مجله آب و خاک (Dec 2021)
Investigation of the Role of Sand- Geotextile-Zeolite Composite Filters on some Wastewater Properties
Abstract
Introduction: Nowadays, the use of effluent in irrigation and especially drip irrigation systems has increased. The findings uncovered that drip irrigation is assumed as the only method which is capable of overcoming specific problems caused by wastewater usage. In this study, the efficiency of sand and geotextile filters with zeolite on wastewater properties and their application in the filtration of the drip irrigation system was investigated. Materials and Methods: This study was conducted to investigate the changes in important chemical properties in the municipal wastewater of a university after passing through sand filters, geotextiles, and zeolites in the drip irrigation filtration system. A factorial experiment was performed in a completely randomized design with three replications. Treatments included sand filter (control-CTRL treatment), geotextile filter (G), sand filter with zeolite (SZ), and geotextile filter with zeolite (GZ). The sand used in this study was the usual silica sand which was in three sizes of 3-5, 5-8, and 8-12 mm. In order to remove any contamination and soil particles and increase the accuracy of the measurement of suspended solids in the effluent, the sands were washed several times with water before usage. The geotextiles used in this study had three types with weights of 300, 500, and 1000 grams per cubic meter. The zeolite used in this study was clinoptilolite modified with hydrochloric acid. The wastewater used in this study was obtained from the effluent of Shahrekord University. System flow rate, Pressure, nitrate, suspended solids, sodium, calcium, magnesium, electrical conductivity, effluent pH were measured before and after entering the filters at different hours. Statistical analysis was done by SAS software and the Duncan test was used to compare the means of the data. Results and Discussion: The results showed that the sand-zeolite treatment had a good performance in terms of pressure and the geotextile-zeolite treatment was able to provide pressure for a short time. The amount of nitrate in the wastewater of the sand filter was not significantly different from the amount of inlet, but in other filters was significantly reduced. The amount of nitrate input of all treatments was 26 mg/l.The average output nitrate in the sand filter was about 25 and in the other filters was less than 20 mg/l. The average amount of suspended solids in the effluent was about 110 mg/l, while the average amount of suspended solids in the wastewater was reduced to less than 72 mg/l. The sand and sand-zeolite treatments increased the total amount of calcium and magnesium in the wastewater more than geotextile and geotextile-zeolite treatments, respectively. The average Ca + Mg of effluent in the total operating hours of the system was higher than the average input in all filters. The percentage of EC changes in total hours increased about 4% in sand and geotextile treatments and 14% in geotextile- zeolite and sand -zeolite filters. The highest percentage of pH changes was related to sand-zeolite filter, which reduced the pH of incoming wastewater by about 4.5%. After that, geotextile- zeolite filter reduced the pH of the incoming wastewater by 4%. The average pH of the effluent of all filters is lower than the average of their inlet. Conclusion: Sand and geotextile filters alone cause pressure drop and dropper clogging. However, the sand-zeolite treatment has performed well in this regard. The geotextile-zeolite treatment has the potential to be used in terms of supplying the necessary pressure for a short period by applying special treatment measures before this filter. These conclusions are only in terms of pressure drop due to the ability of filters in practical use and do not refer to their ability to filter the parameters and provide the desired flow. All treatments, especially zeolite treatments, significantly reduced nitrate, and these filters can be used to reduce effluent nitrate in cases where the amount of nitrate is more than allowed. However, since the sand filter had no effect on nitrate reduction, the effluent must be treated for nitrate before using sand filters. The geotextile filter had a higher percentage of suspended solids removal at all hours. The addition of zeolites to both geotextile and sand base filters reduced their ability to treat suspended solids. Therefore, geotextile filters can be a good alternative to ordinary sand filters in terms of this parameter. All treatments increased Ca + Mg relative to the input. The sand- zeolite treatment reduced the pH of the incoming wastewater more than other treatments (about 4.5%). Also, desalination of salts from zeolite treatments increased the EC of effluent in the sand-zeolite and Geotextile- zeolite treatments. According to this study, the use of sand-zeolite in terms of reducing nitrate and suspended solid, increasing calcium and magnesium, and reducing pH and no pressure drop is recommended.
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