day. Third, influent temperature sits inside Pure Aqua's stated 68–86°F (20–30°C) operating window for most of the year in central Texas, so biological kinetics and membrane flux are within design range — but the engineer still must check the design-temperature floor of 68°F (20°C) against January lows.

The 5-Step Sizing Workflow for a Containerized MBR

A defensible Austin sizing follows a fixed sequence. The five steps below outline the process an engineer should complete before a supplier's presales team reviews a population number.

1. Establish the design population. For a subdivision, use full-time residents. For a camp or resort, use peak-occupancy headcount for hydraulics and average daily occupancy for organics, and document the seasonal occupancy curve.
2. Convert population to average daily flow. Apply a per-capita value and document the source. Pure Aqua's MBR-C sizing chart uses 50 gpd per capita; TCEQ Chapter 305 typically references higher residential design values, so the governing number must be confirmed by the engineer of record before submission.
3. Apply a peaking factor. Small residential and camp systems commonly use a peaking factor in the 2.5–4.0 range to convert average daily flow to peak hourly flow, since containerized MBRs have limited equalization volume relative to the daily flow they handle.
4. Match peak flow and HRT to a container format. A 20-ft HC container typically covers low single-digit m³/day; a 40-ft HC container covers tens of m³/day up to the ceiling MENA-Water cites for a single 40-ft unit.
5. Confirm the reuse or discharge pathway. Lock the post-MBR polishing step (UV or chlorine dioxide) to whichever Texas rule applies before the equipment list is finalized.

MENA-Water reports that more than 1,200 m³/day can be filtered in a single 40-ft ISO container, with all mechanical equipment and plant control pre-assembled for plug-and-play site delivery. That ceiling makes a single-container solution realistic for many small community, subdivision, and camp projects in the Austin region.

Sizing Inputs and Parameter Ranges to Confirm With Your Engineer

The project engineer should have a written set of inputs before a supplier quote is generated. The table below maps the equipment-side parameter to its source and the Texas-side question it triggers.

For projects where the upstream biological step needs a higher-rate or anaerobic front end — a camp kitchen with high COD, for example — the EGSB reactor process flow reference documents a complementary configuration. Site constraints (container footprint, set-back distance, noise, and whether a relocatable I-Version per MENA-Water is needed for a phased or mobile camp) belong on the same checklist.

Worked Example: 200-Person Summer Camp Near Austin

Running the workflow on a Hill Country case requires specific attention to occupancy variables. The inputs are: peak headcount of 200 campers, a weekend-to-weekday occupancy ratio of roughly 3:1, and a site where the developer wants landscape irrigation reuse.

Step 1 — Population. Use 200 for peak hydraulics and an average daily occupancy that reflects the 3:1 weekend-to-weekday ratio for the organic load calculation.

Step 2 — Average daily flow. At the 50 gpd-per-capita baseline that Pure Aqua's MBR-C sizing chart uses, 200 × 50 = 10,000 gpd average on the peak-occupancy day. That average must be reconciled with the TCEQ Chapter 305 per-capita value before the design package is submitted — the manufacturer number is the equipment baseline, not the regulatory baseline.

Step 3 — Peaking factor. Apply a 3.5 peaking factor to capture the morning shower and laundry surge on a Saturday check-in. The peak hourly flow drives equalization tank sizing, and because a containerized MBR carries limited equalization volume, an upstream buffer tank or lift station is normally required for a camp case.

Step 4 — Container selection. The resulting 10,000 gpd average (≈ 38 m³/day) is well inside the >1,200 m³/day ceiling MENA-Water reports for a single 40-ft unit, so a 20-ft HC unit covers the lower bound and a single 40-ft HC unit covers the upper bound. The deciding factors are the equalization strategy and how much hydraulic surge the camp wants to absorb inside the membrane tank versus an upstream buffer.

Step 5 — Effluent pathway. If the camp intends landscape irrigation, the City of Austin reuse criteria govern the polishing step downstream of the MBR; if surface discharge is proposed, TCEQ Chapter 305 limits apply instead. Lock this before specifying the post-MBR skid — for irrigation reuse, see the containerized MBR system train and pair it with a UV polishing skid sized to the reuse criteria.

Matching the Container to the Reuse or Discharge Pathway

The container choice and the polishing step are linked: the reuse pathway sets the post-MBR equipment list, and the equipment list feeds back into the container size.

For irrigation reuse under City of Austin criteria, the MBR's solids-free, low-BOD effluent is the basis of design, but the city requires a polishing step — typically UV or chlorine dioxide — to meet bacterial limits for landscape application. MENA-Water's product literature notes that the membrane step alone delivers 99.9999% virus and bacteria reduction, with only 1–2 maintenance clearings per year; that maintenance budget should be on the operator's plan from day one. Pair the MBR container with a UV polishing skid for irrigation reuse to close the loop.

For surface discharge under TCEQ Chapter 305, the same MBR effluent is the starting point, but a disinfection step is required to meet the bacterial limits in the discharge permit. The container envelope is unchanged; the downstream skid changes based on the permit requirements.

For phased developments, mobile camps, or sites where the plant may need to be redeployed rather than abandoned, specify MENA-Water's I-Version relocatable containerized MBR format. The I-Version is built for the same ISO container envelope but is designed to be shifted to a new location, which protects the capital outlay if the camp's footprint changes.

For sizing context outside Austin, the Birmingham MBR sizing guide walks through a UK residential case, and the Busan hotel packaged MBR selection guide covers a hospitality case — both are useful comparisons for the peaking-factor and container-selection logic.

Frequently Asked Questions

How accurate is the 50 gpd-per-capita rule on the manufacturer's sizing chart?

It is an equipment-side baseline used by Pure Aqua on its MBR-C sizing chart. The governing number for a Texas project is the TCEQ Chapter 305 design value confirmed by the engineer of record, which is typically higher than 50 gpd per capita. Treat the manufacturer number as a starting point, not the design value.

What drives the cost band for a packaged MBR STP in Austin?

Cost is driven by container size (20-ft HC versus 40-ft HC), membrane area, the equalization or buffer tank needed to handle peak hourly flow, and the post-MBR polishing skid (UV or chlorine dioxide) required to meet either City of Austin reuse criteria or TCEQ Chapter 305 discharge limits. A buyer should request a written scope that itemizes the container, the membrane area in m², the polishing skid, and the equalization volume before comparing supplier quotations.

How long does delivery and commissioning take for a containerized MBR?

MENA-Water states its containerized MBR plants are pre-assembled as ISO containerized systems, with factory quality testing enabling plug-and-play start-up at site. A buyer should request a written lead time from the supplier that covers fabrication, factory acceptance testing, shipping to the Austin-area site, and on-site commissioning.

What compliance risk should an Austin buyer flag before signing a purchase order?

The risk is a mismatch between the manufacturer sizing rule and the TCEQ Chapter 305 design value the regulator expects. The buyer should require the supplier's proposal to state which per-capita value was used, the source of that value, and a written confirmation from the project engineer of record that the value matches TCEQ Chapter 305 and, for irrigation reuse, the City of Austin reuse criteria. Without that confirmation, the equipment list may require resizing after submittal.

Related Equipment

• flat-sheet MBR membrane module — specifications, capacity range, and technical data

Further Reading

• EGSB reactor process flow reference