Abstract: An exemplary method of treating nitrogen-contaminated wastewaters, especially those with high ammonia concentrations, according to the invention includes the steps of ammonia degassing and recapture, and of nutrient assimilation with microalgae. Organic nitrogen, organic carbon, phosphorus, heavy metals and other compounds may also be removed in different embodiments of the invention. Examples of applicable wastewaters include landfill leachate, municipal solid waste anaerobic digester effluent, agricultural anaerobic digester effluent, municipal wastewaters, agricultural wastewaters, and other similarly contaminated wastewaters.