TOC/TNb Determination in Refinery Effluents Application Note · multi N/C 2100S

Introduction

The petrochemical industry generates large volumes of wastewater or effluents that need to be treated before they can be reused or released into natural waterways. Total organic carbon (TOC) and the total nitrogen bound (TNb) content is routinely determined, as these contaminants lead to eutrophication of surface water recourses, endangering aquatic life and groundwater supplies.

According to the European Industrial Emissions Directive (IED), Best Available Techniques (BAT) have to be implemented within the EU for direct wastewater discharges from the refining of mineral oil and gas.1 The BAT reference document (BREF) indicates that, among other parameters, TOC and TNb are of growing importance. They need to be monitored on a daily basis. Furthermore, a preference for the parameter TOC instead of COD is given, as TOC does not require the use of highly toxic compounds, such as dichromate (Cr VI) and mercury.

In many cases, the COD and TN contents are still measured using separate methods. This is a labor- and time-consuming process and is often associated with the formation of chromium-VI-contaminated waste. Through correlation studies, an empirical conversion factor for TOC to COD conversion can be established. Hence, a fully automated analytical process for TOC/TNb determination according to EN 1484 and EN 12260 (also the planned new ISO 20236 for both parameters) can be applied to save resources and time.

Effluent waters from refining processes usually represent demanding samples for TOC/TNb analyzers, since tubing and valve technique feeding the sample into the combustion process are prone to carry-over. Direct injection as applied in the multi N/C 2100S using a septum-free injection port and a wide-bore needle for optimum particle handling can overcome this problem. Direct injection ensures a sample transfer without particle losses and prevents blockages, hence increasing system uptime and reducing wear and tear on sensitive Teflon parts inside the dosing system. In addition, the injection needle is fully thermally cleaned before injecting the next sample, since it stays in the hot furnace inlet zone during analysis time, thus reliably avoiding carry-over. multi N/C 2100S thus offers a robust solution for simultaneous TOC/TNb analysis of particulate or oily samples.