Ammonia stripping for enhanced biomethanization of piggery wastewater

In this study, the effects of ammonia removal by air stripping as a pretreatment on the anaerobic digestion of piggery wastewater were investigated. Ammonia stripping results indicated that ammonia removal was strongly dependent on pH and aeration rate, and the ammonia removal rate followed the pseudo-first-order kinetics. A significant enhancement of biomethanization was observed for wastewaters of which ammonia was air-stripped at pH 9.5 and pH 10.0. The methane productivity increased from 0.23 +/- 0.08 L CH4/Ld of the control (raw piggery wastewater) to 0.75 +/- 0.11 L CH4/Ld (ammonia-stripped at pH 9.5) and 0.57 +/- 0.04 L CH4/Ld (ammonia-stripped at pH 10.0). However, the improvement of methane production from the piggery wastewater pretreated at pH 11.0 was negligible compared to the control, which was thought to be due to the high concentration of sodium ions supplied from sodium hydroxide for pH adjustment. From these results, it was concluded that ammonia removal through air stripping at the alkaline pH could be a viable option for preventing the failure of anaerobic digestion of the raw piggery wastewater. Additionally, it was also found that a high concentration of sodium ion originated from sodium hydroxide for pH adjustment inhibited methane production. (C) 2011 Elsevier B.V. All rights reserved.