Nitrification Treatment of Swine Wastewater Under Cold Temperatures

In addition to N load, cold weather nitrification is an important consideration for stabilized performance of biological processes applied to continuous animal production systems. A winter simulation experiment was conducted in the laboratory to evaluate performance of immobilized bacteria for treatment of swine wastewater under cold weather conditions. Bench fluidized reactors (1.2 L) containing 120 mL polyethylene glycol nitrifying pellets (10% v/v) were operated under continuous flow using swine wastewater containing 330 to 450 mg NH4-N/L, and 140 to 290 mg BOD5/L. Water temperature in the reactors was controlled using a refrigerated circulating bath with car antifreeze liquid. Starting at 15C and a hydraulic residence time (HRT) of 18 hrs, wastewater process temperatures were decreased 2.5-3C every three weeks to a low of 3C. Ammonia was completely removed in all of these runs, which precluded calculation of nitrification potential. For this reason, the continuous flow experiment was repeated using higher N loads obtained with HRT of 12 hrs, each temperature run lasting 2 weeks. In addition to continuous flow, batch tests were also done at various process temperatures to determine nitrification rate at cold temperatures with a different method, each batch temperature test lasted 8 hrs and was replicated three times. As expected, the effect of process temperature on nitrification rate was well described by an exponential function. But nitrification activity was not severely affected by the lower temperatures in the experiment (3-5C) as previously thought, indicating acclimation of the entrapped nitrifying bacteria to the winter conditions. The temperature coefficient (Q10) obtained was consistent between continuous flow and batch conditions and averaged 1.41. This means that nitrification rate decreased only by 29% for each 10C decrease in water temperature. This decrease is significantly different than the Q10 of 3 (70% rate decrease per 10C) commonly used to predict activity of nitrifying bacteria under cold weather conditions. Thus, the immobilized technology appears well suited for nitrification of high-ammonia livestock wastewater under cold weather conditions.