BIOLOGISK FÖRBEHANDLING MED LÅNGSAMFILTRERING / Biological pretreatment with slow sand filtration
The focus on environmental aspects in the society has increased the strive to find sustainable sysrems for drinking water production. This has lead to a greater inrerest in biological filtration, for example slow sand filtration (SSF). Biological pretreatment of raw water might reduce the need for chemicals in the following treatmem steps, with reduced sludge production as a positive consequence. To investigate this a combined pilot-laboratory test on a reversed process was performed at Norsborgs Waterworks (NWW), where the SSF was placed before the chemical treatment instead of after. The results showed that NWW, with excisting plant and SSF area, would achieve almost the same water quality based on organic matter (TOC och CODMN) at the same coagulant dose, with and without biological pretrearment of the raw water. The cleaning fi-equency would probably increase (from 2 times/year to approximately 4-8 times/year), which is negative for the operation and economy.