Agronomic aspects and environmental impact of reusing marginal water in irrigation-A case study from Egypt

摘要

Egypt produces about 2.4 million m~3 of secondary treated wastewater (TWW) annually used for irrigation directly or indirectly by blending with agricultural drainage water (BDW). The annual reuse of (BDW) is about 4 million m~3. The safe and efficient use of marginal water (BDW & TWW) is a core objective of this case of study which has been operating since 1997 until now. After six growing seasons the main results can be summarized as follow: Maximizing Crop production: TWW can be used for high production of oil crops, (canola, soybean sunflower or maize) compared to fresh water, while BDW can be used for high production of tolerant crops, (cotton and sugar beet). Crop Quality: using marginal water increased the concentration of elements (Pb, B, Ni, Co) in all crops but these elements were under critical levels (there were no toxicity hazards). It is better to use alternative irrigation by fresh water with marginal under drip irrigation system to maximize crop production and minimize the adverse effect of such water in field crops quality. Soil Pollution and salinity build up: Drip irrigation system under alternative irrigation by fresh with TWW or BDW reduce salinity build up risks and the levels of elements (Pb, B, Ni, Co) in soil compared to reuse marginal water. Soil Pathogens: using marginal water slightly contaminated the soil with total fecal coli form, (TFC), mites, shegella and salmonella Plant Anatomy: No great changes in anatomical disturbance induced in different structure of plant which have been reduced at maturity stage. Primary Guidelines for reusing marginal water: From obtained results it can be recommend the use of marginal water with salinity content ranged between 1.1 to 3. 64 dS/m, and elemental contents ( Pb 3.0-3.51 ppm), (B 0.05 -1.67 ppm), (Co 0.04 -0.07 ppm),( Ni 0.08 -0.15 ppm) for safe (field , vegetable and medicinal) crops production. Reuse Bio solids for crop production: Sewage sludge produced from treated wastewater can be safely used by mixing with rice straw (1:1 w/w) for economic crop production and saving mineral fertilizers. General conclusion: In North Nile Delta marginal water (especially BDW) can be safely used without significant negative impacts on the environment, but there is a need for multi-disciplinary, long-term research to investigate irrigation with marginal water in terms of the environment, public health and agricultural productivity.