Development and verification of a decision support system for the selection of optimum water reuse schemes

The selection of an optimum scheme for treatment of agricultural drainage water for reuse in specific applications is a challenging and tedious task that necessitates the evaluation of a long train of optional treatment processes which involve, among others, alternative desalting systems. The decision maker is requested to compromise between multiple factors including technical and economic considerations. Over the last two decades, considerable advances have been achieved in the development of expert systems as a decision support tool for the solution of various engineering and management problems. This paper addresses the development and verification of an expert system for the intelligent selection of the optimal scheme for the treatment of agricultural drainage water. As typical of expert systems, the adopted approach includes a knowledge base, inference engine and working memory. The developed system encompassed the formulation of the logic tree and the rule base according to the experts’ knowledge and engineering algorithms. The system has been verified for agricultural drainage water for reuse in several applications requiring water of varying quality. Outputs include the selected treatment trains, intermediate and final water characteristics and capital and operating costs for two typical cases. It is concluded that the developed expert system could be used for rapid and reliable decision making on the optimum management scheme for treatment of agricultural drainage water for reuse.

characterized by high concentrations of dissolved organics in addition to microbiological and heavy metals contaminants. The first case has relatively lower BOD and DS than the second. The treated water is to be reused for applications requiring low to high quality (A to D as given in Fig. 2). 4.2. Results The printouts of the results of the expert system for the two cases are presented in the figures and tables of Case I and II respectively (see Appendix). It is noticed that the optimum treatment scheme has been selected in view of the wastewater characteristics and the prevailing constraints. In the first case, where the BOD and DS are relatively low and limited land is available, the selected biological treatment method is the trickling filter while EDR has been the selected desalting method. Further, an RO unit has been added to treat the brine from the EDR thus reducing the cost of treatment of 1 m3 from $0.64 to $0.52 for water of quality D. In the second case, due to the relatively higher BOD, the method of choice for biological treatment has been activated sludge. Also, due to the relatively higher DS content, RO has been the selected desalting scheme. The cost of treatment The crucial need for reuse of agricultural drainage water necessitates the comparison between alternative treatment schemes on technical, economic and environmental grounds to produce water suitable for particular purposes under prevailing conditions and constraints. The developed DDSS proved to be an efficient and reliable approach for identifying treatment train and cost estimates when provided with the wastewater characteristics and governing requirements and limitations as verified by typical case studies. It is recommended that this approach would be • compemented with process design routines to provide preliminary process designs and cost estimates for a specific case under consideration. • extended to optimize integrated management and reuse schemes for a geographical area. Abreviations AC AS AS ChOx Ch.T ChOx — Activated carbon — Activated sludge — Aerated lagoons — Chemical oxidation — Chemical treatment — Chlorination Dis DMF ED IE MF NF NS PL PT RO Sec. Sed TF WL — Disinfecation — Dual media filter — Electrodialysis — Ion exchange — Microfiltration — Nanofiltration — Natural sedimentation — Polishing lagoons — Pretreatment — Reverse osmosis — Secondary sedimentation — Trickling filter — Wet land