The dissolved organic nitrogen (DON) portion of effluent total nitrogen species is of increasing concern because of increasingly tighter effluent nitrogen limits. The predominantly low molecular weight DON in wastewater effluents indicates the difficulty of removing this material. Overall DON increases with passage through biological treatment. The type of biological treatment affects the effluent DON concentration. Conditions during treatment, such as startup and upset conditions, can increase effluent DON. Of the various methods for DON removal, granular activated carbon, reverse osmosis, and soil-aquifer treatment appear to be the most effective. Much of the effluent DON comprises humic-like material which suggests that part of the DON can be removed by enhanced coagulation. The amount of DON removed by enhanced coagulation depends on the initial DON concentration. In general, final DON concentrations are approximately 69% the initial DON concentration. Adjusting pH to an optimal value maximizes DON removal by enhanced coagulation.