A method reuses produced water resulting from a fossil fuel extraction operation. The method includes providing the produced water as an input to an electrodialysis system. The method also includes running the electrodialysis system to produce a diluate and a concentrate. The diluate is contaminated so as to have a conductivity of no less than 0.1 Siemens/meter. The method also includes reformulating the diluate to produce fossil fuel extraction fluid. The method also includes using the produced fossil fuel extraction fluid in the fossil fuel extraction operation. An electrodialysis system includes first and second stacks. The electrodialysis system also includes first and second voltage sources, coupled to the first and second stacks, so as to apply a first voltage to the first stack lower by at least about 10% than a second voltage to the second stack.

Water treatment systems including electrically-driven and pressure-driven separation apparatus configured to produce a first treated water suitable for use as irrigation water and a second treated water suitable for use as potable water from brackish water and methods of operation of same.

A method reuses produced water resulting from a fossil fuel extraction operation. The method includes providing the produced water as an input to an electrodialysis system. The method also includes running the electrodialysis system to produce a diluate and a concentrate. The diluate is contaminated so as to have a conductivity of no less than 0.1 Siemens/meter. The method also includes reformulating the diluate to produce fossil fuel extraction fluid. The method also includes using the produced fossil fuel extraction fluid in the fossil fuel extraction operation. An electrodialysis system includes first and second stacks. The electrodialysis system also includes first and second voltage sources, coupled to the first and second stacks, so as to apply a first voltage to the first stack lower by at least about 10% than a second voltage to the second stack.

Water treatment systems including electrically-driven and pressure-driven separation apparatus configured to produce a first treated water suitable for use as irrigation water and a second treated water suitable for use as potable water from one of brackish water and seawater and methods of operation of same.

Water treatment systems including electrically-driven and pressure-driven separation apparatus configured to produce a first treated water suitable for use as irrigation water and a second treated water suitable for use as potable water from brackish or saline water and methods of operation of same.

Systems and methods are provided for processing metal sulfate compounds and sequestering CO.sub.2. These systems and processes involve one or more electrochemical cells for producing an alkali-containing catholyte and involve a CO.sub.2 absorption reactor operatively connected to the electrochemical cell and to a CO.sub.2 source. The CO.sub.2 absorption reactor receives the alkali-containing catholyte and CO.sub.2 gas for forming an alkaline carbonate solution. The alkaline carbonate solution is directed to a vessel where it reacts with an acidic sulfate solution comprising metal ions resulting in precipitation of solid metal carbonate compounds. The acidic sulfate solution may comprise sulfide leachates from acid mine drainage, sulfide mine tailings and/or reacted pyrite concentrate. The acidic sulfate solution may be circulated through an optional SO.sub.2 reduction reactor prior to reaction in the vessel. The SO.sub.2 reduction reactor reduces trivalent metal compounds present in the acidic sulfate solution to divalent metal compounds.