Solving treatment of wastewater sewage sludge with new HTL technology to produce hydrocarbons, asphalts and fertilizers

The environmental problem faced is that related to the disposal and management of sewage sludge produced by wastewater treatment.
The project proposes an ecological alternative through the creation of an innovative plant that contributes to the development of the state of the art in the economically sustainable recovery of sewage sludge waste.
At present in Europe, sewage sludge production, has reached 10.9 million tons dry solids in 2005 (Milieu Ltd et al., 2008), and is expected to exceed 13 million tons by 2020 (Kelessidis and Stasinakis, 2012). About 50% of these are recovered directly in agriculture, whereas the rest is disposed in landfill or incineration.
However, the usual sludge management routes face problems that have never been solved.

Moreover, sewage sludge disposal routes should be designed according to the waste hierarchy introduced by the Waste Framework Directive (EU Directive, 2008/98/EC), which indicates an order of preference for action to reduce and manage waste, i.e., prevention, minimization, reuse, recycling, energy recovery and, as final and undesired option, landfilling. In the next years, with the implementation of the Landfill Directive (EC Directive, 1999), which obliges the member states to reduce the amounts of biodegradable waste, the amount of landfilled sewage sludge has to decrease.

This project wants to prove the validity of a novel technology able to solve the presented problem. It aims at demonstrating the large-scale application of a technology that follows a completely new sludge recovery path, alternative to the current management routes. The thermochemical liquefaction process, also known as hydrothermal depolymerization or liquefaction (HTL), could represent an innovative and promising solution to largely reduce sewage sludge volume, recover raw materials from such waste and upcycle it into renewable bio-fuels or bituminous conglomerates. The produced crude oil, composed of a mixture of hydrocarbons, analogous to fossil ones, can have multiple applications. One of the main aims of HTL plant is to demonstrate the technoeconomic viability of producing such synthetic crude oil suitable for integration into a conventional oil refinery, in asphalt, or cement industry. Finally, another important environmental aspect of the proposal is phosphorus recovery. Phosphorus is a key natural resource for agriculture and other industrial sectors, but natural phosphate sources are getting scarce. This in turn results in a price increase and makes Europe strongly dependent on phosphate imports. The P-content in the sewage sludge produced in Europe could replace up to 20 or 30% of the phosphate imports into the EU.


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