On-site nitrogen recovery from urine

Funding

The project Novaquatis (www.novaquatis.ch) received the swiss-academies award for transdisciplinary research 2008 for its visionary, innovative and integrative approach in urban water management. The prize money from td-net, donated by Stiftung Mercator Schweiz, is to be used for a follow-up project, which is described below.

Summary of Novaquatis follow-up project

With raising energy prices, nitrogen recycling gains importance and straightforward technologies are needed, e.g. for emerging countries. Several simple process engineering technologies for recycling nitrogen from urine exist, but are unsustainable due to high consumption of chemicals. As an example, precipitation of nitrogen with phosphorus and magnesium is technically simple, but extremely unsustainable due to high phosphorus consumption. However, the resulting product, Magnesium Ammonium Phosphate (MAP) would allow recovering nitrogen by ammonia stripping and recycling magnesium phosphate back into industry. This is a technically tempting process, but extremely high recycling rates are needed to avoid wasting phosphorus. Similarly uncomplicated technologies are acidification or on-site nitrogen stripping followed by evaporation.

These technologies are only interesting if one considers large-scale industrial processes for regenerating chemicals (e.g. magnesium phosphate) and/or further processing of products (e.g. acid-trapped nitrogen) and/or energy cascading. One aim of the td-net follow-up project is to assess the material and energy fluxes arising from such on-site processes and identify the necessary industrial processes for regeneration of chemicals. The environmental benefits and shortcomings of all technologies will be quantified and potential environmental tradeoffs (e.g. the impact of energy-consumption versus that of resource use) will be revealed.

A second aim is to identify industrial stakeholders and elicit their objectives and preferences using Multi-criteria decision analysis (MCDA). This methodology is a participatory stakeholder process that helps structuring difficult decision problems. The outcome is a transparent ranking of the different technical-industrial options for nitrogen recovery from urine, based on the stakeholders’ points of view.

Contacts

tove.larsen@eawag.ch; judit.lienert@eawag.ch

Cooperation partner

Prof. Dr. Stefanie Hellweg, ETH Zürich, Institute of Environmental Engineering