Practical guidance to determine NMVOC emissions from refinery wastewater collection and treatment facilities

Report no. 5/25: Wastewater from refinery operation contains various pollutants that shall be purified prior to wastewater emitted to sea. A major pollutant is hydrocarbon remains. Wastewater collection and treatment facilities in European refineries are generally not fully closed systems and therefore recognized as a non-negligible contributor to the overall site non-methane volatile organic compounds (NMVOC) emissions.

Measurement of emissions from wastewater is often difficult due to their specific location and system configuration. Wastewater collection systems are located across the entire site, and it is not always feasible to measure the emissions. The emissions in wastewater treatment facilities occur at various places, mostly from uncovered areas. They are therefore often diffuse in nature and cannot be measured as point sources, which makes quantification complicated.

The two most common practices used today to estimate emissions from wastewater are emission factors and emission models. Published, general emission factors are not site specific and could result in over- or underestimation of the emissions. They also give no information where emissions occur. Emission models inform where emissions occur but require detailed information on system configuration and operation. Examples of tools to model NMVOC emissions are TOXCHEM and, more specifically for this application, the EPA Refinery Wastewater Emission Tool (RWET). Furthermore, atmospheric dispersion modelling can be used to simulate result of VOC emissions. It is performed with computer programs that include algorithms to solve the mathematical equations that govern the pollutant dispersion. Software using a Gaussian dispersion model (not probabilistic), which most operators are familiar with as it is also used for other purposes can be used for this. Suitable programs are e.g., PHAST, AERMOD, or ADMS. More advanced computational dynamics software can also be used to estimate VOC emissions in complex situations, but this requires more specialistic knowledge and/or contractor to execute. This is outside of the scope of this practical guidance document. To confirm the representativeness of a model a validation with measurements is advised.

This practical guidance document explains how to use ‘simple’ measurements to estimate the NMVOC emissions of wastewater facilities. The measurements should be repeated several times to better understand the NMVOC emission sources and their variability and reduce the uncertainty in estimating annual emissions. Two independent measurement methods are proposed, which should result in comparable emission rates.

In case a higher measurement accuracy is required, the measurements can also be used as a basis to perform specialized measurements by a contractor. The EN 17628 can be used as a framework to execute such measurements for a few complementary methods.