I believe the gentleman is ...

I believe the gentleman is referring to water used for hydro testing in a large O&G, Petrochemical or Pipeline project. At best, there may be corrosion metals/ residue, which, in terms of concentration, will be small due to the large amount of water. If you're referring to effluent from Pickling-passivation activity, they usually use an acid-base solution in alternating cycles. Pls use a small PP tank and neutralize it, test it in a lab & if found within reasonable limits (as specified by Pollution Control Board) disposed it to a rainwater collection pond & soil will act as a filter. If not, treat it in an STP, preferably using a filtration mechanism (MF/UF) as the final step. Hope this helps.