Design Methodology of Free Water Surface Constructed Wetlands

Simple criteria, guidelines and models are established for free water surface (FWS) constructed wetland selection and preliminary sizing. The analysis employs models for FWS constructed wetland design, considering simultaneously the removal requirements and the hydraulics of the system. On the basis of these models, a step-by-step methodology is developed outlining the design procedure for new and performance evaluation for existing FWS constructed wetland systems. This methodology is combined with simple equations predicting the maximum wetland capacity in summer, so as to assist designers in sizing installations in tourist areas with increased summer populations. Furthermore, this methodology is further simplified, based on sensitivity analysis of the unit area requirements for wastewaters of various strengths, and various design conditions and performance criteria. In addition, comparison of the unit area requirements of FWS constructed wetland systems, subsurface flow (SF) constructed wetland systems and stabilization pond systems for wastewaters of various strengths and design conditions, provides designers with general guidelines concerning the preliminary selection between alternative natural treatment systems in areas where the use of natural systems is favored because of their low-cost, simple operation and high removal performance.     

Sensitivity Analysis and Comparative Performance of Outfalls with Single Buoyant Plumes

This paper presents a new approach to analyze the performance of outfalls with single buoyant plumes in flowing ambient sea water, taking into account all three dilution mechanisms: the initial, the dispersion, and the effective dilution due to the decay of nonconservative substances. Simultaneous consideration of all dilution mechanisms, study of their functional relationships, sensitivity analysis of outfall behavior, and graphical presentation of the results, allows recognition of patterns of practical importance that remain otherwise obscure. The generated graphs afford an overview of the relative performance of outfalls with a single port and perpendicular line diffusers over a broad range of operating conditions, and portray the sensitivity of the single-port outfall behavior. The results show that, contrary to common belief, outfalls with a single port outperform those with perpendicular line diffusers over a broad range of operating conditions. They also show that higher rather than lower current speed is the critical factor in the design of single-port outfalls. These findings affect the construction cost of outfall systems and bear a significant impact on the sizing of new outfalls as well as on the performance evaluation of existing ones.