Abstract: Methods and systems for treating wastewater and process water streams are provided. In some embodiments, the wastewater and/or process water to be treated contains a target chemical (e.g., ammonia and/or ammonium). The methods and systems described herein may include recovering the target chemical from the water stream and/or producing a desired product (e.g., a fertilizer such as an ammonium salt) from the target chemical. In one set of embodiments, a method of treating wastewater and/or process water involves introducing the water stream into a system that includes a combination of two or more of, or all of, a reverse osmosis system, a reaction and separation system (e.g., a vacuum distillation system or other suitable separation system), and a membrane reactor system.