Strategy for nitrogen removal from piggery waste

Abstract

This study was conducted with an influent containing about 20% solids, obtainable from scraper type separation resulting in about 40 g/L TCOD and 5.5 g/L TKN, to find an optimum operating condition for nitrogen removal. Both laboratory scale reactors and a full scale treatment plant removed 80 to 90% nitrogen by biological means up to 35 degrees C with 10% by ammonia stripping. The full scale plant however was operated at 35 to 45 degrees C, and at 45 degrees C, 30% nitrogen was removed by biological means, 50% by ammonia stripping, 14% by chemical coagulation and 6% by activated carbon adsorption, respectively. Struvite formation could not be observed at 30 degrees C or higher. Nitrite nitrification and denitrification could save about 35% in tank volume and 50% in carbon requirements at 25 degrees C, respectively. For a complete denitrification with a proper temperature, the influent TCOD/TKN ratio must exceed 6 with oxic/total reactor volume ratio of 0.5. The influent TCOD level or organic load should be lower so as not to increase the reactor temperature above 35 degrees C and avoid nitrification inhibition. The estimated optimum nitrogen loading rates were 0.15 for summer and 0.23 kg TKN/m3/d for winter, respectively. With a cooling facility, the nitrogen loads could be increased to 0.35 kg TKN/m3/d equivalent to an organic loading rate of 2.5 kg COD/m3/d.