Testing compact filtering technology for storm water treatment

In collaboration with Krüger A/S and Nordvand A/S, we tested and analysed two filtering technologies for the decentralised handling of storm water.

The majority of storm water in the Copenhagen catchment area in Denmark is discharged into combined sewer systems. This can cause frequent hydraulic overload, which may reduce the efficiency of municipal wastewater treatment plants. Increased precipitation intensity in recent years has magnified the problem.

Adapting the Danish wastewater infrastructure to account for this change is essential. As part of a development project with Krüger A/S and Nordvand A/S, we tested two filtering technologies: Flexible Fibre Filter Module (3FM) and Hydrotech Disc Filter.

The 3FM system:

• achieved a treatment efficiency of 50-70% for Total Suspended Solids (TSS), which corresponded to an outlet concentration of 5-10mg TSS per litre
• achieved a treatment efficiency of below 20% for Total Phosphorus (TP) and Chemical Oxygen Demand (COD)
• reduced copper (total) and zinc (total) by more than 60%

By adding a coagulant (chemicals that promote particle clotting and settling) in the 3FM system, we reached a water quality level that fulfilled the environmental quality standard for freshwater bodies for TSS, phosphorous and bisphenol A. For polycyclic aromatic hydrocarbons (PAH), a removal of 34%- 96% was obtained for individual compounds.

The Hydrotech Disc Filter system:

• achieved a treatment efficiency of 50-60% for TSS, which corresponded to an outlet concentration of 10-15mg TSS per litre
• achieved a treatment efficiency of between 28% and 64% for TP and below 15% for COD
• reduced copper (total) and zinc (total) by up to 45%
• reduced the four PAHs by less than 35%

By adding a coagulant and flocculant (chemicals that help particles clump together), we achieved a water quality level that fulfilled the quality standard for freshwater bodies for TSS and phosphorous. With respect to PAH, the Hydrotech Disc Filter system achieved a removal rate of almost 75% for individual compounds and reduced benzo(b,j,k)fluoranthene to a level below the detection limit.