Every SewTreat biological wastewater treatment plant runs the same five-phase treatment process. What changes between formats is the vessel that process is built into, and that single choice drives what you pay upfront and how long the plant lasts.

SewTreat manufactures five formats, ranging from compact SewPro units treating 1,000 litres per day through to Steel Tank installations handling 5 million litres per day. Choosing correctly means matching the format to your flow volume and available space, then weighing budget horizon against site conditions.

This guide compares all five against those criteria, with a decision framework and verified project outcomes to support the choice.

What Every SewTreat System Shares

The treatment process does not change between formats. Every plant moves wastewater through the same five phases:

Screening removes solids at the point of entry, using either a manual or automated screen.
Anaerobic digestion runs in two stages, separating solids by specific gravity and breaking down fine particles. De-nitrification happens here, converting nitrates to nitrogen gas.
Aerobic digestion takes place in a bioreactor where aerobic bacteria consume the remaining organic load. Fixed bed cross flow media enhances bacterial colonisation and assists oxygen transfer, reducing BOD and driving nitrification.
Clarification settles cell material into a sludge blanket, which is recirculated back to the first anaerobic phase to seed incoming raw sewage.
Disinfection prepares effluent for discharge. SewTreat uses ozone sterilisation as its primary method because it leaves no residual in the water, with chlorination or ultraviolet available where requirements differ.

Two features of this process are worth understanding before comparing formats, because they apply regardless of which vessel you choose.

The returned activated sludge means no sludge extraction is required. The bacteria continually break down the sludge, which makes these zero waste plants and removes the need for drying beds entirely.

Micro bubble diffusion delivers optimal dissolved oxygen transfer, and the final effluent needs no mechanical filtration before discharge. That effluent contains no chemicals and is safe for reuse in irrigation or dust suppression.

Operationally, every format shares the same profile:

No permanent labour is required to operate the plant
Electricity consumption is low
Operating and maintenance costs stay low
Modularity allows plants to be added to as demand increases
Footprint is minimal relative to conventional civil works

The differences that matter are structural rather than biological.

Five Wastewater Treatment Formats Compared

Format	Standard Flow Range	Installation	Best Suited To
Steel Tank	50Kl to 5Ml per day	Above ground, 50% faster than civil builds	Industrial, municipal, large commercial
Underground	5Kl to 5Ml per day	Below ground, full civil or fibreglass and LDPE	Developments where appearance matters
Containerised	5Kl to 300Kl per day	ISO High Cube containers, plug and play	Remote sites, lodges, temporary deployments
Plastic Tank	10Kl to 200Kl per day	Above ground on a concrete slab	Medium-flow commercial, greywater recycling
SewPro	1Kl to 100Kl per day	Single tank, flat-packed for transport	Small sites with tight space or budget

Steel Tank BWWTP

The corrugated steel tank format covers the widest capacity range at the top end, from 50,000 litres per day to 5 million. It is the most cost-effective system in the industry for large scale applications.

What sets it apart:

Life expectancy of 20 to 30 years, the longest SewTreat publishes
Installation 50% faster than comparable systems
Civil construction can be subcontracted locally, reducing overall cost
Designed to scale up as demand grows
Incorporates the full treatment spectrum

The trade-off is footprint. These are large above-ground structures, so sites with severe space limits or aesthetic constraints should look at the underground range instead.

Underground BWWTP

The underground range matches the steel tank at the top end for capacity, handling 5,000 litres to 5 million litres per day, but places the entire system below ground. Vegetation covers the installation, which suits developments where a visible plant would be unacceptable.

Two construction routes are available: full civil engineering and construction, or fibreglass and LDPE tanks. Most installations are gravity fed depending on invert and contour levels.

A gravity-fed plant can operate for 48 hours without electricity. That load-shedding resilience is a practical advantage in South Africa that no other format in the range offers.

Containerised BWWTP

Containerised plants build the complete system into ISO High Cube containers, producing a plug-and-play unit that treats 5,000 to 300,000 litres per day. The container provides security during transport and while operating.

The commercial logic here differs from the other formats:

Capital cost is a once-off spend, since the plant moves between sites rather than staying stranded at one location
Only a concrete slab or plinth is needed on site
Modular construction allows straightforward expansion later

This makes it the natural choice for mining camps and remote lodges. Emergency deployments suit the format equally well, since the requirement may end.

Plastic Tank BWWTP

The plastic tank range covers medium flows from 10,000 to 200,000 litres per day. Installation requires only a concrete slab with the feed sump or screen, which keeps setup costs low.

Because the system sits above ground and is modular, expansion is straightforward as demand grows, and the plant relocates easily when circumstances change. SewTreat notes the range is well suited to greywater recycling systems specifically.

Consider it where flows are moderate and the operation may need to scale or move.

SewPro BWWTP

SewPro is the entry point of the range, treating 1,000 to 100,000 litres per day with the complete process housed in one steel tank. That single-vessel design gives it the smallest footprint SewTreat offers.

Key characteristics:

life expectancy of 8 to 12 years
Units arrive flat-packed for easy transport
Submersed bio-media with a Return Activated Sludge circuit
Low electricity consumption

For a site where capital is tight or space is constrained, SewPro delivers compliant treatment without the cost of a larger format.

A Framework for Choosing Your System

Start With Flow Volume

Flow narrows the field faster than any other criterion:

Above 300,000 litres per day, only Steel Tank and Underground remain viable
Between 200,000 and 300,000, Containerised joins them
Below 100,000 litres per day, all five are technically capable

Once several formats qualify on flow alone, the decision moves to site conditions.

Then Assess Your Site

Space and appearance decide the next cut. Developments that cannot accommodate a visible structure need the underground range. Sites with severe footprint limits point toward SewPro.

Remote locations without reliable access favour containerised units, which arrive complete and need only a concrete plinth.

Then Weigh Lifespan Against Capital

A Steel Tank plant at 20 to 30 years covers roughly two to three SewPro replacement cycles, so the higher upfront cost buys a materially longer horizon.

For a permanent facility with stable long-term flows, the longer-life format is usually the better financial decision even at higher capital cost. For a temporary or uncertain requirement, paying for a 30-year asset makes little sense.

Finally, Confirm Effluent Requirements

All five formats produce final effluent within legislative discharge requirements, suitable for release to the environment or for non-potable reuse. No mechanical filtration is needed at the discharge point.

Sites with unusual contamination profiles, including high FOG or elevated COD, need that load assessed before the format is locked in. SewTreat’s industrial water treatment systems handle pre-treatment where the biological stage alone would be overwhelmed.

What These Systems Deliver in Practice

At Eastlands Mature Living Estate in Benoni, a failed competitor installation was retrofitted into a 120,000-litre-per-day underground plant. The estate now saves R2.07 million per year, with treated water reused for irrigation across the development.

At Samancor Chrome’s Lesedi Mine near Rustenburg, a 200,000-litre-per-day steel tank plant was built with the architecture to reach 400,000 litres per day as the mine expands. The existing 120,000-litre sump was integrated as a buffer tank rather than replaced.

Download the full case studies for verified project data across mining, commercial and residential applications.

Where to Start

The format decision is easier once flow volume and site constraints are documented. Those two inputs alone eliminate most of the range, and the remaining choice usually comes down to how long the facility expects to operate.

Use SewTreat’s calculator to estimate what on-site treatment could save at your current municipal tariff, or contact SewTreat directly to have your site assessed and a format recommended.