Reducing the specific energy consumption of 1st-pass SWRO by application of high-flux membranes fed with high-pH, decarbonated seawater.

A new operational approach is presented, which has the potential to substantially cut down on the energy and cost demand associated with seawater reverse osmosis (SWRO) desalination, without changing the currently-installed infrastructure. The approach comprises acidification/decarbonation of the feed seawater followed by high-pH single RO pass using high-flux membranes. Since the limitation imposed by CaCO3(s) precipitation is overcome, the recovery ratio can be significantly increased. This work presents a new operational concept aimed at maximizing the benefits that can be obtained from new low-energy RO membranes available on the market. Results obtained from operating a pilot RO system revealed that following an acidification and decarbonation step, recovery ratio of 56% could be practically attained, along with effluent TDS and boron concentrations of 375 and 0.3 mg/l, respectively (feed water pH was adjusted to pH9.53 following the decarbonation step). The specific energy consumption (SEC) of this operation was calculated to be 5%-10% lower than the SEC typically associated with "conventional" SWRO operation. Two further scenarios were theoretically considered, under which the limiting operational parameter became Mg(OH)2(s) and BaSO4(s) precipitation. It was concluded that despite the fact that higher recovery ratios could be obtained, the high pressure required in these scenarios made them less appealing from both the SEC and cost standpoints. The normalized cost of the suggested approach was found to be ∼$0.07 ± 0.02/m(3) cheaper than the currently-practiced SWRO approach for obtaining product water characterized by TDS < 500 and B < 0.5 mg/l.

A new algorithm for design, operation and cost assessment of struvite (MgNH4PO4) precipitation processes.

Deliberate struvite (MgNH4PO4) precipitation from wastewater streams has been the topic of extensive research in the last two decades and is expected to gather worldwide momentum in the near future as a P-reuse technique. A wide range of operational alternatives has been reported for struvite precipitation, including the application of various Mg(II) sources, two pH elevation techniques and several Mg:P ratios and pH values. The choice of each operational parameter within the struvite precipitation process affects process efficiency, the overall cost and also the choice of other operational parameters. Thus, a comprehensive simulation program that takes all these parameters into account is essential for process design. This paper introduces a systematic decision-supporting tool which accepts a wide range of possible operational parameters, including unconventional Mg(II) sources (i.e. seawater and seawater nanofiltration brines). The study is supplied with a free-of-charge computerized tool (http://tx.technion.ac.il/~agrengn/agr/Struvite_Program.zip) which links two computer platforms (Python and PHREEQC) for executing thermodynamic calculations according to predefined kinetic considerations. The model can be (inter alia) used for optimizing the struvite-fluidized bed reactor process operation with respect to P removal efficiency, struvite purity and economic feasibility of the chosen alternative. The paper describes the algorithm and its underlying assumptions, and shows results (i.e. effluent water quality, cost breakdown and P removal efficiency) of several case studies consisting of typical wastewaters treated at various operational conditions.

Accurate approach for determining fresh-water carbonate (H2CO3(*)) alkalinity, using a single H3PO4 titration point.

A new, simple and accurate method is introduced for determining H(2)CO(3)(*) alkalinity in fresh waters dominated by the carbonate weak-acid system. The method relies on a single H(3)PO(4) dosage and two pH readings (acidic pH value target: pH~4.0). The computation algorithm is based on the concept that the overall alkalinity mass of a solution does not change upon the addition of a non-proton-accepting species. The accuracy of the new method was assessed batch-wise with both synthetic and actual tap waters and the results were compared to those obtained from two widely used alkalinity analysis methods (titration to pH~4.5 and the Gran titration method). The experimental results, which were deliberately obtained with simple laboratory equipment (glass buret, general-purpose pH electrode, magnetic stirrer) proved the method to be as accurate as the conventional methods at a wide range of alkalinity values (20-400 mg L(-1) as CaCO(3)). Analysis of the relative error attained in the proposed method as a function of the target (acidic) pH showed that at the range 4.0

A new post-treatment process for attaining Ca2+, Mg2+, SO42- and alkalinity criteria in desalinated water.

A novel post-treatment approach for desalinated water, aimed at supplying a balanced concentration of alkalinity, Ca(2+), Mg(2+) and SO(4)(2-), is introduced. The process is based on replacing excess Ca(2+) ions generated in the common H(2)SO(4)-based calcite dissolution post-treatment process with Mg(2+) ions originating from seawater. In the first step, Mg(2+) ions are separated from seawater by means of a specific ion exchange resin that has high affinity toward divalent cations (Mg(2+) and Ca(2+)) and an extremely low affinity toward monovalent cations (namely Na(+) and K(+)). In the second step, the Mg(2+)-loaded resin is contacted with the effluent of the calcite dissolution reactor and Mg(2+) and Ca(2+) are exchanged. Consequently, the excess Ca(2+) concentration in the water decreases while the Mg(2+) concentration increases. The process is stopped at a predetermined Ca(2+) to Mg(2+) ratio. All water streams used in the process are internal and form a part of the desalination plant sequence, regardless of the additional ion exchange component. The proposed process allows for the supply of cheap Mg(2+) ions, while at the same time enables the application of the cheap H(2)SO(4)-based calcite dissolution process, thus resulting in higher quality water at a cost-effective price. A case study is presented in which additional cost of supplying a Mg(2+) concentration of 12mg/L using the process is estimated at $0.004/m(3) product water.