TOC/TNb Determination in Municipal Sewage Plants Application Note · multi N/C 2100S

Introduction

In wastewater treatment plants, the organic and nitrogen load have to be measured in the untreated inflow, the pretreated effluent, and the final effluent after the completed treatment process. In many cases, the chemical oxygen demand (COD) and TN contents are measured with separate methods. This is a labor- and timeconsuming process 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 can be applied to save resources and time.

In order to guarantee accurate and efficient analysis, it is recommendable to use a catalytic high-temperature combustion TOC analyzer for simultaneous determination of NPOC and TNb from one single injection. According to these standards, TOC is defined as the sum of dissolved and particle-bound organic carbon compounds. Thus, the challenge is to assure a representative sample transfer, including all the particles, into the combustion system and at the same time to guarantee a complete oxidation of both, difficult-to-oxidize substances and particle-bound organics. This requires an effective sample homogenization on the autosampler rack and a sample introduction technique that ensures no particles get lost on the way to the combustion tube or cause any blockages, which may lead to system downtime or to extended wear and tear on sensitive Teflon parts inside the dosing system. A combustion system capable of providing sufficiently high furnace temperatures to assure a complete sample digestion is required as well. This application note describes a method using the multi N/C 2100S TOC/TNb analyzer. The samples were measured at a customer’s site (wastewater treatment plant) in Germany using a direct injection system for optimized particle handling.