Extended Abstract



Introduction:

The limited water resources of Hamedan Province and the decline in groundwater levels will lead to the risk of drying up of the wells that supply water as a source of irrigation for the province's important crops, including garlic and potatoes. This issue, in turn, can seriously threaten the sustainability and durability of their cultivation and work in the suburbs of Hamedan. Therefore, the possibility of using treated urban wastewater in a legal and healthy manner, in addition to providing part of the water needs of these products, will help maintain and sustain the cultivation and cultivation of two important crops, garlic and potatoes in the suburbs of Hamedan. On the other hand, wastewater is considered an unconventional source of water, and its use in agriculture requires careful and necessary management in controlling and purifying it to ensure the health of soil, plants and humans while avoiding environmental hazards (Yargholi and Taran, 2024). Therefore, the present study was conducted to use treated wastewater from Hamedan city to irrigate two crops, garlic and potato, by investigating its effect on soil chemical properties, distribution, and soil contamination with heavy metals such as copper, cadmium, chromium, lead, nickel, and arsenic.

Materials and Methods:

Initially, before planting the crops, samples were taken from the soil, treated wastewater, and water extracted from a well that was used to irrigate the two crops of garlic and potato. In order to enable the practical application of treated wastewater for the irrigation of garlic and potato cultivation, a suitable land parcel was identified, and a farm with convenient access to the treated wastewater supply was chosen. In the next step, soil samples, treated wastewater samples, and water extracted from the well were transferred to the laboratory and various tests were performed on them. Twenty soil samples from the designated cultivation area for both crops, along with twenty samples each of well water and treated wastewater, were collected randomly and in equal quantities. Irrigation was applied by driple tape irrigation system, using 16 mm diameter tubes with dripper spacing of 33 cm and a discharge rate of 1.6 liters per hour, placed on the ridges. The amount of water consumed was measured using calibrated flowmeters. In these tests, the amount of nitrogen and nitrate, EC value, acidity level, exchangeable sodium percentage (SARadj), saturation index, amount of B-, Cl-, Na+ and So4-2 ions, and levels of heavy metals such as chromium, arsenic, cadmium, copper, nickel, zinc and lead were determined. At the end of the growing season and after harvesting the crops, soil samples were taken from the studied farm and the physical and chemical properties of the soil were also determined. Other chemical properties of the soil, such as salinity levels, pH changes, nitrate nitrogen levels, and heavy metal levels of chromium, cadmium, arsenic, copper, nickel, zinc, and lead, were also measured.





Results and Discussions:

By evaluating the results of the chemical characteristics of well water and treated wastewater, it was determined that well water and treated wastewater were close in terms of electrical conductivity (EC) and pH, and based on the standards proposed by the Food and Agriculture Organization of the United Nations (FAO, 2004) and the World Health Organization (WHO), there are no restrictions for irrigation and growth of the studied crops. The amount of bicarbonate in well water and treated wastewater was found to be 5.25 and 1.75 milliequivalents per liter, respectively. The much lower bicarbonate content of treated wastewater compared to well water is an important advantage, especially in this regard, in the soil of the area in question, which also has a relatively high pH, it has a positive effect on reducing the fixation of cations such as calcium and magnesium, and there is less inhibition of phosphorus absorption in irrigation with treated wastewater water (Albaji and Asgari, 2017). The amount of sulfate ion in treated wastewater is significantly higher at 3.6 milliequivalents per liter than in well water (average 0.9 milliequivalents per liter). This amount of sulfate is considered an important advantage, especially since it can also be useful in the absorption and transport of elements such as iron, manganese, and zinc by helping to lower the pH of the root environment (Sokolova and Alekseeva, 2008; Chaudhary et al., 2023). The concentrations of calcium and magnesium, as well as the trace elements iron, zinc, and manganese, were significantly lower in well water than in treated wastewater (Tables 1 and 2). The high levels of all these elements in treated wastewater also contribute to its value as a source of essential plant nutrients and can be very useful in providing part of the nutritional needs of crops, especially garlic and potatoes. By examining the results of measuring the amount of heavy metals in treated wastewater, it was determined that all five heavy metals that are considered sources of contamination of wastewater are, fortunately, present in very small amounts in the treated wastewater. There was no significant increase in EC, saturated soil reaction, and bicarbonate in the soil in both garlic and potato crops after harvest in the plot where treated wastewater was used. In contrast, the amount of chlorine, sulfate, and copper ions in the soil, in two stages before planting and after harvest, showed a different situation compared to other nutrients, so that after harvest, their amount in the soil increased relatively. The amount of phosphorus, potassium, and nitrogen in the soil, as well as micronutrients, decreased relatively after harvesting of the both crops. The concentration of heavy metal pollutants in the soil in both plots dedicated to garlic and potato cultivation, especially nickel and arsenic, was higher than copper, chromium, and cadmium. However, in terms of pollution and necessary standards, they were lower than the maximum permissible and harmful levels and were of less concern. Conclusion:

The findings of this experiment collectively demonstrate that the treated wastewater effluent from the Hamadan Province treatment plant is of a satisfactory quality. It meets acceptable standards for EC, sodic salinity, bicarbonate, and chloride. Crucially, levels of heavy metal contaminants, specifically arsenic, nickel, chromium, and cadmium, were below the established maximum limits, indicating no adverse impact on soil pollution or the accumulation of harmful residues. Thus, this treated effluent can serve as a viable alternative water source for irrigating both garlic and potato crops, complementing existing groundwater resources.

Keywords: Soil pollution, Sewage effluent, Soil analysis, Mineral elements