Hafner Sasha D, Bisogni James J
Pasture Systems and Watershed Management Research Unit, USDA ARS, Building 3702, Curtin Rd., University Park, PA 16802, USA.
Water Res. 2009 Sep;43(17):4105-14. doi: 10.1016/j.watres.2009.05.044. Epub 2009 Jun 6.
Anaerobic digestion of high-nitrogen wastes such as animal manure can be inhibited by high concentrations of un-ionized ammonia, NH(3) (aq). Understanding the toxicity of NH(3) (aq) to anaerobic digestion requires a method for determining its concentration. Previous work on ammonia toxicity in anaerobic digesters has utilized a simple equilibrium calculation for estimating NH(3) (aq) concentration from total ammonia, temperature, and pH. This approach is not appropriate for concentrated solutions. In this work, a speciation model for major solutes in anaerobic digesters, based on Pitzer's ion-interaction approach, is presented. Model simulations show that the simple equilibrium calculation (without corrections for non-ideal behavior) substantially overestimates NH(3) (aq) concentration for all but dilute digesters. This error in concentration determination increases with total solids content and is estimated to be greater than 40% for a digester fed dairy manure with 5% total solids or swine manure with 3% total solids. However, including an estimate of the activity coefficient for NH(4)(+) in the simple equilibrium calculation results in much more accurate estimates of NH(3) (aq) concentration. In this case, the estimated error is less than 10% in the absence of struvite precipitation at the highest total solids contents considered.
高氮废物（如动物粪便）的厌氧消化会受到高浓度未电离氨（NH₃(aq)）的抑制。要了解NH₃(aq)对厌氧消化的毒性，需要一种测定其浓度的方法。先前关于厌氧消化池中氨毒性的研究采用了一种简单的平衡计算方法，根据总氨、温度和pH来估算NH₃(aq)的浓度。这种方法不适用于浓溶液。在这项研究中，提出了一种基于皮兹离子相互作用方法的厌氧消化池中主要溶质的形态模型。模型模拟表明，对于除稀消化池外的所有情况，简单平衡计算（不校正非理想行为）会大幅高估NH₃(aq)的浓度。浓度测定中的这种误差会随着总固体含量的增加而增大，对于进料为总固体含量5%的奶牛粪便或总固体含量3%的猪粪便的消化池，估计误差大于40%。然而，在简单平衡计算中纳入对NH₄⁺活度系数的估计会使NH₃(aq)浓度的估计更加准确。在这种情况下，在所考虑的最高总固体含量下且不存在鸟粪石沉淀时，估计误差小于10%。
