Full-scale experiences of nitrogen removal of fish-processing wastewater with flotation and anoxic-aerobic activated sludge system

摘要

This article presents full scale experience of one of the largest fish-processing factoriesnin Europe with a production capacity of about 50,000 tons herring per year and a maximum dailynwastewater discharge of 1,500m3. The wastewater treatment plant is the only direct dischargernin the fish-processing industry in Germany. Thus, very low effluent values have to be keep in,nespecially the nitrogen reduction has to be operated during the whole year even when thentemperature is low. The central point of the multi-stage WWTP (about 90,000 PE) is the biologicalnnutrient removal (BNR) with pre-denitrification. The wastewater pre-treatment with sievesn(0.8mm) and a two staged flotation reduces the nitrogen load – mainly the particle boundednfraction – but the optimal nutrient ratios for biological treatment need to be observed.nThe activated sludge system has maximum OLR of 0.12 g COD/(g MLSS d) and NLRnof 0.015 g TN/(g MLSS d) but a “Stand-By”-Operation with periods without wastewater influentnis unavoidable. Discontinuous operating is one problem. The dependence on temperaturenas one of the main influences of nitrification-activity is the second point. The article givesnan overview about the start-up and the optimisation of the process.