Environmental Operating Solutions (EOSi) is a US-based provider of supplemental carbon sources, nutrient removal solutions and process control systems for municipal and industrial wastewater treatment. The company specializes in optimising biological treatment processes to remove nitrogen, phosphorus and other contaminants while improving operational efficiency and regulatory compliance. It has over 600 customer sites from a network of 20 manufacturing sites across the U.S.

Its MicroC® product range includes carbohydrate-, glycerol- and alcohol-based carbon sources used in denitrification, enhanced biological phosphorus removal and biochemical oxygen demand supplementation. EOSi also provides automated carbon dosing through its Nitrack® control platform and integrated Nitraskid-IQ™ systems, combining process monitoring, chemical feed control and engineering support.

EOSi is part of Axius Water, which was acquired by Oldcastle Infrastructure, a CRH company, in May 2026.