processes) have a higher investment cost and higher running costs due to the conversionover nitrate resulting in f5–10/kg N removed. For the physical/chemical techniques valuesof f 10–25/kg N removed were estimated. These values can change greatly if e.g. energy isfreely or at low cost available. Nevertheless the pretreatment necessary to remove carbon-ates in the physical processes contributes significantly to the price. ConclusionsTwo new concepts for the removal of nitrogen from wastewater have been developed inwhich a substantial reduction in the energy and chemical use is achieved. By the use of thecombined SHARON-Anammox process, the nitrogen removal will no longer require theinput of COD. The combined system can thus be operated independently. This makes itpossible to optimize the COD and nitrogen removal separately. The proposed concept hasbeen tested over a prolonged period showing a stable effluent, high ammonium removalwithout need for process control. Given the positive cost calculation a full-scale implemen-tation can be expected in the near future.AcknowledgementThe research on nitrogen conversion technology was financially supported by theFoundation of Applied Water Research (STOWA), the Foundation for Applied Sciences(STW), the Royal Academy of Arts and Sciences (KNAW), DSM Gist, Paques, andGrontmij consultants. We thank our colleagues for fruitful discussions and collaboration