Water filtration and treatment for plastic recycling lines

After you got the very best, well working system available in the market, you find out you just started because dirt didn't disappear but it is all into water you used to get your scrap clean.
And here you are, scratching your head because the expert of water treatment system wanted to know which kind of contamination he should remove and you don't have the answer.
And nobody does.
According with the country you're living in, cost of water can be very different together with the rules for discharging so a suggestion about how to solve the problem is something difficult at this stage.
Systems can vary according to cost of water first, energy and labour costs.
What you need to have in any case, is a set of mechanical filter, for solids removal along the washing line so the dirt cannot accumulate in any part of the system and, even if water is and remains dirty, contamination level is under control.
For example in the pre-washing circuit system, water shouldn't be clean at all but, at the same time, if you don't have a filtering system. dirt accumulates till the point the pre-washing doesn't have any effect any more.
A little more about some specific water filtering concerning the removal of glue on PET washing lines.
The caustic soda - surfactants glue removal circuit, running with hot water, needs a pretty sophisticated filtering system to remove glue and deliver a clean solution, keeping water as hot as possible to save energy.
Of course, the system does exist but the price of the equipment is high indeed; the story is always the same:
Higher investment equal to lower operating cost.
What's best ?