In January 2018, Valladolid City Council awarded teCH4+ a grant through a competitive bidding process, under its "Subsidies for Circular Economy Promotion Projects in the Municipality of Valladolid" programme.
With this stimulus, and over the period from January to September 2018, we carried out the project "WWTP Sludge: From Waste to Resource (Re2)", the results of which we have recently presented.
The primary objective of the project is to assess the technical and economic feasibility of implementing the thermal hydrolysis process at the Valladolid Wastewater Treatment Plant (WWTP). The application of this technology makes it possible to close the energy and nutrient cycles contained in wastewater, and is linked to the Circular Economy through the following specific objectives:
- Increasing biogas production — a renewable energy source — by 20%
- Converting the final residue into an organic fertiliser that qualifies as EPA Class A, thereby guaranteeing its suitability for agricultural application
- Recovering nutrients such as phosphorus (P) and nitrogen (N) in the form of inorganic fertiliser
- Reducing the operational costs and environmental footprint of the Valladolid WWTP
Project Developments
The first milestone was the establishment of a baseline using operational data provided by the Valladolid WWTP. The mass and energy balances developed characterised current operations and provided the reference point against which the benefits of the proposed improvements could be measured. Given its particular relevance to this project, a detailed study of the anaerobic digestion process was also carried out, based on its most significant parameters.
After quantifying the improvement potential of anaerobic digestion — supported by biomethane potential (BMP) tests conducted by the laboratory of the Recognised Research Group in Environmental Technology (GIRTA) at the University of Valladolid (UVa) — the effect of installing a thermal hydrolysis plant was analysed. Following an assessment of different options, installation of the plant operating in an inter-stage configuration (2+1 digesters) was recommended. One of the key advantages of this configuration is that it allows the thermal hydrolysis plant to be energetically self-sufficient.
Environmental and Social Impact
Beyond its economic benefits, thermal hydrolysis technology offers positive environmental impacts for all Valladolid residents — the generators of the wastewater treated at the WWTP — who stand to benefit from a technology capable of extracting value from what was previously a waste product of their own activities. In this way, AQUAVALL and Valladolid City Council, as managers and ultimate authorities responsible for the WWTP, take a further step towards the goal of building a sustainable city grounded in a circular economy. A compelling measure of the social impact of thermal hydrolysis technology is its contribution to 5 of the 17 United Nations Sustainable Development Goals. A clear example of this is the support it provides to the two central pillars of climate change action:
- Mitigation. The biogas generated is a renewable energy source that displaces fossil fuels.
- Adaptation. The organic fertiliser produced displaces synthetic fertilisers and improves the resilience of the soils to which it is applied.
Energy Self-Sufficiency Study
With the aim of making the WWTP energetically self-sufficient, the installed digestion capacity — together with the additional capacity "created" by the thermal hydrolysis plant — can be leveraged to introduce external organic waste (co-substrates) and increase the volume of biogas generated through anaerobic digestion. This strategy is fully aligned with the circular economy contribution.
To this end, the availability of co-substrates from local industrial and livestock operations was analysed. Among the industrial waste streams, and applying initial selection criteria of a reasonably high volume of waste generated and a distance of less than 20 km from the WWTP, 10 high-potential companies were identified. Taken together, these companies present a biogas generation potential more than sufficient to achieve the energy self-sufficiency target.
The study is complemented by an estimate of the livestock waste potentially available across the province of Valladolid. While this represents an enormous potential, it should be noted that it encompasses several livestock categories — cattle, pigs, sheep, goats, poultry and rabbits — and a considerably broader geographical area.
In conclusion, the thermal hydrolysis plant, operating in the proposed inter-stage configuration, makes it possible to introduce the quantity of substrate required to generate 100% of the electricity consumed. Under this scenario, all key digestion parameters would remain within reasonable operating ranges, and the thermal hydrolysis plant would continue to be energetically self-sufficient, as it would still require only steam generated from the residual heat of the cogeneration engine exhaust gases.
Economic Feasibility Study and Proposal
In light of the strong technical fit of the proposed technology, its economic feasibility was assessed. This study, which is confidential in nature, concluded that achieving the operational cost savings associated with the installation of the thermal hydrolysis plant requires an investment with a simple payback period of 3.5 years.
The project concluded with the drafting of a techno-economic proposal enabling AQUAVALL to implement an improvement that offers undeniable benefits — not only economic, but also social and environmental.
