COD analysis - fast and clean

The paper industry requires large amounts of water due to the production conditions. The German Waste Water Ordinance implied, that the resulting effluent has to be tested on the content of chemical oxygen demand (COD). In comparison with conventional testing methods the use of online COD analysers offers high savings and also enables an efficient water management.

In the manufacturing process of pulp / paper a lot of water is required. The major part of it passes in a re-using cycle. To avoid a concentration and a loss of quality of the ingredients, a small amount of waste water is discharged and fresh water is fed in. The entire process can be characterized by a water temperature of about 35 °C and a COD content of 30,000-40,000 mg/l.

Within the manufacturing process, the parameter COD has no significance. Only when water leaves the process, it becomes waste water and then, it is supplied to a municipal or the plant’s own waste water treatment plant.

In the effluent of a paper mill, the monitoring of COD is very important. It is the only way to identify production losses easily and buffer problematic loads. The waste water treatment plant operators can better estimate the required cleaning performance and control it efficiently. The COD can also be determined by correlation with TOC (total organic carbon). Additionally, the parameter TN_b (total nitrogen bound) is recommended for monitoring because an optimal cleaning performance needs a certain ratio of nitrogen and phosphorus. Further, the waste water toxicity should be tested. Chemicals such as biocides or chlorine, which are added to avoid mold, can significantly affect the biology of a waste water treatment plant. Conventional COD test methods are time-consuming and cost-intensive. Hence, they are unsuitable for an efficient water management. Online measuring systems provide a remedy.

The chemical oxygen demand (COD) of water is determined by the definition of potassium dichromate method (dichromate method DIN 38409-41: 1980-12). A few years ago it was only classified as irritant but today it is considered to be mutagenic, toxic for reproduction and dangerous for the environment as well as carcinogenic. The European Parliament and the Council called 'REACH' (Registration, Evaluation, Authorisation and Restriction of Chemicals) have adopt a ban in April 2013, which prohibits the use of this chemical. Because of the dangerous dichromate method, the varying recovery rates, the known chloride interferences as well as the high demand of time of 2h alternative approaches are urgently required. A first step to use a constant sample matrix, is to adjust a correlation factor, according to the mixture of substances in water. Thus, the fast and reliable Online-TOC-Measurement technology can also be used for COD determination. An additional alternative is the direct measurement of the oxygen demand. With LAR's QuickCOD_ultra, the online analyser to determine the total oxygen demand, both alternatives are possible and thus, without the use of dangerous chemicals.

Depending on the requirements, LAR offers the best solution as its methods operate analytically correct, fast and clean. Due to the ultra-high temperature of 1,200 °C, the complete oxidation of the sample is guaranteed and the XY injection system prevents clogging and carry-over effects. Using LAR analysers operators optimize their water management significantly. Firstly, it is possible to control the discharge of waste water into the waste water treatment plants or buffer tanks. Secondly, the labs will be considerably relieved, since the enormous working efforts and expenses for the COD analysis are no longer needed.