Teknik för förbättrad kväverening i Sverige – Resultat av landsomfattande enkätundersökning / Methods for improved nitrogen removal in Sweden – results from a questionnaire survey
Käppala wastewater treatment plant (WWTP) in Lidingö, Sweden, treats sewage from 520 000 pe in the north east part of Stockholm. The Käppala association has done an investigation in cooperation with KTH about different methods to improve nitrogen removal. The main techniques in focus were addition of external or internal
organic carbon and separate treatment of supernatant from dewatering of sludge. In order to investigate Swedish full-scale experiences and tactics in improving nitrogen removal two questionnaires were sent to all municipalities in Sweden and were focussed on WWTPs that have requirements to remove nitrogen and have loadings over 15 000 pe. Results from the questionnaires showed that the majority of WWTPs (48 out of 66 that have a loading over 15 000 pe) remove nitrogen with traditional activated sludge processes. To improve their nitrogen removal processes 16 WWTPs have separate supernatant treatment, 25 add external carbon and 7 use internal carbon source from hydrolysis of sludge. Internal or external carbon is added for both treatment of wastewater and supernatant. The most common method to treat supernatant is in a Sequential Batch Reactor (SBR). Results also showed operating strategies and advantages and disadvantages of different methods for improved nitrogen removal. Furthermore, possible control strategies are presented as well as removal efficiency of chosen techniques.