INNOVATIVE TREATMENT AND VALORISATION OF WASTE COMING FROM DIMENSIONAL STONES WORKING PLANTS: PIEDMONT SAMPLES

Residual sludge management, for waste material coming from dimensional stones working plants, is a discussed problem, object of legislative changes and potential application developments. The main problems related to their management are: their size distribution (fine materials, potentially asphyxial), the presence of heavy metals (due to the treatment with gangsaw with abrasive shot and diamond framsaw) and the presence of TPH (mainly due to oil machines losses). The residual sludge management, considered according the Legislative Decree 152/06, can be used, as waste, for environmental restoration (R10) or for cement plants (R5). But It is also possible to think about their systematic treatment in consortium plats, for the production of secondary raw materials (filler, etc..) or "New Products" (eg. artificial loam). The paper will report the results of a recent experimentation [AFIB working plant in Trino Vercellese – VC), to recovery such waste for the production of “artificial loam” (Bioremediation treatments (FORNARO & DINO, 2008; MEDINA ET AL., 2009)], basing on the first experimentations run out in Lodrino (CH) and in ACEA plant (Pinerolo – TO) [DINO ET AL. 2006]. During the experimentations a mix was produced, consisting of residual sludge, compost, natural loam, shredded green materials and nutrients. The components were designed to start up and accelerate the process of aerobic degradation, in order to transform the organic matter and obtain a structurally, chemically and biologically stable product. The final (new) product is an “artificial loam” with suitable characteristics to support a consortium vegetable, also once finished the organic fermentable components. The trials lasted from 8 (AFIB) to 12 (ACEA and Lodrino) weeks; during these periods the piles were periodically turned (to aerate and mix the material and stimulate the growth of microbial colonies able to degrade and mineralize organic matter) and monitored (by means of systematic sampling and physical-chemical analysis). In order to evaluate the quality of the artificial loam, phytotoxicity tests were set up on different test plants. It was also estimated the microbial load both on sludge as such and on produced artificial loam, to obtain an indication of the status of organic soils. The results confirm that the developed protocol offers the chance of handling such a waste material to produce a loam potentially useful for land reclamation of industrial and residential areas. They also show a good performance of the process (reduction of the concentration of heavy metals and increasing of organic matter). After all, it should be interesting to implement the experimentations of such applications, which are also interested by international patent (EU Patent No 1299265); several EU projects (past and present) concerned such topic.