First step in water treatment: The drum filter

​Almost ever­yo­ne has done this at least once in their own four walls: For examp­le, you use a sie­ve and water and sim­ply rin­se the dirt away, lea­ving only the clean salad at the end. This is a type of mecha­ni­cal clea­ning that almost ever­yo­ne uses regu­lar­ly. In order to achie­ve a simi­lar effect in a recir­cu­la­ting aquacul­tu­re sys­tem (RAS), a com­pa­ra­ble fil­ter opti­on is used in a figu­ra­ti­ve sen­se: the drum fil­ter, a cylind­ri­cal drum cove­r­ed with a fine-mesh fil­ter net. More than half of the drum is under water, so that the pro­cess water from the pro­duc­tion basin with all its par­ti­cles can flow unhin­de­red into the drum at the open front side. The drum’s fil­ter net allows the water to pass through, but at the same time retains the coar­se par­ti­cles – in com­pa­ri­son to our examp­le with the let­tuce sie­ve, the exact oppo­si­te way.

Which solids are remo­ved by the drum filter?

The­se par­ti­cles to be sepa­ra­ted are bac­te­ri­al flakes, unused food and feces (= excre­ti­ons) from the fish. The­se par­ti­cles are unde­s­i­ra­ble in the water and must the­re­fo­re be remo­ved. The easiest and che­a­pest way to do this is to use the drum fil­ter. The stain­less steel net, the so-cal­led fil­ter gau­ze, collects all solids in the SEAWATER Cube that are smal­ler than 40 µm. The pre-cla­ri­fied water, which hard­ly con­tains any solids after pas­sing through the gau­ze, collects below the drum fil­ter in the so-cal­led pump sump. From the­re the water is trans­por­ted to the other fil­ters via the main pump. This ensu­res the smooth func­tio­n­ing of the down­stream filters.

How does the fil­ter tech­no­lo­gy work?

By mea­su­ring the fill levels in the pro­duc­tion tank and in the pump sump, the drum fil­ter detects whe­ther it needs to be clea­ned. If the height dif­fe­rence bet­ween the basin and the sump is too gre­at, this means that too litt­le water is cur­r­ent­ly get­ting through the drum into the sump. This hap­pens when the fil­ter gau­ze is alrea­dy cove­r­ed with too many par­ti­cles. In this case the drum is rota­ted. On the one hand, the fil­ter gau­ze on the top of the drum is rin­sed free with a high-pres­su­re pump and water nozz­les. On the other hand, fresh, alrea­dy rin­sed gau­ze reaches the bot­tom of the water, which is per­me­ab­le again and can collect new par­ti­cles. This pro­cess is repeated at regu­lar inter­vals. The dir­ty rinsing water collec­ted in a chan­nel is direc­ted into the sedi­men­ta­ti­on. Only after this fur­ther cla­ri­fi­ca­ti­on pro­cess does the water get into the was­te­wa­ter. It the­re­fo­re counts as part of the water that is exch­an­ged in the cube every day (1% per day).

As a type of micro­fil­tra­ti­on, the drum fil­ter is par­ti­cu­lar­ly low-ener­gy and reli­able due to its pump­less (or almost pres­sureless) mode of ope­ra­ti­on. Due to the regu­lar self-clea­ning, the back­wa­shing, the work and main­ten­an­ce effort is also rela­tively low. If a chan­ge in mesh size is requi­red or if the gau­ze is cra­cked, chan­ges can be made to the fil­ter quick­ly and easi­ly. In aquacul­tu­re, the drum fil­ter is a com­mon mecha­ni­cal fil­ter due to its many advan­ta­ges in hand­ling and is the­re­fo­re also used in the SEAWATER Cube.

We get our drum fil­ter from the Senect com­pa­ny in Landau.