Nitrogen removal in industrial wastewater by nitration and denitration--3 years of experience

CPKelco ApS, Denmark is the largest pectin plant in the world and the second largest refined carrageenan plant. The products are used for texturising purposes, primarily within the food industry, but also within the pharmaceutical industry. The products are extracted from imported natural raw materials, like dried citrus peel and special seaweed plants. In the production processes a considerable amount of water and energy are used. The excess water from the production processes is led to CPKelco's own WWTP, which is one of the largest industrial WWTPs in Denmark. In order to obtain higher process stability and lower energy consumption in the WWTP, CPKelco decided to change the nitrogen removal process from a conventional nitrification/denitrification process to a nitration/denitration process, which comprises an oxidation of ammonium to nitrite and a controlled reduction of nitrite to N2. Theoretically this process will decrease the oxygen consumption for oxidation by 25% and the use of carbon source for the reduction will be decreased by 40% compared to the conventional process. This paper presents and discusses the experiences and results from three year's continuous operation of the nitration/denitration process in an activated sludge plant, and the overall performance results are discussed in relation to the previous results. Accordingly the implementation of the nitration/denitration process was done successfully, and today the plant operates with much higher process stability than obtained before, and even the most stringent effluent requirements for nitrogen can be obtained.