Källsorterade systems påverkan på avloppsreningsverk : växthusgaser, energi- och resursanvändning i modellstudie

Sammanfattning: The aim of this study was to evaluate the effects on a simulated wastewater plant regarding GHG emissions and use of energy and resources when implementing source separated wastewater systems. The effects were studied for different restrictions of effluent quality and for different temperatures on the influent. The simulation model BSM2G calibrated for Käppala wastewater treatment plant was used. The task was executed by simulating nine different scenarios with an increase in influent load from new connections equivalent to 3, 10 and 30 % of the present connections. These new connections were served by conventional, urine separated or black water separated systems. All simulations were adjusted to keep the initial effluent load i.e. the effluent load before the number of connections increased. This meant increasing restrictions on effluent load of ammonium and total nitrogen, which were reached by adjusting control parameters such as aeration, internal recycle flow, carbon addition etc. Thus the same effluent load of ammonium and total nitrogen were reached for all scenarios compared to the reference. The simulated results showed that the total use of energy (most evident the aeration energy) decreased with 25-60 % with urine separation and with 50-90 % with black water separation compared to corresponding conventional scenario regardless of degree of new connections and contigous adjustment of control parameters. The same tendency applied for use of resources since total operational cost index decreased with 30-70 % with urin separation and 70-90 % with black water separation compared to corresponding conventional scenario regardless of degree of new connections and contigous adjustment of control parameters. Total production of sewage sludge decreased with 5-20 % with urine separation and with 50-60 % with black water separation. Total methane production decreased with 0-20 % with urine separation and with 60-70 % with black water separation. The total GHG emissions from the simulated WWTP was dominated by uncertain N2O emissions from the activated sludge process for all scenarios. Also emissons of N2O due to sludge management were uncertain. Since the production of N2O varied heavily depending on the adjusted control parameters no certain conclusions could be drawn regarding the impact of source separation on these emissions. Other greenhouse gas emissions, such as carbon dioxide emissions due to use of energy, production and degadation of external carbon source were decreased in the source separated scenarios compared to conventional scenarios. The simulated results also showed that a lower temperature of the wastewater led to a decrease in nitrogen removal and an increase in use of energy for all scenarios at 30 % increased influent load compared to a wastewater of average yearly temperature. The results confirmed some of the previously stated advantages of source separated wastewater and thus contributed to increased probability of these advantages. However, further studies are needed to obtain more certain results regarding N2O emissions from wastewater treatment plants when source separated wastewater is implemented.