Urine separation as part of a real-time control strategy

Considering wastewater from household sources, urine accounts for approximately 80% of the ammonia loads but for only 1% of the hydraulic load. Where classical urine separation deals with the separation and subsequent removal of urine from the wastewater stream, the method promoted here (urine separation for waste design) aims to (1) separate urine from the wastewater stream, (2) store it at the household and (3) release it in a controlled manner into the drainage system. The ultimate goal is on the one hand to average the daily dynamics in the ammonia load to the wastewater treatment plant (WWTP) and on the other hand to reduce ammonia emissions towards receiving waters. All process steps from urine production, separation, harvesting and controlled release of urine have been modelled on a micro-level where all toilets in the system are balanced separately. As a case study the integrated urban drainage system of Vils/Reutte in Tyrol was used where a total of 11 different control strategies – ranging from simple to highly complex real-time control (RTC) applications – have been developed and tested. The evaluation (taking into account both aims as expressed above) showed that the simplest RTC applications are the most effective. The optimal performance achieved in the case study resulted in an ammonia reduction of 62% (load based) compared to the status quo. As such a method would require considerable systems changes, an incremental implementation of associated improvements were also tested in this work. An important outcome was that a large proportion of the final improvement is gained already with the first 25% of installed separation toilets.