SIMPLE BACKWASHING SYSTEM FOR A LOCALLY-DEVELOPED SCREEN FILTER

Abstract

Experiments were carried out in the Agricultural Engineering Department (Hydurlic Lab., Fac. of Agric., Ain Shams University), to design and test a simple backwashing system for a locally manufactured screen filter to be used in micro irrigation system. The important affecting engineering and hydurlic factors, to design the screen filter with backwashing were determined and tested to get the proper dimensions for the developed filter, and to get the maximum backwashing efficiency, reduce water used in filter backwashing and conserve maximum operating irrigation time. The main results are summarized as follows: Maxima backwashing efficiencies of about (90-95%) were observed with the following cases: By using 6 nozzles per rotating backwashing arm. By using 6 nozzles/rotating arm at 300 kPa pressure, and backwashing time 120 sec., due to, the distribution uniformity of spray from nozzles on the rotating arm along projected area on the screen filter, and proper rotation velocity of the arm. At nozzle clearance to the filter screen of 62.45 mm, by using 6 nozzles/rotating arm, and backwashing pressure of 300 kPa. At 60° water cone angle from nozzle, by using 6 nozzles/rotating arm at backwashing operating pressure of 300 kPa. An increase of 26.3% in filter backwashing efficiency (from 70 to about 95 %) was obtained by raising backwashing pressure from 150 to 300 kPa. The developed filter required backwashing when pressure drop reaches to 55 kPa, every about 80m3/cycle. After backwashing cycle, the developed filter is ready for recommended operation condition (pressure drop through the filter, 18kPa). The pressure drop through the developed filter after backwashing decreased from 25 to 18 kPa, (46%), without and with using proposed designed backwashing resp. Consumptive water use during backwashing cycle was decreased from 1.5 to 0.65 m3/cycle, (28%), without and with using the proposed designed backwashing system, resp. Backwashing efficiency for the developed filter, increased from 65% to 95% i.e. (31.6%), without and with using proposed designed backwashing system resp.