Report on general recommendations for the use of the treated sediments in plant nursing

This deliverable presents the results of the activities related to HORTISD Action B2 and C1 from the start of the project (01/10/2015) until the 9th month of the project (30/06/2016), concerning the treatment of sediment, the monitoring of the physical, chemical and biological sediment characteristics during the treatment and the validation of the treatment. On the basis of the results obtained at the end of the sediment treatment, it can be concluded that three months landfarming process was effective in homogenizing the substrate, increasing microbial activity and further reducing organic contamination, reaching physical and chemical characteristics comparable with those of an agronomic substrate (D.lgs 75/2010). In fact, in only three months of landfarming, an appreciable biochemical-functional improvement, evaluated through the improvement of biochemical parameters, such as dehydrogenase (indicative of the total microbial metabolism), but also hydrolytic enzyme activities involved in the cycle of carbon, phosphorus, nitrogen, and sulphur (arylesterase, ?-glucosidase, cellulase, dioxygenase, phosphomonoesterase, phosphodiesterase, protease, urease and arylsufatase), was detected. In addition, there was a significant reduction in both inorganic (available forms) and organic contaminants ( 28% reduction of heavy hydrocarbons), the latter very probably due to aeration carried out with the landfarming, which resulted in an oxidative and very favourable environmental conditions for microbial pollutant biodegradation; this oxygenation was evident also by the reduction in ammonium and the increase in nitrate. As expected after landfarming process, the nutrients (C, N, P) decreased over the time; however, the analyzed nutritional parameters are comparable to those of an agronomic substrate with the only exception for the organic carbon, which has a concentration lower than that established by Italian legislation for an agronomic substrate (D.lgs. 75/2010). Nevertheless, in order to reach the C concentration required by Italian regulation, the mixing of sediments with a source of organic matter rich in Carbon, such as peat or sludge, should be useful. Also pH, electrical conductivity and the physical parameters (bulk density) are in accordance with possible re-use of this matrix as a substrate in horticulture. The addition of organic matter (necessary for reaching the legal C content) could also contribute to little decrease the bulk density of sediment, slightly higher than that indicated by Italian regulation. In order to reuse the sediments for strawberry cultivation, a pH correction should be take into account, since the optimum pH for this species is slightly acidic pH (5-6). Concerning the contamination, even if Zn, heavy hydrocarbons (C> 12), and poly-aromatic hydrocarbons (PAHs) were still higher than the legal limit for the civil reuse (D.lgs 152/2006 Table A), the very low or lack of toxicity of the sediment at the end of the landfarming process, suggested that they not represent a problem for sediment reuse in horticulture. Moreover, the Zn concentration was lower than the limits for agronomic substrate (D.lgs 75/2010). With the aim to further reduce the organic contamination, some little adjustments to the landfarmig process could be taken into account: 1) extension of landfarming process (e.g. 6 months instead of 3); 2) favour the microbial community in the degradation process through the addition of water and nutrients readily available for microorganisms (such as nitrogen and phosphorus); 3) inoculate specific microbial consortia or fungi capable of quickly degrade hydrocarbons. On the other hand, the simple mixing of the sediments with other organic or inorganic matrices, could dilute the contamination, reaching the concentration required by the current lows.