Enhancement of nitrification in submerged flow constructed wetlands

Four laboratory-scale, submerged flow constructed wetland (SFCW) mesocosms (Juncus effesus) were used to evaluate methods of increasing oxygenation within the wetlands to enhance nitrogen removal from applied wastewaters. The SFCW containing a naturally aerated pool had the highest total nitrogen (TN) removal (90 percent) and lowest effluent TN concentration (3.5 mg/L). Lowest TN removals (15 percent) were obtained from a wetland containing a mechanically aerated pool. Nitrification of ammonia was achieved but low organic carbon levels inhibited denitrification, resulting in high levels of nitrate in the effluent. Juncus effesus preferred ammonia to nitrate and grew poorly in waters dominated by nitrate. Providing a naturally aerated pool within a SFCW appears to be an economical method of increasing oxygenation in constructed wetlands treating wastewater.Project # G-2029-01 Agreement # 14-08-0001-G-2029-0

Computational method for singularly perturbed delay differential equations with twin layers or oscillatory behaviour

AbstractIn this paper, we have presented a computational method for solving singularly perturbed delay differential equations with twin layers or oscillatory behaviour. In this method, the original second order singularly perturbed delay differential equation is replaced by an asymptotically equivalent first order neutral type delay differential equation. Then, we have employed numerical integration and linear interpolation to get tridiagonal system. This tridiagonal system is solved efficiently by using discrete invariant imbedding algorithm. Several model examples are solved, and computational results are presented by taking various values of the delay parameter and perturbation parameter. We have also discussed the convergence of the method