DPRIt is complicated but well ...

DPR

It is complicated but well established. There are 2 relatively standard treatment trains that are most interesting. One involves RO and advanced oxidation, the other involves ozone biologically activated carbon. The former is very expensive and essentially produces distilled water, the latter is less expensive but will have higher TDS.  The oldest operating system is in Windhoek that has been successful since the 1960s. It is a very complicated aggregation of treatments that was added to over time. They should reexamine it and can substantially simplify it. The WHO is about to release its Guideline for potable reuse, which is very practical. It will be available for free download very soon.  The difference between Direct Potable Reuse and planned Indirect Potable Reuse is that the treated water is put through either a surface reservoir or a groundwater to distinguish it from recycled water, mostly in the public sense. Putting highly treated water in the environment sounds like a good idea, but actually it can recontaminate it and require another stage of drinking water treatment. Some regulators do not seem to understand that. See:

Cotruvo, JA,   Direct Potable Reuse: Then and Now. World Water: Water Reuse and Desalination . Volume 5, Issue 1, pp 10-13. Spring, 2014.

http://edition.pagesuite-professional.co.uk/Launch.aspx?EID=192226ee-85e9-4277-9129-9ff8272ac622