CCD series no-17: application of the BWRO-CCD technology for high-recovery low-energy desalination of domestic effluents

Abstract

Gigantic amounts of potable water for domestic and industrial consumption end up in sewage treatment centers worldwide and then disposed except in few isolated cases where such clean domestic effluents are reused on large scale for irrigation (e.g. Israel) or for potable water production after RO desalination (e.g. Orange County, California, US and Singapore). The declined availability of fresh water due to increased deterioration of ground and surface water as well as climate changes will ultimately dictate the large scale use of “NEWater” derived from treated (MF and RO) clean domestic effluents for all common applications. The present study describes the application of the newly emerging BWRO-CCD technology for high-recovery low-energy desalination of clean domestic effluents with the ME4 (E = ESPA2-MAX) pilot unit comprising ordinary size (8′′) elements. The pilot was located in the SHAFDAN sewage treatment center in Israel and received feed of clean domestic effluents in the salinity range of 628–857 ppm (1,100–1,500 μS/cm) after pretreatment with multimedia and ultrafiltration units. The pilot unit was operated in the flux range of 17.5–27.5 lmh and the volumetric recovery range of 85–90% with emphasis placed on 90% recovery. The specific energy of desalination of the variable salinity SHAFDAN feed source with 90% recovery is found in the normalized range of 0.329–0.538 kWh/m³ with lower salinity feed and flux associated with the lower energies—the term normalized is used in the context of 25°C temperature and pumps efficiencies of 75% for high-pressure pump (HP), 65% for circulation pump (CP), and 55% for HP booster (HPB). The TDS of permeates from the desalination of the variable salinity SHAFDAN feed source with 90% recovery is found in the temperature normalized (25°C) range of 40–56 ppm (80–116 μS/cm) with lower TDS of permeates associated with the lower feed salinity, lower recovery level, and higher flux ranges. BWRO-CCD is a modular technology of high-recovery and low-energy performance irrespective of the number of elements per module, and the performance characteristics revealed hereinabove for the single module pilot of four elements should be same for plants of many such modules with their inlet and outlet connected in parallel to the closed circuit, except for productivity which is a function of the number of modules. The BWRO-CCD technology can apply to large-scale desalination of clean domestic effluents with projected performance analogous to that described for the pilot.

Keywords:

• CCD
• BWRO
• RO of clean domestic effluents
• high recovery
• low energy
• reduced fouling
• “NEWater”

Acknowledgments

The granting of permission by Mekorot (Israel) to operate in its SHAFDAN experimental center facility and funds to Desalitech Ltd. by AQUAGRO FUND L.P. (Israel) and by Liberation Capital LLC (USA) are gratefully acknowledged.