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Abstract. Harsh environment, severe aridity, and climate change create chronic water shortages in the Middle East. Technical challenges, socio-economic factors, and competing uses of water have escalated the difficulties in water planning at national and institutional levels. This research identifies opportunities and challenges associated with wastewater treatment systems and the potential for wastewater reuse in the West Bank, Tunisia, and Qatar through the following objectives: (1) identify the factors associated with successful and unsuccessful reuse schemes, (2) compare treated wastewater quality with end use application of treated wastewater, and (3) identify the governance and social challenges preventing the use of treated wastewater, specifically in agricultural applications. Water quality analyses and consultations with farmers, local stakeholders, and water and agriculture experts were conducted. Opportunities and challenges for treated wastewater reuse in agriculture are identified as the proximity of the treatment facility to agricultural areas, water quality, and motivation of farmers. With proper maintenance and appropriate monitoring, the modest (natural) treatment facilities in the West Bank and secondary treatment technologies in Tunisia are capable of producing effluent safe for use in production of certain agricultural products; however, in Qatar, despite massive investments in producing high-quality treated wastewater using advanced treatment technologies, there is little demand. Water policies, laws and acts, and action plans are urgently needed to be coupled and integrated for implementation. Keywords: Arid lands, Food security, MENA, Wastewater treatment, Water reuse.

Intermittent infiltration percolation of wastewater through unsaturated sand bed is an extensive treatment technique aimed at eliminating organic matter, oxidizing ammonium and removing pathogens. The main purpose of this study was to determine the depuration efficiencies of a sand filter to remove contaminants from secondary wastewater effluents. Elimination of pathogenic bacteria (total and faecal coliforms, streptococci) and their relationship with the filter depth were investigated. Results showed a high capacity of infiltration percolation process to treat secondary effluents. Total elimination of suspended solids was obtained. Mean removal rate of BOD(5) and COD was more than 97 and more than 81%, respectively. Other water quality parameters such as NH(4)-N, TKN and PO(4)-P showed significant reduction except NO(3)-N which increased significantly in the filtered water. Efficiency of pathogenic bacteria removal was shown to mainly depend on the filter depth. Average reductions of 2.35 log total coliforms, 2.47 log faecal coliforms and 2.11 log faecal streptococci were obtained. The experimental study has shown the influence of the temperature on the output purification of infiltration percolation process.

This study was conducted to evaluate the treatability of OMW (olive mill wastewater) with sewage and sewage sludge, which could supplement nutrients and microbes required for OMW treatment and reduce its possible toxicity. The amount of OMW added to an aeration tank was based on the loading difference between the designed and actual COD loads, while the amount added to anaerobic digestion for energy recovery was determined by CH4 production. The COD removal efficiencies were 70-85% for both systems. Compost of OMW with dried sewage sludge also showed a similar temperature profile without OMW addition. This strongly suggested that OMW can be treated at a sewage plant without pretreatment and the treated effluent can be reused in irrigation for an arid region.