Assessing the Suitability of purified wastewater from the WWTP in southern Algeria (Saïd Otba -Ouargla) for agricultural reuse

Abstract

The aim of this study, which was conducted on the results obtained for the year 2019, is to analyze the results of polluted water purified using the aerated lagoon method for the Said Otba (Ouargla) plant, and to compare the results obtained with Algerian and international standards. By measuring some of the physico-chemical characteristics of wastewater and treated water, the results showed the characteristics of the water discharged to SebkhetSefioun (Ouargla), where it was concluded that: The average yield of removing organic pollutants: BOD5 and COD (73.25%, 70.44%) and SS (45.86%). As for the average yield of removing nitrogenous pollutants: NH4+ (6.58%), NO3- (24.52%), and TN (7.44%), as for the average yield of removing phosphorous pollutants: TP (22.06%) and PO43- (26.06%). In general, most pollution factors comply with Algerian and international standards, with the exception of electrical conductivity, in other words, salinity, which exceeds admissible limits. Calculating the water quality index (WQI) showed that the water quality is not suitable for irrigation due to high salinity, as WQI = 136.07 > 100, which is higher than the limit allowed in the standards of the water quality index. The software also addressed the principal component analysis (PCA) to determine two main axes F1 and F2, which together represent 51.96% of water quality index (WQI). the information. Axis F1 (29.65%) is correlated to suspended matter, ammonium, salinity, pH, chemical oxygen demand, dissolved oxygen and nitrate. As for F2 (22.31%), it is correlated to salinity and phosphate, with less association with dissolved oxygen and nitrate. The results indicate that the composition of pollutants in raw wastewater consists mainly of organic matter, nitrogen compounds, and phosphate. For heavy metals, the F1 and F2 axes represent 68.72% of the total variance, as the F1 axis is associated with 45.65% with lead and nickel, while the F2 axis is associated with 23.08% with cadmium, chromium, and lead to lesser degrees.