The effect of using bi-levels geocomposite sheets on the chemical and biochemical characteristics of soil under wastewater reuse

Abstract
Introduction
The reuse of wastewater in agriculture, especially for crop irrigation, can be one of the most important options to alleviate the water shortage problem and reduce environmental pollution through land based wastewater treatment. The presence of more organic matter and food and the presence of fecal matter in sewage effluent, increase the activity, survival, growth and development of bacteria. Those are as factors increasing soil cloiform in the condition of irrigation with sewage. Subsurface irrigation is one of the proved method that can minimize soil contamination in comparsion with other method of irrigation. It has been showen that, subsurface irrigation systems with geotextiles can reduce environmental pollution and the risk of soil and plant contamination when using wastewater. So far, many studies have investigated the effects of wastewater application on soil characteristics; but there is no information on the effect of wastewater application using SSTI (Subsurface Textile Irrigation) systems on soil properties. In this study, the effects of wastewater application in subsurface irrigation with geocomposite sheets on the chemical and biochemical characteristics of soil were investigated. In the present study, the changes in chemical and biochemical characteristics of soil due to the application of Shahrekord University wastewater using subsurface irrigation with geocomposite sheets were investigated.
Materials and Methods
This research was conducted as a factorial experiment based on a completely randomized design with three replications. The studied factors included the measurement location at two levels above (0-40 cm) and below the injection layer (40-80 cm) and the distance of the drain from the injection layer at two levels of 35 (D35) and 70 (D70) cm. To conduct the experiment, four meter long, 40 cm wide and 75 (D35) and 110 (D70) cm deep trenches were dug in the soil. The bed and walls of the trenches were covered with plastic and greased to prevent preferential flow from the plastic walls. Then the geocomposite layers were used as a drainage layer with a length of four meters and a width of 20 cm. After that, according to the desired treatment (35 and 70 cm thick), soil was poured on the drain to a depth of 40 cm from the ground surface. To conduct the research, geocomposite-sheets were used for the water influx layer and drainage layer. The treatments included two distances of 35 and 75 centimetres between the water influx and the drainage layer. In both treatments, the water influx layer was 40 centimetres below the ground surface. Wastewater was injected 12 times with a weekly frequency. At the beginning and end of the study period, soil samples were taken from two depths of 0-40 and 40-80 cm and pH, EC, total calcium and magnesium, carbonate and bicarbonate, nitrate and fecal and total coliform were measured.
Resullts and discussion
The results showed an increase in electrical conductivity, nitrate, carbonate and bicarbonate, total coliform and faecal coliform in the soil at the end of the study period compared to beginning of the study period. The pH of the soil has decreased in both the upper and lower areas of the water table. Probably, the decrease in soil pH under the conditions of using wastewater is due to the nitrification of ammonium and the leaching of cations from the soil. However, the results of the ANOVA of the effect of depth of measurement, depth of drain application, and their interaction on soil pH changes showed that the effect was not significant. The electrical conductivity of the soil has increased in both areas above and below the water table for both treatments. The results of ANOVA of the effect of measurement depth, depth of drain installation, and their interaction on percentage changes in soil electrical conductivity showed that the effect was not significant. The total soil calcium and magnesium in D70 and D35 treatments decreased on average by 6.66 and 8.48% compared to the beginning of the period, but this difference was not significant. According to the presented results, the amount of soil nitrate has increased as a result of irrigation with wastewater at both depths compared to the beginning of the research period. The amount of total coliform and faecal coliform in the soil at the end of the period has increased compared to its value at the beginning of the period.

Conclusion
As a conclusion, the use of geocomposite sheets for land treatment during the period of study did not have a negative effect on the chemical and biochemical properties of the soil, and this method can be used without worrying about soil contamination.

Keywords: Subsurface Irrigation, Geocomposite, Land Treatment, Soil contamination, Urban Wastewater
Article Type: Research Article

Acknowledgement
We would like to express our sincere gratitude to the University of Shahrekord for the financial and logistical supports who significantly contributed during the research project.

Conflicts of interest
The authors of this article declared no conflict of interest regarding the authorship or publication of this article.

Data Availability Statement:
The datasets are available upon a reasonable request to the corresponding author.

Authors’ contribution
Sayyed-Hassan Tabatabaei: Conceptualization, Analysis, Manuscript editing
Sajad Googoochani: Running test, Software, Analysis
Mahdi Ghobadinia: Formal analysis and investigation, Supervision
Hamidreza Motaghian: Manuscript editing
Azimeh Asgari: Writing - original draft preparation