Abstract:
Using oxidation ponds for polishing the effluent from the secondary treatment usually face theproblems of high algae contents which results to the increase of organic and turbidity in thereceiving water.In this research, the performance of the two-stage horizontal-flow roughing filtration (HRF) wasstudied in order to remove the algae and reduce the turbidity. In the first-stage, two types ofcoininercial plastic media, that were 240 m2/m3( SBM) and 105 ~*/I~"BBMa)n d in second-stage.small gravel size 2-6 mm. were applied. The variable factor in this study was flow velocity.The results showed that under flow velocity of 0.3 mh, the average algae reinoval efficiency of 89percent froin SBM was better than that of 84 percent from BBM. The turbidity removal efficiencieswere 64 and 58 percent, in SBM and BBM respectively. The algae removal efficiencies increased to91 and 86 percent and turbidity removal efficiencies increased to 66 and 62 percent, when passedtbrough secondary stage of small gravel filter for SBM and BBM respectively. The results alsoshowed that after the flow increased from 0.3 m/h to 1.0 m/h in SBM, the average algae andturbidity removal efficiencies reduced to 59 and 63 percent, respectively when influent algae werein the range of 35 to 143 pg/l. The overall average efficiencies of algae and turbidity removal intwo-stage HRF were 65 and 70 percent, respectively. The results also showed that after the flowincreased from 0.3 m/h to 2.0 m/h the average algae and turbidity removal efficiencies reduced ro41 and 64 percent, respectively when influent algae were in the range of 30 to 327 pg/l. The overallaverage efficiencies of algae and turbidity rc~noval in two-stage HKF were 50 and 70 percent.respectively. The dissolved oxygen (DO) in the effluent of evely run was over 2 mg/l and CODefficiency was average to 30 percent in each run.