Clear, Sweet, Fresh Water. And the Art of Recyling It
"Why Waste Water?" is the slogan proposed by the UN for World Water Day 2017. This question can be read at various levels: why do we waste water? Why don't we filter sewage before releasing in into the environment? Why don't we recycle valuable elements contained in wastewater? It is therefore an invitation to apply the paradigm of the circular economy to water services, especially those that involve wastewater treatment. From a circular point of view, water purification is no longer seen as an end-of-pipe solution to the problem of wastewater, but as a phase of a larger water cycle aimed at re-inserting purified water into the environment, favoring water reuse, and the recovery of materials and energy. The areas just described have been analyzed from technological, market, and regulatory perspectives.
The reuse of water, especially for irrigation purposes, does not pose any technological problems, and is widespread in Italy. Demand for purified water is increasing in particular where rainfall shortage is creating irrigation problems. From a regulatory point of view, the very stringent emission parameters for the reuse of filtered wastewater discourages some operators because of the huge investments that need to be put in place.
Energy recovery is mature from a technological perspective, in particular for the bio-gas and bio-methane produced from anaerobic fermentation of sewage sludge. There are also cases of wastewater being used in power systems based on heat pumps or in the production of electricity via micro-hydroelectric turbines. A lot of energy is needed to power water treatment plants themselves, though. Also, from a regulatory point of view, there are still uncertainties about the use of bio-methane in facilities outside the plant.
Lastly, there is the commercial exploitation of materials extracted from wastewater: sands, metals and minerals, nutrients, proteins, and so on. This is the area where research has yet to provide definitive answers. From a technological standpoint, there are pilot plants for the extraction of particular materials. It is necessary to understand the cost of building plants to extract the various materials, and when such cost will become economically competitive in relation to the availability of natural resources, in particular phosphorus. It is also necessary to verify whether current EU and national legislation enables the extraction of such materials.
At the EU level, the Commission's Circular Economy Package does not mention sewage sludge as a source of recyclable nutrients in the projected revision plan regulating the use of fertilizers. At the Italian level, the classification of purification byproducts as waste does not facilitate their valorization, deterring even the most enthusiastic operators. Finally, the limits on the reuse of water treatment drains for irrigation purposes are among the most stringent on the globe. Therefore, in order to stimulate a more sustainable management of water resources, it is necessary to rewrite the existing norms in order to encourage water recycling and reuse, while ensuring the protection of the environment and human health.