اثرات زیست محیطی بازیافت فسفر از فاضلاب شهری
Abstract
1- Introduction
2- Materials and methods
3- Results
4- Discussion
5- Conclusions
References
Abstract
Phosphorus mining from phosphate rock is associated with economic as well as environmental concerns. Through phosphorus recovery from municipal wastewater, countries could decrease their dependency on the global phosphate rock market, however, conceivably leading to an increase in environmental impacts from fertilizer production. In this work 18 phosphorus recovery technologies are evaluated in terms of cumulative energy demand, global warming potential and acidification potential with the methodology of life cycle analysis. These indicators are then contrasted with other environmental criteria, i.e. recovery potential, heavy metal and organic micropollutant decontamination potential and fertilizer efficiency, to determine their overall environmental performance. The LCA shows that a broad spectrum of changes in gaseous emissions and energy demand can be expected through the implementation of P recovery from wastewater. Linkage to further environmental performance results exposes certain trade-offs for the different technologies. Recovery from the liquid phase has mostly positive or comparably little impacts on emissions and energy demand but the low recovery potential contradicts the demand for efficient recycling rates. For recovery from sewage sludge, those technologies that already are or are close to being applied full-scale, are associated with comparatively high emissions and energy demand. Recovery from sewage sludge ash shows varying results, partly revealing trade-offs between heavy metal decontamination, emissions and energy demand. Nevertheless, recovery from ash is correlated with the highest potential for an efficient recycling of phosphorus. Further research should include implications of local infrastructures and legal frameworks to determine economically and environmentally optimised P recovery and recycling concepts.
Introduction
Phosphorus (P), as an essential nutrient for all life, takes on a substantial and non-replaceable role in our environment. Nevertheless, current P use practices are accompanied by various environmental concerns, as mining of P from raw phosphate rock (PR) leads to emissions to the air and eutrophication of water bodies, land degradation through phosphogypsum stacks near the mining site (phosphoric acid production) and soil contamination through cadmium (Cd) and uranium (U) application with fertilizers (FEI, 2000; Silva and Kulay, 2003, 2005; Spiegel et al., 2003; Smidt et al., 2012; Hakkou et al., 2016; Kratz and Schnug, 2016). While these environmental concerns cannot be neglected, it were economic concerns, i.e. the increasing awareness of the concentrated PR-mining in only a handful of countries worldwide, the overall increasing demand for P and the fact that PR is a nonrenewable resource, that led the European Commission to declare PR as a critical raw material in 2014 (EC, 2014). Simultaneously, research, governments and industry recognised the importance of another, for the major part unexploited P source: municipal wastewater. Municipal wastewater has the potential to substitute a significant portion of the demand for PR (Binder et al., 2009; Egle et al., 2014; Zoboli et al., 2016a,b) and therefore to increase circular economy while simultaneously reducing overall environmental impacts from current P use practices. Intensive research and innovation in recent years has led to the development of a broad spectrum of technologies for phosphorus recovery from wastewater. Their development was accompanied by comparative studies, dealing mainly with the technical and economic assessment of these technologies, in order to identify those that are technically applicable and can be considered market-feasible alternatives to PR-mining and conventional fertilizer production (Cornel and Schaum, 2009; LfU, 2015; Fux et al., 2015; Egle et al., 2015, 2016; Nättorp et al., 2017). However, to provide a more comprehensive picture for legislators dealing with how future P-recycling can be best put into action, knowledge as to how different technologies could impact the environment is an additional prerequisite.