An investigation into side stream technologies as a potential solution for reducing nitrogen emissions from municipal waste waters in the Irish situation

Abstract

This study explicated the requirement to substantially increase the level of nutrient removal facilities at municipal waste water treatment plants on a national scale. This requirement has resulted from recently enacted legislation. The research then considered the options for realisation of these infrastructural improvements. Revolutionary methods of nitrogen reduction have been established and developed, which target nitrogen-rich side streams from sludge handling processes, for more sustainable nitrogen removal from the main process effluents. Dundalk WWTP was chosen as a case study site, to assess the viability of applying these new technologies in Ireland, and to provide comparison with conventional means. An evaluation o f the nitrogen mass balance at Dundalk showed that 45.7% of the main plant total nitrogen load is contained within the ammonium-rich recycle effluents, currently returned untreated to the headworks. Approximately 20% Total Nitrogen reduction is possible at this facility through side stream treatment application. Two options for side stream treatment were assessed; based on efficiency predictions, both systems would shift the operation of the B-stage treatment process at Dundalk from oxygen limited to ammonium limited, reducing the Total Nitrogen emissions to within acceptable limits. When compared against conventional biological nitrogen removal processes, applying a unitary operational cost driver, the cost of conventional treatment is significantly greater than the side stream options examined. Reduction of nitrogen in a side stream treatment process is more sustainable and energy efficient than nitrogen reduction in a conventional stream. This study demonstrated that certain side stream technologies exist, which can provide an economically viable option for the various Irish plants requiring such reduction in emissions, whilst reducing the carbon footprint of these facilities. For this reason, the potential use of side stream technology should be afforded due consideration on a national scale. Pilot plant installation in advance of full-scale implementation at Dundalk is recommended. An opportunity for further study also exists in determining the suitability of this technology for sustainable phosphorus removal from waste waters and for leachate pre-treatment.