Methods for treating produced water to remove boron and ammonia

A method of treating produced water produced from an oil or gas well, comprising:

• a. recovering the produced water comprising a mixture of water, oil, solid particulates and dissolved solids from a well extending into a subterranean formation;
• b. pretreating the produced water to remove a portion of the oil and solid particulates therefrom, to produce a clarified water having a turbidity of no more than 0.5 NTU units, an oil content of at most 5 ppm, solid particulates that are at most 5 μm in size, a boron content of greater than 25 mg/L, and an ammonia content of greater than 10 mg/L;
• and
• c. removing boron content and ammonia content from the clarified water using a first reverse osmosis membrane module and a second reverse osmosis membrane module to form purified water;
• wherein:
• the clarified water is passed through one of the first or second reverse osmosis membrane modules at a first pH from such that the boron content is reduced to less than 5% of the boron content of the clarified water;
• and
• the clarified water is passed through one of the first or second reverse osmosis membrane modules at a second pH such that the ammonia content is reduced to less than 5% the ammonia content of the clarified water.