efficiency of horizontal roughing filter in removing nitrate, phosphate and chemical oxygen demand from effluent of waste stabilization pond

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.