In this phase we will examine the possibility of material recovery from byproducts generated with the previous energy recovery of different sludge produced by wastewater treatment plants of the tanning district or from other types of waste.
Kind of byproducts:
- sulphate solutions or sulfur suspensions resulting from the desulphurisation of biogas;
- ash (non-gaseous residue) resulting from the test of pyro-gasification;
- digestate resulting from the phase of anaerobic digestion.
It is obvious as the theme to be addressed is rather heterogeneous due to the fact that:
- In the first two cases, we have to consider products at "end of life" (so the research aims to identify ways of processing to give at the material a commercial value or minimize the costs for disposal).
- For the third case, the process of materials recovery provide an alternative to the recovery of energy from digestate by pyro-gasification.
With reference to the last by-product, we need to address a problem that has a strategic value far more important in the context of the whole project.
A first detail that needs to be addressed by this objective, relates the matrices to investigate that will have predictably different features depending on the conditions of the treated waste and/or process conditions in the early stages of energy recovery from which they derived.
A key aspect is therefore to study these qualitative and quantitative variations and correlate themselves both to the conditions of the origin processes, and the possible consequences that these changes may have on the subsequent processes of material recovery.
This analysis is particularly important for the digestate, which will have reasonably quantitative and qualitative characteristics quite different, depending on the rate of degradation achieved by the anaerobic digestion.
From this detailed analysis could be that some materials, systematically, or as a result of specific operating conditions of energy recovery processes, may not have characteristics suitable for recycling.
The knowledge of these limiting factors, in addition to being element of feedback for the objective 2, to direct the management of energy recovery on pathways that produce waste more compatible with the next stage of the material recovery, may lead to consider the need/opportunity of pre-treatment of the materials prior to initiating the experimentation on the recovery of the same material.
To develop adequately this critique analysis on the characteristics of the input materials in the different processes of material recovery assumed in the project:
- Recovery of metals
- Ash stabilization
- Fertilizer production
- Production of filler
- Composting
- In this way will need to investigate what are the factors that may affect the different mentioned processes.
Before the experimentation of the various conceivable solutions, on a pilot scale, it will be important to perform a series of exploratory tests can simulate the materials that will be generated in reality only by the development of the experimental specific energy recovery.
It is therefore expected to use:
- replacing the suspension of sulfur (from desulfurization): suspension of sulfur prepared in the laboratory in substitution of the ashes from pyro-gasification;
- samples of ashes obtained by treatment in a furnace at 450 ° C of samples of sludge, organic waste or mixtures of the same (determination of the "ash" second classical analytic method) in place of bio-digestate;
- samples of sludge as such or in mixtures with other organic waste finely ground and possibly conditioned at different levels of residual moisture.
Through this series of tests will be possible, preventively and not waiting for the real samples, have some important information on critical materials, conditions and process management, as well as information on the type of the tests and experimental protocols to be adopted.
The experimental activity on the pilot plant for recovery of materials, will be designed on the basis of experience gained from preliminary laboratory tests through techniques Experimental Design (DoE) to carry out tests with the highest level of information. The type of work carried out in this phase is very innovative and as already shown in the previous operational objective.