A novel approach for SWRO desalination plants operation, comprising single pass boron removal and reuse of CO2 in the post treatment step

A different approach is presented for the operation of seawater RO desalination plants in which the boron concentration in the product water should not exceed 0.3 mgB/l. The approach is based on strong acid (either H2SO4 or HCl) dosage to the feed water to attain pH ∼ 4.3, followed by CO2 stripping and subsequently strong base addition to pH 9.00–9.25. At this high pH range, a high B removal efficiency is attained, and since the water is practically devoid of carbonate species, no CaCO3(s) scaling takes place, and pH elevation is limited by Mg(OH)2(s) precipitation, expected only at pH > 9.45. The approach enables operation in the absence of antiscalants. Furthermore, CO2 stripping is effected in stripping towers in two steps: the high CO2(aq) concentration is first stripped by vacuum-operated stripping towers and the CO2-rich air is used for dissolution of calcite in the post treatment stage. The remaining CO2 mass is stripped to the atmosphere using blower-assisted stripping towers. This paper aims at introducing the new concept and providing “proof of concept”. The paper addresses experimental and theoretical aspects of the proposed process, as well as engineering and economic evaluation. The proposed approach is shown to be both technically feasible and cost effective, as compared with conventional boron removal alternatives.

► A new design approach is presented for removal of boron within SWRO operation. ► Low B is attained by elevating feedwater pH, in one RO stage, without antiscalants. ► CaCO3 scaling is avoided by removing inorganic carbon from feed by acid stripping. ► CO2 from feedwater is reused for calcite dissolution in the post-treatment step.