This invention relates to a wastewater treatment process for treating nitrogen-deficient wastewater. The process enables the production of a low soluble nitrogen processed wastewater, and avoids the need for nitrogen supplementation in the wastewater treatment process. The process includes providing a supply of nitrogen-deficient wastewater to a controlled environment. The conditions in the controlled environment encourage the proliferation of nitrogen-fixing microorganisms in particular by control of the stability of the dissolved oxygen level. This process may be used alone or in conjunction with a conventional wastewater treatment process, relying on non-nitrogen-fixing microorganisms, without the need for nitrogen supplementation.