Modelling and sustainability evaluation of optimal designs for decentralized urban wastewater treatment

Abstract

Decentralized solutions are becoming increasingly favourable in urban wastewater management, provided they can meet regulatory effluent limits and overcome the unique challenges of the urban environment (e.g. emerging contaminants (ECs) treatment, limited land availability). Equally important is the need for such solutions to be sustainable throughout their service life in terms of financial obligation and environmental burden. In sight of this, this work has sought to advance a packaged integrated fixed-film activated sludge (IFAS) technology into a sustainable solution for the treatment of urban wastewater following the completion of its trial phase. Possible sustainability gains have been considered in several areas. First, the sustainability of five tank materials are evaluated, finding stainless steel to incur the greatest costs while high density polyethylene is found to be the superior option. Second, six aeration strategies are compared using a developed index that encompasses the differences each will have on performance, favouring intermittent over continuous aeration. Third, using a developed process model, the IFAS is configured in different ways to target nitrogen removal by different pathways including conventional and simultaneous nitrification denitrification. The optimum design and operational settings are identified to maximize nitrogen removal in both cases. The sustainability of these different configurations are then assessed using the developed index, identifying the conventional approach (separate aeration and anoxic zones) to be the most sustainable due to the greater treatment performance outweighing its higher costs. Finally, in consideration of incorporating EC removal into the decentralized system, the sustainability of three graphene-based adsorbent filters are assessed and contrasted against a pulsed power oxidation technology as an energy-centric alternative. At all breakthrough times greater than one day, the filters are found to be the more sustainable solution for the ECs removal.