Filtration

Filtration in an aquatic life support system removes suspended solids using sand, bead, drum or microscreen filters; it is usually the largest equipment item in the system and the biggest driver of equipment room footprint.

Types used in aquatic systems

High-rate sand filters are the workhorse of water parks, pools, and many exhibit systems. Media beds capture solids; backwashing flushes them out. Reliable, well understood, and demanding on backwash water and drainage.

Bead filters use a floating plastic media bed and provide mechanical capture plus biological surface area in one vessel. Common in aquaculture and in smaller exhibit systems where footprint is tight.

Drum and microscreen filters remove solids across a fine screen continuously, typically with automatic backwash. They are widely used in recirculating aquaculture and other applications with heavy, continuous solids loading.

Cartridge and bag filtration serves polishing duty and small process streams.

Regenerative media filters hold perlite or a similar medium on flexible tubes and clean by bumping the media loose and re-depositing it rather than by backwashing, which removes finer particles and uses a fraction of the backwash water. They are common on water features, pools and hydroponic nutrient tanks.

Biological filtration is a separate function from solids removal. Moving bed bioreactors (MBBR), fluidized sand beds, trickling filters and fixed-film media convert ammonia to nitrite and nitrate and are sized on feed or biological load, not on system volume. Bead filters combine some biological capacity with mechanical capture.

Where it’s used

Every application with a life support system. The type changes: water parks lean on high-rate sand, RAS facilities on drum filtration and beads, aquarium exhibits on a mix driven by water clarity requirements and space.

Why specification matters

Turnover rate drives everything downstream. How many times per hour the full system volume passes through filtration determines the filter size, the pump duty, and the pipe sizing. Health codes set minimum turnover for public water contact. Animal systems are set by biological load, target clarity, and species requirements. Get the turnover wrong and no other equipment in the loop can compensate.

Filtration rate and vessel area are not the same thing. Sand filters are sized on surface loading, flow per square foot of bed area. Two filters with identical vessel diameters can carry very different ratings depending on the specified loading rate. A schedule listing vessel size without loading rate is incomplete, and pricing against it is guesswork.

Backwash is a system requirement, not merely a filter accessory. It requires adequate supply flow, drain capacity, and an approved destination for the waste stream. On some projects, the filters are correctly specified while the backwash provisions remain unclear or fall between trade scopes.

Media matters. Sand, gravel, glass, and specialty media perform differently and have different replacement intervals. Media is consumable and belongs in the operating cost conversation, not just the capital one.

Mechanical and biological are different jobs. Solids capture and ammonia conversion are separate functions. Some vessels do both. Assuming any filter handles both is a common and expensive error in animal systems.

How SIVAT helps

We review the specified filtration against system volume, target turnover, and expected loading. We check that backwash provisions exist and are accounted for. We price the vessels, media, and the valves and controls that make them work as a system.

If the filters as specified will not make turnover, we would rather tell you before the bid closes.

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Common questions

What types of filtration are used in aquatic life support systems?

Pressure sand filters, high-rate media filters, bead filters, drum and microscreen filters, and cartridge filtration each occupy a different position. The right choice depends on the solids being removed, the backwash water available and the space the equipment room allows.

How often does filter media need replacing?

It depends on the medium and the duty. Sand, gravel, glass and specialty media perform differently and carry different replacement intervals, and a filter selected without accounting for that carries an operating cost nobody planned for.

What does backwash cost in water?

Backwash is the largest single water loss in most recirculating systems. Filtration approach and backwash strategy determine how much water leaves the building each week, which on a large system is a meaningful annual figure.