The Horizontal Roughing Filtration (HRF) has been developed as a proper pretreatment for Slow Sand Filtration during 20thi century. In some cases it was used for iron and manganese removal from ground water resources. The performance of this kind of filters was improved, by a limited dose of coagulant agents like iron or aluminum salts during the two last decades of 20th , and named as Direct Horizontal Roughing Filtration (DHRF). This kind of filters with a simple design, construction, operation and maintenance and using natural filter media, without any complicated mechanical parts, are classified as Low Cost Treatment Methods and used for villages and. small communities.The main problem in operation and maintenance of HRF and DHRF is the weak cleaning performance with conventional hydraulic washing methods.
The main targets of this research study were:
I. Evaluation of the effects of the hopper shaped under drain compartments on head loss control and development of sediment washout efficiency, regarding the increasing of washing velocity and shear stress through the porous filling media.
2. Evaluation of the effects of air application on the cleaning efficiency of DHRF system during the hydraulic washing process.
The results of this study in comparison with the reports presented by other researchers show that, with preparing hopper shaped compartment, at the bottom of the filter box, it acts as the sediment accumulation zone, and with continuous deposit removal, the head loss development during a filter run would be controlled, as well as, it causes a very good improvement in washing performance and cleaning efficiency. The results of pilot study with a maximum run time of one week between two washing applications, show that with a filtration rate up to 5.6 m/h, the head loss was less than 3 centimeters and maximum accumulation of deposits on the filter media was 2% in weight. The results of air application in pulses during the washing process causes a reduction in deposit accumulation rate form 18% up to 24% in different compartments of pilot filter in DHRF conditions.
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