Investigating intake system effectiveness with emphasis on a self-jetting well-point (SJWP) beachwell system

Abstract

A well-designed subsurface SWRO intake not only yields good quality feed that requires none or a minimum of pretreatment, but also when used instead of surface type intake results in a significant saving in plant captital investment and in cost of plant O&M. An SJWP subsurface intake system was tested at the SWCC Al-Jubail site, on-shore, at the high-tide seawater line and mid-tide point at depths of 3.5 m, 3.5 m, and 4.5 m, respectively. The project objective is to investigate the suitability of this relatively new subsurface SJWP as an intake for some SWRO plants. The best SDI values with an average of SDI ave = 2.9, which compares reasonably well with SDI ave = 2.6±0.2 for conventionally pretreated surface seawater feed, were obtained when the well-points were fixed at sea mid-tide point at depth of 4.5m. The filtrate TDS, total hardness and pH values were lesser than those of seawater indicating mixing of seawater with underground or surface water. At zero incubation time, bacteria count was in the range of 5×10 2 to 4×10 3 colony forming units (CFU), but high after-growth rates and short bacteria generation time were observed in the SJWP pretreated feed after 24 and 72 h of incubation. Based on SDI measurements, as well as on other physical and chemical measurements, a good quality SWRO feed can be derived from subsurface well-point beachwells located on a clean non-polluted site, which is expected to diminish the high after-growth rate and short generation time of bacteria found in the present case. Accurate information on this point can be established by testing the effect on SWRO membrane performance of feed derived from the SJWP beachwell located on a clean non-polluted site which is to be conducted under Part 2 of this program.