Plastics recycling

Washing also separates plastics by density: PET and PS sink in ordinary water, while HDPE and PP float. The plastics are therefore washed and sorted simultaneously. Water additives can adjust which plastics float or sink.

The water is generally recirculated for a period and cleaned through physicochemical treatment. Without treatment, contamination would accumulate and water service life would be very short.

Treatment generally uses a coagulant and a flocculant. A cationic flocculant may suffice, but a two stage approach usually gives the best results. Requirements also depend on the waste plastic: PET bottles introduce different contaminants from film or toothpaste tubes.

Some contaminants affect recycling water pH, requiring correction. Water is often too acidic and needs sodium hydroxide to reach a neutral range in which the flocculant works effectively.

pH correction → coagulation → flocculation

Depending on plant size and wash water volume, the entire stream or only a portion can be treated.

Treatment uses a continuous flow system with inline chemical dosing, because a continuous water supply is required and a volume cannot be temporarily removed for batch treatment. Continuous make up water is needed to compensate for evaporation and water lost with sludge.

Contaminants can be separated using a DAF unit, lamella separator or Dortmund settling tank.

Contact us to discuss the possibilities for your project.