Measuring VOCs in Process Water both On-Line and Off-Line
Posted on January 20th, 2015
Manufacturing sites often generate significant amounts of waste water that has to be treated before it can be discharged into the environment.
Volatile solvents are commonly used in manufacturing and are one of the important classes of compounds that have to be measured and controlled.
In terms of separation and measurement, these applications aren’t too challenging, however some thought has to be given to the practicalities of sampling to ensure that the measurements can be made in a dependable and efficient fashion.
Recently we were asked by a customer to come-up with a way of measuring volatile organics in waste water that would enable them to make continuous measurements of water entering and leaving their treatment facility. If elevated levels of VOCs were detected, the customer also needed to be able to take and run samples as they worked their way up-stream, until the source of the problem was located.
Most of the time, the instrument needs to run unattended and only when a problem is flagged, will an operator be available to troubleshoot the issue.
The solution that we came up with was to fit a Dual Head GERSTEL MPS with a flow-cell through which a part of the waste stream would flow continuously; then, three or four times every hour, the MPS transfers a 1ml portion of the waste stream into a sealed 10ml headspace vial. The sample is then heated and agitated so that the VOCs equilibrate between the water and the headspace; after this, a 1ml aliquot of the headspace is taken with a heated syringe, and injected into the GC for analysis. This system can also be used with smaller 2ml Vials, taking 0.75ml sample and 300ul of headspace.
By providing a tray with 240 vial capacity, this meant that the instrument could run continuously for several days without the operator intervening.
This took care of the routine measurements; should an elevated VOC concentration be discovered, then a change of method on the MPS permits samples collected from around the site (in headspace vials) to be run and the source of the problem located.
This is a great illustration of what the GERSTEL MPS is capable off. If you have a similar requirement and would like to discuss how we may be able to help, please call us on +44 (0)1223 279210 or email firstname.lastname@example.org.