Comparative economics for desalting of agricultural drainage water (ADW)

Increasing water shortage in Egypt approaches an alarming level. Treatment and reuse of secondary water sources (comprising brackish water and wastewater) is of current national and international concern. The Egyptian Academy of Scientific Research and Technology (ASRT) allocates considerable funding for numerous R/D projects addressing key issues pertinent to water quality and reuse. One recent project entitled Novel Technologies for Drainage Water Treatment financed by ASRT and executed by National Research Center (NRC) comprised a detailed assessment of the desalting technologies for reclamation of ADW. The investigations focused on functional analysis and financial assessment of membrane-based systems and pertinent pretreatment requirements. This paper addresses the comparative economics of the following systems (a) activated carbon (AC)/ultrafiltration (UF)/reverse osmosis (RO), (b) UF/ electrodialysis reversal (EDR)/RO, (c) AC/ED/ion exchange (IE), (d) microfiltration (MF)/UF/RO1/RO2 and (e) slow sand filtration (SSF)/AC/IE. The selected schemes cover the variations of ADW characteristics geographically and seasonally and also copes with demand characteristics of potential users. The results reveal promising indicators for ADW reuse within selected sectors (e.g. industrial applications) in some geographical locations in desert areas adjacent to central agricultural drains. The most important recommendations point to the importance of field demonstration in selected locations to explore the system reliability and performance under actual applications. Also, desalination of ADW should be restricted to small- and medium-scale plants in the near future.

Numerous desalting schemes have been addressed for agricultural drainage water with medium salinity (1400 ppm) and slight organic content. The candidate technology for treatment is the scheme comprising micro filtration, ultrafiltration and reverse osmosis. This option offers the following technical and economic merits: • Complete removal of organic pollutants. • The use of high recovery membrane system due to relatively low salinity feed water treated. • The produced water could be used safely for many industrial purposes. • Less cost per m3 of product water as compared to the other proposed schemes. The candidate scheme, though manifesting numerous technical and economic merits, yet, its dependence on imported supplies essential for operation (e.g. membranes) can hinder wider application. Planning for RO and UF, MF membranes supply through regional and international cooperation must be developed taking into consideration the possible role of the local investment and industrial sectors.