PROJECT DESCRIPTION
BACKGROUND
In Europe, annual sewage sludge production reached 10.9 million tonnes in 2005 and was expected to exceed 13 million tonnes by the end of 2020. About 50% is recovered directly for use in agriculture and the rest is disposed of in landfills or incinerators. However, the traditional disposal systems present many problems, including:
- unpleasant odours
- the possible presence of heavy metals or organic pollutants in agricultural applications
- CO2 emissions due to transportation
- issues in the leachate in landfills
- high costs
- opposition of citizens to incineration plants.
Therefore, there is a need for environmentally-friendly alternatives to disposal, including creating innovative and economically-sustainable plants for the recovery of sewage sludge waste. Hydrothermal liquefaction (HTL) technology showed promise as a means of transforming municipal wastewater solids into feedstocks for biofuels and other industrially-useful materials.
OBJECTIVES
The objective of the LIFE FREEDOM project was to demonstrate at pilot-scale the technical and economic viability of hydrothermal liquefaction (HTL) technology for the treatment of sewage sludge. The aim was to use the new HTL technology to reduce the volume of waste sent to landfill and incineration, and to produce secondary raw materials of widespread industrial use, including asphalts for roads, binders for industrial applications, and fertilisers for agricultural use.
The project beneficiaries expected to install HTL equipment in an urban wastewater treatment facility in Cassano D'Adda, in Milan (Italy), connecting the LIFE FREEDOM system directly to the purifier. A range of environmental benefits would also be evaluated.
By doing this, the project would contribute to the implementation of the following EU policies:
- Urban Waste Water Treatment Directive (1991/271/EEC)
- Sewage Sludge Directive (1986/278/EC)
- Landfill Directive (1999/31/EC)
- Water Framework Directive (2000/60/EC)
- Closing the loop: An EU action plan for the Circular Economy.
RESULTS
The beneficiaries designed and assembled an innovative hydrothermal dewatering (HTD) prototype for the treatment of sewage sludge. The prototypal plant was installed in the urban wastewater treatment facility in Cassano D'Adda near Milan (Italy) and its functioning was validated over 3 years of testing.
The mineral fraction obtained from the hydrothermal dewatering of the sludge was compressed to achieve hydro-char and this recycled material has been successfully tested in the following industrial applications, as:
- a filler in the mixture of bituminous conglomerates used to pave roads
- a Phosphorus-based fertiliser in agriculture.
- a component in the formulations of cement and other geopolymers
- bricks with good thermal and sound insulation.
Thus, if the by-products resulting from the treatment are reused, up to 100% of the sludge can be recovered and the disposal could be avoided.
Environmental benefits were achieved during the project.
- Elimination of 750 tonnes of waste sludge in the Cassano D'Adda water treatment facility, thus avoiding some landfilling or incineration. As a consequence, 750 m³ of water (separated from the solid fraction) were not disposed of but were returned to the river network as clean water.
- CO2 emissions reduced by 4.5 tonnes due to lower fuel consumption for the transport of sludge to landfill or other disposal sites.
Although the project showed that, from the technical point of view, it is possible to use the solid fraction in the above industrial sectors, the related value chains are not yet in place due to various constraints (the quantity of available hydro-char is not sufficient, need for additional pre-treatments or preparation of the materials, etc.) and it is difficult to envision the modification of existing production systems, deemed necessary to use this recycled material.
In the After-LIFE period, thanks to the up-scaling of the LIFE FREEDOM prototype by the project leader, the amount of treated sludge is expected to double and, as a result, also the related environmental benefits.
