Strategy for nitrogen removal from piggery waste

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 35degreesC with 10% by ammonia stripping. The full scale plant however was operated at 35 to 45degreesC, and at 45degreesC, 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 30degreesC or higher. Nitrite nitrification and denitrification could save about 35% in tank volume and 50% in carbon requirements at 25degreesC, 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 35degreesC and avoid nitrification inhibition. The estimated optimum nitrogen loading rates were 0.15 for summer and 0.23 kgTKN/m(3)/d for winter, respectively. With a cooling facility, the nitrogen loads could be increased to 0.35 kgTKN/m(3)/d equivalent to an organic loading rate of 2.5 kgCOD/m(3)/d.