Chlorine monitoring (again!)

[Garry]

Reference to 10min EBCT hiding in plain sight! ISO 26722:2014 and I assume in the latest BS ISO 23500

[Ian Wilde]

Have you purchased a copy of either standard Garry?

The goal is to have a library of the standards owned by ART for members to be able to access.  (not sure if there's a workaround under copyright/distribution infringement though)

Thanks for highlighting - I was only looking in the RA Guidelines on water treatment facilities etc.. and couldn't see it.  We don't have a copy of the ISO standards mentioned in the guideline though.

[Ian Wilde]

Highlights from this document:

Adsorption is a natural process by which molecules of a dissolved compound collect on and adhere to the surface of an adsorbent solid.  
Granular activated carbon is a particularly good adsorbent medium due to its high surface area to volume ratio.
One gram of a typical commercial activated carbon will have a surface area equivalent to 1,000 square meters.

As a contaminated water stream passes through a confined bed of activated carbon, a dynamic condition develops which establishes a mass transfer zone. This “mass transfer zone” is defined as the carbon bed depth required to reduce the contaminant concentration from the initial to the final level, at a given flow rate.

As the mass transfer zone moves through a carbon bed and reaches its exit boundary, contamination begins to show in the effluent. This condition is classified as “breakthrough” and the amount of material adsorbed is considered the breakthrough capacity. If the bed continues to be exposed to the water stream, the mass transfer zone will pass completely through the bed and the effluent contaminant level will equal the influent. At that point, saturation capacity is reached.

To take full advantage of the adsorption capacity difference between breakthrough and saturation, several carbon beds are often operated in series.

When sizing an activated carbon system, it is necessary to choose an appropriate contact time for the wastewater and the carbon. EBCT (empty bed contact time) is the terminology used to describe this parameter. EBCT is defined as the total volume of the activated carbon bed divided by the liquid flow rate and is usually expressed in minutes.
The appropriate EBCT for a particular application is related to the rate of adsorption for the organic compound to be removed. While this rate will vary for individual applications, experience has shown that for most low concentration dissolved organics an EBCT contact time of 10 to 15 minutes is normally adequate.

I'm sure there's an ART National Conference presentation in there somewhere...

[Ian Wilde]

Also a very enlightening document here.

Highlights:

De-chlorination
A second very important property of GAC is its ability to catalytically reduce chlorine from an oxidizer (NaOCl) to a salt (NaCl) by taking away the reactive oxygen. This is a very fast reaction requiring an EBCT of only 30-40 seconds.

A 10 inch cartridge with a flow of 0.5 gpm is about 25 seconds EBCTand can remove 95% of incoming chlorine for 2500 gallons.

A cubic foot of the same GAC flowing at 5 gpm (EBCT = 1.5 minutes) can do the same job for 1,000,000 gallons.

A cubic foot of GAC can make about 40 cartridges (with an implied capacity of 40x2500 = 100,000 gallons). The difference is in the longer EBCT allows the GAC to work better for a longer time because the longer EBCT allows more of the GAC to take part in the process.

More communities are switching from chlorine to chloramine (usually NH2Cl, the mono-chloramine) as a means of reducing the tendency for chlorine to form THMs when used as the primary disinfectant. The deactivation of chloramine can be accomplished with GAC but the filter has to be sized about four times the size of a regular GAC filter used for chlorine. To increase the EBCT, filter units can be strung in series. Catalytic carbon, which has an oxidizing capability is more effective for chloramine reduction with EBCTs of about 5 minutes.


I would think the above explains why you can still bring your chlorine level down below the limit using a cartridge filter in the home dialysis environment.

[Ian Wilde]

Also this document stating just 2 minutes!?

But if the ISO says 10 minutes then 10 minutes it should be...  perhaps it is covering all bases by including chloramines?

Also interesting that "Chlorine is not adsorbed – it is a catalytic reduction reaction"

[Garry]

Hi Ian, yes we have ISO 13959:2014 but not the latest all encompassing ISO 23500:2019