Just some thoughts. first, why add FeCl - when once the pH is raised you can oxidize using ozone, or electrolysis, etc and utilize the iron in solution to create the iron oxide. seems your adding more metal and getting more sludge creation then you need to - which increases polymer addition as well as the filtration requirement and disposal cost unless you have secondary market for the heavy metals you captured (nickle, magnesium, copper, aluminum, etc). Second - your talking about a pickling batch wastewater - why hypro for dsinfection at the end? Where's the bacterial contamination? Third - what is the end use-discharge of the wastewater? - How will you address the chloride and sodium salts issue? Seems UF then either RO or forward osmosis would be applicable at such a low flow rate.