How do petrochemical industries recycle their waste water?

Oil field trash is correct - it depends on a lot of things. Here's my take - one big consideration for whether the wastewater can be recycled back into the plant is whether or not the wastewater is considered "hazardous waste" - at least in the US. You might aware that that hazardous waste is a subset of solid waste - and that "solid waste" can include aqueous wastes - the term "solid" has nothing at all to do with the phase of a substance - "solid wastes" can be solids, liquids, or even gases. Now, non-hazardous wastewater, or efluent from hazardous wastewater treamtent that is not hazardous anymore, may be used for potentially any number of things - e.g., cooling water for various industrial processes, feed water, and I even heard of one company proposing to re-use their wastewater for fire control systems - in that last case, we were quite concerned as to whether or not the wastewater was hazardous or not. If they used hazardous wastewater for fire control - they could get in ...  more