Quantified expected results and impacts
The final goal of the project is to realize a plant for the transformation of sludge by HTL reaction, in real scale and connected to a municipal sewage treatment plant of medium size.
This result is essential for the spread and application of HTL technology on other purification plants, so that this method can quickly be established and represent a new alternative to the disposal of sewage sludge which, owing to their chemical features, or to managerial or political choices, cannot be recovered. In addition to the technical know-how that will be acquired, and which will be essential for the construction of future HTL systems, the following results are expected:
- The production of waste sewage sludge (European waste code ERC 190805) will be eliminated. This means that, by considering only the CAP Holding treatment plant at the service of the municipality of Cassano d’Adda (producing sludge unsuitable for agricultural use), the landfill or the incineration of about 4,000 tons per year of biological sewage sludge will be avoided with a clear environmental advantage. More than 80% of the water contained in the purification sludge mass, currently leaving the treatment plant, will be recovered, returning to the plant head.
- Sludge transport from the purifier to the disposal site will be avoided. Assuming a minimum distance of 100 km round-trip on heavy-duty vehicles (average load 28 – 30 tons), it is equivalent to avoiding consumption of diesel fuel for the journey of more than 14,000 km per year. This is equivalent to avoiding the emission of 13,160 kg of CO2.
- In place of sludge disposal, the purifier could potentially produce: 380 tons of bio-oil and tar with similar characteristics to crude oil (about 2,700 barrels) to be used in bituminous conglomerates for the production of road surfaces. As the mixture of bituminous binders and gravel contains up to 20% of tar, by considering 10 cm as thickness of a road surface, could be is possible to produce a road surface of 9,500 square meters per year.
- As fuel for thermal use it could be possible to obtain about 3800 MWth.
- 250 tons of mineral fraction for the production of novel binders.
- 50 tons of phosphorus (as P2O5) per year for the fertilizer industry. This quantity could be sufficient to cover the phosphorus need for a common crop such as maize, for an area between 300 and 400 hectares.
In the future, after the end of Life Freedom, the experience gained will make it possible to reduce sludge management costs, to the benefit of citizens. The disposal cost of sewage sludge mass (today 180 Euro or more, per ton of sludge as it is) will be greatly reduced thanks to the fact that the mass
(mainly water recovered and relaunched to the head of the purifier) to be handled and transported is greatly reduced. Thanks to a good marketing activity, it will be possible in a future, to obtain revenues from the sale of the produced raw materials. This will appear in the economic management hypothesis below.