Seyed Mostafa Khezri - Associate Professor, Department of Environmental Engineering, School of Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran
Gharib Majidi - MSc in Environmental Health Engineering, School of Public Health, Qom University of Medical Sciences, Qom, Iran
Hossein Jafari Mansoorian - Lecturer, Environmental Health Engineering Research Center, Department of Environmental Health, Kerman University of Medical Sciences, Kerman, Iran
Mohsen Ansari - MSc in Environmental Health Engineering, School of Public Health, Qom University of Medical Sciences, Qom, Iran

Background: The effective size of the end grain of horizontal roughing filters (HRFs) is larger than 2 mm. This study aimed to examine the efficiency of HRFs in removing nitrate, phosphate, and chemical oxygen demand (COD) from effluent of a wastewater stabilization pond.Methods: This experimental study was conducted in 2013. The pilot project was transferred to the Karaj wastewater treatment plant (stabilization pond), and the installation, equipping, and start-up of the system began using an effluent treatment plant. Sampling was done from March to August in 3 rates, 0.5, 1 and 1.5 m/h, and included simultaneous sampling from inlet and outlet filtering to determine the concentrations of nitrate, phosphate, and COD.Results: At filtration rates of 0.5, 1, and 1.5 m/h, the average nitrate removal equaled 25%, 32%, and 34%, respectively, average phosphate removal equaled 29%, 26%, and 28%, respectively, and the average COD removal at filtration rates of 0.5, 1, and 1.5 m/h equaled 62%, 66%, and 68%, respectively. Outlet values of phosphate and nitrate were lower than the standards set by the Environmental Standards Organization (ESO) (P < 0.05).Conclusion: According to the results of this study, the HRF function was approximately adequate in COD removal, but its efficiency in nitrate and phosphate removal was lower.

Wastewater stabilization pond, Horizontal roughing filter, Nitrate, Phosphate, Chemical oxygen demand