waste water treatment

sewage from domestic / agricultural sources has to be treated to remove harmful microbes before it is put back in rivers or lakes - could be very polluted, health risks

where does waste water come from?

• domestic sewage

• agricultural systems

• industrial processes

  • Haber process

what is the process of sewage treatment?

1. before treatment, screened

   • remove twigs, grit, plastic bags

2. stands in settlement tank

   • sedimentation

   • heavier solids sink - produce sludge

   • liquid waste floats to the top

3. sludge removed to large tanks

   • broken down by bacteria

   • anaerobic digestion

     • releases methane (used as energy source)

     • remaining waste = fertiliser

what extra steps are there for waste water containing toxic substances?

• adding chemicals

• UV radiation

• reverse osmosis

how does sewage treatment compare to desalination of sea water?

• more processes

• less energy