Need for online COD analyzer

[ema]

Can anyone suggest producers for online COD analyzers? Are they really analyzing "COD" or they just correlate it with dissolved organic compounds (using SAC)? What are the possible alternatives for monitoring effluent COD concentrations "delay-free"?
Regards,
ema

 

[BertGielen]

What is your need ?

The COD analysis procedure requires chemical destruction of the organic material, and this takes some time. The standard method requires 2 h; using more aggresive chemicals, some suppliers can do faster, e.g. 15 - 30 min, depending on the type and composition of the organic material present in the water stream.

1) You need a fast response:

For emergency control (e.g. detection of COD-peaks in order to activate an emergency buffer tank), it is more common to use an online TOC-analyzer. Typical TOC/COD ratios are 1/4. The actual TOC/COD ratio is measured by the traditional manual methods.
TOC uses a high temperature destruction method and is much faster (e.g. 1 - 2 min).

2) Water quality monitoring or control of slow steps of the process

If it is necessary to have more or less exact figures, but some delay (e.g. 15 min - 1 h) is acceptable, then several suppliers can propose you a solution.
Typical applications are water quality monitoring (signal is not used in a process control loop) or slow processes (e.g. control of the addition of nutrients like ammonia or phosphorus in some industrial WWT plants).

Some suppliers : using "on-line COD analyser" in google leads to at least 5 brands.

 

[ema]

Thank you for your reply.

How accurate are those TOC analyzers? Is it possible to monitor low concentrations of effluent within a range of 20-40 mg/L COD? I would like to use this analyzer to detect COD peaks so that we could divert the peak discharge to the city main instead of receiving river (where the effluent standards are stricter).

Instead of diverting the discharge to city main, how can we install an emergency buffer tank? The authorities are only monitoring COD concentrations not the load, so what can we do to to buffer highly concentrated discharges with the use of such an analyzer?

 

[BertGielen]

Dear ema

1° COD in range 20 - 40 mg/l typically stands for a TOC of 5 - 10 mg/l. This is -/+ the lower limit for reliable TOC-concentration measurement. Wheater or not a TOC-analyser is able to do the job in your application, depends mainly on the rest of the waste water. Check with a supplier of TOC-analysers.

However, I understand that your application is mainly fast detection of peak loads (e.g. in order to close the normal discharge and to activate an emergency buffer tank or activate the emergency discharge to the city sewer system). Normally this is not a problem.
(Also : it is a good idea to check if the peak loads can be detected also by a shift in pH or conductivity; this leads to a solution which is much cheaper).

2° Design of emergency buffer tank.
Everything depends on the origin of the peak loads. So first step is anyhow to gather some facts and figures about origin, frequency, and composition of the peak loads.
- If the origin is well known, then generaly a solution that avoids or buffers the peak loads at the place where they are formed is much cheaper.
- If the origin is not known, then design is based on frequency and composition of the peak loads. Design of the buffer tank is based on the volume that must be contained, not on the actual COD-load. In the US, design guidelines for storm water systems could be an inspiration.