Device and a method for filtering stormwater

Abstract

A device for filtering stormwater inside a storm drain includes a filter unit and a floating carrier for carrying the filter unit. The filter unit includes a bottom portion and a top portion. The carrier includes an axially extending recess for receiving the bottom portion of the filter unit, so that at least a part of the bottom portion of the filter unit is arranged below a surface of the stormwater inside the storm drain when the device is arranged therein. Through apertures extend radially from an outer surface of the carrier to the recess, so that stormwater at the surface can pass through the apertures and reach the bottom portion of the filter unit. Also a method for filtering stormwater inside a storm drain is disclosed.

1 . A device for filtering stormwater inside a storm drain, wherein the device comprises a filter unit and a floating carrier for carrying the filter unit,
 wherein the filter unit comprises a bottom portion and a top portion, and wherein the carrier comprises
 a recess for receiving the bottom portion of the filter unit, which recess extends axially through the carrier so that the filter unit can be arranged on top of the carrier while the bottom portion of the filter unit is arranged in the recess, whereby at least a part of the bottom portion of the filter unit is adapted to be arranged below a surface of the stormwater inside the storm drain when the device is arranged in a floating condition inside the storm drain; and 
 through apertures extending radially from an outer surface of the carrier to the recess, so that stormwater at the surface can pass through the apertures and reach the bottom portion of the filter unit when the device is arranged in a floating condition inside the storm drain. 
   
     
     
         2 . A device according to  claim 1 , wherein the top portion of the filter unit comprises an inclined surface for guiding non-filterable objects to the surface of the stormwater inside the storm drain. 
     
     
         3 . A device according to  claim 2 , wherein the top portion of the filter unit is tapered. 
     
     
         4 . A device according to  claim 1 , wherein the filter unit comprises an absorbing material, a heavy metal filtering peat and activated carbon. 
     
     
         5 . A device according to  claim 4 , wherein the filter unit comprises a first filter layer including a first absorbing material, a second filter layer including heavy metal filtering peat, a third filter layer including activated carbon and a fourth filter layer including a second absorbing material. 
     
     
         6 . A device according to  claim 5 , wherein the filter layers are arranged in sequence and wherein the fourth filter layer at least partially is arranged in the bottom portion of the filter unit. 
     
     
         7 . A device according to  claim 5 , wherein the first absorbing material of the first filter layer comprises a granular synthetic fibre, the heavy metal filtering peat of the second filter layer is formed as granules, the activated carbon of the third filter layer is formed as granules, and the absorbing material of the fourth filter layer is a synthetic fibre felt or fleece. 
     
     
         8 . A device according to  claim 1 , wherein the floating carrier is made of expanded plastic, such as expanded polystyrene. 
     
     
         9 . A device according to  claim 1 , wherein the filter unit comprises a perforated plastic cover. 
     
     
         10 . A device according to  claim 1 , wherein the device is narrower than the storm drain in which it is to be arranged, thereby allowing formation of a gap between the device and an interior wall of the storm drain. 
     
     
         11 . A device according to  claim 1 , wherein the device comprises an RFID transponder having an ID-number and a pressure sensor for monitoring the weight of the device. 
     
     
         12 . A method of filtering stormwater in a storm drain, including the steps of
 a) providing a filter unit having a bottom portion and a top portion,   b) providing a floating carrier having a recess extending axially through the carrier so that the filter unit can be arranged on top of the carrier while the bottom portion of the filter unit is arranged in the recess; and through apertures extending radially from an outer surface of the carrier to the recess,   c) arranging the bottom portion of the filter unit in the recess of the carrier,   d) arranging the carrier and the filter unit in the storm drain, so that at least a part of the bottom portion of the filter unit is arranged below a surface of the storm water inside the storm drain and at least a part of the top portion is arranged above said surface,   e) providing stormwater to the bottom portion of the filter unit through the apertures of the carrier, and   f) by means of the top portion of the filter unit, receiving at least a major part of any storm water entering the storm drain.   
     
     
         13 . A method according to  claim 12 , including the step of arranging the carrier and the filter unit in the storm drain, so that a gap is formed between them and an interior wall of the storm drain. 
     
     
         14 . A method according to  claim 13 , including the step of guiding non-filterable material to the gap by means of an inclined surface of the top portion of the filter unit. 
     
     
         15 . A method according to  claim 12 , including the steps of detecting the weight of the device by means of an RFID transponder having a pressure sensor, and sending a signal to a central monitoring unit when a predetermined weight has been exceeded or a predetermined weight change during a specific time period has been exceeded.