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.

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Two stabilization pond systems are examined. A sensitivity analysis is undertaken, aimed at investigating the influence of the pond depths on stabilization pond surface area and pond volume for the specific combination of temperature, wastewater characteristics and effluent requirements. The dependencies are presented in a functional form, allowing for the graphical solution of the unit pond volume, area, and hydraulic residence time as a function of the respective pond depths. Based on these graphs, designers can determine the most appropriate depth value for each type of pond that minimizes the required area or volume, or balances excavation versus land acquisition and floor lining costs, taking under consideration the topographic and other local characteristics of the site area.

This paper presents a methodology that uses a knowledge base and inference procedures for developing rational wastewater management schemes for small to medium size communities with emphasis in the protection of human health, the reuse of treated wastewater, and the pollution minimization of water receivers. The system provides an optimal year-round treatment/reuse/disposal plan, which maximizes the wastewater reuse for irrigation, meets the applicable minimum municipal wastewater treatment requirements and observes the water quality standards of receivers with the minimum treatment costs. The solution is dynamic in the sense that varying monthly design values can be assigned to the input variables used in the computation of irrigation requirements, assimilative capacity of receivers and performance of natural systems. The above procedure shows that the use of multiple receivers over the year is often highly advantageous; combining for example the increased treatment efficiency and reuse potential for irrigation during summer with the increased assimilative capacity of a river during winter. The expert system incorporates a number of design and ambient quality models, for which graphical solutions have been developed, so as to enable manual application if desired. The entire procedure is implemented in an integrated computer program that facilitates and refines problem solution. The expert system provides interactive guidance for collecting the necessary field information. Finally, the results of a case study for the management of wastewaters from the six communities of the Municipality of Keramoti are presented.

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