Sample before the water chemistry changes
Request total and dissolved iron and manganese, pH, dissolved oxygen and sampling conditions. State whether the sample was aerated or preserved according to the analytical method. A bottle that changes colour after reaching the laboratory does not necessarily represent the original chemical form in the well.
Review the abstraction system, tanks, pumps, piping and blending points. Air ingress or an open tank can change chemistry before the RO. Identify iron from corrosion and coagulants as well: a reddish deposit does not automatically establish that the aquifer is its source.
| Input | Distinguishes | Supports |
|---|---|---|
| Total and dissolved metals | Particles and soluble species | Separation or chemistry control |
| pH and oxygen | Oxidation conditions | Treatment location |
| Sulphide and blends | Potential interactions | Complete process review |
Choose a coherent pretreatment strategy
One approach is controlled oxidation followed by separation of the resulting solids before the membrane. Selection needs reaction conditions, filtration and backwash-residual management. Iron and manganese do not necessarily oxidise at the same rate or respond identically to pH, so treatment must address both constituents.
An alternative may retain an anoxic circuit under explicitly verified conditions. This is more than simply omitting a filter: oxygen entry, blending, shutdowns and chemistry all need review. Hydrogen sulphide introduces additional precipitation risks and must be assessed together with metals rather than as an unrelated afterthought.
Check what actually reaches the membrane
Sample after pretreatment and track cartridge pressure drop. Turbidity and SDI help assess particles, but cannot replace metals analysis or establish that a dissolved constituent will not precipitate later. Include sampling points and operating trends in the proposed plant scope.
For a load example rather than an allowable limit, 20 m³/h containing 1 mg/L of iron carries 20 g/h. If it precipitates, that load goes to filters, washwater or deposits. This balance explains why solids separation and residual handling matter even when a concentration appears numerically small.
Coordinate oxidation, dechlorination and acceptance
When the oxidant is incompatible with the membrane, its removal and verification must form part of the process. Removing residual oxidant does not itself remove particles created during oxidation. Check filter-media carryover and performance during start-up and backwashing as well as during stable operation.
Acceptance should verify RO inlet quality under representative conditions, cartridge consumption and stable membrane performance. Reassess when sources or chemicals change. A filter that performs satisfactorily with one well-water blend is not automatically validated for every possible feed proportion or seasonal operating condition.
Common questions
Can a cartridge remove all iron?
It retains only particles appropriate to its rating and installation. It does not guarantee dissolved-iron removal or prevent later precipitation.
Does dechlorination solve oxide carryover?
No. Neutralising the oxidant addresses chemical exposure, while the solids already formed still require appropriate separation upstream of RO.