Drum Filters

Drum filters for aquaculture farms are mechanical, self-cleaning microscreen filters designed for high performance in water-treatment systems. They carefully handle solids removal to minimize particle break-up, thus achieving high filtration efficiency.
We have three models to choose from, each in a range of sizes:

Freestanding stainless steel tank

Stainless steel frame

How drum filters and disc filters work

As the name indicates, the drum filter is built around a drum- shaped skeleton enclosed with external filter panels. The untreated water flows into the drum, and gravity drives the water through the filter panels and out of the drum.

As particles accumulate on the filter cloth and the resistance increases, the water level inside the filter will rise with time. Common to both types of filters is that a backwash cycle is automatically initiated when the water level reaches a certain level.

The filter panels are then sprayed from the outside to clean the filter cloth. Reject water containing particles is collected in a long trough located inside the filter, along which it exits, e.g. to a collection tank for further sludge treatment.

Larger filter area in a smaller space

Backwash water and energy consumption

The tests were performed in parallel with water from the same fish tank. The reject water was collected, and the sludge volume was measured after sedimentation. Following a proper mixing of the sediment, a sample was taken to measure the concentration of suspended solids (SS). The trial was repeated 10 times. The result showed that the SS concentration in this experiment was almost twice as high in the reject water from the disc filter compared to the drum filter.

So, what are the benefits of being able to minimise the amount of reject water beyond reducing the water consumption?

Firstly, the operating cost is reduced corresponding to the reduction of the backwash water. The energy consumption – which is mainly spent on pumping backwash water and rotating the drum – is therefore 45% lower in a disc filter than in a drum filter. Secondly, there will be less volume of sludge that must be stored and dewatered. This in turn can reduce the need to invest in sludge storage and dewatering equipment.

Rapid removal of large solids

In RAS, rapid particle removal is essential to maintain good water quality. The aim should be to remove the faeces that the fish produce as quickly as possible. This reduces the risk of large particles dissolving into finer particulate matter that is more difficult to remove from the system.

A disc filter is significantly more efficient at removing large particles, such as waste feed and feces, than a drum filter. A particularly good result has been achieved by fitting the filter cassettes with “collars” that help lifting out the solids. A test was performed to compare how quickly different filter panels and cassettes lifted out 100 ml of feed pellets with a diameter of 5 mm.

The reject water from the drum filter also contains more dissolved suspended fine particulate matter than the disc filter.

In general, a larger filter area will provide a better filtration effect in all types of microscreens. Our recommendation is to avoid loading the filters so heavily that they are run more or less in continuous backwash, as this reduces the filtration effect and probably also increases water consumption. The filter is more effective at catching particles if the particulate matter has time to adhere properly to the filter cloth before the drum starts to rotate and backwash. For best results, we believe it is wise to size the filter with extra filter area. This also helps to avoid getting into trouble if a lot of fouling should eventually occur in the filter cloth.