Evaluation of N2O emissions of MABR treating SDE

Abstract

Anaerobic digestion is commonly used on bigger wastewater treatment plants to transform organic matters of surplus activated sludge into biogas to gain energy. The effluent from this anaerobe digestion is dewatering which results in a highly ammonium loaded effluent called sludge dewatering effluent (SDE). It is said, that the amount of ammonium in SDE contributes up to 25% of the nitrogen load of a wastewater treatment plant (Meyer et al., 2004). The emission of the greenhouse gas nitrous oxide (N2O) at wastewater treatment plants is gaining attention over the last years. N2O is a byproduct in the process of converting ammonium to nitrite (nitritation) and denitrification, therefore the treating of highly ammonium loaded wastewater such as SDE has a high potential for emitting N2O. A new concept for treating SDE in the side stream before recycling the stream into the main stream basin was introduced, which leads to a reduction of the energy costs for aeration (Krampe et al., 2016). One possible way to achieve nitritation of SDE in side stream is a membrane aerated biofilm reactor (MABR), which is investigated in this thesis. Therefore, SDE from a municipal wastewater treatment plant was treated over 98 days in a lab scale MABR, focusing on the ammonium removal rate, the nitritation rate as well as the N2O emissions during the process. At the end of the process time an ammonium removal rate of 12.8gNH4-N/m²/d was achieved while the N2O emissions of the plant was 1.7%N2O-N/ NH4-Nconv.