The RecoPhos Project , with a running time of three years and recently concluded (February 2015), has investigated the technical, economical and environmental viability of a new process for phosphorus recovering from the ashes resulting from the mono-incineration of sewage sludge from urban wastewater. Its objective is the future industry-wide implementation in order to reduce Europe’s dependence on Phosphorus import, counteracting the depletion of natural sources. To that end, a consortium of several European universities and various companies from different countries have joined to design and build a small pilot plant, where experiments have been carried out with success in phosphorus recovering. INERCO belongs to that consortium and has participated in the works related to industrial safety and environment.
This project has been funded by from the 7th Framework Programme of the European Union (activity code: Eco- innovation), under the grant agreement nº 282856 (FP7-ENV-2011).
Although sewage sludge is often used in agriculture as fertilizers, the trend is toward the decrease of this practice, because of the high concentration of heavy metals and pathogens that can be harmful to health and the environment. In some countries this practice is restricted or not even allowed. The other current alternative treatment of the sludge is the incineration (mono-incineration or co-incineration), with the possibility in some cases of use the ash as raw material for other applications (mainly construction and fillings), or otherwise taking them to landfill . The ashes that result from the mono-incineration processes have significant contents of phosphorus so this valuable substance is lost in most current applications.
While many methods have recently been developed for recovering phosphorus from sludges or ashes after incineration, none has been carried out on an industrial level. The main reasons are the complexity, the costs and the low efficiencies achieved. Additionally, it must be pointed out that the thermo-reductive RecoPhos process can produce either elemental phosphorus or, after a process of oxidation and hydration, thermal phosphoric acid. This thermal approach makes this project unique compared to other researches focused on the fertilizer production.
The success of the RecoPhos Project and its potential implementation to industrial scale would prevent the loss of phosphorus from the ashes, offering alternatives to the current treatment. This recovery of Phosphorus also implies a reduction in European imports and a slowdown in the depletion of this natural resource.
From the point of view of the environmental impact and under the perspective of the life cycle, the RecoPhos Project would benefit from the positive effects from the substitution of conventional production processes of elemental Phosphorus or thermal phosphoric acid from rock phosphate and mineral extraction processes. Furthermore, there is additional space for important positive effects from the consideration of slag as a valuable by-product substituting clinker, given that it has shown excellent cementitious properties; as well as from the potential recovery of energy of the process.
Moreover, from the point of view of industrial safety, the design of the RecoPhos process has been revised for both, the small-scale plant as well as the pilot scale plant using advanced risk management tools. Specifically, we applied risk analysis methodologies such as checklists ‘What if?’, HAZOP Studies (HAZard and Operability) and SIL Studies (Safety Integrity Level), obtaining as result actions or measures to be implemented in the design in order to improve process safety and minimize the potential impact on people, the environment and facilities.
To finish the project and to show the results obtained, a demonstration event took place on the 24th February 2015 at the University of Leoben (Austria), which was attended by numerous participants from the industry, as well as by several administrations.