**4. Conclusion**

Inappropriate management practices in the use of wastewater in phosphorus deteriorate surface and ground water quality, mainly by causing nitrate pollution. The HYDRUS-1D model was calibrated and then validated with different datasets from a lysimeter experiment, and then used to simulate phosphorus leaching through soil under different irrigation treatment (wastewater, effluent, mixture of freshwater and effluent, and freshwater) on three types of soil (sandy loam, loam, and clay loam) to explore and develop better and safer wastewater land application strategies.

Phosphate transferred to the depths was insignificant and it was between 1.6 and 6% of inflow phosphate, which was lower than the maximum standard value of phosphate discharge to surface and groundwater.

Soil and plant systems showed high potential in filtration and removal of nitrate and phosphate, so that the concentration of nitrate and phosphate in drained treatments in all cases was lower than the limit of discharge to surface water and groundwater. It can be confirmed that through proper management and research, in addition to maintaining surface water and groundwater, the effluent, as an available and cheap source, can be used in agricultural irrigation. As there was no significant difference on nitrate leaching between treatments mixture of freshwater and effluent, and freshwater, this demonstrates that it can dilute wastewater as a suitable management strategy for reducing the leaching of impurities in the wastewater and also reduce the effects of probable hazards on soil properties. Simulation study on the process of nitrate leaching to root zone during growing season showed more matches the needs of the plant. Thus, at the time of minimum plant nutrient requirement, we can take suitable management solution such as wastewater dilution to lower leaching of elements to root zone.
