The effect of using bi-levels of geocomposite sheets on the quality of Shahrekord University wastewater

Introduction
Due to the scarcity of freshwater resources, treated wastewater is increasingly recognized as a sustainable alternative for irrigation and other purposes. One effective method of wastewater reuse is its application in agricultural fields. Subsurface irrigation systems, which fall under the category of land treatment systems, are commonly employed for this purpose. The land treatment system is a wastewater treatment and reuse technology that enhances wastewater quality by allowing it to pass through the soil, where it undergoes natural treatment processes. Numerous studies have demonstrated that underground irrigation systems can significantly reduce environmental pollution and minimize the risks of soil and plant contamination associated with wastewater usage. Furthermore, the wastewater collected from irrigation can be harvested for reuse by improving its microbial and biochemical quality. Additionally, land treatment technology is environmentally friendly as it reduces the adverse effects of wastewater discharge on the environment. It achieves this by reducing and eliminating the amount of pollutants present in wastewater, minimizing energy and chemical consumption, and ultimately reducing the overall cost of wastewater treatment and reuse compared to other methods. In this study conducted at the University of Sharkard, the researchers examine the effect of utilizing geocomposite plates at two different levels for sewage utilization. They also investigate the resulting changes in the chemical properties of sewage within the context of land treatment.
 
Materials and Methods
This study investigated the effectiveness of bi-levels of geocomposite sheets in wastewater irrigation, drainage water collection, and land treatment at Shahrekord University. Geocomposite sheets were used for the water influx layer and drainage layer. The treatments included two distances of 35 and 75 cm between the water influx and the drainage layer. In both treatments, the water influx layer was 40 cm below the ground surface. The wastewater used in this research was obtained from a sewage manhole at Shahrekord University. Before use, the wastewater was subjected to preliminary treatment by passing through a mesh strainer, a sand filter, and a geotextile filter. The research was conducted as a factorial experiment based on a completely randomized design with three replications. The factors studied included the injection stage of wastewater (time) at twelve levels and the distance of drainage from the influx layer in two levels. Wastewater was injected 12 times with a weekly frequency. The measured parameters in all injections included: EC, pH, sum of calcium and magnesium, carbonates and bicarbonates, volume of input wastewater, and volume of drainage water. Sodium, BOD5, and nitrates of wastewater and drainage water were measured only in the 2nd, 4th, 6th, and 8th of wastewater injection. The urban wastewater of Shahrekord University has an average salinity of 0.67 dS m^-1, sodium of 1.4 meq l^-1, nitrates of 15.7 mg lit^-1, and bicarbonate of 4.41 meq l^-1, which has an average limit for use in agriculture.
 
Resullts and Discussion
The results showed that passing wastewater into the soil was caused increasing in EC, sum of calcium and magnesium and bicarbonates of the wastewater while decreasing in SAR, BOD₅ and nitrates. According to the results, the treatment with a thickness of 70 cm caused a significant increase in salinity, bicarbonate and total calcium and magnesium in the drain water by 31.34, 31.97 and 161.9%, respectively, compared to the wastewater and 11.39, 20.29 and 10.0% compared to the treatment with a thickness of 35 cm. The amount of nitrate in the drain water was significantly reduced in the treatment with a thickness of 70 cm by 19.80% compared to the wastewater and 6.04% compared to the other treatment. In the period of the study, as the number of injection stages increased, the percentage of nitrate changes in wastewater due to passing through the soil decreased. In other words, the ability of the soil to remove nitrate from wastewater gradually decreased. In addition, land treatment in treatments with a thickness of 70 and 35 cm, respectively, caused a decrease of 19.28 and 15.71% of sodium, 16.36 and 13.87% of BOD5, and 54.29 and 50.75% of SAR and an increase of 10.10 and 8.7% pH of drain water compared to wastewater. However, the percentage of changes of these indices between the two treatments with a distance of 70 and 35 cm between the water influx and the drainage layer did not show a significant difference.
 
Conclusion
The study aimed to assess the soil's ability to enhance wastewater quality when combined with geocomposite plates. Overall, the passage of wastewater through the soil layer increased pH, salinity, total calcium, magnesium, and bicarbonate levels, while reducing sodium, nitrate, BOD5, and SAR in the wastewater. Notably, the 70 cm thick treatment significantly increased salinity, bicarbonate, and total calcium and magnesium levels in the sewage compared to other treatments. Additionally, the nitrate content in the sewage decreased more significantly in the 70 cm thick treatment. However, the percentage of changes in these indicators did not significantly differ between the treatments with a distance of 70 cm and 35 cm between the water and drainage layer. Based on the experiment's results, applying a drainage layer at a distance of 35 cm from the water and drainage layer created better conditions for wastewater reuse, especially when the drainage volume is not high. In such cases, the passage of wastewater through the soil layer at a distance of 35 cm appeared to contribute to improved wastewater conditions. However, it is important to note that the use of wastewater may also initiate soil degradation, requiring further investigation for potential solutions in future research.