# Ask the Membrane Expert

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### What filtration system will remove soluble iron, manganese and salt from bore water

Soluble iron and manganese can be removed by using a Manganese Greensand Filter. However, in order to separate salt from water, either Reverse Osmosis or Evaporation have to be used. See also: What filtration system will remove soluble iron...

### Please suggest an appropriate antiscalant and dosage for use with feed water having a TDS of 1500 ppm

Antiscalant dosage cannot be determined by TDS (Total Dissolved Solids).  The reason is that TDS can be made up entirely of sodium and chloride which do not have a scaling potential, or it could be made up entirely of calcium and sulfate w...

### Can chlorine dioxide be used effectively in place of sodium hypochlorite for prechlorination of bore well water, RO feedwater and Permeate water?

Chlorine dioxide is a highly potent biocide that has a higher efficacy than hypochlorite in destroying protozoa, bacteria and viruses, without allowing them to build a tolerance.  It is effective over a wide pH range as both a biocide and ...

### If silica is not removed by ion exchange, does that mean it is colloidal silica?

It is not possible to have colloidal silica in your feedwater unless your silica concentration is above the solubility limit under those conditions, resulting in polymerization and hence colloidal silica formation. The difference between re...

### How do I pretreat H2S in Reverse Osmosis feed water?

H2S acts as a weak acid, much like carbonic acid: $${H_2S \Leftrightarrow HS^- + H^+}$$$${HS^- \Leftrightarrow S{^2}{^-} + H^+}$$ If your pH is above 5.5 and oxygen is allowed to contact with air, then sulfide ions will oxidize to element s...

### What will happen to antiscalants when we discharge them to the enviroment ? Are they toxic? Are they biodegradable? If so how long will they take to decay?

There are different types of antiscalants. Some are phosphonate based,and some are polymer based. Many are blends to provide synergistic effects of the two chemistries. Antiscalants have to be non-toxic, or they would not be approved by NSF...

### What is the relationship between pH and alkalinity? How are they different? How does temperature affect them?

What is the relationship between pH and alkalinity? In simple terms, pH is the concentration of acid protons [H+]. On the other hand, the alkalinity of a solution is its ability to neutralize acids. Alkalinity consists of ions that incorpor...

### What does differential pressure or delta P (ΔP) mean when logging RO data?

What is delta P (ΔP) and what does it mean when logging RO data? The differential pressure (dP) is the pressure lost due to friction as water passes through the system. You take a reading before the pressure vessels and after the pressure ...

### When does it make sense to clean elements, and when is replacement the only option in high purity applications?

In the case of high purity applications, the main criterion for clean vs. replace is salt passage. Any increase in salt passage to the demineralizers can be enough financial justification for replacement. As an example, even a slight decrea...